THE GOOD, BETTER, BEST OF DEHUMIDIFICATION

The good, better, best of Dehumidification

It is understood that at any point air will have a specific quality in terms of temperature and humidity.

If you look at a psychometric chart, the dry bulb, web bulb and its associated dew point, relative

humidity and vapor pressures can be determined. (Feel free to read psychometrics for the common

man).

In most cases, dehumidification occurs whenever you cool. Air hits a cooling coil, the dry bulb drops

and the relative humidity rises to 100% (at the dew point) and the extra moisture comes out of the

air by means of the condensate.

In cases where there is an elevated amount of moisture in the air compared to the sensible heat, a

high humidity condition can occur. Think of a summer day after a rainstorm; it‘s cloudy and not very

hot, but it‘s sticky. (i.e., 75F and 85% RH). If the relative humidity is high but the dry bulb is correct

there is a challenge for standard equipment. The thermostat will say satisfied but an uncomfortable

condition will exist. To pull moisture, the thermostat would have to be lowered which would lower the

dew point in the space but a ―cold clammy‖ situation will occur.

The above paragraph can occur more often in spaces where there is moisture introduction regularly-

high people, a lot of outside air, or a process like a shower or wash down (kitchen, laboratory, etc) If

this is the case, a commercial dehumidifier may be required.

There are many types of units that can accomplish dehumidification and like in most comparisons

have their pros and cons.

The most common type of dehumidification is using hot-gas reheat. Essentially a humidistat would

determine a need for dehumidification and would engage the compressor to wring out the moisture

and use a secondary condenser coil downstream of the cool coil to heat the air back to the proper

temperature. It works well but in terms of energy and first cost one needs to consider the fact that in

many cases with high moisture designs, the compressors need to be oversized in order to overcool

the air to achieve optimal dehumidification. In addition, the compressor will work harder to deliver

lower discharge temperatures which equates to higher energy usage (this is regardless of usage of

energy recovery).

For make-up air applications a heat-pipe run-around loop may be a better option. Essentially, the

sensible heat (ie going from 95 dry bulb to 75db without hitting the dew point) would be ―moved‖ to

after the cooling coil. Similar to hot-gas reheat of using waste heat, it is more effective, as the

compressor is not doing any work on this process. The warm air gets pre-cooled and lowers the work

and potential size of the compressor. (figure 75db, 85%rh to 55db, 100%RH) and the ―moved‖

sensible heat brings the dry bulb back to comfortable condition (75, 50% RH). Unlike hot-gas reheat

where the compressor sees the whole load, the compressor in this case only does the latent capacity.

The next option is to use a desiccant dehumidifier. Unlike using a cooling coil to remove the moisture,

a desiccant wheel is used to pull the moisture out. The wheel is essentially warmer and dryer than

the air it‘s treating (known as ―process air‖) and will literally pluck the grains out. It is a very efficient

way of removing moisture and is used in applications where cooling coil cannot be used (ie, ice rinks

are cold enough that the condensate coming off the coil would literally freeze on the coil making the

coil ineffective).

In order to keep the desiccant wheel warm and dry, it needs a regeneration process once it has

retained the process air‘s humidity and this requires heat. For highly industrial processes, the heat

source would be an electric coil, steam coil or direct fired burner. While you can see a performance of

7.8% RH in the summer or lower (think leaving air of 75db/49 WB for and entering air of 95/75), for

commercial applications, it is a very expensive first cost as it will require a post cooling coil to bring

very warm, bone dry air (125F+, ~2%RH) down to the required temperature.

Another option for regenerating the wheel is using a passive process. Unlike the above which is

considered active (because the heat source is the driver of the output), the desiccant wheel gets

regenerated by the leaving exhaust air. The lower amount of heat available will not give as much dry

air compared to a direct fired burner, but the output may be better suited and will cost way less. The

one thing to mention, however, is because it is passive, the capacity is directly coupled to the outside

air being used. Using the tepid humid day as an example, the passive desiccant will not be very

effective.

Perhaps a good compromise to the above two scenarios is an active regeneration process which is a

bit less complex than a gas fired desiccant but can deliver lower dew points regardless of the ambient

condition. A desiccant wheel will work best when the air has the highest RH. That said, a small

refrigeration circuit is used to essentially precool the air which reduces the entering air dry bulb but

increases the RH. The wheel removes the moisture and slightly heats the air in the process (but the

air was precooled!) and this results in dry neutral air (75 DB, 40 dew point/~30%RH). The condenser

coil in this case becomes the heat source to regenerate the wheel. This is a very effective means to

dehumidify.

When the space humidity levels are lower, there is a lot of advantages- comfort, operating costs,

indoor air quality. Please This email address is being protected from spambots. You need JavaScript

enabled to view it. 973-536-2220 for an unbiased solution to all of your humidity needs!

The good, better, best of Dehumidification

Hot-Gas Reheat, Hot-Gas Bypass, Low Ambient, Modulating Compressors- The rundown:

Getting to Know Refrigeration

Desiccant Dehumidification

Energy Recovery... More than just wheels!

P trap design

Formulas and Rules of Thumb

Basic Pool Design and Layout

Psychometrics for the Common Man

Humidification 101

Hot Gas Reheat Retrofit?

DESICCANT DEHUMIDIFICATION

Commercial Desiccant Units- When is it best?

Unlike Industrial Desiccant Dehumidifiers which are very expensive and in some cases inflexbile, a

Commercial Grade Desiccant unit delivers the best performance for many applications without

overdoing it which meets the application more precisely in simplicity and cost.

- Low Dew points are great for Chilled Beam Applications as if the humidity is reduced, the

risk of condensation is reduced as well. WHY? Because a lower dew point means a lower relative

humidity and that allows more room for error (45 RH to 100% RH is better than 55 % RH).

- Desiccant Units are more Efficient. The silica gel of the desiccant wheel is "thirsty" vs a

compressor in a hot-gas reheat system which needs to work harder (higher head) delivering lower

discharge temperatures. WHY? Head is the difference between the ambient temperature that the

compressor is rejecting to verses the discharge temperature, typically lower to "overcool". That is why

desiccant units are eligible for NJ Smart start rebates.

- Commercial Desiccant units are perfect for Freezer Doors and Display Cases in

Supermarkets. WHY? The lower dew point allows the air to not condense and freeze on the door

when it is open.

- Get more capacity from the equipment that is already there. WHY? Again, direct expansion

equipment (DX) performance will improve with reduced head pressure and removing latent capacity

will achieve this. The same unit with a lower entering dew point will result in a lower discharge

temperature which leads to higher EER (because of the higher dry bulb delta T). This can also be

achieved with a chiller: increase the chilled water temperature to increase the kw/ton and as you get

more MBH.

- Packaged DX equipment can typically deliver 55F dew point; Industrial can get to 10F or even lower

(with a high price tag). The commercial desiccant unit we offer is about 40 F dew point.

How It Works:

Unlike using a cooling coil to remove the moisture, a desiccant wheel is used to pull the moisture out.

The wheel is essentially warmer and dryer than the air it‘s treating (known as ―process air‖) and will

literally pluck the grains out. It is a very efficient way of removing moisture and is used in applications

where the cooling coil cannot be used (ie, ice rinks are cold enough that the condensate coming off

the coil would literally freeze on the coil making the coil ineffective).

In order to keep the desiccant wheel warm and dry, it needs a regeneration process once it has

retained the process air‘s humidity and this requires heat. For highly industrial processes, the heat

source would be an electric coil, steam coil or direct fired burner. While you can see a performance of

7.8% RH in the summer or lower (think leaving air of 75db/49 WB for with an entering air of 95/75),

for commercial applications, it is a very expensive first cost as it will require a post cooling coil to

bring very warm, bone dry air (125F+, ~2%RH) down to the required temperature.

For a commercial desiccant unit, a small refrigeration circuit is used to essentially precool the air

which reduces the entering air dry bulb but increases the RH. The wheel removes the moisture and

slightly heats the air in the process (but the air was precooled!) and this results in dry neutral air (75

DB, 40 dew point/~30%RH). The condenser coil in this case becomes the heat source to regenerate

the wheel. This is a very effective means to dehumidify.

When the space humidity levels are lower, there is a lot of advantages- comfort, operating costs,

indoor air quality. Please This email address is being protected from spambots. You need JavaScript

enabled to view it. 973-536-2220 for an unbiased solution to all of your humidity needs!

Additional Articles: THE GOOD BETTER BEST OF DEHUMIDIFICATION

ADDITIONAL THINGS WE DO (HOME PAGE)

HRVs and ERVs For Classroom Ventilation Applications

Recovering sensible or total heat, wheels or cubes, optional add-ons like fans and filters

and assorted sensors ... it takes some homework to specify the right energy-saving

recovery ventilator for your school application.

FIGURE 1. Basic ERV unit. (Photo courtesy of Ruskin.)

FIGURE 1. Basic ERV unit. (Photo courtesy of Ruskin.)

FIGURE 2. This map from the EPA shows the financial payback of using an ERV in different zones

across the U.S.

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May 1, 2014

Steven Liescheidt

KEYWORDS classroom ventilation / energy efficiency

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It doesn‘t get much more sensitive in HVAC design than designing ventilation systems for the schools

that our youth occupy during their learning years. These students are the future of America. These

are the youth whom we want and need to be in optimum learning environments.

There are studies that have been done on noise levels in classrooms. Students may be hindered from

hearing the teacher if the noise level of an HVAC unit is too loud. There are also studies and debates

on how much ventilation air is acceptable. Without proper ventilation, the IAQ may reach the point of

restricting learning abilities of the students. Without proper ventilation, the CO2 levels in the

classrooms may rise to a point that the students become tired and are less able to learn.

Historically, when it comes to energy savings, the basic school systems have been provided with the

least expensive types of HVAC products due to budget restraints. Energy savings was less of a

priority, if a priority at all.

Designing the HVAC for new modern schools and retrofit of older schools requires

balancing objectives that are covered in ASHRAE Standards 55, 62, and 90 along with USGBC LEED

guidelines and building code requirements, which vary by location. The application of heat and

energy recovery ventilators is one way to help with compliance of codes and standards. The reality

seems to be that one day, all buildings will require some form of HRV or ERV device to meet the

building codes in the United States. There are already products on the market that utilize solar heat

to preheat outside air going into the building ventilation systems.

Overview

A heat or energy recovery ventilator is an essential piece of mechanical equipment that is used to

pre-heat or pre-cool the outside air that is brought into a building for ventilation. The technology can

be such that it can recover only sensible heat (called an HRV) or total heat, sensible and latent (called

an ERV). The technology can be a rotating wheel or a fixed cube-type device. There are other

technologies to recover energy; however, this article will focus on wheels and the cube-type media

technologies. In some situations and applications, a water or DX coil may be more appropriate than a

media type heat transfer material.

The material of construction of the wheel or cube varies by manufacturer, and each will promote their

product based on their performance advantages. There are pros and cons to both technologies.

Suffice it to say that the engineer needs to have a conversation with the manufacturer and then apply

reasonable good engineering judgment to discern which media material best meets the application

needs.

Sizing and Selection

When sizing an HRV or ERV, the engineer must consider the ventilation load and also the intended

use of the unit throughout the year. In some climates and applications there is no need (and it is

possibly a detriment) to install an ERV versus an HRV.

The applications of energy recovery ventilators and sizing of these units takes a clear understanding

of the fundamental tool of the HVAC industry — the psychometric chart. The psychrometric chart, by

definition, is a graphic representation of the properties of mixtures of air and water vapor.

Most manufacturers have software programs to select their HRV and ERV units using basic input data

that is needed to plot the conditions on a psychometric chart. The product selection program does all

of the analysis and provides a performance printout that can be used as the basis-of-design unit

requirements. Care must be taken to review the performance data and allow for discrepancies

between manufacturers. Not all products are tested under the same conditions; therefore it is

difficult to compare product performance.

Obviously, the application of an HRV or ERV depends on a source of building air that is being

exhausted or relieved as part of the HVAC system. The goal is to recover a portion of the sensible or

total heat in the exhaust or relief air in a manner that is safe and saves energy. Sources of exhaust

could be toilet rooms, locker rooms, showers, kitchen areas, or laboratory spaces.

Some municipalities do not allow the use of wheels in toilet exhaust air streams because there is a

bypass air factor for all wheels even when purge sections are used. However, the exhaust air

compartment in the unit is generally more negative than the supply air chamber, so this may not be

an issue of concern. The AHJ should always be consulted on any HRV and ERV application to ensure

the proper type of unit is utilized.

Performance

An ERV and HRV may or may not be rated and tested under independent testing standards such as

the AHRI standards. If not, then certainly engineers and facility owners may have a concern about

the performance claims by a manufacturer. Even when tested, the testing may not be the same from

one manufacturer to another, therefore the comparison of units is difficult at best and practically

impossible. This affects design decisions and comparison for evaluation. Also, keep in mind that no

performance is guaranteed past the day of purchase. The performance data of all wheels and cubes

that this author is aware of is not guaranteed beyond the first day of the unit installation and

operation. The industry does not have any type of fouling factors like with piping or other products

that give some guidance on de-rating of performance over time.

Proving and verifying performance after installation becomes a challenge as with any product that is

tested under ideally controlled conditions. Commissioning or enhanced commissioning of new or

existing ERV and HRV units can be a challenge to prove or disprove the unit is indeed giving the

performance that the owner paid for. Many variables exist, including installation and maintenance,

that may impact the air streams in the ERV or HRV. It may be worth considering specifying an annual

recommissioning of ERV and HRV units to verify performance on an ongoing basis.

Performance ratings of products by AHRI Standard 1060 third-party testing include leakage ratings at

various pressure differentials and thermal effectiveness ratings for sensible, latent, and total energy

transfer for both heating and cooling. These conditions are difficult at best (and at worst, impossible)

impossible to replicate after installation, so calculations are necessary to determine if the unit is

indeed performing as promoted in the manufacturer‘s literature.

Installation, Operation, and Maintenance

An ERV or HRV, like any other mechanical device, needs to be maintained. The maintenance of the

ERV and HRV depends on the materials used and the technology of the wheel. Some media may

require more labor-intensive maintenance than others. Some media requires basic vacuuming, and

others require washing or perhaps even steam cleaning.

Some ERV‘s for inside installation are essentially outdoor units less the weather enclosures yet not

much modification to account for limited inside serviceability. This gives engineers a challenge on

retrofit projects and may be a product enhancement opportunity for manufacturers looking for a way

to provide units that are sensitive to maintainability for the enduser. Design features that minimize

the size of the ERV, minimize the access clearances, and provide multiple unit duct connection

locations are just a few of the indoor unit criteria some engineers and architects look for.

The design of the intake of the outside air is important to understand so as to not take greater risk

than necessary in impacting the media. Care must be taken to follow the manufacturer‘s installation,

maintenance, and operation instructions to optimize the length of the effectiveness of the media.

EPA Design Tools

The EPA has a section called ―IAQ Design Tools for Schools‖ on their

website. (http://www.epa.gov/iaq/schooldesign/ervassumptions.html). This page has a section called

―ERV Assumptions‖ which has a System Financial Applicability Map.

They also have software (http://www.epa.gov/iaq/schooldesign/saves.html#ERV) called the Financial

Assessment Software Tool (EFAST). Although the map gives a good starting point for consideration of

ERV applications, the engineer should still do the due diligence of lifecycle cost analysis of the

application based on specific project locations and conditions and operating conditions. Arbitrary

application of any products that are marketed by manufacturers as energy-saving products with no

detailed analysis can be costly to an enduser.

LEED

The LEED compliance initiative across the U.S. affects almost every aspect of a building design and

HVAC systems. Although engineers have worked diligently for years before LEED came into being to

design energy efficient buildings and HVAC systems, the LEED program has helped the industry focus

on these essentials in good stewardship of materials and resources more than ever before.

The LEED-NC for new construction and major renovations gives credit for achieving increasing levels

of energy performance above the prerequisite standard to reduce environmental impacts associated

with excessive energy use. Some manufacturers have claimed that their customers have realized a

reduction in total building energy use of 10-15% by using energy recovery as part of their HVAC

systems. In these cases, according to the Energy and Atmosphere Credit 1: Optimize Energy

Performance, this customer would receive two points for new construction and four points for a major

renovation.

The USGBC also recognizes the contribution of higher outdoor air ventilation rates with better IAQ.

The Indoor Environmental Quality Credit 2: Increased Ventilation gives one point for outdoor air

ventilation rates 30% above the minimum required by ASHRAE 62.1. The credit also suggests to use

heat recovery, where appropriate, to minimize additional energy consumption associated with higher

ventilation rates.

Energy Star

The EPA has a Tier 1 and a Tier 2 level of compliance for ERVs. These can be seen at their website.

According to Energy Star, ―Tier 1 (effective January 1, 2010) Products to be sold as Energy Star

qualified must be tested and meet SRE requirements at 32°F (0°C) and -13°F (-25°C). The net supply

airflows (in cfm) used during testing at these two different temperatures must be within 10% of each

other, and specified in product literature and labeling.‖

For qualification under Tier 2, the climate zone map is used to determine the product criteria to

comply as Energy Star.

The Basic Components

In general, ERV/HRV units consist of a supply fan and an exhaust fan, and an energy recover wheel

or cube. A unit may also come with associated motors, filters, and other accessories and options that

are needed to accomplish the required unit functional criteria. It is essential to understand the needs

of the application before selecting and specifying the units. The list below is a general list of some

features of units that may or may not be standard by various manufacturers. Most manufacturers will

have certain basic features as part of their unit, then additional options and accessories can be added

as needed. This method of marketing ERV/HRV products helps keep the first cost of the products at a

minimum. This list is not exhaustive and not in any particular order of priority.

Supply fan

Exhaust fan

Energy transfer media

Material warranty and performance

warranty on energy transfer materials

Low ambient kit for frost control

Coil freeze protection

Start-stop-jog fan control for economizer

compatibility

Vibration and seismic isolation

Remote on/off motion detector

Remote speed controller

VFD drives for supply and exhaust fans

VFD drives for energy recovery wheel

Remote timer option

Integral digital controls or BAS signal

compatibility — LonWorks, BACnet, etc.

Dirty filter sensor

Purge section

Equipment labels with performance

capacities on and in the units

Drain pan construction material, positive

sloping, and trapping

NEMA enclosure disconnect switch

Single or multiple point electrical

connections

Temperature sensors for return, exhaust,

outside, and supply air

Supply motor current sensor

Exhaust motor current senor

Wheel rotation sensor

Clogged wheel sensor

CO2 sensor

Service receptacle

Lockout/tagout electrical service door.

Vapor tight lights in the units

Space temperature and humidistat

Outdoor air and return air filters

Optional intake hoods and louvers for

moisture/snow entrainment control

Mist eliminators on intake hood or wind-

driven rain louver

Airflow measuring station or louver

Motorized intake damper in compliance

with energy codes

Seismic curb options

Certifications by and testing in accordance

with AHRI, AMCA, ETL, UL, etc.

Multiple duct connection options for unit

installation compatibility

Service door gaskets made of closed cell

materials

Low voltage control transformers

Intake wire mess mist/snow eliminator

Pros and Cons of Heat Recovery Ventilators

Posted January 17, 2010 by h2oblogged in Uncategorized. Leave a Comment

HEAT RECOVERY

Energy Recovery Systems

Energy Efficiency and Energy Recovery

Fresh air is essential to healthy people – and healthy buildings. That‘s why commercial buildings are

required to bring in fresh air – typically 15-20 cubic feet per minute (cfm) for every occupant. This

unconditioned air greatly increases your building‘s air-conditioning load – and since an equal amount

of air must be vented outdoors, you‘re basically ―throwing away‖ air you‘ve paid to cool.

Energy recovery ventilation systems – or ―ERVs‖ – help reduce this waste and lower your energy

costs. What‘s more, an FPL incentive program now helps businesses pay for this technology – so you

can save even more when you install a qualifying ERV unit on a new or existing HVAC system.

Energy recovery systems typically incorporate heat exchange equipment to reduce energy costs by

extracting heat from the facility‘s exhaust air stream before it is vented outside. Energy recovery from

the laboratory‘s exhaust should be considered when significant portions of operating hours are at

ambient temperature of 50°F (10°C) and below. Another recoverable energy source is provided by

chiller/DX condensers. Water cooled condensers can be piped to reject waste back into the labs HVAC

system to provide reheat capacity, to augment run-around coil systems, and to dry regenerative heat

wheels. When properly designed, these energy recovery systems can reduce installed HVAC system

capacity by one-half; reduce operating energy from one-third to two-thirds, depending upon mode of

operation; and have life-cycle cost paybacks from immediate to three years. The four major energy

recovery systems include run-around coil systems, regenerative heat wheels, heat pipes, and fixed-

plate exchangers

Plate heat exchangers (recuperators)

A minimum effectiveness of 50% (based on sensible energy transfer under balanced flow conditions).

Internal leakage < 1% (for units >0.2m3/second rating)

Pressure drop <250 Pascal (Pa) NOTE: where pressure drop data is not documented, the fan power

consumption must be consistent with a pressure drop within this limit.

Thermal wheels

A minimum effectiveness of 70% (based on sensible energy transfer under balanced flow conditions).

Internal leakage < 5%

Pressure drop <200 Pa

Run around coils

A minimum effectiveness of 45% (based on sensible energy transfer under balanced flow conditions).

Pressure drop <100 Pa across each coil

Water side pressure drop < 25 kPa per coil

Heat pipes

Disadvantages of Energy Recovery Ventilation.

Unlike air handling units on unit ventilators, energy recovery systems do not have the capability to

provide sufficient outside air for cooling overheated rooms. This can lead to overheating, especially in

the late spring and early fall. Any building employing energy recovery ventilation should have a by-

pass sytem for ERV ‗s or operable windows (or air conditioning) to provide cooling during warm

weather.

Energy recovery ventilation is not a good choice for interior spaces unless those spaces are air-

conditioned.

A second area of concern involves the fact that there is little standardization in the heat recovery

industry. Manufactures and products come and go, and there is some concern that products specified

today may not have manufactures‘ support a few years from now.

Heat exchangers to recover heat increase the pressure drop of the air handling system, and increase

the power demand of the fans.

This is however typically only 5-10 % of the recovered energy.

Energy Recovery in Laboratory Exhaust Systems

Due to the toxic nature of laboratory exhaust effluent, these systems require 100% outside air for

safe ventilation. Normally, laboratory exhaust cannot be recirculated. Depending on the size of the

lab, the make-up air heating and cooling can be a majority of the energy used in a lab. With the cost

of energy going in one direction only (UP!), energy recovery can usually provide short payback

periods and makes good sense for a long term energy policy as well.

Air-to-air energy recovery is the process of recovering energy and/or moisture from an air stream at

high temperature and/or humidity and transferring it to an air stream of lower temperature and/or

humidity. Energy can be recovered in either sensible (temperature only) or latent (moisture) form, or

a combination of both. Devices that transfer sensible energy only are known as heat recovery

ventilators (HRV‘s). Devices that transfer both heat and moisture are called energy recovery

ventilators (ERV‘s)

There are four typical devices used to recover energy from an air stream: The Energy Recovery

Wheel, Plate Heat Exchangers, Heat Pipes and Runaround Coil Loops. We will discuss the pros and

cons of each system here.

Rotary Air-to-Air Energy Exchanger

The Energy Recovery Wheel, or rotary enthalpy wheel, technology utilizes a light-weight polymer

enthalpy wheel with a silica gel desiccant permanently bonded to the polymer. This device provides

long and reliable energy transfer life, has low pressure drop characteristics and requires minimal

maintenance. This is the only energy recovery device that allows total (sensible and latent) energy

transfer. Energy recovery is in the 75 – 80% efficiency range.

The disadvantage to using an Energy Recovery Wheel in a lab exhaust application is the potential for

cross contamination of the incoming fresh air. Standard comfort ventilation energy recovery wheels

cannot be used because of the minimal leakage between airstreams. Toxic exhaust contaminants in

the incoming fresh air would be unacceptable. The energy recover wheel system must be fitted with a

purge section to keep the exhaust contaminants out of the fresh air. This purge circuit will reduce the

heat transfer efficiency somewhat, but the potential for cross contamination still exists in the event of

duct or seal failure.

Fixed Plate Heat Exchanger

Air to Air Plate Heat Exchangers are another option for energy recovery. The plate heat exchanger is

very simple, with no moving parts. Energy recovery can be very high, up to 80% and pressure drops

across the heat exchanger are minimal. The plate heat exchanger does sensible heat transfer only.

The major disadvantage with a plate heat exchanger is that the contaminated exhaust air must be

brought to close proximity to the incoming fresh air. With the possibility of corrosive elements in the

exhaust gas, cross contamination of the two air streams is possible if the plates corrode, and they

may corrode in an area of the heat exchanger that is not readily visible. Latent heat transfer may also

occur, where the moisture in the warm exhaust gas is cooled to the point of condensation by the

incoming cold outside air. The condensation process allows the latent heat of condensation to be

transferred to the outside air as sensible heat. However, this condition could exacerbate the corrosive

nature of the exhaust stream, thus accelerating the corrosion of the plates. In some instances, a plate

exchanger made from corrosion resistant polymers may be a cost-effective option. Periodic cleaning

of the plate surfaces is the only maintenance required, however, this may require the use of a high

pressure cleaning system to clean all interior plate surfaces.

Heat Pipe Heat Exchanger

A heat pipe system utilizes a hollow pipe filled with a vaporizable liquid, usually a refrigerant. Heat

from the exhaust air stream is absorbed at one end of the pipe (evaporator section), boiling the fluid

to vapor phase. A vapor pressure gradient drives the vapor inside the pipe to the other end of the

pipe (condenser section), where the cold incoming fresh air is flowing. Heat is released to the cold

air, condensing the vapor to liquid phase, releasing the latent energy of vaporization. The liquid then

returns by gravity to the lower end of the pipe, where it is revaporized to start the cycle again. The

heat pipe produces sensible heat transfer only.

Heat Pipe Structure

A traditional heat pipe is a

hollow cylinder filled with a

vaporizable liquid.

A. Heat is absorbed in the

evaporating section.

B. Fluid boils to vapor phase.

C. Heat is released from the upper

part of cylinder to the environment;

vapor condenses to liquid phase.

D. Liquid returns by gravity to the

lower part of cylinder (evaporating

section).

For HVAC applications, heat pipes typically use copper tubes with aluminum fins. For protection from

corrosion, the tubes and fins can be coated with an epoxy or Heresite coating with minimal effect on

thermal performance. A plate partition separates the two air streams. A vented double wall partition

can be used for added protection against cross-contamination. Attaching an exhaust system to this

partition space will withdraw any leakage between the two ducts.

HEAT PIPE ENERGY RECOVERY MODULE

A heat pipe heat exchanger requires very little maintenance since it has no moving parts. The fresh

air stream should be filtered to prevent dirt build-up on the coil, and periodic cleaning of the coil will

be required.

Runaround Coil Loops

A typical coil energy recovery loop uses finned-tube water coils in the supply and exhaust air streams.

The coils are connected in a closed loop and a heat transfer fluid (typically water or an antifreeze

solution) is circulated with a pump. The primary advantage of the runaround coil loop system is that

there is no possibility of cross contamination of the air streams. Supply and exhaust streams are

maintained in separate ducts or air handlers. This allows design flexibility in that fresh air and exhaust

systems may be physically separated by longer distances within the building. This also allows

simultaneous transfer of energy between multiple sources.

The runaround coil loop system does sensible heat transfer only. Typical effectiveness values range

from 45 to 65%. Minimal maintenance is required since the only moving part is the pump. Coil

surfaces will require periodic cleaning.

Heat transfer fluid should be selected carefully. Water provides the most efficient heat transfer but

has no freeze protection. Ethylene glycol solutions provide freeze protection but are toxic if spilled

and breaks down to an acidic sludge at temperatures above 275oF. Propylene glycol is not toxic but

has less heat transfer capability than ethylene glycol.

The Greenheck Vektor ERS (Energy Recovery System) is a Vektor laboratory exhaust fan system with

an expanded air plenum that includes an energy recovery coil (and optional filter). The Vektor ERS

can be supplied with either the Vektor MD mixed flow in-line fans or the Vektor CD centrifugal

blowers. With a second energy recovery coil installed in a suitable make-up air unit, the loop is

closed.

Vektor ERS systems can be supplied up to 200,000+ CFM, providing up to 55% sensible energy

recovery with no possibility of supply and exhaust cross contamination. Single source responsibility

for make-up air and laboratory exhaust can provided from Michigan Air Products and Greenheck Fan

Corporation.

For more information, contact your local Michigan Air Products salesman or visit Heat Pipe

Technology or Greenheck.

Does a Home with an HRV Also Need Bath Fans?

Most homeowners find that an HRV with dedicated ductwork moves enough air to clear

condensation from bathroom mirrors

POSTED ON APR 25 2014 BY MARTIN HOLLADAY, GBA ADVISOR

An HRV provides balanced ventilation. If the HRV is properly adjusted, stale air is exhausted

from the building at the same rate that fresh air is being introduced. Ventilation always exacts an

energy penalty, though, so it's important not to overventilate. Builders who are leery of

overventilating homes sometimes wonder whether the recommended air exchange rates for whole-

house ventilation are adequate to clear condensation from bathroom mirrors.

A balanced ventilation system — for example, a system with a heat-recovery ventilator (HRV) or an

energy-recovery ventilator (ERV) — exhausts stale air from some rooms in a building, while

simultaneously introducing fresh outdoor air to other rooms. The best balanced ventilation systems

use dedicated ventilation ductwork. Usually, these systems pull exhaust air from damp, smelly rooms

— bathrooms and laundry rooms — and introduce fresh air to the rooms where people spend most of

their time — bedrooms and the living room.

Some of these balanced ventilation systems operate at a low speed for 24 hours a day. Others have

timers that operate the fans for a certain number of minutes — perhaps 20 or 40 minutes — per

hour. These controls aim to ventilate the house at a pre-determined rate — for example, the rate

recommended by the ASHRAE 62.2 standard. Depending on whether you use the old ASHRAE

formula or the new ASHRAE formula, and depending on the size of the house and the number of

occupants, a single-family house might require anywhere from 45 cfm to 120 cfm of ventilation air.

Many HRV manufacturers advise builders that the exhaust function of an HRV is adequate for

removing moisture and odors from bathrooms. However, a few HRV manufacturers and some

builders provide different advice; they advise that even when a bathroom has an exhaust grille

connected to HRV ductwork, it‘s still important for every such bathroom to have a separate bath

exhaust fan.

RELATED ARTICLES

Designing a Good Ventilation System

Are HRVs Cost-Effective?

HRV or ERV?

A New Way to Duct HRVs

Ventilation Rates and Human Health

How Much Fresh Air Does Your Home Need?

Q&A: HRV with bathroom exhaust fan?

Q&A: Bathroom vents through HRV?

Q&A: For a house with an HRV, is there a good plan for ventilating both bath and toilet room?

Which approach makes the most sense?

Advice from Venmar

Venmar Ventilation is a manufacturer of HRVs with headquarters in Quebec. According to specialists

at Venmar, it‘s perfectly possible to use an HRV system as the only method of exhausting air from a

bathroom.

John Pothier, a technical specialist at Venmar, told me that most Canadian homes take that approach.

A Canadian rule of thumb calls for the HRV system to be commissioned so that, with the bathroom

booster switch on ―high,‖ the exhaust airflow from the most important bathroom in the house is at

least 50 cfm, while the exhaust airflow from from secondary bathrooms is at least 30 cfm. According

to Pothier, this approach satisfies most homeowners.

Advice from Zehnder

The advice from Zehnder, a Swiss manufacturer of HRVs, is similar to the advice from Venmar. Barry

Stephens, the U.S. representative of Zehnder, advises builders that the exhaust side of their HRVs is

adequate to handle the needs of bathrooms.

Zehnder HRVs have three speeds, and the manufacturer recommends that the systems be set up so

that the medium speed meets the requirements of ASHRAE 62.2. When Stephens commissions a

system, he aims for 20 to 24 cfm of continuous ventilation from each bathroom, 10 cfm from each

half bath, and 35 cfm from the kitchen. With this type of ventilation system, it‘s not unusual for a

single-family house in the U.S. to have 4 or 5 exhaust grilles.

―We want continuous ventilation at medium speed to be at about 50% of the airflow capacity of the

HRV,‖ Stephens told me. ―I advise homeowners to use the boost switch when they take a shower.

The Zehnder has a wireless bathroom boost switch with a timer. I tell people to punch the switch to

high speed for 30 minutes. This usually provides about 30 or 35 cfm. It‘s enough. Remember, we‘re

commissioning 100% of our systems, so I‘m talking about verified airflow rates. We have about 1,000

systems installed, and we‘ve had almost no issues at all with this approach.‖

Stephens pointed out that when the timer that controls the boost function turns the fan back to

medium speed, the system is still exhausting enough air to help remove remaining humidity from

towels and bathmats. When I asked about separate bath exhaust fans, Stephens said, ―It doesn‘t

make sense to install redundant systems. Do you really want two more 6-inch holes in your house,

with cold air streaming in?‖

Advice from Broan-Nutone

Broan-Nutone is a major manufacturer of bathroom exhaust fans, as well as a distributor of relabeled

HRVs manufactured by Venmar. The company‘s interest in selling bath exhaust fans may explain why

the manufacturer‘s advice differs from the advice given by Venmar and Zehnder.

According to Judi Weber, assistant manager of the technical support group at Broan-Nutone, ―When

you have an HRV, you size it for the whole home, not for the bathroom, shower stall and tub. If you

are getting 20 cfm of exhaust when your HRV is operating, that is not going to effectively remove the

humidity as fast as most people want it to be. Bathroom mirrors may get foggy on you. Our position,

definitely, is that people will be happier if they have separate bathroom exhaust fans, and not to

depend on the HRV to remove humidity.‖

A longstanding debate

When HRV systems were first installed in the 1980s, the system designers surely intended the HRV‘s

exhaust function to fulfill homeowners‘ expectations for bathroom exhaust. Yet this time-honored

approach is often questioned.

The current debate touches on several issues:

Code requirements;

The length of time takes to remove excess moisture from a bathroom;

Simplicity vs. complexity; and

Affordability.

Code requirements

In the 2009 International Residential Code, bathroom fan requirements can be found in section

R303.3 and section M1507.3. As long as a bathroom or toilet room is equipped with a window that

has at least 3 square feet of glazing, and as long as half of the window can be opened, most building

codes do not require the installation of a bathroom exhaust fan.

If the bathroom or toilet room has no window, however, it must have an exhaust fan with a minimum

ventilation rate of 50 cfm if it is operated intermittently or 20 cfm if it is operated continuously.

Let‘s imagine an example: a typical HRV might be adjusted to operate at 70 cfm to meet ASHRAE

62.2 requirements. Typically, such systems include a booster switch in each bathroom to allow users

to bump up the air flow rate of the HRV from low speed (in this case, 70 cfm) to high speed (say, 150

cfm).

If an HRV operating at 70 cfm (continuous) is installed in a house with four bathrooms, each

bathroom might end up with 17.5 cfm of continuous exhaust or 37.5 cfm of intermittent exhaust.

These flow rates aren‘t enough to meet minimum code requirements for windowless bathrooms.

(Needless to say, actual air flow rates are likely to be significantly less than the numbers given in this

example, because of static pressure drop associated with the duct system.)

Some builders have wondered whether it‘s possible to install motorized dampers in exhaust ducts,

with controls that close the exhaust ducts of all bathrooms except for the bathroom where an

occupant has activated the fan speed boost switch, so that the entire exhaust air flow of the HRV is

pulled from one bathroom. According to John Pothier, technical specialist at Venmar Ventilation, such

a system wouldn‘t work and to his knowledge has never been attempted. The main technical problem

with the proposal is that individual exhaust ducts aren‘t sized to handle to full air flow of the HRV.

Although it‘s quite possible that some installed HRV systems don‘t meet minimum code requirements

in the U.S., few building inspectors are likely to attempt to verify the exhaust airflow rates of these

systems. After all, a code inspector doesn‘t usually show up at a job site with a flow hood. Moreover,

it‘s probable that most homeowners with fully ducted HRV systems will be completely satisfied with

the performance of the system, even if the system doesn‘t quite meet minimum code requirements.

In Canada, where HRV systems are far more common than they are in the U.S., the building code

differs. In Quebec, for example, the above-code energy efficiency program NovoClimat (a program

that resembles the Energy Star Homes program) requires that all homes include an HRV. When I

discussed the NovoClimat program with Jean Pothier, he told me, ―If you follow NovoClimat, no bath

fans are allowed in these homes. You need an HRV to each bathroom. This is how they do it.‖

However, Pothier later amended his explanation of NovoClimat requirements. The latest version of

NovoClimat requires that the two most-used bathrooms in a house must be exhausted by the HRV

system and must have a minimum exhaust airflow of 40 cfm each. If the house has more than two

bathrooms, the remaining bathrooms can either be tied into the HRV system (as long as the minimum

exhaust rate is at least 40 cfm) or can be served by independent exhaust fans.

Are HRV exhaust rates effective?

If a house has an HRV that continuously exhausts air from the bathrooms at a rate of 20 cfm per

bathroom, are the owners likely to be satisfied? There is no clear answer to this question.

Posting on GBA, Doug McEvers, a builder from Eden Prairie, Minnesota, wrote, ―I have used this

system [an HRV for bathroom exhaust] for 25 years and never had a complaint.‖

On the same GBA thread, Mark Klein, a builder from Amherst, Wisconsin, commented, ―We have been

using HRVs for 25 years and have experimented with a few different approaches. Early on we tried

using the HRV as the only exhaust in baths and our clients felt that they did not have sufficient

exhaust.‖

Another GBA reader, T.J. Elder, noted, ―I‘d suggest it makes more sense to omit the exhaust fan

when installing an HRV, and understand the difference in airflow. It will not perform as well at

immediately clearing the air as a dedicated exhaust fan, because it‘s designed to operate continuously

at low speed.‖

I asked John Pothier from Venmar whether the HRV-only approach ever resulted in homeowner

complaints. Pothier answered, ―Sure. Some homeowners don‘t want a foggy mirror. Once I had a

case — well, this bathroom had a big hot tub. The homeowner also had a rain shower system. His

ventilation system was working. It was exhausting more than 50 cfm. There were only two exhaust

locations in this house. But he said, ‗My mirror is fogging up, and I don‘t like it.‘ So I told him, ‗Put in

supplementary ventilation. If you think that the HRV is not powerful enough for your activities, it is

your prerogative to put in a bath fan.‘ ‖

Simplicity versus complexity

Builders who prefer simple systems to complex systems are likely to balk at the idea of a fully ducted

HRV system plus separate exhaust fans. When I asked Joseph Lstiburek about this approach, he

answered, ―I do not like combining systems. It is the old engineer in me showing through. I do not

like complexity. Controls become more complicated. Programing them correctly and operating them

correctly adds to the complexity.‖

I told Lstiburek that, in my experience, most owners of homes with fully ducted HRVs and no

independent bath fans are happy with the performance of their systems. Lstiburek answered, ―My

experience is the same as yours. … [But] HRVs are not as reliable as exhaust fans. It results in a

bigger and therefore more expensive HRV. In cold climates it increases defrost problems. Having said

that, I can live with it, and many times do. The setup is far better than no HRV. So if I can get an

HRV in the structure by having to economize by eliminating the additional cost of extra stand-alone

exhaust fans, I will, if the alternative is just exhaust fans with no HRV.‖

Homeowners who are willing to pay for a balanced ventilation system probably don‘t want the system

to include components that put the system out of balance. According to GBA reader Matt Fletcher,

―As a Passive House Consultant-in-Training and a design/build contractor I recall there was significant

discussion over this particular subject during my consultant training courses. Both sides of the

argument were explored. Adding an exhaust fan to the building envelope that utilized an HRV to

perform the ventilation would unbalance the interior air pressure. … If you exhaust air separately out

of an airtight balanced system then it defeats the whole principle of the balanced system.‖

The cost question

HRV systems are expensive. If homeowners pay $5,000 to $8,000 for a fully ducted HRV system, they

probably don‘t want to hear that the system won‘t be able to exhaust air from their bathrooms. It's

hard to imagine that these homeowners want to pay extra to install redundant systems.

For homeowners who are worried that an HRV won‘t clear steam from their bathroom quickly

enough, it might make more sense to skip the expensive HRV and just install separate exhaust fans in

each bathroom. If one of these exhaust fans is controlled by a 24-hour timer, the homeowners might

be completely satisfied with this simple exhaust-only ventilation system.

What about ERVs?

A final note of caution comes from Max Sherman, a senior scientist at Lawrence Berkeley National

Laboratory and former chairman of the ASHRAE 62.2 committee.

―From the [ASHRAE] 62.2 compliance point of view, 20 cfm continuous extract complies, which

should be easy for a ducted HRV to meet,‖ Sherman pointed out. ―So for an HRV, I think there are

plenty of reasonable designs without having a separate exhaust. The situation for an ERV, though,

needs a bit more thought. Since an ERV recovers moisture (and maybe formaldehyde), you are not

really exhausting moisture from the bathroom, you are redistributing it. There may be times of the

year where that is just fine, but there will be times when you really just want to exhaust it. So I have

more sympathy for adding the extra exhaust (e.g. instead of a booster fan) when the system is an

ERV.‖

Commissioning is essential

Remember, if you don‘t commission your ventilation system, you really have no idea what your

exhaust airflows are.

If the performance of your HRV system is disappointing, check the airflow rates at each exhaust

grille. You can‘t conclude that your HRV system is wimpy unless you have first verified that the

system is properly balanced and providing the exhaust airflows specified by the system designer.

Martin Holladay‘s previous blog: “All About Radiant Floors.”

Click here to follow Martin Holladay on Twitter.

Read more: http://www.greenbuildingadvisor.com/blogs/dept/musings/does-home-hrv-also-need-

bath-fans#ixzz3kdjuaRfb

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Apr 25, 2014 7:17 PM ET

Steamed Mirrors

by Kye Ford

I find it interesting that often the criteria for a successfull level of ventilation in a bathroom is wether

or not the mirrors fog. When I take a shower I sometimes forget to turn on our Panasonic fan/light

units and our vanity mirrors hardly fog at all...

When my wife showers even with the fan on and door wide open there is literally condensation

dripping down the mirrors.

What is the difference? Occupant behavior. My wife's shower is so much hotter it would scald me.

We have lived in several different houses and yes the dedicated bath fans all worked fine and were

sized according to bathroom volume but there is no getting around differences in the amount of

steam created.

The dew on the mirrors clears quickly but should dew on mirrors be the defector "rule of thumb" by

which we judge success?

I can live with a little dew if it means eliminating an air leaking bathfan in favor of an HRV.

Apr 26, 2014 6:29 AM ET

Edited Apr 29, 2014 3:24 PM ET.

Response to Kye Ford

by Martin Holladay, GBA Advisor

Kye,

I agree with you. I understand that the amount of condensation on a bathroom mirror has more to

do with occupant behavior than the effectiveness of the exhaust system.

If you have a high-flow showerhead, and you like long, very hot showers, you're likely to get

condensation on the bathroom mirror -- especially if your bathroom is small.

I also understand the energy penalty associated with overventilation. From an energy perspective, I

don't like high-cfm exhaust fans that run longer than necessary. I much prefer the approach

suggested by most HRV installers: providing continuous ventilation at a low rate, without separate

exhaust fans. That's the energy nerd approach. It works. If you're a Buddhist, you get it. Be a little

patient; your bathmat is going to dry. Breathe in, and then breathe out. Everything is OK.

But the final arbiter -- to person who needs to be satisfied -- is the homeowner, not me. If the

homeowner wants a big honking fan that will dry the bathroom mirror in 60 seconds, then sometimes

a builder has to install the exhaust fan.

Apr 26, 2014 1:42 PM ET

Why so expensive?

by Robert Connor

For a machine that is sheet metal with 2 fans and a heat exchanger, why are one of the devices so

expensive? More so than a furnace? Are the manufacturers gouging us?

Apr 26, 2014 1:59 PM ET

Booster fans / Commisioning

by Kim Kornylo Walton

We have recognized for a long time that (E) HRV's are clumsy in the exhaust department. Boosting

whole house ventilation for one person showering seems like a funny thing to do. The inability of

(E)HRV's to spot exhaust is a shortcoming.

We have experimented with the installation of inline (in the duct) fans dedicated to each exhaust duct

(very near the recovery unit). We started with 150 cfm fans connected to a timer for each exhaust

location (bathrooms, laundry and kitchen)

The results were:

- initially there was cross duct exhaust, some of the fans redistributed the exhaust through the

interconnected ductwork to another room! inline Butterfly dampers fixed this problem by preventing

back flow.

- The kitchen needed more umph so the inline fan was switched out to a 350 cfm with better results.

- The laundry room exhaust is never used, would not install a booster fan from this location in the

future.

Seems to be a decent and not terribly expensive solution without energy or envelope penalties. The

issues mentioned above (different habits for different people) affect the effectiveness of this or any

exhaust system. The booster fan solution does the job that a dedicated exhaust for each room would

do.

We had this system commissioned, which is not normal procedure for a residence. For $250 the

system was balanced and the performance perceptibly improved. When investing thousands into a

mechanical system it is a no brainer to have proper commissioning done so that the system actually

does what it is supposed to do!

Apr 27, 2014 8:53 AM ET

Response to Robert Connor

by Martin Holladay, GBA Advisor

Robert,

You can buy a Panasonic one-room ERV for $320 online. Ducting (only two ducts are required rather

than the usual 4) is extra. In a cold climate, this device will only work from April to November -- you

can't use it in December, January, February, or March.

A fully ducted Zehnder (manufactured in the Netherlands for Zehnder, a Swiss company), installed, is

likely to cost you $8,000.

If a good Chinese company enters the market, prices may eventually drop.

Apr 27, 2014 8:56 AM ET

Response to Kim Kornylo Walton

by Martin Holladay, GBA Advisor

Kim,

You are the kind of innovator who sometimes discovers a new way of installing equipment. Your

suggestion may work, or may cause unexpected problems.

In the meantime, it's safe to say that installing an inline booster fan in the exhaust duct connected to

an HRV or ERV is contrary to manufacturer's installation instructions and may void the warranty.

Apr 28, 2014 12:57 PM ET

a few points ..

by Jin Kazama

First off, simple electronic devices come with user manual, cars come with an owner manual...

houses should ... that is 1 reason why we get so many user errors

On the pricing issue ...

Most of the "good to ok " models of HRV cost in the 700-1200$ range . All all those are strong

enough to be used as bathroom exhaust using boost function.

Paying more than 3000$ for the installed item is just getting ripped off.

As far as i know, it doe not take much more than 6-8 hours to install a simple HRV in a house

with a few ducts and grills as the only additional expenses.

Mirror fogging : if the consumer reason to complaint it is ... i don't see much hope on having them

figure out what's right and wrong about energy efficiency.

Instructing homeowners about usage and their attemps toward HRV/bathroom exhaust

could be a priority of the isntaller/builder then ?

This winter i hardly ever operated the panasonic exhaust fan on the small bathroom we are using

( the main one is not operational yet ) or only 2-3 minutes at the end of my long and steamy hot

showers to change the bathroom air somewhat ..

might be much more necessary in the future when i'll have finish sealing up the house,

which is the case with low ACH number houses.

And although i plan on intalling the HRV soon, i might keep the panasonic fan just to get a little 5-20

minute boost during summer time, where humidity is high and the "lost energy" is lower .

I have the exhaust fan installed with a 5-10-20-30 timed switch with is simple and works really well

during high humidity season ( mainly through summer )

and was inexpensive system

There is probably not much penalty occured in using a high flow exhaust fan when the temperatures

are within 10c to 30c .

Lastly, i am pretty sure that there is a spot on the market right now for lower

cost , high effiency low cfm HRV for small high effiency houses. 5000-8000$ cost for an efficient

system in a small efficient but budgeted house is too far of a stretch to be justified.

Easy to push high end stuff in a 400K-700K$ passive house,

but it is also easy to include Alcatara dashboard finish on a 350 000$ Ferrari .

Apr 28, 2014 2:11 PM ET

HRVs and fans

by Marc Rosenbaum

- Often will add bath fans if the HRV size doesn't allow a boost rate of at least 50 CFM per bathroom.

Put the bath fan in the 1/2 bath first, then the bath likely to get used the least. Don't need a 200 CFM

HRV in most cases even for large houses, in terms of normal ventilation rates (62.2-2010, not 62.2-

2013).

- Placement of the exhaust location in the bath has an effect on mirror fogging (as does shower

temperature and duration). In our "new" DER, we balanced to 25 CFM continuous from each

bathroom, and haven't needed the boost. The exhaust grilles are high and close to the shower.

Apr 29, 2014 3:09 PM ET

competing objectives, and more on ERV's

by David Butler

@Martin, thank you for an excellent and much needed article. Many aspects of building science

involve competing or even incompatible objectives. Your response to Kyl (comment #2) is spot on.

Assessing/managing homeowner expectations is paramount. Sometimes a conversation about pros

and cons of a particular design element is necessary to guide homeowner expectations. I find this to

be an essential step when properly sizing AC capacity. Ditto with ventilation.

The bigger problem is when the designer or specifier doesn't understand the trade-offs. That's why

peer discussions like these are essential in our industry. You won't find this in a book, nor sadly, in

many classrooms.

Regarding ERV's... I'm glad to see you touch on that but I think it deserves its own article. We're

seeing a lot more ERV's go into high performance homes and we're also seeing more winter moisture

problems as envelopes get tighter. Contrary to common practice (and manufacturer installation

guidance), I do not recommend an ERV as primary exhaust for high-use baths. Too much moisture is

recycled back into the house. Whether or not this causes problems in a given home depends on many

factors, but it's not a risk worth taking.

To wit, Panasonic specifically prohibits WhisperComfort (ERV) to be installed in baths and other high

moisture areas. Good for them! Other manufacturers should follow their lead or at least highlight this

risk in their application and installation guides.

As for those super high efficiency (and high dollar) ERV's... I can't help but wonder how much more

energy might be saved if a standard model were installed, with remaining $$ diverted to RE or more

productive EE enhancements! To me, an $8k ventilator is green-washing at its worst. Ok, maybe not

the worst.

Apr 29, 2014 3:22 PM ET

Edited Apr 29, 2014 3:23 PM ET.

Response to Marc Rosenbaum and David Butler

by Martin Holladay, GBA Advisor

Marc and David,

Thanks to both of you for your helpful comments.

Apr 30, 2014 4:23 PM ET

Bath Fan HRV

by Steven Landau

I put in occupancy sensors in each bathroom, with a 15 min off delay. The sensors connect to the

lights, and the Zehnder HRV Boost input. I never have fogging, or a smelly bathroom due to someone

forgetting to hit the switch.

Works great!.

Apr 30, 2014 5:52 PM ET

Edited Apr 30, 2014 5:58 PM ET.

mirror fogging

by charles CAMPBELL

I take short, not-so-hot showers in a small bathroom with a low-flow showerhead and 50 cfm bath

fan running. The mirror fogs anyway. Guessing it has to do with the temperature of the condensing

surface - it's on a thin, exterior wall with no outsulation. But I'm in Georgia, where you would think

outdoor temperatures would lead to less condensation, not more.

Apr 30, 2014 9:47 PM ET

on the lighter side

by Andy Kosick

Everybody's thinking it, I'm just saying it... heated mirrors.

May 1, 2014 12:35 AM ET

Not all HRVs and ERVs are created equal.

by Barry Stephens

There are some considerations to be taken in to account with this discussion.

Robert, there are significant differences in products. Efficiency can translate in to a significant

difference in comfort with regards to temperature of incoming air. For example, with outside air at

30F and inside air at 70F, a ASE of 75% will result in 60F incoming air temperature, while a ASE of

90% results in incoming air at 66F. Quite a difference in comfort. Similar differences in sound levels

are also an important consideration, and that is reflected in the size and insulation of the box.

With regards to Max Sherman's comments on ERVs, I am hoping that LBNL will one day realize or

acknowledge that ERVs vary widely, and that their assumptions are in some cases misguided. For

example, ERVs with enthalpy wheels, notorious for cross-flow leakage, should not be compared to

well designed and manufactured cross-counter-flow ERVs with dPoint membrane based heat and

moisture exchangers. Wheels are known (and certified) to leak at 10-50%, while dPoint units are less

than 3%. This is third-party verified by both HVI and PHI. So pontificating with broad-strokes

declarations is misguided and incorrect. And the formaldehyde theory. Data please. I thought we had

put that one to bed, pending some actual data. And again, enthalpy wheel, or otherwise?

And with regards to the theory that ERVs will retain too much moisture if used for bath exhaust, can

we also recognize that ERV SYSTEMS are not all created equal either? Take a typical whole house

system. There would be perhaps four to five exhaust points (bathrooms, kitchen, possibly basement

or mud room or laundry) and an approximately equal number of supply points. So assume a 50% RH

in the home, and 90% in the bathroom with the shower going on. The bathroom with the shower

going on represents 20-25% of the total exhaust flow, so 75-80% of the exhaust is at 50%, and 20-

25% is at 90%. Do the math. Not as significant as presented. And that bath with shower is only

intermittent, and the remainder of the time, the bathroom is at close to ambient. If the incoming air

is at low humidity, you transfer some of the moisture to the incoming air. If the outside air is at high

humidity, you still transfer a large percentage of incoming humidity to the outgoing air.

I still don't think it makes sense to punch more leaky holes in the walls and stick bath fans in them if

you have a properly designed, installed and commissioned HRV OR ERV system.

May 1, 2014 10:17 AM ET

Kitchens and jumper ducts

by kim shanahan

Martin,

Great article on a subject we will all be learning more about in coming years. The Zehnder rep, and

others in comments, mention exhaust grills in kitchen areas. I was told explicitly by the makers of the

HRV we used that kitchens exhausts should not be included in the ducted system, presumably

because greasy air could foul the heat exchangers. Is that not true with some manufacturers?

Another key consideration for us was the concern that if laundry rooms and bathrooms were the only

exhaust ports for whole-house ventilation, then how would the home perform with occupants who

kept all bath and bedroom doors closed all the time? Because we couldn't guarantee how the

occupants behaved, we used stud wall cavities with high and low grills to create passive jumper ducts

for all baths, laundry and bedrooms. I'm surprised neither you nor any posters have mentioned this

as a precaution when using baths-only for whole-house air exchanges. Were we just being overly

cautious? Or should this be a consideration?

May 1, 2014 10:37 AM ET

Edited May 1, 2014 10:38 AM ET.

Response to Kim Shanahan

by Martin Holladay, GBA Advisor

Kim,

Q. "I was told explicitly by the makers of the HRV we used that kitchens exhausts should not be

included in the ducted system, presumably because greasy air could foul the heat exchangers. Is that

not true with some manufacturers?"

A. You are correct. All HRV manufacturers agree that an HRV should never pull exhaust air from a

range hood. However, many HRV manufacturers permit -- and Zehnder encourages -- the installation

of an exhaust grille in the kitchen ceiling, as far from the stove as possible. This method is often

preferred by Passivhaus builders, who sometimes (if local code officials permit) also install a

recirculating range hood fan equipped with a charcoal filter rather than a range hood fan that

exhausts outdoors.

For more information on this method, see Makeup Air for Range Hoods and Kitchen vent fan options

to control cooking odors.

Concerning the question of whether bathrooms need jumper ducts: bathroom exhaust airflows are

relatively low, in the range of 20 cfm to 50 cfm, as the article points out. Door undercuts are usually

adequate for these low air flows, although you are free to install a jumper duct if you want (with

some loss of acoustical privacy).

May 1, 2014 1:42 PM ET

ERV Bath Fan - UltimateAir

by Jason Morosko

I own, built, designed, and live in a passive house. Plus designer / engineer heat/energy recovery

ventilation. Bathroom exhaust, as noted above, can vary greatly. Foggy mirror... please. Define

'unacceptable' ventilation exhaust rate from a bathroom in terms of measurement of bathroom indoor

air quality / comfort. The science is still being determined. I have had no negative results of venting

the two bathrooms in my passive house with our rotary enthalpy wheel heat exchanger over the past

two years (this personal reflection). Keep in mind I actively monitor humidity, CO2, and radon. In the

bathroom- the humidity goes from 40% up to 65%.. and then back to 40% within... an hour. 25 CFM

being exhausted. No noticeable change in the overall house humidity level. To add- we have been

making this ERV since 1992 and have not seen a problem concerning topics relevant to this

discussion.

To Max Sherman- please stop with the formaldehyde thing until you have data. The way the

information is presented- those that read it might think that no ventilation is better than ventilation

that might recirculate formaldehyde... and there is no data even to support re-circulation of

formaldehyde. Also note- the majority of commercial ventilation that use heat exchangers are

enthalpy and heat wheels.

May 1, 2014 1:49 PM ET

Edited May 1, 2014 1:52 PM ET.

Heated mirrors?

by David Butler

Wouldn't that be like shooting the canary in the coal mine?

Regarding jump ducts in baths, etc... Martin is correct, door undercuts are generally adequate for the

flow rates we're talking about. But it needs to be designed, not left to chance. The Manual D

guideline for undercuts is to allow 2 CFM per square inch of gap. Pocket doors are generally leaky

enough to ignore.

May 1, 2014 8:04 PM ET

Thank you Barry. There is no

by Morgan Audetat

Thank you Barry. There is no substitute for knowledge and experience.

We use ERVs exclusively and try to ignore competitor arguments like; too much moisture is

reintroduced into the house with an ERV...Seriously?

We use a lot of Renewaire and have not used a flatulence fan for years. Timed fans with push-button

point of use 20 minute timers work perfectly in my home and dozens of others we have remodeled or

designed for.

If anyone can show me how to install a whole-house ERV or HRV in 6-8 hours I will pay to learn or

better yet have them install all of our units from now on!

Kudos to Jason as well. I have more, rather than less, interest in the manufacturers perspective so

often discounted if not mocked in some circles.

May 1, 2014 8:17 PM ET

How to mitigate losses of bathfans

by Kye Ford

In reading the above comments, there seems to be a hung jury as to wether or not a stand alone

HRV will suffice for ventilation in a bath, good points and concerns both sides. So why not just include

an exhaust vent and give ourselves the option of additional ventilation if needed? To me in the

planning stages of a to be built "tight home" I am concerned about the unregulated air movement,

heat loss out these exhaust fans. Wether in use or not. Ever stick your hand below an bath fan in the

winter, cold air flows right through. I've tried various exterior dampners but I can still feel cold air

flowing in.I even order Battic Doors in line exhaust sock which was supposed to collapse under

pressure differences from outside to inside but that didn't seem to do much as the dampner built into

the exhaust vent stills rattles whenever the wind blows.

I like the option of including the bath fan with the HRV but I liked to tighten up the conventional

exhaust unit.

Any ideas?

May 2, 2014 8:45 AM ET

Response to Kye Ford

by Martin Holladay, GBA Advisor

Kye,

Concerning this dilemma, my own conclusions parallel those of Barry Stephens, who said, "Do you

really want two more 6-inch holes in your house, with cold air streaming in?‖

I don't think that there is any way to prevent infiltration and exfiltration through the ducts and

termination vents of bath exhaust fans. If I had an HRV system, I'm pretty sure that I would be

satisfied with the way that the HRV handled bathroom exhaust. I think that the imagined advantages

of separate bath exhaust fans are overshadowed by drawbacks.

May 2, 2014 11:38 AM ET

Edited May 2, 2014 11:49 AM ET.

Alternative method to fixing foggy mirrors

by David Lam

Here's a product that should solve the problem:

http://www.rainx.com/product/glass-and-cleaners/rainx-anti-fog/#.U2O--Pl...

Takes a little bit of maintenance and money to buy the product, but I bet it's cheaper than to oversize

the exhaust fans (capital cost) and over ventilate (operating cost)

May 8, 2014 4:06 PM ET

Edited May 8, 2014 4:07 PM ET.

understandg potential risks is requisite to good design practice

by David Butler

Barry wrote: "with regards to the theory that ERVs will retain too much moisture if used for bath

exhaust... a typical whole house system... (has) perhaps four to five exhaust points... (this issue is)

not as significant as presented."

Perhaps, or perhaps not. I see plenty of homes with one or two exhaust ports. In fact, there's nothing

wrong with having a single exhaust inlet with multiple supplies if the objective is primarily ventilation

as opposed to heat recovery from every exhaust. Not many homes are built to PH standards.

"that bath with shower is only intermittent, and the remainder of the time, the bathroom is at close to

ambient."

I agree that continued operation of the ERV will typically keep moisture levels under control. But what

about those periods of cool wet weather followed by a deep cold snap, as often happens? A home

reacts much quicker to changes in temperature than to changes in moisture. And what about

homeowners who decide to only run the ERV during showers (I've seen this on more than one

occasion)?

I'm not saying ERV's should never be used for bath exhaust. What I *am* saying is that designers /

installers / specifiers better know what they're doing. Playing down the risks doesn't help anyone. As

we tighten homes to unprecedented levels, it's incumbent upon industry practitioners to fully

understand the potential problems and unintended consequences, and apply appropriate design

strategies as well as homeowner education regarding moisture management. Manufacturers also

have an important role to play and, I believe, an obligation to at least describe potential risks in their

installations guides.

May 23, 2014 9:22 PM ET

separate toilet "closet"

by Erica Downs

How would you treat a separate toilet "closet" within a main bathroom? The door would presumably

be shut while in use, then open the rest of the time.

May 26, 2014 6:28 AM ET

Response to Erica Downs

by Martin Holladay, GBA Advisor

Erica,

The usual choices apply: if the house has an ERV or HRV system, the room can either be equipped

with an exhaust grille and a booster switch, or it can be equipped with a dedicated exhaust fan. The

advantages and disadvantages of the two approaches are discussed in the article.

Read more: http://www.greenbuildingadvisor.com/blogs/dept/musings/does-home-hrv-also-need-

bath-fans#ixzz3kdjpfG3p

Follow us: @gbadvisor on Twitter | GreenBuildingAdvisor on Facebook

MVHR - Mechanical Ventilation with Heat Recovery - pros and cons

Discussion in 'Home energy' started by eamonn123456, Feb 28, 2010.

Page 1 of 212Next >

I am looking for a good summary of the pros and cons of MVHR - Mechanical Ventilation with Heat

Recovery.

Obviously I would like to find something written from an independent viewpoint, not something

written by one of the firms selling these systems.

I would be particularly interested in something written in the context of the irish climate.

Reports from real-life experience of installing and running an MVHR system would be very welcome,

so if you have one in your house and would share your thoughts, that would be much appreciated.

PS I know there already is a thread on this here but its a bit out of date, am looking for an up to date

perspective if possible please.

MHRV

pros.

1. controlled ventilation system independent of outside wind and pressure.

2. Air quality and filtration.

3. steady stable heat delivery.

4. Humidity reduction (very important for Ireland with av RH of over 80%

5. Heat recovery.

6. Can deliver heat through the ventilation system for near passive spec. removing the need for

radiators, you can just put some underfloor in tiles areas and maybe a couple of towel rails and the

MHRV will distribute

7. can run at multiple speeds depending on occupancy c02 meters.

8. Feels fresh inside.

9. Cost neutral over 4 years.

10. New part F ventilation requirement means 4% bigger hole in wall vents.

11. can halve space heating bills.

12. adds future proof value to house, even if you just install the ducts now, as if you sell it in ten

years, the market will want MHRV.

13. Improves BER asset rating if combined with airtighness below 3 ach@50pa

cons.

1. Cant use open fire must use room sealed stove( why would you use an open fire)

2. Filters need cleaning twice a year (suppose you cant do that with your lungs0

3. perception of risk of mould growth in ductwork. This is due to early installers using flexi's for main

ducts instead of metal ducts. However generally if ducts are insulated where fresh air is brought in,

mould cannot happen because of reduced humidity.

4. dosent work with our speculator based construction methods of build it cheap and feck off.

Therefore hole in the wall vents seem more economical at build stage when occupancy costs are

ignored.

5. Most self builders use substandard designers and builders who dont understand that energy

efficiency can be incorporated at zero cost with a little bit of planning. For bolla sake, lettin engineers

design houses! madness. Moreover to be a builder in Ireland all you need is a Navarra and a mobile

phone, a plumber needs a four year aprenticeship and his papers.

6. Only makes sence to homebuilders as part of an integrated systems approach to building comfort.

Dosent work for eejits who throw up a building reg standard house with chimneys and vents. 'oh i've

only got €240k to build my one off, that means I can only go with cavity with kingspan, chimney, wall

vent, massive oil boiler, 3000 square foot, with corridors everywhere. maybe stick on a ecobling heat

pump to an inefficient house.' The problem is our designers and builders havent a clue. The people

building efficient passive or near passive houses are self builders who have gone and done the

research themselves and realised that spending on insulation and airtightness instead makes sence.

Hi buildright, many thanks for such a long and detailed reply, it's very convincing in favour of MHRV /

MVHR.

I have a few questions if that's OK:

1. What is the basis of your expertise and experience?

(a) Do you have MHRV in your own home?

(b) Do you install these systems? or

(c) have you been in charge of building a house where these systems have been installed?

2. How do you arrive at the calculation that it is cost neutral over 4 years?

For a 2500 sq ft 1.5 storey house, airtightness work has been estimated at 3k, and about 6k for

installing the system itself (ducting and unit).

Space heating for a well insulated house of this size should only take a *max* of 1500 litres of oil,

which should be less than 1000 euro this year (currently < 900 euro).

If space heating cost is halved, that brings it to 500 euro per annum, or a saving of about 2k over 4

years.

Even allowing for a lot of inflation in oil prices over 4 years, I can't see how it is cost neutral over that

time frame.

I am not trying to doubt what you say or contradict you, I would just like to be clear on what you are

saying.

Many thanks again.

Hi Eamon,

My background is in designing and supervising the build of passive and near passive houses. I also do

airtest and thermography investigations. Your max space heating is 60kWh per meter square, even

for a hypothetical figure, thats far too much, half your heat will go to heat the pavement outside and

your roof tiles. You need to eliminate the cold bridges. You should be concentrating on detailing the

insulation continuity and airtighness before looking at MHRV. Then again once you decide to go with

MHRV you start to go towards passive. Hopefully its early enough to make the sensible decisions on

insulation.

Taking a price of 5k for the unit, and not including airtightness, (building a house over 3 ach @50pa

is just shoddy building work). I immediately reduced the boiler size and eliminated a full 1990's type

central heating system and instead put in a system with 1000l tank feeding heat exchanger feeding

underfloor to the tiles areas. To meet part L of the building regs, i assumed solar is required and the

tank is part of the solar budget. The savings in plumbing are about 3 grand, leaving 3 grand to cover.

While modeling looks at supplying energy to keep the house temp over 20 degrees for the 2,200

degree day hours, in practice because of the lowered humidity of the MHRV, 18 degrees is fine as a

comfort level, In our monitoring of completed buildings, we find that houses of that size would rarely

use more than 400l for space and hot water when solar is installed. So its a saving of about €600 per

year, so that's about 5 year payback.

Payback is a bit of a nuisance term, what payback have your other purchases like your car or the

kitchen, you'll notice that most kitchens get replaced after 15 years anyway.

Buildright said: ↑

..................... Most self builders use substandard designers and builders who dont understand that

energy efficiency can be incorporated at zero cost with a little bit of planning. For bolla sake, lettin

engineers design houses! madness. Moreover to be a builder in Ireland all you need is a Navarra and

a mobile phone.........................

Thats a great bit of a rant you went off on there.

Couldnt agree with you more !

Bit misleading to claim there'll be a five year payback.

In order to have mvhr you need to start looking at having airtightness membrane around the house

so there are no leakages affecting the system . Before all of this you should be considering insulation.

How could you possibly

1 insulate

2 install membrane

3 plaster surfaces

4 not to mention ducting and heat recovery unit for 3 grand.

A lot of the comments above are valid re air tightness, buyil quality etc. Assuming you have a great

build quality then not sure you should be looking at the payback scenaio of a MVHR unit.

Their main aspect is controlling the interior air quality of a house. If you use either trickle vents or

hole in wall vent then you have an uncontrolled method of venting your rooms.

If you install a MVHR unit that is set up with proper baffles, booster for wet areas, etc then you can

control the ventilation requirements of all the rooms, moisture levels, condensation, etc.

I have seen so many cheap installations that are poorly designed that therefore do not offer value for

money and in some instances purely don't work. Be carefull you get what you want. The cheapest

option may not be the best. Performance is what should be the first bottom line.

Vincenzo said: ↑

Bit misleading to claim there'll be a five year payback.

In order to have mvhr you need to start looking at having airtightness membrane around the house

so there are no leakages affecting the system . Before all of this you should be considering insulation.

How could you possibly

1 insulate

2 install membrane

3 plaster surfaces

4 not to mention ducting and heat recovery unit for 3 grand.

Vincenzo,

Look at the big picture for a minute, Even if you just use hole in the wall vents 10 air changes at 50

pascals is equivalent leakage area to leaving a door open. You dont need membrane. Hardwall plaster

and OSB do the job better. The membrane is not technically an airtight barrier, its a vapour control

layer. It is essential to have vapour control no matter what build up you select. This generally means

lining the dormer in OSB and taping as a vapour control. This creates a services cavity with battens

between osb and plasterboard. I usually put softboard on the rafters, as wind acting on the insulation

reduces its performance.

In Germany and Austria they design houses to last 60 years, in Ireland every weekend I'm testing

houses often no older than 2 years old, which are impossible to heat, have condensation problems

and are drafty. The way we build houses is 'shocking bad'.

Solar is now mandatory to meet regulations. The new ventilation regulations say you need to increase

the size of the hole in the wall vents by 40% if under 7 air changes, and boilers have to have

efficiencies of over 86%. This is the extra cost in building, its coming from regulation, so that extra

cost is just for good practice. In this type of house having to heat the air twice an hour is an

expensive task. The MHRV retains about 90% of the heat. The extra over good practice building for

adding MHRV is about €3k. Ya sure if you compare a bog standard one off and leave out the

mandatory renewables and stick kingspan in the cavity and drill big holes for services and cables it

will cost about €15k to add MHRV.

The fact is to build celtic tiger type houses now is a stupid idea. Bolting heat pumps or renewables

onto a minimum standards build is ridiculous unless your a speculator who can sell it fast and leave

the homeowner with an underperforming asset. The way we build now has changed dramatically but

many builders are left behind because of the low levels of knowledge and skills in the industry.

Anyone still building bog standard will probably see me visiting their house in a couple of years to

show them the uninsulated knee walls, or the wind blowing through downlighters and dormer crawl

spaces, uninsulated boiler pipes, blocked wall vents and closed trickle vents, the underfloor leaking

heat through the rising walls, the open fireplaces which get used just twice a year, quilt insulation on

the slope, I could go on.

All I'm saying is, think about where your wasting energy in a home and think about what comfort is.

You'll soon arive at the inevitable conclusion that you need to pay attention to maintaining the

integrity of the insulation using thermally storing insulats like cellulose and softboard in the roof.

You'll need to remove the rising wall, eaves and windoe cill/head/reveal cold bridge and you'll need to

prioritise minimising heat loss over buying a huge boiler. In the end of the day you'll have a future

proofed home that will be comfortable and healthy and pretty close to passive. So good luck with that

Hi buildright, thanks for the response, great to get help from someone who knows what they are

talking about.

A couple of things:

1. the house is planned to have a standard central heating system so no saving in plumbing there

(you may argue that there is no need for standard central heating, but would that be true in a non-

passive house?);

2. assuming solar is included then we are not comparing like-with-like to a traditional heating system,

so the installation, running and maintenance costs of solar would have to be factored in for

comparison;

3. I really do think payback is absolutely relevant for these energy saving measures. You might say

that air quality is the main reason for MHRV, but I don't think so - surely air quality is adequate in

most houses in Ireland? Assuming the main reason for MHRV is energy efficiency, which most people

would agree, then installation, maintenance and running has to be seen as an additional cost. That

cost needs to at some point be recouped by means of savings in energy bills compared with the same

house without the system. Otherwise, why bother?

(I don't agree with the comparison with a car or a kitchen - the function of a car or a kitchen is not to

save energy, so payback is not an issue, but that is the point of an energy saving system, so you

expect to break even on costs at some point and then start saving).

Open to correction on any of the above, thanks again for the advice.

1. Look at the design of most standard central heating systems the porpose of which is to

compensate for the massive heat loss through fabric and windows. Its very ineeficient, the heat rises

and draws in cold air at your feet. You'll always have cold feet . The hot air rising, blows out through

the top of the house drawing cold air in at low level. You shouldn't need to heat upstairs, the natural

stratification of air should mean that the warmest air is at the top of the house. Underfloor downstairs

is all thats required just to the tiles areas, the combination of rising air and HRV distribution will

elliminate the need for central heating. The central heating is an analogy to a massive engine over-

compensating for the fact that you designed your car with square wheels. Evan a half passive house

with 30kWh per m2 heat demand benifits from such a strategy.

2. Solar is a seperate decision to MHRV. Its mandatory and is a regulatory burden.

3. Air quality is bad in most houses. Air quality is related to humidity, particulate matter, organic

matter, microorganisms, odours, carbon dioxide and monoxide. The heat recovery is a free added

benefit. You are designing your house to achieve comfort for human habitation. The house should be

designed as a system, you cant look at each element in isolation. I've worked with clients who are

building to passive standard at very close to conventional cost, but it does take a little more work to

find cost effective solutions. Just get out of the mindset of the celtic tiger era. Thats over and it'll be

ten years before we have growth above inflation. You're building for future energy shocks and long

term asset value. Most the property we've built in the last ten yyears i svirtually worthless beyond its

land value. Protect your investment by building a house that will still be relevent in ten years time.

We all have regrets after completing a build, I don't want to say I told you so, measure twice, cut

once.

Good points well made buildright. Thanks for taking the time.

Lots to think about.

(Haven't heard too many dissenting voices either which is interesting in itself.)

PS I know there already is a thread on this here but its a bit out of date, am looking for an up to date

perspective if possible please.

If 18 months is out of date for info/technology, think of what your unit will be at the end of projected

payback time.

yesterday morning outside temp was 4c. inside house was 18 to 20c. the air temp coming out from

the supply vent was 19c.

is MVHR thesame as HRV ?

Capt. Beaky said: ↑

If 18 months is out of date for info/technology, think of what your unit will be at the end of projected

payback time.

Click to expand...

Fair point Capt Beaky but as I don't have either a crystal ball or a time machine, all I can do is find

out the latest up to date info and opinions and make the best judgement based on those.

What's your own opinion / experience on MVHR / MHRV ?

Hi all,

interesting thread,

buildright you quoted

2. Solar is a seperate decision to MHRV. Its mandatory and is a regulatory burden.

what exactly does the building regs say re solar - would HRV not be a from of renewable energy

which would suffice for building regs??

kfh said: ↑

what exactly does the building regs say re solar - would HRV not be a from

of renewable energy which would suffice for building regs??

Click to expand...

No, HRV is not a renewable energy source!

kfh said: ↑

Hi all,

interesting thread,

buildright you quoted

2. Solar is a seperate decision to MHRV. Its mandatory and is a regulatory

burden.

what exactly does the building regs say re solar - would HRV not be a from

of renewable energy which would suffice for building regs??

Click to expand...

Nearly all renewable is Solar at source.

Geo thermal is a more limited endless supply, taking heat from the earth.

Its arguable that this is solar/ambient in nature withing say 10-100M of the surface, but if you go

deeper you're tapping the heat of the core.

Solar is an virtually endless supply [2 billion years to go - sure we won't find it at all].

Wood is just solar energy trapped in complex hydrocarbon chains by biological systems called trees.

Wind, wave and hydro [rivers] power are solar power that's motivated the atmosphere and the seas

to do things with convection, conduction, radiation and evaporation.

Passive heating and ventilation also comes from solar power acting directly on heat stores.

The more advanced houses in America use ducts with the slab to heat air and disperse it around the

house.

Moving air around requires special measures to prevent fire spread.

I'll stop rambling now.

FWIW

ONQ.

http://www.oneillquigley.eu

All advice on AAM is remote from the situation and cannot be relied upon as a defence or support - in

and of itself - should legal action be taken.

Competent legal and building professionals should be asked to advise in Real Life with rights to

inspect and issue reports on the matters at hand.

2 otions for Parl L compliance

10 Kwh/m2/annum has to be delivered from renewables. Thats either group heating, pellet boiler,

solar or the heat delived from a Heat pump above a coefficient of performance of 2.5 (60% of electric

energy is lost between power station primary fuel and delivery to your house, so the heat pump is

only efficient above and beyond producing 2.5 times more heat energy than its supplied electric

energy.

or a combination.

see page 15

http://www.environ.ie/en/Publicatio...g/BuildingStandards/FileDownLoad,16557,en.pdf

or

4kWh/m2/annum of elecric power

Hi Buildright, I am very interested in your views on this topic and at the expense of being labelled

clueless I would like your opinion on whether it is worthwhile installing MVHR in a 2,800 sq ft 1 1/2

storey new block build with high levels of insulation, i.e. in excess of manadatory min. I'm not up with

the technical issues associated with air tighteness etc but I have been told that it is possible to

achieve high levels of air tightness with a block build - obviously if the builder does his job! I suppose

the real issue here is if not going with an airtight timber frame of SIP system is MVHR still

worthwhile?

A secondary issue here relates to the Building Regs and the installation of solar panels. I was of the

view that if you installed a renewable heat source like a geothermal heat pump this obviated the need

to go with solar panels, at least that is what I have been advised. Thanks in advance

1. ...I'm not up with the technical issues associated with air tighteness etc but I have been told

that it is possible to achieve high levels of air tightness with a block build - obviously if the builder

does his job! I suppose the real issue here is if not going with an airtight timber frame of SIP system

is MVHR still worthwhile?

A secondary issue here relates to the Building Regs and the installation of solar panels. I was of the

view that if you installed a renewable heat source like a geothermal heat pump this obviated the need

to go with solar panels, at least that is what I have been advised. Thanks in advance

You've caught my eye with mention of SIP (it's what I do), so a few things there:

1. Even built well, unless you undertake a specific airtightness 'programme' in a block build, it will not

be airtight. This is simply a reflection of the properties of blocks/etc. You can of course make it

airtight, but that is a distinct separate task, and trade. And it brings a cost with it.

Another limitation is that you're only talking about walls - the roof is another huge issue, as is the

connection of it, to the walls. Again, you're talking about time and materials. And , again, money. As

you probably know what a SIP is, you'll know this is a non-issue in a SIP system.

2. As to the value of going with MHRV etc, well the fact is, that airtightness is now a measured

requirement, so if you have a particularly good reading, you're probably going to need it anyway.

Simply put, the choice of your building method shouldn't be influencing your decision on the MHRV,

as your requirement for airtightness is the same, irrespective of the build type you choose.

3. In any modern house, built to a high standard, and working well, it's requirement for heating will

be (relatively) low. This being the case, heating system choices, and their costs, need to be

considered even more carefully than before. I like solar, because, in a new build, it is not a big cost

as part of a new system, and imho, it does make a measurable contribution. As usual, YMMV and all

that

4. I'm still not personally convinced about heating systems that are heavily reliant on electricity.

Again, this is not a reflection on the systems themselves, but more the cost of electricity itself.

Hi I recently installed a heat recovery system into my home. Initially I intended to do a diy job on it

myself as posts here say it's diy friendly but decided to get a crowd home heat recovery to do it for

me as i was busy working. Glad i did in the end as they had two ductors that spent 4 days doing the

work so i greatly under estimated the amount of work on rigid ducting and the expertise required to

do the job right. You pay for what you get and if i done the job i would have done a cheap job far

less professional to what the guys done.

I have spent a fair bit of time researching MHRV and concluded it's not the way to go for me. Will be

going with a Mechanical Extract Fan system that's humidity and presence sensitive with ducts

extracting moisture from wet rooms. In habitable rooms, I plan to install either hole in the wall /

trickle vents in windows, both of which would be humidity sensitive.

Hi,

Can anyone shed some light on the running costs ?

Hi All,

Very good thread and some very valid comments. Can I ask a question which is related to what we

are discussing? Is timber frame the way to go in lieu of blockwork? e.g timberframe with 50mm cavity

and external blockwork with render. I know of some people who are using cavity wall with 80mm

cavity insulation and sand cement, urethane board mushroom fixed to interna face of external walls.

I would have imagined timber frame is the way to go but this all depends on the quality of the timber

frame contractor etc.

You can't ask a qustion comparing timber frame versus masonery. Its can't be done. Quality control is

a big problem on our domestic building sites and generally results in a low quality product.

I have 2 specifications, both deliver near passive performance levels at slightly over conventional

build rates. Performance levels are walls 0.14 u-value. I have other standards at 0.16 and 0.18.

Airtighness is 1 air change @50pa underpressure. MHRV is used to run at 0.75 air changes per hour

wit polyetheelenr ducts. Heating oil boiler with underfloor to tiled areas and 2 towel rails on a

seperate circuit. 5m2 solar evc tube. 1000l buffer. room sealed stove.

One is masonery, 250 mm wide cavity masonry, precast first floor, cellulose filled double rafter roof

with cellulose fill and softboard racking. Foamglass and Quinlite inner leaf starter blocks on standard

rising wall.

Two is timber frame, vapour diffuse to outside: aquapanel renderboard rainscreen, panel vent racking

board, 220 stud with 75 rail, cellulose filled, osb inner board, insulated services cavity, osb substrate,

plasterboard. On an insulated formwork EPS raft.

Heres where the fun starts..... Firstly, I need to build a thermal bridge free rising wall/edge beam and

get the Radon barrier right. I need to get the building windtight from outside, softboard on the roof

does this. Then when the windows are in, I get the inside airtight using OSB rather than intello. Then

the trades come in and poke holes everywhere... thats why I use OSB.

There is no difference in performance if you detail the build well and have good quality control on

site. The build spec I have selected, is the optimum level which balances enhanced performance

against cost. It is an affordable spec which delivers a thermally stable, good quality indoor climate

and healthy air, with a spec designed for longevity and very low running costs. The spec, its devised

using a systems approach. What is saved on heat pumps is simply put into insulation. Its common

sense, heat pumps with a payback of 20 years vs insulation and airtightness with a payback of 3.

Running costs can be calculated from your PHPP (passive house planning package) MHRV will half

your space heating bill. The house to the above spec, is a celtic tiger design, two storey with gables

and dormers and stuck on stone. Perched on a hill. ' hey look at me' you know the type. At about 250

square metres it will cost about €700 a year for space heating and hot water, pumps etc.

MHRV uses a pair of Santos units with solid ducts (no flexis or flatpacks). two 25w fans in each

running continuously.

Patrick2008 said: ↑

Hi All,

... Can I ask a question which is related to what we are discussing? Is timber frame the way to go in

lieu of blockwork? e.g timberframe with 50mm cavity and external blockwork with render. I know of

some people who are using cavity wall with 80mm cavity insulation and sand cement, urethane board

mushroom fixed to interna face of external walls.

I would have imagined timber frame is the way to go but this all depends on the quality of the timber

frame contractor etc.

Buildright said: ↑

You can't ask a qustion comparing timber frame versus masonery. Its can't

be done. Quality control is a big problem on our domestic building sites and

generally results in a low quality product.

Click to expand...

And buildright has nailed it on the head, in one. Naturally, I have an interest, as I build homes in a

timber based system, but the single biggest issue is, and will continue to be, quality. Good materials,

poorly assembled, still gives a poorly built house.

The current downward ratcheting of prices, is only going to end in tears, as you always, always, get

what you pay for. Get a quote for X, and then get the job done for x/2 - then, you don't need to be

scientist to figure out that that saving is coming from somewhere..........and it isn't your future energy

bills !

When we did our accrediation with the BRE, a major thing for them is 'How do you manage quality

on-site' ? And every second visit that they make to us is to a site, to check. For us, the simple way to

control quality, is use factory-employed staff directly - we don't use subbie's - for too long, they've

been paid on a per sq ft basis (and bring your own fixings ! ), and that only gets you one result.........

Back on-topic, btw - quick question - if people are considering NOT using MHRV, I'd love to know

what they ARE planning to use, in lieu.......

Hi Galwaytt. Can I ask the name of your company. By all means PM me.

Mhrv

re topic: has anyone any experience with or comment on finewire HRV? am

considering this on grounds of cost and simplicity

A thought struck me recently. Why do MHRV systems need filters (and need regular replacing of

those filters) while the old hole in the wall and demand/humidity driven ventilation systems don't. Is it

to keep debris/insects out of the fans to prevent damage or is it an air quality issue?

feileacan said: ↑

re topic: has anyone any experience with or comment on finewire HRV? am

considering this on grounds of cost and simplicity

Click to expand...

Hi,

Looks very impressive and simple. Will be looking more into it. I think it will be the

way to go

Really interesting posts. I was hoping to reignite the discussion as we are now in 2013. Have any of

the original contributors any updates? Or does anyone else have a view ?

Are heat recovery systems more advanced now?

I am in the midst of choosing a builder for a 2300 sq foot house and today the builder who are

leaning toward told me he thought they weren't worth the money. It goes against my research to

date.... I'd love to hear any opinions

Cheers

sunnyside said: ↑

I am in the midst of choosing a builder for a 2300 sq foot house and today

the builder who are leaning toward told me he thought they weren't worth

the money. It goes against my research to date.... I'd love to hear any

opinions

Cheers

Click to expand...

there not worth the money when a builder cant achieve a decent standard of air-

tightness!

if you dont have a performance spec for your builder forget about it.

btw do you have a provisional BER done?

Thanks very much for the reply.

The site we have bought has just the foundation poured and services in so, no Ber yet.

What do you mean by a builders Performance spec?

Any other tips when choosing a builder ?

Am I to take it that your a fan of hRv systems?

Any and all advice appreciated.

Thank you

Mvhr

It is important to clarify exactly what you want from the building. I am not sure what details are

included in your drawings, but sometimes you need a list of specifications.It is better to have

everything agreed before engaging with the builder.

A MVHR system is great if you have suitable insulation and air tightness levels in place. Current

regulations require an air tightness minimum level of 7m3/hr/m2, but you really need to be under

3m3/hr/m2 for the system to operate more efficiently. Otherwise you are looking at trickle vents,

extractor/intermittent vents and permanently open vents for rooms with combustion appliances.

The preliminary BER or DEAP calculations is a condition for certain County Councils which must be

issued with the commencement notice. It serves a vital purpose in that from the outset you are

confident that the design is compliant with the current building regulations.

sunnyside said: ↑

Thanks very much for the reply.

The site we have bought has just the foundation poured and services in so,

no Ber yet.

1. What do you mean by a builders Performance spec?

2. Any other tips when choosing a builder ?

3. Am I to take it that your a fan of hRv systems?

Any and all advice appreciated.

Thank you

Click to expand...

am in the midst of choosing a builder for a 2300 sq foot house and today the

builder who are leaning toward told me he thought they weren't worth the

money.

Click to expand...

your choosing a builder and you have mentioned detail tender/constriction drawings and you dont

know what a performance specification is.

2. you need an architect to specify and detail the drawings so there is no squirming in an builders

price. you need an engineer because you dont know what foundations/floor you bought, and you

need to do a BER assessment at a minimum, so you can comply with building regulations

3. HRV is the least of your worries as others have said - the road your heading down seems more like

this

i wish you all the best

HRV in old house

Hello!

Looking for some advice please.

Can you install HRV in an old house, or are there any 'stand alone' type units that could be installed

in the damp / hot rooms such as bathrooms / kitchen?

Any advice much appreciated - and are they worth the money in terms of heating bills and comfort?

Thanks!

Can you install HRV in an old house, or are there any 'stand alone' type units

that could be installed in the damp / hot rooms such as bathrooms / kitchen?

Click to expand...

How air-tight is the house? This will play a significant role in the efficiency of MHRV.