heating losses- infiltration and ventilation

Heating Losses-Infiltration and VentilationARCH-432

AttendanceWhich civilization made it a point to layout whole cities to take advantage of passive heating? In what direction did the city streets run?

A. GreeceB. RomeC. EgyptD. PersiaE. Babylonia

AttendanceThe ancient Greeks did this. What was shown is Priene (Priēnē); (5th Century B.C.), which had all of the streets laid out in an East-West fashion, thus allowing all homes to point South.

Attendance

“Only primitives and barbarians lacked knowledge of houses turned to face the winter sun, dwelling beneath the ground like swarming ants in sunless caves.”Aeschylus

Aeschylus

Greetings Capt.

Kirk

AttendanceAeschylus pronounced Ess ca less

One of the earliest writer of Greek tragedy – before him plays had single actors who could only respond to a chorus (group of people). Aeschylus increase the tragedy to two actors with dialog.

Big Picture Momentroofroof

ExteriorExteriorwallwall

GlassGlassconductioconductio

nn

FloorFloor

Infiltration Infiltration and and VentilatioVentilationn

CeilingPartition

Five main types of heat loss1. Transmission (conduction)2. Infiltration (convection)3. Ventilation (convection)4. Radiation (radiation)5. Moisture migration

roofroof

ExterioExteriorr

wallwall

GlassGlassconducticonducti

onon

FloorFloor

InfiltratioInfiltration and n and VentilatioVentilationn

Ceiling

Summary of Heat LossesWallRoofFloorWindowsDoorsInfiltrationVentilation

Envelope Losses

What You Need To KnowThe difference between ventilation and infiltrationCalculation methods for both ventilation and infiltration

What You Need To Be Able To Do

Calculate infiltration/ventilation loadsBe able to reduce/mitigate infiltration and ventilation loadsEmploy techniques for increasing ventilation effectiveness

TermsInfiltrationExfiltrationVentilationDirect Outside Air System (DOAS)

Infiltration

“The uncontrolled introduction of outside air into a building.”

Infiltration

The uncontrolled introduction of fresh air into a building.

1. Most subjective of all losses2. Oftentimes the largest of all heat losses.

Sometimes comprises up to 30% of the total

heating load.3. Ends up being an “educated guess”

Why Is This Important?All buildings leakA tight building will leak .5 AC/HA leaky building can leak 3 AC/HRegardless of climate, air leaking into walls causes problems

VentilationThe mechanical introduction of outside air (OA) to: Replace Oxygen Dilute contaminants Pressurize the building

Moisture LoadMoisture Load for a Typical Commercial Building

Ventilation72%

Infiltration11%

People13%

Doors4%

Permeance0%

Infiltration Calculation Methods

Crack methodAir Change Method‘Averaging’ method (‘I don’t know so I’m going to throw a dart’ method)

Crack MethodPresumes that an accurate estimate can be obtained by estimating the rate of infiltration per foot of crack for doors and windows

CFM = Ft. of Crack x Infiltration Rate

QS = 1.1 x CFM x (T2 – T1) in BTU/HR

Add Infiltration Through Open Door

Determine Door Usage Number of People per Minute = תDetermine CFM per person (D)

CFM = ת x D LEED-NC Credit EQ 5 for providing vestibules.

Infiltration by Crack Method

Add CFM from Crack losses to CFM for Open Door losses

Mitigate These LossesHow do you reduce or mitigate these losses?

(Review)

Mitigation StrategiesPressurization

QS = 1.1 x CFM x (T2 – T1)

Vs.

QS = 1.1 x (CFH/ft of crack x ft of crack)/60 x ΔT

You own the variables!

Infiltration VariablesReview

Wind velocity and directionStack effectsCorner roomsExhaust fans on or offPressure zoningFrequency of useMaintenance

Stack EffectReview

Air Change MethodOften used in residential construction and in large warehouses and similar buildings

CFM = A.C.H. x Volume (ft3)/60or

CFM = Volume (ft3)/Frequency (minutes)

Air Change MethodUses same formula for sensible

Equals one room changeDesigner will use 0.3 to 2.0 air changes per hour (ACH) Occupancy Climatic condition (i.e. winter vs. summer) Construction (tight or loose)

Least accurate of the three methods

Qsens = 1.1 x CFM x T

Table 2-8

Heat Loss Due to Infiltration

Infiltration Btu H = (.018) x (ACH) x V x (Ti –

To)ACH = air exchanges per hourV = volumeTi = inside temperature To = outside temperature

Heat Loss Due to Infiltration

OR

Heat Loss Due to InfiltrationInfiltration Btu H = 1.1 x CFM x (Ti – To)CFM = (ACH x volume) / 60 min per

hour

Heat Loss Due to InfiltrationInfiltration Please Note: For tight construction use 0.5 for ACH.For medium construction use .85 for ACH.For loose construction use 1.3 for ACH.For really bad construction use 2.0 for ACH

For the summer months (cooling) use 70% of the winter values.

Btu Hour Loss due to Infiltration Main Area

CFM Ht. W. L. 1.10 air exch. vol. In cf / 60Temp. Ch.

  12 46.66 74.66 1.10 0.5 41,803.63 348.36 76 29,123.19                   

Btu Hour Loss due to Ventilation Main Area

Ht. W. L. 1.10 sfcfm

exchange Occup.Temp. Ch.

  12 46.66 74.66 1.10 3,483.64 0.180 34.84 76 66,983.35

Ra RpOccup/

10000.18 5 10.00

Infiltration & Ventilation

Heat Gains Due to Infiltration

Latent LoadBtuH = 4500 x (air exchanges x

(volume) /60) x(W Final – W Initial)

(W Final – W Initial) = Difference Ratio Pounds of Moisture per dry air

Heat Loss Due to Ventilation

Ventilation Btu H = 1.1 x [(Ra x square feet of

building ) + (number of people in the building x Rp )]

x (Ti – To)

Heat Loss Due to Ventilation

Heat Loss Due to Ventilation Ventilation Ra = Area Outdoor Air Rate Rp = People Outdoor Air Rate

Example: Pharmacy Ra = .18 Rp = 5

Heat Loss Due to Ventilation

VentilationBtu H = 1.1 x [ (.18 x 3,632) + (30 x 5)] x

76o

= 67,214

Ventilation and / or Infiltration