how to avoid the 5 common mistakeseuroheat-11242.kxcdn.com/guides/euroheat-5-common...in the pages...

THE 5 COMMON

MISTAKESthat will make your FLOOR HEATING

system USELESS and IMPOSSIBLE to

repair

HOW TO AVOID

2 www.euroheat.com.au

Phil Pacak

Efficiency engineer

Euroheat Australia (Perth)

Ph. 08 6468 8895

[email protected]

STOP,Before you put

the first pipe in…

Hydronic floor heating systems are all the

rage… and rightly so:

The hydronic system lowers energy costs.

It’s fully automated. And it gives your home

a feeling of comfort, no matter what the

temperature is outside.

However, all this happens only if it is

designed and installed properly.

You see, several times a month we get

calls from people who have a hydronic

system… but it doesn´t work as the

salesperson/architect/designer/builder/

installer promised.

The client is cold, out of pocket, unhappy

and paying a fortune in running costs

… and the architect, builder and floor

heating installer are scratching their heads

trying to find out what went wrong (and

who is responsible).

Unfortunately, once a floor heating system

is installed, it’s very difficult, and in most

cases impossible, to fix: The “repair” would

actually involve ripping up the concrete

slab. Pulling down walls. Basically building

the house all over again. And that´s why

people with poorly designed floor heat-

ing systems have no other option than to

turn the system off. And even though they

paid tens of thousands of dollars for it, they

have to find (and pay for) another way to

heat and cool their house.

Getting the hydronic heating system right

the first time is therefore essential… and

that´s why I have written this guide for you.

In the pages ahead, you’ll see the five most

common mistakes made with hydronic

floor heating systems and, most crucially,

how to avoid them.

As professional engineers and experienced

installers, we’ve been designing and

installing these systems for houses and

commercial buildings in Western Australia

for over 26 years (since 1992).

The following tips are therefore only a

snippet of what we had to learn over this

time to make all our systems run… and run

efficiently.

And no matter if you decide to work on

designing and installing your hydronic

heating system with us or not, I hope these

tips will help you make sure your floor

heating works the way you want it to.

Because once it´s installed, there is

virtually no way to fix mistakes made at the

beginning…

© 2018 Euroheat Australia Pty Ltd.

3

50mm THICK HEATED SCREEDWITH THERMAL INSULATION

257mm THICK HEATEDSUSPENDED SLAB

Heat from the warm pipes doesn´t rise only

upwards (the mistake of placing pipes into

suspended slabs)

Mistake #1

Like you already know, hydronic floor

heating works by circulating warm water

through pipes installed in the floor. The

heat from the water is soaked up by the

concrete in the floor. And once the floor

is warmer that the temperature of the

air around it, it begins to pass the heat

onwards.

The essential fact is that heat doesn´t rise

only up to the room above it… but the heat

diffuses into every direction equally within

the concrete.

Therefore:

1. The more concrete (or any other mass),

the more energy is required to heat it up.

2. The greater the mass, the longer it takes

to heat up.

3. Larger volumes of mass have greater

surface areas, resulting in greater heat

losses.

This means it costs a lot to heat up a

suspended slab. It takes a long time to do

it. And a lot of the energy escapes to the

sides and below and is therefore wasted.

I will show you the physics of how this

happens…

Let’s compare two different floor

constructions that include a hydronic

floor system; a classic 3-course 257mm

thick suspended slab, and a 50mm thick

insulated screed on slab.

We’ll assume that both the screed and

the slab are of the same material and

density (concrete), and subject to the same

conditions to make the comparison fair.


How much more energy does the

suspended slab need to heat up,

compared to the screed?

If we assume a 100m² heated floor area,

the suspended slab mass is 100m² x

0.257m thick = 25.7m³ = 61.68 tonnes of

concrete. The screed on the other hand

has a mass of 100m² x 0.05m thick =

5.0m³ = 12.00 tonnes of concrete. To raise

the temperature from 15˚C to 30˚C, the

suspended slab will require 226.16kWh of

energy, yet the screed only 44.0kWh

So we can see the initial heat-up of the

suspended slab alone requires more than

5x the energy, compared to the insulated

screed – but take into account this does

not factor in any additional heat losses from

the suspended slab.

How much longer will the suspended slab

take to heat up, compared to the screed?

This is determined by the maximum

amount of energy that can be input into the

system at any one time. For a moderately

insulated building, a 100m² floor heating

system would require a heat source of

about 8.0kW capacity.

The screed system requires 44.0kW hours

of energy to rise from 15˚C to 30˚C, so

44.0kWh/8.0kW heat source, results in a

heat up time of 5.5hrs (again, excluding any

heat losses). The suspended slab, however,

requires 226.16kWh/8.0kW resulting in a

heat-up time of 28.27hrs – again, 5 times

longer than the screed.

But won’t a bigger heat source heat it up

quicker? Yes, definitely… but after the initial

heat-up the unit would be working at a

fraction of its designed output, drastically

reducing the efficiency and lifespan of the

heat source. It would also cost multiple

times more to install such a large heat

source, and the cost of the energy input

would be super high. It would be like

driving a road-train to buy milk from the

corner store.

But once the suspended slab is heated

up, doesn’t it retain heat, and just need

topping up?

Yes… and no. If the building, and particularly

the floor structure, were insulated super

well, then yes, it would retain some heat

and give it off to the internal environment.

But most houses in Australia aren’t that

well insulated… and most suspended slabs

aren’t insulated well (generally not at all).

What’s problematic is that it’s very difficult

to insulate these suspended slabs well

– because there are still so many thermal

bridges for the energy to leak through.

Let’s compare heat losses from the

typical suspended slab to an insulated

screed:

50mm THICK HEATED SCREEDWITH THERMAL INSULATION

257mm THICK HEATEDSUSPENDED SLAB

EXTERNAL 7°C

INTERNAL 20°CEXTERNAL 7°C

INTERNAL 20°C

EXTERNAL 7°C

INTERNAL 20°C

Mistake #1


5

You can see the main difference between

the two is there is much more heat

escaping (especially downwards) from the

heated suspended slab.

But doesn’t heat rise? Yes, but this in only

applicable in fluids, such as water and air. In

solid objects, such as concrete, heat travels

in every direction… and it travels the most to

where it’s the coldest.

So, as we can see above, the heat travels

in all directions, even through adjoining

building elements (conduction across

solids), radically increasing the heat losses

incurred.

The detail shown above isn’t even that

bad compared to other common building

details/methods, where the energy loss is

very severe.

Check some of the common heated slab

energy loss situations out…

Heat Emission and Leakage from Exposed Slab Soffit:

Thermal Bridge Through Exposed Edge Beam:

INTERNAL 20°C

INTERNAL 20°C

INTERNAL 20°C

EXTERNAL 7°C

EXTERNAL 7°C

EXTERNAL 7°C

INTERNAL 20°C

INTERNAL 20°C

INTERNAL 20°C

EXTERNAL 7°C

INTERNAL 20°C

INTERNAL 20°C

INTERNAL 20°C

EXTERNAL 7°C

EXTERNAL 7°C

EXTERNAL 7°C

INTERNAL 20°C

INTERNAL 20°C

INTERNAL 20°C

EXTERNAL 7°C


Thermal Bridge Through Slab to Balcony:

From the examples shown it’s obvious

that the two biggest issues with heating

suspended slabs are:

1. Huge heat losses from exposed surfaces

to the external environment, because the

heat flow is stronger to where the mass is

coldest (outside!).

2. Heat losses through conduction to other

building elements such as walls or steel

structures, which are difficult to avoid.

All these wasteful heat losses greatly

contribute to the running cost of the

system. We can see this if we compare

the approximate running costs for different

situations. For a 100m² heated floor area,

with a heat pump as the energy source,

would cost per hour:

ÌAverage-insulated building with insulated

heated screed: $0.42/hr

ÌAverage-insulated building with heated

suspended slab: $1.67/hr

The suspended slab system cost 3.97

times more to operate (It would even be

50% cheaper to use aircon!)… And this is the

difference between getting an $88 dollar

monthly power bill for heating, and a $350

monthly power bill.

So why is it commonly done like this

in Australia (and no-where else in the

world)?

Most often the reasoning is “because it’s

easier”, or “because it’s cheaper”. Both of

these statements are true – it is easier

and cheaper to ‘whack’ some pipes in a

suspended slab – but the result is multiple

times better if it’s done the right way.

Many ‘enviro’ or ‘eco’ plumbers/contractors

say “We’ve installed heaps of these into

suspended slabs before!” And they are

INTERNAL 20°C

INTERNAL 20°C

INTERNAL 20°C

EXTERNAL 7°C

EXTERNAL 7°C

EXTERNAL 7°C

INTERNAL 20°C

INTERNAL 20°C

INTERNAL 20°C

EXTERNAL 7°C

Mistake #1


7

How to avoid mistake #1

The steps are simple:

1. Avoid putting heating into suspended

slabs (unless you want an unhappy

client).

2. The place to put the pipes is on top of

a suspended slab and always only so in

combination with an insulated screed

or other well insulated system (such as

diffusion plates or a dry system). This

means a slightly larger initial investment,

but only properly thought out and

installed insulation will stop 50 - 90%

of the heat from being wasted over the

lifetime of the building. The cost of the

wasted heat will definitely outweigh the

cost of the insulation.

right: Their system does heat the rooms

above it a bit. But it also heats the bricks,

walls and rooms below. On the sides.

The garage. The pantry. The alfresco. The

balcony. The air outside. And instead of

having a system that is sustainable and

energy-saving, they actually pay more in

running costs than if they had installed a

simple air-conditioning system. All because

the heat they make ends up in other areas,

and not the rooms they want to heat.

We hear the same feedback over and

over from people that have had heating

installed into ‘normal’ Australian suspended

slabs all the time: the floor is cool (at best

not cold), and the running cost is sky high

… and the physics (explained briefly above)

confirms this outcome.

What if the screed is poured directly on

the top of a slab?

This doesn’t work. There MUST be thermal

insulation between the screed and the

slab, otherwise the screed and slab are

bonded together and behave thermally as

one thick mass.

“ In solid objects ..heat trav-

els in every direction .. and

it travels most to where it’s

the coldest.


“Hiding” the heat pump (a.k.a. try breathing with a

plastic bag over your head)

Mistake #2

The warm water that circulates in the floor

pipes is produced by a “heat pump”.

This is a machine of some size. It does

some humming. And the a lot of the time,

people think of hiding it somewhere:

garage, store room, or even sometimes a

ventilated roof space.

The thinking behind this is usually

twofold:

1. The heat pump is hidden from view, so

it doesn’t stick out like a sore thumb,

compromising the hard work put into

designing an exceptional building.

2. The heat pump will be protected from

the elements, saving it from water,

corrosion, dust, and an early demise.

This is a good idea… until you understand

the physics of how a heat pump works.

Because when you do, you´d never ever

do what´s essentially the same as pulling a

plastic bag over your head.

Let me explain …

The air/water heat pump is based on the

principle that it collects low-value energy

from the air, temporarily stores it, and turns

it into high-value energy that is useful.

For example, in winter it may be 10°C

outside... To you and I, this is cold… but to

the heat pump, this is a treasure trove of

heat energy.

COMPRESSOR

EXPANSION VALVE

REFRIGERANT / WATERHEAT EXCHANGER

REFRIGERANT / AIRHEAT EXCHANGER

HYDRONIC FLOORHEATING SYSTEM

CIRCULATOR PUMP


9

Picture a hydronic floor heating system

is requesting heat… so the heat pump

compressor turns on, compressing a batch

of refrigerant that heats up to 40°C. Water

from the hydronic system extracts this heat

from the refrigerant, cooling it down to

35°C. The refrigerant is then decompressed

(expanded), and becomes cold, say 5°C.

The heat pump then moves this 5°C

refrigerant in front of its fan, and the fan

starts spinning.

After a minute, the 5°C refrigerant in front of

the fan has become 7°C refrigerant.

And after another minute, it’s jumped up to

10°C. This is because the air is warmer than

the refrigerant – the refrigerant is collecting

heat from the air.

Once again, this 10°C refrigerant is

compressed, turning it into useful 40°C

refrigerant, ready for transfer to the

hydronic system water… and this happens

on continuous basis as long as there is call

for heating.

So we can see from the above process that

low-value heat from the air is collected

and made into high-value heat that can be

used.

We must remember that the higher the air

temperature, the higher the efficiency of

the heat pump, as it’s easier to collect heat

from 20°C air than it is from 10°C air.

This process is identical to an air

conditioner condenser unit, and similar to

how a fridge works (but in reverse). The

heat pump is actually a complex piece of

equipment that must be understood well

to gain the most out of it - the explanation

above is very simplified for our discussion

here.

15°C 10°C 2°CThe heat pump needs to breathe…

Imagine the heat pump is enclosed in a

garage. There are three walls, a roof, and

a closed garage door. It’s 10°C outside, but

15°C inside the garage.

The heat pump turns on and starts

collecting heat from the 15°C air at a high

efficiency, from the high air temperature

available.


15°C 10°C 2°C

15°C 10°C 2°C

Mistake #2

But after 15 minutes it’s not 15°C in the

garage anymore… it’s 10°C.

The heat pump keeps going though, still

producing heat, but at a lower efficiency.

Another 15 minutes pass by, and it’s now

5°C in the garage. The heat pump is

working harder and harder to produce the

40°C heat. It’s still keeping up with the heat

demand, but is now working twice as hard

to do it (lower efficiency, higher running

cost).

After 40 minutes of run time, it’s 2°C inside

the garage, and the heat pump is working

three times as hard to produce any heat.

The efficiency has drastically reduced,

costing more every minute it runs.

Then someone comes home, and opens

the garage door…

The 2°C air from the garage spills out

the open door and is replaced with 10°C

outside air, and the efficiency once again

increases, and the running cost decreases.

Just like getting a breath of fresh air after

having a plastic bag over your head.

Will a ventilated room provide enough

air?

We’ve now established that enclosing

an air/water heat pump results in poor

performance. And that it’s really important

that an air/water heat pump (or air-

conditioner condenser) has 100% free air

exchange with fresh external air always.

Because it’s from this air that the heat

pump collects heat energy.

But what about enclosing an air/water heat

pump in a ventilated room?

It’s only marginally better than completely

enclosing it, as the majority of the same air

recirculates within the enclosed space.

Even an obstacle (such as a fence) closer

than 1 metre from the face of fan can also

result in mass air recirculation, decreasing

the energy efficiency of the heat pump by

up to 50%.


11

Compare the examples below of heat pumps outside with fences in front of them:

It’s clear that even outside, when there’s not

completely free air circulation, that exhaust

air from the heat pump gets sucked back

in – significantly reducing the heat pump’s

efficiency.


Boreped que parundi tiusdae omnis dolent quibus molupis aut eturibusam es volent et rerferi buscian dipsus idelitis et aspiditiant ommol.

Any unit with air exchange should have the

air exchange component positioned so it

has 100% access to fresh air at all times.

Units without air heat exchangers, such as

water/water or ground/water heat pumps

(i.e. water source or geothermal) can be

positioned 100% internally.

Do we need to protect the heat pump

from rain, dust, sunlight etc.?

You might think that covering or enclosing

the unit in something will make it last

longer, as it won´t become damaged by

rain, rust, dust, extreme sunshine etc.

But good air/water units are designed for

the outside environment: They actually

make them for the outside. They are built

to last in the conditions. Just like a car is

made to run outside in rain and sunshine

and does not need to be garaged at all

times.

Making the unit work harder by enclosing

it will increase the wear on the heat pump

parts more (especially the compressor and

fan) than letting it rain on it.

Mistake #2


13


ÌTake care when you position the heat

pump so that the exhaust air is not

easily again sucked in as the supply air

(short-circuiting). You can avoid this by

positioning the heat pump in open area

where there are no obstacles within 2

metres (minimum) in front of the exhaust

fan.

ÌPlan the position of the heat pump when

designing the building… otherwise it will

probably end up shoved into a corner

somewhere with poor air circulation.

Ì If the heat pump does need to be inside,

within a plant room for example, use a

purpose-built internal heat pump which

is ducted.

Forgetting “thermal comfort” when installing

controllers and thermostats (in the wrong place)

Mistake #3

The reason we heat and cool our houses

is to feel comfortable in them. Modern

heating systems allow us to tell it what

temperature we want to have in the room:

The thermostat reads the temperature in

the room. And the controller then increases

or drops the heat coming from the heat

pump to achieve and maintain it.

That´s easy to understand and do, sure.

But when you start setting the system up,

you have to consider a lot of details that will

later decide if the occupants will actually

feel comfortable

… because there’s a huge difference

between the comfort of a room that´s being

heated up by “blasts” of heat. And a room

that has been heated up gradually and

thoughtfully.

Here’s a short explanation why…

On the surface the controls for the system

are easy to set up:

Decide on the time periods you want the

rooms to have a certain temperature.

Programme this into the controller. And

when the thermostat finds out that the

temperature has dropped below or

exceeded the set temperature, it will turn

the heating on/off.

The problem with this approach is huge:

This approach works with heating/cooling

units that provide immediate warmth/

chill: Instant gas heaters. Air-conditioners.

Electrical heaters. Etc.


You turn these on, they heat up to 100 %

and give out as much energy as possible as

fast as possible. And when the thermostat

tells them “that´s enough”, they switch off

again.

Technically, the room has been heated

to the set temperature. You will see this

temperature on the thermostat. So the

occupants should be happy, right? But

they’re not.

The trouble is that “instant” heat is not as

comfortable as “gradual” heat.

You know this from your own experience

outside: One day, you may feel hot, sweaty

and uncomfortable. Another day, you will

feel ok. But how is that possible, when

during both days the temperature was

exactly the same?

Outside, our “thermal comfort” is

determined by humidity, sea breeze,

shading, etc.

Inside, the majority of thermal comfort is

achieved by gradually heating the rooms

up. And this is really the secret behind the

natural and comfortably feeling of houses

with hydronic floor heating: The occupants

don´t get blasts of instant heat. But the

rooms get heated up gradually. Just as we

like the warm morning and afternoon sun

rays more than the direct midday scorching

heat.

To achieve this thermal comfort however,

we cannot just put in the thermostat

controller and turn it on.

We need to calculate the “temperature

gradient”. This is a relatively complex

mathematical calculation based on the

amount of glass in the room, it´s positioning

towards the sun, the materials the house

has been built from, the surroundings and

a number of other factors that determine

how quickly the room and the house will

gain/lose/retain heat.

Only then can we decide how long to turn

the heat pump on before the rooms need

to be warm. And only this way will we

actually be able to lower the energy costs

and achieve thermal comfort:

Only then will the system stop turning 100%

on/100% off/100% on/100% off

…but will (depending on the amount of heat

in the room already), send 30% now, then

drop to 17 %, then increase to 19%, then

drop to 5% etc.

You don´t drive your car by starting up

the engine, flooring the gas pedal and

slamming on the brakes only after you

get to your destination. This wouldn´t be

the most efficient way to run your car. And

neither is it for the heating your home.

For the system to really work efficiently,

the designer, architect and installer

need to work over the floor plans. Do

the calculations. And also place the

thermostats and controllers in the right

places…

You see, if the thermostat “thinks” it’s cooler

than it actually is, then it will keep heating,

eventually overheating the building. On the

other hand, if it thinks it’s warmer, it won’t

heat enough, leaving the building cold and

people uncomfortable.

Mistake #3


15

The 5 most common thermostat positioning mistakes are…

1. Controls Floor Temperature Only: If the thermostat regulates only the floor temperature,

and not the room temperature, then it can lead to over heating or under heating of the

room, as the slab (floor) temperature DOES NOT equal the room temperature.

2. Hidden in Cupboard: The thermostat cannot get a read of the actual temperature of the

room – it’s generally either warmer or cooler in the cupboard compared to the room,

resulting in over/under heating of room.

3. In unheated area: Thermostat cannot get a good read of the room it’s heating… it’s

reading the temperature of a part of the house that’s not even being heat... so it doesn’t

actually control the comfort level.

4. In direct sunlight (or close to it), drafty area, or next to oven/stove/other heat source:

Thermostat gets a ‘false’ reading, influenced by heat or chill from other sources.

5. For aircon, the sensor is often placed on the return air duct… But this is often not a

true representation on the temperature experienced by the occupants in the room

(the return air may be sucked only from the top layer of air in a room – not a good

representation of the occupied zone lower down).

Most importantly, it’s forgotten (or

misunderstood) that the thermostat does

not read only the air temperature… and

that air temperature alone does not show

the whole story of thermal comfort in a

room. There’s air velocity, humidity, air

temperature, and radiant temperature to

consider - and also the metabolic rate

and level of clothing worn by occupants

in the room – but we won’t consider

these here. In fact, right now, we’ll only

consider air temperature and mean radiant

temperature, because they have the

largest impact on room comfort.

So out of the two factors we’re discussing

– air temperature and mean radiant

temperature – almost all HVAC designers

and contractors only consider one: air

temperature. Yet air temperature gives you,

approximately, only one half of the story!

For this reason, thermostats need to be

positioned so that they receive an accurate

radiant temperature reading of the room…

this means exposing the front panel of

the thermostat to the most frequently

occupied area of the room… allowing it the

get both a good radiant reading, and air

temperature reading, of the room where

people spend the majority of their time.



1. If you just put the pipes in and stick

a thermostat in each room, any

system can heat up the house to the

desired temperature… but you will

have no guarantee you will actually

feel comfortable in it. (Remember

the example of sweaty/nice feeling

outside during two days with the same

temperature?)

2. For you to feel thermally comfortable

in each of the rooms, fairly complex

calculations need to be done. And the

people doing them need to understand

the effects of sunlight, positioning,

building materials, neighbouring rooms

etc. to work it out properly.

3. Take care to position thermostats out of

direct sunlight: Ideally they’ll be around

1600mm above the floor in the room

that’s being heated or cooled. Don’t

forget to watch out for other sources of

heat/chill that can affect the thermostat

reading!

4. Choose a good thermostat: one that

takes into consideration both the room

air temperature AND the room radiant

temperature - allowing it to regulate

to room temperature accurately.

Thermostats also need to be time-

programmable, so they automatically

turn on and off when desired by the

occupants, and don’t excessively heat the

room when not required.

Forgetting that heat leaks (a.k.a. you wouldn’t keep

water in a bucket full of holes)

Mistake #4

When moving and storing water in the

garden, we know that we need to avoid

holes in the hose or the bucket. Otherwise

the water would leak. Disappear. And we´d

be paying for water which we didn´t end up

using.

The same thing happens with heat too:

When allowed, it will also leak.

How?

Thermal energy always moves from hot to

cold, and never the other way around:

If you have produced heat, it will “look” for

the coldest place in your house... And heat

that up first. This is fine, if by doing this it

heats up the furniture, walls and the whole

room you are inhabiting. But it’s not if it

first leaks to (for example) the uninsulated

garage, ceiling, roof space, pantry or

windows.

Mistake #3


17

Obviously, installing the right type of

insulation (which works as a thermal barrier)

in the right positions helps prevent the

flow of heat out during winter (and heat in

during summer).

So, where do the majority of heat losses

happen in buildings?

Generally they can be attributed to three

areas:

ÌGlazing: Heat escapes via both radiation

passing through the glass outwards,

and convection from warm internal air

through the glass to the cold external air.

It’s not practical or desirable to limit the

amount of glazing to reduce heat losses

in most buildings, so where possible, use

double glazing with high R-value glass.

ÌRoof: Heat from warm air under the

ceiling escapes into the roof space

(mainly through convection), and then

through to the external environment. This

type of heat loss is not a big problem

when radiant heating is installed as the

room air is not the main thermal energy

carrier in this case, hence a lower air

temperature is maintained under the

ceiling in comparison to systems where

air is heated (aircon). Insulating the ceiling

and roof well with bulk or rigid insulation

to mitigate heat losses in winter solves

this issue.

ÌThermal Bridges: These can be found in

the floors, walls, windows and roof, where

a building element directly connects

the internal and external environments,

allowing unhindered energy transfer

between them (via thermal conduction).

An example is un-broken window frames,

where heat from inside only has to travel

a short distance (not more than 100mm)

to the colder outside through the

aluminium frame construction (a good

heat conductor).

What you must know about thermal

bridges in connection to floor heating

Out of the above, thermal bridges are the

largest threat to floor heating efficiency.

Let me explain…

With traditional aircon systems, only the

air in the room is heated… the building

structure itself is not directly heated. The

warmest air in the room gathers near the

ceiling (losing vast amounts of energy to

the roof space). The lower you get in the

room, the lower the air temperature… so the

coldest layer hangs out at the floor level

(making it uncomfortable for occupants).

This low layer air passes some of its heat

to the slab, which then passes it on to the

external environment. Because the air near

the slab is already cool, and because the

air is not a good energy carrier, the heat

loss rate to the slab (and then outside) is

relatively low.

“Thermal energy

always moves

from hot to cold,

and never the

other way around.


It looks something like this:

25°C

15°C

35°C

25°C

15°C

20°C

15°C

15°C

20°C

25°C27°C

20°C

15°C15°C

15°C

20°C

25°C

15°C

15°C

27°C

20°C 20°C

20°C20°C

20°C

15°C15°C

15°C

25°C 25°C

15°C 15°C

Floor heating flips this situation on its head…

The floor structure is heated to a higher

temperature than the air in the room and

emits ~55% of heat energy predominantly

as thermal radiation, ~30% through the air

convection, and ~15% via conduction to the

structure and room furniture.

BUT

This is only applies to an insulated screed

(or super well insulated slab). It looks

something like this:

Mistake #4


19

25°C

15°C

35°C

25°C

15°C

20°C

15°C

15°C

20°C

25°C27°C

20°C

15°C15°C

15°C

20°C

25°C

15°C

15°C

27°C

20°C 20°C

20°C20°C

20°C

15°C15°C

15°C

25°C 25°C

15°C 15°C

You can see the difference immediately...

The structural floor slab is still cool, but the

heated floating floor is warm (because of

the insulation between the slab and the

heated screed). The air temperature drops

with increases in room height (resulting

in lower energy losses through the roof).

The rooms radiant energy emitted from

the floor is absorbed by the surrounding

structure and furniture, and re-emitted

(balancing out the mean radiant room

temperature).

A BIG difference is obvious in a heated

structure slab, where thermal bridges

and heat losses have been ignored… the

output can be as little as 25% radiation,

5% air convection, and 70% conduction to

surrounding structures or the ground.

This is because there is a direct link

between the warm concrete slab, and the

cold external environment. The majority

of the heat is being sucked away outside

(where there is a high temperature gradient

= high energy flow), instead of warming the

inside of the building.

… So 70% of the energy that’s being sent

to the slab doesn’t end up heating the

room, but rather heating the air and

ground outside! You can see that here:


25°C

15°C

35°C

25°C

15°C

20°C

15°C

15°C

20°C

25°C27°C

20°C

15°C15°C

15°C

20°C

25°C

15°C

15°C

27°C

20°C 20°C

20°C20°C

20°C

15°C15°C

15°C

25°C 25°C

15°C 15°C

The greatest heat losses from heated

slabs are from the slab edge – either to

the ground, or to adjoining structures –

this is well known. Energy losses form the

underside of the heated slab are the next

major culprit.

Examples of common thermal bridges

from on-ground heated slabs:

Exposed heated slab edge to sand/soil:

Often it’s said that “WA has sandy soils

that insulate”. Dry sand, however, has

a specific heat similar to concrete and

aluminium (the amount of heat it can hold),

and has thermal conductivity 10x that of

polystyrene, 2x of plywood timber, and a

quarter that of standard concrete.

The thermal conductivity of soil is

even higher when moisture is present

(downpipes disposing water to underside

of slab, overflowing soak-wells, high

groundwater, leaking water pipes)…

meaning the thermal conductivity can be

equivalent to that of concrete.

Mistake #4


21

Above you can see an indication of heat

losses from an exposed heated slab edge

to the atmosphere, conduction to the

adjoining paving and window frame, and

conduction to the footing and soil below.

70% of the heat from the floor is easily lost

this way.

Heated slab edge adjoins conductive

structure:

This is the most detrimental situation,

as the heat flows away so aggressively

that the floor heating system is rendered

useless. The most common occurrences

are when pools, in-situ concrete paving,

cast-in planters, or other external concrete

structures directly abut the heated slab.



1. To prevent these drastic heat losses, thermal breaks MUST be used.

2. Insulation to the underside of an on-ground slab is not required by the BCA/NCC in

most climate zones – but we highly recommend it. In WA 25-50mm of polystyrene, or

similar rigid insulation, is sufficient.

3. The BCA/NCC does however stipulate that on-ground slabs have at a minimum

R1.0 slab edge insulation, extending the full vertical edge of the slab, or minimum of

300mm below the ground level. THIS IS IMPORTANT – it will save you the architect, the

builder, and the client many headaches. 30mm of Extruded Polystyrene (XPS) or 25mm

of Phenolic Foam is sufficient for this purpose.

4. Suspended slabs have by far the highest heat losses (see Mistake #1) – just one of the

reasons we don’t recommend floor heating installation within a suspended slab. By

BCA/NCC, suspended slabs require, in addition to slab edge insulation, insulation to

underside/soffit.

5. The best result comes from an insulated screed system, as this eliminates energy

leakages due to carelessness or unintentional mistakes. Often screeds are installed

directly over a slab with no thermal insulation. However, this is a corner cutting

approach ending with a poor result, as a huge amount of heat from the screed is drawn

downwards by the concrete slab below. Remember, thermal energy in solid materials

travels in all directions, not only upwards, and the heat flows most to where it is the

coldest. A well installed screed heating system is thermally insulated from all other

structures (such as walls, window frames and slabs below).

Hydronic systems are not created equal (and while

some will heat your building well, others will fail)

Mistake #5

Search the web for hydronic heating and

the two most common phrases quoted are

‘hydronic heating is 30% more efficient

than aircon’ and ‘water is a better heat

conductor than air’.

The problem isn’t that these promises

aren’t true. They can be. The problem is, it

is assumed that they apply to every system

and building. That ALL hydronic systems

are efficient, regardless how designed and

constructed.

… and this is NOT true.

Mistake #4


23

Since we design and install hydronic

heating systems, we should be extolling

only the virtues of the system.

But we are the first ones to say that

hydronic systems are good and suitable

only sometimes:

Only when the system is designed and

installed with knowledge, physical

calculations, and care.

You see, just because the principle is

efficient, it doesn’t mean the system (or the

building) is efficient by default.

Regularly, efficiency is wiped out in a

hydronic system from at least one, if not

more, of these mis-takes:

1. Floor heating pipes within too large

a concrete mass – expensive to heat,

long response time.

2. Thermal bridges from heated slabs to

unheated masses or external elements

– heat escapes unintentionally,

doubling or even tripling running cost,

and extends heat-up time.

3. Uninsulated piping between heat

source and the floor system manifold

– heat is lost before it reaches its

destination, increasing running cost and

extending heat-up time.

4. Water flow rate too low – not enough

energy being delivered to where it’s

needed, leaving cold spots.

5. Heat source over-sized – works at a

low efficiency level and leads to early

equipment failure.

6. Floor heating pipe spacing inadequate

– system cannot produce heat output

as required.

7. Thermostat controller in wrong position

or utilised for wrong function - over or

under heating.

8. Heat source installed in poor position -

works with low efficiency and leads to

early equipment failure.

9. Poor design of heating loops – cold

spots, poorly heated areas where higher

thermal losses need to be covered

(ie. near tall windows, high ceilings),

overheated areas with solar gains.

10. Building heat losses not properly

calculated.

11. Loops design not taking in

consideration flooring type or furniture

layout.

12. Poor installation – kinked pipes,

unequal piping spacing, pipes surfacing

on surface of slab.


These mistakes unfortunately happen a

lot. It’s really easy to stuff it up. And usually

impossible to fix.

This comes from a unique characteristic of

hydronic systems…

The excellent results that come from a

hydronic system – in terms of running

efficiency and comfort – come from

combining both a well-designed and

well-executed hydronic system WITH a

well-designed and well-executed building.

This is because the hydronic system is

integrated into the building itself. The two

have to be in perfect harmony, working

together… not working against each other…

Because a well-designed hydronic system

installed into a poorly executed structure

ends in disappointment… the same as

when a poorly designed hydronic system is

installed in a well-designed structure.

What you need to know about air-

conditioning and hydronic heating

systems before selecting one

The internet articles promise that hydronic

heating is better than aircon. They say water

is a better heat conductor than air. And that

floor heating does not consume that much

electricity. But is it true?

Does water really transfer heat better

than air?

Water is certainly a better heat conductor

than air… but people don’t swim in the warm

floor heating water, but they do reside

within the warm room.

Because water has a higher ‘specific heat’,

and hence can carry more energy than

air, you can transfer more energy with

less volume and power. For example,

with aircon, you may need to move 200

litres per second of air to transfer 2.5kW

of energy…. But you can transfer the same

2.5kW of energy with 0.06 litres per second

of water. This means less mechanical power

is needed to move the energy (the pump

for water will use a fraction of the power

than that of the fan for the aircon).

A beneficial by-product of this (difference

in transferred volume) is there are lower

energy losses from the smaller water

pipe (e.g. 20mm diameter) compared to

the large air duct (e.g. 300mm diameter),

because of the smaller external surface

area.

Mistake #5

“Just because

the principle

is effficient , it

doesn’t mean the

system is efficient

by default.


25

Air & Waterat 20°C

and 100kPa

1000L of Air = 1m³Density = 1.204 kg.m³

Specific Heat = 1.006 kJ/(kg.°C)= 1.21 kJ.°C= 0.000336 kW per °C per m³

1000L of Water = 1m³Density = 998.19 kg.m³

Specific Heat = 4.18 kJ/(kg.°C)= 4172.43 kJ.C°= 1.159 kW per °C per m³

Water can carry3448x more

energy than air atthe same pressureand temperature.

Is hydronic heating really 30% more

efficient than aircon?

Is hydronic heating 30% more efficient than

air? Yes – it can even be up to 50% more

efficient. But, as with all sciences, there are

many factors which influence the result.

The 30% is generally quoted in reference

to the room thermostat being set 2°C lower

for radiant heating than air heating, whilst

maintaining the same perceived comfort

by the occupants. As a rule-of-thumb in

the HVAC industry, it’s said that for every

1°C lower room temperature set, up to 15%

running cost savings can be realised. So

instead of 21°C with aircon, you can get

away with 19°C with radiant, and still be

comfortable.

This is evident in some of the previous

illustrations shown, where with aircon hot

air collects at the ceiling level, and the heat

escapes through the roof. The occupants

also have cold feet and warm heads, which

humans perceive as very uncomfortable.

With floor heating, the savings are even

greater if the water temperature utilised is

very low (~35˚C), the building well insulated,

and has high ceilings.

But we have to make sure we’re comparing

apples to apples here…

If you compare a refrigerated type aircon

in heating mode to hydronic floor heating

(in-screed) with a heat pump, it’s a fair

matchup. The condenser unit for the aircon

works identically to a hydronic heat pump,

only the heat is transferred to water instead

of air. The main difference, if we keep it

simple, is how the energy is distributed (air

vs water) and utilised (or wasted with heat

losses). In this instance, the hydronic floor

heating would be much more economical

to run compared to the aircon.

If you compare the aircon and floor heating

as above, however change the floor heating


from in-screed to in-suspended slab, then

apples are being compared to oranges…

The suspended slab would experience

much higher unwanted heat losses (as

explained in Mistake #1), meaning that the

floor system would cost multiple times

more to operate than aircon.

Apples are also being compared to

oranges when aircon is compared to a

hydronic in-screed heating system with a

gas boiler…

The aircon condenser unit (and heat pump)

can be assumed to have an efficiency

of 300%. If electricity costs $0.25/kW, it

costs $0.083 per kW of heat produced. A

condensing gas boiler can be assumed to

have an efficiency of 95%. With gas costing

$0.15/kW, it costs $0.158 per kW of heat

produced. Now, if we take into account

the overly simply and commonly quoted

‘hydronic is 30% more efficient’ – due to

the method of energy distribution and

consumption – we have a cost of $0.11/

kW. So, in this instance with a gas boiler as

heat source, the running cost of aircon is

25% lower than a hydronic system (ignoring

heat losses through ceiling from hot air,

and lower level of comfort created by the

aircon)

25°C

15°C

35°C

25°C

15°C

20°C

15°C

15°C

20°C

25°C27°C

20°C

15°C15°C

15°C

20°C

25°C

15°C

15°C

27°C

20°C 20°C

20°C20°C

20°C

15°C15°C

15°C

25°C 25°C

15°C 15°C

25°C

15°C

35°C

25°C

15°C

20°C

15°C

15°C

20°C

25°C27°C

20°C

15°C15°C

15°C

20°C

25°C

15°C

15°C

27°C

20°C 20°C

20°C20°C

20°C

15°C15°C

15°C

25°C 25°C

15°C 15°C

So be VERY careful when listening to

“facts” about hydronic heating… from what

we’ve seen and heard in WA over the past

26 years, 95% of installers don’t really

understand the systems at all. Having said

that, it’s not because they’re charlatans or

liars… it’s because hydronic systems are

much more than plumbing…

It requires a solid engineering knowledge

and experience to get it right (that’s why

hydronic systems are ALWAYS designed

by ‘hydronic’ or ‘heating’ engineers in other

countries)... It’s necessary to understand

and integrate multiple disciplines to create

a successful hydronic system.

Mistake #5


27

What to do now to make sure your hydronic floor

heating system really works

The lowdown: While anyone can put in the

pipes, install the thermostat and turn the

heat pump on, only a few technicians and

companies have the experience, technical

education and knowledge to make the

system actually as efficient as you want it to

be.

At Euroheat Australia, we’ve been designing

and installing these systems for houses and

commercial buildings in Western Australia

for over 26 years (since 1992).

As engineers specialised in sophisticated

and cooling and heating systems, we don’t

just calculate a building’s energy gains/

losses.

We don’t just do ventilation.

We don’t just do hydronic floor and wall

systems.

We don’t just do aircon.

We don’t just open/close windows or

blinds.

Or just cool cellars. Or just heat pools.

Instead, we will help you optimise the

building design to reduce the required

energy in the first place.

We will then design every millimetre of the

system, install it and continually monitor &

optimise it. (The systems can completely

integrate natural ventilation, floor heating/

cooling, aircon heating/cooling, pool

heating, cellar cooling, tap hot water.)

And we will make sure it all works together

seamlessly, so that the occupants are

comfortable all year round without having

to do anything… and happy with the bills as

well as the eco-footprint.

I would like to say that clients marvel about

the natural and non-artificial feel of the

climate in their houses, but they don’t:

They find the warm feeling in winter and

cool in summer so natural (without rapid

spikes of temperature or being blown hot/

cold air at them from vents) that they don´t

notice they have a system doing this at all

… and I suppose that is the ultimate

compliment and sign of user happiness.

If you’d like to create a similar climate in

your buildings, perhaps we should meet in

your office, for a quick, 15 minute chat. Over

your current projects. And over ideas on

how to make them more energy efficient.

I promise no salesy pitching, just info

on building physics, energy flows,

thermal efficiency and how to use it all in

seamlessly heating/cooling your buildings…

Efficiency engineer

Euroheat Australia - Hydronic

Systems & Building Engineers

Ph. 08 6468 8895

[email protected]

Phil Pacak

08 6468 8895 [email protected] www.euroheat.com.au

how to avoid the 5 common mistakeseuroheat-11242.kxcdn.com/guides/euroheat-5-common...in the pages...

Documents