Heating and cooling: exhaust air source heat pumps - a cautionary tale

1 to 30 of 170

- CommentAuthordjh
- CommentTimeSep 10th 2012
http://www.bbc.co.uk/news/business-19511637

"... the heating system used in their homes is costing up to four times more than expected"

"The Energy Performance Certificates which accompanied the new properties, estimated electricity costs for heating and water to range from £400 to £500 each year. But hundreds of families on housing estates throughout the UK have paid three to four times that amount."

Anybody know anything more about this story?

Are there common factors? (I'm thinking consultants or contractors perhaps)
- CommentAuthorRobinB
- CommentTimeSep 10th 2012
It seems that because the unit was undersized* the immersion, supplied to allow the occasional top-up in extremely cold weather, was doing most of the work and negating any benefit of the heat pump.

*undersized not necessarily for the building per se, but for the way the heating system was usedby the occupants. Also seems as if the insulation levels in the buildings may have been overestimated - meanng the system couldn't cope.

The piece also said housing associations are "ripping the out" even though only a few months old. There may be bargains to be had.

Sad story really and I don't know who is responsible.
- CommentAuthordjh
- CommentTimeSep 10th 2012
I just watched the programme. The only common thing I spotted was that the houses shown all used radiators for space heating. Well, apart from the programme makers' emphasis on the heat pump manufacturer and it's not clear what drove that emphasis. Not much information at all, but I suppose that's the telly for you.
- CommentAuthorseascape
- CommentTimeSep 11th 2012
Watched it last night - ooh dear. What's the betting that the house insulation/airtightness spec was reduced to cut costs and there was no 'joined up' thinking...all those high temperature radiators! Some heads are going to roll I think. The housing association guy looked a bit sweaty and nibe vigourously defending their product and going into the homes to check everything. Heating engineer expert tight lipped "it's to do with heat loss" and no mention of the contractors at all.
- CommentAuthorJonti
- CommentTimeSep 11th 2012
I suspect it is the quality of build that is the problem. This is one of my 'pet hates' but here in the UK many builders think air-tightness is not important. There needs to be a much better training program in place if all these eco regs are going to really work. To me it seems that many people are spending large amounts of money on insulation and other products only for the effectiveness to be diminished by shoddy workmanship and a 'we have always done it this way' type of attitude

Jonti
- CommentAuthorMike (Up North)
- CommentTimeSep 11th 2012
Hi,
Actual thermal performance being less than expected was a conclusion of the report quoted in the recent thread see - Joseph Rowntree Report on retrofit.

Basic errors in the construction of the test houses were still being made even when the builders new that they were under constant observation.

One key finding was:
“The architects appeared to have attempted to minimise penetrations through the air barrier and building fabric; a principle not adhered to so rigorously by the services designers. A number of these penetrations appeared to be ad hoc decisions made by the installers and not through design. The installers regularly appeared to bear little regard for the integrity of the air tightness barrier and thermal performance”, likewise - gaffa tape used on membranes instead of the pro clima type etc etc, that sort of thing.

The heating engineer might have made a 10-15% increase on the calculated level to give a bit of lift or leverage to get the house up to temp. But a further 20% should have covered deviation through build quality.
So maybe theoretical heat required + 50% would have given a unit size for these properties – a UK factor?

Should have knocked them down and built them properly then put the heating systems back in . . .

Cheers, Mike up North
- CommentAuthordavidfreeborough
- CommentTimeSep 12th 2012 edited
I’m sure fabric heat loss & airtightness are part of the problem, but I also think that exhaust heat pumps should not be routinely specified for domestic heating applications. Unlike, air source or ground source heat pumps, they do not move heat from outside the building; they move heat from one place in the building (the air) to another (the air, heating system &/or domestic hot water). There may be cases in industrial applications where excess heat is available &/or high levels of ventilation are required, but this is not usually the case in domestic applications.

All the air extracted will be replaced by cold outside air drawn in through trickle vents. So, for an exhaust heat pump with an exhaust air temperature equal to outside air temperature, all the heat extracted by the heat pump will be required to heat the cold outside air drawn in. No heat will be available to replace heat lost through the fabric of the building & so all of this heat will need to be provided by electrical resistance back-up heaters. As the fabric losses are typically higher than the ventilation losses, the electrical resistance heaters will typically be consuming a lot more than the heat pump compressor.

In addition, for every 3kW of heat transferred from the exhaust air to the inlet air, the heat pumps compressor will consume 1kW of electricity. An MVHR type heat exchanger would cover 90% of the ventilation heat loss, while consuming just a few 10s of watts. A gas boiler could provide enough energy to cover ventilation & fabric heat losses for less money than that required to run an exhaust heat pump & electrical back-up heaters. So you’d be better off using continuous extract ventilation and a gas boiler.

In theory an exhaust heat pump can extract more energy from the exhaust air flow than an MVHR heat exchanger, but in practice heat pumps work with temperature differentials of 15°C or less. So, while they can extract more energy in summer when outside temperatures are high, they cannot do better than an MVHR unit in typical winter conditions where there is 15°C differential between outside and indoor air temperatures. In other words, they can help with domestic hot water heating in summer, but cannot help with space heating in winter.

The heat pump compressor can be increased in size. However, this requires a corresponding increase in exhaust air flow & therefore an increase in cold air drawn into the building. So all the additional power will be required to cover the increased ventilation heat loss.

An exhaust heat pump connected to the exhaust port of a balanced flow MVHR unit, so that the MVHR heats the incoming ventilation air & the heat pump uses residual heat in the MVHR exhaust to provide space heating &/or domestic hot water. However, the limited air flow required for ventilation means that the power available from the heat pump will only be sufficient for domestic hot water pre-heating or space heating in a Passivhaus or other very low energy house. In the vast majority of cases, an additional heat source will be required for domestic hot water &/or space heating. So you’d be better using an air source or ground source heat pump dedicated to domestic hot water & space heating.

In summary, if gas is available you’d be far better off using a gas boiler with continuous extract ventilation than an exhaust heat pump. If gas is not available then you’d still be better off using an air source or ground source heat pump to bring in energy from outside than paying to move it around inside the house. If you want to recover the heat lost in ventilation then an MVHR unit can recover 90% while consuming orders of magnitude less energy.

David
- CommentAuthorSteamyTea
- CommentTimeSep 12th 2012
Posted By: davidfreeboroughn summary, if gas is available you’d be far better off using a gas boiler

Did strike me as odd that they took some out and put in gas boilers, why was that not done at the beginning as gas was available.
I think it must have been a very smooth presentation.
- CommentAuthorDarylP
- CommentTimeSep 12th 2012
.... to get the SAP rating up, to clear C4SH Level 3 (or 4) perhaps...?

Typical waste of money and resources due to lack of communication, and short-cuts and cost-cutting

Ah well....
- CommentAuthorwavy
- CommentTimeSep 12th 2012 edited
<blockquote><cite>Posted By: davidfreeborough</cite>All the air extracted will be replaced by cold outside air drawn in through trickle vents. So, for an exhaust heat pump with an exhaust air temperature equal to outside air temperature, all the heat extracted by the heat pump will be required to heat the cold outside air drawn in. No heat will be available to replace heat lost through the fabric of the building & so all of this heat will need to be provided by electrical resistance back-up heaters. As the fabric losses are typically higher than the ventilation losses, the electrical resistance heaters will typically be consuming a lot more than the heat pump compressor./blockquote>

Thanks for your explanation, davidfreeborough. It seems to confirm my suspicions (just expanded on the R4 NIBE investigation thread) that these systems actually dont work in a dwelling. The ones I saw were in Code 4 dwellings (well below passivhaus) but I havent been able to find out how they are performing (not well, I would guess)
- CommentAuthormike7
- CommentTimeSep 12th 2012
Posted By: wavy
Thanks for your explanation, davidfreeborough.

Seconded. Just had a look at the NIBE.co.uk website, from which I copied this:-

"controlled domestic ventilation with heat recovery reuses the energy from the exhaust air. Not only that, the additional heat generated internally from lighting, people and domestic appliances is also utilised through heat recovery. Our FIGHTER exhaust air heat pumps facilitate heat recovery and supply the energy recovered from exhaust air for the domestic hot water and even the heating. Not only does energy recovery ensure a healthy and comfortable form of heating, it also produces savings with CO2 emissions."

It is just possible to read that and think they are saying their energy recovery ensures a sufficient stand-alone heating system. I think a responsible firm would make it clear that in most cases it only makes a contribution to the heating, and try to ensure that their equipment was being correctly specified.
- CommentAuthorEd Davies
- CommentTimeSep 12th 2012
What davidfreeborough said is all good but it does neglect the humidity of the air. That might mean that in some cases an exhaust air pump can do a bit better than he implies but I don't think it changes the basic situation much.
- CommentAuthorChrisEngland
- CommentTimeSep 12th 2012
Interestingly,

http://www.nibeonline.com/pdf/639398-2.pdf

suggests a temperature drop across this unit of 37C - although whether that's real or simply 'illustrative' I don't know. That would seem to make the units more practical under UK conditions.

Also, although in an ideal world houses would be well sealed, many aren't and probably can't be realistically, making MHVR impractical, so an extract ventilation unit that does reclaim heat may have some merits.
- CommentAuthorRobinB
- CommentTimeSep 12th 2012 edited
Posted By: DarylP.... to get the SAP rating up, to clear C4SH Level 3 (or 4) perhaps...?

They did say in the R4 interview something about putting them as a means to achieving Level 3.
- CommentAuthorNick Parsons
- CommentTimeSep 12th 2012
Lord save us when builders are using 'goodies' to achieve CSH Level 3 (which really isn't very exciting! I've certainly seen SWH being used to help achieve level 3, alongside some very uninspiring U values.
- CommentAuthorqeipl
- CommentTimeSep 12th 2012
Posted By: davidfreeborough...exhaust heat pumps ... move heat from one place in the building (the air) to another ...

Correct. The energy doesn't leave the building.

All the air extracted will be replaced by cold outside air drawn in through trickle vents. So, ...all the heat extracted by the heat pump will be required to heat the cold outside air drawn in.

The energy isn't extracted by the heat pump, it remains inside the house, in the water in the cylinder, or the UFH system, or the air. The incoming cold air doesn't cause any energy to be lost from the house.

No heat will be available to replace heat lost through the fabric of the building & so all of this heat will need to be provided by electrical resistance back-up heaters.

There are lots of ways that the energy can be replaced.

If the house is designed to benefit from solar gain then much of the energy loss via the fabric is replenished via the windows.

In the absence of sun, yes, the NIBE's immersion heater will kick in to replace the lost energy but this is a design feature of the NIBE, not an inherent feature of an exhaust air heat pump.

As long as the temperature differential between the top and bottom of the tank is greater than the programmed setting the Ecocent's heat pump will run, extracting energy from the air in the house, which is constantly being replaced by cold air from outside.

The energy in the outside air, along with the electrical energy used by the heat pump, replenishes the energy that's lost via the fabric of the building - no different to an external ASHP.

If the heat pump is unable to extract enough energy from the incoming air to replace the energy lost via the fabric, then the house will cool down.

When this happens in my house in the winter months I burn solid fuel to warm the air in two rooms that feed the heat pump. If mains gas was available I might choose to use it. I wouldn't use mains electricity.

In theory an exhaust heat pump can extract more energy from the exhaust air flow than an MVHR heat exchanger, but in practice heat pumps work with temperature differentials of 15°C or less.

In practice my heat pump works very well with a temperature differential of 27°C (45C water temp v. 18C air temp).

.. they cannot do better than an MVHR unit in typical winter conditions where there is 15°C differential between outside and indoor air temperatures.

The difference in outside and inside air temperature is irrelevant. The air supply to the heat pump is at indoor temperature (18C in my case).

The heat pump compressor can be increased in size. However, this requires a corresponding increase in exhaust air flow & therefore an increase in cold air drawn into the building. So all the additional power will be required to cover the increased ventilation heat loss.

Assuming the heat pump exhaust temperature is the same as the outdoor air temperature there is no increased ventilation heat loss from increased air flow. All of the energy exchange occurs inside the building.

... if gas is available you’d be far better off using a gas boiler with continuous extract ventilation than an exhaust heat pump.

Possibly, but if your house benefits from solar gain this set-up doesn't take advantage of excess solar energy. My Ecocent set-up does.

If gas is not available then you’d still be better off using an air source or ground source heat pump to bring in energy from outside than paying to move it around inside the house.

Why? An exhaust air heat pump is using exactly the same energy source as an external ASHP but it's operating at a higher COP in cold weather because the heat pump is being fed warmer air.

I bought the Ecocent because it does the job of a solar collector, MVHR, DHW cylinder, and UFH supply all for £1,600. It works very well for most of the year but I suspect solar gain is the key factor in its success.

David,

I can understand why you're making this argument because I shared your concerns when I first thought of using an Ecocent in this way. I thought that bringing cold air into the building must reduce the temperature inside the building, but I was confusing heat and energy.

There's energy in the warm air inside the building and there's energy in the cold air coming into the building.
The cold air adds energy to the building - energy that the heat pump extracts, transfers to the water, and transfers back into the air.
Energy is lost from the building via the fabric, the heat pump exhaust, and in hot water going down the drains.
No energy is lost via the incoming air.

Malcolm
- CommentAuthorSteamyTea
- CommentTimeSep 12th 2012
Posted By: qeiplbut I was confusing heat and energy.

Do you mean that, heat is energy, what confuses it is temperature. Anything above absolute zero (0K) will have heat, or energy, in it. The word heat tends to be old terminology and we use energy now (blame the French and the SI).
But I know what you mean
- CommentAuthorqeipl
- CommentTimeSep 12th 2012
Yes, I was using heat in terms of temperature differential. Sorry for being sloppy.
If you talk about heat it sounds plausible that cold air coming in will cool down the warm air that's inside, but when you call it energy you have to think about where the energy is going.
- CommentAuthormike7
- CommentTimeSep 13th 2012
Crikey
- CommentAuthorfuncrusher
- CommentTimeSep 13th 2012
I'm not familiar with the precise set-up in this case but let's get down to basic laws of physics. Let's assume the heat pump is WITHIN the house and all electrical energy used by the pump is added to the house as heat. If you extract heat from say waste water that is going down the drain, then you are conserving energy. If you are extracting it from hot exhaust gas (eg air ex-tumble dryer, or stale air from extractor fan or other ESSENTIAL ventilation) then the same applies. If you merely extract heat from air within the house eg loft, there is no gain because you are shifting from one place to another within the house. You might in fact make the house less comfortable because the loft will become colder and the heat loss through the bedrooms ceilings increase. If you extract from your loft and exhaust the cooled air, then that's crazy, because the lost air is simply replaced by ingress of cold outside air, and that ingress is likely to cause a draughty loft and/or cause air ingress in the rooms below. If the heat pump machinery itself is located in the loft and not the habitable part of the house, it is unlikely that all the electrical energy will be captured in heating the house.

Thus it is quite likely that heat recovery from air in the loft is going to produce larger electricity bills without a net benefit.

On the wider issue of construction and performance there is an over-riding paradox which is almost always ignored by politicians and campaigners. Put simply: technology which is entirely dependant on human cooperation is rarely effective in practice. Solutions which are theoretically less efficient but entirely passive (ie automatic / no human copoeration required) are more efficient in practice.

That applies in every aspect of human activity, from disease prevention to aircraft safety. The uncomfortable truth is that the vast majority of people adopt behaviour patterns in their homes that are wasteful of energy, food, time etc. It also applies to construction workers: they do not work to aircraft standards, are not adequately expected, and they rarely suffer for their grotesque errors. In most cases occupiers are oblivious to the fact that the performance of their house is sub-standard, or if they are, what is the cause.
- CommentAuthorSteamyTea
- CommentTimeSep 13th 2012
Posted By: funcrusherand they rarely suffer for their grotesque errors.

Should have a scale of fines based on ACH and U-Values.
- CommentAuthorChris P Bacon
- CommentTimeSep 13th 2012
Posted By: funcrusherIf you merely extract heat from air within the house eg loft, there is no gain because you are shifting from one place to another within the house.

That's only true if the exhaust temperature from the heat pump is at or above ambient. In fact exhaust temperatures on these types of heat pumps can typically go down to -15C so they are extracting a lot more energy from the house air than if they were exhausting it an ambient.

Having said that I am no fan of exhaust air heat pumps. I looked at installing a Nibe F750 with the SAM 40 supply air module which transforms it into a balanced HRV system.

For a number of reasons I concluded it wasn't the way to go and although a more expensive option I will install separate HRV and air source heat pumps.

When I was making my decision one piece of advice I got from a Finnish gentleman on the subject was that "exhaust air heat pumps are the work of Satan!"
- CommentAuthorqeipl
- CommentTimeSep 13th 2012
Posted By: funcrusherIf you merely extract heat from air within the house ... there is no gain because you are shifting from one place to another within the house.

Yes, the energy that's already in the air in the house is merely moved from air to water within the house.
This energy can be transferred to the air again via UFH to warm the fresh air.
The advantage of warming the fresh air is that the COP of the heat pump increases.

Regardless of whether you warm the incoming air it has energy, which the heat pump can extract. This is an energy gain.

You might in fact make the house less comfortable because the loft ...

The loft is a distraction...
The heat pump is fed from air that's inside the house.
All of the energy exchange happens inside the insulated envelope.

.. technology which is entirely dependant on human cooperation is rarely effective in practice. Solutions which are theoretically less efficient but entirely passive (ie automatic / no human copoeration required) are more efficient in practice.

I agree. My exhaust ASHP is entirely automatic, apart from winter when I have to light the boiler to feed it some warm air.
- CommentAuthorqeipl
- CommentTimeSep 13th 2012
Posted By: Chris P Bacon
When I was making my decision one piece of advice I got from a Finnish gentleman on the subject was that "exhaust air heat pumps are the work of Satan!"http:///newforum/extensions/Vanillacons/smilies/standard/bigsmile.gif" alt="" title="" >

The devil's work is working well for me!
- CommentAuthordavidfreeborough
- CommentTimeSep 14th 2012 edited
Posted By: qeiplThe incoming cold air doesn't cause any energy to be lost from the house.
It doesn't cause any energy to be lost from the house, but it needs to be heated to room temperature if its not going to cause the house to get colder. If you use the exhaust heat pump to heat it to room temperature then most if not all of the exhaust heat pump capacity will be required to do this.

Posted By: qeipl
In theory an exhaust heat pump can extract more energy from the exhaust air flow than an MVHR heat exchanger, but in practice heat pumps work with temperature differentials of 15°C or less.

In practice my heat pump works very well with a temperature differential of 27°C (45C water temp v. 18C air temp).
I was talking about the differential in temperature between the exhaust heat pump inlet & its exhaust.

Posted By: qeipl
.. they cannot do better than an MVHR unit in typical winter conditions where there is 15°C differential between outside and indoor air temperatures.

The difference in outside and inside air temperature is irrelevant. The air supply to the heat pump is at indoor temperature (18C in my case).
It is relevant if you have an exhause heat pump expelling air from the house & you're using it to heat the cold air drawn into the house. If you don't connect to the outside air then it isn't an exhaust heat pump. Its an air source heat pump placed indoors.

Posted By: qeipl
If gas is not available then you’d still be better off using an air source or ground source heat pump to bring in energy from outside than paying to move it around inside the house.

Why? An exhaust air heat pump is using exactly the same energy source as an external ASHP but it's operating at a higher COP in cold weather because the heat pump is being fed warmer air.

Its not. The air source heat pump is moving heat from outside to inside. The exhaust heat pump is moving heat you've already paid for from one place in your house to another. If you have excess heat from log burning then thats fine, but thats not the case for a typical domestic installation.

David
- CommentAuthorqeipl
- CommentTimeSep 14th 2012
Posted By: davidfreeborough
Posted By: qeiplThe incoming cold air doesn't cause any energy to be lost from the house.

It doesn't cause any energy to be lost from the house, ..

Correct, but the second part of the sentence is contradictory...

..but it needs to be heated to room temperature if its not going to cause the house to get colder.

The only way the house can get colder is if energy is lost from the house.
The incoming air, regardless of its temperature, doesn't cause any energy to be lost from the house.

If you use the exhaust heat pump to heat it to room temperature then most if not all of the exhaust heat pump capacity will be required to do this.

The heat pump doesn't heat the air to room temperature.
The heat pump removes a chunk of warm air to make space for a chunk of cold air.

When cold air is drawn into the house there is an exchange of sensible energy between the internal warm mass (air + internal building fabric) and the cold air until the temperature reaches equilibrium.
All of this exchange of energy occurs inside the house so there is no energy loss in this part of the system.

The energy loss is all at the other end of the system - the heat pump's exhaust.
The heat pump strips as much energy (sensible and latent) out of the warm air as it can and transfers it to the water.
This exchange occurs inside the house so no energy is lost.
The energy that the heat pump is unable to capture from the air is lost via the exhaust.

In theory an exhaust heat pump can extract more energy from the exhaust air flow than an MVHR heat exchanger, but in practice heat pumps work with temperature differentials of 15°C or less.

I understand now. Sorry for being thick. You're right, when the inside temp is 18C and the outside temp gets down below c.5 degrees on a dull day the exhaust air is noticeably warmer than the outside air. At this point the system is losing more energy than its getting from the fresh air and it's time to light the stove.

The exhaust heat pump is moving heat you've already paid for from one place in your house to another.

Yes, and that's useful work. It's moving excess energy from the air into the water so that I can use it later for DHW or space heating. Some of this excess energy comes from the incoming air (some from the sun).

An exhaust ASHP transfers energy from outside air into a house using exactly the same mechanism as an external ASHP.
The difference is that the exhaust ASHP is being fed air at a higher temperature, which increases the COP, so more of the energy from the incoming air is transferred to the house.
- CommentAuthordjh
- CommentTimeSep 14th 2012
Posted By: qeiplThe only way the house can get colder is if energy is lost from the house.

That's wrong, I'm afraid. You must misunderstand what temperature is. Temperature is a measurement of the average kinetic energy of the molecules in an object or system. So adding fresh air with a lower average kinetic energy (i.e.with a lower average kinetic energy i.e. colder) reduces the average kinetic energy of the whole. i.e. houses get colder when you have cold drafts.
- CommentAuthordavidfreeborough
- CommentTimeSep 14th 2012
Posted By: qeiplAll of this exchange of energy occurs inside the house so there is no energy loss in this part of the system.
This not true. The energy loss from a house is made up of fabric heat loss, air leakage heat loss & ventilation heat loss. The ventilation heat loss is the heat loss due to the need to replace the internal air by deliberate ventilation. In this case the ventilation heat loss will be determined by the number of air changes per house caused by the exhaust heat pump & any additional air changes caused by using trickle vents as air inlets.

Posted By: qeiplAn exhaust ASHP transfers energy from outside air into a house using exactly the same mechanism as an external ASHP.
The difference is that the exhaust ASHP is being fed air at a higher temperature, which increases the COP, so more of the energy from the incoming air is transferred to the house.
The mechanism is the same, but the exhaust heat pump is taking heat from inside the building using an air supply which is limited by the required ventilation rate while the external ASHP is taking heat from outside the building using an unlimited air supply.

If the exhaust heat pump achieves a COP of 3-4 then I don't think this is particularly good value for moving around heat you've already paid for. If the external ASHP achieves a COP of 3 then this compares well with the running cost of a gas boiler.

I take your point that it is a useful technology which has its place. My point is that it should not be routinely specified for domestic heating applications. There is a real risk that this will happen if people think that they can replace a gas boiler & MVHR or ASHP & MVHR with a single exhaust heat pump.

David
- CommentAuthorqeipl
- CommentTimeSep 14th 2012
Posted By: djh
Posted By: qeiplThe only way the house can get colder is if energy is lost from the house.

That's wrong, I'm afraid. You must misunderstand what temperature is. Temperature is a measurement of the average kinetic energy of the molecules in an object or system. So adding fresh air with a lower average kinetic energy (i.e.with a lower average kinetic energy i.e. colder) reduces the average kinetic energy of the whole. i.e. houses get colder when you have cold drafts.

You're right. I'm confusing temperature with energy again. Sorry.
The cold air coming in will reduce the temperature, but only slightly, especially in a house with lots of internal thermal mass.
In practice I never notice any draughts.
- CommentAuthormike7
- CommentTimeSep 14th 2012 edited
"I understand now. Sorry for being thick. You're right, when the inside temp is 18C and the outside temp gets down below c.5 degrees on a dull day the exhaust air is noticeably warmer than the outside air. At this point the system is losing more energy than its getting from the fresh air and it's time to light the stove."

Yea - result! Qeipl, it seems your particular method of accounting for energy flows caused some puzzlement, but all's pretty much well now, I'd say. (Edit some days later:- Hmm , was I wrong about that!) Whether you regard the air coming in as containing energy or not really depends on what temperature you choose as a datum. Whatever that datum temp is, when one does the sums it is the temperature differences that count. One exception to this would be when calculating the theoretical maximum COP, when one needs to use absolute zero as datum.

1 to 30 of 170



	Site Map \| Home \| View Cart \| Pressroom \| Business \| Links	Contact Us
Logout
© Green Building Press

Green Building Forum

Categories

Feeds

Heating and cooling: exhaust air source heat pumps - a cautionary tale