Air to water heat pumps

g1983d

Looking at a heating system for a new house with UFH and was just wondering what the general consensus on air to water heat pumps is? Hearing so many different stories

Dartz

It needs to have a properly designed system to go with it.

Ideally, your heat pump would be feeding a thermal store. This'll let you do things like heat the store up on night rate and the like, then draw off heat from it during the day. A thermal store is a buffer tank, filled with between 600-1000L (or more) of water, depending on the system you have.

Air-to-water heat pumps generally need to go into a defrost cycle every now and then to clear the ice off themselves. It's not odious, but the heat pump can't produce heat when its in a defrost cycle, so your thermal store will allow the heat-pump to run its defrost cycle without interrupting your hot water, or heating flow.

What you don't want, is a big slab of concrete around your underfloor heating to do that same job - some companies like to do that to save money, but it'll make the system uncontrollable. Your underfloor heating only begins to really heat the room when the surface of the floor gets hotter than the room air temperature. The faster this happens the better. You wont be sitting cold.

A big slab of concrete will take hours to heat up to the point where it'll be able to release heat, by which time conditions might've changed.

Also. If you have a big slab of concrete it'll keep releasing heat until the slab of concrete and the room are at the exact same temperature.... with a thick slab of concrete, that's a lot of heat it has to keep releasing to get to that point. You'll end up overheating your room.

Of course, all this depends on your home, how you've designed it and how you're living it. I'm barely even skimming the surface. Any reputable company will take the time to sit you down and talk you through this - and they'll have numbers to back up their claims.

froshtyv

g1983d wrote: »

Looking at a heating system for a new house with UFH and was just wondering what the general consensus on air to water heat pumps is? Hearing so many different stories

There are plenty of house throughout the country using air source heat pumps no problem.
We dont get cold enough temperatures here for it to affect the performance of a heat pump significantly.
Yes the output will be reduced as the temperatures drop but not to a point where the heat pump wont work.
Geothermal will work out considerably more expensive, between the unit itself and then the ground works for the collector pipe, either horizontally or vertical bore holes.
Even though you will get better COP's with the geothermal i dont think its enough of a difference to justify the extra capital cost and longer pay back period.

g1983d

froshtyv wrote: »

There are plenty of house throughout the country using air source heat pumps no problem.
We dont get cold enough temperatures here for it to affect the performance of a heat pump significantly.
Yes the output will be reduced as the temperatures drop but not to a point where the heat pump wont work.
Geothermal will work out considerably more expensive, between the unit itself and then the ground works for the collector pipe, either horizontally or vertical bore holes.
Even though you will get better COP's with the geothermal i dont think its enough of a difference to justify the extra capital cost and longer pay back period.

Thanks for that, I had come to the same conclusion myself re geo, payback is too long.

That's why I'm interested in air to water and people's experiences

froshtyv

g1983d wrote: »

Thanks for that, I had come to the same conclusion myself re geo, payback is too long.

That's why I'm interested in air to water and people's experiences

Any new build house adhering to the new building regs is a well built house that will work well with UFH and a heat pump.

I dont see the need for a buffer tank with an air to water heat pump.
By heating a buffer tank at night time, and going with the theory of it heating the house during the day, the underfloor heating would take from the buffer pretty quick which would mean your bringing on the heat pump to heat the buffer again.
Water isnt the greatest way of storing heat, yes it will do it, but when you go to transfer the water from the buffer tank to the heating circuits you will have significant losses.

I would definitely go with an installer who has done several systems to what you are after.
At least you know that they are familiar with the products.
Also I would also see what back-up service they offer from themselves and from the supplier of the heat pump unit.
If a part goes in the unit, is the installer qualified to replace it,
Does the supplier of the heat pump offer support?

dathi

froshtyv wrote: »

.
We dont get cold enough temperatures here for it to affect the performance of a heat pump significantly.
..

depends on what part of the country you are located here in kilkenny we get an average 50 frost days per year coupled with high humidity levels . this means for 20% of your heating season an air source heat pump is working well below its quoted COP

murphaph

dathi wrote: »

depends on what part of the country you are located here in kilkenny we get an average 50 frost days per year coupled with high humidity levels . this means for 20% of your heating season an air source heat pump is working well below its quoted COP

They install loads of them in much colder parts of Germany than anywhere in Ireland. The winters here are long and cold and these things still work. We want geothermal but if I was building in Ireland I would be much more inclined to go air water.

dathi

murphaph wrote: »

They install loads of them in much colder parts of Germany than anywhere in Ireland. The winters here are long and cold and these things still work. We want geothermal but if I was building in Ireland I would be much more inclined to go air water.

yes and in Scandinavia, but they do not have our high humidity it is not only the cold that affects their COP but also the humidity. which forces the heat pump to go into defrost mode regularly. never said that they will not work what i am saying is that the manufacturers stated COP of 3.5 to 1 or 4 to 1 or whatever will fall close to parity ie. 1kw in 1kw out, on the frost days mentioned in my first post, this will coincide with the greatest heat demand of your building, as the heat loss from the fabric of your building will be at its highest, because of the temperature difference between the outside temp and inside temp .

froshtyv

dathi wrote: »

yes and in Scandinavia, but they do not have our high humidity it is not only the cold that affects their COP but also the humidity. which forces the heat pump to go into defrost mode regularly. never said that they will not work what i am saying is that the manufacturers stated COP of 3.5 to 1 or 4 to 1 or whatever will fall close to parity ie. 1kw in 1kw out, on the frost days mentioned in my first post, this will coincide with the greatest heat demand of your building, as the heat loss from the fabric of your building will be at its highest, because of the temperature difference between the outside temp and inside temp .

I cant speak for all models but from data sheets I have seen for an air-to-water heat pump @ -20°C and flow @35°;C the COP is rated at 1.95.
That is an extreme scenario which we do not get here.

Yes the output of the machine will reduce as the outside temperature drops, but it would be a poor design if it couldnt meet the heat demand of a house.

Once you get your house up to temperature you are then just keeping it at the temperature so your heat demand shouldnt be that large.

This is where a heat pump with an inverted rated compressor is ideal.

blast06

dathi wrote: »

yes and in Scandinavia, but they do not have our high humidity it is not only the cold that affects their COP but also the humidity. which forces the heat pump to go into defrost mode regularly. never said that they will not work what i am saying is that the manufacturers stated COP of 3.5 to 1 or 4 to 1 or whatever will fall close to parity ie. 1kw in 1kw out, on the frost days mentioned in my first post, this will coincide with the greatest heat demand of your building, as the heat loss from the fabric of your building will be at its highest, because of the temperature difference between the outside temp and inside temp .

How many days do we really get with high humidity coupled with very low temps?!?!? 1 every 5 years i'd say!

dathi

blast06 wrote: »

How many days do we really get with high humidity coupled with very low temps?!?!? 1 every 5 years i'd say!

not according to met eireann you can look it up there rather than speculating

MicktheMan

blast06 wrote: »

How many days do we really get with high humidity coupled with very low temps?!?!? 1 every 5 years i'd say!

Define "high humidity" please.

mark2003

Just a quick question,do you need a air ventilation system in the house if you are going installing an air to water heat pump, if not what are the other options.

murphaph

No you don't have to install any particular ventilation system purely because you install an A2W heat pump but heat pumps are only a good idea in a well insulated and air tight property. It's just madness to install one in anything else. Given that, a ventilation system clearly makes a lot of sense, especially one with heat recovery.

In a new build I wouldn't even think of anything except airtight + MHRV, regardless of the heat source used. It's just madness to be venting out warm air with energy costs going the way they are.

Condenser

murphaph wrote: »

No you don't have to install any particular ventilation system purely because you install an A2W heat pump but heat pumps are only a good idea in a well insulated and air tight property. It's just madness to install one in anything else. Given that, a ventilation system clearly makes a lot of sense, especially one with heat recovery.

In a new build I wouldn't even think of anything except airtight + MHRV, regardless of the heat source used. It's just madness to be venting out warm air with energy costs going the way they are.

High levels of insulation and air tightness are not a prerequisite of installing a heat pump. Heat pumps have been installed in houses with little more than 50mm aeroboard in the walls with excellent results. The most important consideration when installing a heat pump is having a distribution system that can run at as low a temp as possible, i.e a well designed ufh system, and a well designed installation

murphaph

But if you are heating a draughty old property with a heat pump (and yes you're right a low temp distribution system like floor or wall heating is the ideal for max efficiency) then it'll be on all the time and you'll effectively be heating your house with electricity. It is a bad idea in any case regardless of the heating system to improve or replace said system without tackling insulation and air tightness. Energy, be it electricity for a constantly running heat pump or gas for a constantly running boiler is getting more and more expensive.

Reducing the energy requirement of the building should be priority no. 1, then look at the heating system.

Condenser

murphaph wrote: »

But if you are heating a draughty old property with a heat pump (and yes you're right a low temp distribution system like floor or wall heating is the ideal for max efficiency) then it'll be on all the time and you'll effectively be heating your house with electricity. It is a bad idea in any case regardless of the heating system to improve or replace said system without tackling insulation and air tightness. Energy, be it electricity for a constantly running heat pump or gas for a constantly running boiler is getting more and more expensive.

Reducing the energy requirement of the building should be priority no. 1, then look at the heating system.

I'm not disputing that insulating would be better but you'll still run for quarter the cost of oil even in an badly insulated house with a hp once the distribution system is right.

murphaph

For your statement to be true I would have to install a heat pump that could match the demand of the draughty house WITHOUT using its fallback (which is an electric immersion heater!!). You would need to install a massively over rated heat pump for that to be the case and it would cost you in both the installation and running costs.

If you install the same rated heat pump in your draughty house as you would in the equivalently sized airtight etc. house then the heat pump won't be able to supply the demand without constantly engaging the immersion element (COP is then 1 as you are directly heating the water with electricity and not using the electricity to move energy from one place to another)

If you on the other hand have 2 equivalent gas boilers then in the draughty house you will have the problem of a constantly running gas boiler instead of a constantly running immersion heater, but gas is much cheaper to heat a property with than electricity, so in a poorly insulated property a heat pump really is going to cost more than gas. If your statement were true, nobody would install oil over a heat pump, ever. Many people are even asking themselves why bother with a heat pump in a really well insulated & airtight house because the amount of gas required to maintain a comfortable environment is actually really low and gas boilers are significantly cheaper than heat pumps still so the payback for a heat pump in such a house can take decades...you may never see it if you move house again.

For the record, we're planning a new build here in Berlin and we're planning ground source heat pump but are being heavily influenced by the fact our site has no gas supply and to get one will cost about 8k. If we had gas to the site it would be a much harder decision probably.

The rules for heat pumps remain largely as the EST found: use them in a well insulated house, only use them with underfloor heating or low flow temperature radiators and have a separate heat source for DHW, ideally solar panels. Flaunt the rules and we have an expensive machine with high running costs and CO2 emissions. - See more at: http://www.homebuilding.co.uk/advice/key-choices/green/real-cost-heat-pumps#sthash.9HhCaE4R.dpuf

http://www.homebuilding.co.uk/advice/key-choices/green/real-cost-heat-pumps

Condenser

murphaph wrote: »

For your statement to be true I would have to install a heat pump that could match the demand of the draughty house WITHOUT using its fallback (which is an electric immersion heater!!). You would need to install a massively over rated heat pump for that to be the case and it would cost you in both the installation and running costs.

If you install the same rated heat pump in your draughty house as you would in the equivalently sized airtight etc. house then the heat pump won't be able to supply the demand without constantly engaging the immersion element (COP is then 1 as you are directly heating the water with electricity and not using the electricity to move energy from one place to another)

If you on the other hand have 2 equivalent gas boilers then in the draughty house you will have the problem of a constantly running gas boiler instead of a constantly running immersion heater, but gas is much cheaper to heat a property with than electricity, so in a poorly insulated property a heat pump really is going to cost more than gas. If your statement were true, nobody would install oil over a heat pump, ever. Many people are even asking themselves why bother with a heat pump in a really well insulated & airtight house because the amount of gas required to maintain a comfortable environment is actually really low and gas boilers are significantly cheaper than heat pumps still so the payback for a heat pump in such a house can take decades...you may never see it if you move house again.

For the record, we're planning a new build here in Berlin and we're planning ground source heat pump but are being heavily influenced by the fact our site has no gas supply and to get one will cost about 8k. If we had gas to the site it would be a much harder decision probably.


http://www.homebuilding.co.uk/advice/key-choices/green/real-cost-heat-pumps

Going on your logic, every heat pump installed in Ireland and the UK before 2007 was a waste of time, because up until that point good insulation was regarded as 50 - 60mm Kingspan in a 100mm cavity, same on the floor and between 150 -200mm rock wool in the roof. Air tightness wasn't even heard of. Yet amazingly I know houses of over 300sqm running both heating and hot water for under €700 per year.


These houses were not "massively oversized" as you put it, they were adequately sized for the heat loss they had. I also know of houses that were burning €2,500 - €3,000 per year in oil at the time, installed a heat pump and knocked their bills down to €800. Hardly decades of payback time there I would estimate.


As for the article, while its not the worst article I've ever read on heat pumps, I would question the knowledge of someone who would write a lot of what he has written. Rubbish like needing solar or a separate hot water heat pump in order for a heat pump to be efficient. Theres dozens of people on this board alone who would attest to different. He also likes to talk about the variability of COP but seems certain that an installation can only see a COP go down, there is no reference to the fact that a good installation will see a COP increase.


Btw not all heat pumps have immersion heaters installed, well designed systems don't need them or have them, not even for hot water production.

murphaph

You do accept that a heat pump in a poorly insulated property has to be larger than a property of the same type that is well insulated or the result is that the heat pump's fall back method of heating will be called upon and that in most cases that fall back is an immersion heater?

Simply saying "I know of houses that had oil bils of x and they replaced with a heat pump and now spend y on heating" is anecdotal evidence. You don't know the psychological effect of the "big ESB bill" and how it caused those switching to a heat pump to modify their usage of their heating source. Did these people you know all have UFH before switching to a heat pump or did most have rads or did they switch to a heat pump and keep the rads?

The article does have some things I'd question too, but the basis of the article is a report by the UK's Energy saving Trust and they agree that heat pumps should only be used in well insulated properties.

Condenser

murphaph wrote: »

You do accept that a heat pump in a poorly insulated property has to be larger than a property of the same type that is well insulated or the result is that the heat pump's fall back method of heating will be called upon and that in most cases that fall back is an immersion heater?

Simply saying "I know of houses that had oil bils of x and they replaced with a heat pump and now spend y on heating" is anecdotal evidence. You don't know the psychological effect of the "big ESB bill" and how it caused those switching to a heat pump to modify their usage of their heating source. Did these people you know all have UFH before switching to a heat pump or did most have rads or did they switch to a heat pump and keep the rads?

The article does have some things I'd question too, but the basis of the article is a report by the UK's Energy saving Trust and they agree that heat pumps should only be used in well insulated properties.

Off course it has to be larger, that was never in question, that same would be true of a gas or oil boiler, its not unique to a heat pump that a larger heat loss needs a larger heat producer.


There was no "psychological effect". These heat pumps were ready to heat the property 24/7 and maintain a constant temp except at night when the whole house would reduce by 3C for comfort. Hot water 24/7 also.


All the houses had ufh which was my entire point, heat pumps need a low temperature distribution source in order to be successful, they do not need a well insulated airtight house.


The EST should probably broaden their knowledge if that's the extent of it, hardly surprising for a government body however.

murphaph

A gas boiler doesn't have to be larger...it just has to stay on more, burning more gas. A heat pump HAS to be larger or it will fall back to its immersion heater, at which point you have zero benefit from the heat pump because it's now just an expensive immersion and heating water directly with electricity is as expensive a heat source as you'll get.

Condenser

murphaph wrote: »

A gas boiler doesn't have to be larger...it just has to stay on more, burning more gas. A heat pump HAS to be larger or it will fall back to its immersion heater, at which point you have zero benefit from the heat pump because it's now just an expensive immersion and heating water directly with electricity is as expensive a heat source as you'll get.

You're just grasping at straws now. If it was properly sized in the first place it wouldn't be able to meet demand. You could argue the same with a HP if that was the case saying it could run 24hrs instead of the usual 8-10 they normally would in winter.

Mixupat

I'm working on detailed tendering plans for my new build and currently deciding on heating system with BER assessor. He is having trouble getting Part L compliance using an Air Source Heat Pump (COP not high enough) along with a Wood Burning Stove. I will be using MHRV and underfloor heating.

Would I be better off having Solar or Thermodynamic Solar Panels as a Water Heating Source to go alongside ASHP?

Is it better to have a seperate water heating source other than the heat pump but then there is added cost of this also?

What would compliment ASHP if another system is required for part L compliance?

I am staying away from ground source as I had my soil checked before and the conditions were advised as not great for GSHP.

I'm no expert on any of this so I would appreciate any advice and opinions.

Condenser

Mixupat wrote: »

I'm working on detailed tendering plans for my new build and currently deciding on heating system with BER assessor. He is having trouble getting Part L compliance using an Air Source Heat Pump (COP not high enough) along with a Wood Burning Stove. I will be using MHRV and underfloor heating.

Would I be better off having Solar or Thermodynamic Solar Panels as a Water Heating Source to go alongside ASHP?

Is it better to have a seperate water heating source other than the heat pump but then there is added cost of this also?

What would compliment ASHP if another system is required for part L compliance?

I am staying away from ground source as I had my soil checked before and the conditions were advised as not great for GSHP.

I'm no expert on any of this so I would appreciate any advice and opinions.

You'll have a job get an ASHP to comply without additional backup systems. What type of soil have you and why was it not suitable?
I'd go GSHP everytime if I were you as a good ASHP will cost as much if not more than a GSHP. A cheap ASHP won't last half as long.

froshtyv

Mixupat wrote: »

I'm working on detailed tendering plans for my new build and currently deciding on heating system with BER assessor. He is having trouble getting Part L compliance using an Air Source Heat Pump (COP not high enough) along with a Wood Burning Stove. I will be using MHRV and underfloor heating.

Would I be better off having Solar or Thermodynamic Solar Panels as a Water Heating Source to go alongside ASHP?

Is it better to have a seperate water heating source other than the heat pump but then there is added cost of this also?

What would compliment ASHP if another system is required for part L compliance?

I am staying away from ground source as I had my soil checked before and the conditions were advised as not great for GSHP.

I'm no expert on any of this so I would appreciate any advice and opinions.

What size is your house?

Mixupat

2800 Square Ft..I will have airtightness with MHRV but after that I'm not fully sure.

murphaph

Condenser wrote: »

You're just grasping at straws now. If it was properly sized in the first place it wouldn't be able to meet demand. You could argue the same with a HP if that was the case saying it could run 24hrs instead of the usual 8-10 they normally would in winter.

If you want to stick to the line that a HP is always 75% cheaper to run than oil then there's no point in arguing. I refer you back to the article I posted in which real world data was collected by the Energy Saving Trust. You've dismissed that data and stand by your own claims. If a heat pump was really 25% the cost of oil to run then not a single oil boiler would have been installed in years...but even today here in Germany you still have large numbers of people choosing gas over heat pumps. The decision simply isn't that easily made and Germans like to save!

froshtyv

Mixupat wrote: »

2800 Square Ft..I will have airtightness with MHRV but after that I'm not fully sure.

It obviously depends on what the SPF of the heat pump you are using is.

I have done plenty of XML files where an air source heat pump is the only heat source in the house and no solar or PV is required.

Is the house an A3 or A2 rating at the moment?

Where are you falling down in the compliance?

EPC, CPC or renewable contribution?

Is it underfloor throughout or low temp rads?

Condenser

murphaph wrote: »

If you want to stick to the line that a HP is always 75% cheaper to run than oil then there's no point in arguing. I refer you back to the article I posted in which real world data was collected by the Energy Saving Trust. You've dismissed that data and stand by your own claims. If a heat pump was really 25% the cost of oil to run then not a single oil boiler would have been installed in years...but even today here in Germany you still have large numbers of people choosing gas over heat pumps. The decision simply isn't that easily made and Germans like to save!

You're referring me back to an article which you yourself admitted is flawed yet you decide to cherry pick the items you want to support your position. I am telling you that having installed over 300 systems, many as retrofits to replace oil boilers on ufh systems that the 75% reduction is a very accurate portrayal of the amount a well installed heat pump can save you.
If you choose not believe that then that's your prerogative.
You seem to have on from your original fight that a highly insulated air tight house was essential.

Mixupat

froshtyv wrote: »

It obviously depends on what the SPF of the heat pump you are using is.

I have done plenty of XML files where an air source heat pump is the only heat source in the house and no solar or PV is required.

Is the house an A3 or A2 rating at the moment?

Where are you falling down in the compliance?

EPC, CPC or renewable contribution?

Is it underfloor throughout or low temp rads?

It's an A3 rating currently. Underfloor throughout. I'm not sure where compliance is the issue and my assessor is on leave for the week. So many opinions out there, it's hard to know. Want to do the best I can without spending a fortune on various systems.

froshtyv

Mixupat wrote: »

It's an A3 rating currently. Underfloor throughout. I'm not sure where compliance is the issue and my assessor is on leave for the week. So many opinions out there, it's hard to know. Want to do the best I can without spending a fortune on various systems.

It depends so how close you are with compliance.

If you went for natural ventilation as opposed to mechanical the heat pump would contribute more towards the renewable.

Depends on what you want for your build though, and its impossible to say without seeing your xml file.