Do radiators with a heat pump make sense?

[colinmac]

I'm looking at a new build bungalow, and the builder has specified a Vaillant Arotherm Plus heat pump and CenterRad compact radiators. The heat pump spec claims 75⁰C output, and therefore it can drive radiators, but that feels to me like it's designed to retrofit into older properties.

I would expect that a new build bungalow would have underfloor heating with a heat pump. So is this combination of pump and radiators ok? Is the builder just being cheap by going with radiators?

 

[muggles]

Don't get a builder to specify your heating system, you need a properly qualified and experienced heating engineer. Yes, the Arotherm Plus can do 75ºC flow temperature, but it'll be horribly expensive to run. Also, since June 2022 Building Regulations have required new heating systems to be designed to run at a maximum of 55ºC flow temperature. Yes, radiators are fine on heat pumps, but they need to be increased in size in order to lower the flow temperature to a point where it is in its efficient operating range.

EDIT:-- Just seen you're in Scotland. Building Regs are different there. Running at heat pump at 75ºC is still a damn silly idea though

 

[colinmac]

Don't get a builder to specify your heating system, you need a properly qualified and experienced heating engineer. Yes, the Arotherm Plus can do 75ºC flow temperature, but it'll be horribly expensive to run. Also, since June 2022 Building Regulations have required new heating systems to be designed to run at a maximum of 55ºC flow temperature. Yes, radiators are fine on heat pumps, but they need to be increased in size in order to lower the flow temperature to a point where it is in its efficient operating range.

EDIT:-- Just seen you're in Scotland. Building Regs are different there. Running at heat pump at 75ºC is still a damn silly idea though

Ok, when I say "the builder has specified" I don't know who exactly it was. It's in the house spec, in any case. It's a development of 19 properties, so I assume there were specialists involved somewhere.

I did wonder how a heat pump was going to get up to 75⁰C without being effectively just electric heating. The 75⁰C feature appears to be to avoid the risk of legionella in the heat store, or at least to avoid the need to regularly crank up the temperature to kill it off. But in any case the whole thing just feels a bit odd.

 

[Johntheo5]

I'm looking at a new build bungalow, and the builder has specified a Vaillant Arotherm Plus heat pump and CenterRad compact radiators. The heat pump spec claims 75⁰C output, and therefore it can drive radiators, but that feels to me like it's designed to retrofit into older properties.

I would expect that a new build bungalow would have underfloor heating with a heat pump. So is this combination of pump and radiators ok? Is the builder just being cheap by going with radiators?

The heat pump can be operated at temperatures up to 75C but as you say the COP (efficiency) would then be approaching direct electrical resistance heating efficiency, (100%, COP of 1.0).
Assuming a 38C/40C DHW temperature is acceptable then the HP can operate at 45C, the DHW temperature can then be boosted to 60C once per week for legionella protection. The rad(s) output will then be 35.41% of their rated output assuming flow/return temps of 45C/40C with a required room temp of 20C which may provide sufficient heat if the HP is run 24/7, with a COP of ~ 2.8 to 4.0. If new rads are installed then they should be oversized (theoreticall) by a factor of 2.8.

 

[colinmac]

The heat pump can be operated at temperatures up to 75C but as you say the COP (efficiency) would then be approaching direct electrical resistance heating efficiency, (100%, COP of 1.0).
Assuming a 38C/40C DHW temperature is acceptable then the HP can operate at 45C, the DHW temperature can then be boosted to 60C once per week for legionella protection. The rad(s) output will then be 35.41% of their rated output assuming flow/return temps of 45C/40C with a required room temp of 20C which may provide sufficient heat if the HP is run 24/7, with a COP of ~ 2.8 to 4.0. If new rads are installed then they should be oversized (theoreticall) by a factor of 2.8.

I asked the builder and their response is that the idea that underfloor heating is better is a matter of opinion, and that they value responsiveness - basically a radiator valve will manage the heat in a room quicker than underfloor can manage.

The Vaillant heat pump is described as low-medium output, in the 35⁰C to 50⁰C range, so it should work fine with radiators I guess and I assume the radiators specified for the build are appropriate for the rooms they are in.

In short, I don't think I need to be particularly concerned by the choice of radiators over underfloor.

 

[ericmark]

What we are looking at is response speed, and if it needs a high response speed?

It a home takes 4 days to cool, then responce speed is unimportant, but if 4 hours, then it would make sense not to heat the home while out at work, or even over night, so the faster the heating system can heat rooms the better.

Life style and how the home is used, will make a huge impact. The theory of kitchen, then dinning room, then living room then bedrooms will not work if children return home at 3:30 PM but dinner is not until 8 PM and in the mean time they are doing home work in their bedrooms.

The fan assisted radiator is fast, and can cool and heat, if you have a method to remove the condensate, heat pumps can work both ways. Pump heat in or out, but the problem is cost and the requirment is so dependent on other items.

 

[Madrab]

There are also other alternative low temp UFH systems (low profile overlays to name 1) that are not heating up a traditionally large thermal mass and are just as responsive as radiators. At the moment they are more targeted towards retrofit's to minimise floor height uplift though absolutely no reason not to fit them as a 1st fix/clean install option.