High KW Air Source Heat Pump options

Wir-Gild

Hi,

I've a largeish renovated property (320sqm) which is well insulated, has wet underfloor heating down stairs and radiators upstairs. It has an Oil boilder at present. I've had ASHP suppliers around who look nervous suggesting stardard ASHP at around the 12kw to 16kw or suggesting hybrid systems that keep the oil boiler (which defeats the point of moving to a ASHP)due to the open plan nature of the downstairs and the high volome of circulating air. 

Since getting the aforementioned quotes I've been working with the DNO to upgrade the property to three-phase supply. This is going ahead in the next four weeks or so. I'm now researching options for high capacity domestic ASHP and struggling to find much over 16kw.

Does anyone have any exepriance/ knowledge of any over 20  - 25kw and/or strings two or more smaller ones together?

Thanks,

Reed_Richards

Sorry, I can't give you a direct answer to your question but:

The first thing you need to do is to calculate the actual heat requirement of your property.  I understand that there are various software tools you can find that will do this.  Or if the installer works to MCS standards this calculation is the first thing they would do; you might find some who would do it for free in order to give you a quote.

Also, you generally have to run radiators at a higher water temperature than UFH and if so the heat pump will run less efficiently than if it was just supplying cooler water for the UFH.  Therefore it might make economic sense to have one heat pump to supply your UFH and another one, working less efficiently, for your upstairs radiators.

Rodders53

Reed_Richards said:

Also, you generally have to run radiators at a higher water temperature than UFH and if so the heat pump will run less efficiently than if it was just supplying cooler water for the UFH. 

That's a fallacy, as I understand it. 
Most people expect/want radiators to be hotter, but they can work at lower temps as long as the radiator size and delta T has been calculated correctly. Radiators may well need changing for larger emitters in this refurbished property, though to do the job required?

The UFH manifold will thermostatically mix to an even lower temperature, if necessary, than the low flow temperature from a heat pump and still have the HP running efficiently.  Unless the UFH was designed to run at a relatively high temperature when installed.

Hot water for showers, baths etc is likely to need the highest temperatures (and for Legionalla may need supplementary 1:1 immersion use once a week or so).

The important thing is to get proper heat loss calcs done and that should have been done as part of the original refurb build?  That'll allow proper heat pump kW rating / house needs to be calculated.

Not sure that a working oil burner will be economically replaced by an electric heat pump.  But the OP has invested in 3 phase electric already.  Larger units may be 'commercial' rather than intended for domestic but should still be available.

The installers consulted so far don't seem to be well trained or confident in their abilities so may be best avoided?  Keep calling in others.

You'll need full Planning Permission for two heat pumps.  May even need it for a larger single unit as well.  Do your due diligence.

Reed_Richards

Rodders53 said:

Reed_Richards said:

Also, you generally have to run radiators at a higher water temperature than UFH and if so the heat pump will run less efficiently than if it was just supplying cooler water for the UFH. 

That's a fallacy, as I understand it.

Then possibly you don't understand it correctly?

Rodders53 said:

The UFH manifold will thermostatically mix to an even lower temperature, if necessary, than the low flow temperature from a heat pump and still have the HP running efficiently.  

Efficiently perhaps, but not as efficiently as if it was supplying water at the "even lower temperature" that the UFH requires.  Which is the point I was trying to make.

Now if you have sized your radiators large enough that the water temperature they require is the same as the water temperature required for the UFH then there is no loss of efficiency; but people very rarely do that.

matt_drummer

Rodders53 said:

You'll need full Planning Permission for two heat pumps.  May even need it for a larger single unit as well.  Do your due diligence.

Yes, anything where the outdoor unit is bigger than 0.6 m3 requires planning permission.

QrizB

Wir-Gild said:

I've had ASHP suppliers around who look nervous suggesting stardard ASHP at around the 12kw to 16kw or suggesting hybrid systems that keep the oil boiler (which defeats the point of moving to a ASHP)due to the open plan nature of the downstairs and the high volome of circulating air.

I'm going to second the comment from R_R that you need to start with a heat loss calculation. Your installer should be able to put a piece of paper - or an iPad - under your nose and say "here's the heat loss calc, to achieve an indoor temp of 21C at -3C ambient you need XXkW of heat input. I'm thereofre recommending [insert solution here]."

If they haven't done that, they're not taking the job seriously enough.

There are far too many houses with oversized gas boilers because sizing wasn't properly considered. With a gas boiler it's a bit more expensive to buy big, and perhaps slightly more expensive to run, but overall people don't really mind. ASHPs are not gas boilers and size really does matter.

lohr500

In 2020/21 when we had a survey done for an ASHP in our large converted farmhouse, the installation engineers advised that we would need twin ASHP units (I can't find the details but I think they were suggesting twin 13kW ) working together and a three phase supply to support them.

In the end when I did the calculations, and leaving green issues aside, is was far more economical to replace the old oil boiler with a new condensing high efficiency oil boiler. That was based on the one off installation costs and the projected running costs over 10 years using the fuel costs in place at the time.

When we were looking at switching the grant available was around £12k for our installation. Now I understand the grant has reduced to £5000.

As far as I am aware, if you keep the oil boiler in a hybrid system then you won't even be eligible for the £5k grant. If the ASHP advisors didn't tell you this, then I would also question their abilities.

markin

How many L of oil are you using a year, average over 3 years, converted to kwh, That will give you good idea of your demand, But find the numbers from the EPC/SAP.
 

MultiFuelBurner

Wir-Gild said:

Hi,

I've a largeish renovated property (320sqm) which is well insulated, has wet underfloor heating down stairs and radiators upstairs. It has an Oil boilder at present. I've had ASHP suppliers around who look nervous suggesting stardard ASHP at around the 12kw to 16kw or suggesting hybrid systems that keep the oil boiler (which defeats the point of moving to a ASHP)due to the open plan nature of the downstairs and the high volome of circulating air. 

Since getting the aforementioned quotes I've been working with the DNO to upgrade the property to three-phase supply. This is going ahead in the next four weeks or so. I'm now researching options for high capacity domestic ASHP and struggling to find much over 16kw.

Does anyone have any exepriance/ knowledge of any over 20  - 25kw and/or strings two or more smaller ones together?

Thanks,

If the house is well insulated the heat loss.survey is key. As an example our 180sq m home requires a 8.5kw ASHP as it is a high efficiency house with wet UFH heating. 

The trick is finding an ASHP specialist that hasn't jumped on the band wagon but knows the subject well.

HL365

...or just go HVO when it gets approved for domestic use . Keep existing oil boiler with £500/600 conversation costs

HL365

Some rural areas like mine with OH feeds can't support 3 phase power so no chance of larger ASHP and higher rate EV charging