Air Source Heat Pump for 2 bed bungalow

plumz_2

Hi,

I live in 2 bedroom bungalow and I am looking at the possibility of having an Air Source Heat Pump installed. It currently has one layer of insulation in the loft so will need topping up. It also has cavity wall insulation, although I'm not sure on the quality of it as it seems to track water across to the inner leaf. Is 270mm loft insulation and cavity wall insulation good enough? There is no floor insulation as it was built in 1969, and i don't want to dig the floor up.

I'm currently looking at either Dimplex, Panasonic or Samsung for the ASHP.

Im also looking at using Dimplex Smart Radiators, Smiths Ecovectors or Aluminium Radiators as i have heard that they work better than standard radiators. Im aware that underfloor heating is the best option but again i don't want to dig the floor up. I currently have only about 30mm screed on top of the concrete slab so by the time i have put down insulation and then screed it will be too high, which would mean moving all the doorways up.

I'm just looking to see if anyone has been in a similar situation of if anyone else has an opinion.

Cheers

matelodave

No one can guess whether your house will be suitable nor whether the kit you've chosen will do the job either.


For a start you need to understand (or take the trouble to learn) how a heatpump system works. You need to look as the heat loss for the bungalow on a room by room basis taking into account the insulation in the walls, windows, ceiling and should you choose it, the floor.


Once you know how much heat you need you need then need to know how you are going to deliver this heat to the rooms taking into account the temperatures you want in each room. Bear in mind that you will only be running the system at 30-35degrees so the radiators or heat emitters have to be able to do the job at these low flow temperatures. You can also get an idea of the heatpump sizing as well (have a look at the Daikin website and download their simulator)


When you've got your understanding then you can get some quotes (at least three) because you'll be able to understand them, question them and know if the offered system will do the job.

Cardew

plumz wrote: »

I'm currently looking at either Dimplex, Panasonic or Samsung for the ASHP.

Is there a reason why you are not looking at the two most popular manufacturers - Daikin & Mitsubishi.

lovesgshp

You can use fan coil type radiators for the heating if you are not going for a underfloor system. These will blow the warm air into the room @ circa 50C.
The output figures that Matelodave gave are for a underfloor system, and not for a radiator type unit.

matelodave

Most heatpump COP figures are given for a flow temp of 35 degree with an outside temp of 7 degrees.
Running the system with a flow temp of 50 degrees will reduce the COP from somewhere around 4 down to 3 or less which becomes even worse when the outside temperature drops to zero. It is desirable to reduce the flow temp to improve the efficiency of the heatpump. However it will take longer to heat the room with a lower flow temp so its a difficult balance to decide what is going to be most economical.
That's where good system design, excellent insulation and an understanding of how to set up and operate the system is required. Get it wrong and the system becomes expensive to operate and users don't get a system that works properly.

Robwiz

I've been reading up a lot on renewable heating. It appears that most of the people who are happy with their ASHP have under floor heating – which is compatible with lower flow temperatures enabling the pump to operate efficiently.

The horror stories about ASHP (and in my view there are too many for comfort) are from people who have retro-fitted an ASHP to a wet radiator system.

From reading between the lines, their reasons for dissatisfaction are: a) they kept the same radiators from their oil/lpg system which can't keep up with the house's heat demand at the lower flow temperatures; b) problems arise from the choice of pump – either it's too big and has problems cycling in milder weather or it's too small and can't cope on sub-zero days and c) ASHPs with immersion heaters fitted to provide hot water can be scarily expensive to run.

My conclusion is that ASHP is a viable option in a new build, where UFH and high levels of insulation are designed in and solar thermal can also be used for hot water. In retro-fit situations it's a case of buyer beware – some installers are competent and others have the patter but can't deliver.

Further, I would be tempted to avoid any system that's eligible for RHI payments. The scheme appears to attract too many suppliers with the wrong motivation – the government subsidy makes it too easy to specify over-expensive (and profitable) boilers and ancillaries. However, for someone with an older or listed home with a high heat demand (and limited scope to improve insulation) then biomass can potentially be lucrative, if the project costs are kept sensible.

Air to air heat pumps offer the lowest cost per kWh of heat for fairly modest capital costs.

Cardew

As you might have seen from other threads of Heat pumps, the second phase of the EST trial of heat pumps achieved an average 'system COP' of 2.54 for all the ASHPs tested.


That COP figure of 2.54 was only achieved after all the manufacturers were allowed to examine and improve the installed systems - sometimes with major modifications.


The other factor that manufacturers - understandably - ignore, is that ASHPs have to be run very long period - continuously in some situations - because with the low flow temperatures it takes a long time to heat up a property from cold.


Thus, where people are out during the day or even when asleep in bed, the ASHP has to continue to produce heat.


Therefor if a property needs, say, 15,000kWh of heat from an ASHP, a conventional gas/oil/LPG CH system, with water at much higher temperatures, will not need to use the same 15,000kWh as it can bring the property quickly up to temperature and doesn't need to run when occupants are out at work and in bed.

matelodave

I'd argue that if a property needs 15,000kwh for heating & hot water then it needs that from what ever source you feed it with whether its a heatpump, immersion heater, gas, oil or wood boiler.
The difference being how it's delivered and how much it costs.
Using an immersion heater with electricity at 12p/kwh it will cost £1800 a year. Using a gas boiler at 90% efficiency it will take 16500kwh at 4p a kwh = £660. Using a heat pump with a COP of 2.54 = 15000/2.54 = 5900kwh x 12p/kwh = £708 which compares pretty well with gas. If you get the system set up properly and can average a COP of 3 then it's cheaper than mains gas at only £600 and a lot cheaper than oil or LPG.
I would agree that if it's not designed or set up properly and you aren't comfortable so you've got it flogging away all the time at a high flow temperature then it won't be cost effective.
If the heat emitter's can't deliver the 15000kwh hour to the house at the optimum flow temperature then it will be cold, the only way to counteract that is to increase the flow temperature until they do, but that has an adverse effect on the COP. That's why most retrofits using existing radiators don't work - you need rads or whatever to be correctly sized

lovesgshp

Retrofits with radiators do work and without resizing them. We have many over here.
The solution can be to have the heat curve for the buffer tank increased (Rad circuits should always have one) . It is after all the tank that the pump is heating initialy.
Just as a aside, we had a client with a GSHP and underfloor who changed a user setting by mistake to the level for a radiator circuit. The house got so hot they had to open the windows to let the heat out, as the floor got to about 50C!!!!
We have had no complaints with retrofits using the existing installation.

matelodave

It's still got to compromise your COP if you heat the water to 50 degrees rather than 30-35. I'm not saying that it won't work because it obviously does but the system has to be designed properly and to recognise all the variables - the biggest of which is the user.
You have to decide whether a higher COP and longer running periods is as efficient or more/less costly to install & run as a system with a lower COP and but shorter running times.

lovesgshp

matelodave wrote: »

It's still got to compromise your COP if you heat the water to 50 degrees rather than 30-35. I'm not saying that it won't work because it obviously does but the system has to be designed properly and to recognise all the variables - the biggest of which is the user.
You have to decide whether a higher COP and longer running periods is as efficient or more/less costly to install & run as a system with a lower COP and but shorter running times.

I can see what you are trying to say, but there is no point in trying to keep a radiator system running at a temperature of 30-35C.
Heat pumps are designed to run at 2 output levels, one for underfloor and the second for rad based systems and yes, the COP is lower for a radiator system, but the buffer tank is designed to help reduce system operating time.
Just looking at some data here that I have on file, for a ASHP of close to 9Kw output. At +7/35C it gives 8.8 kwh output for a consumption of 2.4 kwh. Change to -7/35C then you get 6.0/2.3.
Certainly, I would not go with your suggestion of running a radiator system at 30-35C, as the pump would be running virtually all the time, to try and recover the heat loss from the rads, which have a far smaller surface area than a UHF system.