EPC ratings: Air source heat pump vs. old storage heaters

BulliJudd4

I've just had an air source heat pump system and associated hot water tank installed in my home, replacing ancient electric storage heaters and old hot water tank. 

I've had an assessor round to provide an updated Energy Performance Certificate, and was shocked to find my shiny new (and very expensive) system is rated at only 2-out-of-5 stars for efficiency. Can this possibly be correct? The storage heaters were rated 3-out-of 5! How can my heating system now be less efficient? The new hot water system is also rated at 2 compared with the previous 3.

I appreciate that no electric heating set-up is particularly efficient, but air source heat pumps generate three or four units of heat per unit used, and by that measure are extremely efficient. 

Gerry1

I'm no expert but I understand that you'd be very lucky to get a Coefficient Of Performance figure of four, and that three might be more realistic.  Even at four, I'd effectively be paying 3p/kWh whereas with gas it's only a whisker above 2p/kWh, so it would cost me close to 50% more.

Also, a heat pump isn't very efficient for anyone who's out all day because you can't just switch it on when you return and be warm as toast within half an hour: you probably have to leave it on most or all of the day, so that increases the cost significantly as well as ruling out Economy 7.

It may be green if your energy source is renewable and it might be a bit cheaper than storage heaters, but that's about all that it has going for it.

BulliJudd4

Thanks for your comment Gerry.
The heating can be switched on remotely via app and has the usual timer option you'd expect, so it's a very controllable setup. I understand it will be more expensive than any gas or oil options, but I was still surprised at the low efficiency rating. 

My main concern at this stage is that I may encounter an issue when applying for the Renewable Heat Initiative; if anybody knows whether the efficiency of the heating source affects the decision on whether you get it/how much you get then I'd be keen to know.

matelodave

The RHI is based on the EPC of the whole building, not just the heating & hotwater so it take into account insulation, double glazing and even lightbulbs.

Unfortunately I don't think that some surveyors (box tickers) really know what they are doing. Has the energy rating moved up a notch or two from say F or G to E or even D (I think you need a minimum of an E to claim the RHI)
My EPC went up from a G-32 to a D-66 when I got my ASHP but I also improved the roof insulation from 50mm to 300mm as well which would have helped

Bear in mind that you should learn how to use it properly - don't have your water too hot (we have ours at 45), dont have your circulating water too hot either (ours is between 30 and 40) and dont keep turning it on and off use the thermostats to just set the temperature back a 2-3 degrees otherwise it will take a long time to reheat your place. Higher flow temperature will increase your costs so avoid letting the unit use the back-up heater (anything above 50-55 degrees will kick in the heater)

Keep an eye on your leccy consumption - read the meter regularly and then you'll see how any tweaks or adjustments affect your use. If you dont monitor it you cant control it. We dont have E7 but get the cheapest single rate tariff as the unit runs all day and evening and not so much overnight.

BulliJudd4

UPDATE: I queried the ratings with the assessor and after some recalculation/corrections, the air source heat pump has been reclassified from 2/5 to 4/5. This has also contributed from the overall efficiency rating going from a D to a C.

He noted that ASHP's are regularly provide assessors problems when compiling an EPC. Interesting.

matelodave

Thats because they tick boxes without really understanding what they are doing - I had to sit down and explain to my assessor why his assessment was wrong and how to tweak it to make it a bit better. However that said, some of the recommendations were patently just stupid.

Part of the problem seems to be the water heating - if he ticks the box as electrically heated then it gets a poor rating whereas if it's heated via the heatpump (as mine is) then it's rating should be much better but it relies on the assessor getting his head around it and the software being sufficiently flexible to understand it.
  
My EPC was issued in 2013 when ASHP were still a bit rare but I would have hoped that the software and assessor knowledge would have been revised a bit by now and could cope with the technology