I bought a Heat Pump

shinytop

michaels said:

Reed_Richards said:

During the last 5 days of cold weather the average power consumption by my heat pump has been 2.5 kW.  That doesn't seem too bad to heat the entire house but I was paying an average of £920 per year for oil and in the last two months I have spent over £400 on electricity for the heat pump so I am not very confident I will be able to match my previous fuel costs.  

Are you comparing like with like in terms of temperature in the house?  Obviously it has been a particularly hard test of heat pumps as at least where we are the average temps have bene below the monthly norms and heat pumps don't like the cold.

From what I've read oil will beat the heat pump for price when it's cold like it's been but the HP may catch up when it's a bit milder. In my case I have NSHs and immersion heater and these have cost an average of £180/month over the last 3 months. 

Is it not a fair assumption that a the running costs of a properly designed and used ASHP should roughly equate to the EPC figure based on a sensible SPF?  So a 20000kWh EPC rated house should cost about £1200 with an SPF of 2.5 and 15p/kWh.  

Not sure if this has been posted before https://myhomefarm.co.uk/ but there is a lot of info and discussion about ASHPs.  The author has a huge (by most standards) ASHP in an old house and his experiences are interesting. 

Reed_Richards

michaels said:

Are you comparing like with like in terms of temperature in the house?  

No, certainly not.  All I can say so far is:

• The heat pump is having no trouble keeping the house warm.
• It is costing me more per day than in the worst winter with my oil boiler.  But my oil boiler experience was only the previous two winters and supposedly we (the UK) have just had the coldest January since 2010. 

Reed_Richards

Pile_o_stone said:

Yes, sorry I thought your comment "Even then I elected to tolerate being short of heat in two rooms." meant that you didn't have heat in those rooms, rather than having some heat in there.

We had a small en-suite with a radiator/towel rail and a relatively new radiator in the kitchen.  In both cases they gave about 70% of the new required heat output but I elected not to do anything about it because of space considerations.  As a result the kitchen is quite cool first thing in the morning but warms up during the day. The en-suite is okay but cooler than the main bathroom, where we added an extra radiator.  

Reed_Richards

shinytop said:

Is it not a fair assumption that a the running costs of a properly designed and used ASHP should roughly equate to the EPC figure based on a sensible SPF?  So a 20000kWh EPC rated house should cost about £1200 with an SPF of 2.5 and 15p/kWh.  

The very comprehensive survey used to calculate the heat loss of the house produced an estimate of my oil bill that was over 2 times the actual value.  Whilst the much more rough-and-ready EPC came close to the actual value.  Go figure.

ASavvyBuyer

You may have seen this before, but someone has done a very detailed analysis of before & after the installation of a heat pump.

Heat pump performance and home energy 2020

They are achieving COP's in the 3-4 range.

michaels

ASavvyBuyer said:

You may have seen this before, but someone has done a very detailed analysis of before & after the installation of a heat pump.

Heat pump performance and home energy 2020

They are achieving COP's in the 3-4 range.

Really interesting - but they use hardly any 'hot' water at a temperature that probably wouldn't be high enough for a hot bath and don't heat very warm either - and then compare against gas at 30% more per unit than we pay and boiler efficiency of 80%....

Martyn1981

If I'm reading the graphs correctly they look OK to me. They appear to consume around 50kWh (leccy) pm for DHW, providing ~180kWh of water heating a month, so roughly 6kWh per day. It appears the UK average is about 5kWh/day (that's assuming I'm understanding it, and converting 16.8MJ correctly, which I may not be).

michaels

Martyn1981 said:

If I'm reading the graphs correctly they look OK to me. They appear to consume around 50kWh (leccy) pm for DHW, providing ~180kWh of water heating a month, so roughly 6kWh per day. It appears the UK average is about 5kWh/day (that's assuming I'm understanding it, and converting 16.8MJ correctly, which I may not be).

UK average, hmm - no wonder the tubes and trains always small so bad.  5 of us use 33kwh gross of hot water heating a day, in the summer when the incoming is 10+ degrees warmer than now.

6kwh is only 170l of water, less in the winter.

shinytop

michaels said:

Martyn1981 said:

If I'm reading the graphs correctly they look OK to me. They appear to consume around 50kWh (leccy) pm for DHW, providing ~180kWh of water heating a month, so roughly 6kWh per day. It appears the UK average is about 5kWh/day (that's assuming I'm understanding it, and converting 16.8MJ correctly, which I may not be).

UK average, hmm - no wonder the tubes and trains always small so bad.  5 of us use 33kwh gross of hot water heating a day, in the summer when the incoming is 10+ degrees warmer than now.

6kwh is only 170l of water, less in the winter.

That's a lot of hot water.  I reckon 2 of us use 3-4 kWh/day.  Not soap dodgers and use a dishwasher.        

shinytop

michaels said:

ASavvyBuyer said:

You may have seen this before, but someone has done a very detailed analysis of before & after the installation of a heat pump.

Heat pump performance and home energy 2020

They are achieving COP's in the 3-4 range.

Really interesting - but they use hardly any 'hot' water at a temperature that probably wouldn't be high enough for a hot bath and don't heat very warm either - and then compare against gas at 30% more per unit than we pay and boiler efficiency of 80%....

I think it's an extreme example of heat pump usage; very frugal users, a small house, a mild year.  Maybe the intention was to come out cheaper than gas.  It's a bit like these people who hyper-mile in their cars.  At least our heat pump guy isn't annoying the hell out of everyone else on his street.  It is interesting to see what can be done though.  

The homefarm example I quoted a few posts back is perhaps more realistic.