Heat pumps - how to make the numbers work?

joefizz

Mickey666 said:

There is talk of new gas central heating boilers being banned.

Yes, Talk.

Anyone who honestly believes government will ban new gas boilers in the near future is living in cloud cuckoo land. Besides, the 'talk' is only about gas boilers in new-build houses so the 99% (or whatever the figure is) of existing gas CH systems in current homes will not be affected. 

Its only about gas only boilers as well. If anyone has any gas safe fitters in the family ask them about hydrogen being included in their recertification. Not 100% sure but know it has been included for a while now. Hydrogen mix first with little adapation to existing boilers and then possible full adaptation where possible (study out last week/month? saying little adaption required for the majority?)

Going back to the OP, my ashp hasnt really been on at all this 'summer'. Had to put the oil back on last night for hot water as the temperature dipped significantly and battery has been flat for a day or two now. I did use it as air con last week though ;-)
Ive been working installing a second oil tank over the last month and just drained the old one into the new one and will make a new base for the old one and refill it if it ever stops raining. Im hoping that pushes me out long enough for something viable for our particular rainy season which lasts for 50 weeks of the year!
The ASHP is just not an option here in winter months, they are great in places where the temperature stays in the optimum operating range or you buy one designed for colder climates (and a lot more expensive).
On the other side, the increased insulation has worked wonders with little or no heating required since the US started flying again (I digress ;-)) The positive ventilation in the loft (bungalow) has been enough to transfer the heat from the loft at night into the house with internal temperature not dropping below roughly 20C for a couple of months now.

Cardew

Pile_o_stone said:

Cardew said:

 For occupants out of the house during the day for work/school you still need to keep a heat pump running to avoid the house cooling down and taking hours to bring back to the required temperature; and thus heating an empty property. At night you have a similar problem.

With gas/oil CH with Central heating water at a high temperature you can set the heating to come on, say, 30 minutes before you get up, or return to the property, and have the required room temperature.

Is that not more of a comparison of underfloor heating vs radiators, rather than heat pumps vs boiler?
We have UFH in the annex that my parents live in and the gas boiler goes on and off at all hours as it maintains the temperature of the limecrete slab the UFH pipes sit in. It's a condensing boiler but with such short cycles, I doubt that there is much condensing going on.

I take your point, but gas heated water underfloor heating(UFH) is typically at 27C to 31C (according to WHICH) and as you point out the boiler is continually cutting on and off to maintain that room temperature; and it will do this during the periods when the property is unoccupied or at night*. If you turned the gas UFH off it will still take a long time to heat up the property.  I suppose you could set it at a much higher water temperature for, say, 30 minutes before you returned to the house.

However the OP’s post is about Heat Pumps which typically run at 30C to 35C for UFH and the larger radiators that are required. Many posters on here state that their heat pump is run 24/7 because of the inability to quickly warm up the property if the room temperature has been allowed to fall. So you are still heating an un-occupied property.

·    *     I am aware you can set back a degree or two.

michaels

We occupy 24/7 so the lack of boost heat is not such an issue but I still think we need a flow temperature in the rads of 50 degrees plus when the temperature outside is below zero.  Our current boiler is weather comp and modulates from 19kw right down to 4kw with the intention that it will run pretty much non-stop in winter so the problem is back to electricity costing so much more per kwh than gas so any realistic COP is not enough to make up the difference.

Are we forecasting that the relative price difference might come down when oil and thus gas prices return to more normal levels or do electricity prices move with gas prices anyway?

ASavvyBuyer

Found this “article” from someone that replaced their gas boiler with a heat pump.

https://foresightdk.com/why-i-replaced-my-new-gas-boiler-with-a-heat-pump/

"Assuming a 20-year lifetime for the heat pump, the embodied carbon emissions a year are just 78 kg CO2e a year or 4% of the operational carbon emissions from fuel use."

Also, Interesting points concerning the carbon savings as the grid becomes greener.

michaels

Still trying to make the maths work I looked at historic gas and electricity prices and it is true that the multiple is currently at a historic high.  Unfortunately that is mostly due to all the regulatory costs being loaded onto electricity and the glut in gas supply with all the LNG coming onstream and the US fracking by product, none of which looks like ending anytime soon.

Does anyone have any knowledge of realistic seasonal coefficients that people with ASHP and GSHP are actually achieving?

Martyn1981

I thought you were looking for the green option? Anyways, I wouldn't bet too much on the US fracking industry, they are not doing too well. Here's a recent Bloomberg report on them:

How Fracking Became America's Money Pit

For most any nation, let alone a superpower, energy independence is considered the geopolitical holy grail. So when fracking lured in American investors, everyone had high hopes the country would finally break free of OPEC. But oil is a complex game, and 2020 saw sharp declines in demand caused by the cartel’s maneuvering, shale oil’s oversupply, and now the devastating effects of the coronavirus. What’s worse, the startup mentality of the U.S. fracking industry promised investors mythical growth and nonexistent returns. In the end, it burned a $340 billion hole in Wall Street’s pocket.

Cardew

michaels said:

Does anyone have any knowledge of realistic seasonal coefficients that people with ASHP and GSHP are actually achieving?

The Energy Saving Trust(EST)  sponsored a 12 month trial in 2010 of both ASHP and GSHP and the results were dreadful. They ran a further trial a couple of years later and the results although better were well short of the claims made by the manufacturers.

This thread started the discussion and there are further threads on the later trial.

https://forums.moneysavingexpert.com/discussion/2968958/ashp-should-do-better-must-do-better/p1

Unfortunately the 10 year old links to the lengthy EST reports now do not work - although they may be available from the EST website if you are interested.

It would appear that even with manufacturers getting involved, you will be doing very well on a retrofit installation if you achieve a SYSTEM COP of 3.0, several installations had a COP below 2.0.

It is extremely difficult to measure the SYSTEM COP of an installation, and most reports are from owners who quote their overall electrical consumption before and after the installation. It is pertinent that owners who have paid for their installation are not as critical as those private/social/council tenants - many of which are scathing about running costs and effectiveness.

michaels

Cardew said:

michaels said:

Does anyone have any knowledge of realistic seasonal coefficients that people with ASHP and GSHP are actually achieving?

The Energy Saving Trust(EST)  sponsored a 12 month trial in 2010 of both ASHP and GSHP and the results were dreadful. They ran a further trial a couple of years later and the results although better were well short of the claims made by the manufacturers.

This thread started the discussion and there are further threads on the later trial.

https://forums.moneysavingexpert.com/discussion/2968958/ashp-should-do-better-must-do-better/p1

Unfortunately the 10 year old links to the lengthy EST reports now do not work - although they may be available from the EST website if you are interested.

It would appear that even with manufacturers getting involved, you will be doing very well on a retrofit installation if you achieve a SYSTEM COP of 3.0, several installations had a COP below 2.0.

It is extremely difficult to measure the SYSTEM COP of an installation, and most reports are from owners who quote their overall electrical consumption before and after the installation. It is pertinent that owners who have paid for their installation are not as critical as those private/social/council tenants - many of which are scathing about running costs and effectiveness.

Thanks.  That suggests the ashp 2.8 / gshp 3.5 reported in the earlier in this thread above which sound on the low side according to suppliers are actually on the high side

I can see how hard it is to actually know what the SCOP/SPF is as the 'counterfactual' depends on the specific annual temperature variation not the historic average usage.

Reed_Richards

I am seriously considering replacing my oil boiler with an Air to Water heat pump.  Does anyone actually have one of these with good results?  I wonder if maximum outputs have increased since the EST trials?

Cardew

Reed_Richards said:

I am seriously considering replacing my oil boiler with an Air to Water heat pump.  Does anyone actually have one of these with good results?  I wonder if maximum outputs have increased since the EST trials?

The difficulty is that those with an ASHP cannot calculate their System COP themselves. It would be possible to measure the input to the Heat Pump, immersion heater and defrosting. However measuring the annual heat output of the pump is a different matter.

In that respect it is no different to oil/gas/LPG. I know how much gas I use in kWh but don't know how much heat my boiler delivers.

There are also many other factors that determine the System COP and a specific make/model of an ASHP(say an Ecodan) can produce widely different results in different properties.

P.S. with the current low price of oil, the same factors as discussed above of comparison with gas prices apply.