Power consumption heat pump

Cardew

Reed_Richards said:

Cardew said:

Also people tend to ignore the fact that heat pumps must be kept running very long periods each day, even 24/7 when really cold outside, as the lower capacity output and low water temperature means it takes a long time to get the house back up to temperature if the house is allowed to cool down. 

This canard is so often repeated.  If you have underfloor heating it will take a long time to get the house back up to temperature, whatever the heat source.  It makes good economic sense to couple a heat pump with underfloor heating in a new build because the lower water temperature requirement of underfloor heating lets you run the heat pump particularly economically.  But a heat pump is not underfloor heating and underfloor heating is not a heat pump!  

You can, as I do, have a heat pump and radiators in which case it is principally the output capacity of the radiators that determines how long it takes the house to get back up to temperature.  The fact that the water circulating through those radiators is cooler than it would be with a gas or oil boiler is irrelevant, it's the balance between the heat output of the radiators at temperature and the heat loss from the house that determines how long it takes to warm up.  

It is often repeated because it is true - and not a canard.

I wonder why you introduce underfloor heating into the equation when it hadn't been mentioned.

Both paragraphs in your post are correct, but irrelevant to the point I was making.

I went away for two weeks in the winter and set gas boiler to frost stat. Boiler was switched on a couple of hours before we arrived back and with a 30+ kW boiler circulating water at 80C the house was warm on our arrival.

Heating in my house goes off around 10pm and on around 6:30am and house is at required temperature by 7am. I suspect the majority of gas/oil CH properties adopt a similar practice - albeit with timings of their choice.

Just to pre-empt the inevitable post about dampness if you leave a house cold. If you have a dampness problem you have a fault!

I have a detached annex( a converted stable) with gas CH. I leave it on frost stat all winter and have done for 30+ years and there is no dampness.

matelodave

I'm more than happy to save the planet if it saves me money as well or if it's even cost neutral but I'm less inclined to spend more on something that I cant see a tangible benefit just to satisfy the green lobby.

I do have a heatpump and I'm very happy with it but I'd still swap it for a mains gas boiler if we had the infrastructure to do so  where I live.

My next car for instance will be a diesel just like my present one, mainly because of the type of driving I do and the extra expense of an electric or hybrid car and installing a charging point. 

FreeBear

Reed_Richards said:  Seriously, most new builds are on small plots of land so a Ground Source Heat Pump would require one or more boreholes.  Apart from the additional drilling expense, is there room?  How close to the foundations of your house should you have a borehole?  How many boreholes can you have per unit area on a housing estate?        

Having looked at some of the recommendations from a few drilling companies. boreholes need to be 4m+ away from a building and 10m+ from another one. Depth required varies depending on how much heat is required. 300m of boreholes seems to be typical for a 12-14KW system. If the property is very well insulated, then the heat requirement is reduced as is the depth/number of boreholes.

Certainly makes sense to drill the boreholes before construction of the houses takes place. A large drill rig could probably do a 300m borehole in a day. To get a rig in after the property is built would be next to impossible for most modern housing estates..

Been looking at the feasibility of drilling for a GSHP here. Access is limited to 1.2m width and most rigs that would fit through the gap would only be able to drill to 30m max. Got space out back for multiple boreholes, but they need to be 100m+ to be effective.

Ectophile

Take dirty diesel for example , with all the recent yrs of bad press it's still outselling petrol by 2 to 1

Not any more, it isn't.  Sales of new diesel cars have collapsed in the last few years.  The best selling car in the UK in September was electric.

Effician

Ectophile said:

Take dirty diesel for example , with all the recent yrs of bad press it's still outselling petrol by 2 to 1

Not any more, it isn't.  Sales of new diesel cars have collapsed in the last few years.  The best selling car in the UK in September was electric.

Didn't say cars, just diesel.

QrizB

Cardew said:

I went away for two weeks in the winter and set gas boiler to frost stat. Boiler was switched on a couple of hours before we arrived back and with a 30+ kW boiler circulating water at 80C the house was warm on our arrival.

Heating in my house goes off around 10pm and on around 6:30am and house is at required temperature by 7am. I suspect the majority of gas/oil CH properties adopt a similar practice - albeit with timings of their choice.

Your 30kW gas boiler took 2 hours to warm your house, so your house needed 60kWh to warm it. If you had a 12kW heat pump you would have had to turn it on 5 hours befofe you arrived home to get the same effect.

In the morning, your boiler takes 30 minutes so your house needs not more than 15kWh to warm from overnight. With a 12kW heat pump you'd need to turn it on at 0545 not 0630.

None of this is rocket science.

Effician said:

Ectophile said:

Take dirty diesel for example , with all the recent yrs of bad press it's still outselling petrol by 2 to 1

Not any more, it isn't.  Sales of new diesel cars have collapsed in the last few years.  The best selling car in the UK in September was electric.

Didn't say cars, just diesel.

For cars and light vans, where alternatives to diesel exist, market share for diesel cars is collapsing (although, notably, there's no real upswing in petrol sales). For heavy vehicles, there's currently no alternative to diesel so it's not surprising that diesel still sells.

Total annual road fuel sales have fallen slightly since 2007 (even ignoring 2020, which was a special case).

Data here: https://www.racfoundation.org/data/volume-petrol-diesel-consumed-uk-over-time-by-year

ispookie666

Maybe the way forward is Air to Air heat pumps and solar tubes for hot water. At least you get cooling during summer!

Reed_Richards

QrizB said:

Your 30kW gas boiler took 2 hours to warm your house, so your house needed 60kWh to warm it. If you had a 12kW heat pump you would have had to turn it on 5 hours befofe you arrived home to get the same effect.

In the morning, your boiler takes 30 minutes so your house needs not more than 15kWh to warm from overnight. With a 12kW heat pump you'd need to turn it on at 0545 not 0630.

None of this is rocket science.

I agree, but don't forget about the radiators.

I have a 12 kW heat pump but 9.6 kW of radiator output at the specified operating temperature.  Before that I had an oil boiler with 12.7 kW of radiator output, assuming 75 C flow and 65 C return.  Even in a cold house the only way to boost the radiator output is to boost the central heating water temperature and previously I had no way of doing that except by removing the facia of my oil boiler (which was external to my house) and turning the temperature control up.  So even though the oil boiler had a 24 kW output capability I could not use all of it to heat my house quickly.

Gas boilers are smarter than heat pumps or oil boilers and a modern one can probably raise it's flow temperature beyond normal if there is a big demand ("load compensation", a feature of Opentherm).  This would raise the heat output capacity of your radiators beyond their rated values.  Even so, you might not be able to match the heat output capacity of a 30 kW boiler so if it took two hours to warm your house from cold, the likelihood is that the house needed less that 60 kWh to warm it.
         

shinytop

ispookie666 said:

Maybe the way forward is Air to Air heat pumps and solar tubes for hot water. At least you get cooling during summer!

That's exactly why A2A is not being funded (to date).  Just like heating your house to 25 degrees in the winter, cooling it in the summer in the UK is a waste of resources and not something, as a taxpayer, I want to subsidise.

Cardew

Reed_Richards said:

QrizB said:

Your 30kW gas boiler took 2 hours to warm your house, so your house needed 60kWh to warm it. If you had a 12kW heat pump you would have had to turn it on 5 hours befofe you arrived home to get the same effect.

In the morning, your boiler takes 30 minutes so your house needs not more than 15kWh to warm from overnight. With a 12kW heat pump you'd need to turn it on at 0545 not 0630.

None of this is rocket science.

I agree, but don't forget about the radiators.

I have a 12 kW heat pump but 9.6 kW of radiator output at the specified operating temperature. 
         

Agreed.

Also iirc you run your ASHP at considerably higher water temperatures  than the 'normal' 35-40C