UPDATED: Air Source Heat Pumps/Air Con - Full Info & Guide, is it cheaper to run than mains gas?

Cardew

For new readers, it should be made clear that Richard's system is an 'air to air' heat pump system i.e. blows warm air(or cold in summer!) and not the more popular 'air to water' ASHP(Mitsubishi ecodan etc) that is used in conjunction with underfloor heating and/or radiators.

With 'air to air' you need another method to heat domestic hot water.

richardc1983

Cardew wrote: »

For new readers, it should be made clear that Richard's system is an 'air to air' heat pump system i.e. blows warm air(or cold in summer!) and not the more popular 'air to water' ASHP(Mitsubishi ecodan etc) that is used in conjunction with underfloor heating and/or radiators.

With 'air to air' you need another method to heat domestic hot water.

What's your opinion Cardew? Would you like me to post over on your should do better must do better post for debate?

Need someone to work out with me which is better. I prefer the heat from the air con as rooms warm up quicker.

Cardew

In my opinion there are too many variables to make comparisons valid. However given you have to use gas for Hot Water, and to 'assist' the Heat pump, it seems that gas is indeed cheaper; confirming the recommendations of EST etc.

Also using comparisons with 'Air to Air' is not much value for those with Air to Water, and in any case to fit a full ASHP system with a fuctioning gas CH system is unusual.

You could of course have the Gas CH water temp turned up to 80C initially to heat up rooms quickly, and then turn the water temp down.

TiredGeek

Or you could have the GSH set a touch lower and use the ASHP to get the room up to temp quickly and let the GSH maintain the temp thereafter....
Don't know if that would work out cheaper overall though

Silent_Dancer

bernithebiker wrote: »

Interesting stuff, nice to have some cold, hard figures.

I always had in my mind that ASHP would be hard pushed to beat mains gas, as this is the best value fossil fuel in the UK by far. Interesting though that they're more or less in the same ballpark.

Clearly, had you been using LPG or oil, you would definitely be quids in with the ASHP.

We use small 5kW ASHP units in our holiday houses to help reduce the LPG or all electric heating bills, and it works!

Whilst it easy to beat LPG, ASHP installations often to fail beat oil. Even when people claim to have beaten oil the savings are down to improved insulation and heat emitters not the ASHP. Those savings would also apply to a condensing oil boiler.

Silent_Dancer

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Silent_Dancer

Cardew wrote: »

In my opinion there are too many variables to make comparisons valid. However given you have to use gas for Hot Water, and to 'assist' the Heat pump, it seems that gas is indeed cheaper; confirming the recommendations of EST etc.

Also using comparisons with 'Air to Air' is not much value for those with Air to Water, and in any case to fit a full ASHP system with a fuctioning gas CH system is unusual.

You could of course have the Gas CH water temp turned up to 80C initially to heat up rooms quickly, and then turn the water temp down.

I'd second what Cardew is saying.

By the way the split system that you have is complex and not the most efficient. It will run to the output independent of whether the room is in use.

Far better to install separate units for each room. As you say it heats up and cools pretty quickly and this way you'll reduce the cost of bills coupled with a simpler install.

richardc1983

Silent_Dancer wrote: »

By the way the split system that you have is complex and not the most efficient. It will run to the output independent of whether the room is in use.

Thank you for the reply. Couple of points though. The outdoor unit was brought from my previous address and as there is nothing wrong with it would have been a waste of money to have bought new outdoor units when you want heating/cooling in all rooms. Also there isnt the space outside to install 4 outdoor units so one big one is the best alternative.

Having the one big outdoor unit is more economical having one big compressor running than having 4 individual ones running... However I do agree that my unit is probably not the most efficient out there any more as it is probably 5 years old now but comparing it to the new LG models it isnt much different on power output and inputs etc.

What do you mean it will run to the output independant of whether the rooms is in use or not? It has an inverter compressor so adjusts it output to the room conditions the only thing it cant do is if only one room is calling for heating it cannot ramp down any further than approx 1.1kw input whereas with all 4 indoors running and it maintaining set point that 1.1kw input will be shared across all 4 indoors. Max input approx 3kw.

Ecodave

I saw an interesting presentation at Ecobuild yesterday regarding the development of heat driven air-source heat pumps. Apparently, the COP is likely to be about 1.3, so will be about a third cheaper to run than modern condensing gas boilers. The unit they are built into will sit in the exact position of a present boiler, with an external unit that will be the same as on conventional heat-pump systems.

Has anybody heard of these before?

grahamc2003

Ecodave wrote: »

I saw an interesting presentation at Ecobuild yesterday regarding the development of heat driven air-source heat pumps. Apparently, the COP is likely to be about 1.3, so will be about a third cheaper to run than modern condensing gas boilers. The unit they are built into will sit in the exact position of a present boiler, with an external unit that will be the same as on conventional heat-pump systems.

Has anybody heard of these before?

It's not clear what type of heatpump you are describing, and neither its function. Is it air to air, air to water, or possibly an exhaust recovery heat pump? Does it heat a tank of water, or radiators directly, or blow out hot air?

If the cop is 1.3, then it will still cost about 2.5 times the cost of heating by gas, so I think that number is wrong. To beat gas and assuming gas is 1/3rd the price of electricty, you need a (average) cop greater than 3. The cop varies all the time, especially with outside temperature, which is why it's difficult to guage whether a heatpump would be cheaper than gas, but generally, I think the usual advice is only to consider a heatpump when you are off the gas grid. Because of the subsidies heatpumps usually attract, the hardware costs are inflated quite a bit, as are the installation costs by mcs approved if you go for some sort of subsidy.