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

John_Pierpoint

Today I had to do some work on my electrics.
[Over the Xmas break a time clock had developed a lose connection and we only noticed the resulting arcing damage, when we smelled smoke in the cupboard]

So the repair involved a fair amount of switching the house electrics on and off; at the end of the day I noticed a similar number of short duration failures in the trace of the output from the inverter "Aurora" inverter (The voltage was steady and under 250v on the mains today).

Without those interruptions, I might have generated one whole kWh today

hebridean

I've now returned home and had a good look at my set up. The upstairs radiators pipework is coming of the end of the UFH manifold between the flow and return bars. There's a Grundfos pump there with a Reliance thermomix below it which has the radiators flow and return pipes coming from it.
Yesterday i set the system to run allday and though the house is nice and toasty i suspect that a couple of the UFH room thermostats are faulty in that they are not cutting off at 20c but had the kitchen at 24c so i've turned it down to 15c to see what happens. I'm not to bothered about this as the sparky is coming to fit new Danfoss set back thermostats on Monday which i hope will be accurate. I've also set all the upstairs radiators to low and the rooms are hovering around 18-19c which is fine.
So i suppose it seems to be running ok, but then what do i know and any tips would be appreciated.

hebridean

As an update to my previous post, it seems that the pump i mentioned was for the UFH and the sparky came round on Friday fitting the setback thermostats. These are working well and i also noticed that the upstairs radiators though coming on are only doing so haphazardly. On further investigating it seems that they will only come on when the UFH pump is working so there is no heat upstairs during the night when the UFH thermostats are setback. So it would seem that i need to get a seperate pump and controller for upstairs independent of the UFH. Last night i didn't setback the hall UFH leaving the heat to come up the stairs leaving the bedroom doors open which helped a bit.

John_Pierpoint

As you can buy less than half price electricity between 24:00 & 07:00, does it not make sense to charge up the UFH floor slab during this time?

zeupater

John_Pierpoint wrote: »

As you can buy less than half price electricity between 24:00 & 07:00, does it not make sense to charge up the UFH floor slab during this time?

Hi

I thought that too when I read the post earlier, especially so considering the opening post stated that was normal practice anyway .....

hebridean wrote: »

... We are on economy 10 and have been running the heating and heating the water during the periods that the cheap rate comes on ...

When it's something like -4C at night and -1C during the day there's likely very little between the daytime/nighttime COP so in my opinion it's a no brainer .... run it at night for around a third the cost and have enough internal thermal mass to maintain temperature throughout the day, depending on the new-build house design of course, but I would expect a property designed with UFH to have a relatively high thermal mass ...

Anyway ... on the insulation/thermal mass front, we're currently still providing the majority of heating with the log burner, this being fuelled for around 8Hrs/day, and topping up with around 1hour (~30kWh.t) of GCH every second day .... property thermal performance getting better each year ... :cool:

HTH
Z

John_Pierpoint

zeupater wrote: »

Anyway ... on the insulation/thermal mass front, we're currently still providing the majority of heating with the log burner, this being fuelled for around 8Hrs/day, and topping up with around 1hour (~30kWh.t) of GCH every second day .... property thermal performance getting better each year ... :cool:

HTH
Z

Does this (~30kWh.t) mean that your heat pump is creating about 30kWh output of heat when running over night (ie 30 "units" in electrical supplier speak, from the consumption of 10 units of electricity) ?

zeupater

John_Pierpoint wrote: »

Does this (~30kWh.t) mean that your heat pump is creating about 30kWh output of heat when running over night (ie 30 "units" in electrical supplier speak, from the consumption of 10 units of electricity) ?

Hi John

..... no, it's Gas Central Heating, the ~30kWh.t relating to the thermal element (.t), not the energy input, so that'd would be ~32/34kWh of gas consumption over two days .... the note was simply to convey that in a well insulated property with adequate thermal mass there's very little need for continuous heating.

We used the heating for ~1Hr yesterday and therefore today's internal temperature startpoint was ~1C higher than yesterday's when I was lighting the fire (~13:30), so no need for anything other than the logburner today ....

HTH
Z

richardc1983

I had my multi split LG inverter air con system installed in my new house in May last year. House is a 1930's end of terrace. Consists of a 9.38kw (FM25AH UE1) heating outdoor unit and 2 x 3.9kw (LIBERO range) (lounge & kitchen) & 2 x 2.1kw (LIBERO rang) (bedrooms) indoor wall mount units purposely oversized so the units can be run constantly in low fan speed. The system is used for cooling in the summer and heating in the winter.

The house also has a GCH system fitted radiators and combi boiler etc. Boiler approx 6 years old manufactured by Glow Worm & is 30kw in capacity.

Having done some tests to see which is cheaper this winter by trying to compare similar temperature weeks one week running GCH then one week running the air con system it appears that it is cheaper to run the GCH. The house gets upto temp quicker by using the air con system but as its warm air you dont get that nice radiant affect you get with radiators which seem to provide a more comfortable even heat and being under the windows they keep the room warmer and at a more consistant temp.

I can keep the flow temp of the rads down on the gas boiler to about 50C and the house maintains about 21C downstairs (TRVS open fully) and about 19C upstairs with the TRVs set lower as dont like it hot in bedrooms. With the air con system we have to have a set point of 22/23C in the downstairs rooms to compensate for the cooler areas near windows where the radiators normally stop any cool draughts from the windows. Bedrooms still set at 19C on the controllers the same as with the GCH. I found that with higher flow temps on the boiler to get the rooms upto temp quicker rooms end up feel stuffy even though TRVs are used reaction times are too slow so the rooms overheat when the TRV shuts off. So a lower flow temp means the boiler is just ticking over and the rooms dont tend to overheat but are slower to warm up but sometimes I turn the boiler up to get the house upto temp then reduce it right down. The air con doesnt even struggle on the colder days. Maybe I bump the fan speeds up a bit or start the upstairs units later once downstairs is close to set temp. When only one indoor unit is running there is a limit to what the outdoor unit can ramp down to so its usually best to have all 4 indoors running for max efficiency as the outdoor unit will still ramp down to the lowest setting and room temps are maintained. A multi unit is designed to run multiple units at the same time and not just one unit otherwise it becomes inefficient.

Cost of using air con per week during period (05th Nov - 24th Dec) ranges between £19-£26 (total elec usage for the house). Cost of using GCH per week during period (31st Dec - 4th Feb) is between £12-£19. Even when just using the air con system at temps below 5C outside I was still finding that I had to use the GCH radiator in the bathroom and the bottom of the stairs otherwise those areas were cold. This was costing £6-£8 per week on gas including the hot water rather than just the £4 for hot water. Over the summer gas usage is just for hot water and is approx £2-£3 per week, so about £2-£4 gets added on top if using the boiler to heat two radiators when using the air con system bringing the total to between £6-£8 for the week on gas alone.

On the weeks where GCH only was used my total electric consumption for the week cost between £10 & £13 as we have a tumble dryer also so some weeks this was used more. Its confused me with all the figures so maybe you can make more sense of the details I have profided. I have also attached my readings for the weeks so you can see roughly what I am using on the weeks without air con and with weeks of just using 2 radiators for the GCH. Above in bold are the dates I used air con and GCH so you can see from the attachments costs for those weeks.

Electric


Gas


There is much debate on if Air Con is cheaper to use for heating than GCH. Looking forward to your views. What do you think based on the data I have provided taking into account usage of electricity without the air con and usage of electric with air con etc.

Kind Regards
Richard.

bernithebiker

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!

richardc1983

I'm struggling with the figures now but do you think the gas is cheaper than the electric. I am being thick now lol.