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

zeupater

matelodave wrote: »

Our 11kw Daikin has been heating the hot water all summer, using about 2.5-3kw a day, the heating was turned on last week but as the weather has now warmed up it's not doing anything or costing any more. Our detached bungalow is 1350 sq.m and we haven't used any other form of heating over the past three winters as the system keeps the bungalow warm enough even for my wife.

As discussed above, the heating is slow to respond to rapid temperature changes but just gently ticks over keeping the u'f heating warm. We are at home all day and each room is thermostatically controlled (programmable stats) by regulating the flow in each room. The heatpump flow temperature is weather compensated - ie it gets warmer as it gets colder outside - the max temp is set to 42 degrees when it goes down to -5 outside. The min is 25 degrees when its +15 outside. I can tweak it a bit if it gets a bit colder (we had a couple of days last year when it went down to -14 outside) - the unit has an inbuilt 6kw back-up heater for the really cold days.

Our total energy usage last year was about 8800kw which is up a bit on my 8500kw estimate due to the long and cold winter and I'd guess that the heating/hotwater accounts for about 4500-5000kw of that.

We don't shut it down overnight but the stats "set back" by about 3 degrees so the place doesn't get cold.

Hi

A couple of points which could be useful ....

1350sqm is about 1/3 acre, or roughly the equivalent floorspace of 10 modern 4 bedroom houses ... are you sure that you don't mean 1350sqft ??

If you've been using 2.5kWh to 3kWh of energy per day to heat the water during the summer, either the efficiency (COP) of the system is pretty poor (what temperature are you heating the water to ?), there is a parasitic load when not being used, or you have an unusually high hot water consumption at somewhere close to (/well over) 2500kWh.t(2.75kWhx365daysx2.5SCOP) on a pretty average COP .... any idea which ??

Depending on your own particular energy usage & pattern, using industry standard figures and a little experience in energy saving gained over the years, unless your usage is atypical it's likely that the heating could be consuming more than 5000 of the 8800kWh you mention ... this is simply based on the average dual fuel electricity demand for a household being ~3300kWh - that would suggest that if you are not particularly energy aware (ie average) it's more likely that the heat provision would be ~5500kWh (8800-3300), and if you are energy aware and have taken a number of the usual electricity saving measures (low energy bulbs etc) the heat provision would probably be closer to consuming 6000kWh (8800-2800) .... that would suggest a range of 5500-6000kWh as opposed to 4500-5000kWh ... just a guess, but have a think ...

HTH
Z

matelodave

You are right, my bungalow is 1350sq.ft

My estimate of the H/P consumption is actually measured using a clamp on wireless energy monitor (courtesy of BG several years ago) and it does over read compared to the electricity meter, probably as the H/P load has a poor power factor compared to one that is purely resistive.

Regarding my estimate of energy, we are all electric and try to be relatively energy efficient but do leave stuff like routers, sky box, power-line adapters and a couple of surveillance cameras as well as a fridge and freezer on all the time. They use just under 4kw a day (as that's what gets used whilst we are on holiday with everything else properly turned off or unplugged). Our average usage in the summer months (ie no space heating but heating hot water) is about 9.5kw a day which includes a couple of computers on all day, washing machine and dishwasher average 3 loads each per week, cooking, lighting, vacuuming and even mowing the lawn = approx 3470kw, add to that extra lighting and significant use of the tumble dryer when the weather is inclement then I reckon we aren't far off 3750-4000kw for our normal non heating consumption.

Even if it isn't as efficient as it might be I still reckon that a total electrical usage of under 9000kw a year isn't bad - we got away with 7955kw in 2011/12 so the longer colder winter of 2012/13 did increase our consumption by 9%. My target is to try and get it back down to about 8000 this year although it's not easy to persuade my wife to turn stuff off when it's not in use.

We only heat the hot water to 45 degrees but I'd suggest that the heatpump isn't all that efficient when its just heating the hot water as the tank coil probably can't transfer the heat fast enough although it is a Daikin 200l tank.

One aspect with our heatpump which doesn't seem to get mentioned is that the there is a sump heater which keeps the refrigerant in a gaseous state to prevent the compressor from trying to pump liquid refrigerant - I'm sure that most units do the same but it's something else that consumes energy as well as the water circulation pump. I'm not sure that these additional loads are included in the pump COP specs - I noted that the latest EST survey did try to take pump loads etc in their calculations

dricer

I have been looking into air source heat pumps for about 2 months now and found this:

http://www.reinagrouptools.co.uk/hp.aspx

I note that they don't ask about heating flow temperature. Without knowing the temperature you won't know the SPF and the renewable portion so in theory can't work out the RHI income so I am guessing they are making some assumptions.

erach08

I have a Victorian 3 bedroom house, gas centrally heated, with 3 kw solar panels generating electricity which work well.
The Energy Saving Trust (government funded) contacted me to say I could save a lot on my gas bill by changing to an air to air heat pump system (I am over 65)
The salesman for the installer called to-day and recommended a 3 unit hot air system, two downstairs and one up, which he assured me would maintain the whole house at a desired temperature in the winter and cut my annual £1200 gas bill by 90%.
Reading as much as I can find on the Internet I can see no evidence that the bill would be reduced that much, and I would be paying additional electricity costs overnight.
Any advice please?

richardc1983

If you have gas it's still cheaper to heat your house with this if you have that option as our electricity prices here are a rip off. Speaking from experience here as I have both and use the air con in summer.

Is it a modern boiler?

Cardew

erach08 wrote: »

I have a Victorian 3 bedroom house, gas centrally heated, with 3 kw solar panels generating electricity which work well.
The Energy Saving Trust (government funded) contacted me to say I could save a lot on my gas bill by changing to an air to air heat pump system (I am over 65)
The salesman for the installer called to-day and recommended a 3 unit hot air system, two downstairs and one up, which he assured me would maintain the whole house at a desired temperature in the winter and cut my annual £1200 gas bill by 90%.
Reading as much as I can find on the Internet I can see no evidence that the bill would be reduced that much, and I would be paying additional electricity costs overnight.
Any advice please?

Are you sure the Energy Saving Trust contacted you? I would wager they didn't; so I suggest you ring the EST(on a number you can find on-line) and ask them.

I believe there has been no change to the EST advice that if you have mains gas you should stick with that and not get a heat pump.

That especially applies to older houses without modern insulations measures.

As for reducing your bill by 90%, that is absolutely ludicrous - I doubt there will be any savings.

Also with an Air to Air ASHP you will still need to heat water by gas.

Get this firm to put the above claims in writing, including their connection to the EST. They won't of course!

Please post any correspondence here, as the EST representatives sometimes read.

Sounds like you are being conned.

Cardew

Further to the above, I have just looked up the latest EST information on Heat Pumps:

http://www.energysavingtrust.org.uk/Generating-energy/Choosing-a-renewable-technology/Air-source-heat-pumps

An air-to-air system produces warm air which is circulated by fans to
heat your home. They are unlikely to provide you with hot water as
well.
Is an air source heat pump
suitable for me?


To tell if an air source heat pump is right for you, there are a few key
questions to consider:

• Do you have somewhere to put it? You'll need a place outside your home where a unit can be fitted to a wall or placed on the ground. It will need plenty of space around it to get a good flow of air. A sunny wall is ideal.
• Is your home well insulated? Since air source heat pumps work best when producing heat at a lower temperature than traditional boilers, it's essential that your home is insulated and draught-proofed well for the heating system to be effective.
• What fuel will you be replacing? The system will pay for itself much more quickly if it's replacing an electricity or coal heating system. Heat pumps may not be the best option for homes using mains gas.

There are reports of firms purporting to be the EST, and as you can see above your property is not the EST's ideal candidate for a heat pump.

More information might expose these firms.

TiredGeek

TBH I'd be ringing Trading Standards about these people.

Cut the gas bill by 90% - well actually it would!

You'd be using the gas only to heat water and (probably) for cooking, that'd use a fraction of the gas central heating uses.
What they didn't mention is your electric bill will soar, more than covering any saving to your gas bill.
If you're on mains gas your bills will be cheaper overall than with ASHP. Simple facts.
I love my heat pumps, they're a fantastic alternative to oil or LPG, just so long as you know what you're getting yourself into

erach08

Thanks for all those very useful replies. I will show them to the surveyor who is coming on Monday morning.

lovesgshp

Stay with the mains gas, it is not worth changing. If you were on LPG then it may be worth it, but otherwise not for the capital investment involved.