aircon?

200

Could a high efficiency aircon (room airconditioner) be cheaper to run than a
gas combi?

answers greatfully accepted

Cardew

You mean an Air Source Heat Pump(ASHP) presumably?

There are several threads running on this forum.

Obviously you have to take into account the price you get gas, the price of electricity and the efficiency of your boiler.

In general terms Electricity costs about 3 to 4 times more than gas, and the efficiency of a gas combi might reduce this down quite a bit.

An ASHP system with the latest equipment will achieve a COP between 3 and 5 in a normal winter(The COP indicates the amount of heat you get for 1 unit of electricity so a COP of 4 means you get 4 times the heat from 1 kWh of electricity)

Don't forget that an ASHP does not produce Hot Water.

So all in all I suspect that running cost are pretty even.

paceinternet

Just to be clear, an "airconditioning" ASHP, which is an air to air system, will not produce hot water, so an electrical immersion heater may be necessary.

An air to water ASHP, which has a separate or built in heat exchanger, will produce hot water at around 50 deg C (higher with some systems), and will often have a control system which switches an immersion type heater on to boost the temperature at least once a week to avoid biological issues with the hot water.

stevehead

deffinetly

Having both gas heating and aircon I'm in a good position to vote on this and the answer is a resounding YES IT IS! I've had my aircon long enough now to be able to do a month on month comparison and the savings are in-yer-face obvious.
Last winter I was paying £90 pcm for gas (gsh/water/cooking)
This was a mild winter, and I have since added a loft to heat.
So factoring price rises but not the cold, I should be paying £135 pcm this winter for gas.
In March I installed a couple of Mitsubishi aircon units, and these are the only form of heating I now use. The gsh is still there as a backup.
This December I'm using a tad under £1 a day to run the aircon, and £3 a week for gas (water & cooking) So thats about £43 for heat/hot water/cooking this December instead of £135 or more I would have paid for gas alone.

The poll asks to compare combi to aircon. This means that you have access to mains gas and don't have to throw away gas water heating in favour of an electric immersion heater. As I stated above, I now only spend £3 a week on gas for cooking & all hot water - a fine use for an old boiler.
And I like it warm - teeshirt warm - all for a quid a day. Simply unbeatable.

Cardew

stevehead wrote: »

Having both gas heating and aircon I'm in a good position to vote on this and the answer is a resounding YES IT IS! I've had my aircon long enough now to be able to do a month on month comparison and the savings are in-yer-face obvious.
Last winter I was paying £90 pcm for gas (gsh/water/cooking)
This was a mild winter, and I have since added a loft to heat.
So factoring price rises but not the cold, I should be paying £135 pcm this winter for gas.
In March I installed a couple of Mitsubishi aircon units, and these are the only form of heating I now use. The gsh is still there as a backup.
This December I'm using a tad under £1 a day to run the aircon, and £3 a week for gas (water & cooking) So thats about £43 for heat/hot water/cooking this December instead of £135 or more I would have paid for gas alone.

The poll asks to compare combi to aircon. This means that you have access to mains gas and don't have to throw away gas water heating in favour of an electric immersion heater. As I stated above, I now only spend £3 a week on gas for cooking & all hot water - a fine use for an old boiler.
And I like it warm - teeshirt warm - all for a quid a day. Simply unbeatable.

Stevehead,
I have followed your posts on this subject and your enthusiasm for ASHP is understandable and I have little doubt that this system if the future of electrical heating in UK.

I would also add that I have the system installed in a large property I own abroad, so I speak with some knowledge.

However your figures in the post above simply do not add up.

According to your post, gas would cost you approx £120 a month for heating alone(£135 less £3 a week for cooking and Hot water)

You claim to produce that same amount of heat for £30 a month with your ASHP and that is simply not possible.

Gas is about one third if the price of electricity. If you have a really old inefficient boiler that might reduce the effective cost of gas to a half that of electricity.

So that means that your COP would have to be an average of approx 8 and that is just impossible.

I suspect that in the real world there is little difference between running costs of Gas CH and a good ASHP system.

stevehead

deffinetly

Cardew wrote: »

You claim to produce that same amount of heat for £30 a month with your ASHP and that is simply not possible.

Gas is about one third if the price of electricity. If you have a really old inefficient boiler that might reduce the effective cost of gas to a half that of electricity.

So that means that your COP would have to be an average of approx 8 and that is just impossible.

I agree I don't have a COP8 system, but the numbers are correct. You have to see from my original gas usage that old boilers can be very inefficient. This arises not only from the boiler itself, but also from the crude control system.

But what I ought to have mentioned is the insulation measures I also undertook over the same period. (Loft/Cavity/Draught). I have mentioned these in previous posts Cadrew and their importance should not have been understated.
So, I don't claim to produce the same amount of heat, but do claim to keep my house as warm for a lot less money.

A response would be that if I'd done the insulation and bought a new combi my heating costs would have been about the same. Well that is something that can never be truly answered; but imeasure / friends & neighbours usage tells me that my costs are waaaaay down. So I get COP5 out of the aircon, and another 3 from the insulation :-)

thechippy

deffinetly

If you ignore hot water and make the comparison only with heating, ashp's are generally cheaper to run.

One example is how quickly they bring the room up to temp. If your house is cold and you turn on the gch, as it heats by convection, it takes a while for the room to heat up (boiler running flat out)

The ashp's deliver instant powerful forced air heating, so the room warms very quickly. Not only that, as the room setpoint is reached, the units begin to unload and use less current. They then attempt to "tick over" on a low load to maintain the setpoint.

They are economical to run due to the high c.o.p and the very clever electronics.
As some of you may have realised, I am in this trade, but nonetheless, due to the nature of this site, were they less economical than some would have you believe, I would be honest and say so. They are also getting cheaper by the minute. Now is the time to have them installed, as remember, the suppliers are normally air conditioning manufacturers and in the winter, thier sales fall through the floor, so they will give much better discounts to the trade. They hike prices in the summer, as the units become in demand!

Cardew

thechippy wrote: »

As some of you may have realised, I am in this trade, but nonetheless, due to the nature of this site, were they less economical than some would have you believe, I would be honest and say so. They are also getting cheaper by the minute. Now is the time to have them installed, as remember, the suppliers are normally air conditioning manufacturers and in the winter, thier sales fall through the floor, so they will give much better discounts to the trade. They hike prices in the summer, as the units become in demand!

I assume that remark in bold is directed at myself as I had the temerity to challenge Stevehead's figures.

As I have said before I have had such a ASHP system in a property abroad for a while. I am a fan of the concept and if you look through posts I have made over the past few years I have been a constant advocate of heat pumps.

I believe they are the future for heating - particularly for properties without gas - so I don't need to be convinced.

However much as people with vested interests(like yourself) wish to heavily promote them, it is important to get the costs into perspective. Stevehead's figures in his original(unqualified) post of £30 a month for heating which would cost £120 with gas is just fantasy.

Everyone seems to bandy about a COP of 5 as if it is obtainable all the time - well it ain't. The Energy Saving Trust talks of a COP of 3.

Mitsubishi have an excellent website and this is an extract from a report(dated Oct 2008)

Heat pumps are movers of heat energy – they use a refrigerant circuit to upgrade naturally occurring low temperature heat into useful high temperature heat to reduce primary fuel consumption,” commented John Kellett, General Manager of Mitsubishi Electric’s Heating Department. “With a conventional gas boiler, one kilowatt of energy delivers less than one kilowatt of heat to a building. With Ecodan, one kilowatt of energy delivers a heat output in excess of three kilowatts – that’s a 300 per cent increase in energy efficiency – and that is set to grow as the technology develops.

I also question why the hurry if the efficiency will increase as "technology develops"

Heat Pumps will certaintly figure prominently in highly insulated new build properties as they are far better incorporated into the design of the building than retrofit. Particularly using air to water with underfloor heating.

Good they are - but let us not go overboard!!

P.S.
For a more balanced view of ASHPs I suggest those interested read this thead:
http://forums.moneysavingexpert.com/showthread.html?t=702257

The OP has had his system a year now and hopefully he will post some objective figures soon.

P.P.S.
I particularly liked the comment in post#7

stevehead

deffinetly

OK look yes, I am a cheerleader for this ashp stuff but that's for no other reason than I am genuinly impressed with their performance. The presence of the likes of Cadrew in this thread adds a credible balance to my posts' claims. What I can bring to this discussion are accurate kwh energy usage figures for my ashp heating. In 2 days time, I will have the total kwh electricity for December's heating.

Can I refer y'all to a formula to answer the OP's question?
http://www.bsee.co.uk/news/fullstory.php/aid/5038/Air_source_heat_pumps_-_how_do_they_compare_to_condensing_boilers_.html

Here we can see we get a break-even COP of 2.3 so the answer is YES.
However I would argue that this is slewed in favour of gas on the grounds that
gas is given a 90% efficiency constant in the formula - but it won't always perform that well.

stevehead

deffinetly

Cardew wrote: »

Stevehead's figures in his original(unqualified) post of £30 a month for heating which would cost £120 with gas is just fantasy.

I see the problem here.... I can only quote my energy monitor figures and utility bills, but can't qualify them. This will inevitably lead to an impasse.

Cardew

stevehead wrote: »

OK look yes, I am a cheerleader for this ashp stuff but that's for no other reason than I am genuinly impressed with their performance. The presence of the likes of Cadrew in this thread adds a credible balance to my posts' claims. What I can bring to this discussion are accurate kwh energy usage figures for my ashp heating. In 2 days time, I will have the total kwh electricity for December's heating.

Can I refer y'all to a formula to answer the OP's question?
http://www.bsee.co.uk/news/fullstory.php/aid/5038/Air_source_heat_pumps_-_how_do_they_compare_to_condensing_boilers_.html

Here we can see we get a break-even COP of 2.3 so the answer is YES.
However I would argue that this is slewed in favour of gas on the grounds that
gas is given a 90% efficiency constant in the formula - but it won't always perform that well.

One could also argue that the electricity price used is a little on the low side and gas price a little on the high side.(bear in mind the link is to a firm that sells ASHP systems!!)

I certainly don't want to be cast in the role of an anti-heat-pump campaigner - because I am a fan. I just want to get costs into perspective and have a balanced debate - and all the issues brought into the open.