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

nande2000

Hi, does anyone know if there is any detriment to powering an ASHP down over summer ?
We haven't used ours in a month now (Immersun providing all our hot water), but the ASHP (an Ecodan 8.5kw) is using 0.5 kw/day to do nothing. I can power it down, but will that cause any problems ?

albyota

Hi, I have the same unit, and I prefer to leave it on as it does my hot water cylinder a couple of times a day whilst taking advantage of any PV being generated. The Ecodan has a crankcase heater to stop the refrigerant and oil from separating, the heater only uses a small amount of power and I would sooner the small cost of keeping it on as opposed to having to replace the compressor at about £900.
Hope this helps

John_Pierpoint

All I can add is that the air conditioning unit in cars has something built in to turn it on from time to time, independent of the needs of the vehicle and its driver. So it is not a good idea to leave the kit turned off ?

nande2000

Sounds like good enough reason to leave it on. In fairness my pv panels are covering the load in daylight hrs so it would probably only save about £5 until the heating season starts again.

Well impressed with the immersun though. Works well with my pseudo thermal store (only connected to DHW circuit).

Alfiethefish

I am sure there is no simple answer to this question but I will ask it.

We have an 1800 sq ft end of terraced home, 18 years old, cavity wall insulated, deep insulation in loft, up to spec double glazing and hot water supplied from roof panels ( bolstered by heater in winter ) and photo voltaic panels which are linked into the grid as usual. We have LPG central heating because there is no gas. So we have been looking at a Panasonic Air to Water unit and await a survey fro this. However there is clearly a huge amount of really good info on this site but can anyone tell me - shud we really be looking at replacing an LPG boiler for CH with and Air to Water system or shud we really just concert to electric panel central heating which we recently used in Germany and which seems really efficient and would possibly cost less to install but am unsure about running costs.

We are in Taplow Bucks - is there a good advice sentre locally?

John_Pierpoint

.........electric panel central heating which we recently used in Germany.

Do you have a link ?

zeupater

John_Pierpoint wrote: »

.........electric panel central heating which we recently used in Germany.

Do you have a link ?

Hi John / Alfiethefish

Whatever the type/make of electric panels they will simply be very close to 100% efficient at converting electrical energy to heat. The only variables are the relative costs of the systems and the realistic seasonal COP of the heatpump.

Personally, I'd stay well clear of pure restive electric heating and would look at almost any alternative source, but of course the installation cost vs any fuel savings must be considered when making a decision ....

One point which comes to mind is that 1800sqft seems to be rather large for a modern end of terrace property (larger 4 bedroom modern detached are usually somewhere around 1250sqft), but I have seen a number of larger 3 storey 4/5 bedroom terraced properties which could be of a similar size built quite locally in the past few years in order to pack more house value onto the same size plot ....

Anyway, I suppose that a place for the OP to start would be to estimate the annual energy consumption based on recent years, work out what that would cost for electricity at a COP of 1.0 and at an estimated seasonal ASHP efficiency of somewhere between 2.0 & 3.0 (might as well use both to bracket the range!) and see how it compares to current fuel costs, multiply the difference (savings) by a reasonable system life (10years ?) and you'll get an idea of relative max purchase prices and see which is the most realistic option.

HTH
Z

John_Pierpoint

After making all the reasonably possible improvements in the thermal performance of the building's envelope, you might be able to get close to "Passiv Haus" standard, in which case the heating system stops been particularly important.
However for the rest of us, who are not living in a south facing unshaded cave, the heating challenge is then all about improving the "efficiency" of space heating.

The problem with electricity is that the power in the original source of energy has been dissipated by (let us say) 50% in various production and transmission losses before it arrives in the consumers meter.
This has to be compared with the 90% efficiency (when working hard) of a gas boiler in the winter.

Then we need to discuss capital costs and carbon costs and put our own factors amd future guesses on those figures.


I was rather wondering if the poster was suggesting the concept of collecting heat on the outside of the building, not by blowing large quantities of air through an air conditioning unit running in reverse, but just by air and day time sunlight passing over thermal panels.

I remember you were able to help debunk some salesmen's estimated of the fortune to be saved with solar thermal hot water. You published some simple conversion/storage factors for raising the temperature of hot water, in terms of kWh, in a buffer tank.

Now we are seeing suggestions of serious additions to space heating using panels "that don't even need to face South" plus a freezer sized heat pump. It would seem this concept of black panels is coming up from Spain.

Here is a suggestion for storing "summer" heat for "winter" use in a three tonne tank, rather than trying to find a large area or volume of wet subsoil..

http://www.minus7.co.uk/how-it-works/

Do I feel an attack of oil and snake coming on?

Are we talking about heating something like this
http://www.zoopla.co.uk/for-sale/details/29073121?search_identifier=762c12f419526d5c9460ff61bd47f4d6

Cardew

John_Pierpoint wrote: »

I remember you were able to help debunk some salesmen's estimated of the fortune to be saved with solar thermal hot water. You published some simple conversion/storage factors for raising the temperature of hot water, in terms of kWh, in a buffer tank.

I posted this some years ago - and it still is relevant.

Have you seen this exaustive trial of 8 systems carried out for the Dti at Cranfield?
*

http://www.dti.gov.uk/files/file16826.pdf

*
For those not conversant with the units used! For the 8
systems tested(evacuated Tube and Flat plate) the annual output ranged from 3440 MJ(megajoules) equal to 955kWh to 4,820MJ(1,339kWh)

However from that total had to be deducted the ‘parasitic’ energy to run the pump and electronics. This ranged between zero and 390MJ(108kWh) pa. This of course is daytime rate
electricity.

The average for the 8 systems was just over 1,000kWh per year.

John_Pierpoint

Cardew wrote: »

I posted this some years ago - and it still is relevant.

To be charitable about £100 saving against gas or economy 7 electricity. Nearly double this if the occupier is forced to use full price electricity for water heating..

I was thinking more in terms of it takes "x" kWh of power to raise the temperature of a litre of water by "y" degrees, so raising the temperature of (let us be generous) 3 tonnes of water from 4 degrees to 60 degrees in a big tank (insulated with aerogel) stores "z" kwh and only requires an input of "n" kWh of daily input from the black panels to carry it through the Autumn season.