Thanks SteamyTea -

yes it should have said 2011 later on - well spotted.

Ahh- caught us out there about the night time usage! We know we are not using it much. I did run the washing machine etc at night but stopped when we got the dogs (woke them up). However - i'm sure we could sort something out and start using them again. I used to heat the water for 1 hour overnight but we ended up setting it for 1/2 hour at night then 1/2 hour at about 5pm - I could put this back to how it was. 2 showers take water from the tank, attic room shower = electric.

We knew we would be getting rid of the convectors - and didn't put in temporary storage heaters because we thought heat pump technology and (possibly a buffer tank to make good use of night-time tariff) was probably the best way forward plus we wanted a bit of controlled ventilation ... but time has moved on and we've paid over the odds for our level of heat in that time. I think storage heat technology has advanced just recently - not just on or off. My husband says - "lets just swap to storage heaters and have done with it" - perhaps he is right. We can't swap to another electricity provider - can only get via Jersey Electric Company (some from France, some generated locally).

I have just about halved my space heating by improving insulation and airtightness (checked for Radon when bought the place as on granite, though house is 1987 vintage). One thing I do notice about storage heaters/water heating is that the first hour (11PM to Midnight) everything comes on as it is thermally depleted, it then goes back to normal rate for an hour (Midnight till 1AM). Comes on again at 1AM for a bit, then often 'tops itself up' later on.
Thing is that I am asleep or do not need the first hour of heating (not got the water up to temp anyway), so looking into isolating the heaters and water until about 3 AM, so that it only recharges the stores for a maximum of 4 hours (will possibly play around with the timings).
I did find that changing the convection heaters to fan heaters for that 'little boost' made a huge difference, though sometimes forget to turn them off when out if they are not running at the time. Also found that keeping all the internal doors open spreads the heat about nicely. Though the design (a crap design really) of the house lends itself to that.
Have you considered Solar Thermal and a very well insulated cylinder for your DHW?

SteamyTea - great article. I'll get them on a treadmill to generate some electric & also attempt to harness the copious amount of methane.

Thanks Paul and GaryB - an 'air conditioning' system to supply heat or an air source heat pump seem to be the options - and some minor form of MVHR but not whole house MVHR.

A guy came to the house yesterday - i had asked about MVHR & Exhaust heat pumps - he took one look and said "not suitable" (which I knew by then because of these posts-thanks everone!). Seemed to know his stuff. Essentially - he thought we needed a 14kW air-source heat pump. He's coming up with figures for two different systems. One system he is familiar with (Nibe air-source) another I asked him to check (New Panasonic which seems to run higher water temperatures like the Co2 Sanyo which has been discontinued).

This just leaves the possibility of an air-conditioning system - which do you think would be best for us in terms of comfort, short-term and long-term costs (1) air-conditioning (can run ducts ok I think) or (2) air-source heat pump (have room for the main units and can fit radiators and associated pipework)?

Are those ASHP on the MCS list?

Janetta:

There are a number of other considerations which should be taken into account when selecting a heat pump.

1. All nominal ASHP COPs are quoted at 7 deg C outside, which correlates to the average winter temperature in most of the UK. COPs at 0 deg C are typically 20-25% worse and at -7 deg C are typically 30-35% worse.

2. The ASHP COPs are quoted at a nominal flow temperature of 35 deg C, which only works with underfloor heating or Smartrads (fan assisted heaters specifically designed to run at low temps). Flow temperatures of 45 deg C will result in COPs 20-25% worse and it is well nigh impossible to find information on COPs at higher temperatures (they are much lower) - you have to ask the manufacturer's technical bods for this information. Once the COP drops to 2.0 or less it is cheaper to use oil. BTW, in natural gas areas, unless you can achieve a COP better than 3.2, gas is normally cheaper per kWh.

3. The air-to-air system (ducted AC) distributes low temperature air (approx 35 deg C) and is therefore only affected by outside air temperatures.

4. The effects of RHI (if and when implemented) should be taken into account. Note that the air-to-air system will not qualify for RHI and this will affect future running costs and paybacks.

5. All AS heat pumps will reverse cycle to defrost and will remove heat from the buffer vessel. Some systems will maintain the heat output during defrost by using an immersion heater - avoid these as they cost a lost more to run.

6. Keep hot water and space heating systems separate, unless a dual compressor ASHP designed to deliver hot water is used. I personally favour solar thermal plus back-up heating. In winter it is cheaper to run an ASHP at 45 deg C and top up using an immersion heater than to run the system at 55-60 deg C to heat water.

For my own house I have an ASHP system on order and will be running it at a maximum flow temperature of 45 deg C through an existing radiator system. The system will also be weather compensated so that the flow temperature is less in milder weather, improving efficiency and COP. To achieve this low flow temperature, I have installed additional insulation and an extra rad in the Living Room.

My hot water is on a separate system with solar - this provides all hot water from mid March to mid October. I have oil / log burner available for top-up in winter.

Probably not generally accepted, but still true!

To heat cylinder from 10 deg C inlet to 60 deg C:

Delta T overall = 50 K
Heating to 45 deg C by ASHP @ 3.2 COP is 35/50 = 70% of the heating
Balance of 30% heating is via immersion @ COP of 1
Average COP = (0.7 x 3.2) + (0.3 x 1.0) = 2.54

If anyone can produce evidence of an ASHP which can produce 60+ deg C hot water at a COP of 2.54 or better with a nominal external ambient of 7 deg C, I will stand corrected

I saw an Eco Cute heat pump in the laboratory in the Hitachi Europe factory 3 weeks ago and it was still under development for the UK climate.

Are there any units currently available using ambient air in the UK?

Hi Gary

Good point to raise, but I think your calculation is not correct.

Suppose 1 kWh directly heating some water gets it from 10 to 60 degC.

Heat a similar quantity to 45C with a COP of 3.2 willl use 0.7/ 3.2 = .218 kWh
Heating it the rest of the way directly uses 0.3 x 1.0 = .300 kWh

So the total consumption is .518 kWh, compared with the original 1 kWh, and the overall COP is thus 1/ 0.518, or 1.93.

I've been wondering about this issue for my air to air HP, but not for temps as high as 60C. What we'd like to know from the manufacturers is what the marginal COP is for each increment of temperature.

Mike7:

Just checked the calcs again and your version is correct.

Apologies!

However, the immersion will be 100% efficient whereas the higher heat losses in the primary circuit have to be taken into account. Also the immersion may only heat the top of the cylinder depending on location / type. A Willis or side-arm immersion will only heat a small volume of water.

Personally, I will be setting mine at a lower temperature and sterilising the cylinder once a week in winter using the log boiler.

Janetta,

just something to consider...looks like you're spending £500/year on electricity. I assume (perhaps wrongly) this covers all usage - heating/hot water/lights/cooking/power...

Let's guess at £250 being for your heating. If you did really well, you might cut that cost in half, so saving £125/year. Just consider what the payback will be against any system you purchase/install against that £125 saving. In other words, if you want better than a 20 year pay back, don't spend more than £2500 on the system. Doubt anything above will be less than £2500.

Solar must be something to consider where you live (can't remember what the sun looks like, but I think it used to be over head where the rain now comes from). If you were considering re-working your hot water system anyway, then solar thermal could be worth doing. Again looks like savings might be in the £100 to £200 region per year, so need to be wary of cost versus payback - though you might consider a longer payback, due to the psycological payback of harvesting free solar energy??

WillinAberdeen:

Firstly, thanks for posting your actual COP performance - we need more of this on ASHPs! Did you measure this using a heat meter + electric meter and what average temperature did you run the system at?

My earlier post recommended keeping DHW and space heating separate for efficiency unless a 2 stage ASHP (such as your Altherma HT) was used.

Too many single stage monobloc systems are being run at high temperatures for DHW purposes without an understanding of what this does to the COP and running costs. I blame the sales & marketing people who present facts in the brochures / sales patter, such as:

'Flow temperatures up to 60 deg C'
'Heat output of 11 kW'
'COP of 4.10'

(actual statements from ASHP brochures)

all in close proximity, without clarifying that some of these are mutually exclusive. The small print usually confirms that the figures are for 35 deg C flow and at 7 deg C ambient. No information is provided on real world performance.

To be fair, some of the manufacturers of the HT equipment do state the performance and COP at 60 deg C in the brochures and these normally show a COP figure of around 2.5. These are for units specially designed to operate at these temperatures, standard monobloc ASHP units will be worse. Also, these are based on laboratory testing and are not 'real world' figures inclusive of defrost cycles and primary circuit losses in the pipework to the cylinder.

I see the Altherma HT brochure appears to claim a COP of 2.9 to 3.1 in HT mode, depending on model size, and a seasonal COP of 3.2. This is higher than I was expecting - I thought the limit for HT units was around 2.5 but I note that your experience as an informed user doesn't quite match the Daikin figures!

Regards, Gary

But isn't that going to double the costs and the space requirements (and make a complete CH/DHW ASHP system to your liking impossible to get within the new GPDO)?

Rgds

Damon

Sure, though that cost thing cuts out much of the possible benefit to the population? But even the nuisance factor of the extra heat exchangers (I really don't have the space for example) and planning permission is quite daunting IMHO...

So for most of us a good compromise with one system is likely to be best.

Rgds

Damon

I like the controllability of separate systems, seems to work for me (with 3).
Have we fallen into the trap of 'one size fits all' rather than look at what really needs to be achieved.

If we took a 'normal' house we could split up the systems needed and see which each technology can deliver and the associated pros and cons.

So a house needs:
Lighting
Heating
Ventilation
Fresh Water
Waste Water
Hot Water
Electricity
Security
Entertainment
Maintenance
Refrigeration
Cooking

Now is is better to combine all those into one integrated package or treat them as stand alone entities?