Air Source Heat Pumps

TiredGeek

Cardew wrote: »

How about passive solar gain?

Zeupater's house I believe has a high solar gain.

I have a detached annex that I don't heat unless occupied(or in danger of frost damage) and inside it gets well above the outside ambient temperature.

My place has low solar gain, I wish it was better but quite often I have seen it warmer outside than in.
The thermal mass is huge as it's 700+mm thick solid stone walls, some solid stone floors and relatively small windows. Couple that with a very northern Scotland location and it takes a lot of sun to make a difference to the thermal lag.

There's one room with five French doors fitted, now that does get nice when the sun shines, but then the heat just leaks away through the same doors when it goes in. We monitor the individual rooms for temp fluctuation, all the rest stay pretty steady regardless of weather, that one room fluctuates up and down depending on sun shine.
It will make a small difference to the house overall, but not one worth taking into account.....

zeupater

Cardew wrote: »

Zeupater's house I believe has a high solar gain.

... Not that it's making much difference at the moment with the lack of solar to gain ....

Log-burner back to daily usage (~10Hrs/day) over the last three days and raising the temperature of the thermal mass nicely in preparation for the next few days of cold weather ....

Z

[Deleted User]

matelodave wrote: »

We are in our third winter of having an 11kw Daikin LT split heatpump system coupled to a polypipe overlay underfloor heating system laid on top of the existing floor and this has been the coldest winter of the three.

It's installed in a 1986 140sq/m detached bungalow, out in Fenland, so its cold, exposed and windy. The loft is insulated with 300mm rockwool, the walls are insulated (but I'm not sure how well), it's double glazed and the flooring is ventilated suspended timber, which is not insulated (ran out of money and inclination to take up the whole floor)

I am quite happy with the performance and cost of the system although this prolonged cold winter is probably going to use about 500-600kw more than last winter.

I read the electric meter weeky but cant seperate heating from everything else (lighting, water, washing, cooking, drying etc) but our total consumption last year was about 8000kw which I dont think was bad. The highest useage we've had is 1500kw for the 31 days of January 2013 = £160 but in the last couple of summers its averaged only about 250- 300 units in July (we presently pay 10.6p/kw). The unit actually uses just under 3kw a day just keeping itself warm which is a cost that isn't obvious.

We heat the whole place to about 17 degrees all the time with an uplift to 19-20 in the bedroom, bathroom and kitchen in the mornings & evenings and all day in the lounge and study.

We find that with the u'f heating we can keep the temperature a bit lower as it's even all over rather than having hot & cold spots.

We only run the system temperature at 35-40 degrees (except when the temp drops below 0 when it goes up to about 45). We do find that it's a bit slow to respond mainly because its running at a low temperature so it's best not to let the house get cold

I have half seriously considered PV but we wouldn't get any real benefit as the unit uses most energy when the sun isn't shining and we haven't had all that much sun in the past 12 months.

If we'd had the option of mains gas then I would have gone for it with a condensing combi boiler but the alternatives of LPG, Oil or wood pellets were not attractive due to their cost and storage requirements. Everyone where I live have has had to have 2-3 deliveries of their chosen fuel since just before Xmas so I dread to think how much it's costing them.

Nice to read your post.

One of my best friends has the same system which works brilliantly. Also on UFH.

Yes... nobody ever seems to mention the electricity useage by ASHPs in 'standby.' Though in our case there is also 13 fan convectors sitting in standby not to mention their runnings costs to. Our base line power useage seems to be around 700-850watts. Though I suppose this is often covered during the day by the solar pv. But... is still is one of the many reasons for humming and ho-ing over the ImmerSun. Rapidly coming round to the idea that changing all MR11 and MR16 halogen spots to quality LEDs with appropriate drivers is significantly cheaper to install [<£100] with excellent and pretty much immediate ROI. Bung in some more loft insulation. Jobs a goodun

Cheers

PS Like TiredGeek little all solar gain... Thanks to the wife's plants I'd like to chop

nande2000

My 8.5kw Ecodan has now used 2386 kwh in exactly 115 days. Even more impressive as this winter has been so prolonged.
I'd be well into a second tank of oil by now (tank was 1250 litres) with our previous system.

Cracking bit of kit.

zeupater

nande2000 wrote: »

My 8.5kw Ecodan has now used 2386 kwh in exactly 115 days. Even more impressive as this winter has been so prolonged.
I'd be well into a second tank of oil by now (tank was 1250 litres) with our previous system.

Cracking bit of kit.

Hi

Cost aside, would that be accurate ? ....

Let's say that the Ecodan had been achieving a COP of 3.0 for the entire time that it's been running (including background consumption ) ... then 7158kWh of heat would be delivered ...

1250litres of heating fuel would have a potential to deliver between 10 & 10.5kWh/litre, so with a modern oil heating boiler efficiency of around 95%(SEDBUK), let's say 85% average, that would mean that ~10600kWh (1250*10*0.85) could have been delivered ...

...therefore providing the same heat would, on above assumptions, mean the oil tank would still be ~32% full ((7158/10600)-1)

HTH
Z

Cardew

I wrote roughly the same, but MSE crashed and it didn't post.

In fact Nade wrote well into the second tank of oil.

Also an ASHP would do very well to achieve a COP of 3.0 from the end of Nov up to date. Most struggle to achieve 3.0 on an annual basis.

nande2000

My oil boiler was probably about 75% efficient. Last service said 68-70%, but the chimney did radiate some heat too. The control system was hardly space age either(pipe thermostats and TRVs).

The ASHP reading is accurate - has a dedicated electric meter. COP is another question though, i dont know. I've got an immersun fitted too and that says it has saved my 160kwh over the same period as well.

zeupater

Cardew wrote: »

I wrote roughly the same, but MSE crashed and it didn't post.

In fact Nade wrote well into the second tank of oil.

Also an ASHP would do very well to achieve a COP of 3.0 from the end of Nov up to date. Most struggle to achieve 3.0 on an annual basis.

Hi

I simply used good/best seasonal performance from the ASHP & compared it to an oil at the lower end of it's calorific range with a boiler which would be underperforming on specs by somewhere around 10% so that no one tried to shoot the figures down ....

However much oil would be left in the tank isn't really the point ... it's really down to the comparative cost of 7158kWh of electricity to ~850litres (1250x0.68) of fuel oil, the price of which can be open to negotiation & seasonal fluctuation .... then there's the cost of ASHP vs Oil Boiler written down over their expected lifespan .....

HTH
Z

Silent_Dancer

nande2000 wrote: »

My oil boiler was probably about 75% efficient. Last service said 68-70%, but the chimney did radiate some heat too. The control system was hardly space age either(pipe thermostats and TRVs).

The ASHP reading is accurate - has a dedicated electric meter. COP is another question though, i dont know. I've got an immersun fitted too and that says it has saved my 160kwh over the same period as well.

So you could have installed a condensing oil boiler 90% efficient and made most of the savings that you have observed and saved yourself £1,000s.

Note that most of the savings from the heat pump are from improved insulation, the upgraded heat emitters and improve controls, things that could also have been done to improve the efficiency of an oil boiler.

Cardew

zeupater wrote: »

Hi

I simply used good/best seasonal performance from the ASHP & compared it to an oil at the lower end of it's calorific range with a boiler which would be underperforming on specs by somewhere around 10% so that no one tried to shoot the figures down ....

However much oil would be left in the tank isn't really the point ... it's really down to the comparative cost of 7158kWh of electricity to ~850litres (1250x0.68) of fuel oil, the price of which can be open to negotiation & seasonal fluctuation .... then there's the cost of ASHP vs Oil Boiler written down over their expected lifespan .....

HTH
Z

Also a most important point is that an ASHP needs to run when occupants are out at work and in bed.

An oil or gas CH system with water at up to 82C can be set to come on, say, 20 minutes before getting up in morning and also before returning from work. Most of the posts from(presumably) working occupants talk of having heating on for, say, an hour in the morning and 5 hours in the evening.

Not so an ASHP with water at 35C or so, as it cannot bring the property quickly up to the required temperature.

The proponents of ASHPs always talk of the COP as the main factor in running costs. 200kWh input giving 600kWh output etc. However an Oil/Gas CH system would not need anywhere like 600kWh to provide the same temperature - when it is required. A fact conceeded by the EST.