Heat pump / inverter DIY

stevehead

Well done all for keeping this a flame free thread - good standard of input.

I was thinking why not apply the same vigilence to these A Rated gas-combi boiler based systems?

For starters - and I know it's not much - but Which? found that most A rated boilers were actually a high B.

And I picked up on this thread (Post 663) which states that the annual electrical consumption of an Eco Hometech Boiler was 600KWh - I could do a lot with that, like November & December!

Thats before we go anywhere near the slow response time of wet systems (like when the sun's come out but the rads are still warm)

One thing that gets me.... you typically buy a 24-32Kw Boiler. When it first fires up you're pumping what's equal to having 30 Electric Bar fires switched on all at once into your home. You'd think you'd roast!

thechippy

I agree Steve,

Everyone here has remained civil and put thier points accross as best possible without getting nasty. It's been very interesting "speaking" to you all!

With regard to your previous post.......
My old boiler was a Potterton flamingo 20-30 (being replaced next week) It's a heat only, gravity hot water, pumped CH.
The 20-30 stands for btu's, so basically it's capable of around 8.8kw (heating). This works out about right for the house.
I'm having it replaced with a combi that is rated 24kw! This is because combi's are on demand hot water, heat as you go so to speak and a 8.8kw heat exchanger would give a pretty poor flow indeed in this set up.
I don't pretend to know too much about gch, but I can see why the combi's need a high kw output.
I've never really wanted to lose the hw cylinder and the simple reliable setup of an open vented system, to go combi, but our house is not huge and the extra space gained in the airing cupboard will be usefull. As we will lose the tanks in the loft, we can now convert that central section into a studio for the wife - she's a portrait artist so finally, we can get the use of the dining room table back!

G.

mech_2

stevehead wrote: »

Well done all for keeping this a flame free thread - good standard of input.

I was thinking why not apply the same vigilence to these A Rated gas-combi boiler based systems?

There's not a lot of point until we have information of a similar quality for ASHPs with which to compare. The SEDBUK rating is a seasonal figure, so it's already a real-life figure. Information of a similar quality for aircon units seems relatively thin on the ground. I think I'll wait until there are some figures and then compare measurement methodologies when there's something to compare.

For starters - and I know it's not much - but Which? found that most A rated boilers were actually a high B.

Hmm. I've had a look. Which? only seemed to test the boilers at maximum load, so that might explain the discrepancy. The SEDBUK figure uses full-load and part-load efficiencies to get a seasonal figure (The 'S' in SEDBUK).

And I picked up on this thread (Post 663) which states that the annual electrical consumption of an Eco Hometech Boiler was 600KWh - I could do a lot with that, like November & December!

That doesn't seem like a very likely figure to me, but who knows; perhaps the electronics in that boiler are particularly inefficient. Maybe there's an ASHP out there with a standby consumption of 60 watts as well. After all they do have a controller in them.

I would be very surprised if my boiler consumed more than about 200kWh of electricity a year. At 12p/kWh that would be £24. Quite a lot less than reported costs I've seen for the pilot light in many older gas appliances. Like a gas-fired instant hot water heater, for example.

Thats before we go anywhere near the slow response time of wet systems (like when the sun's come out but the rads are still warm)

Any heating system will overshoot if it has got the house up to temperature and another few kilowatts start streaming in through south-facing windows. Doesn't matter if it's hot air, radiators or underfloor heating. The question is whether this has any meaningful affect on efficiency.

richardc1983

paceinternet wrote: »

Thanks to "thechippy". Apologies to "stevehead". I've only ever seen what you describe as the "larger systems" method, but your manual on page 10 does show the power supply going to the indoor unit.

This is how my system is wired. It is a larger system 1 outdoor unit capable of running 4 indoor units.,

stevehead

mech wrote: »

I would be very surprised if my boiler consumed more than about 200kWh of electricity a year. At 12p/kWh that would be £24.

So lets pretend all ashp are born equal and deliver an average COP of 3 during the 6 month heating season. Cost per Kw, this would be on parity with gas. And let's estimate that by using either ashp or gsh you use £30 worth of energy per month. The heating bill for the 6 months is then £180 for either system.

But then we have to add
£24 (gch elec cost) + £176 (eon gsh service contract) = +£200 annual overhead
or
£24 (gch elec cost) + £76 (est RGI service) = +£100 annual overhead

Therefore the total annual running costs of a new Gas Combi are 50 - 100% higher than ashp.

Annual service of ashp is a diy job that consists of simply cleaning the crap out of both units.

mech wrote: »

Any heating system will overshoot if it has got the house up to temperature and another few kilowatts start streaming in through south-facing windows. Doesn't matter if it's hot air, radiators or underfloor heating. The question is whether this has any meaningful affect on efficiency.

ASHP doesn't overshoot; it doesn't have 50 gallons of useless hot water to dissapate if the sun comes out.

richardc1983

Hows ur system doin today!

Its -4 here and im on 2.7kw for the outdoor unit and the system is giving out 7kw of heat (2 indoors)

3.5 across both units output.

Got in house at 830 was 12C and now im at 21C!!! Central heating would prob only bring it upto 18C in 2hours!

Cardew

richardc1983 wrote: »

Hows ur system doin today!

Its -4 here and im on 2.7kw for the outdoor unit and the system is giving out 7kw of heat (2 indoors)

3.5 across both units output.

Got in house at 830 was 12C and now im at 21C!!! Central heating would prob only bring it upto 18C in 2hours!

Your system might take 2 hours!

CH Bolilers can output up to 30kW and radiators at 80+C warm a room up pretty quickly.

richardc1983

the boiler is on full 85C and its due to the house having very high ceilings and no insulation. The boiler is a huge boiler bigger than 30kw.

megohm

New to this forum but considering the Mitsubishis. Currently on full electric and using around 5-6kW with the -3 outside at present (a large 3/4bed detached but well insulated!).

Problem is I don't want them high on the wall as usually recommended. I know I could use floor units, but they're a lot more expensive. Has anyone experience of mounting at say 600cm - 1m from the floor? Obviously the breeze hitting you in the neck if seated nearby could be a problem, but anything else?

stevehead

richardc1983 wrote: »

Hows ur system doin today!

Just business as usual here Rich!
Noticed some white stuff on the fins this morning which is unusual - it's been -1C - 1C this morning which is colder than normal for Plymouth. Only one more day to go, then we're back in the 6-10C range
COP goin' UP