Heat pump / inverter DIY

mech_2

richardc1983 wrote: »

Heating appliances that use electricity that also use it efficiently may help though do you not agree.

Yes of course, it's excellent for electric-only households. I just question whether it's sensible to pit electric heat pumps against gas when gas is cheap and there is a huge installed base of UK households (10 percent?) still using dreadfully expensive and inefficient resistive electric heating.

The future of heating for gas heated homes could well be gas-fired air-to-water absorption heat pumps. (http://www.robur.com/products/e3-systems/e3-a/description.html) Or maybe micro-CHP. Either way, I think it would be best to exploit the existing gas infrastructure and eliminate the need for more power stations which tend to waste more than half the energy in their primary fuel before it gets to your heat pump.

mech_2

stevehead wrote: »

There is no way of measuring the COP of a system - not for the end user anyway. All you can measure is the amount of energy used to keep yourself comfortable and everything else is a variable.

What you need to know is the heating load of your home. Otherwise it's not possible to make honest claims that your aircon units are the cheapest way to heat your home. You just don't know if they are or not.

I thought I would be able to get accurate usage statistics on how much electricity my ASHP was using by plugging each unit into the mains via a Maplin Energy Monitor. These obviously don't work properly as the KWh result they gave me at the end of 1 month are aa Complete Fantasy.... much lower than it 'should' be.
I'm just off to phone the electricity board to get my meter checked - it's going round much too slowly and it must be busted!

I thought it was made quite clear that the "complete fantasy" was your running cost comparison between ASHP and gas where you forgot to mention you had insulated your house since you got rid of your old boiler.

stevehead

mech wrote: »

What you need to know is the heating load of your home. Otherwise it's not possible to make honest claims that your aircon units are the cheapest way to heat your home. You just don't know if they are or not.

I thought it was made quite clear that the "complete fantasy" was your running cost comparison between ASHP and gas where you forgot to mention you had insulated your house since you got rid of your old boiler.

I've also expanded it, and this winter is more demanding than last, so yeah... too many variables.

What I can do is turn off the Aircon for (say) 10 days and run the old GSH; other than the weather that'll give me as best a comparison as I can reasonably hope for. Is that fair?

stevehead

mech wrote: »

The future of heating for gas heated homes could well be gas-fired air-to-water absorption heat pumps. (http://www.robur.com/products/e3-systems/e3-a/description.html) Or maybe micro-CHP.

Interesting link Mech, I like that.

About micro-CHP. These run Stirling heat differential engines, which even with solar concentrators only achieve a 25% efficiency tops.
My understanding is that they are powered by the excess heat from your boiler. Surely with modern boilers there's virtually no exhausted heat to recover and use for running a generator?

Cardew

stevehead wrote: »

There is no way of measuring the COP of a system - not for the end user anyway. All you can measure is the amount of energy used to keep yourself comfortable and everything else is a variable.

I thought I would be able to get accurate usage statistics on how much electricity my ASHP was using by plugging each unit into the mains via a Maplin Energy Monitor. These obviously don't work properly as the KWh result they gave me at the end of 1 month are aa Complete Fantasy.... much lower than it 'should' be.
I'm just off to phone the electricity board to get my meter checked - it's going round much too slowly and it must be busted!

Stevehead,
I am trying to understand your system, and figures.

As I understand it you are stating that you have achieved the total heating of your 3 bedroomed, 3 storey house for the whole month of December with 304 kWh with 2 Mitsubishi srk20zgx ASHPs.

You reach that figure of 304 kWh by plugging in the two inside units via Maplin type power measuring units.

So each of those units is using approx 5 kWh per day.

Now as these inside units are plugged into the mains via a 13 amp plug , this means that the inside units must each supply the power to each of the the 2 outside compressor units?? These outside compressor units obviously will consume the majority of the power.

It seems to me an extraordinary arrangement that the outside compressor units would not be supplied with their own power supply from the mains.

Are you saying that your installer fed a mains supply power cable cable from each inside power unit to its outside compressor? That would be the only way the Maplins meter could measure the consumption of both units.

I am not up to date on the latest electrical regulations, but I would have thought that probably illegal and certain bad practice.

Certainly the wiring diagram(page 11 of the link you provided) shows both the indoor unit and outdoor unit should have a separate power supply!!

Or have I missed something?

My suspicion is that the 304kWh is simply for the fans and control mechanism of the 2 indoor units. Bear in mind that is only an average load of 200 watts.

Last year just your heating with gas(not HW) in December cost £120.

Depending on what you paid per kWh that would be between 3,000kWh to 4,000kWh.

This December you have extended your house, albeit increased insulation, and this December has been much colder. Yet you have heated your house with 304kWh!!!

Something doesn't add up>

Cardew

Further to my post above you state that:

Whilst on, they pull between 8 and 360 watts each. Thats 720 watts heating my whole house!

However the technical spec from the link you gave (and quoted at me!) gives the input power for each unit as up to 1.27kW (1,270 watts each)

Also if I understand the tech spec correctly, at maximum input of 1,270 watts the maximum output is 4,600 watts(under ISO conditions 7C/20C etc) so that is rather less than a COP of 5.45 - is it not 3.62??

mech_2

stevehead wrote: »

Interesting link Mech, I like that.

About micro-CHP. These run Stirling heat differential engines, which even with solar concentrators only achieve a 25% efficiency tops.

I think you're quoting a whole-system solar-to-electricity efficiency figure there, though I could be wrong.

Micro-CHP using ceramic fuel cells has also been tried, but I think they are currently too expensive to manufacture.

My understanding is that they are powered by the excess heat from your boiler. Surely with modern boilers there's virtually no exhausted heat to recover and use for running a generator?

You're thinking about it the wrong way around. The house is basically heated from the waste heat from generating the electricity. Therefore efficiency isn't really crucial as long as it's quiet, reliable and cheap to manufacture. Though obviously the more electricity from the unit the better, especially if you don't have an export meter.

They use all of the heat from the boiler, not the excess heat. Flue losses would be the same as for a modern boiler, so the house is heated at ~90% efficiency, but you get some of your electricity from the same heat rather than having to burn fuel in a power station somewhere and supply it to homes at 40-50% efficiency.

I'm not sure which option I like better: gas-fired heat pumps or micro-CHP, but both are technologies still under development, so maybe the better option will be more obvious by the time I next buy a new heating system. At the moment though, so long as I'm in a gas-supplied property, I haven't seen a compelling reason why I would want go down the electric air-conditioning route.

mech_2

stevehead wrote: »

I've also expanded it, and this winter is more demanding than last, so yeah... too many variables.

What I can do is turn off the Aircon for (say) 10 days and run the old GSH; other than the weather that'll give me as best a comparison as I can reasonably hope for. Is that fair?

Ah, the GSH is still installed? So it should be measurable! So long as we know the efficiency of the boiler it should be possible to work out the heat demand.

Though for a comparison we also need to be sure you're measuring all the electricty consumed by the aircon. If Cardew is right and the outdoor units consume significant ammounts of power which is not presently being measured, then we would need to factor that in too.

Weather isn't a problem. It should be possible to find figures for heating degree days online somewhere.

richardc1983

@ Cardew:

The outdoor units feed the power to the indoor units. The way Stevehead has it wired in is that his wiring is inside the house at a domestic plug socket. This is how my a/c system is wired in also. Whilst i dont have individual plug sockets it is wired into a fused spur with an on off switch to isolate the outdoor unit which in turn would isolate the indoor units. Steve head has the same but he has them wired into a plug socket hence the plug in energy monitor he has for each system (1 outdoor unit & 1 indoor unit). because they are inverter systems they can happily run off a 13amp plug socket due to them having low running amps and start up currents. When they quote you the system they do reccomend you to have a separate fuse for it on your consumer unit. But to keep costs down and as a friend was installing my system for me at a cheaper price it did not matter that he was not putting it to the consumer unit directly and it would still run safe as long as I can isolate it via the fused switched spur should any problem arise.

What in actual fact Steve has it set up for is the plug socket that supplies power to the outdoor unit in turn then has a wire coming back to the indoor unit from the outdoor unit (carried alongside the refrigeration pipes) it is this plug that he is monitoring the power usage for. As a whole system from the socket. So the figures he has quoted usage for this month is each system as a whole, indoor and outdoor unit.

As a comparison, my systems which are 3.5kw capacity units, at a stretch they can output 4.3kw using 1.32kw to get that at ISO conditions, I can only count total consumption for the the whole flat which is a victorian 1900s house no insulation and draughty double glazing.

We used 23kwh on Monday, the units were maintaining a set point of 20C all day long and we had the washing machine on a couple of times and tumble dryer going for an hour also. Along with lights etc. Temperatures were about 1C outside. My units output upto 3.5kw each when running at full capacity.

Now my which are 3.5kw capacity units, at a stretch they can output 4.3kw using 1.32kw of electricity now most of the day I checked what they were using individually by switching everything else off and they were using about 1.2kw if only one unit was working to maintain the indoor temp.

So you can see im using 23kw a day if the heating is on all day, im talking a 24hr period including all the other appliances using power.

Rich

rothers8080

I can confirm mine work in the same setup, from one indoor socket. The power cable travels with the pipes and water overflow from the indoor unit to the outside (in this case 4 meters).