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Author Topic: One year in... some GSHP numbers  (Read 21775 times)
Mikel
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« Reply #30 on: December 16, 2016, 04:35:26 PM »

@brackwell. You're welcome!

Don, thanks. Looks like a good system. Useful to see a well performing ASHP with oversized rads. I think it is really important to show that as there is a tendency to reject heat pumps unless delivering through UFH.
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rogeriko
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« Reply #31 on: December 16, 2016, 10:12:36 PM »

Ground source heat pumps are a hot item right now. The RHI is paying 20p per kwh so they are basically paying your entire electric bill, we are installing lots right now.
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davec
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« Reply #32 on: December 17, 2016, 02:39:47 PM »

Aye, the way I looked at it was: EITHER you get back the extra capital expense of the system in only 7 years; OR you get the electricity bill paid for the next 20+ years. Win-win? Even with flat energy prices, it still looks that way.
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ringi
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« Reply #33 on: December 17, 2016, 03:37:44 PM »

Would anyone in the UK be fitting ground source heat pumps if the RHI payments were not more than for an air source……
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rogeriko
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« Reply #34 on: December 17, 2016, 07:10:25 PM »

No-one would be fitting any type of heat pump without the RHI. Who wants to pay the high electric bills they generate.
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DonL
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« Reply #35 on: December 17, 2016, 10:04:20 PM »

No-one would be fitting any type of heat pump without the RHI. Who wants to pay the high electric bills they generate.
less than £200/year for heating is high?
Don
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Schuco solar hot water - 3300kWh/annum, 16 BP 4175N PV panels - 2.8kWp, log burner and back boiler and 18 Ying Li 235 PV panels - 4.2kWp, 42kW ground mount PV, 9kW Panasonic ASHP
ringi
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« Reply #36 on: December 17, 2016, 10:18:37 PM »

No-one would be fitting any type of heat pump without the RHI. Who wants to pay the high electric bills they generate.

If you don't have mains gas, and you don't want to spend your life looking after a fire, it is hard to beat a heat pump.   (Unless you want heat 24hr a day, then E7 storage heaters can work.)
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rogeriko
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« Reply #37 on: December 17, 2016, 10:20:57 PM »

Your normal 4/5kw (electric) heat pump running for about 12 hours a day heating the house and water uses over £7 worth of electric per day. Thats why the RHI will pay you up to £6600 per year.
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DonL
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« Reply #38 on: December 18, 2016, 09:55:00 AM »

Your normal 4/5kw (electric) heat pump running for about 12 hours a day heating the house and water uses over £7 worth of electric per day. Thats why the RHI will pay you up to £6600 per year.
It is misleading, to estimate running costs in this way. We need to look at the annual demand and the COP of the system.
The heat pump very rarely uses anything approaching full power; at least in the case of a modern well controlled heat pump it will match power consumption to demand.
If I did not run the log burner which is free for me except for chainsaw consumables and some very valuable sweat, and the house were heated to RHI levels, the annual heat demand is about 15000kWh.
Taking a fairly conservative overall COP of 3.0 the absorbed power would be 5000kWh. At 13.5 p/kWh that gives an annual heating bill of £675.
Don
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Schuco solar hot water - 3300kWh/annum, 16 BP 4175N PV panels - 2.8kWp, log burner and back boiler and 18 Ying Li 235 PV panels - 4.2kWp, 42kW ground mount PV, 9kW Panasonic ASHP
DonL
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« Reply #39 on: December 18, 2016, 10:11:44 AM »


Don, thanks. Looks like a good system. Useful to see a well performing ASHP with oversized rads. I think it is really important to show that as there is a tendency to reject heat pumps unless delivering through UFH.
Mikel, you are absolutely right. I continually preach to people about how good a system it is, partly because of the controllability and comfort. By having low temperature radiators and the temperature being modulated in response to outside temperature you get accurate room temperature control with none of the thermally induced draughts which you get with conventional heating and controls. With our oil boiler, the thermostat would turn the boiler on the radiators get hot and once the thermostat was satisfied they'd go cold and then the thermostat ......... The result is a continual temperature variation of about 2C and this is what most people live with! With the ASHP and a decent thermostat the temperature is virtually constant and you can comfortably live with a temperature a degree or two lower. Subjectively the improvement is really significant.
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Schuco solar hot water - 3300kWh/annum, 16 BP 4175N PV panels - 2.8kWp, log burner and back boiler and 18 Ying Li 235 PV panels - 4.2kWp, 42kW ground mount PV, 9kW Panasonic ASHP
titan
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« Reply #40 on: December 18, 2016, 11:18:36 AM »

Your normal 4/5kw (electric) heat pump running for about 12 hours a day heating the house and water uses over £7 worth of electric per day. Thats why the RHI will pay you up to £6600 per year.

The RHI for heat pumps is only available where mains gas is unavailable. The payment is to offset the high capital cost of installation. Running costs are comparable to a gas system on normal rate electricity. It is part of the governments commitment to reducing emissions. Just checked, a GSHP is actually cheaper to run than gas
http://www.nottenergy.com/energy_cost_comparison/
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Mikel
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« Reply #41 on: December 19, 2016, 10:08:25 AM »

Don, we have an experimental control system installed as we volunteered for a DECC trial. We merely set the temperature we would like and the system sorts it out. I have programmed a schedule when we are In, Out and Asleep but in practice the system comes on overnight and during the day. We can program going away and it will turn off the heating and then bring the house back up to temperature for our return.

If you want to increase the temperature setting, the heat pump will run continuously raising the flow temperature quite high (up to about 45C) with long run times until the house reaches the new setting. It then just adds heat as required. We have far fewer heat pump cycles compared with the original system, which used weather compensation and set times of heating. This new system, as I understand it, takes the local weather forecast as part of its control system. Like you, we have a log burner and we normally set the thermostat to 16C for most of the winter and then boost for particularly cold spells.

In practice, we have a design SPF (as required by the RHI) of 3.1; the original control system gave a CoP of 3.2 (based on Feb 2014 data only); the experimental system has consistently given an average winter CoP of 3.4. BTW, the actual CoPs include DHW from the heat pump at 50C.

The advantage of volunteering for the trial was that we got a free monitoring system installed and I still get the data sent weekly even though the trial finished in 2015.
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ringi
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« Reply #42 on: December 19, 2016, 11:24:29 AM »

@Mikel,

What control system do you have?
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ringi
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« Reply #43 on: December 19, 2016, 11:27:13 AM »

Heat pumps often cost a lot more then gas heating to run, it all comes down to the building and how people live in the building.   There was an experiment some time ago with a social landlord fitting heat pump, but the tenant demanded they were removed, as the tenants could not understand that a thermostat was not a on/off switch…..

The building also needs to be well enough insulated and draft proofed that it makes sense to keep the building heated while people are out at work etc.   Otherwise the heat pump has to operate at a high flow temperature so at to reheat the building quickly.
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Mikel
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« Reply #44 on: December 19, 2016, 01:18:48 PM »

@ringi,

I do not have much detail for you. The company that installed the system put in an electricity meter and heat meter on the heat pump and an additional electricity meter on the house supply. There are a number of sensors around the house measuring various room temperatures and some modification to the heat pump itself. All the data collected is fed back to the company via our router.

I can provide program the temperature and schedule via a wireless control panel. I can also login to see the record of internal and external temperatures and the number and duration of heat pump usage.

The heat pump modifications were done with full knowledge and support of the manufacturer and I have a guarantee that the warranty would not be invalidated.

The control software is proprietary, so no details.

You make a very valid point that heat pumps are best at maintaining a consistent temperature rather than rapidly heating up as you would with gas or oil boilers.

If you are interested, I can post some example charts for days this month.
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