GSHP - I need help with making it as efficient as possible!

countryhouse39

Reed_Richards said:

If you got the RHI you should have an MCS certificate for your installation.  On the certificate it should tell you a flow temperature and an SCoP (Seasonal Coefficient of Performance) - or at least mine tells you this.   It would be helpful to know what these are (and whether the flow temperature currently being used is the same as on the SCoP).

we do have MSC certification, but it doesnt tell me this...just "Estimated Annual Generation (kWh): 40000.00

Declared Net Capacity (kW): 10.00"

michaels

Do you know how much hot water you actually use, our household of 5 use 12-15kwh compared to the EPC which I think is about 3000 like yours.  Hot water is particularly inefficient for heat pumps due to the higher temp required.

In terms of heating, we use a lot but probably max day is about 120kwh for gas heating - I would have thought with ground source your cop should never go below about 3 unless you need the flow really hot so it appears you are putting in huge amounts of heat or something is not working properly.  Has your demand been similar every year or has it increased over time (suggesting a fault)

Reed_Richards

countryhouse39 said:

Reed_Richards said:

If you got the RHI you should have an MCS certificate for your installation.  On the certificate it should tell you a flow temperature and an SCoP (Seasonal Coefficient of Performance) - or at least mine tells you this.   It would be helpful to know what these are (and whether the flow temperature currently being used is the same as on the SCoP).

we do have MSC certification, but it doesnt tell me this...just "Estimated Annual Generation (kWh): 40000.00

Declared Net Capacity (kW): 10.00"

Oh dear, they must have improved the MCS certificate since yours was issued.  Do you know what water temperature your heat pump was set up for? 

shinytop

countryhouse39 said:

Thanks for replies. Will have a look through the thread you suggested. Regarding the age of the heat pump its was installed in 2012. The previous occupants didn't even know about the RHI payments they could get so when we bought the house we applied and have been having them almost 7 years now and I'm sure that it said 7 years only, but I will double check!

Its a vaillant heat pump - 10kW geotherm. we have UFH downstairs (off 2 separate manifolds) all of which have room thermostats, and rads upstairs. Our EPC from just after we bought the house reckons we are a band C(73) and that our 'heat demands' are just under 40,000kwh for heating, 3000kwh for water. We use around 20000kwh a year which I think means that the COP is only about 2...when it should be better than that?

It is an old house that was extensively 'modernised' by the previous owner, however they left rolls of insulation uninstalled in the loft etc, but since we moved in we have installed more insulation, replaced most of the single glazing with double (at great expense as its a conservation area so very particular requirements!) and also changed the settings on the pump as when we first moved in they had the immersion heater on all the time (!) which meant we got a horrific first months bill as it was in the winter!

I don't have a GSHP but have an ASHP so similar.  The three things that make my ASHP work inefficiently are (1) cold weather (2) high flow temperatures and (3) working hard.  I get the best efficiency when the HP is running steadily at low-mid power and the flow temps are 35-40C.  I try and avoid letting the house heat up and cool down too much because that makes my ASHP work hard to warm it up and so keep the heating on most of the time.  I use weather compensation, which varies the flow temp according to the outside temperature; I don't know if you have this.  

Your COP probably should be better than 2 but you don't know what it is.  The EPC consumption is at best an educated guess and could be way out either way.

Is the 100kWh/day just for the ASHP? If it is, that's a run rate of more than 4kW, which is quite a lot for a 10kW GSHP to use.  I've never seen my 14kW ASHP use that much except when starting from cold; even at 2-3 degrees out it's using well under 3kWh to heat the whole house

Verdigris

I would be inclined to set the flow temperature at 35 degrees, which is the reference temperature that the official COP value derives from.

countryhouse39

michaels said:

Do you know how much hot water you actually use, our household of 5 use 12-15kwh compared to the EPC which I think is about 3000 like yours.  Hot water is particularly inefficient for heat pumps due to the higher temp required.

In terms of heating, we use a lot but probably max day is about 120kwh for gas heating - I would have thought with ground source your cop should never go below about 3 unless you need the flow really hot so it appears you are putting in huge amounts of heat or something is not working properly.  Has your demand been similar every year or has it increased over time (suggesting a fault)

not sure what our hot water usage is  - how would I separate that out? there are 5 of us (2 adults 3 small children) and demand has steadily gone up since we moved here but from approx 19000/year-20/21000 - (we originally had 1 small child..!) Most days in winter we use 100-120kwh of electricity total  - we both WFH so some of that is all the other stuff, but in summer our kwh usage is max 25 a day. 

countryhouse39

shinytop said:

countryhouse39 said:

Thanks for replies. Will have a look through the thread you suggested. Regarding the age of the heat pump its was installed in 2012. The previous occupants didn't even know about the RHI payments they could get so when we bought the house we applied and have been having them almost 7 years now and I'm sure that it said 7 years only, but I will double check!

Its a vaillant heat pump - 10kW geotherm. we have UFH downstairs (off 2 separate manifolds) all of which have room thermostats, and rads upstairs. Our EPC from just after we bought the house reckons we are a band C(73) and that our 'heat demands' are just under 40,000kwh for heating, 3000kwh for water. We use around 20000kwh a year which I think means that the COP is only about 2...when it should be better than that?

It is an old house that was extensively 'modernised' by the previous owner, however they left rolls of insulation uninstalled in the loft etc, but since we moved in we have installed more insulation, replaced most of the single glazing with double (at great expense as its a conservation area so very particular requirements!) and also changed the settings on the pump as when we first moved in they had the immersion heater on all the time (!) which meant we got a horrific first months bill as it was in the winter!

I don't have a GSHP but have an ASHP so similar.  The three things that make my ASHP work inefficiently are (1) cold weather (2) high flow temperatures and (3) working hard.  I get the best efficiency when the HP is running steadily at low-mid power and the flow temps are 35-40C.  I try and avoid letting the house heat up and cool down too much because that makes my ASHP work hard to warm it up and so keep the heating on most of the time.  I use weather compensation, which varies the flow temp according to the outside temperature; I don't know if you have this.  

Your COP probably should be better than 2 but you don't know what it is.  The EPC consumption is at best an educated guess and could be way out either way.

Is the 100kWh/day just for the ASHP? If it is, that's a run rate of more than 4kW, which is quite a lot for a 10kW GSHP to use.  I've never seen my 14kW ASHP use that much except when starting from cold; even at 2-3 degrees out it's using well under 3kWh to heat the whole house

we do have weather compensation - not sure i fully understand it and if its set up most efficiently though!

countryhouse39

Reed_Richards said:

countryhouse39 said:

Reed_Richards said:

If you got the RHI you should have an MCS certificate for your installation.  On the certificate it should tell you a flow temperature and an SCoP (Seasonal Coefficient of Performance) - or at least mine tells you this.   It would be helpful to know what these are (and whether the flow temperature currently being used is the same as on the SCoP).

we do have MSC certification, but it doesnt tell me this...just "Estimated Annual Generation (kWh): 40000.00

Declared Net Capacity (kW): 10.00"

Oh dear, they must have improved the MCS certificate since yours was issued.  Do you know what water temperature your heat pump was set up for? 

no idea what it was set up for, no.

countryhouse39

Verdigris said:

I would be inclined to set the flow temperature at 35 degrees, which is the reference temperature that the official COP value derives from.

if I set it at 35 deg that's a lot lower than it seems to be currently, so would i nee to do anything else to ensure we arent freezing..? Also, we have weather compensation, does that effect the flow temp? thanks

Reed_Richards

shinytop said:
I don't have a GSHP but have an ASHP so similar.  The three things that make my ASHP work inefficiently are (1) cold weather (2) high flow temperatures and (3) working hard.  I get the best efficiency when the HP is running steadily at low-mid power and the flow temps are 35-40C.  I try and avoid letting the house heat up and cool down too much because that makes my ASHP work hard to warm it up and so keep the heating on most of the time.  I use weather compensation, which varies the flow temp according to the outside temperature; I don't know if you have this. ... 

(1) You have a GSHP so it will be much less sensitive to the weather outside than an ASHP.
(2) This is an intrinsic property of all heat pumps, the higher that water flow temperature the less efficiently and economically they perform.
(3)  This is true for @shinytop but it may or may not be true for all heat pumps.

The thing that you can do that will work for all heat pumps is to make sure the water temperature you are using is not higher than it needs to be.  Since the temperature it needs to be will depend on the outside temperature hopefully your heat pump will incorporate 'Weather Compensation' which automatically adjusts the maximum water temperature according to the outside temperature.   This feature may or may not have been engaged and may or may not have been set-up optimally.