Criticisms please

[Beelbeebub]

We managed about 16kwh/day average for heating and DHW over a year.

 

130m2 "dorma bungalow", 8" glass wool cavity fill between alight blocks. 12" same in roof with 2" of wood fiber over the top. 8" of XPS foam under floor slab with beam and block. 

 

High performance DG windows (not triple). Very air tight with MHRV.

 

Solar thermal panels for summer DHW and a (rarely used) wood stove that coukd feed the heating and DHW in winter.

 

Our winter peak use was obviously higher than 16kwh/day as some summer days we used 0kwh gas.

 

 

[waxingsatirical]

Just to be clear, 15.5kWH is the energy drawn by the heat pump not the heat loss for the house.

 

But yes, it does seem low, the house is not especially well insulated, it's a mix of filled cavity/unfilled cavity, pretty-well draughtproofed though and loft-insulation is good. It's a semi and a cube, so that helps, and only 1500sqft.

 

I'm now thinking that the heat-pump is under-estimating the energy it's generating. I don't know how it's working it out. I guess the difference between flow and return temp multiplied by the flow rate. Would explain the low heat-loss and the poor COP.

 

I put the hot water on the immersion for a few days, to take that out of the equation, and it didn't make much of a difference to the COP, still only just above 3.

 

Also, my COP figures are "energy-weighted", meaning I take a day's worth of energy out and divide it by a days worth of energy in. So this would give a lower COP than "time-weighted", where you would take multiple readings of the COP throughout a day and average them.

[SteamyTea]

2 hours ago, waxingsatirical said:

I guess the difference between flow and return temp multiplied by the flow rate

SHC of water (~4 kJ.kg^-1.K^-1) x Flow Rate (kg.day^-1) x Delta T (Flow Temp - Return Temp) x 0.00027778 = kWh.day^-1

 

  

2 hours ago, waxingsatirical said:

Also, my COP figures are "energy-weighted"

I think that is the proper way to do it, though I am not sure if that is how the Seasonal Performance is calculated.

 

 

Edited December 30, 2024 by SteamyTea

[PhilT]

18 hours ago, waxingsatirical said:

Just to be clear, 15.5kWH is the energy drawn by the heat pump not the heat loss for the house.

 

But yes, it does seem low, the house is not especially well insulated, it's a mix of filled cavity/unfilled cavity, pretty-well draughtproofed though and loft-insulation is good. It's a semi and a cube, so that helps, and only 1500sqft.

 

I'm now thinking that the heat-pump is under-estimating the energy it's generating. I don't know how it's working it out. I guess the difference between flow and return temp multiplied by the flow rate. Would explain the low heat-loss and the poor COP.

 

I put the hot water on the immersion for a few days, to take that out of the equation, and it didn't make much of a difference to the COP, still only just above 3.

 

Also, my COP figures are "energy-weighted", meaning I take a day's worth of energy out and divide it by a days worth of energy in. So this would give a lower COP than "time-weighted", where you would take multiple readings of the COP throughout a day and average them.

Do you know how much gas you used last Dec? That will give you a broad sense check. This Dec is very similar re temperature and weather conditions, in my area at least. 

[SteamyTea]

8 hours ago, PhilT said:

This Dec is very similar re temperature and weather conditions, in my area at least. 

Sometimes when I go up to Aylesbury, which is frequently, it is lovely and warm, other times, really cold.  Down here it seems to have been just wet.

[PhilT]

3 hours ago, SteamyTea said:

Sometimes when I go up to Aylesbury, which is frequently, it is lovely and warm

Yes the number of new houses that have been built is so huge, it all acts like a gigantic storage radiator