What's your monthly SCOP

NedS

Spies said:

Worst days COP so far was Thu 9th Jan, generated 124kWh of heat for 52kWh of electric = 2.38, average unit rate for that day was around 19.5p meaning 8.19p per unit of heat so slightly more expensive than gas on that day. 

We've managed to stay just above the psychologically meaningless value of 3, with 3.06 on the 8th and 3.10 on the 9th. My heat pump is nicely oversized for the property, so we've been running flow temps of 30C overnight, and 32-35C during the day which has helped keep the COP above 3 (just!) on the coldest of days.

michaels

NedS said:

Spies said:

Worst days COP so far was Thu 9th Jan, generated 124kWh of heat for 52kWh of electric = 2.38, average unit rate for that day was around 19.5p meaning 8.19p per unit of heat so slightly more expensive than gas on that day. 

We've managed to stay just above the psychologically meaningless value of 3, with 3.06 on the 8th and 3.10 on the 9th. My heat pump is nicely oversized for the property, so we've been running flow temps of 30C overnight, and 32-35C during the day which has helped keep the COP above 3 (just!) on the coldest of days.

Isn't the flow temp (and thus efficiency) about the power output of the rads compared to the heat loss rather than the size of the heat pump (as long as it is sufficient)?

NedS

michaels said:

NedS said:

Spies said:

Worst days COP so far was Thu 9th Jan, generated 124kWh of heat for 52kWh of electric = 2.38, average unit rate for that day was around 19.5p meaning 8.19p per unit of heat so slightly more expensive than gas on that day. 

We've managed to stay just above the psychologically meaningless value of 3, with 3.06 on the 8th and 3.10 on the 9th. My heat pump is nicely oversized for the property, so we've been running flow temps of 30C overnight, and 32-35C during the day which has helped keep the COP above 3 (just!) on the coldest of days.

Isn't the flow temp (and thus efficiency) about the power output of the rads compared to the heat loss rather than the size of the heat pump (as long as it is sufficient)?

Yes, but because the heat pump puts out more heat than the house needs, we can only run continuously once ambient temps fall to around 5C and below. This is the first time since installation last summer that we've been able to run constantly without overheating the house. As you say, that doesn't really alter the efficiency as long as any runs are reasonably long (not short cycling)

matt_drummer

A bit early again.

SCOP for January is 4.50

Includes space heating, DHW, circulation pump and controller as usual. MID certified also as usual.

Electricity consumed is 493kWh at a cost of £34.51 (at 7p per kWh on IOG)

Gas would have cost about £158 (including the standing charge) at 6p per kWh and a boiler efficiency of 90%

Heat produced is 2,216kWh

Average outdoor temperature was 3.5c and the room temperature measured in a bedroom was 19.7c, downstairs is about 2c warmer.

michaels

matt_drummer said:

A bit early again.

SCOP for January is 4.50

Includes space heating, DHW, circulation pump and controller as usual. MID certified also as usual.

Electricity consumed is 493kWh at a cost of £34.51 (at 7p per kWh on IOG)

Gas would have cost about £158 (including the standing charge) at 6p per kWh and a boiler efficiency of 90%

Heat produced is 2,216kWh

Average outdoor temperature was 3.5c and the room temperature measured in a bedroom was 19.7c, downstairs is about 2c warmer.

The 3.5C is considerably the coldest for several years too so a great result

Our heat meter is definitely not reading right - any suggestions for how to check the input and output temps compared to the meter temperature readings?

FreeBear

michaels said: Our heat meter is definitely not reading right - any suggestions for how to check the input and output temps compared to the meter temperature readings?

Are you able to read the meter at regular intervals and log the data ?

My L&G T230 updates every 5 minutes, and I had been getting some erratic plots. Popped a new one in, and the curves are much smoother. The old meter was a 2.5m³/h (1"BSP connection), whilst the replacement is rated at 1.5m³/h (3/4"BSP). Not sure if my problem was related to a faulty meter or turbulent flow..

Popping the temperature sensors in a bowl of water & crushed ice should give you reading close to 0°C - Not all meters will display the flow/return temperatures, so you'll need to read the manual.

NedS

SCOP for January is 3.55 including pumps/controller etc, or 3.95 for just the heat pump (useful for comparison with oil/gas).

Electrical usage (MID meter) for the heat pump alone was 512.45kWh, total house usage was 742.32kWh at a cost of £146.77 (average 19.8p, Octopus Cosy tariff)

Heat produced was 2019kWh, which would have cost £146.71 for a gas boiler at the current price cap, assuming a gas boiler of 90% efficiency. That's the same as our whole house electricity bill.

Even at the Ofgem price cap of around 25p per kWh, a COP of 3.95 breaks even with the price of oil/gas. If you can reduce your electricity unit costs using TOU or heat pump tariffs, then savings are possible.

As this is my first winter, I'm really happy to see a COP of above 3 for what is likely the coldest month. On the coldest (worst) day, we achieved a COP of 3.05 (3.35 for just the ASHP, excluding pumps etc), and broke even with the price of gas. We were only able to achieve this by keeping the flow temps low. We are running 32C flow temps during the day, bumping up to 35C in the cheap Cosy slots as required. We set back to 30C overnight, turning off between midnight and 4am (unless it's below freezing overnight), turning back on for the cheap Cosy slot at 4am. The house was maybe 1C cooler than ideal on the coldest day, but we kept the COP above 3.

We generated around 100kWh of heat on the coldest day, (average around 0C I'm guessing) giving a heat loss of around 4.2kW. This compared to our heat loss survey of 7.4kW for our installed 12kW heat pump - so somewhat oversized! However, I'm coming to appreciate this is no bad thing - even on the coldest days, the heat pump is barely idling and this helps minimise defrosts. Heat pumps are also more efficient when the compressor is running in the 30-70% range, not to mention the reduced noise. The other thing to consider is the ability to reheat rather than merely maintain the house temperature. We are able to recover quickly when the heat pump is not performing space heating due to DHW cycles, and we also switch off for 3h during the peak Cosy slot of 4-7pm during which time the house temp does drop significantly. If the heat pump was not oversized, we may struggle to regain that lost heat on the coldest of days, not to mention what would happen if there were an extended power cut during the coldest winter period and the house got really cold - the system may really struggle to bring the house back up to temp.

Spies

January Scop 2.93

My Daikin Altherma 6kw produced 2582kWh heat for 880kWh electricity in January, however  the second half of the month I decided to setback an extra degree to 17c and have an automation raise the LWT by 4c when in an IOG period so this will have hurt the COP a little, but brought costs down overall

On the hot water side I can't reliably tell because the graph only shows the maximum value, which was in December, however I decided to allow the immersion to kick in after 30 mins if the tank wasn't up to temperature due to defrosts causing the HW to not reach required temperature, this did use more electricity than in December by around 10kWh

If I had to make an educated guess, the water SCOP is about 1.9

matt_drummer

I can split my space heating and DHW so for January my space heating was 4.58 and DHW was 3.69.

As I use a heat meter, it also records negative heat (the heat taken from the house to remove ice from the heat pump) from defrosting, the heat produced is what actually ended up in the house. Data from the Daikin MMI and all other manufacturer data doesn't take account of heat lost to defrosting.

Your 6kW Daikin should do better. Raising the lwt by 4c will certainly reduce the COP, are you sure it actually reduces costs?

Spies

I'm trying to bring the temperature up from 17c to 19c at the end of the IOG period (1c in 1 hour) in order to avoid the peak rate, I then have the temperature set to 20c from 8am and I plug the car in around then to get the IOG rate again, the theory being you use more energy to increase the temperature, then when the IOG rate finishes it can just tick away maintaining it.

IOG is 7p
Peak is 26.84p