I don't have thermostats but I do have a Vaillant sensoComfort which I believe acts as some kind of thermostat. It is used to set temperatures for house and the Hot Water. I do have TADO smart TRVs which I have used to set up my zones. I have a TADO extension kit but it is disabled at the moment while Vaillant investigate my COP.
The data I have is from the Vaillant sensoApp and the Passive Living monitoring Vaillant have installed to investigate the COP.
I haven't got Passive data for the occasion the the system drew 4kW, it was way back just after install, but on a scan of the data the other maximum is 3kW and at various times when the flow temperature was high 40s with outside temperature 3 degrees. this is a random selection so Id have to study a lot of the data to be more certain of the results.
Other than the low COP I am very happy with the system so far.
I did read that the R290 refrigerant performs better at lower temperature than other refrigerants it range is quote as -25 to +46. is the just waffle or is there evidence that it is so?
There are three main factors which affect the efficiency of a heat pump, the heat demand (heat loss), the size and type of your heat emitters, and the difference between the indoor temperature and the outdoor temperature.
The heat demand increases as the outdoor air temperature falls, and hence the heat pump has to work harder.
If the heat emitters are undersized, or the water flow through them is being restricted by TRV's or partially closed valves, then the heat pump will need to produce a higher water flow temperature to meet the heat demand.
If your systems requires a water flow temperature in the high 40's at an outdoor temperature of 3C, then it is possible that one of the above parameters is not quite correct.
I really hope I'm not putting you to any bother Derek.
1a) the COP via the Vaillant sensoApp is calculated by dividing the sum of Electrical Consumption and the Yield by the Electrical Consumption.
1b) the PassiveLiving divides the Energy Produced by the Energy Consumed.
The figures form both are pretty close apart from small rounding error.
The sensoComfort stays in the lounge on a table
At Install I changed (upgraded from K2 to K3 or P+ to K2) a number of radiators in line with the MCS spreadsheet for the losses against required temps for each individual space. I only have radiators.
The other parts of your reply I think points to the problem Vaillant are working on. when we have set the maximum flow temperature to 50 or even 45 it has no effect on the flow temperatures observed in the PassivLiving kit.
I really hope I'm not putting you to any bother Derek.
1a) the COP via the Vaillant sensoApp is calculated by dividing the sum of Electrical Consumption and the Yield by the Electrical Consumption.
1b) the PassiveLiving divides the Energy Produced by the Energy Consumed.
The figures form both are pretty close apart from small rounding error.
The sensoComfort stays in the lounge on a table
At Install I changed (upgraded from K2 to K3 or P+ to K2) a number of radiators in line with the MCS spreadsheet for the losses against required temps for each individual space. I only have radiators.
The other parts of your reply I think points to the problem Vaillant are working on. when we have set the maximum flow temperature to 50 or even 45 it has no effect on the flow temperatures observed in the PassivLiving kit.
Thanks for your advice
Hi Duncan,
It is no bother, my goal is to help as many people as possible to reduce their energy consumption.
Do you know to which of the various heat curves your system has been set? For most systems the 0.6 or 0.8 setting would probably be a good start.
Check that none of the TRV's or lock shield radiator valves are partially closed in the room in which your SensoComfort controller is located.
Keep a record of the water flow temperature at different outdoor air temperatures, along with the COP value. This will help to identify if any changes actually improve efficiency.
I live in the South West of Scotland and originally I was repeated told that the heat curve should be 1.2, but recently as part of their investigation I was asked to activate the Adaptive Heat Curve and make the Heat Curve 0.8. after a week the system had changed the Heat Curve to 1.29. I was the told to deactivate the AHC and make the Heat curve 0.8 its been that way for over a month now.
Im sure the TRVs and lock shields are performing the way they should.
LOL I have spreadsheets of data on everything.
My MCS Certificate quotes my system to have a SCOP of 3.91 however in the 9 months the system has been running, late April till now, I the very best monthly COP I have achieved is 3.0 (June 2021) with the SCOP since install currently standing at 2.52.
Am I being unrealistic to expect something closer to the 3.91?
I estimate the extra cost to buy electricity over what the MCS certificate says is currently about £100 but this is only because I am on the TESLA Energy plan and only paying 11p per kWh.
I know the system works but I was hoping for even better results.
Please be honest if the think I'm being ridiculous over this.
Probably the best way to set up the weather compensation curve would be to open all the radiator valves fully (both ends), except on the radiators in any used bedrooms. Allow the room temperatures to stabilse, and then see which room is the coolest. If the temperature in the coolest room is above the desired temperature, then lower the heat curve until you achieve the desired temperature.
What size and type of radiators do you have?
If you wish to send your spreadsheet data I can see if there is any apparent reason for low COP values.
I live in the South West of Scotland and originally I was repeated told that the heat curve should be 1.2, but recently as part of their investigation I was asked to activate the Adaptive Heat Curve and make the Heat Curve 0.8. after a week the system had changed the Heat Curve to 1.29. I was the told to deactivate the AHC and make the Heat curve 0.8 its been that way for over a month now.
Im sure the TRVs and lock shields are performing the way they should.
LOL I have spreadsheets of data on everything.
My MCS Certificate quotes my system to have a SCOP of 3.91 however in the 9 months the system has been running, late April till now, I the very best monthly COP I have achieved is 3.0 (June 2021) with the SCOP since install currently standing at 2.52.
Am I being unrealistic to expect something closer to the 3.91?
I estimate the extra cost to buy electricity over what the MCS certificate says is currently about £100 but this is only because I am on the TESLA Energy plan and only paying 11p per kWh.
I know the system works but I was hoping for even better results.
Please be honest if the think I'm being ridiculous over this.
My MCS calculation spreadsheet shows a COP of 3.3, which claims to be the 'manufacturers SCOP' I don't know where they got the number from. The MCS certificate has 3.7 and I know this comes from the link below, using my ASHP and my average flow temperature at design conditions, which was 45 deg. You can look up your ASHP.
I don't know exactly how these numbers are calculated but they should be following the same standard. However ...
These COPs are steady state values under test conditions. There are a lot of factors that reduce that in real life, e.g.
- cold starts (1). These test figures assume flow and return are quite close, maybe 5 degrees. If you're heating up flow from say 20 to 40, COP will be reduced.
- cold starts (2). ASHPs can be less efficient when they are working flat out. Mine definitely is. When the ASHP starts up it may try and work extra hard when it 'knows' it has a lot of work to do. Mine definitely does this.
- defrosts. Can add 10-15% to electricity consumed in the right (wrong?) conditions.
- Hot water. If your calculations include DHW it may drag the COP down if your HW set temperature is high. (I just realised today that when my ASHP is on 'normal' DHW setting, it will increase the flow to maximum - 55 degrees - until the set DHW temp is met. This works quickly but the COP is low. 'Economy' setting doesn't do this.)
- heat losses from pipes, electricity to run pumps
I'm achieving the number quoted on the MCS calcs but not quite the one on the certificate. I'm getting a COP of about 3.5 at the moment for heating and HW combined when it's 7-8 degrees outside. But my flow temps are low at about 36 deg and the COP will go down when it's colder.
I do believe that you should be getting higher COP values than you are doing so at present.
If everything is set up and functioning correctly, I would anticipate that you should be getting a COP of between 3 and 4 under the present weather conditions. That is assuming that your heat loss calculations are reasonably accurate and your heat emitters are not being restricted.
Check for drafts and other forms of heat loss that may be higher than calculated.
I have attached a spreadsheet that will give some idea of how the required water flow temperature and hence COP varies under different operating parameters. Column B is the outdoor air temp., Column C is the calculated heat demand, Column D shows the estimated COP, LWT and power input. I have set the parameters in C1, H1 and P1 based on the information that you provided, but by varying these values you can see the effect in Column D. The data is for Midea ASHP's but should not be too far away from the Vaillant data. Sheet 1 is for an 8kW heat pump and sheet 2 is for a 6kW one.
Do you have a buffer tank or low loss header in your system along with additional water pumps? If you get mixing of the flow and return water it can reduce the temperature of the water going to the radiators, which in turn means that the heat pump needs to produce warmer water to meet the heat demand.
If you have a suitable thermometer then try measuring the temperature on the pipework going into and coming out of each radiator. Then compare these readings to the flow and return temperatures on the pipework connected to your heat pump. The temperature of the water going into your radiators should be approximately the same a the water flow temperature, and the temperature of the water coming out of the radiators should be approximately the same as the water return temperature. Even a few degrees difference would possibly indicate some mixing within the Decoupler.
