I have just had a Mitsubishi Ecodan R290 10 kW heat pump system installed. The system performance is excellent in most aspects, the house is warm, the temperatures are evenly distributed. An internal temperature of 22C at a flow temp of 35C and an external temp of 7C. Flow rate is 18 litres per minute and the delta T is 3C. However, under these circumstances the COP is 1.4.
There is no buffer tank.
It takes about 45 minutes to heat the 180 litre hot water tank to 50C, the COP for this is 1.2.
Does anyone have any suggestions why the performance is so poor.
It may be cycling on and off a lot. Do you have any graphs of the compressor frequency, water outlet/inlet temperature, other relevant data... over say a 24 hour period?
Grant Aerona 290 15.5kW, Grant Smart Controller, 2 x 200l cylinders, hot water plate heat exchanger, Single zone open loop system with TRVs for bedrooms & one sunny living room, Weather compensation with set back by room thermostat based load compensation
I cant remember what Ecodan reports but some heat pumps report energy consumed and environmental gain. In this case cop = energy consumed/(energy consumed + environmental gain). Still not good, just not so bad if it is that that the Ecodan reports.
Have you got any thermostats or TRVs operational which might cause forced cycling
Is there a LLH (low loss header) included in a Mitsubishi pre-plumbed cylinder which might cause system distortion. How many water pumps are there?
Whats your house floor area and construction which might indicate an oversized heat pump causing excessive cycling.
FWIW BUS requires a min SCOP of 2.8 so as it stands the system is not compliant and installer has to fix it. Probably worth understanding whats happening though,
4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.
I cant remember what Ecodan reports but some heat pumps report energy consumed and environmental gain. In this case cop = energy consumed/(energy consumed + environmental gain). Still not good, just not so bad if it is that that the Ecodan reports.
Have you got any thermostats or TRVs operational which might cause forced cycling
Is there a LLH (low loss header) included in a Mitsubishi pre-plumbed cylinder which might cause system distortion. How many water pumps are there?
Whats your house floor area and construction which might indicate an oversized heat pump causing excessive cycling.
FWIW BUS requires a min SCOP of 2.8 so as it stands the system is not compliant and installer has to fix it. Probably worth understanding whats happening though,
I am using my Powervault electricity monitoring App to monitor the electrical power, and I have calculated the heat transferred from the heat pump using the Mitsubishi data which gives flow rate, flow temp and return temp. See attached
I am using my Powervault electricity monitoring App to monitor the electrical power, and I have calculated the heat transferred from the heat pump using the Mitsubishi data which gives flow rate, flow temp and return temp. See attached
Heat transferred = F*DT*.0633=18*3*.0633=3.4kW Power consumed = 2.4kW
3.4kW delivered to the house is not unreasonable at current temperatures in a 7-10kW house, so that stacks up
However a 10kW heat pump wont consume anything like 2.4kW other than when its running flat out or if a supplementary immersion heater is running. Are you confident of this figure (I'm struggling to interpret figure 15 - the scale doesnt seem to tally with the numbers and there is no unit on the scale)? What power consumption does the ecodan itself report, are the compressor and fan at max or thereabouts and is there any possibility a supplementary heater is running? 2.4kW is a lot of energy to dissipate! Is this consistent with your meter readings - I reckon the average between 0 and 9 is 4kW (assuming the units are kW), which is 36kWh.
If these figures are correct then it is, as you say, a serious fault most likely with the machine itself.
This post was modified 3 weeks ago 5 times by JamesPa
4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.
It takes about 45 minutes to heat the 180 litre hot water tank to 50C, the COP for this is 1.2.
My 4KW Daikin will heat my 180L tank in 30 mins to 48C. Most likely less demand but in the ball park. The COP is not as mine reports 2 at worst.
I opened you first PDF and the first thing that jumped out was the Delta T of 3C. If you have UFH then OK but if you have rads then they should be between 5C (common) to 10C. The higher delta will allow your pumps to work more slowly. Do you have 2 or 3 pumps total (including the HP one if integral). That's a fair amount of power draw just there if trying to reach a Delta T of 3C.
I opened you first PDF and the first thing that jumped out was the Delta T of 3C. If you have UFH then OK but if you have rads then they should be between 5C (common) to 10C. The higher delta will allow your pumps to work more slowly. Do you have 2 or 3 pumps total (including the HP one if integral). That's a fair amount of power draw just there if trying to reach a Delta T of 3C.
Not sure I agree with that.
Thermodynamically lower deltaT=higher average emitter temperature for any given flow temperature = lower FT needed at the heat pump for any given emitter output = higher efficiency. Obviously this has to be traded off against the electrical power needed to drive the water pump, some folks on openenergymonitor did some calculations and for their particular set of circumstances deltaT of about 3 was actually the best trade off.
Many, possibly most, heat pump systems are designed for deltaT of 5 at the design OAT. With an OAT of 7 the DT will be correspondingly less, unless the heat pump modulates down the speed of the water pump (some do, some don't). DeltaT of 10 is, at least in my book, a last ditch measure if your pipework is too small, but this comes with an efficiency penalty of ~10% relative to deltaT of 5.
Mitsubishis dont have integral pumps to the best of my knowledge so OP has 2 pumps, not sure why. This may be contributing a bit but cant possibly explain 2.4kW power draw by the heat pump (apparently).
4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.
If the Delta T is easy to configure then just try it as you appear to have very good data collection as standard. So if the pumps are external and not included in the HP calculation then yeah that's very poor and needs addressing.
3.4kW is in line with calculations and data that I collected last winter before having the heat pump fitted.
I don’t have any way of extracting the power consumption data from the heat pump, but I am very confident that the power being consumed by the heat pump was at least 2.4kW, the Powervault App is reliableHowever, it gives total power for the house hence my allowance of 300W for the rest of the house. In figure 15 the scale on the left is kW, showing a peak of 13kW at just after midnight, this is 4.3kW battery charging, plus about 300W for the house, plus water heating, plus running the dishwasher. The next peak at about 1.30 is when the heating comes on, it then runs continuously until switched off at about 08.45.
The period between about 03.30 and 08.45 is just the heat pump and the house. I included a label showing the consumption at 08.20, 2.7kW.
The dip at 06.20 can be seen by a reduction in flow temperature in figure 8.
The energy consumption shown in Fig 15 is consistent with my meter readings.
The highest consumption that I have seen from the heat pump is over 5kW.
The Mitsubishi controller does not provide pump control modulation to vary the pump speed, hence the Delta T of 3 degrees, it is designed for Delta T 5C at -3C.
The Mitsubishi does not have a pump, hence my system has 2 pumps, which I find strange, but I don’t think that it could explain such poor performance.
In that case there is something very wrong. 2.4kW consumption would normally require the heat pump to be running nearly flat out. If its not doing so, then where is the energy going (it has to be going somewhere!).
There is really nothing more that I can say. Compressor or compressor control must be faulty so far as I can tell, that's the only part of the heat pump that can consume anything like 2.4kW, unless there is an element somewhere. If its this faulty its amazing its working at all or not making a racket/pouring out smoke.
