@kev-m 

For those interested, here is a closer look at the energy used.  Each cycle is remarkably consistent, with an initial peak and a smaller plateau then a drop to near zero. The data points the monitoring sends each have marker; stop, heating, hot water,  etc.  At the data points at the peaks, the marker says heating but at the plateaus, it's stop. I assume parts of the system are still going but others aren't?  The peaks are about 1.6kW. and the plateaus 0.9kW.  Any ideas?  

Good morning Kev,

Excellent data once more.

I'm not 100% certain, though you may be able to prove by simple observation of your ASHP (or if it is cold outside, get your wife to do the observing).

What I think may be happening is this:-

During the first peak, the compressor, the fan and the water pump will all be running.

At the lower plateau, the compressor has stopped, but the fan and water pump continue to run.

As I say, I don't know for certain, but observation may prove me wrong.

@derek-m if its like my system its topping up the water temperature and then just running the pump to push the warm water around. If you go into the operations settings you'll see the flow temperature is X during that time. There is no need to add heat to the water. Once its flowed round a bit, the compressor will probably kick on again as it'll cool down slowly.

I thought it wss worth comparing with a similar day last month. Here, the heating comes on in the morning and evening set to 21 degrees

Total power used is actually less than yesterday at 7.2kWh.  It's hard to make a comparison on one day however, especially when heating demand is so low. Also, here, the house was only warm for 3 or 4 hours; now it's warm for 24.  

Posted by: @batalto

@derek-m if its like my system its topping up the water temperature and then just running the pump to push the warm water around. If you go into the operations settings you'll see the flow temperature is X during that time. There is no need to add heat to the water. Once its flowed round a bit, the compressor will probably kick on again as it'll cool down slowly.

 

Hi Batalto,

What I suspect, though observation may prove me wrong, is that once the refrigerant gas is up to pressure and temperature within the condenser, the compressor will stop. The heat energy contained within the gas will start to be transferred to the central heating water and the gas will start to condense. The condensing gas will flow from the condenser into the evaporator, via the expansion valve. In the evaporator the condensed gas absorbs energy from the ambient air and in the process evaporates. For this process to continue, a fresh supply of ambient air is required, so the fan needs to continue operating for a while, until the useful energy has been obtained from the flow of gas and the fan would then stop. The specification data may show the power requirement needed to operate the fan at varying speeds.

The water pump of course would continue to run, but would probably only draw about 50 Watts of electrical energy.

I hope this makes sense.

Posted by: @kev-m

I thought it wss worth comparing with a similar day last month. Here, the heating comes on in the morning and evening set to 21 degrees

Total power used is actually less than yesterday at 7.2kWh.  It's hard to make a comparison on one day however, especially when heating demand is so low. Also, here, the house was only warm for 3 or 4 hours; now it's warm for 24.  

It's situations like this that make this subject quite grey (i.e. not black and white).

A good COP is not the be all and end all. Depending on how the property is occupied throughout the day it may be more economical to have a lower COP and have the pump run at higher flow temps for shorter periods of time.

Similar to your data I ran the ASHP for a month at 50ºC flow but had the heating set at 18ºC for 20 hours and 22ºC for 4 hours each day.

Resulting in a cooler house, COP at 2.7 but using less electricity.

By contrast I'm now using the curve, heating is 22ºC all day and night, COP currently around 5, but this will use more electricity I suspect.

@markc 

You are perfectly correct that it is very difficult to make comparisons of one day to the next, since no two days are exactly the same.

At the moment the weather is quite mild, so it may not be a good test of how well your ASHP is performing. As we have seen from the data kindly supplied by a number of active members, their heat pumps are still starting and stopping quite frequently. As the weather gets colder and the heat pumps run more frequently, it may be possible to obtain more meaningful results.

If you read the article that Jeff posted yesterday, you will see that part of the discussion was about occupancy. Is it necessary to fully heat an area if there is no one occupying it at the time?

At present on the forum, we are exploring the different ways in which an ASHP system can be operated for highest efficiency, but that may not equate to best economy.

As you all gain familiarity and confidence in how to operate and adjust your systems, you will be in a better position to decide how to operate your individual system to your specific requirements.

Agreed.  To use the car analogy, higher mpg is good but not if you have to drive a lot further.    

@kev-m 

I suppose what we need now is a day with a large temperature swing, say 10C or more. That will then allow the various members who have embraced weather compensation (and have gone over to the dark side), to see just how well it copes with a large change in ambient air temperature.

Other factors like solar gain, wind chill and rain effects should also be monitored if possible.

@derek-m my system always had weather compensation. For me the big issue was actually radiator balance as before that point I needed the high heat to get everywhere warm. Now I can easily turn down the weather comp

@derek-m from my experience, without a very large thermal mass, whether compensation will struggle with rapid, large fluctuations in the ambient temperature. Without this thermal mass to buffer it, do not expect a stable internal temperature. As stated before, low thermal mass buildings on radiators need load compensation or an internal thermostat.

Posted by: @heacol

@derek-m from my experience, without a very large thermal mass, whether compensation will struggle with rapid, large fluctuations in the ambient temperature. Without this thermal mass to buffer it, do not expect a stable internal temperature. As stated before, low thermal mass buildings on radiators need load compensation or an internal thermostat.

I don't disagree.

Hi Everyone,

For those of you considering having an MMSP system installed, here are a few aspects to consider.

Temperature measurement, whilst fairly straightforward, still needs to be installed correctly. If the temperature probe is to be mounted external to the pipework it is important to ensure that good thermal contact is achieved. The actual temperature sensor is normally located at the probe tip, so once in good physical contact with the pipework, it should then be adequately insulated from the surrounding air.

To achieve reasonably accurate flow measurement, the flowmeter needs to be mounted in the longest straight section of pipework that is accessible, with a length of at least 5 times the pipework diameter of straight pipework, before and after the flowmeter. i.e. If the diameter of the pipework is 15mm, then you need at least 75mm of straight pipework before and after the flowmeter. The accuracy of flowmeters can be affected by turbulence caused by bends and pipe fittings.

Reading some of the documentation about the MMSP package, it would appear that temperature measurement should have an accuracy of +/- 3% and flow measurement should have an accuracy of +/- 5%. So don't expect complete accuracy, in theory the heat energy measurement could have an accuracy of +/- 11%.

For those considering a DIY route, Googling 'heat energy meter' revealed quite a number of meters with prices ranging from £150, though I cannot comment on their performance.