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Air Source Heat Pumps (ASHPs)
Last Post by Derek M 4 years ago
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 Derek M
(@derek-m)
Illustrious Member Member
Joined: 4 years ago
Posts: 4427
01/12/2021 11:12 pm  

@mike-patrick 

Hi Mike,

Thanks for the reply. There is no problem with the delay in replying, I realise that people are busy, it is when they don't have the common courtesy to reply that I find annoying.

I am pleased to hear that you are becoming more confident when making adjustments to the controller, it can be quite traumatic the first time. I still remember the first time I made adjustments to the control systems for a 500MW generating unit, when it was in full operation.

A further problem is that most end users, and it would appear many of the installers, don't fully understand the terminology, and what adjustments may be necessary, and how to make them.

It may be useful if I explain the data that you collected.

00 Circulating water return temperature - as the name suggests, this is the temperature of the water coming back from the heat emitters. So the water coming back to the heat pump is at a temperature of 32C.

01 Compressor operating frequency - this is a measure of how fast the compressor is running. As I am no doubt your are aware, the mains frequency is 50Hz, so the compressor is running at just over 1.5 times the speed at which it would be operating, if it were fed from a mains supply directly. It may be useful to record the frequency when the compressor is running at full speed, so you can gauge how hard the compressor is working.

02 Discharge temperature - I do believe that this is the temperature of the refrigerant gas coming out of the compressor on its way to the condenser.

03 Power consumption - this is self explanatory.

04 Fan control number of rotation - this is the speed of the fan in rpm, which, like the compressor, can also be varied.

05 Defrost temperature - I presume there is a sensor within the ASHP that decides when the unit needs to operate the defrost cycle.

06 Outdoor air temperature - this is self explanatory.

07 Water pump control number of rotation - this is the speed of the pump in rpm, which, like the compressor, can also be varied.

08 Suction temperature - this is the temperature of the refrigerant gas coming out of the evaporator on its way to the inlet of the compressor.

09 Circulating water flow temperature - as the name suggests, this is the temperature of the water going out to the heat emitters. So the water coming out from the heat pump is at a temperature of 39C.

Looking at the above data, at an ambient air temperature of 4C, a water flow temperature of 39C seems a little on the high side, but of more concern is the fact that a 9kW ASHP is drawing 2.8kW of electrical energy, which would indicate that the unit is working near its maximum output or that the COP is quite low.

What is the total floor area of your home? Do you have any heat loss calculations or what is the level of insulation? What are the type and size of all the heat emitters?

I would suggest that you try raising the setting of one of the thermostats by 1C again, and seeing if the temperature in that room still increases. This would indicate that the weather compensation requires further adjustment to lower the water flow temperature.

It would also be useful to record further sets of data at different ambient air temperatures, to quantify how the system is responding.

I will leave you to carryout the above as time permits, and will be here to assist, as necessary, in the future.

 


   
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