Cop values, my air source

[tommy12398]

Thanks to everyone who replied to my last posts. (Getting rid of my ashp) 

Can anyone tell me the cop values of a heat pump in low temperatures say 0 and below.

They say my 14kw samsung has a cop well over 3.

But I'm not so sure. I found a survey of 17 heat pumps and the average cop in real world testing was just under 2.5! 

[JohnMo]

CoP depends on outside temp and flow temp.  In your last post I asked your flow temp but you never replied?

 

It also makes a big difference if the heat pump starts and stops, so how the house is zoned makes a difference.

[tommy12398]

I'm not that clued up. Will the flow temp be whats running around the system. That's around 45. 5 zones all on same setting 19 through day down to 17 through night

[JohnMo]

That could well be your issue.

 

You need to get rid of the zones, if your smallest zone is the only one asking for heat because the other thermostats have had their demand met, the flow will be too small for the ASHP and it will short cycle.

 

Plan of actions.

 

1. Have only two zones one upstairs one down stairs.  Wiring center will need to be modified, use a central thermostat as the controller.  You want all the loop actuators opening and closing at the same time, ideally all staying open.  Sort that in step 2

 

2. You need move your thermostats to say 24 degrees, so they do not affect anything.   Slowly reduce the flow temperature 2 degrees per 12 hours until your house (main living space) no longer gets hot enough.  You mentioned 19 degrees was your set point.  So keep reducing flow until your temp is only getting up to 18.  Then increase the flow temp up by 2. degree. 

 

3. Now some rooms will be hotter or colder than others, to increase room temperature your UFH flow needs to be increased, if too cold reduce the flow.  The flow gauge on the UFH manifold turn anticlockwise to increase flow.  Move it a half a turn, leave it for 24 house.

 

4.  Your thermostats are now to limit room temperature instead of control it, so set those to 20/21.

 

The above should reduce flow temperature, which will in turn increase CoP.

 

Short cycling in where the boiler/heat pump does not run long enough to fully heat up, the heat up cycle is the most inefficient, so short cycling is running for a few minutes, stop for 10, repeat.  A CoP of 1 or could be less may be seen.

[ReedRichards]

My heating controller imposes a minimum cycle time of 20 minutes.  So I don't think I have to worry about short cycling - and it might be the same for the OP.  In any case, for any heating cycle, long or short, my heat pump starts at around 2 kW of power draw and works its way up as the temperature of the output water increases.  If this water temperature never needs to get very high to satisfy whichever thermostat is calling for heat then it ought to be operating very efficiently.  

[JohnMo]

So what is your CoP?

[ReedRichards]

11 hours ago, JohnMo said:

So what is your CoP?

I have no way of knowing my CoP.  But based on a comparison with my former expenditure on oil, my SCoP must be approximately 3.