Observations Commissioning ASHP

[JohnMo]

Long while no update.

 

Messed about with hybrid (gas and ASHP) last winter and after doing the total running costs, decided I was approx £100 plus to have a hybrid system, mostly due to additional standing charges - so gas has to go. Meter being disconnected tomorrow, by Octopus at zero cost to me.

 

Ignoring the hybrid settings, current settings are 

No thermostat, WC on heating and WC on cooling (very small amount of 0.5 Deg flow temp change). Change over (between heat and cool) by a single repurposed light switch.  In addition to that I have a second set point which adds 3 degs to heating curve and 1 Deg is removed from cooling curve, this activated by a Shelly relay if I have excess solar PV.

 

CoP when running has been great, high 4s to high 5s. When coupled with standby time it hasn't been the best (measuring all electrical input in the ASHP system and heat meter). So heating CoP overall was mid 3s. Cooling high 3s.  However between heat pump cycles the circulation pump was kept on, with pump, valve, performance monitoring and other stuff drawing 117W during standby. Switching the pump off with everything else on, brings the standby down to 31W. 

 

So to fix the issue I have implemented the circulation pump to run in sniffer mode, so circulation pump runs for 4 mins after heat pump compressor has stopped and then stays off for 40 minutes, before starting again.  If heat pump senses the return temp isn't within limits the heat starts again.

 

Current running cooling and in the last 24 hrs including one DHW heat cycle at night (15 degs) the daily CoP has increased to 4.91.

 

A similar average temp day a week ago the CoP was 3.88, with one DHW cycle in the day at 20 degs. So CoP has increased a full point. Rough calculation is a saving of about £50 per year.

[-rick-]

Good result.

 

I assume you are just running the pump in an on/off form. Any thoughts about speed control? Reason for mentioning is when I've thought about what I might want to do, if it ever happens, is that the pump might serve as a useful way to distribute heat/cold between rooms to try and keep things equalised despite some rooms having higher heatloss/gain than others.

 

Edit: Clarification, idea being that to do that equalisation you'd likely want to run the pump more than for a short period every 40 mins. Running slow for longer might be better than more frequent full on pulses. I've done no maths on this as don't want to start detailled work until I actually have a project.

Edited Wednesday at 20:29 by -rick-

[JohnMo]

5 minutes ago, -rick- said:

Good result.

 

I assume you are just running the pump in an on/off form. Any thoughts about speed control? Reason for mentioning is when I've thought about what I might want to do, if it ever happens, is that the pump might serve as a useful way to distribute heat/cold between rooms to try and keep things equalised despite some rooms having higher heatloss/gain than others.

The controller does all the on off stuff, the pump also run variable speed, more so in heating than cooling. It has various control strategies for the circulation pump. So it's currently on periodic running and proportional regulation.

 

 

An hour or so of the data from the heat pump monitor 

The flow rate is the light blue line. Speed control works trying to control dT. 

 

My main reason for running 24/7 was to distribute heat evenly, but the intermittent nature doesn't seem to affect the way the house feels. So at the moment I see no reason to pay for it to run it.

 

 

[ReedRichards]

Are you sure your cooling actually has an effect?  On another thread, you suggested that because it was 30 C outside and 22 C (or so) inside that it did, but I achieve exactly the same with no cooling whatsoever.  I presume this is because the thermal mass of my house keeps the inside temperature nearer the average outside temperature rather than following all the outside peaks and troughs.  We also use window blinds to limit solar gain.  

[JohnMo]

2 minutes ago, ReedRichards said:

Are you sure your cooling actually has an effect?  On another thread, you suggested that because it was 30 C outside and 22 C (or so) inside that it did, but I achieve exactly the same with no cooling whatsoever.  I presume this is because the thermal mass of my house keeps the inside temperature nearer the average outside temperature rather than following all the outside peaks and troughs.  We also use window blinds to limit solar gain.  

Yes definitely has an effect. The floor surface temperature is maintained at around 18 degs through out the building. We have massive windows 30m²+ in the lounge. Compared to pre heat pump cooling, when we struggled to keep room temperature in check, would get to 27 most sunny days and that was with the blinds closed. Now even when it is hot air temperature wise you feel it's cooler. Room temperature doesn't get as hot and it recovers relatively quickly. It's not Aircon, but you also don't have a continuous draft either. Makes the house a comfortable environment to be in. Without the need for external blinds etc.

[marshian]

On 17/07/2024 at 15:48, JohnMo said:

Forgot to include the weather compensation curve.

 

It starts at 10 degs OAT at a target flow temperature of 26 degs and goes down to -5, where flow is 31 degs. So flow temperature increases 0.33 degs with every degree drop in OAT. 

 

Really interesting @JohnMo  and prompted me to work mine out - good way of looking it it