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HP Cycling, Expected or Undesirable

 
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Air Source Heat Pumps (ASHPs)
Last Post by bontwoody 2 years ago
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 HughF
(@hughf)
Honorable Member Member
Joined: 4 years ago
Posts: 489
10/07/2024 10:43 am  
IMG 5069
IMG 5072
IMG 5070
IMG 5071

Off grid on the isle of purbeck
2.4kW solar, 15kWh Seplos Mason, Outback power systems 3kW inverter/charger, solid fuel heating with air/air for shoulder months, 10 acres of heathland/woods.

My wife’s house: 1946 3 bed end of terrace in Somerset, ASHP with rads + UFH, triple glazed, retrofit IWI in troublesome rooms, small rear extension.


   
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 Anonymous 5011
(@Anonymous 5011)
Joined: 3 years ago
Posts: 562
10/07/2024 12:35 pm  

Just did a trial with the thermostat forced on. Set flow target to 26 and 3.0 Deg overshoot. Heat pump for just over an hour at 12 degs outside. Then it took a break for 1.5 hrs. So got a great increase in run time, have now reduced the overshoot to 2.5 degs to see effect. Will leave it running the rest of the day to see what it does and what it does to the house.



   
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bontwoody
 bontwoody
(@bontwoody)
Noble Member Contributor
Joined: 4 years ago
Posts: 1009
Topic starter 10/07/2024 4:13 pm  

@derek-m So I turned up the warm weather end of the WC curve to 33 C flow temperature and made sure the spare bedroom radiator was on. The cycling seems to be less now and probably within tolerance. I will have to check how to make some of the setting changes suggested with a Samsung and see how that affects things.

Thanks for all the help everyone.

image

House-3 bed partial stone bungalow, 5kW Samsung Gen 6 ASHP (Self install)
6.9 kWp of PV
5kWh DC coupled battery
Blog: https://thegreeningofrosecottage.weebly.com/
Heatpump Stats: http://heatpumpmonitor.org/system/view?id=60


   
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 HCas
(@hcas)
Estimable Member Member
Joined: 2 years ago
Posts: 132
10/07/2024 5:38 pm  

@bontwoody I've previously heard a rule of thumb to limit to 3-4 start/stops per hour. 
Maybe a stupid question: Do you need the heating today? How warm is it inside the home?


CEO and co-founder at HavenWise


   
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Toodles
 Toodles
(@toodles)
Famed Member Contributor
Joined: 4 years ago
Posts: 2727
10/07/2024 6:31 pm  

@hcas We were using ours yesterday as we felt 19 degrees C was just too cool with the addition of the rain! (South East England. Regards, Toodles.


Toodles, heats his home with cold draughts and cooks food with magnets.


   
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bontwoody
 bontwoody
(@bontwoody)
Noble Member Contributor
Joined: 4 years ago
Posts: 1009
Topic starter 10/07/2024 6:40 pm  

@hcas Well I guess that always going to be a subjective question 🙂 I do feel the cold as my circulation in my extremities isnt the best, but actually it was my wife who wanted it on today.  Its 22C indoors now which I know is way too hot for some, but we are never going to be comfortable at 19C like a lot of people. (Kiss my high COP goodbye!)

The heat pump is drawing less than 400W and our solar panels are producing way more than that so it is purely a matter of comfort rather than cost.

 


House-3 bed partial stone bungalow, 5kW Samsung Gen 6 ASHP (Self install)
6.9 kWp of PV
5kWh DC coupled battery
Blog: https://thegreeningofrosecottage.weebly.com/
Heatpump Stats: http://heatpumpmonitor.org/system/view?id=60


   
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Toodles
 Toodles
(@toodles)
Famed Member Contributor
Joined: 4 years ago
Posts: 2727
10/07/2024 6:46 pm  

@bontwoody That is pretty much the same as our situation; our comfort level is 22.5 degrees C. and 19 with rain just does not cut it for us! Toodles.


Toodles, heats his home with cold draughts and cooks food with magnets.


   
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bontwoody
 bontwoody
(@bontwoody)
Noble Member Contributor
Joined: 4 years ago
Posts: 1009
Topic starter 10/07/2024 6:51 pm  

@toodles At least we are living proof that heat pumps can heat a house toasty! 🤣


House-3 bed partial stone bungalow, 5kW Samsung Gen 6 ASHP (Self install)
6.9 kWp of PV
5kWh DC coupled battery
Blog: https://thegreeningofrosecottage.weebly.com/
Heatpump Stats: http://heatpumpmonitor.org/system/view?id=60


   
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 HCas
(@hcas)
Estimable Member Member
Joined: 2 years ago
Posts: 132
10/07/2024 6:55 pm  

Totally makes sense @bontwoody and @toodles! Comfort is #1. Location and person dependent.

With that in mind, you'll always have some cycling during milder weather. But based on your graph, looks like that is now under control.


CEO and co-founder at HavenWise


   
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 HughF
(@hughf)
Honorable Member Member
Joined: 4 years ago
Posts: 489
10/07/2024 10:08 pm  

We heat the house to 24-25 all winter and keep it at 22-23 the rest of the summer. The heating has been on for around 17hrs a day these last few days with the rain. We’re in the south west.


Off grid on the isle of purbeck
2.4kW solar, 15kWh Seplos Mason, Outback power systems 3kW inverter/charger, solid fuel heating with air/air for shoulder months, 10 acres of heathland/woods.

My wife’s house: 1946 3 bed end of terrace in Somerset, ASHP with rads + UFH, triple glazed, retrofit IWI in troublesome rooms, small rear extension.


   
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 Anonymous 5011
(@Anonymous 5011)
Joined: 3 years ago
Posts: 562
11/07/2024 9:11 am  

↑

We heat the house to 24-25 all winter and keep it at 22-23 the rest of the summer.

Our last house was similar, but this one is very well insulated and UFH throughout, now above 21 is starting to get a little to warm. Normally once the average temp increases to 10 degs that's when our heating goes off. Taking advantage of the cool July (11 today) to fine tune some cycling. 

 

Back on topic.

Did some adjustments yesterday. Increased the over temp margin above target temperature to increase run time got an hour+ run. Which is to long. But didn't restart again for over 18 hrs. So reduced the upper stop margin to 2.0 degs, but also decreased the undershoot temp to allow a sooner restart. Looking ideally for a 15 to 20 min run but not a massive off time other the summer houses too much. Bit of a balancing act.



   
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 Anonymous 5011
(@Anonymous 5011)
Joined: 3 years ago
Posts: 562
11/07/2024 6:12 pm  

Made some adjustments based on information provided here and on buildhub.

Prior to stating

Below Target start delta was 8 degs

Above Target stop delta was 0.4. 

Target flow temp 30.2. with a small WC curve rise to 35 flow at -3.

This morning it was close to 11 degs, which is above where I would normally heat. After some tuning got to 2 starts per hour and a 15 to 20 min run time. The sun came out at lunch and the heat pump hasn't restarted, living room at 21.6. ASHP return temp is sitting at 21.1. which is good as it's now self managing and matching output to required load 

So setting are quite different 

Below Target start delta is now 5.8 degs. Was 8 degs

Above Target stop delta is now 2.0 degs. Was 0.4 degs.

Target flow temp 25 at 14, with a WC curve to -5 and max flow temp of 32.6 degs. (Think the 32.6 may be a little high, but too warm to test)

Upside is it should run without any house thermostats and generally look after it's self. Once room temp is at 21 or above the heat pump should not get a permission to start heat. Have set the circulation pump run continuously, when not heating the flow rate drops to minimum flow, so should pull very little power.

Just need some warm weather to set up cooling.

So the take away are 

 1. An aspect never discussed is how the heat pump responds to target flow temp, and how this managed. Been through lots of different manuals to see what they say, most are silent.

2. What manufacturer default to, may be miles away from what is needed.

3. You don't have to suffer short cycling, it fixable with a little time.

4. Base running target temp has been reduced a whole 5 degs - which should see an uplift of 0.5 in CoP.



   
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