Luke1 Posted December 6, 2022 Share Posted December 6, 2022 I'm not sure of the ability of other heat pumps, however I have the ability to adjust the compressor curve in the service menu. (It has an auto setting) From what I understand, it is generally better to run a heat pump for a longer duration, and that is certainly how you can see "Heat Geek" using their heat pump. https://emoncms.org/heatgeek My system in auto mode would generally cycle the heat pump 35 mins on, 20 mins off. In which time the flow temperature would go from 32C to 42C as the 'degree minutes' catch up. Now I have adjusted my compressor curve for heating so that the maximum output it can generate is generally only 1-2C higher than the required flow temperature, leading to much longer run times. So do we think I will get a better COP this way, or by letting the controller manage the compressor curve itself? Im tempted to think manually controlling the compressor curve is better because I can get a better COP if the system doesn't have to heat way over the required flow temperature to catch up the degree minutes. (I have noticed that is the degree minutes still end up over 150mins then it does go above the compressor curve to catch up with the degree minutes again) Link to comment Share on other sites More sharing options...
SteamyTea Posted December 6, 2022 Share Posted December 6, 2022 Interesting. Does it actually change the compressor speed, pressure or volume (via a bypass). Or does it adjust the water flow rate out of the ASHP? Or adjust the flow and return temperature? Link to comment Share on other sites More sharing options...
Luke1 Posted December 6, 2022 Author Share Posted December 6, 2022 It reduces the compressor Hz, and the power use drops fairly significantly. The cycling conditions it would peak at 1.0kW and in similar outdoor conditions it would run at 0.550kW approximately. I will check the exact figures. If I calculate that would make sense because running for 35mins at 1.0kW would be approx 580Wh if my maths are correct? Compared to 550Wh with no cycling running for 1hr. It appears to work to a deltaT of about 5C and controls the flow rate through the heat pump to maintain this. Link to comment Share on other sites More sharing options...
john0wingnut Posted February 19, 2023 Share Posted February 19, 2023 On 06/12/2022 at 18:47, Luke1 said: I'm not sure of the ability of other heat pumps, however I have the ability to adjust the compressor curve in the service menu. (It has an auto setting) From what I understand, it is generally better to run a heat pump for a longer duration, and that is certainly how you can see "Heat Geek" using their heat pump. https://emoncms.org/heatgeek My system in auto mode would generally cycle the heat pump 35 mins on, 20 mins off. In which time the flow temperature would go from 32C to 42C as the 'degree minutes' catch up. Now I have adjusted my compressor curve for heating so that the maximum output it can generate is generally only 1-2C higher than the required flow temperature, leading to much longer run times. So do we think I will get a better COP this way, or by letting the controller manage the compressor curve itself? Im tempted to think manually controlling the compressor curve is better because I can get a better COP if the system doesn't have to heat way over the required flow temperature to catch up the degree minutes. (I have noticed that is the degree minutes still end up over 150mins then it does go above the compressor curve to catch up with the degree minutes again) Hi Luke How do you do that in the SMO controller. Mine constantly overshoots the target by about 7 degrees. Would rather it stay on longer as per your view John Link to comment Share on other sites More sharing options...
DanDee Posted February 20, 2023 Share Posted February 20, 2023 10 hours ago, john0wingnut said: Hi Luke How do you do that in the SMO controller. Mine constantly overshoots the target by about 7 degrees. Would rather it stay on longer as per your view John https://www.nibe.eu/assets/documents/23940/231758-7.pdf Page 38 Menu 5.1.23 - compressor curve Link to comment Share on other sites More sharing options...
john0wingnut Posted February 20, 2023 Share Posted February 20, 2023 7 minutes ago, DanDee said: https://www.nibe.eu/assets/documents/23940/231758-7.pdf Page 38 Menu 5.1.23 - compressor curve Thanks Dan I had a look at that, but from what I can tell, thats not to do with flow and return temps. In that menu it would appear you are setting min and max frequencies at a particular outdoor temperature. Page 37, 5.1.3 allows you to set the max flow differential, which by default is 10 degs, so in essence, the heatpump can overshoot the calculated flow temp by 10 degs. I have reduce this to 2 degs, and this has actually caused me more short cycling, as it reaches required temp quicker and thus cuts out the heat pump. Page 38, 5.1.14 is an interesting one. dT at DOT. My DOT is set to -2.0, but i cannot seem to find where one can actually tweak the dT that the heat pump works to. John Link to comment Share on other sites More sharing options...
ReedRichards Posted February 22, 2023 Share Posted February 22, 2023 I know short cycling is held to be bad, but 35 minutes on 20 minutes off seems like a particularly long cycle where the cooling of your rooms during the 20 minutes off might be noticeable. Do you actually feel a difference after the adjustment in terms of a more even room temperature? Link to comment Share on other sites More sharing options...
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