Hi everyone, this is my first post, so I hope I’m in the right place!
I’m looking for some advice on interpreting data from my air source heat pump (ASHP). I’ve attached two screenshots showing performance on days with similar weather conditions.
Please ignore the internal room temperature shown in the data—our front door has been left open a lot due to bathroom tiling work, so it’s not relevant. The system is running on full weather compensation, so internal temperature isn’t a factor anyway.
I’ve read a lot about cycling and understand that ASHPs are designed to perform several cycles per hour. Based on the data:
Why does the ASHP complete more cycles on one day compared to the other, given the similar weather conditions?
Why are there so few cycles overall?
What should I expect in terms of cycling behavior during warmer weather and how will the efficiency be affected?
Looking forward to hearing your thoughts and insights!
I can assure you the data is correct. We have the full Level 3 Heat Pump Monitoring Bundle (emonHP) installed.
If I were to use the myVAILLANT App for the same dates it would show my COP >8 for the same period as the intergrated sensors on the Heat Pump under report the electric consumption and over report the heat output. Our flow rate would be fairly normal around 25deg as you can see on the screenshot.
Well actually, ASHPs are designed to run continuously when the conditions are ideal, and will only need to cycle when the heating system isn’t able to deliver all the heat that is produced.
The behaviour of your system looks fine for 7°C, which shows your installation is well matched to the heat loss of the property. It might get more interesting when it gets milder, say around 12°.
Is COP/SCOP envi reaaly a thing? 3 is definitely underwhelming—Daikin ASHPs should achieve >3.5, even if oversized. I assume you have double checked your heat loss could it be that your heat loss is undersized so your emitters are also undersized forcing everything to work harder? Are you running weather compensation? Is your flow rateoptimised? are you running full open-loop no bypasses or mixing valves causing inefficiency have you any unnecessary pumps and is all pipework is well insulated?
I don’t want to derail your thread but yes to WC, it does its own thing with flow rate, no bypasses or mixing valves, all brand new rads (K2s and K3s), some of the pipework is beneath a slab so not ideal in that regard but all the new pipework is insulated, internally and externally.
Your indoor temperature actually matters. If it is really colder inside because the door is open, the radiators will be putting out more heat despite everything else being equal. Looking at your first graph I see less cycles; and this coincides with long periods of low indoor temperatures. In the second graph your door looks closed, it is warmer inside and the radiators emitted less heat - hence the increased cycling.
Vaillant’s full Weather Compensation mode is set to “inactive,” the system dose not use the internal temperature sensor for its calculations. The flow temperature of the heating system is adjusted solely based on the external temperature and the heating curve.
If it’s colder inside the house the system can shed the heat via the emitters, so the energy integral doesn’t rise as quickly before needing to shut the system off.
It it’s already warm in the house, the system can’t shed the heat via the emitters so the energy integral counter rises more quickly, reaches zero, heat pump clicks off.
Energy Integral is working in the background regardless of which weather comp mode you’re in.
Yes that’s true, but the radiators’ output depends on (T_radiator - T_room)^1.3. If T_room is lower, you output more power at the same flow temperature.
Excellent points. I’m hopeful that with good system design, we’ve addressed this effectively. The UFH has 100mm pipe centres, 35mm pipe throughout, a 125mm thick slab, and significant thermal mass in the 225mm thick walls with EWI. Am hopeful that as long as the shutdown period exceeds the startup bump, any cycling won’t have a negative impact?
Or even playing with “Compr.start heat.from” and increasing from -60 (default) to -100 to increase runs times. But you do risk overheating if the runs are too long and Energy Integral doesn’t click the cycle off.
But might be worth having a look at.
End of the day though, at 7C outside, i’d say that’s around the tipping point when most well designed system start to cycle. It’s what they are meant to do.
Thanks, we’re really happy with our design and are just holding our breath a bit for when the temperature rises. Any previous systems we’ve installed have performed well and been reasonably efficient, but we’re hoping this one will be our best yet!
the Daikin heat pumps which have been switched out for a more reasonable size are hitting scop of closer to 5
with some alterations to the standard setting left by installer ( octopus in my case )
I can assure you the data is correct. We have the full Level 3 Heat Pump Monitoring Bundle (emonHP) installed.
