For this test I set a WC curve to target 90C flow temp at 0C, however the heat pump only managed 46C. I’ve always been concerned with designing systems to run much higher than 45C, in my experience looking at monitoring data high temperature heat pumps struggle to reach 50C, let alone 60C+ in cold weather. For a system to reach high temperatures, it would need to be significantly oversized, resulting in a very inefficient system all year round.
As far as I understand heat pumps are lab tested using standard European climate data, which is colder and drier than UK, ASHPs suffer more from the effect of defrost in UK, this is not a problem, it just needs to be taken into account during system design.
Installers have a tough job avoiding over-sizing and under-sizing a heatpump. Better data is needed to inform this design, IMO. Hopefully this is something we can help with using data from https://heatpumpmonitor.org/ and real-world capacity testing like this.
i have been shocked by the efficiency of most heat pumps on heat pump monitoring when defrost cycles are often( in certain weather conditions that we are currently having , this is certainly under discussed and often forgot about in a lot of reporting.
even though this is my first winter with a heat pump and i new about defrost cycles i was unaware of impact it has on efficiency and costs of running.
NW of England i do seem to be suffering a lot at the moment (my system Emoncms - app view
i have been thinking about using the emersion heater for the hot water cycles as hot water cycles seem to kick off some kind of chain reaction where the defrost cycles are becoming more often as the heat pump works harder , thoughts ?
wonder if the manufacturers took a different approach after a defrost cycle this would improve thing ( instead of trying to quickly recover the flow temps with working the heatpump harder they should just increase the load gradually recovering the flow temp slower)
ive setup some automations to turn off the HP hot water cycles when it below 0 degrees C outside and use my emersion instead to see if this improves the defrost cycles . this is just a experiment but if anyone has any thoughts would be appreciated.
the idea behind this is the HP works harder for the hot water cycle which when its cold causes defrost cycling , and once these start the hp works harder to recover the flow temp , so hopefully this will reduce the defrost cycles and keep the heating efficiency higher at the expense of 100% efficiency of the emersion heater
Great experiment. I might try this with my 10 kW unit this weekend. To better compare systems with in different humidity scanarios it would make sense to also allow humidity as an input feed to the heatpump app and show related stats like dew point.
you can see here how the 50 degree flow temps (hot water cycle) triggered the defrost cycling at 8 pm last night and in the early hours of this morning caused the amount of times to increase
