Hi Jonathan,
Yes, it suffered today.
But for a slightly different reason this time I think.
I haven’t seen any ice but I wasn’t awake all night so it may have done.
It stopped just before 03.00 and then struggled to get going again.
I have this problem with it at the moment, once it is running in a stable state it keeps running.
I am sure it is not immune from ice and defrosts but I think I can make it better.
My problem is that at such a low flow temperature my radiators cannot deliver the heat produced at the high flow rates in the initial start up. The return temperature rises too much and as the flow rate drops the heating cycle sometimes fails as the flow and return are too close.
I am running with radiators and it has a fixed dt of 10c which I never get at these flow temperatures of course.
My solution with the 9kW was to limit the pump speed and I am going to try this on the new heat pump.
This stops the return temperature rising so much and results in a wider dt between flow and return through the initial phase of the heating cycle.
It might work, it might not.
The 9kW was certainly better like this.
My 8kW is quite new, I have no evidence or science behind this but I feel that there is a bit of a running in period.
I tried to run at less than 30c flow at the beginning but it wouldn’t run continuously like this, it failed every time but yesterday I tried again and managed to get it to start and run at 29c.
I learnt quite a lot just sitting and watching the 9kW during the initial phase of the heating cycle and worked out where the most inefficient parts of this were.
I always found this the worst part of the 9kW, it was painful at the start of a heating cycle and limiting the pump speed made it much better.
Of course, that is in my house with my heating system and aiming to run at low flow rates and as wide as possible dt between flow and return.
My 9kW did not defrost every 20 minutes in freezing conditions so I don’t think that there is any fixed logic in this respect. Once I had changed my radiators, limited the pump speed and got the flow temperature down it was pretty good.
Look at my data for 18 January 2024, the 9kW was icing up all day, it was immediate after defrosts but ran for much longer, I remember the day well as it was the day that proved my heat loss and after that I had conclusive proof that the 9kW was too big, not that I really needed any more proof!