The system was installed three years ago as part of the EoH trial run for BEIS by OVO and was pretty good from the start. Everything was new radiators, pipework, hot water cylinder and all (we had warm air heating previously).
Right from the start I found the COP for my DHW cycle was better than expected compared to the heating cycle. It was suggested that the flow rate had something to do with that. I can see that for DHW the flow rate is around 22 l/min whereas for heating it levels out to around 7 l/min.
So now I’m hoping I can get the flow rate up for the radiators. How should I go about this ?
For the Daikin Altherma monoblocs that are discussed on here, we have seen that they are inclined to ramp their flow rate down to the minimum.
When I had my dT set at 5C, heating would invariably head towards this minimum flow, around 6.75 l/min. Recently a couple of us have been lowering the dT to 3 or 4C and have found that with that setting the Altherma’s seem to modulate their flow rate more pro-actively (my system).
Here’s a comparison of my own system between 5C dT (blue) and 4C dT (red). It’s not night-and-day but I’ve seen slightly improved COP and slightly reduced energy consumption.
To adjust the flow rate unit of measurement to l/min from m3/hour, I’ve added a couple of steps to the process list for the flowrate input, this multiples the value by the conversion factor then logs that value to a separate feed, which I then use in the app.
Thanks Sam, your chart looks very different to mine. As a beginner here I’m not sure what to make of it ! More studying ahead, also for altering the flow rate units.
@mortstar - I’m interested to hear about your experiments with lowering dT. It has occurred to me that a HP with a min flow rate of 6lps (or so) and dT=5C implies an energy transfer rate of >2kW, which is likely to be more than heat loss from the building for a well-insulated house in fairly mild weather. It seems, therefore, that dropping dT, particularly as the LWT is reduced, is a sensible option to get the HP into more steady-state operation (as opposed to cyclically topping up the buffer). My hunch is that the main effect of lowering dT is that it reduces the rate at which heat can be removed from the HP, while the “hit” on the idealised Carnot efficiency is minimal and plausibly out-weighed by the improvement of overall system efficiency from steady-state balanced operation.
I am, therefore, interested in the extent to which your experience supports or refutes that conjecture!
