Programming a Mitsubishi heat pump (peak and off-peak rates)

[Garald]

I have a Mitsubishi Ecodan heat pump with a wifi controller; I've been using the MelCloud app (and the wireless thermostat). So far I've been using the app just to monitor energy usage and to shut down heating and hot water remotely when I don't remember doing so before leaving for a couple of days.

 

I'll soon switch to an energy plan with different rates for off-peak and peak electricity usage. Obviously, I would like electricity to be consumed during off-peak hours (eight hours; they will probably be late at night).

 

a) What should I aim for: have a target temperature (with the system choosing flow temperature) during off-peak hours, and just shut off the heat pump during peak hours, unless the temperature drops below 17C, say? I think a post somewhere in this site suggests setting a fixed flow temperature during off-peak hours and a target temperature during peak hours; is that better?

 

(I should add that, while I am aware that it would be best for the heat-pump to run on low settings during long periods of time (and a Mitsubishi is supposed to modulate well), what I find when I let the heat-pump  have a target temperature and choose flow temperature is that the heat-pump heats water to a temperature higher than that given by the curve I set, and then it stops. The heat-pump is probably overdimensioned; I did the calculations, but I couldn't find an installer who was willing to do a tighter fit.)

 

b) MelCloud does have a "weekly programming" menu that allows one to "add events", but the documentation is very sparse on what to do there. Are there more detailed or useful third-party instructions on how to use MelCloud to do whatever you recommend for (b)? Or should I get Home Assistant instead, say? (I take it must work with the Mitsubishi WiFi controller?)

[PhilT]

11 hours ago, Garald said:

what I find when I let the heat-pump  have a target temperature and choose flow temperature is that the heat-pump heats water to a temperature higher than that given by the curve I set, and then it stops. The heat-pump is probably overdimensioned

 

At warmer ambient temps the ASHP cannot modulate low enough to achieve the equivalent WC curve flow temp without cycling, so in target temp (auto) mode it runs at no lower than the minimum continuous power level, allowing the flow temp to gradually increase to a pre-programmed level, then it pauses with the circulation pump still running. To extend run time even further the room stat allows a room temp overrun (hysteresis) of one degC. I spoke to Mitsubishi about this and they say it is absolutely fine and the way it is designed to operate to maximise efficiency.

[Gary68]

The Melcloud app is easy to program, just choose your unit, go to timer, I add in the start of the off peak time and till it to run at a fixed flow during the winter.

The flow temp can only be set from the main controller not the app.

Then at the end of off peak I tell it to run change back to WC.

 

In spring and autumn, I still run it at night but only in WC mode so 32C rather than 45C in winter.  At this time of year it probably won't come on till the next off peak period, so no peak use.