Power consumption heat pump

Reed_Richards

shinytop said:

 I’ve just had MMSP monitoring installed ....

MMSP = Monitoring and Metering Service Package.  Was it just installed because it arrived late or did you make a retrospective application?

shinytop

Reed_Richards said:

shinytop said:

 I’ve just had MMSP monitoring installed ....

MMSP = Monitoring and Metering Service Package.  Was it just installed because it arrived late or did you make a retrospective application?

I didn't ask for it until after the main installation.  My main RHI is done but I haven't applied for the extra MMSP RHI yet because  it's not working properly (it's supposed to record energy delivered as well as consumed, but isn't).  I haven't paid for it either though.

BikingBud

Reed_Richards said:

BikingBud said:

Legacy, inefficient, gas boilers never had the complex control systems that are common now.

I'm not actually saying half of the things you assert, @BikingBud. 

In 1998 I bought a gas boiler that was condensing, could modulate and also did both weather and load compensation.  It annoys me that in 2020 I bought a heat pump that was not capable of the latter control feature.  I subsequently found out that Viessmann heat pumps using a Viessman controller can do this but why on earth is it not standard?       

I bought a Mondeo in 1998 it had manual gears but I could have bought any number of other cars that had auto and cruise control. 

In 2003 we had gas powered wet underfloor heating driven by a Viessman boiler that coped with temps down to -25 deg C automatically, this was in Munich with a well insulated house. So we both recognise that the control systems were available. I cannot account for the fact that you purchased a system that did not have this widely available technology but this is different to not being capable.

BikingBud

shinytop said:

Reed_Richards said:

shinytop said:

I’ve just had MMSP monitoring installed and although it’s not quite up and running yet, it is giving some data. This is the heating only energy consumption from my ASHP for 3 hours last night.  It starts at 6pm.  It’s about 10 C outside and the flow temp is about room temperature in the high teens. I manually switched the thermostat up at just before 6:30. It seems to increase energy use in steps until it gets to the flow temp it wants.  It then lets it drop a bit before slowly increasing. It then seems to find a level at which it can maintain flow temp. Sometime after 8, the thermostat stops calling for heat and the flow temp drifts down. 

This doesn’t look like an unmodulated on/off situation.  

That's very interesting; I wish I had such monitoring equipment.  It looks as if the heat pump is modulating to try to achieve a flow temperature of approximately 40 C when there is a demand for heat.  When you overshoot it corrects itself, in the first instance by turning off and in the second instance by modulating down to about 26 (%?).  My heat pump goes off completely when there is no demand for heat, that certainly includes the pump that circulates water around the central heating and, as far as I can tell, the pump inside the unit.  Is that true of your system?

The failing of this control system, as I see it, is that when the heat pump is modulating its output between 18:45 and 20:15 it does not know if it is adequately heating the room/house or not.  So it takes from 18:30 until 20:15 for your room to reach its desired temperature.  I would have it override the 40 C weather control setting to take the flow water hotter whilst there is a big difference between the room and the set temperature but then use a lower flow temperature than 40 C when the room reaches its set temperature in order to maintain that temperature.  

It's just the limitations of weather compensation; the flow temp depends solely on the outside temp.  Like I said, I think something cleverer is available if I lose the 3rd party thermostats.  The manual says this setting is available:

" In room temp. (Auto adaptation) mode the controller uses temperature sensors around the heating system to monitor space and flow temperatures. This data is regularly updated and compared to previous data by the controller to predict changes in room temperature and adjust the temperature of water flowing to the space heating circuit accordingly. By monitoring not only the outdoor ambient, but the room and heating circuit water temperatures, the heating is more consistent and sudden spikes in required heat output are reduced. This results in a lower overall flow temperature being required."

I could do this now but the wired in control unit with the room temperature sensor is currently in the cupboard with the tank so I'd have to move it outside or use Mitsubishi's own wireless stats, which apparently do communucate room temps back to the central unit.  They are a hundred quid each or so but with the price of electricity they might pay for themselves.  Whether this will heat the room quicker or be cheaper or both I don't know though.

I think when the thermostat stops calling for heat, everything stops part from a very little background stuff.  When the ASHP decides its flow temps are high enough (e.g. after my first high peak), it's still using some power - I assume it's still pumping water around but not heating it, hence the rapid drop in flow temp.

In Room Temp (Auto adaption) mode - Sounds very much like the way to go.

On your current set up the flow temp response curve looks fairly smooth, with the energy also settling fairly quickly indicating a well damped system but with the auto-adaption the system should "learn" and should reduce the oscillations in energy use, ideally (for economy) you would hit the flow temp requirement without the overswing. But rapid response time and economy are often conflicting demands.

It would be good to compare that to a typical short cycle response and see how the energy trace differs.