@batalto A couple of questions

• what is your heat distribution system? Radiators, under floor
• Do you have a buffer tank or system separator?
• What other control systems do you have for the heating?
• Where did you get the figure of 30w/m2
• How big is your heat pump?
• What is the build of your house, do you have stud walls of brick internally?

Anything else you may think is necessary

The EPC means nothing, it is a document full of assumptions and short on facts. (I am a qualified DEA and can produce them)

In short,

• Radiators - although the upstairs ones basically never come on as it never gets cold up there
• Buffer tank 20l and 210l unvented cylinder for hot water
• Thermostat (nest)
• 30w/2 comes from a room by room survey of the house based on insulation, windows type, window size etc
• 12kw heat pump
• Lower floor of the house is brick with cavity and double glazed. Upper floor is structurally insulated panels with triple glazing and outside solid wall insulation
• Loft is 370mm of insulation
• Insulation between first and second floors
• Insulation between the walls
• Whole downstairs was built to 2015 building regs upstairs to 2020 building regs
• All pipes fully lagged

Oh, 260m2 house

@batalto, Ideally, as your house has a relatively low thermal mass, it should be controlled with an internal thermostat connected to the heat pump controller, the best thing to do is to move the controller to a common area, usually the hall, at the farthest point from the front door is best, but anywhere in the heated envelope is acceptable except close to a radiator. Then re-program the programmer to work as an internal temperature sensor.  If this cannot be moved, as a compromise, set the weather compensation to be 25 Deg C at 15 external and 45 deg C at -3 external. (you may have to play with this to find the right settings for your house. Set the heating on/ off setting to 18 with a 5 degree offset. (I know it is difficult with this controller as there are 5 wires, you can however cut the wire and extend it with a flex, just make sure you do not mix the wires up, it will not break it, but it will not work)

Disconnect the Hive and remove  the TRV actuators off all the radiators except in the bedrooms.

You will find that the heat pump will run nearly all the time below 18 deg C but at a very low level resulting in the best performance, you will also find that it does not frost up as much when it gets cold, and you will have a much more even temperature in your house.

If you want even better performance, remove the second pump the other side of the buffer tank (this costs you £100.00/year to run), remove the return pipes and connect them together, the pump inside the unit is man enough to run the whole system and if most radiators are open, it is very unlikely you will have a low flow error.

Hi Heacol,

It sounds like your description of a system using weather compensation, along with internal temperature measurement, is basically continuous process control utilising a PID controller algorithm.

Do all manufacturers systems have this capability? What level of accuracy can be achieved?

Personally I have a PID controller which varies the radiator water temperature to maintain the indoor temperature within +or- 0.2C of the setpoint.

@heacol these are the settings I have - as recommended by Freedom and programmed by the installer - Link

Hi Batalto,

Having just watched the video accessed by the link you posted, I can now see why people's ASHP systems are not working at their optimum settings, if this is how they are being commissioned.

The controller on our heating system varies the water temperature from 25C up to about 42.5C, when the outside temperature has fallen to -10C. If the outside air temperature was to fall even lower, it would simply raise the water temperature to supply the additional heat loss. In Spring and Autumn the radiators often feel cool to the touch, but are still providing sufficient heat energy to maintain the indoor temperature at the desired 21C.

Dependent upon the heat loss and the size of your heat emitters, you would probably get much better efficiency by setting the minimum water temperature at 25C, when the outside air temperature rises to 16C, and set the maximum water temperature at 45C or 50C, when the outside air temperature falls to -10C. Provided that your ASHP is capable of operating over that temperature range, then you should be able to optimise the operation of your system.

@derek-m, you are correct, it is a great shame that the industry, most manufacturers and merchants are training people to install and commission heat pumps in a way that leads to poor performance and high running costs. However, you must remember that their aim is to shift a box.

@derek-m @heacol - so what's the recommendation? I'm happy to adjust the settings. I think I'll keep the Nest for the time being as it saves me from relocation of the control. It's in a boiler cupboard, so quite a hassle moving it. It would certainly involve some holes through walls.

@batalto, If you do not get rid of the Nest, do not bother to do anything, nothing will make a differance.

Hi Heacol,

With the method of control that you are suggesting, how is the central heating water pump controlled?

Rather than move the Midea controller, I presume an external temperature sensor could be connected to the controller, the sensor being located at a suitable place to measure the average temperature. In that way the controller could replace the Nest to provide better control.

@heacol I don't really see why. Surely the Nest is just an on off control, just like the heat pump controller temperature sensor? The heat pump will still adjust the flow temperature based on weather compensation separately to the Nest so why does it matter? All the Nest does is call for heat until it gets to 21 and then holds it by keeping the pump running? If weather compensation lowers the flow temperature wouldn't the Nest just keep calling it? Or am I missing something between the Nest temperature sensor and the heat pump controller sensor?