Hi @mookyfoo (hope that isn’t a swear word in another language 😊)

Im running my Daikin ASHP (check out Worcestershire ASHP file on this site) for a year controlled by a Nest. I will then switch to weather compensation control. To compare costs. But everything I have read and most people on this site will say low temperature and weather compensation is the way to go for ASHPs. 
Depending on your hot water needs, it might be lower cost to switch to a time of day tariff (Octopus Go?) and only heat hot water tank overnight. Works well for us and means the Daikin isn’t switching between heating and hot water during the day. 

Posted by: @mookyfoo

So we moved to our current property in August 2021. It had storage heaters and was on E7.

From the start we intended to install an ASHP with retro fit UFH downstairs and retro fit radiators upstairs. The reason being theres no gas in the village and it didnt seem the right thing to install an Oil boiler these days.

We only managed to get 2 installers to visit and quote with a 3rd quoting without.

So we chose a company that quoted for 2 x Midea MHC-V16. The reason being for the two is that @ -2 they are only really 13.5kw and one was felt to be borderline for our 280sqm 1988 house (cavity insulted and mixed double glazing from 1988 up to 2010). I have added and will be adding more loft insulation in the near future so most of it will eventually be in the 300-350mm region.

One ASHP is to run the UFH and the other for radiators and DHW.

The later is now up and running for 2 weeks. 

The question I have is that water flow temp has been set to 40 degree and not temperature compensated and is controlled by a wireless thermostat which is set to 19 degrees.

On a 6-7 degree outside temp day this will come on maybe 5-6 times after dropping to 18.6 and then comes back up to 19.2ish, and uses about 16kwh throughout a day and probably a bit less at night although some will be for the DHW.

 

Do you think we will benefit from temp compensation is the question, and am I right in thinking to do this I'd have to set the thermostat higher than required and just let the ASHP controller vary the water temp depending on outside temp, and therefore I need to keep tweaking until I find the right curve that maintains 19 degrees, and thus the thermostat is kind of redundant other than telling the ASHP there is a demand for heat?

 

Hi and welcome to the forum.  To maintain your house at a constant temp, you have to produce as much heat as you're losing, via the hot water in the rads or ufh.  How much you need varies with outside temperature (mainly) so if you have a fixed flow it will be right at one outside temp but wrong at all others.  Too low and your house won't be warm enough and too high and the ASHP will have to switch on and off.  So yes, you should be better using weather compensation because done properly that will use the lowest flow temperature you can get away with, which should be more efficient.  It should also avoid a lot of switching on and off, which is less efficient.  If you're going to use 3rd party thermostats, then your method is a good one.  That's effectively what I do although my stats are just turned up as far as they'll go because the compensation curve never lets the house get too hot.  One thing to be aware of is that if the house cools down, a weather compensated flow takes a long time to heat it up again.

I found weather compensation used 20-25% less energy than a fixed flow of 45 deg so worth trying.

Some manufacturers have more clever controls that use a combination of weather comp and room temperature but this won't work with 3rd party thermostats.  I don't know if Midea is one of them. 

Let us know how you get on.

Thanks guys for the response.

Will certainly be trying a few things when I work out the Midea controller. It doesnt look as configurable as some. Would be interested if theres any other Midea owners on here that could suggest settings to change etc. I have a basic app but it doesnt provide much detail other than heating or DHW on or off.

@mookyfoo it's easy enough to change the settings. I'd advise you just have a look on YouTube for the freedom heat pumps install videos on it. They have one on weather compensation.

Admin pass is 234 as an FYI

@batalto Thanks, yeah I've had a look through settings and seen the videos. The one on temperature comp puzzled me as he changed the 2 values (55 and 37 degrees which seem very high) but the flow temp on the controller didnt change as I thought it would, as in theory the room temp was high enough to set the flow to 37 degrees but it stayed at 40.

Think mine is basically setup as shown in the video so I guess i has some compensation although the flow on the display never changes from 40 regardless of outside temp?

@mookyfoo yes it seems the controller just displays one temperature, I'm not sure why. Mine is always on 38° so I just ignore it.

You just need to alter those figures downwards. The numbers next to them are the set points for those values so 55° @ -2° and 37° @ 16° (I think off the top of my head). Just start tweaking them down and set your thermostat to a couple of degrees more than the target to avoid a boiling house. Then just tweak down until you're about what you're after.

I need to ditch my thermostat and swap to the controller... I've just not got round to that yet

Weather compensation allows the unit to alter the radiator temperature to change with outdoor temperature. In the bad old days we used it all the time. There is a theory that it save you lots of money. It does but nowhere near what you think. 

Us idiots who were around at the beginning of heat pumps are brainwashed into telling you you have to weather comp. You don't.

Nowadays most installers are setting the rads to flat 50 or 55c temperature just like a boiler.

It's time for us old duffers to get up to speed with current trends.

I have to say I'm guilty here too. I wrote your installation manual for your Midea. I'm also the idiot in the video training the guys how to install the midea.

I guess I should re record the video and re write the manual

https://www.linkedin.com/pulse/weather-compensation-heat-pumps-waste-time-graham-hendra I knew I had blogged about this 

Posted by: @grahamh

https://www.linkedin.com/pulse/weather-compensation-heat-pumps-waste-time-graham-hendra I knew I had blogged about this 

Hi Graham,

I read your article with interest, and I am not surprised that you only achieved an energy reduction of 8% using weather compensation with water flow temperatures ranging from 37C to 55C.

I suspect that for most of the time your system would have been responding to the on-off thermostat, rather than being under true weather compensation control by the controller.

Various members on the forum have actually achieved reductions in energy consumption in the region of 20% to 25%, when they switched from a fixed water flow temperature control to a true weather compensated one.

@derek-m I presume by true temp compensation you mean having a sensor in the area being heated thats connected back to the ASHP controller. Therefore not only is the max temp limited (maximum) by outside temp, it can then ramp down if this is more than needed to heat the area and adjust on the fly so to speak?

Posted by: @mookyfoo

@derek-m I presume by true temp compensation you mean having a sensor in the area being heated thats connected back to the ASHP controller. Therefore not only is the max temp limited (maximum) by outside temp, it can then ramp down if this is more than needed to heat the area and adjust on the fly so to speak?

No, I was referring to the parameter settings suggested by Graham Hendra.

If the weather compensation parameters are not correctly adjusted, then the calculated water flow temperature will not produce the required indoor air temperature. If the water flow temperature is too low, then the indoor air temperature would also be too low, if the water flow temperature is too high, then the indoor air temperature will also be too high, unless there is an on-off thermostat which is actually switching the heat pump on and off.

The water flow temperature settings used by Graham, of 37C to 55C, are because his wife complained that the radiators were not warm when the correct lower temperature settings were used.

For the most efficient operation of a heat pump, the weather compensation needs to be adjusted to match the heat loss, with any thermostats that may be installed, set at a value 1C or 2C above the desired indoor air temperature. The thermostat should act only as an upper limit and not as the controlling device.