Question, the HP seems to be cycling off before the thermostat says the room is heated up. Is this normal? Perhaps the return water is warm enough that it's just pumping it round? Could I set my zone valves open manually and just run it that way? Or would it be better just crank up the thermostats and run using weather compensation?

Below are some images of the tank and the downstairs (where the old boiler is still located). Ignore the duvet, my wife moans about the little grundfoss pump humming, so I wrapped it to deaden the hum.

I've also just discovered my minimum flow temperature is 25°. I can't go lower than that

Posted by: @batalto

I've also just discovered my minimum flow temperature is 25°. I can't go lower than that

Good morning Batalto,

25C will no doubt be the lower limit for water flow temperature decided upon by your manufacturer.

The reason that your heat pump is cycling is quite straightforward. If you look at the spreadsheet I sent to you, based on the Midea data that you supplied, you will see that at ambient air temperatures above 7C, the minimum output power of your ASHP exceeds the heat demand. From the spreadsheet you will see that at an ambient air temperature of 10C, with a water flow temperature of 30C, the maximum output power of your ASHP is just over 14kW, while the minimum output power is slightly over 5.7kW, at a time when the heat demand of your home is approximately 4kW.

You should therefore expect your ASHP to run for approximately 70% of the time each hour.

@derek-m I think I need to work on the curves and flow, as it was 19 degrees downstairs this morning, and it should be 21. Its warmed up now, but I need to get things running smoothly and the heat constant. Its no good having a flow temperature which isnt heating up our main room overnight. I know its been very mild, but its annoying to find upstairs and downstairs both fairly chilly. I've adjusted my curve to 25 @ 20 degrees and lets see how that affects things.

Posted by: @batalto

@derek-m I think I need to work on the curves and flow, as it was 19 degrees downstairs this morning, and it should be 21. Its warmed up now, but I need to get things running smoothly and the heat constant. Its no good having a flow temperature which isnt heating up our main room overnight. I know its been very mild, but its annoying to find upstairs and downstairs both fairly chilly. I've adjusted my curve to 25 @ 20 degrees and lets see how that affects things.

Hi Batalto,

The problem with optimising home heating systems, particularly those based on ASHP's, is that they react very slowly to changes. When I have been fine tuning industrial control systems in the past, I would initially just spend some time watching how it was performing and the speed of response to changing parameters. Then I would probably make a small change to the setpoint and see  how the control system responded.

I think that I am correct in saying that you have a Midea 12kW ASHP. Do you know if it has adaptive control based both on the ambient air temperature and the indoor temperature? If you are not certain let me know and I will have a read through the manual.

In the meantime I would suggest that you make a small change to your weather compensation and then monitor the effect over a 24 hour period. Collect as much data as possible during the process, we can then analyse the data and see what changes may be necessary.

@derek-m I am quite lucky that I can view every day via the app, however its not great. I can see a previous day only as a summary and not actual.

below you can see my power use (from my house inverter) and the ASHP use for last night (from the heat pump app). The power spike corelate, but my issue is that the house was somewhat cold. That said, it was very mild last night and that clearly has an impact.

 This is the previous day and you can see the heating being on at night and constant.

@batalto Thank you for the data, very interesting.

I am not yet certain how well weather compensation, on its own, is at keeping a constant indoor temperature, which is why it is important that members, like yourself, feedback as much information as possible.

It is possible that your system is still settling after the changes that were made, or it could be that your home gets warmer during the day due to solar gain and human activity, but then cools down overnight when this heat source is removed. Last night the ambient air temperature was fairly constant, so weather compensation would have had little effect.

The ideal control system would need to measure both the ambient air temperature and also the indoor temperature, along with solar gain, wind speed and rainfall, to adjust for the affects that these parameters have on the heat loss.

@derek-m I think I'm getting somewhere. I've had my thermostat set on 22 all morning, and the house is holding at 21 - it doesn't seem to be gaining any ground, or if it is, its very marginal. 

According to my APP I've used 6kw but delivered 28kw (in heating) - COP 4.6. However its very very mild today, so not exactly an acid test

@derek-m house continues to hold at 21°. Thermostat is set at 21.5 and it just can't make it - so I'd say that's a win for weather compensation. I just need to determine if I need to ditch the thermostats and go single zone with the controller as the main stat. Honestly I'm not sure. I'll probably follow heacols advice and update the diverters to high flow as I'm pretty sure mine are for gas boilers and not heat pumps due to lower volumes

Posted by: @batalto

@derek-m house continues to hold at 21°. Thermostat is set at 21.5 and it just can't make it - so I'd say that's a win for weather compensation. I just need to determine if I need to ditch the thermostats and go single zone with the controller as the main stat. Honestly I'm not sure. I'll probably follow heacols advice and update the diverters to high flow as I'm pretty sure mine are for gas boilers and not heat pumps due to lower volumes

Batalto,

It may be useful if you read the article posted by Jeff a short while ago, which discusses the pro and cons of weather compensation, indoor room control, or a combination of both.

Personally I would not ditch the thermostat just yet, since I think you said that your home suffers from solar gain, and hence the thermostat may help to prevent excessive temperature rise by pulling back on the heating.

Whilst I am not adverse to making changes if they are deemed necessary, before changing anything I would check to see if the problem actually exists. I agree with Brendon that diverter valves will create some restriction to the flow of water around the system, but before replacing them I think that you should ensure that there is not something causing a greater restriction elsewhere. Obviously at the end of the day it is your choice to make.

Before making any major changes I would suggest that you operate your system, as it is, for a period of time and see how it performs. As the saying goes 'if its not broke, don't fix it'.

Some initial feedback on how my weather compensation is going. The main point would be that when it was 13 degrees ambient for 2 days last week my COP was 2.5, yesterday it was 13 degrees and my COP was 4.3.

I've noted a few key moments onto the graph for people. And as a note my current setup is 50@-4 and 25@20. The thermostat is set at 21.5 degrees and the house is being held at 21 and has been for over 24 hours. So I think this is more or less as good as its going to get - I might be able to tweak the edges e.g. 25@19 or something. I'll give it a few days and make a tweak. As a note, my house is now 21 all day - no set back overnight, no changes. That previous one I was cutting the heating around in the evening between certain hours. 

My gas price is 3.29p/kw (after efficiency 85% = 3.87p/kw) and my electricity (if I wasn't using batteries) would be 15p/kw

Looking at that COP for yesterday the price per kw would be around 3.49p - however that's only a single day. I'll find out for the year once I get there (next August)

@batalto, you're now running your system in the same way as I am,  although my flow temps are a bit lower.  Do remember though that although your COP is better, you're ASHP is running for longer.  Having said that, I still think you'll be better off the new way and your house is warm 24/7