@editor If you have a standard on-off thermostat, whether compensation will not work and your system will not be as efficient as it could be.

Posted by: @heacol

@morgan That will work well, tell them you only want TRV valves on the bedroom radiators, and just lock shields on the rest. Tell them also you do not want system separation as it adds 20-50% to your heating bill as it removes the connection between the heat pump controller and the heating system.

@heacol

Can you explain "system separation" please.  What is it so I can be confident telling him I don't want it?

@morgan system separation is where the heat pump circuit is separated from the house circuit. There will be pumps pumping to the heat pump and a separate pump pumping round the house to your radiators. It is either a buffer tank with 2 pipes in and 2 pipes out or an equalizer which is just a small tube with 4 pipes. If you are installing an Ecodan with a pre-planned cylinder, it will come with the cylinder as standard. They mix the water and reduce the usable flow temperature and because you are double pumping the water, you are adding at least £100.00 directly to your heating bill with no benefit. Keeping a low flow temperature is critical for efficient heat pump operation, for every 1 Deg C you raise your flow temperature above the source temperature (outside ambient temperature) you add 2.5% to your heating bill. The is calculated like compound interest, so at higher flow temperatures, every degree gets very expensive and is worth saving. Ask them to remove it (if it is there) and pump directly in to your system.

@heacol 

Well that has me completely confused.  I will have to ask the installer and see where we go.

I've posted an article, where we start to play around with flow rates, and explain why weather compensation doesn't work in our case (thanks for looking into it Derek): https://renewableheatinghub.co.uk/flow-rates-efficiency-and-cop

I will continue this experiment through the autumn and see what it does to our COP.

@editor Hi Mars,

As an Engineer I have always found it very important to use the correct terminology, so I feel it necessary to discourage your use of flow rate, when you are actually describing the Leaving Water Temperature (LWT). Flow is actually one of the more difficult parameters to measure accurately, and in a central heating system would probably be quantified as litres per minute. Flow, dependent on whether it is a liquid or a gas, can be measured in quite a number of ways.

Having read through the manual for your ASHP, it is not clearly stated how they arrive at the COP calculation. and over what period of time the value is integrated. To get a reasonably accurate measurement of COP, it is necessary to measure the LWT and the Returning Water Temperature (RWT), and also the flow rate, (quantity of water that has been heated over a period of time). From these values the Heat Energy can be calculated. I don't know for definite, but the control system may quantify the Heat Energy produced over a 1 hour period and then divide this value by the electrical energy used over that same period to produce the COP reading. Each individual COP reading may then be averaged over a period of time that could be days or even weeks. What historical data does your system show?

The fact that your COP reading is increasing could indicate that the 'average' is rising, because you are now getting higher values. I would be interested to see any historical data from your system.

On page 19 of the User Manual, there is a further adjustment that can be made that is labelled Room Authority. Could you please check to see if it is enabled or disabled. If it is enabled I suggest that you disable Room Authority and re-select Weather Compensation. If my understanding is correct, Room Authority is designed to move the starting temperature of the selected Weather Compensation Curve up or down to correct for variations in room temperature. Because your controller is located in a warm room, this will adversely affect the overall operation of the system if Room Authority is enabled.

Please let me know what you discover.

@morgan Unfortunately it is not simple to heat a house efficiently. To put it in a nutshell, you want the heat pump to  pump the circulation water directly in to your system to the radiators or under floor heating, do not control the common areas and put TRV's or thermostats in the bedrooms only allowing the heat pump to control the temperature in the common areas. It must then divert to the hot water tank with a high quality full bore diverting valve (NOT standard Honeywell or similar heating valves, they do not work). There are many reasons why we do it this way and it is too complicated to go in to full detail, I have tried, but

I am obviously not a good teacher. I have attached a picture showing what we do. Doing it this way will get your best performance.

@heacol thanks for that.  It’s not necessarily that you’re a bad teacher.  More the case that I’m not overly tech savvy and often need things spelled as though to a dunce 😂

Anyway that picture looks very similar to the explanatory sketch the installer did for me. Unfortunately he didn’t leave it for me to compare against.  Appreciate your help.

@morgan Do not worry, I am here to help. A lot of people do things differently and are not too worried about the performance of the system. I have over 30 years worth of experience with heat pumps and performance comes first when I design a system, it is cheaper in the long run to do it properly the first time.

@heacol shame you aren’t my installer. 🤔

@morgan Sorry, not here to get business, just to help.

@grahamh I would be keen if you can pitch into this one. I have a Midea unit supplied by Freedom and fitted by an installer. 

At the moment its using a Nest and not the unit controller. Quite a few people on here telling me that not a very efficient way to run the pump. Could you advise? Would it be better to lose the nest and upstairs thermostat and just use the controller?

Thanks,