@justinsb 

Hi Justin,

Welcome to the forum.

The first thing that I would suggest is that you check if your ASHP is operating on weather compensation. If not, let us know and we can help you set it up.

The other thing that you should do is read the manual for your MELCloud system, since you will be able to obtain operational data that will prove useful in optimising the operation fo your system.

Hi Justin,

I too have an Ecodan 14kW pump. There is some interesting discussions going on in another forum that might be of interest.

https://renewableheatinghub.co.uk/forums/renewable-heating-air-source-heap-pumps-ashps/air-source-heat-pump-performance

@derek-m I'm still learning what all the options are to set up the system. I'm a big believer in reading the instructions, so I have (honestly) been reading them all to bring myself up to speed ASAP. By "weather compensation" do you mean the choice of Room - Flow - Curve under Unit Settings? If so, I did have it set to Curve for the past 24 hrs. However, it is still using the default curve, as I'm pretty sure that the installers didn't change it. They left it just set to Room & I changed it as a result of reading up on here, oddly enough in the article that @markc mentioned. 

In the last 24 hrs I have used 37Kwh and my normal Winter consumption pre-ASHP used to be ~14Kwh per day.

@justinsb yes, but how many KW of gas did you use? That's the consideration

Posted by: @justinsb

@derek-m I'm still learning what all the options are to set up the system. I'm a big believer in reading the instructions, so I have (honestly) been reading them all to bring myself up to speed ASAP. By "weather compensation" do you mean the choice of Room - Flow - Curve under Unit Settings? If so, I did have it set to Curve for the past 24 hrs. However, it is still using the default curve, as I'm pretty sure that the installers didn't change it. They left it just set to Room & I changed it as a result of reading up on here, oddly enough in the article that @markc mentioned. 

In the last 24 hrs I have used 37Kwh and my normal Winter consumption pre-ASHP used to be ~14Kwh per day.

Hi Justin,

Since you are new to ASHP's and the forum, it may be useful if I explain a few things.

ASHP's operate most efficiently when they are running constantly at a low water flow temperature, it is bit like driving your car at a constant 50mph as against driving at 30mph for a period of time, then speeding up 70mph to produce an average 50mph.

Your home has a heat loss, which increases or decreases dependent upon the difference in temperature between the indoor temperature and the outdoor temperature. To maintain a constant indoor temperature, your ASHP has to produce sufficient heat energy to replace the heat lost, it can do this by producing sufficient heat energy over a 10 or 15 minute period each hour at a higher water flow temperature or running constantly for the full hour at a lower water flow temperature. Overall still producing the same amount of heat energy.

So you may say "what's the difference"? The difference with ASHP's is their energy source. Much of the electrical energy used to drive the refrigerant gas compressor is converted into heat energy, but this is only a portion of the energy required. The rest of the heat energy is extracted from the ambient air via a heat exchanger (the pipes with fins that you can see at the rear of your ASHP). Just as water will flow from a higher level to a lower level, the same is true of heat energy, it flows from a higher temperature to a lower temperature. The speed at which the water flows is dependent upon the height differential and the slope down which it is flowing, with heat energy it is the temperature difference and any restriction to the transfer of heat.

Many people find it difficult to understand how an ASHP can extract heat energy from ambient air at a temperature of -10C or lower, and heat water to a temperature of 50C or higher. It can do so, because at the heat exchanger (Evaporator), which is where the heat pump extracts energy from the ambient air, the refrigerant gas inside the heat exchanger will be at a temperature of approximately -40C, so with an ambient air temperature of -10C, there is still a 30C temperature difference across the heat exchanger. Obviously, the greater the temperature differential across the heat exchanger the faster the flow of heat energy. The other important factor is that in the Evaporator, the refrigerant gas temperature cannot be raised to a temperature warmer than the outside air temperature, so this limits how much heat energy can be absorbed. A further limiting factor is how quickly the refrigerant gas is flowing around the system, the longer a gas molecule is within the Evaporator, the more time it has to absorb heat energy.

So, if I have not completely lost you by now, running an ASHP for longer, at lower flow temperatures has the following benefits:-

The refrigerant gas flows around the system at a slower rate, so has more time to absorb the maximum amount of heat energy.

The refrigerant gas entering the compressor already contains more heat energy, so the compressor does not have to work so hard to raise the pressure and temperature of the gas.

The gas coming out of the compressor flows into the Condenser (another heat exchanger) where it transfers the heat energy to the central heating water. Because the refrigerant gas is flowing at a slower rate, it has more time in which to transfer the heat energy.

Because the transfer of energy from the ASHP to the home, via the heat emitters (radiators/UFH), is over a longer period of time, then the water does not have to be as warm.

All of these factors mean that the ASHP does not have to work as hard to produce the required amount of heat energy, which in turn means it will draw less electrical energy, and therefore be more efficient and give higher COP values.

Please feel free to ask for clarification if there are any points that you do not fully understand.

Posted by: @justinsb

@derek-m I'm still learning what all the options are to set up the system. I'm a big believer in reading the instructions, so I have (honestly) been reading them all to bring myself up to speed ASAP. By "weather compensation" do you mean the choice of Room - Flow - Curve under Unit Settings? If so, I did have it set to Curve for the past 24 hrs. However, it is still using the default curve, as I'm pretty sure that the installers didn't change it. They left it just set to Room & I changed it as a result of reading up on here, oddly enough in the article that @markc mentioned. 

In the last 24 hrs I have used 37Kwh and my normal Winter consumption pre-ASHP used to be ~14Kwh per day.

Hi Justin,

Sorry, I forgot to explain about the different methods of control.

Room - This could be temperature control by a thermostat or the Ecodan controller itself, which can provide different levels of performance.

Flow - This is where you instruct the ASHP to produce water at a specified water flow temperature. Using a fixed water flow temperature can be somewhat beneficial, but will not produce best efficiency.

Weather Compensation - This is where the control system monitors the ambient air temperature and automatically varies the water flow temperature. When correctly adjusted, it should produce the best overall efficiency and the highest COP values. On the Mitsubishi system you set the two end parameters of the slope. Following the instructions in the manual, try the following settings, water flow temperature of 45C for an outside air temperature of 0C and a water flow temperature of 20C at an outside air temperature of 20C. In this way when the outside air temperature is 10C your ASHP should be producing water at 32.5C.

Please ask if you need further advice.

@derek-m thank you, that's the first (& possibly only) straightforward explanation of what, why & how that I have been given thus far. As with many things, it is an initial vertical learning curve, with a brand new vocabulary - with a few interestingly counter-intuitive gotcha's thrown in just to keep people on their toes.

I have edited my curve following your temperature guidelines (see photos below) & I hope that this is what you meant for me to do.

@batalto 🤣 I live in North Yorkshire. There's no mains gas anywhere near here, that's why we're going solar & ASHP. After the shock that I gave the moths in my wallet when I coughed for the cost of installing it all, the least I can do is to calm them down by screwing down the running costs as much as is humanly possible. Interestingly, it turns out that the more I learn, the less electricity my ASHP uses. I'm really looking forward to getting my Solar installed in a few days to see how that changes my overall daily consumption figures too. My master plan is to get to the stage where I really don't have to consider the price of gas at all, hopefully - or, at least, as close to that as I can get 😎

@justinsb it's not the best time to rely on solar ... lol

I'd very much consider getting a hybrid inverter if you are getting solar installed. It'll give you the option of batteries in the future. Really really do this as if you want batteries in the future and you don't have a hybrid inverter you'll have to buy one.

@justinsb 

Hi Justin,

You have adjusted the weather compensation correctly, though it will probably take a while for the indoor temperatures settle.

Where in North Yorkshire do you live? I live in East Yorkshire, though just near the border with North Yorkshire, about 10 miles south of Selby.

I will explain a little more about weather compensation. Although at the moment we have a gas fired boiler, I have installed a control system that makes it operate in a similar way to that in which an ASHP should be controlled. Observations and testing over a number of years have shown that for our particular heat demand, for every 1C that the ambient air temperature reduces, the temperature of the water in our radiators needs to be increased by approximately 1C, this in turn maintains the indoor temperature at the desired (by me, but not she who must be obeyed) 21C. This is basically the task that the weather compensation is performing on your system. As the ambient air temperatures falls, the water flow temperature is increased. You should be able to see this on your controller, though you may have to be patient.

What you now need to ascertain for your system is the slope of the weather compensation curve for your home. Having now established initial 'ball park' settings, it is now a matter of monitoring the operation of your system to see if further adjustments may be required.

So that I can assist you to fully optimise your system, could you please provide a list of the installed equipment along with its location within your home.

@justinsb 

Hi Justin,

When you have your solar PV system installed, if you have an immersion heater in your how water tank, then you should consider having a power diverter installed. Whilst solar PV may not be too productive in the Winter months, it is highly useful from Spring through to Autumn.

In basic terms, the power diverter can be used to provide much of your hot water requirement from Spring through to Autumn without the need for you to run your ASHP, when heating is not required.

The diverter takes any excess generation from your solar PV system, and diverts it to your immersion heater rather than sending this power back to the grid. It is an electronic device which monitors the power flow from and to the grid, so that if you are exporting say 1kW back to the grid, this would instead be diverted to the immersion heater.

There are a number of different diverters on the market, just Google Power Diverter and you should be able to get more information.

I have one fitted to my solar PV system, so if you require more information then please ask.