Daikin ASHP: Optimising Setting

[wytco0]

Hi All, I have recently moved into a new house with a Daikin heat pump, its all working well but my electricity bill is very high approx £250 per month (I have a smart meter).

I had the installer come in and check a few things and we found some incorrectly set thermostats which have been corrected. I have also switched off the additional hot water circulation system that was installed as this just seems to rob the tank of hot water and cause the pump or booster to constantly cycle. Currently I have also switched off the booster heater as it seems keen to switch on for about 15 minutes each hour.

While the installer was here he said that they normally set heat pumps to run all the time topping up heating and hot water when required. However looking at my smart meter it seems to be doing a fair bit of water heating during the night and I don't think this is needed.

I am tempted to switch the water heating function off from about 2200-0500 but Is this sensible ? is it possible to control when the booster heating is used?

There must be a balance between heating the water with the pump and heating it with the boosters but I am not sure how to set this or what the relevant parameters are.

I have a feeling that getting a heat pump equipped house set up for efficient energy use is a little more complex that I thought it would be.

In case anyone can offer some suggestion for optimising my setting here are a few details:

House is a large detached highly insulated timber frame building with 5 bedrooms but with only 2 people living in it.
Most of the living room stats are set to 20 or 21.
Most of the bedrooms and other rooms are set to 17 or 18 or lower.
We have a heat recovery system.
Heat pump outdoor unit is a Daikin ERHQ016BAV3
Heat pump indoor unit is a Daikin EKHBH016BB6V3
Tank is a Daikin EKHW5U300B3V3

[frank]

Hi All, I have recently moved into a new house with a Daikin heat pump, its all working well but my electricity bill is very high approx £250 per month (I have a smart meter).
How does this compare with the energy usage forecasts? I'm assuming that this is a Low Temp system?


I had the installer come in and check a few things and we found some incorrectly set thermostats which have been corrected. I have also switched off the additional hot water circulation system that was installed as this just seems to rob the tank of hot water and cause the pump or booster to constantly cycle. Currently I have also switched off the booster heater as it seems keen to switch on for about 15 minutes each hour.
The hot water secondary is there to ensure you have hot water available the minute you turn on the tap. If you have long pipe runs this is helpful otherwise, you need to pull off all of the cold water sitting in the pipework before hot water arrives at the tank. The other thing to note is that while you are pulling cold water out of the pipework, your cylinder is filling up with cold water, causing the tank temperature to drop.


While the installer was here he said that they normally set heat pumps to run all the time topping up heating and hot water when required. However looking at my smart meter it seems to be doing a fair bit of water heating during the night and I don't think this is needed.
If you have UFH, then I would agree that you should run the system 24/7 during cold weather, when heat losses are greatest - but make sure that Weather Compensation is on.
There are settings available within the software that can be set to control the use of the Booster heater and the differential for when the cylinder is heated, as well as when the cylinder is heated.

I am tempted to switch the water heating function off from about 2200-0500 but Is this sensible ? is it possible to control when the booster heating is used?
Yes, see above


There must be a balance between heating the water with the pump and heating it with the boosters but I am not sure how to set this or what the relevant parameters are.
The outdoor unit can normally raise the cylinder temperature up to 48C...if your set point is above this then the Booster heater is brought in to assist.


I have a feeling that getting a heat pump equipped house set up for efficient energy use is a little more complex that I thought it would be.

In case anyone can offer some suggestion for optimising my setting here are a few details:

House is a large detached highly insulated timber frame building with 5 bedrooms but with only 2 people living in it.
Most of the living room stats are set to 20 or 21.
Most of the bedrooms and other rooms are set to 17 or 18 or lower.
We have a heat recovery system.
Heat pump outdoor unit is a Daikin ERHQ016BAV3
Heat pump indoor unit is a Daikin EKHBH016BB6V3
Tank is a Daikin EKHW5U300B3V3
The heat losses from the house fabric will be the same no matter how many people are living in it. If the heat pump has been carefully matched to the building heat losses, installed correctly, with all pipes insulated, and the software parameters set up correctly, then your system should be able to heat your house and hot water with ease.

I have spent a good deal of time these last 3 months trouble shooting poorly designed and installed systems though.

[wytco0]

Hi Frank thanks for the info.

How does this compare with the energy usage forecasts? I'm assuming that this is a Low Temp system?

Yes its a LT system, we didnt have any expectations of price but at the moment it does seem to be a bit high, I think this because the system is trying to keep the hot water tank hot all the time and I am not sure that this is nescessary.


The hot water secondary is there to ensure you have hot water available the minute you turn on the tap. If you have long pipe runs this is helpful otherwise, you need to pull off all of the cold water sitting in the pipework before hot water arrives at the tank. The other thing to note is that while you are pulling cold water out of the pipework, your cylinder is filling up with cold water, causing the tank temperature to drop.

OK thanks thats pretty much what I thought it was doing, I have switched it off at the moment as we don't use much hot water and I would rather keep it hot in the tank untill we need it, and accept that it will take a while to reach the taps.


If you have UFH, then I would agree that you should run the system 24/7 during cold weather, when heat losses are greatest - but make sure that Weather Compensation is on.
There are settings available within the software that can be set to control the use of the Booster heater and the differential for when the cylinder is heated, as well as when the cylinder is heated.

Yes we do have UFH and its working brilliantly wth good control. I am pretty sure its the hot water that is the problem.


The outdoor unit can normally raise the cylinder temperature up to 48C...if your set point is above this then the Booster heater is brought in to assist.

Ok I have the commissioning sheets and there are a number of set points mentioned, Space Heating is set to 43 and DHW to 48.


The heat losses from the house fabric will be the same no matter how many people are living in it. If the heat pump has been carefully matched to the building heat losses, installed correctly, with all pipes insulated, and the software parameters set up correctly, then your system should be able to heat your house and hot water with ease.

Understood, and I am happy that the system cope with heating the house easily it aslo produces plenty of hot water but I would like to optimise the DHW, a bit for example by turning it off at night. I woudl like to understand how the heat pump decided how to heat water? mine seems to use the booster even though the set point is lower that the pump max, I wonder if it trys to work out how well it can heat from the pump and then decides?


I have spent a good deal of time these last 3 months trouble shooting poorly designed and installed systems though.

I think our design is sound (it also has solar thermal although thats not contributing much at the moment) I am really interested in optimising its performance taking into account our requirements. I think its been setup for a average user with some assumptions that may not be best for us.