Posted by: @beagles

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Hello

 

We moved into a 6 year old house 4 years ago, it has a Daikin air source heat pump with underfloor heating, it also has 2 solar thermal panels that just heat the hot water cylinder. Over the years we have tweaked the system to be as efficient as possible. Our heating is on 24/7, the leaving water temp is 40’c, the hot water heats up twice a day, 45’C at noon and 55’C at 7pm. Once a week it does a 60’c heat up. We use 12500 units a year. This seems to be double what other air source heat pump users use. There are only 2 people in our household and he is away 50% of the time, we dont charge any electric vehicles at our home. It’s a 3 bed detached bungalow in Scotland. The winter months are 1500-1800units a month. We have had several engineers out to the house and system seems to be running well. Does anyone have any suggestions on where we are going wrong?

What is the size of your home and level of insulation? Do you have any heat loss calculations for your home?

@derek-m 

hello, thank you for your reply. House is 210m2. Insulation wise, walls and loft have insulation which I presume were up to building regs of a house built in 2012. We haven’t done any heat loss calculations but we considering hiring a thermal camera to see if there are any weak areas, if that would help. 

@beagles

Are you operating your heat pump on a fixed LWT or Weather Compensation (WC)?

Posted by: @beagles

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@derek-m 

hello, thank you for your reply. House is 210m2. Insulation wise, walls and loft have insulation which I presume were up to building regs of a house built in 2012. We haven’t done any heat loss calculations but we considering hiring a thermal camera to see if there are any weak areas, if that would help. 

The EPC for your property should have a heat demand number - it's an informed guess as to how much heat your property will require annually. 

Does your heat pump provide any monitoring? Power in for heating and hot water? Flow temperature? Does your heat pump run constantly or is it turning off and on frequently? What temperature is the heating set for? What temperature are your rooms? How is the room temperature controlled? Why the two different temperatures for hot water? How is the 60c heating achieved/ controlled? What power is the heat pump? What else do you do with electricity - cooking? Towel rails?, old incandescent lighting?, green house heaters? 

sorry but the more information you have the more likely you are to be able to get to the issue.

Can you find a local to help - you mention other heat pump users? 

Good Luck

@Beagles,

the main thing that catches my eye is your LWT.  40 deg is high for ufh; a well designed ufh system with average room temps should run a lot lower than that most of the time.  I have radiators and they are rarely above 40 deg to keep my house at 21-22 deg.  Have you tried using a lower fixed flow or weather compensation? 

Posted by: @beagles

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@derek-m 

hello, thank you for your reply. House is 210m2. Insulation wise, walls and loft have insulation which I presume were up to building regs of a house built in 2012. We haven’t done any heat loss calculations but we considering hiring a thermal camera to see if there are any weak areas, if that would help. 

If you know who installed the heat pump, then they should be able to provide the heat loss calculations.

@steevjo @derek-m @kev-m

Hello

Thank you all for your replies, your help is very much appreciated. Here are your answers:

I’ve found the EPC and it states 14,639kWh per year for space heating and 2,534 for water heating.

We have a 16kW Daikin Altherma Low Temperature Split (good for temps down to -25degC which is useful for some of the harsh winters we have) which provides heat for our underfloor heating and domestic hot water tank.

The flow temperature varies between 35 and 41degC normally and the heat pump coming on is controlled by thermostats in each of our rooms set at 19degC in bedrooms and 23degC in living/kitchen.

The hot water tank temps are set at 55degC and 45degC, the former being for showers in the morning and the latter for general hot water use, dishes etc. We have changed the times to noon and 7pm. The 55degC heat up used to be at 5am but we changed it as there were concerns this would be more demanding due to it being colder at that time of day.

The heat pump can produce up to 45degC water temp and 2x 3kW booster heaters are used to get above for heating the hot water further if desired.

Our other main electric consumers in the house are our ovens and induction hob, as well as our washing machine, quooker tap. We have found that on a sunny day with normal appliances usage, we can use 9-12kWh a day. That same day but in a winter month will use 70-80kWh.

Weather dependent mode is active. I’m not sure if I can change the LWT

The house was built as a one off and unfortunately not part of a housing development so can’t easily compare our usage to similar households.

Thank you all in advance!

All i know is 23degrees is quite warm and costly especially when its v cold outside. Would you try21 in living areas? Our bodies get used to a nice temperature.

@beagles Lots of useful information in your post - really helps.

The heat demand in the EPC translates to about 5000 units per year assuming an unremarkable heat pump CoP of 3. 10kWH per day on other stuff - means 3650 unit a year give or take.

Hot water demand is 2500 so add all that up and you get 11150 units per year.

This is sort of good news as your 12500 is only 12% or so higher per year - means everything is probably working OK - but you can make changes to make it better.

Two things stand out - the room temperatures - we have our main living area set for 20C in the evening, 18 during the day and 17 overnight. Bedrooms rarely get above 18 - we don't have independent control. You don't say if your thermostats have any kind of schedule - if they do dropping bedroom temps during the day and living room temps during the night would definitely help. Our system is controlled by a temperature sensor in the living room - not a thermostat - the temperature sensor supplies temp data to the heat pump and the heat pump modulates its power to maintain the set temperature. We've found this to be much more comfortable than the boom and bust you get with a Thermostat - we used to have the oil CH set to 22/23 to feel warm but with the sensor control 20 feels comfortable.

Second area is water heating - as your heat pump is limited to 45C you are using the auxiliary heaters to heat the water between 45 and 55C. Don't know how big the water tank is but for a 250L tank heating from 45 to 55 takes around 3kW. You could halve that by heating to 50C which is plenty warm enough for a hot shower. 

The weather dependent mode will modify the flow temperatures depending on the temperature outside - 35-41 seems quite warm - ours typically runs between 30-40 (but we're not in Scotland!. You might be able to save a bit by adjusting the weather curve - maybe others can better advise the likely impact.

Reducing room and flow temperatures is a win win as heat demand will fall and heatpump CoP will increase - if your Cop was 3.5 then EPC demand reduces from about 5000 to about 4000. Saving another 500 by reducing water temp and your 12500 units annually becomes 11000 - pretty close to the EPC number.

Hope that helps.

@beagles Can you clarify – is 12,500kWh your total house electricity usage or the annual consumption reported by the heat pump? Does it give you a figure for the energy it produces? And does it break those down to heating and hot water?

I would certainly have a look at your HW setup. Is 55° necessary? I know mixers state they should have a hot water supply of 60° but a lot of us are managing with a top temperature of 50 or even 45°. That extra 10° is being done more expensively with immersion heaters if your heat pump can only manage 45°. And a lot of us are not running the 60° legionnella cycle either as we think there is only miniscule risk.

A tank of water heated to 50° or so should go almost all the way to meeting your daily usage whenever it is heated, especially when there is only one of you at home. Unless perhaps you take really long power showers! I suspect having it set to heat twice means you get the forced energy usage of starting two cycles even if the remaining water in the tank is hot. And with a couple of thermal panels as well it seems unnecessary if not overkill. The panels will do a lot of heating on a sunny day, and if you start with a full tank at 45° you might be in danger of hitting an upper limit on tank temperature. Last year I had my tank set to heat once at about 4pm to allow the solar thermal to do what it could but then allow for a decent input from pv into the heat pump to top up if required, which it often did not have to. The was still enough hot water for showers in the morning over 12 hours later.