Air to water energy consumption too high

bumblebeemouth

We recently got underfloor heating with an air to water system and got an unfortunate surprise in our first electricity bill. Consumption is way too high, over 800kwh a month! We left it as the installer advised and haven't changed a thing. Any advice as to what could be using so much energy??

John.G

What heating system did it replace and how much energy was this consuming?. what was your elect consumption/month prior to HP installation.

What temperature is the HP hot water?.

My house averaged 40kwh/day to heat/hot water it for the last 11 days of october so the very most it could have been (as the first 1/2 of Oct was very mild) was 1240kwh, if you assume you had similar demand and assuming 10kwh/day normal usage = HP usage of 490kwh = COP of 1240/490, 2.5, about what you might expect but probably worse as first 1/2 of month was relatively mild.

bumblebeemouth

This is our first proper heating system since our old night storage system so it's not really comparable. So is 800kwh not way out of expectation here? At €0.25 per kwh (unless I'm not understanding the bill correctly) this seems way too high.

bumblebeemouth

Our DHW is set to 45oC and the tank temperature seems to vary throughout the day. Right now its at 60oC

John.G

You will have to check this out ASAP, heat Pumps give their highest efficiencies (COP) with the lowest possible water temperatures, its vital that this temperature is set at 35/45C, the lower the better, if you settle for 45C then you should still get a reasonable COP of say 2.8/3.0, the cylinder HW temp will then be 40c which is OK for showering, washing etc and the electric immersion should be programmed to heat the whole cylinder to 60C once per week for legionella protection.

Your system may programmed to heat the (cylinder) HW to 60C all the time which will really kill the COP and result in very high electrical consumption.

You also say the DHW is set to 45C but you are seeing 60C sometimes. What is the CH set to?

Does the HP itself record its energy consumption?.

What make HP and power output do you have?.

bumblebeemouth

The DHW reading always reads close to the set value of 45C, but the "water outlet" value on another screen can vary between 60C and 40C. Its at 40C now, was 60C lastnight. Its controlled automatically from what I can tell. The water from the tap which I assume should be 45C is much hotter most of the time also.

Its a Samsung AE120RXYDEG/EU

Controls are the same as in this vid:

https://www.youtube.com/watch?reload=9&v=Trdtt0tmkJI

John.G

The video shows the setting method for the DHW temperature, see what the settings are and compare with the actual temperature. Ditto with the CH temperature settings.

Defrost settings are also very important, can't remember coming across them in the video.

bumblebeemouth

Tried changing DHW to 40. It adjusted to 40 (on the display) but is still way hotter from the tap. CH not adjustable

bumblebeemouth

Got into service mode. Brought some max values down from 65 to 40.

John.G

That may help but a bit surprising that you have no control over the system water temperature?, the various COPs are given based on different temperatures.

bumblebeemouth

All settings are under "water law" so i guess it's some level of control keeping it between a max and min, just not an absolute value

John.G

Have you come across any info re defrost cycles etc?.

bumblebeemouth

Theres a defrost temp which is set at 15C.

John.G

Just keep a eye/ear on that as it probably just initiates a timer that does cycle every 30, 45 or 60 minutes but you probably can't do much about this except monitor it.

A bit of nightcap reading for interest.

https://www.energyvanguard.com/blog/why-are-heat-pumps-so-dumb-about-frost/

John.G

https://www.boards.ie/discussion/comment/118228345#Comment_118228345

It is probably the immersion that's boosting the DHW temperature, you may be able to programme that to only boost once/week for legionella protection.

bumblebeemouth

Thanks a million for all the help with this

bumblebeemouth

Another thing that's separate to the energy issue. When the underfloor heating is on, theres quite a loud whirring throughout the ground floor (concrete). We have it upstairs (wood) and there's no noise. I have read that this might be a motor or pressure setting, but have no idea where to look. Any thoughts on how to reduce the noise?

John.G

Has the UFH got a separate pump or pumps and if so can you see what the are set to?.

bumblebeemouth

Yes it is a wilo para pump that is connected between the cylinder and the undefloor heating. Its set to constant differential pressure.

John.G

It may help to reduce the CP setting if its very high but you would want to carefully note the individual loop flow rates and restore them to their original settings. Some Wilo pumps like mine (a 6M Wilo Yonos Pico) on a conventional heating system, can incrementally change the CP (or PP) settings in 0.1M steps.