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Heat Pump Running Costs

gandalfio

Hi,

How many units/kwh per day should a Samsung/Joule heat pump and hot water system use?

How many units/kwh would be average daily or monthly total for all electricity including heat pump?

Our smart meter is showing we've used over 500 units over the past 12 days since the beginning of the billing cycle. Cannot fathom how we're using so much. The heat pump used 120kwh last week. We've figured out why and have brought it down to about 9 or 10 kwh per day. So there's something else causing massive energy use. We're careful and take all the usual measures, switching appliances and lights off when not using them etc.

Could the meter be faulty?

It's in a new build A2 rated 3 bed semi. No gas.

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ECO_Mental

Here is my moving 7 day average of my heat pump to take up the ups and downs over the last 12 months practically. A1 new build house 210m2 House (A2 without Solar PV)

As you can see during an average winter day its between 20-25 kWh/day, from about April to October I was doing about 5 kWh/day or less

The big spike in December was obviously the very cold snap we had for a week or so. 2 adults and a 17 and 19 year old that like to take VERY long showers at least once a day so that contributes a lot to the consumption. Underfloor heating everywhere including upstairs and I think I have 13 zones!

I am happy with it no stat set above 20 deg and all bedrooms and halls set to 19 degs. I log it using home assistant so I can see if its on all the time and usaully someone has set a stat to 22 degs or something.

Nelbert

https://www.boards.ie/discussion/comment/120196470#Comment_120196470

Well insulated yes. House is 1970s semi-D post renovation (full gutting, 90mm dry lining on main house, 120mm on extension, 150mm underneath ground floor, spray foam in the attic dormer) still some queries on air tightness but nothing major.

Heat pump set to heat on night rate gives us a pleasant wake up then solar gain can take us through to night rate most of the time (sometimes overheat us!).

Recent automation to boost hot water if below a certain temp at 7am means less likely to heat water on day rate too.

So mixture of insulation and being smart as possible on when to call for heat to keep costs down.

With the milder weather of the last week I'm already seeing drop off in energy usage (improved efficiency and less heat demand).

DC999

https://www.boards.ie/discussion/comment/120196455#Comment_120196455

https://www.boards.ie/discussion/comment/120195313#Comment_120195313

Hats off @theintern + @zoom_cool. That's an amazingly low amount per day. To give a comparison, heating our 5x5m sitting room / kitchen (old 'leaky' house) is using the same as your whole house. That's heated between an electric rad and gas boiler rad and set to 20.5C.

zoom_cool

@DC999 thanks for comment I think more is to do with the auxiliaries and not the heat pump like flilow rates on the manifolds and heat pump on weather compensation and lots of plumbers don't want to know how to setup correctly. You need to tweak them until you hit the sweet spot.

gandalfio

Cheers for all the replies. We've managed to bring the daily usage right down through lots of tinkering. Last few days read 9.2, 8.8. 7, 6.6, and 4 yesterday.

We've been leaving the downstairs stat at 18 once we go to bed and pretty much leave it there until the following evening.

However, whilst our overall energy usage has come down greatly, it has plateaud and we're using the same amount of units per day whether the heat pump is running at 9kwh or 4. All other appliances, lights etc are being used in the same way each day.

Any reason why this could be happening?

Another issue were having is the following. Two of our bedrooms don't heat as well/retain heat as well the master bedroom.

The master bedroom is always really warm and the rad is never turned above 3. Whereas the other rooms' rads are all turned to 5 and still have issues heating and retaining heat.

It seems that its more retaining the heat is the issue as the radiators have been tested and are working well.

Nelbert

If it's heat retention check for air tightness. Seals around windows and properly installed vents (with seals around it so that air travels through the intended part and not gaps around it).

Other thing is location. Our rooms with south east facing windows call for less heat than our north west ones especially in winter.

893bet

Are those rooms on the north side of the house?

Is there potentially additional air leakage in them?

Your problem sounds like a heat retention issue overall. Was there an Airtightness test done on your house during build?

graememk

https://www.boards.ie/discussion/comment/120200127#Comment_120200127

Most likely that it is warmer outside.

Do you notice a rise when more showers or baths are taken in a day? Your heating your hot water too.

A 200L tank if heated by an immersion could easily use 10kwh.

gandalfio

One of the rooms is dual aspect, one window facing east and the other facing south. The other bedroom is facing west.

No difference re shower usage etc. The overall meter reading is consistently the same every day the last week day. Even when one day on the heat pump was 9 and yesterday was 4.

gandalfio

We're only living in the house 6 weeks. Builder has sent Joule heat pump technicians round. They recalibrated the thermostats (stats were reading the temperature 2 degrees above what our own thermometer showed). But the heat retention issues remain in the two bedrooms and the downstairs bathroom. Joule suggested the stats might need to be moved, or the rooms need bigger radiators. But the builder is refusing to budge and won't offer anymore assistance. Is there anything else we can do here?

graememk

https://www.boards.ie/discussion/comment/120200358#Comment_120200358

No idea where to go re the builder. (although 4kwh a day for heat is pretty good!)

but

Wheres the thermostats for the bedrooms, All individual? or a shared stat?

My thinking is : Changing the thermostatic valve, doesnt create a call for heat, just tries to put a upper limit of the heat.

Master bedroom gets warm first, maybe its the first on the loop, the thermostat is also satisfied, heating turns off, other bedrooms get nothing. (even though they are at 5)

What happens if you turn the master bedroom off completely?

Are you taking meter readings for the Kwh value or is that just the heatpump?

gandalfio

The 4kwh per day was just yesterday when it pretty much no heat was called for for the day.

There are 2 stats. One in the hall, and one on the landing.

Haven't tried turning any rads off completely. We were told by the plumber never to turn any to 0. Any idea why?

The readings I've been taking are under the daily/weeks usage statistics on the panel attached to the tank in the hot press. I'm also taking daily unit readings from the main energy meter for the house.

graememk

https://www.boards.ie/discussion/comment/120200585#Comment_120200585

I understand, so the 4kwh is heat only then? Not the rest of the house.

Don't know why not to turn off completely, possibly to do with efficiency but once temperature is reached for the rad valve it would be closed see this : (heat geek)

https://youtu.be/zpTVIeUh04E

But as one room is too warm I'd be considering closing the lockshield on the other side of the radiator a bit more, to restrict flow to that radiator and allow more heat to go to the other rooms.

The other rooms might not be properly heated as the thermostat could be cutting out too soon. Thats why I suggested to turn the master bedroom off completely, just to see what changes.

gandalfio

https://www.boards.ie/discussion/comment/120200814#Comment_120200814

Yeah the 4kwh is for heat only. But the meter readings for entire house are the same each day even though the heat is fluctuating from 10kwh per day to 4kwh. Can't understand why.

theintern

The only way to work this out is to get something like a Shelly EM (I have one of these) and hook it to your heat pump circuit and the main circuit. Or get an _Emporia Vue 2_ (I think that's the name) that seems to have a bunch of clamps so you could clamp every circuit.

Then buy some power monitoring plugs to monitor specific appliances like the washing machine etc.

You'd be surprised how much some appliances use like the cooker, washing machine etc. A night rate meter and sticking these on timer can make a big difference. Home Assistant provides a great dashboard to bring this all together.

EDIT - I was thinking of the Emporia Vue 2.

theintern

I just went into the settings of my unit. My above estimations weren't including power used by the indoor unit, just what was used by the outdoor unit (different circuits on my fuse box), so were under estimating overall system usage. The nice thing is now I have readings for the total electricity input to my A2W system over the year. Here it is.

140sqm new build, A2. Thermostats generally @ 21 degrees.

Figures are total energy units used / total heat units generated (heat pumps being greater than 100% efficient

Jan - 467 / 1396

Feb - 318 / 956

Mar - 262 / 726

Apr - 136 / 367

May - 69 / 153

June - 65 / 146

July - 68 / 134

Aug - 62 / 139

Sep - 87 / 215

Oct - 204 / 645

Nov - 339 / 1084

Dec - 683 / 1657

Total - 2760 / 7618 - 276% efficiency.

7.56 units per day consumed

Max units per day across a month - 22.03 (Dec)

Min per day across a month - 2 (Aug)

On my current price plan (EI, 5.5 discount, day/night meter, assuming usage of 66% day rate vs 33% night rate usage) works out at a hair under €1000 for the year. €998 to be precise. Assuming 2023 is like 2022. In reality the cost was less than this for 2022, as I was on a better plan.

gandalfio

How do you find the total units for indoor and outdoor combined? Are the units shown on the digital panel on the hot water tank for indoor or outdoor?

Separate question, is 60 degress for 20 minutes once a week sufficient for anti-legionella?

theintern

https://www.boards.ie/discussion/comment/120244837#Comment_120244837

It's a Daikin unit and shows the total units consumed. The units it displays as used for heating are the exact same as what my clamp is measuring on the 'outdoor' circuit in my circuit board, and then on top of that there's energy used to heat water. It shows each separately and also shows the total.

Nelbert

https://www.boards.ie/discussion/comment/120244603#Comment_120244603

This is good info, my usage is similar, but my monitoring only started properly in August and I've been eager to establish what my water heating requirement is to consider an Eddi for hot water in summer. I thought it would be a purchase based on convenience rather than return on investment financially. But if you consider your March to September usage it's ~3 years payback (rough day rate of 40c longer if you consider night rate but with my hot water usage profile day is more appropriate for me) which is reasonable given the additional convenience Vs cheaper alternatives that wouldn't be as smart in terms of limiting to excess.

DC999

https://www.boards.ie/discussion/comment/120248809#Comment_120248809

If you have a D/N meter heat the water at night and stop just before cheap rate ends. Then you only need to boost during day.

If it's a well insulated tank, and ideally large enough too, set the immersion to a hotter temp. Means you've stored hotter water and dropping a bit in temp during the day matters less. Then it won't need much boost immersion heat for showers later in the day.

You can try that before getting an Eddi and see how it goes.

Nelbert

https://www.boards.ie/discussion/comment/120248879#Comment_120248879

I already do that. The water gets a boost at 7am back up to 50⁰.

An Eddi could bring me to 65⁰ on a sunny day which would eliminate the need for the boost (post Legionella Cycle to 65 we get 2 showers and it drops to 50-55 depending on length).

We have random daytime showers and baths for the small people in the house as necessary along with washing up etc that often means another boost on day rate. I could avoid the day boost and likely the 7am boost during summer with an Eddi is the thinking.

gandalfio

Is 60 degress for 20 minutes once a week sufficient for anti-legionella?

Nelbert

https://www.boards.ie/discussion/comment/120250316#Comment_120250316

Mine goes to 65 every 15 days for 30 mins (goes to 67 before turning off so never drops below 65 that quick anyway given its done at 2am).

I've no idea what the guidance is on it.

graememk

https://www.boards.ie/discussion/comment/120250316#Comment_120250316

Generally yes. Vid about it from heat geek

https://youtu.be/oJeyc_cGIMU

staples7

Bumping this thread, what types of kWh usage are people seeing from Heat pumps this winter.

Im averaging out around 10 this month 2.5 of that is hot water.

The remaining 7/8 is on night rate at 14c so happy enough.

When we get a cold snap that daily usage will go up a little. House constant 20-21 degrees.

*EcoDan Mitsubishi HP. 2800sqft A2 house, family of 5 home at home all day

dominatinMC

https://www.boards.ie/discussion/comment/121379597#Comment_121379597

That seems like very reasonable usage. I have same HP, same size house (roughly) and same temperatures, and I'm using 14kWh/day on average. Tbh I was happy enough with that before seeing your post 😂

keno-daytrader

https://www.boards.ie/discussion/comment/121379597#Comment_121379597

3.06kWh/day heating

2.37kWh/day hot water

so about 5.5kWh/ day for both, 16 days so far this month.

Ecodan hp , 2450 sqft A1 house. 21.5c house 48c hot water

staples7

https://www.boards.ie/discussion/comment/121379759#Comment_121379759

I think you're still pretty good there, I could easily be up to that if I ran the HP a little longer. And will hit that at colder temps too.

staples7

https://www.boards.ie/discussion/comment/121380193#Comment_121380193

Some going, you air tight?

keno-daytrader

https://www.boards.ie/discussion/comment/121380352#Comment_121380352

Yeah, I went and took the course and did the airtightness myself. It was a real pain in the ass, but so worth it in the end as most builders dont give a hoot once it comes in under regs, and the current regs are a bit of a joke.

Although Im not on night rate, so I only run the hp between 10am and 6pm.