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Mitsubishi ecodan 11kW ridiculously expensive running costs. Help!

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Air Source Heat Pumps (ASHPs)

Last Post by HughF 3 years ago

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Parmstar

(@parmstar)

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Joined: 3 years ago

Posts: 51

Topic starter 11/12/2022 7:29 pm

Hi all,

first post please be nice 😄 I am after some help and advice if possible

so I recently had 6kw of solar installed which is currently not generating much due to shading from neighbouring property

i have also had a ASHP fitted - Mitsubishi ecodan 11kw

prior to the install we were using approx 48000kw of gas to heat our 7 bed house - a lot I know, borderline commercial usage.

I was hoping switching to an ASHP would save us money as our heating is on at home constantly as my disabled sister lives with my family and requires the heating on (quite high)

the ASHP is currently set to 22c thermostat and a weather comp curve has been set. It’s struggling to reach temp - possibly because of the location of the thermostat (hallway - prone to be draughty)

my main concern is my bills the last week due to the cold spell we are averaging around 150kw A DAY! this is obviously costing an arm and a leg

the survey carried out by the company indicated an average annual spend of £2300 to run the heat pump. At this rate this will be the cost for December and Part of January alone!!

what should I do!? I have insulated my loft with top up insulation and it’s got underfloor insulation and cavity wall 1990s build. At the moment I am regretting my decision to install the ASHP😞

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batalto

(@batalto)

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11/12/2022 8:15 pm

I hate to break this to you, but 48,000kW of gas at the current cap is £4,800. I can't see how you are going to get cheaper bills with or without an ASHP - at least in the winter. Can I ask how big your house is? That amount of heat is crazy. But we are also in the coldest snap for years so it's going to need a lot of kW regardless of gas or ASHP - it's just cold outside right now.

Also, for your use, that seems a very small heat pump?! I have a 12kW and I've used 5500kw on my heat pump this year. At a cop of 3 you are looking at 16,000kw - which is still a crazy amount. I just can't imagine a 11kw heat pump is suitable. What are your weather comp settings?

12kW Midea ASHP - 8.4kw solar - 29kWh batteries
262m2 house in Hampshire
Current weather compensation: 47@-2 and 31@17
My current performance can be found - HERE
Heat pump calculator spreadsheet - HERE

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Parmstar

(@parmstar)

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Topic starter 11/12/2022 8:54 pm

Thank you for getting back to me so quickly - comp curve is around -1 50c and 15 40c - tried to attach a pic but it’s not letting me. House is approx 400sqm plus over 2 floors. The company initially said I needed a 24kw but after doing a heat loss survey they said a 11kw would be sufficient. I’m starting to think that is because of the location I wanted the ashp to be - a 24kw wouldn’t have fit. At my wits end now with all this - wish I could just go back to the gas boiler but want to explore my options so any help is much appreciated

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HughF

(@hughf)

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11/12/2022 9:18 pm

48,000 kWh of gas into an 80% efficient boiler would give you 38,400 kWh of heat.

An ecodan running at a SCOP (note the seasonal bit there) of 3.25 (probably realistic at those flow temperatures ) would need 10,971kWh of electricity. At the current backstop rate that’s £3730

Still cheaper than if you were on gas. Don’t look at the cost now, look at the cost for the year.

Off grid on the isle of purbeck
2.4kW solar, 15kWh Seplos Mason, Outback power systems 3kW inverter/charger, solid fuel heating with air/air for shoulder months, 10 acres of heathland/woods.

My wife’s house: 1946 3 bed end of terrace in Somerset, ASHP with rads + UFH, triple glazed, retrofit IWI in troublesome rooms, small rear extension.

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Parmstar

(@parmstar)

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Topic starter 11/12/2022 9:30 pm

@hughf the rate at the moment for elec is 0.48pkw for me so would be over £5k 😞

my sister is dead against smart meters for her own reasons so that isn’t an option for us atm

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HughF

(@hughf)

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11/12/2022 10:29 pm

@parmstar tell your supplier you’re struggling to pay, they’ll put you onto prepayment and you’ll automatically end up on the backstop rate. Easy way out of your excessive electrical contract

😀

Your sister might well be dead against smart meters… I’m dead against paying council tax and a TV license, that doesn’t excempt me from those - just like being ‘against’ smart meters won’t excempt you from ending up with one. Although I fail to see the relevance of smart meters to the cost of your running your heating?

This post was modified 3 years ago by HughF

Off grid on the isle of purbeck
2.4kW solar, 15kWh Seplos Mason, Outback power systems 3kW inverter/charger, solid fuel heating with air/air for shoulder months, 10 acres of heathland/woods.

My wife’s house: 1946 3 bed end of terrace in Somerset, ASHP with rads + UFH, triple glazed, retrofit IWI in troublesome rooms, small rear extension.

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Parmstar

(@parmstar)

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Joined: 3 years ago

Posts: 51

Topic starter 11/12/2022 10:48 pm

Excellent idea thank you Hugh - re smart meters it may work out slightly cheaper as we have a battery with our solar install so could charge it on a cheaper rate overnight approx 10pkwh

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HughF

(@hughf)

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12/12/2022 7:11 am

Posted by: @parmstar

↑

Excellent idea thank you Hugh - re smart meters it may work out slightly cheaper as we have a battery with our solar install so could charge it on a cheaper rate overnight approx 10pkwh

Please give us more details, are you currently on a TOU tariff?

If you’re paying 48p/kWh then that would suggest so. In which case there are some optimisations to your heating strategy that can be done to maximise the use of the off-peak rate.

My comment about moving to prepayment was tongue in cheek by the way…

This post was modified 3 years ago by HughF

Off grid on the isle of purbeck
2.4kW solar, 15kWh Seplos Mason, Outback power systems 3kW inverter/charger, solid fuel heating with air/air for shoulder months, 10 acres of heathland/woods.

My wife’s house: 1946 3 bed end of terrace in Somerset, ASHP with rads + UFH, triple glazed, retrofit IWI in troublesome rooms, small rear extension.

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Parmstar

(@parmstar)

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Posts: 51

Topic starter 12/12/2022 8:11 am

@hughf 🤣 I suspected as much. I checked my recent bill and I am on the capped rate - they itemise it slightly differently in that they show a deduction as opposed to charging it at 34pkwh.

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HughF

(@hughf)

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Posts: 489

12/12/2022 8:15 am

Posted by: @parmstar

↑

@hughf 🤣 I suspected as much. I checked my recent bill and I am on the capped rate - they itemise it slightly differently in that they show a deduction as opposed to charging it at 34pkwh.

OK, so you are paying 34p/kWh - good... Then my above maths adds up.

We just need to get these settings tweaked so that the weather compensation is at it's most optimal. Do you have a copy of the heat loss calculations for the property?

When you say thermostat, do you mean the Ecodan controller, or an external thermostat like a nest/hive/other?

Off grid on the isle of purbeck
2.4kW solar, 15kWh Seplos Mason, Outback power systems 3kW inverter/charger, solid fuel heating with air/air for shoulder months, 10 acres of heathland/woods.

My wife’s house: 1946 3 bed end of terrace in Somerset, ASHP with rads + UFH, triple glazed, retrofit IWI in troublesome rooms, small rear extension.

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Parmstar

(@parmstar)

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Joined: 3 years ago

Posts: 51

Topic starter 12/12/2022 8:24 am

@hughf thank you for your help with this.

I don’t have a copy of the heat loss calcs but I could try to get them from the installer.

I have a ecodan controller with matching thermostat which is located in the hallway

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HughF

(@hughf)

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Joined: 3 years ago

Posts: 489

12/12/2022 8:37 am

Please provide some photos of these items so we can identify versions etc….

please also photograph the unvented cylinder and associated pipework

Off grid on the isle of purbeck
2.4kW solar, 15kWh Seplos Mason, Outback power systems 3kW inverter/charger, solid fuel heating with air/air for shoulder months, 10 acres of heathland/woods.

My wife’s house: 1946 3 bed end of terrace in Somerset, ASHP with rads + UFH, triple glazed, retrofit IWI in troublesome rooms, small rear extension.

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