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Massive Electricity Cost

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(@lucgw)
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Morning all,

We recently had installed a Grant Aerona 13kw R3 inverter drive ASHP, cylinder and under floor heating throughout the house. I’ve been shocked at the daily cost of running it. Until a day or so ago I was setting each room thermostat to come on for an hour in the morning and an hour and a half in the evening (and also running around frantically turning off lights and appliances at their sockets). The daily usage was around £20 - which is not sustainable. Spoke with the manufacturer on Monday and they advised keeping thermostats in rooms at a low temperature rather than coming off and on. So I did this, but yesterdays usage was the most expensive it has been at nearly £24. 

Should daily costs be this high even with inflated energy prices? Right now I am looking at over £600 a month. 

Does anyone have any suggestions for trying to get costs down to a more sustainable level? The immersion switch at the front of the cylinder is off too.

Thanks in advance for any help that can be given.

Lucas

 

This topic was modified 1 year ago by lucgw

   
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(@benseb)
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Not sure how Grant ASHP work, but as an indication we have a 1700s old stone house, 250sqm and we’re paying about £15 per day. 

With an ASHP the secret to efficiency is to run it low and slow. So the water temp needs to be low and it needs to run 24/7 with a slight setback overnight. Don’t run it like a gas boiler!

What we did was take all the TRVs off. So everything was running. Then set it to 19c during day, 17c at night. 

then tweaked the weather compensation curve. For example today it’s -2c outside and it’s running at 41c flow temp. If you’re is up at 50/55 it will be very expensive. 

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(@oswiu)
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Posted by: @lucgw
Spoke with the manufacturer on Monday and they advised keeping thermostats in rooms at a low temperature rather than coming off and on. So I did this, but yesterdays usage was the most expensive it has been at nearly £24.

Hi Lucas, welcome to the forum.

The key thing with this is that if you're keeping it on all day (which is indeed the correct solution with an ASHP and UFH), then you can significantly lower the flow temperature of the water in your UFH as well. I don't know how your controller works, but you need to find a setting called something like "weather compensation". This is where the temperature the water is heated to in your system is varied depending on the outside temperature, ie when it's colder outside you need hotter floors and when it's warmer outside you don't need them quite so hot. When you find it, firstly make sure it's turned on, and secondly post what the settings are here so we can help you adjust them.

The most efficient way to run an ASHP is constantly on with water in the system as cool as it can be without making the house uncomfortable. In addition, you should reduce the temperature the heat pump is set to heat your hot water as cool as is not uncomfortable, possibly down to 45C if your usage isn't too high.

 


   
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Mars
 Mars
(@editor)
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Based on your £20/day figure that equates to roughly 50kWh, which at this time of year is not an unreasonable amount for a heat pump to be using depending on the size and insulation of the property. What makes it very painful is that the electricity tariff is hitting the pocket – two winters ago that figure would have been closer to £5/day for the same level of consumption.

My recommendation would be run the system 24/7 but drop the flow temperature to a level where it's keeping your house warm. This will obviously depend on your insulation levels. Our heat pump was set to 45C flow temperature, which can get costly when it's cold outside. Dropping that to 40C reduces consumption – not a huge amount, but every little bit counts. 35C drops that consumption even lower, but the question is will it keep your house warm when it's 0C or below outside. Probably not. Ours wouldn't. So ours has to run at 45C when it's that cold outside. 

Also, if you've got a wood burner, try to heat some rooms using that.

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(@kev-m)
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Posted by: @lucgw

Morning all,

Should daily costs be this high even with inflated energy prices? Right now I am looking at over £600 a month. 

Does anyone have any suggestions for trying to get costs down to a more sustainable level? The immersion switch at the front of the cylinder is off too.

Thanks in advance for any help that can be given.

Lucas

 

Lucas,

Good suggestions so far.  Can you give us an idea of the size, age and type of house?  It's hard to say whether your costs are high without knowing this.  Do you know how much of the £600 is the ASHP and how much is everything else?  Also, do you have the numbers in kWh or do you know how much per kWh you pay?

 


   
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 mjr
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Posted by: @oswiu

The most efficient way to run an ASHP is constantly on with water in the system as cool as it can be without making the house uncomfortable.

The caveat to that is each pump has a minimum output, below which it will cycle inefficiently, so in a way it's not constantly on even if the power is. However, that probably shouldn't be a problem for any reasonably-appropriately-sized pump until February.


   
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(@lucgw)
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@kev-m - thanks for your response

the house was built in 1970s/1980s. It’s end of terrace and has three floors with a loft space on top. It is 159 sqm. 

we have just finished a big refurb project, so all windows were replaced with double glazing, doors replaced and more insulation was put down in the loft. 

we have tried to make it as efficient as possible….

I do not think there is a lot of other electrical usage being used… I’m only there in the evenings so aside from the oven and tv on in the evening, phone charging, I can’t think of lots. 

 

im not sure of the daily kWh usage as my app only gives the cost. The bill when it comes  probably give more information. I’m going to call my provider this afternoon as well. 

This post was modified 1 year ago by lucgw

   
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(@lucgw)
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Thanks for everyone’s responses. Really appreciate it. Will read through and get back to you. 


   
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(@oswiu)
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Posted by: @mjr
The caveat to that is each pump has a minimum output, below which it will cycle inefficiently, so in a way it's not constantly on even if the power is. However, that probably shouldn't be a problem for any reasonably-appropriately-sized pump until February.

I don't really understand your point. Yes they cycle more in warmer weather, but does anyone suggest turning the flow temp up to combat this? Or do you mean having boiler-style timings in spring/autumn but with low flow temperatures? I could see there being an argument for that.

 


   
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(@lucgw)
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@editor is it ok to change the flow temperature from say 35 degrees and then if it gets cold a week later to turn up to 45? 

im very new to ashp - is this thermostat on the front of the cylinder. Ours is currently reading usually around 48/49 but does drop on its own accord to 44 at times.

 

thanks 


   
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(@lucgw)
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@mjr thanks for this. What’s happening in February?


   
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cathodeRay
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Posted by: @benseb

Not sure how Grant ASHP work, but as an indication we have a 1700s old stone house, 250sqm and we’re paying about £15 per day. 

With an ASHP the secret to efficiency is to run it low and slow. So the water temp needs to be low and it needs to run 24/7 with a slight setback overnight. Don’t run it like a gas boiler!

What we did was take all the TRVs off. So everything was running. Then set it to 19c during day, 17c at night. 

then tweaked the weather compensation curve. For example today it’s -2c outside and it’s running at 41c flow temp. If you’re is up at 50/55 it will be very expensive. 

This is interesting. I have a similar age and construction house, but a lot smaller, near half the size, and I am using 40kWh/day, or also about £15/day at cap prices. Pro rata, I should be using less than you - unless my house is especially leaky, or yours is especially well insulated for an old stone building. I also have to have the weather curve set much higher, 53 degrees or perhaps even more as -2, to stand any chance of getting adequate warmth, you are managing it with 41 at -2. I'm curious! Maybe it is because I had physical restrictions on the maximum size of rads I could fit in the available space, and that in turn meant a system that needs a higher LWT.

Midea 14kW (for now...) ASHP heating both building and DHW


   
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