Air Source Heat Pumps

albyota

eugeneg, thats a lot of juice to run per day, my total kWh use with the HP boiler for the day is about 48 units, but thats for everything, last 3 month bill was £343 so heating and HW accounts for around £185.

eugeneg

If I could find someone else with the same sort of set up I could compare settings. Trouble is, I don't know how to find any such. All I know id that £15 a day for HW, 14 radiators, lighting and this PC is a lot - way more than I was paying before I had the heat pump, although electricity prices have never been this expensive per unit before.

Cardew

eugeneg wrote: »

If I could find someone else with the same sort of set up I could compare settings. Trouble is, I don't know how to find any such. All I know id that £15 a day for HW, 14 radiators, lighting and this PC is a lot - way more than I was paying before I had the heat pump, although electricity prices have never been this expensive per unit before.

Why are you paying £15 a day for 100kWh in SE England? You can get electricity with an on-line account for around 10p/kWh.

According to the link you gave you have a 13.5 kWh Immersion heater in the 125litre heat store? So where are the 4kW and 2 kW immersion heater.

Looking at the Tech spec figures your ASHP has a COP of 2.2 at -7C up to a COP of 4.0 at 7C - however it is only producing water at 35C at that COP. In the cold weather we have been having, I suspect that the average COP will be around 3. I doubt the temperature is been above 7C in the past few weeks.

The crucial aspect is that it 'only' produces 6.9kW to 10.6kW between -7C and 7C with an average probably around 9kW

It then states that you must reduce those figures by 10% during defrosting(how often is defrosting?)

A 14 radiator house is pretty big and will require a lot of heating?

I suspect that your 'problem' is that the ASHP will be working almost flat out for much of the day using close to 3kW input and at 13.5kW the immersion heater, to boost the radiator water temperature, only needs a couple of hours a day to add another 27kWh to a hard worked heat pump.

Provided you could get your electricity for £10(for 100kWh) I really don't think that £70 a week for all electricity including heating and hot water is excessive for a large 14 radiator house in one of the coldest winters for years.

eugeneg

You're quite right - I should look for a cheaper electricity supplier. I have been waiting until our last gas appliance was removed - this was done on Thursday. I think much of my surprise at the cost of running the new equipment stems from the far cheaper prices for gas over the last 2 years. The marketing material for the ASHP makes a lot of it being used extensively in colder Nordic climes and so I did not realise how much of a boost the immersion heaters would be required to provide. As you say, this has been a particularly cold winter. And the house is only reasonably well insulated right now.

Thank you for the input Cardew - most helpful in putting my anxiety into perspective.

Cardew

A question?

As the water produced by the heat pump is only between 35C and 50C your original radiators for Gas CH would not be adequate to heat the house.(Gas CH water can be 80+C - mine ranges from 54C to 82C)

What steps were taken to increase the size of radiators? Or does the 14 you have include extra radiators?

eugeneg

Good point. All 14 are new radiators sized 20% above recommended output downstairs and 10% upstairs. I am surprised how much more efficient the new radiators are than the old ones. Perhaps positioning them under windows where possible is in part responsible. What came out of the old radiators was black gunge where once there was crystal clear water.

richardc1983

eugeneg wrote: »

If I could find someone else with the same sort of set up I could compare settings. Trouble is, I don't know how to find any such. All I know id that £15 a day for HW, 14 radiators, lighting and this PC is a lot - way more than I was paying before I had the heat pump, although electricity prices have never been this expensive per unit before.

YOu need to look into if the immersion heaters are stayin on perhaps when they should not.

I looked at the tech specs for your electric boiler:
Output immersion heater13.5 kW

And your heat pump section doesnt appear to give clear info on how much electricity it draws. Or perhaps im not understanding it...

But I notice that the starting currents are very high:

Starting current24 A 33 A

This is indicating that this is a fixed speed system. So the system will run at full speed whether it is required or not whereas the inverter systems do not require these high start up currents.

Please advise if I have got your figures wrong.

Thanks.

thechippy

richardc1983 wrote: »

YOu need to look into if the immersion heaters are stayin on perhaps when they should not.

I looked at the tech specs for your electric boiler:
Output immersion heater13.5 kW

And your heat pump section doesnt appear to give clear info on how much electricity it draws. Or perhaps im not understanding it...

But I notice that the starting currents are very high:

Starting current24 A 33 A

This is indicating that this is a fixed speed system. So the system will run at full speed whether it is required or not whereas the inverter systems do not require these high start up currents.

Please advise if I have got your figures wrong.

Thanks.

The manufacturers figures are a bit vague.

I agree, the start current (albeit a soft start system) would suggest fixed speed, so not as economical to run as an inverter. Also, the system is on R407c which is not as efficicient as the latter systems on R410a.
13.5kw heater for the water could be a real killer!!
This does seem a rather expensive system to run!.......

Something does not add up.

richardc1983

I do think the immersions are coming on too much so perhaps the settings are not correct.

thechippy

...Quite possibly.
13.5 kw is a huge amount of current to draw and at todays elec prices........:eek: