Communal heat pump kWh cost

iambigred

Hi,

Hopefully a simple question regarding kWh costs in heat pump installations!..

I live in a new build apartment building which has an air source heat pump system installed that provides a source of hot water for the underfloor heating. Each apartment has a heat meter that measures the amount of heat transferred through the underfloor heating system.

The first 4 quarters heating bills showed the kWh reading from the heat meter as the number of 'units' then an equivilent kWh figure that is the number of units divided by 3. e.g. heat meter says 600 kWh, so 600 'units' reading on the bill = 200 kWh on the bill. This results in a cost of 0.039p per kWh (0.117625/3)

I assumed this was correct since a heat pump with a co-efficient between 3-4 means that for every 1kW into the heat pump produces 3kW of heat energy. Therefore is it correct that I'm billed 1/3rd of the kWh cost?

Recently I received a letter from the apartment management saying that 'due to an error in the base calculation of the kilowatt hours consumed, all the previous invoices which you have received have been incorrect (the units were divided by 3 in error)'. Obviously I was annoyed by this and questioned with development management, however they were clueless.

Anyone have any ideas which is right? Either they're right and the promise of cheap underfloor heating was a lie, or they're trying to make a quick buck by charging three times the cost.

Thanks!

Swipe

You will be billed for the amount of kWh consumed by the heat pump and it should not be divided by 3. The co-efficient of performance is irrelevant to your bill as it just relates to the actual heat output by the heat pump compared to the electricity used.

Cardew

Agree with Swipe above!

There is no way anyone can measure the output of the Heat pump. The COP(Co-efficient of Performance) might well be 3 as you suggest - it could be 2.0 or 4.0.

Using your example, if the heat pump uses 200kWh you simply pay for one third of that amount. However it sounds as if it has used 600kWh and you pay for one third of that amount.

iambigred

Cardew wrote: »

Agree with Swipe above! Using your example, if the heat pump uses 200kWh you simply pay for one third of that amount. However it sounds as if it has used 600kWh and you pay for one third of that amount.

Thanks for your help but I'm not sure I understand, you say that agree with Swipe but then go on to say that you only pay 1/3rd!

I don't know how much power the heat pump itself has consumed, all I know is how much heat energy transfer (in kWh) that has passed through my underfloor system from the heat meter.

If you search on Google for 'heat pump economics' (sorry it won't let me post the link as I'm a new user) then the first link on the pipex.com domain suggests that the kWh should be divided by the COP, resulting in a per kWh price of 3.9 pence (as I was originally being charged, rather than 11p).

Cardew

Can you put that link on here leaving gaps i.e. www. pipex/xyz. com

I don't know what you mean by 'heat meter'. Unless it is just a device for measuring the amount(volume) of warm water that has passed through your underfloor heating(UFL).

As you said it was a communal heat pump, I assume the pump feeds all 3 apartments?

All that matters is how much electricity the heat pump consumes and how it is apportioned between the 3 flats. If the cost was split equally between the 3 flats and it consumed 600kWh you would each pay for 200kWh. If this heat meter is some way of charging according to usage it might be that you have used, say, 50% of the warm water and the other two flats 25% each.

iambigred

That website is www. arca53.dsl.pipex .com/index_files/hpfrig5.htm

The heat meter measures the volume and temperature of warm water passing through the UFL, and gives a kWh reading. There are actually 85 apartments (not 3).

Cardew

iambigred wrote: »

That website is www. arca53.dsl.pipex .com/index_files/hpfrig5.htm

The heat meter measures the volume and temperature of warm water passing through the UFL, and gives a kWh reading. There are actually 85 apartments (not 3).

That link explains how a COP is derived.

It is your 'heat meter' than needs explanation i.e. How does it give a kWh reading?

A flow meter is one aspect, but what was the 'start' temperature of the water,

What temperature is the water when it leaves your flat?

What about the electricity to run the pump(to pump the water) and go through the defrost cycles in winter.

The heat pump will just measure total electricity consumed, no way of determining the electricity just used by the pump, defrost cycles, and the heat lost in the pipes leading to the various apartments.


More info on 'heat meter' required.

P.S.
A problem with all heat pumps, even in a single house application, is there is no easy way to measure the overall COP of the heat pump system, as without sophisticated measuring instruments it is not possible to measure the heat produced in a water circulating system.

iambigred

I just need to know if being charged £0.11 per kWh is correct or not.

Everything I've read about heat pumps claims how efficient they are, yet how are they more efficient if the unit cost that I'm being charged is the same as from Southern Electric?

This time of year my underfloor heating is on almost constantly and it's costing me a fortune to heat an average sized 2 bedroom flat, and it doesn't even seem that warm

Edit: incoming water is 29-31deg, outgoing is around 22-23deg initially, flow rate (I think) is up to 0.2m³. Heat meter is one of these qundis.com/ fileadmin/images/download/datenblaetter/en/N5333en_110419_WaeZ_WFx2.pdf

Swipe

iambigred wrote: »

I just need to know if being charged £0.11 per kWh is correct or not.

11p/kWh sounds correct. However, for each kWh used by the heat pump you may be getting up to 3KW of heat, so you are getting a good deal as far as electric heating goes.

Cardew

iambigred wrote: »

I just need to know if being charged £0.11 per kWh is correct or not.

Everything I've read about heat pumps claims how efficient they are, yet how are they more efficient if the unit cost that I'm being charged is the same as from Southern Electric?

This time of year my underfloor heating is on almost constantly and it's costing me a fortune to heat an average sized 2 bedroom flat, and it doesn't even seem that warm

Edit: incoming water is 29-31deg, outgoing is around 22-23deg initially, flow rate (I think) is up to 0.2m³. Heat meter is one of these qundis.com/ fileadmin/images/download/datenblaetter/en/N5333en_110419_WaeZ_WFx2.pdf

Sorry to make this appear complicated - but it is!

OK your sophisticated heat meter will produce a figure for the heat used and converts that into kWh.

Do you know how many flats are run by a communal heat pump?

However as you alluded to in the first post there must be a COP factor that reduces the price per kWh that you should pay. e.g. if the overall COP of the system was, say, 3.0 you should pay 3.66p per kWh(11p/3) if the COP was 2.0 you would pay 5.5p per kWh etc etc.

However the COP in the mild November might have been 3.18 and this cold December it will be 1.8. So how are you charged?

Even more complicated is how can they possibly work out the system COP? The only way would be to add up the total kWh from each individual heat meter and divide by the consumption of the heat pump.

e.g. Take 4 flats, in a month their heat meters indicate the flats have used 4,000kWh. The input to the heat pump was 1,500kWh thus the COP is 2.67. So the effective cost per kWh at the flat is 11p/2.67 = 4.125p.

In practice they could never work this out for 85 flats. I suspect they either estimate an overall figure and take/return any discrepancy from/to the Service Charge.

or

They estimate a figure - say COP = 2.5 - and set the heat meter so that if you use 250kWh the meter reads 100kWh and you pay for that at 11p/kWh.