Octopus Heat Pumps

Reed_Richards

My cheap rate electricity lasts until 7 am (which is a bit more convenient than 5 am).  My heating is set back to 18 C overnight but the temperature rarely drops that low so it rarely comes on.  It's set to come on and start heating the house at 04:30.  The hot water tank is set to heat from 06:15 and it usually takes about 40 minutes to top-up the tank temperature.  I heat the hot water to 55 C, as much as the heat pump will do on its own.  I used to make it 50 C before I got the cheap night-rate electricity.

You're right about heat pumps being at their least efficient when it's coldest outside and so you need the most heat.  But it evens out over the year; when it's milder out they're much more efficient.  Hence the figure you will see quoted is the Seasonal Coefficient of Performance, an average for a full year.    

michaels

Reed_Richards said:

My cheap rate electricity lasts until 7 am (which is a bit more convenient than 5 am).  My heating is set back to 18 C overnight but the temperature rarely drops that low so it rarely comes on.  It's set to come on and start heating the house at 04:30.  The hot water tank is set to heat from 06:15 and it usually takes about 40 minutes to top-up the tank temperature.  I heat the hot water to 55 C, as much as the heat pump will do on its own.  I used to make it 50 C before I got the cheap night-rate electricity.

You're right about heat pumps being at their least efficient when it's coldest outside and so you need the most heat.  But it evens out over the year; when it's milder out they're much more efficient.  Hence the figure you will see quoted is the Seasonal Coefficient of Performance, an average for a full year.    

Thanks

What are your day and night temperatures and how big is your house and what EPC/energy efficiency?  Do you know how much power it consumes hourly for different outside temperatures maintaining that temperature?

Reed_Richards

My set temperatures (C) are:

22:00-04:30 18 
04:30-06:59  20 (doesn't reach 20)
[06:15-~06:55 Off whilst heating water]
06:59-09:30  19.5
09:30-15:00  20
15:00-22:30  20.5

My detached bungalow has a floor area of 167 m2 according to my EPC
It scored a D rating on the EPC when I bought it, raised to a B two years later, largely because I got solar panels.  This was before my heat pump was installed.  My EPC estimates I use 15900 kWh per year for heating and 2987 kWh per year for hot water.

I don't think my hourly power consumption would be consistent enough to be meaningful.  I record the daily consumption after 22:30 when it is "off".  The highest daily consumption so far this month was recorded on 17th January when the temperature got down to about -5 C overnight and around 0 during the day.  That was 43.26 kWh.  Yesterday the outside temperature rose to about 11 C and the power consumed was 18.99 kWh, the least this month.  These figures cover hot water as well as space heating.

My running average power consumption in the 3 years and 1 month since I got an ASHP is 16.2 kWh per day.       

michaels

Reed_Richards said:

My set temperatures (C) are:

22:00-04:30 18 
04:30-06:59  20 (doesn't reach 20)
[06:15-~06:55 Off whilst heating water]
06:59-09:30  19.5
09:30-15:00  20
15:00-22:30  20.5

My detached bungalow has a floor area of 167 m2 according to my EPC
It scored a D rating on the EPC when I bought it, raised to a B two years later, largely because I got solar panels.  This was before my heat pump was installed.  My EPC estimates I use 15900 kWh per year for heating and 2987 kWh per year for hot water.

I don't think my hourly power consumption would be consistent enough to be meaningful.  I record the daily consumption after 22:30 when it is "off".  The highest daily consumption so far this month was recorded on 17th January when the temperature got down to about -5 C overnight and around 0 during the day.  That was 43.26 kWh.  Yesterday the outside temperature rose to about 11 C and the power consumed was 18.99 kWh, the least this month.  These figures cover hot water as well as space heating.

My running average power consumption in the 3 years and 1 month since I got an ASHP is 16.2 kWh per day.       

Interesting your hourly consumption is not equal as for us for gas with the modulating boiler it tends to look very flat, only increasing where there is hot water heating and a bit higher early morning and into the evening when outside temps are lower.

Your area and EPC demand seem very similar to ours on paper, not sure if our leakage is as good as the EPC suggests in reality unfortunately.

One area where we use well above EPC is hot water heating as we are big on baths and showers and also have some long pipe runs.  Don't suppose you have any way to separate heating and hot water demand?  I did think just comparing summer and winter would do this but given the variation in old mains water temp I suspect there may be more to it than that.

Reed_Richards

michaels said:
 

Interesting your hourly consumption is not equal as for us for gas with the modulating boiler it tends to look very flat, only increasing where there is hot water heating and a bit higher early morning and into the evening when outside temps are lower.

That's probably because I use a third party controller that overrides the manufacturer's controller.  This means that the heat pump has no idea of how close the room is to it's set temperature so cannot do any form of Load Compensation.  It has a water temperature target set by Weather Compensation but that is too easily upset by solar gain or frequent comings and goings letting cold air in.  The only time it maintains near-constant electricity consumption is in the early part of the day when it is actively making the house warmer so the third party room thermostat does not intervene.   

Spies

Reed_Richards said:

michaels said:
 

Interesting your hourly consumption is not equal as for us for gas with the modulating boiler it tends to look very flat, only increasing where there is hot water heating and a bit higher early morning and into the evening when outside temps are lower.

That's probably because I use a third party controller that overrides the manufacturer's controller.  This means that the heat pump has no idea of how close the room is to it's set temperature so cannot do any form of Load Compensation.  It has a water temperature target set by Weather Compensation but that is too easily upset by solar gain or frequent comings and goings letting cold air in.  The only time it maintains near-constant electricity consumption is in the early part of the day when it is actively making the house warmer so the third party room thermostat does not intervene.   

Are you happy with the overall performance? 

Reed_Richards

Spies said:
 

Are you happy with the overall performance? 

Yes, I'm very pleased with it.  If I was starting again from scratch there a few things I would change but I don't think these would have much influence on the actual performance.     

MultiFuelBurner

I am guessing those that retro fit ASHP are where the best details comparisons for running costs can be found such as @Reed_Richards @Spoonie_Turtleand @matt_drummer installs.

I do think the grant of £7500 is an amazing opportunity not to be missed and should at the very least cover all the parts required for a retrofit including radiators (unless we are talking above average property)

I also believe with electricity prices forecast to be an average 22/23p kWh over the next year from April (my guesstimate from the info available)even without a fancy smart TOU tariff it could be a good time to take the plunge as well for those on the fence. 

I eagerly await other knowledgeable people to take the plunge such as @QrizB

Alnat1

I've gone for it but after a second visit by the surveyor last week, it has been confirmed that we need planning permission for the 8Kw Daikin unit at our 4 bed detached. It will be placed centrally at the back of our house and we're told it exceeds the noise assessment. If a detached can't meet the requirements, how can anyone in a semi or terraced house expect to ever get one installed?

Luckily Octopus have said they will deal with and pay for the planning application, with no increase in our £3000 cost but that does mean we haven't yet been given an install date. We made the initial £500 payment at the end of September.

Martyn1981

That's nice to know about Octopus dealing with the planning permission. In Wales you need PP if any part of the unit is within 3m of the boundary (1m in England), so PP looks like being necessary for the majority of properties here (currently).