Heat Pump - KwZ usage through the roof

NedS

john-306 said:

matt_drummer said:

My water tank has just been heated using 700W at a COP of 4.46

It generated 3.05kWh of heat

I get 15p per kWh for solar export.

The cost of heating my tank with the heat pump was 10.5p (15p x .0.7, the solar export I gave up) and if I had used any form of direct water heating it would have cost me 45.75p

So I am 30.25p better off today by using the heat pump.

That's excellent COP for HW

I'm due to have same as your heat pump fitted in 2 weeks, but nowhere near your sized radiators. 
I've only got solar with 6.4kwh battery at present.

I'm assuming I'd struggle with heat pump in winter to only use the battery through the higher pricing hours if I go to the Cosy tariff?

Thanks.

I'm thinking the same as you - that Cosy looks a great tariff for those with an ASHP and batteries that can shift the majority of their usage to the cheap Cosy slots. The battery basically needs to be large enough to allow it to be fully charged during the cheap 3h slots, and then last for the next 6h of normal/peak rate. If you can load shift other usage a bit too, into the cheap slots, that will help (put the washing machine on at 6am and the dishwasher on at 10pm). At least you should be able to fully recharge between 1-4pm and then completely avoid importing in the 4-7pm peak. You can also try increasing the house temps slightly in the Cosy cheap slots and setting back the temp by a degree or so outside of that, which may help, depending how quickly your house loses heat and how much fluctuation you can tolerate.

Unfortunately we don't have batteries, so I'm planning on sticking with Agile, but we are tracking Cosy closely on the Octopus Compare app to see how it compares.

As Matt says, it's all about the average price you pay. You may struggle on the very coldest days, but for 95% of the year, you may be able to run at or near an effective import price of 11p, and with a SCOP of 4 it will be less than half the price of gas.

NedS

john-306 said:

matt_drummer said:

My water tank has just been heated using 700W at a COP of 4.46

It generated 3.05kWh of heat

I get 15p per kWh for solar export.

The cost of heating my tank with the heat pump was 10.5p (15p x .0.7, the solar export I gave up) and if I had used any form of direct water heating it would have cost me 45.75p

So I am 30.25p better off today by using the heat pump.

That's excellent COP for HW

Just checked our data for June, July and Aug where we've been running a DHW cycle once daily (and mostly no heating), our monthly SCOPs have been 3.52, 3.72 and 3.78. The heat pump was only installed in June so we were still tweaking the setup at the start, hence the small improvement into July and August, so I'll say we are averaging a SCOP of 3.75 during summer just heating DHW.

Pile_o_stone

NedS said:

We can schedule the DHW cycle to run at the cheapest time of the day, and then shower at our convenience. It would be far less flexible trying to limit showering using the electric shower to the cheaper Agile slots. I don't think the family would take well to showering at 3:30am or waiting until 2:30pm in the afternoon for a shower. For this reason, the amount paid for that 1kWh to heat the DHW tank may be significantly less than the amount paid to take that electric shower using the same 1kWh.

For us an ASHP is a more efficient and ultimately cheaper way to heat DHW.

A good point, well made! 
I hadn't considered the possibility of heating a tank of HW during off-peak tariffs. Thanks.

JEdelman

Update: we’re currently in the process of having the inspection carried out but already a number of major issues have been identified. This is the insulation on the pipes going into the house which I’m told is seriously inadequate.