Heat pump hot water cylinders 22 January at 5:00PM edited 22 January at 5:02PM in Green & ethical MoneySaving 2 replies 50 views

waqasahmed

So, most of these have a COP of 3.6 (theoretical)

Ie: At 35.4p/ kWh per unit, they theoretically they cost 9.83p/kWh vs 10p on gas. Or they don't technically but it's easy comparison and helps compare apples to apples somewhat 

The heat batteries can be charged at 12p/KWh at night and that's not theoretical. That's just a normal tariff

My question is, could you "charge" these at night? So they're actually costing you a theoretical 3.3p/kWh instead?

If you can, that gives them a big leg up on heat batteries 

Reed_Richards

The Seasonal (average) COP will depend on how hot you make the water.  If you quote the COP you have to quote the water temperature also or it is a meaningless number.

Yes, of course you can charge them at night.  Anything electrical has the potential to be operated at night on an Economy 7 tariff or similar.  But depending on where the heat pump is situated the noise could potentially disturb you or your neighbours.  You could probably avoid this with a little care but it's worth giving a bit of thought to.  

waqasahmed

Reed_Richards said:

The Seasonal (average) COP will depend on how hot you make the water.  If you quote the COP you have to quote the water temperature also or it is a meaningless number.

Yes, of course you can charge them at night.  Anything electrical has the potential to be operated at night on an Economy 7 tariff or similar.  But depending on where the heat pump is situated the noise could potentially disturb you or your neighbours.  You could probably avoid this with a little care but it's worth giving a bit of thought to.  

Thanks. FWIW, I have an attic and they do not so that's something. My boiler is in my attic 

That does make a heat pump cylinder look substantially better then from a cost POV. The water temperature would probably be at 40-45C?ie: showering, washing dishes

And then obviously 60C periodically

But even if the COP was 1.3, that's still cheaper than gas (if you don't count the cost of the actual cylinder) given that 12/1.3 = 9.23