Heat pump hot water cylinder + boiler

waqasahmed

I've currently just got a combi boiler 

I was wondering if say I put a heat pump hot water cylinder in there, would that work? Like this, but instead of a hybrid ASHP/gas but instead a hybrid HP hot water cylinder solution

https://www.youtube.com/watch?v=nce8VuXmgrU

My rationale is:
I'll eventually get a full heat pump system anyway but it's a way of making costs a tad more manageable , and I'm not aware of the government giving any grants for just the cylinder bit? Also, if it's smart enough it'd hopefully get that high COP when the temperatures are more reasonable too, and then go back to gas for when the COP is below say a defined amount 

Screwdriva

You could get a heat pump integrated into a hot water cylinder. These are compatible with ASHPs and also come with small immersion elements (1.2 kW if memory serves). 

Reed_Richards

Okay, for heating and hot water you have two choices:

1. A heat pump with suitable pipes, radiators and hot water cylinder
2. A hybrid system combining a gas (or oil) boiler with a heat pump (as per the video).  At current fuel prices that would probably be a bit more expensive to run but would enable you to keep your current pipes and radiators.

For just hot water you can get cylinders with a dedicated heat pump.  This can potentially draw air from:

1. Inside - but then you'll be cooling your inside to heat the hot water.  And there might be noise.
2. Outside
3. Outgoing - a sort of combined extractor fan and heat pump

You can usually install one heat pump without the need for planning permission but if you got one heat pump for your hot water you might then need planning permission if you wanted a second one to heat your house.
  

waqasahmed

Reed_Richards said:

Okay, for heating and hot water you have two choices:

1. A heat pump with suitable pipes, radiators and hot water cylinder
2. A hybrid system combining a gas (or oil) boiler with a heat pump (as per the video).  At current fuel prices that would probably be a bit more expensive to run but would enable you to keep your current pipes and radiators.

For just hot water you can get cylinders with a dedicated heat pump.  This can potentially draw air from:

1. Inside - but then you'll be cooling your inside to heat the hot water.  And there might be noise.
2. Outside
3. Outgoing - a sort of combined extractor fan and heat pump

You can usually install one heat pump without the need for planning permission but if you got one heat pump for your hot water you might then need planning permission if you wanted a second one to heat your house.
  

Thanks. If I want to move fully to heat pumps anyway, I guess it'd have to be the first option?

I do need to seriously upgrade my pipes and radiators anyway 

waqasahmed

Reed_Richards said:

Okay, for heating and hot water you have two choices:

1. A heat pump with suitable pipes, radiators and hot water cylinder
2. A hybrid system combining a gas (or oil) boiler with a heat pump (as per the video).  At current fuel prices that would probably be a bit more expensive to run but would enable you to keep your current pipes and radiators.

For just hot water you can get cylinders with a dedicated heat pump.  This can potentially draw air from:

1. Inside - but then you'll be cooling your inside to heat the hot water.  And there might be noise.
2. Outside
3. Outgoing - a sort of combined extractor fan and heat pump

You can usually install one heat pump without the need for planning permission but if you got one heat pump for your hot water you might then need planning permission if you wanted a second one to heat your house.
  

Would it be better to have two heat pumps? Or could you just rip out your existing one and upgrade? 

Reed_Richards

If you had an air-to-water ASHP to heat your house then it could do your hot water as well so I see no reason to spend money on another one that can only do hot water.  If you used one or more air-to-air heat pumps to heat you house then you would need some other means of heating your hot water (as things stand).  You should be able to run an air-to-air heat pump more economically than an air-to-water type.

70sbudgie

If you had a hp integrated cylinder for dhw would it enable a smaller air to water hp for the central heating? Would this enable increased efficiency?

waqasahmed

Reed_Richards said:

If you had an air-to-water ASHP to heat your house then it could do your hot water as well so I see no reason to spend money on another one that can only do hot water.  If you used one or more air-to-air heat pumps to heat you house then you would need some other means of heating your hot water (as things stand).  You should be able to run an air-to-air heat pump more economically than an air-to-water type.

So realistically I should just save up to get it for both? 

Reed_Richards

waqasahmed said:

So realistically I should just save up to get it for both? 

That would be my recommendation.

70sbudgie said:

If you had a hp integrated cylinder for dhw would it enable a smaller air to water hp for the central heating? Would this enable increased efficiency?

Unless your house is really energy efficient you will use a lot more power keeping it warm than you will in heating your hot water.  So your heating heat pump could only potentially be a little bit smaller if it was not required for hot water.

waqasahmed

Reed_Richards said:

waqasahmed said:

So realistically I should just save up to get it for both? 

That would be my recommendation.

70sbudgie said:

If you had a hp integrated cylinder for dhw would it enable a smaller air to water hp for the central heating? Would this enable increased efficiency?

Unless your house is really energy efficient you will use a lot more power keeping it warm than you will in heating your hot water.  So your heating heat pump could only potentially be a little bit smaller if it was not required for hot water.

Thanks. I'll get the other stuff sorted first though like the pipes, radiator size, air tightness etc. 

70sbudgie

Reed_Richards said:

waqasahmed said:

So realistically I should just save up to get it for both? 

That would be my recommendation.

70sbudgie said:

If you had a hp integrated cylinder for dhw would it enable a smaller air to water hp for the central heating? Would this enable increased efficiency?

Unless your house is really energy efficient you will use a lot more power keeping it warm than you will in heating your hot water.  So your heating heat pump could only potentially be a little bit smaller if it was not required for hot water.

Last time I calculated the contribution of hot water to gas consumption for our house, it was about 15%. 

I appreciate that wouldn't translate directly to a 15% reduction of a heat pump, but I'm trying to get my head around where a threshold might make sense for it being worthwhile or not. I guess it would come down to individual assessment for a property, how much hot water, how efficient the central heating (radiators) etc are, and as you say, how energy efficient the house is in general.

But another upside to a hp integrated cylinder is that it could allow a staged investment. Rather than having to save up to pay for a cylinder at the same time as overhauling the entire heating system, a hp cylinder could be installed ahead of time and with some thoughtful implementation of tou tariffs, may allow savings in the short term that would help with saving up for the bigger purchase of the central heating hp.