Heat pump hot water cylinder + boiler

70sbudgie

waqasahmed said:

70sbudgie said:

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. 

I guess you could also potentially use the heat pump cylinder whilst still on gas? And when the time comes, pop it onto an ASHP? 

Yes, that is what I meant. Switch your hot water to a heat pump cylinder and keep the gas boiler for heating. This would probably need some pipework reconfiguration to separate the DHW from the CH. This would allow you to significantly reduce your gas consumption (to zero unless you cook on gas) during the summer months when you're not using the heating. 

But then when it was time to replace the boiler, you'd keep the heat pump cylinder. You might have to get planning consent for the heating heat pump as permitted development only covers one heat pump. (Unless the rules change before then). But it would also allow a smaller main heat pump, as it doesn't need to supply DHW - that is already sorted with the HP cylinder. 

anon_ymous

70sbudgie said:

waqasahmed said:

70sbudgie said:

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. 

I guess you could also potentially use the heat pump cylinder whilst still on gas? And when the time comes, pop it onto an ASHP? 

Yes, that is what I meant. Switch your hot water to a heat pump cylinder and keep the gas boiler for heating. This would probably need some pipework reconfiguration to separate the DHW from the CH. This would allow you to significantly reduce your gas consumption (to zero unless you cook on gas) during the summer months when you're not using the heating. 

But then when it was time to replace the boiler, you'd keep the heat pump cylinder. You might have to get planning consent for the heating heat pump as permitted development only covers one heat pump. (Unless the rules change before then). But it would also allow a smaller main heat pump, as it doesn't need to supply DHW - that is already sorted with the HP cylinder. 

Thanks. That does seem pretty decent, though I've since seen this

https://www.vaillant.co.uk/for-installers/products/arostor-domestic-hot-water-heat-pump-58880.html

Which you could surely use instead of a regular "heat pump ready cylinder" given it actually heats up water pulling the air around it, and therefore has a COP

70sbudgie

waqasahmed said:

Thanks. That does seem pretty decent, though I've since seen this

https://www.vaillant.co.uk/for-installers/products/arostor-domestic-hot-water-heat-pump-58880.html

Which you could surely use instead of a regular "heat pump ready cylinder" given it actually heats up water pulling the air around it, and therefore has a COP

This is actually what I thought you were talking about - a cylinder with an integrated heat pump.

How does a heat pump ready cylinder differ from a modern hot water tank? When we needed to replace our combi boiler several years ago, we changed to a system boiler and installed a modern hot water tank. I actually went for a dual coil tank as I was interested in solar thermal and the increase in price wasn't too significant. In the end I haven't gone down the route of solar thermal, but I would be very disappointed if I couldn't use my tank with a heat pump because I bought it at a time when "heat pump ready" wasn't a thing.

anon_ymous

70sbudgie said:

waqasahmed said:

Thanks. That does seem pretty decent, though I've since seen this

https://www.vaillant.co.uk/for-installers/products/arostor-domestic-hot-water-heat-pump-58880.html

Which you could surely use instead of a regular "heat pump ready cylinder" given it actually heats up water pulling the air around it, and therefore has a COP

This is actually what I thought you were talking about - a cylinder with an integrated heat pump.

How does a heat pump ready cylinder differ from a modern hot water tank? When we needed to replace our combi boiler several years ago, we changed to a system boiler and installed a modern hot water tank. I actually went for a dual coil tank as I was interested in solar thermal and the increase in price wasn't too significant. In the end I haven't gone down the route of solar thermal, but I would be very disappointed if I couldn't use my tank with a heat pump because I bought it at a time when "heat pump ready" wasn't a thing.

Heat pump ready = you can connect those pipes into a gas combi boiler or a heat pump. It therefore doesn't have it's own COP but just acts as a normal thermal store

The heat pump ready ones are those that would connect to your external heat pump, but they don't then have their own COP. I believe that the heat pump water heaters connect into an ASHP AND have their own COP which is kinda cool

The architect I'm talking to, suggests putting a Vaillant Arastor outside instead too

It doesn't help when heat pump "ready" cylinder vendors refer to themselves as being "heat pump cylinder vendors" which imo means that it has a heat pump inside 

Reed_Richards

Much as you need larger surface area radiators to work with the lower water temperature provided by a heat pump, your hot water cylinder needs an internal coil with a larger surface area, which I think is just achieved by making it longer.  With a normal shorter coil it would take too long to heat up the cylinder and your heat pump might cycle while trying to do this because the water passing through the cylinder was not losing enough heat.  

michaels

First name Heath, second name Robinson.  I was gifted a second user ASHP (used as a swimming pool heater) and have just plumbed it in parallel to one rad on the heating circuit where it works in conjunction with the gas boiler (boiler has weather comp so generally needs a lower circulating temp than the heat pump provides so the gas never comes on).  Gas boiler is a '4 pipe' system ie diverter valve and pump are inside boiler so the boiler still does the hot water tank on its own which makes sense as it needs a higher temp so the HP is not really efficient for it.  Immersion in tank works with cheap period electricity and electricity export diverter to support with hot water too.