Do heat pump cylinders have a COP?

anon_ymous

As above. Do they have their own COP alongside ASHPs? Or is the rationale for having it purely based on heating the water using night time storage?

tacpot12

In theory cylinders do have a COP, but in practice nobody really talks about them in the way they do the COP or SCOP for Heat Pumps. It's probably more useful to discuss what affects the cylinder's COP. 

The cylinder's COP is only affected by its level of insulation, because COP is measure of the heat you get out v.s. the heat you put in.

The efficiency of the heat exchanger doesn't materially affect the COP, nor does the source of the heat you use. But the source of the heat you use can have a massive impact on the cost of heating water. If you use the  Heat Pump to heat the water overnight when outside temperatures are low, the cost could would be lower than if you used the immersion heaters that such cylinders are fitted with, but higher than if you heated it using a Heat Pump during the day when outside temperatures are higher. If you can heat the cylinder using the Heat Pump during the day using solar power, this is will give you the lowest cost, and if the cylinder is well insulated, the water will remain hot until the next morning.

50mm of insulation is the bare minium and no manufacturer fits much more than this because it affects the physical size of the units and they know customers are put off if the unit is slightly bigger (but much more efficient) than other units. 

anon_ymous

tacpot12 said:

In theory cylinders do have a COP, but in practice nobody really talks about them in the way they do the COP or SCOP for Heat Pumps. It's probably more useful to discuss what affects the cylinder's COP. 

The cylinder's COP is only affected by its level of insulation, because COP is measure of the heat you get out v.s. the heat you put in.

The efficiency of the heat exchanger doesn't materially affect the COP, nor does the source of the heat you use. But the source of the heat you use can have a massive impact on the cost of heating water. If you use the  Heat Pump to heat the water overnight when outside temperatures are low, the cost could would be lower than if you used the immersion heaters that such cylinders are fitted with, but higher than if you heated it using a Heat Pump during the day when outside temperatures are higher. If you can heat the cylinder using the Heat Pump during the day using solar power, this is will give you the lowest cost, and if the cylinder is well insulated, the water will remain hot until the next morning.

50mm of insulation is the bare minium and no manufacturer fits much more than this because it affects the physical size of the units and they know customers are put off if the unit is slightly bigger (but much more efficient) than other units. 

Thanks. I found this company from the "works with Octopus" link 


https://heatandhotwatercylinders.co.uk/

I asked them what their COP was, if they have one and they responded with 

"Thanks for your email…

 

I’m not sure I fully understand your question.

 

Our cylinders, like all other hot water cylinders, don’t have their own COP.

 

Our cylinders are also different from all other hot water cylinders, they are patent protected as they can provide heating assist as well as hot water.

 

Is this the type of hot water cylinder solution you are after?

 

Thanks"

They market their cylinders as "heat pump ready" but they don't appear to actually have a COP at all? 

Ectophile

The cylinder is just a big water tank.  It doesn't mean anything to ask what the COP is.

If you have an immersion heater in the tank, that will have a COP of 1.  If you heat the tank using your ASHP, then the COP will be that of the ASHP.

anon_ymous

Ectophile said:

The cylinder is just a big water tank.  It doesn't mean anything to ask what the COP is.

If you have an immersion heater in the tank, that will have a COP of 1.  If you heat the tank using your ASHP, then the COP will be that of the ASHP.

Thanks. I took "heat pump cylinder" to mean a cylinder that has a heat pump in it's own right (Like a heat pump tumble dryer)

I didn't realise that it just means a normal water tank that's just made for heat pumps instead 

Martyn1981

waqasahmed said:

Ectophile said:

The cylinder is just a big water tank.  It doesn't mean anything to ask what the COP is.

If you have an immersion heater in the tank, that will have a COP of 1.  If you heat the tank using your ASHP, then the COP will be that of the ASHP.

Thanks. I took "heat pump cylinder" to mean a cylinder that has a heat pump in it's own right (Like a heat pump tumble dryer)

I didn't realise that it just means a normal water tank that's just made for heat pumps instead 

Yep, that's how I read your OP. As you can get HPHW cyclinders, which can 'steal' the heat from inside, or some with outside intake/venting to 'steal' from the garden, just like A2A units. Gaining popularity in the states where many hot water cylinders are located in basements or garages, so they can grab heat from there.

anon_ymous

Martyn1981 said:

waqasahmed said:

Ectophile said:

The cylinder is just a big water tank.  It doesn't mean anything to ask what the COP is.

If you have an immersion heater in the tank, that will have a COP of 1.  If you heat the tank using your ASHP, then the COP will be that of the ASHP.

Thanks. I took "heat pump cylinder" to mean a cylinder that has a heat pump in it's own right (Like a heat pump tumble dryer)

I didn't realise that it just means a normal water tank that's just made for heat pumps instead 

Yep, that's how I read your OP. As you can get HPHW cyclinders, which can 'steal' the heat from inside, or some with outside intake/venting to 'steal' from the garden, just like A2A units. Gaining popularity in the states where many hot water cylinders are located in basements or garages, so they can grab heat from there.

I guess within the UK, they're just cylinders which just so happen to connect to heat pumps? 

anon_ymous

Martyn1981 said:

waqasahmed said:

Ectophile said:

The cylinder is just a big water tank.  It doesn't mean anything to ask what the COP is.

If you have an immersion heater in the tank, that will have a COP of 1.  If you heat the tank using your ASHP, then the COP will be that of the ASHP.

Thanks. I took "heat pump cylinder" to mean a cylinder that has a heat pump in it's own right (Like a heat pump tumble dryer)

I didn't realise that it just means a normal water tank that's just made for heat pumps instead 

Yep, that's how I read your OP. As you can get HPHW cyclinders, which can 'steal' the heat from inside, or some with outside intake/venting to 'steal' from the garden, just like A2A units. Gaining popularity in the states where many hot water cylinders are located in basements or garages, so they can grab heat from there.

I guess something like this would be a "heat pump hot water heater"?

https://www.modernheat.co.uk/product/2484/

Or this? 

https://www.vaillant.co.uk/homeowners/products/the-arostor-domestic-hot-water-heat-pump-96448.html#specification

Why would you get one of those instead of say a water cylinder that's merely ready for heat pumps? 

shinytop

waqasahmed said:

Martyn1981 said:

waqasahmed said:

Ectophile said:

The cylinder is just a big water tank.  It doesn't mean anything to ask what the COP is.

If you have an immersion heater in the tank, that will have a COP of 1.  If you heat the tank using your ASHP, then the COP will be that of the ASHP.

Thanks. I took "heat pump cylinder" to mean a cylinder that has a heat pump in it's own right (Like a heat pump tumble dryer)

I didn't realise that it just means a normal water tank that's just made for heat pumps instead 

Yep, that's how I read your OP. As you can get HPHW cyclinders, which can 'steal' the heat from inside, or some with outside intake/venting to 'steal' from the garden, just like A2A units. Gaining popularity in the states where many hot water cylinders are located in basements or garages, so they can grab heat from there.

I guess something like this would be a "heat pump hot water heater"?

https://www.modernheat.co.uk/product/2484/

Or this? 

https://www.vaillant.co.uk/homeowners/products/the-arostor-domestic-hot-water-heat-pump-96448.html#specification

Why would you get one of those instead of say a water cylinder that's merely ready for heat pumps? 

You can use these to heat your HW without using an A2W ASHP for heating. So you could have A2A for heating and one of these for HW.  

anon_ymous

shinytop said:

waqasahmed said:

Martyn1981 said:

waqasahmed said:

Ectophile said:

The cylinder is just a big water tank.  It doesn't mean anything to ask what the COP is.

If you have an immersion heater in the tank, that will have a COP of 1.  If you heat the tank using your ASHP, then the COP will be that of the ASHP.

Thanks. I took "heat pump cylinder" to mean a cylinder that has a heat pump in it's own right (Like a heat pump tumble dryer)

I didn't realise that it just means a normal water tank that's just made for heat pumps instead 

Yep, that's how I read your OP. As you can get HPHW cyclinders, which can 'steal' the heat from inside, or some with outside intake/venting to 'steal' from the garden, just like A2A units. Gaining popularity in the states where many hot water cylinders are located in basements or garages, so they can grab heat from there.

I guess something like this would be a "heat pump hot water heater"?

https://www.modernheat.co.uk/product/2484/

Or this? 

https://www.vaillant.co.uk/homeowners/products/the-arostor-domestic-hot-water-heat-pump-96448.html#specification

Why would you get one of those instead of say a water cylinder that's merely ready for heat pumps? 

You can use these to heat your HW without using an A2W ASHP for heating. So you could have A2A for heating and one of these for HW.  

Thanks. I guess you use those instead of regular heat pump "ready" hot water cylinders by the likes of Mixergy?