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Do heat pump cylinders have a COP?

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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?

Comments

  • tacpot12
    tacpot12 Posts: 9,247 Forumite
    Ninth Anniversary 1,000 Posts Name Dropper
    edited 26 February 2023 at 3:00PM
    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. 
    The comments I post are my personal opinion. While I try to check everything is correct before posting, I can and do make mistakes, so always try to check official information sources before relying on my posts.
  • anon_ymous
    anon_ymous Posts: 1,997 Forumite
    Part of the Furniture 1,000 Posts Name Dropper Combo Breaker
    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
    Ectophile Posts: 7,975 Forumite
    Part of the Furniture 1,000 Posts Photogenic Name Dropper
    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.
    If it sticks, force it.
    If it breaks, well it wasn't working right anyway.
  • anon_ymous
    anon_ymous Posts: 1,997 Forumite
    Part of the Furniture 1,000 Posts Name Dropper Combo Breaker
    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
    Martyn1981 Posts: 15,377 Forumite
    Part of the Furniture 10,000 Posts Name Dropper Photogenic
    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.
    Mart. Cardiff. 8.72 kWp PV systems (2.12 SSW 4.6 ESE & 2.0 WNW). 20kWh battery storage. Two A2A units for cleaner heating. Two BEV's for cleaner driving.

    For general PV advice please see the PV FAQ thread on the Green & Ethical Board.
  • anon_ymous
    anon_ymous Posts: 1,997 Forumite
    Part of the Furniture 1,000 Posts Name Dropper Combo Breaker
    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
    anon_ymous Posts: 1,997 Forumite
    Part of the Furniture 1,000 Posts Name Dropper Combo Breaker
    edited 26 February 2023 at 6:41PM
    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
    shinytop Posts: 2,165 Forumite
    Eighth Anniversary 1,000 Posts Name Dropper Photogenic
    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
    anon_ymous Posts: 1,997 Forumite
    Part of the Furniture 1,000 Posts Name Dropper Combo Breaker
    shinytop 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? 
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