As much out of curiosity, whats the difference between a solar and a heat pump tank, that accounts for £521 difference in price?

Both are 500l, the cheaper has 2 coils

 

https://www.cylinders2go.co.uk/shop/renewable-energy/telford-tempest-500-litre-twin-coil-solar-indirect-unvented-cylinder/

 

https://www.cylinders2go.co.uk/shop/renewable-energy/500-litre-telford-tempest-heat-pump-cylinder-twin-immersion/

The heat pump coil has a much larger surface area and is much bigger, pretty much filling the whole height of the tank.  It is because heat pumps work better at lower temperatures, so by having a larger area input coil, the heat pump does not have to run at much higher temperature than your target  temperature.

 

If you are planning solar thermal as well, speak to C2G and see if they can do a heat pump coil and a solar coil in one tank?

 

Mine is a 300L cylinder and I don't recall the heat pump coil being anything like that much more.

2 hours ago, ProDave said:

The heat pump coil has a much larger surface area and is much bigger, pretty much filling the whole height of the tank.  It is because heat pumps work better at lower temperatures, so by having a larger area input coil, the heat pump does not have to run at much higher temperature than your target  temperature.

Not quiie sure I understand the maths of all this.

 

As I understand it the less the temprature difference between air temprature and the required water temprature, within the parameters of the ASHP output, the better the COP.

 

Yes the bigger the surface area of the coil the quicker the heat transfers to the water, however the less the temprature change the more efficient the ASHP. This is the same with the heating.

 

So lower and longer should be more efficient than higher and quicker even when the amount of heat exchanged from the output of the ASHP to the heating / hot water is the same in both instances.

 

However the water temp needs to be comparatively high for the hot water.

 

Perhaps I missed something..  

 

M

 

 

10 minutes ago, Marvin said:

Perhaps I missed something

Heating (and cooling) is not linear.

As the store temperature rises, so do the thermal losses. This means that there is less power difference (set by T0 - T1) on the input side, and the transfer area, which is fixed.

T=Tₐ-Ce⁻ᵏᵗ

Edited September 4, 20215 yr by SteamyTea