Sunamp for UFH

[SteamyTea]

1 minute ago, JSHarris said:

Makes resistance heating a great deal easier to interface with a solar system.

One of the reasons I like resistance heating, it is so simple to control.

[Sandybay]

Hi, 

Thanks for your your responses, 

So basically you could have ASHP and storage tank, then solar pv system with a Sunamp, would the two systems work together ok? Or would you recommend any different combinations to run DHW systems in a 150 sqm bungalow? 

[Jeremy Harris]

13 minutes ago, Sandybay said:

Hi, 

Thanks for your your responses, 

So basically you could have ASHP and storage tank, then solar pv system with a Sunamp, would the two systems work together ok? Or would you recommend any different combinations to run DHW systems in a 150 sqm bungalow? 

 

 

I think it's best to split out hot water from heating altogether, when thinking about things initially, as they have different requirements.  Heating only needs low grade heat, 40°C is more than enough.  Hot water needs higher grade heat, you can get away with about 50°C, but if using a Sunamp, or a water filled thermal store, this needs to be ~65°C.

 

An ASHP is ideal for heating (and cooling) the house, as when run at modest temperatures (say, ~40°C) it will be very efficient, so will provide heating at around the same price as mains gas and a boiler.

 

For hot water a Sunamp is probably the most efficient thermal store available, but it needs to be heated to ~65°C to charge.  This means it will happily charge from a boiler, or from electricity (either from the grid or excess PV generation), but won't charge from a normal^[1] ASHP, as most ASHPs really don't like working at that sort of temperature much.

 

You can provide heat, cooling and hot water from an ASHP using a hot water cylinder (a bit larger than you'd normally fit if it was heated by a boiler), but the heat losses from the hot water cylinder will be a bit higher than from a Sunamp.  The ASHP will run with a COP of around 3 to 4 when running the heating or cooling, and this will drop to maybe 2.5 to 3 when running the hot water.  The COP is a measure of efficiency, the ratio of electricity in to heat out, so relates to running cost.

 

 

 

¹ There are some ASHPs around that will deliver hotter water.  Daikin make a hybrid, their Altherma, that includes a boost gas boiler that can be run from LPG or mains gas.  This allows the ASHP to heat to lower temperature for heating, with the hot water being boosted to a higher temperature via the gas post-heater.  There are also CO₂ ASHPs in the pipeline that may be able to operate well at ~65°C, but these aren't that readily available yet.

 

 

[Sandybay]

Thanks very much for all the information, much appreciated,

Alexander.