Heat pump with both UFH and hot water

[smart51]

How do you run a heat pump with both hot water and underfloor heating?  For hot water you want to run at 60°C+ but for under floor heating you want half that for improved efficiency.  Does the heat pump switch temperature when the thermostat signals heating demand or something?

[IanR]

The HP runs at two different temps, depending on whether it is heating the hot water supply or for the space heating. 

 

Typically the DHW would be heated to around 50°C and the space heating to a lower temp, ideally 35°C or less.

[Dave Jones]

and you cant have both at the same time. 

[dpmiller]

Like a gas combi then?

[smart51]

How does that work then?  With a combi, you're only going to run the hot water for a couple of minutes to fill a sink or 15 minutes in the shower?  With a 200l hot water tank, say, an 8kW heat pump would have to be on for an hour and a half to fill it.  Or does heating demand trump a hot water timer?

[ProDave]

A heat pump is more like a system boiler than a combi.  You need a hot water tank with a heat pump.

 

Most of them will only run heating or hot water at any one time and switch between them, and most allow you to set different temperatures for each.  Mine is set to run hot water heating for 30 minutes at a time when the HW tank says it needs some heat, but you can adjust the parameters to either give priority to hot water or to heating.

 

And most of us run the hot water at about 50 degrees or slightly less which plays much better with the way heat pumps work.

[IanR]

1 hour ago, smart51 said:

With a 200l hot water tank, say, an 8kW heat pump would have to be on for an hour and a half to fill it. 

 

Maybe it would take that long if it was heating the tank from cold, but it will only ever be "topping up" (unless you have underestimated your hot water usage). So 30 mins should see it raised from 40°C to 50°C.