Can one heat pump run both radiators and underfloor heating at different temperatures?

SwissMac

I'm doing a renovation and want underfloor heating upstairs and radiators downstairs (it's an upside down house) with both powered by an Air Source Heat Pump. Do I need one or two Heat Pumps for this? If I have one ASHP can it provide water to the radiators at more than 55C and at the same time water to the underfloor heating at 27C with domestic hot water for the taps too?

The house currently has oil fired heating with radiators so new flooring will need to be put in for the underfloor heating upstairs, and I have to balance the cost of new flooring downstairs as well against the extra costs of a more complicated system and would appreciate some good advice as I am being told different things by the different contractors I ask.

Keep_pedalling

You will new rads that work well at lower temperatures 

DougMLancs

One of the easiest ways around this is to size the rads downstairs to work with the flow temp of the UFH- our bedrooms have k22’s under the windows for a 35C flow temp. Depending on your heat loss, you might be able to get that down to 27C whilst keeping the rads in proportion to the room. Assuming the house has/will have some insulation, there should be no need for 55C flow temps, especially since your target temp is going to be lower for the sleeping areas anyway presumably? We only have slightly patchy CWI, all radiators and running a 35C flow with no issues. 

FreeBear

SwissMac said:

I'm doing a renovation and want underfloor heating upstairs and radiators downstairs (it's an upside down house) with both powered by an Air Source Heat Pump. Do I need one or two Heat Pumps for this? If I have one ASHP can it provide water to the radiators at more than 55C and at the same time water to the underfloor heating at 27C with domestic hot water for the taps too?

You are thinking with a mindset locked in to gas/oil boilers. Heat pumps work best with a low & slow method. So you size the radiators and UFH to run at the same low temperature. Size the radiators correctly, and you will never need to run them hot.

Even although I have a gas boiler here, the system will modulate down to a flow temperature of 35°C (only have radiators, no UFH). This is enough to match the heat loss on all but the coldest of days. But if I want to raise the room temperature, I'd need bigger radiators at that flow temp.

Reed_Richards

I have investigated this.  With a mixture of radiators and UFH you will very likely need the water for your UFH to be cooler than the water for your radiators.  Also, you will probably have to run your UFH 24/7 whereas you might want a night-time setback for the radiator-heated rooms, in which case the radiators will effectively be off for a period of time.  So the best compromise is a heat pump with two zones, one for the UFH and one for the radiators.  The heat pump must then reduce the Leaving Water Temperature when the radiator zone is not calling for heat as that will give you the best economy of operation.  A few heat pumps can do that but most cannot.  If your heat pump cannot then you don't get any economic benefits from UFH plus radiators compared to just radiators.

Also, if you are thinking of running your radiators at more than 55 C then you have failed to grasp how to use a heat pump economically.