ᐅ Air-to-water heat pump for underfloor heating and separate heat pump for domestic hot water

Hello, today I visited a heating company for the first time. They gave me an offer for an air-to-water heat pump Fujitsu WPYA 100LA 10 kW, and separately a domestic hot water heat pump for the washing machine Feinwerk 270/200LS. I was surprised to learn that there is no buffer tank for the underfloor heating. Are these heat pumps suitable? And is it better to have separate heat pumps or rather a combined system? I appreciate any information, as I am a complete beginner in this field. Detached house 170 m² (1830 ft²) ground floor and upper floor + 85 m² (915 ft²) basement. Best regards

Hello,

fkay01 schrieb:
.... I was offered an air-to-water heat pump Fujitsu WPYA 100LA 10kW, and a separate heat pump for hot water for the washing machine Feinwerk 270/200LS. ....

In most cases, a separate heat pump for hot water is unnecessary!

fkay01 schrieb:
.... I wasn’t aware that there is no buffer tank for underfloor heating....

For well-designed systems, an additional buffer tank is usually not needed for heating operation. However, as always, there are exceptions.

fkay01 schrieb:
.... Are these heat pumps okay?

How can this be reliably answered without knowing the necessary boundary conditions?
Counter question:
What heating capacity is required for space heating and for hot water preparation? In other words, what are the design heating load and the room heating loads? How was the underfloor heating designed (flow rates, supply return temperature difference, temperature spread)?
What is the actual annual energy demand for heating and hot water?

Best regards,

NB: Manufacturer performance specifications for air heat pumps never refer to the required design point of the individual construction project!

Thank you for the response. Does that mean a separate air-to-water heat pump for heating and a heat pump for hot water doesn’t make sense, and they should be combined instead? Have I understood that correctly? In that case, wouldn’t the air-to-water heat pump always run for the shower water, for example, instead of just the smaller heat pump for domestic hot water? As I mentioned, I’m not an expert in this field. )

Well, of course, there are probably some tricks to optimize the heat pump for higher temperatures, but here you have double the equipment.
We are installing a standard air-to-water heat pump with two buffers (one 300-liter (79-gallon) hot water tank and one 350-liter (92-gallon) separation buffer tank).
The purpose of the separation buffer tank is to allow the heat pump to heat or cool the buffer tank once the domestic hot water is fully heated, especially when the photovoltaic system is still supplying energy.
Additionally, the separation buffer tank reduces the switching frequency of the heat pump; for example, the buffer tank is heated up to 37 or 38°C (99 or 100°F), and when it drops to 33°C (91°F), the heat pump switches on again.
This way, the heating circuit is hydraulically decoupled from the heat source and the domestic hot water circuit.
In terms of efficiency, if I’m not mistaken, it is worse than without the separation buffer tank because there are additional losses. But that doesn’t matter to me since the heat pump is installed on the ground floor in a heated room.

Hi, is 270 liters (71 gallons) actually enough for a family of 4, maybe 5 in the future? What are the advantages of an integrated air-to-water heat pump and domestic hot water storage tank?

merlin667 schrieb:
...Additionally, the intermediary buffer tank reduces the switching frequency of the heat pump, meaning the buffer tank is heated up to 37 or 38°C (99°F or 100°F), and when it cools down to 33°C (91°F), the heat pump starts again...

What is an intermediary buffer tank? Buffer tanks in the heating circuit, except for serial types, are true efficiency killers and should preferably be avoided, which is usually achievable with proper system dimensioning.

merlin667 schrieb:
...This way, the heating circuit is hydraulically decoupled from the heat generator and domestic hot water circuit.

Why would this be necessary here?

merlin667 schrieb:
...In terms of efficiency, if I’m not mistaken, it’s worse without an intermediary buffer tank because it also has losses. But that doesn’t matter to me since the heat pump is located on the ground floor in a heated room.

Standby losses play a minor role as long as the tank is within the building’s thermal envelope. In the energy balance, this is considered as heating gain. For details, refer to the energy saving regulations or KfW verification.
What is critical are the significantly higher heating medium supply temperatures compared to a proper system design. The achievable annual performance factor of such poorly designed systems is rather modest. Higher investment, lower returns! This is an unfavorable combination.

Best regards.