ᐅ Interaction between Air-to-Water Heat Pump and Gas Condensing Boiler?

Hello,
I recently purchased a newly built condominium (KfW-55 standard) that is equipped with an air-to-water heat pump. During the construction phase, the developer informed me that the HVAC system was supplemented with an additional gas condensing boiler to handle high peak energy demands.

Would it have been possible to heat the domestic hot water for showers, kitchen, and sinks using only the air-to-water heat pump? I understand that a supply temperature of about 35°C (95°F) is sufficient for underfloor heating, but what about the rest? What other alternatives could have been installed alongside the air-to-water heat pump?

I’m asking because air-to-water heat pumps are commonly installed in Germany at the moment, and as far as I know, a separate energy source is needed for hot water; otherwise, the electricity costs for operating the heat pump increase significantly. Gas is becoming more expensive and will probably be increasingly subject to a CO2 tax in the future.

Best regards,
Robert

The issue with apartment buildings is that the hot water must be maintained at a minimum of 60°C (140°F) to prevent Legionella bacteria. He is probably trying to solve the problem this way.

Using an air-to-water heat pump for domestic hot water is not a problem at all. The coefficient of performance (COP) decreases as the temperature rises, but it remains sufficiently efficient.

Forsberg21 schrieb:

Would it even be possible to heat the hot water for showers, kitchen, and sinks using only an air-to-water heat pump?

Yes. This is a standard issue, even in multi-family buildings, but it needs to be properly calculated and sized.

Forsberg21 schrieb:

I’m asking because air-to-water heat pumps are currently widely installed in Germany, and as far as I know, a different energy source is required for the hot water; otherwise, the electricity costs for running the heat pump increase significantly.

Electricity costs for hot water are about 50 cents per day at most with an air-to-water heat pump. And no, under normal conditions, only the heat pump is used.

Hello,

Forsberg21 schrieb:

Would it even be possible to heat the hot water for showers, kitchen, and sinks using only the air-to-water heat pump?

That is possible and not a big problem. However, the efficiency of heat pump systems drops significantly at high temperatures (in multifamily buildings, the hot water really needs to be maintained at 60°C (140°F)).

I have often wondered whether a split configuration might be more energy-efficient. For small systems in single-family homes, the effort might be too high, but in multifamily buildings, it could definitely make sense and not just be an emergency solution. In other words, you cover the base heating load with a heat pump optimized for that, achieving relatively high efficiency. Then the gas boiler handles heating the water up to 60°C (140°F), quick reheating, and meeting high heating demand during extreme cold.

The key question is: How large is the multifamily building? If it only has 2–4 apartments, it sounds like an emergency solution to me. If it has more than 10 apartments, it could be a genuinely sensible approach.

Best regards,

Andreas

The apartment building has 25 units, and the gas condensing boiler is intended to be used only during very cold outside temperatures and in the morning when perhaps everyone wants to take a hot shower at the same time.

But how can a heat pump manage to heat the water continuously to 60°C (140°F)? I still don’t understand that. That would require significantly more electricity, and the real advantage of the heat pump diminishes.