Heating / Hot water in the passive house

Hello everyone,

we are currently in the rough preliminary planning of our new single-family house. The whole thing is supposed to be a passive house. We do not yet know how large it will be and whether we might possibly include my parents in the project (house), so I cannot make any statements about heat demand and square meters. In general, I am wondering how to reconcile the low flow temperature of underfloor heating in a passive house (which is desired) with the hot water demand of 4-6 people.

Since the heating energy demand in a passive house is very low and you can work with low flow temperatures in surface heating, a heat pump would be suitable for the heating energy. But from the 27 °C heating water to the >45 °C hot water (which should also, for legionella reasons, generally be raised to 60 °C (???)) is still a long way. With which heating systems can this be economically managed together?

Gas is probably the cheapest to purchase, but with such small capacities, I am not sure if that should be done. I personally find the option with photovoltaics and self-consumption through heat pumps quite appealing, and for a certain degree of independence, we would probably also pay a premium. But which heat pump systems are suitable for the two different requirements (27° vs. 45°)?

I have seen that there are domestic hot water heat pumps. But if the system is then located in the utility room (no basement) and cools down the house in winter to make hot water while taking the warm air that the small-sized heating heat pump provides, from my understanding, that would be counterproductive.

I would appreciate some recommendations for systems or combinations of different systems for this application. Perhaps also a few links for further reading. On the usual passive house sites, it is very general.

Best regards Christian

Hello,

Especially in a passive house, I would have a very precise design of the heat generator done, because with a heat pump that is too large, it will be difficult to regulate the whole system somewhat stably and energy-efficiently, and with one that is too small, you will have to do a lot of electrical additional heating. Many heat pumps can anyway go up to 60° supply temperature (it is still not very efficient). For me, it was like this: when preparing hot water at -14° outside, the coefficient of performance of the heat pump was 2 (3KW electrical input for 6KW hot water output).

My overall system looks like this: a 5.72 kWP photovoltaic system, an Ochsner air-water heat pump GMLW9+HK with a 350L buffer tank and a 300L hot water tank, and a ventilation system with a brine preheating coil, enthalpy heat exchanger, and electric reheating coil. Because of the buffer tank, the circulation pump of the underfloor heating can continue running and thus heat the house during hot water preparation.

I have used about 2300 kWh of heating energy from mid-October until now, plus hot water and defrosting (I don't have exact numbers in my head, altogether about 3100 kWh). Over the winter, my annual performance factor of the entire system (including the heating circulation pump, mixer, touchscreen panel) was 3.1, only what the compressor and outdoor unit used (i.e., what you find in datasheets or annual performance factor calculations) was 3.6 — calculated over the whole year at 4.0, let's see what summer brings... The difference in between was indeed circulation pumps, mixer, touchscreen panel, controls with about 130-140 kWh electricity consumption.

I also have the case that the whole system is located in the utility room (the "waste heat" from the hot water tank benefits the house heating). My air-water heat pump (almost oversized) goes down to -16° without heating rods at my heating load. The first winter was still such that I had to find the correct heating curve and flow rate of the circulation pump for the underfloor heating.

My problem was that the original heating load calculation was far off, as it was calculated with a blower door value of 1.0 and in reality it was 0.28, which makes quite a difference in well insulated houses. Additionally, the ventilation system’s heat provision factor was not quite correctly estimated, because my brine collector is extremely oversized (the excavation did not make much difference) and thus also delivered quite well in winter (depending on outside temperature up to 1.5KW). According to calculations with the new data, my HWBref is about 11.5 kWh/a/m², the real value is somewhat higher because I do not have such a warm climate but like it warm inside.

Best regards Christian

Hello Christian,

The whole thing is supposed to become a passive house ... In general, I wonder how in a passive house the low flow temperature of underfloor heating (which is desired) and the hot water demand of 4-6 people can be reconciled.

A real PH has no underfloor heating ... no heat generator at all!

Rhenish greetings

Just by the way regarding Legionella: This function is only needed if the water remains in the storage tank for a longer period of time (e.g., in a holiday apartment or a weekend house). In everyday life, it is not necessary because Legionella need a certain amount of time to develop. If you are on vacation for 2 weeks, you can run the Legionella protection once.