Replacing gas heating in existing property with heat pump

  • Erstellt am 2022-07-21 10:50:15

tOkra1984

2022-07-21 10:50:15
  • #1
Hello,

I am Thomas and in 2018 we bought an existing property.
The year of construction was 1968.
In 2001, the ground floor (partly underground, due to hillside location) was renovated and a larger extension was accomplished.
Altogether, the ground floor now has 150m² of living space. The extension is single-story (flat roof, greened) and insulated with PUR. Everything according to good standards with KNX etc.
The rest of the old building on the ground floor was also renovated (floor insulated, new wiring, etc.).
New windows (double-glazed) were installed throughout the ENTIRE house. Currently, heating and hot water preparation are provided by gas. A photovoltaic system with 9.9 kWp is present.

To summarize:
Ground floor: 150 m², underfloor heating everywhere except in one children’s room and the bedroom - there are radiators there. A split air conditioning system will also be installed.
1st floor: approx. 70 m², only radiators. Here, too, a split air conditioner with a good COP will be installed for possible heating. Currently, this floor is hardly inhabited.
2nd floor: converted attic with say 50 m². Only radiators. The floor is unoccupied and probably never will be. It serves as storage space or similar. I am not aiming for absolute comfort temperature here. The roof is old but insulated with wood fibers.

According to the energy certificate at the time of purchase, the building has a final energy demand of 70.2 kWh/m².

The heat from the ground floor is almost sufficient for the 1st floor (through the ceiling).

As a quick solution to reduce gas usage, I will soon receive the 2 split air conditioning units.
Next year or so I would like to have a heat pump installed. For the ground floor, I am actually not worried that a low flow temperature will be sufficient. On the 1st floor, I would then have the split air conditioner to catch peak loads. Yes, I know it’s also a heat pump but the flow temperature of the heating heat pump should be kept to a minimum.

I will submit the application to BAFA this week for the split air conditioner and the air-water heat pump.

Now to my first questions (there may be more over time :) ):
1. My technical room is very small and when the builder came for inspection he immediately said "oh dear, we won’t get a buffer tank in here." I have read a lot here and some say that a buffer tank makes little sense anyway. So I would waive the buffer tank. But this is irrelevant for the BAFA subsidy or is it a requirement for the funding?
2. At the next meeting with the builder, I want to have concrete ideas for myself. As far as I have read, a 300l hot water tank would be reasonable for me (2 adults, 2 children currently).
3. What output should the air/water heat pump deliver approximately in my case?
4. Currently, my gas boiler heats the hot water to 60°. Can I safely reduce this to 50° (keyword: legionella)?

I’m sure I’ll think of more but I just wanted to start a thread now - I can expand it.

I am grateful for any tips.
 

Deliverer

2022-07-21 19:44:57
  • #2


Regarding 1: The combination of radiators and underfloor heating does not make it easier. Generally, operation without a buffer can work as well. And if not, a small 50-liter buffer in the return flow can fit well even in the smallest utility room. It can even hang on the wall above the washing machine. For the subsidy, it does not matter.
Regarding 2: 300 liters fits well. If bathing is infrequent (or very rare), 200 liters is also sufficient.
Regarding 3: Exactly as much as the heating load of the building calculated room by room at NAT. Not more, not much less.
Regarding 4: If the hot water tank is small, there is no legionella problem in a single-family house. Flow is more important than temperature, because the latter never reaches everywhere in the pipe network anyway.
 

i_b_n_a_n

2022-07-21 20:19:51
  • #3

Regarding 2, I can confirm, my experience with 2 adults and three children in 2 residential units with a 180-liter combined storage tank (integrated in a heat pump) has so far never led to shortages, but there is no bathtub.
Regarding 4, we also had it lowered during commissioning by the factory service technician (who briefly said that we actually need to press the button to accept the parameter for legal reasons, but then did it himself).
 

Grundaus

2022-07-22 09:52:45
  • #4
A split air conditioner is an air-to-air heat pump, why should it work more effectively at cold temperatures than a normal air-to-water heat pump? Regarding Legionella, regular temperature increases help, either automatically every few weeks or done manually. However, this is not a problem for single-family homes, but only in large systems where water is sometimes not drawn for months.
 

tOkra1984

2022-07-22 09:56:38
  • #5
Regarding the split air conditioning: It is mainly intended for the 1st floor. Only radiators are installed there. However, I naturally want to achieve a low flow temperature with the air-water heat pump, and that will probably not be sufficient to heat the 1st floor. The split air conditioning can then help me if it gets too cold.

About the legionella: If I increase the hot water storage to, say, 60° once a month... to what temperature can I then lower it for the rest of the time? 50°C or even less?
 

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