ᐅ What capacity does the heat pump need to have?

Dalle schrieb:
The system is located 4.5 meters (15 feet) from the neighbor’s house, so acoustics are quite important. Is it better to use one heat pump for our two-family house (two stories) as we do now, or would it be preferable to use two smaller units, each supplying one condominium?

If these are two separate units, two heat pumps and two independent hydraulic circuits are recommended. This way, you can operate two different heating curves without a buffer tank or electronic regulating valve (ERV), and the occupants can set different temperatures for each unit. This can prevent problems, especially if you rent out one of the units. If you buy the heat pumps yourself, the units cost only around €3,000 (approximately $3,300) each.

Regarding noise:
The heat pump only becomes noticeable at about 60% heating output (roughly 3 kW [10,200 BTU/h]) and when outdoor temperatures are below freezing. Above this level, the noise increases significantly; below it, the unit is virtually silent. Nevertheless, I would recommend installing a visual screen facing the neighbor directly or even earlier, because what can be seen tends to be heard, and visually, the Panasonic is not particularly attractive. During the drying phase, our unit ran continuously at 5 kW (about 17,000 BTU/h), and it is acoustically unfavorable positioned in a corner. The neighbor was able to hear it at night from 20 meters (66 feet) away with old windows.

Our unit is now limited to approximately 60% output (around 3.3 kW / 11,250 BTU/h) in whisper mode, and with defrost cycles included, it produces no more than 2.5 kW (8,500 BTU/h) on average throughout the day. I allow it to run freely (4 kW / 13,650 BTU/h) for a few hours during the day using a timer. It cannot be limited below 3 kW (10,200 BTU/h), so it is always slightly audible in cold weather, but the difference compared to 5 kW output is very significant. In general, Panasonic heat pumps are considered very quiet. I am not familiar with other brands and can only speak for our system.

Dalle schrieb:
Using two smaller heat pumps for each household is no longer under consideration because the smaller units start at 5 kW (about 17,000 BTU/h), which would not be effective in our case. It was just a thought.

On the contrary, that’s a very good idea. I recommend going with it! Oversizing is a problem, especially with heat pumps that don’t modulate well or at all, as that causes frequent cycling. The current Panasonic 5 kW (17,000 BTU/h) model (with "H" in the product code) modulates down to about 1.3 kW (4,400 BTU/h) of heat output at less than 200 W of power consumption. If you reduce the heating curve at night with a timer, which is advisable anyway, the unit may not even start during transitional seasons at night. This effectively halves the heat pump’s output and shifts possible noise to daytime hours. It will not cycle excessively if the rest of the hydraulic system is properly designed. From my experience, the unit operates not only quieter but also more efficiently in modulation mode.

Alternatively, you could design the hydraulic system to start with a single heat pump and later separate the two hydraulic circuits completely using shut-off valves. For more detailed advice on this, you might want to consult the HTD Forum.