Heat pump in a partially renovated old building experiences

For all those who are considering the purchase and (energetic) renovation of an existing property...

The day before yesterday, I commissioned a new heat pump (Pana Monoblock) in a 50-year-old attic apartment - simply connected to the old pipes.

Construction condition of the property: 60s era
Windows (almost) all new - delivery difficulties with two small dormer windows
Sloping ceilings (not many) insulated about 15 years ago with 12cm mineral wool WLG 35
Top floor ceiling insulated about 15 years ago with 12cm mineral wool (in the wooden ceiling) and newly insulated with 2x24cm mineral wool on the ceiling
Radiators as large as possible (type 33) new
Exterior walls not yet insulated (planned for next year)
The apartment below the attic is normally heated by the resident – comparable to very good basement ceiling insulation
Heat pump pipes not yet fully insulated, this will follow in the next few days

Result: at 0 degrees, the heat pump runs without short cycling with a flow temperature of 35 and a return of 30 degrees for an indoor temperature of 21-22 degrees (hydraulics not yet adjusted as calculated, valves initially out of the box).

Conclusion: The heat pump operates effectively and efficiently despite the still missing external insulation. The measures undertaken so far have also remained within a manageable scope, as many tasks could be done in-house. Energy consultant as well as engineering office on board. Not everything has to be done completely in order to break free from oil/gas. And a high-temperature heat pump is dispensable with manageable effort.

Thank you for the exciting case report!

A few questions about it:

The day before yesterday I commissioned a new heat pump (Pana Monoblock) in a 50-year-old house in an attic apartment – simply connected to the old pipes.

Wait a minute: Only in the attic apartment? So you installed a separate heating system in the attic apartment of a multi-family house, and it’s a heat pump?
This raises interesting questions:
How was the apartment heated before? Own gas heating or connection to central heating?
Where did you install the outdoor unit? This could only have been done in/on common property and would have required a resolution by the owners’ meeting? Did they just agree to that?
What was the trigger to separate a single apartment from the building’s overall energy concept?

Building condition property: 1960s
Windows (almost) all new – delivery difficulties with two small dormer windows
Roof slopes (not many) insulated about 15 years ago with 12 cm mineral wool WLG 35
top floor ceiling insulated about 15 years ago with 12 cm mineral wool (in the wooden ceiling) as well as newly insulated with 2x24 cm mineral wool on the ceiling
Radiators as large as possible (type 33) new

Exterior walls not insulated yet (to come next year)

This point presents particular challenges in my opinion. For what heat demand is the heat pump designed?
A) For the current state (without insulation)?
B) For the future state (with insulation)?

If A: Then it is oversized with the associated disadvantages (higher investment costs, worse annual performance factor than possible)
If B: What happens if this winter gets really cold? Then it won’t be sufficient?

Result: At 0 degrees the heat pump runs without short cycling with supply 35 and return 30 degrees for 21-22 degrees room temperature (hydraulics not yet adjusted as calculated, valves initially out of the box).

Impressive performance given the building fabric!

Wait: Only in the attic apartment? So you installed your own heating in the attic apartment of a multi-family house and it is a heat pump?

Two-family house. And yes, currently only in the attic apartment.

How was the apartment heated before?

Oil heating. It still runs for the ground floor. There were two circuits.

Where did you install the outdoor unit? This can only have been done on/common property and would have required a resolution from the owners' assembly? Did they just go along with it?

Everything belongs to me. So the community gave their ok ;)

What was the trigger for separating a single apartment from the overall energy concept of the building?

As I said, it is a two-family house that is being renovated overall. Maybe I should have mentioned that. Mainly it was about whether a heat pump can work without a complete renovation.

This point poses particular challenges in my opinion. On what heat demand is the heat pump designed?
A) For the current state (without insulation)?
B) For the future state (with insulation)?

Unfortunately the heat pump is oversized, but designed for the future state. A heating load of just over 4,x was calculated. The monoblocks are usually at 5. But thanks to modulation, it’s totally fine. There will be no short-cycling.

If A: Then it is oversized with the associated disadvantages (higher investment costs, worse annual performance factor than possible)
If B: What happens if it gets really cold this winter? Then it won’t be sufficient?

Since the heating load calculations are always based on lowest temperatures, the days (if any) could be bridged with the electric heater. Based on my own experience, I can exclude that issue. Up to -15 degrees, the heater definitely does not turn on given my circumstances.

Impressive performance given the building fabric!

That was what I wanted to say with the post! Insulating top and bottom + properly designing windows and heating can be a great way to get a heat pump heating system affordably.