ᐅ Heat pump for 148 sqm KfW55 house

Created on: 13 Nov 2022 11:27
J
junijulibaut
Dear heat pump experts and experienced home builders,

I would like to better understand what heat pump capacity we actually need.

Our project:
2 full floors
No basement
148 sqm (1,593 sq ft)
KFW55 standard

In our energy demand calculation, a 6 kW air-to-water heat pump is recommended.
However, the heating load calculation in the plan specifies an 8 kW air-to-air heat pump.
Both calculations seem to follow a standard procedure, as this is a developer project.
Which figures in both documents should I focus on?

To me, 8 kW seems quite high, but this is just a feeling formed by reading here in the forum.

The underfloor heating is already installed, also standard, and the screed has been curing for 4 weeks, waiting for the system to be heated up.
But there is no heat pump installed yet.
The builder would credit us €15,000 if we handle the purchase and installation of the heat pump ourselves.

All these questions are overwhelming us.
Is this even possible? Can we choose a different model or manufacturer?
Is it worthwhile, is €15,000 a reasonable amount?
Is 6 kW enough? ...
We need solid information to stand our ground with the builder.

Help!
Thanks!
P
parcus
23 Dec 2022 17:26
@Tolentino
Monogamy is not the same as bigamy. I can only explain the technical difference, as it is also applied in calculations/software.
A single-source heat pump cannot be operated in a dual-source mode because there is no second heat generator. In your case, this is the electric heating element, since a dual-source heat pump cannot cover these temperature ranges. Dual-source simply means hybrid; it just sounds better for marketing purposes.
Often, the consumption of the electric heating element is concealed by not measuring its energy use at all, only the heat pump’s consumption.

Don’t believe everything marketing departments come up with, or what the industry simply presents.
Heat pumps are not climate-neutral either; by political definition, an electricity mix with storage has been excluded since the Energy Saving Ordinance of 2013.
P
parcus
23 Dec 2022 17:30
@wp.seeker

With inverter heat pumps, also known as modulating heat pumps, the specifications often do not include a buffer tank, as it counteracts their function. For this reason, inverter heat pumps have not become widely adopted, but this is due to implementation planning rather than the heat pump itself.
wp.seeker1 Mar 2023 23:17
Brief update:

Since January 26th, our large heating system outside the house has been running quietly. So far, we don’t have any room temperature controls installed; it’s operating at a constant supply temperature of 25°C (77°F). The indoor temperatures are at least 19°C (66°F), reaching up to 22°C (72°F) due to solar gain.

So far, it has consumed 403 kWh of electricity and produced 2017 kWh of heat. No domestic hot water has been generated yet.

It shuts down during frost without displaying an error message. Once, water was added to the heating circuit, which seemed to help temporarily, but the issue has occurred again. We are continuing to monitor the situation.

We’re not living in the house yet.

Looking forward to seeing how this develops.
P
parcus
2 Mar 2023 09:07
Does the entire system run through the electric meter, or only the heat pump without the heating element?
wp.seeker2 Mar 2023 10:31
I don’t fully understand the question. The entire system? Both the outdoor split unit and the indoor tower unit (let’s call it that) are powered. The figures for power consumption and heat output were taken from the indoor unit’s display.

If it shuts off during subzero temperatures, it could be due to low water pressure, which according to the display was always around 0.8 bar at those times. After adding water, it operated normally, but it was no longer below freezing. When we turned it off ourselves, for example because it was too warm to work and a flow temperature below 25°C (77°F) cannot be set, it showed 1.1 bar.
P
parcus
2 Mar 2023 10:48
Typically, both the indoor and outdoor units are wired so that they run through the meter. However, I have often seen instances where the electric heating element was not connected through the meter, which then artificially improves the annual performance factor.

Similar topics