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!
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!
A
Alessandro8 Dec 2022 12:27Wärmepumpe.seeker schrieb:
And picture 3
The "solution": the 11 in the middle stands for 11kW
I don’t understand that.
Daikin apparently offers two heat pump capacity classes:
4-8kW
11-16kW
If the Daikin system calculates the heating capacity (7.48kW) plus an additional allowance for domestic hot water, it automatically leads to the 11kW unit.
So, a surcharge on top of a surcharge on top of a surcharge?
Braces-belt-suspenders?
Where does the heating output of 7.48kW come from, I mean the number?
We started with a solid 5kW standard heat load.
According to the energy certificate, we have such a large house.
Hmm...
Another project in the same development area is 2m² (22 sq ft) larger, with just under 6kW standard heat load. That one resulted in an 8kW system.
Same builder.
Braces-belt-suspenders?
Where does the heating output of 7.48kW come from, I mean the number?
We started with a solid 5kW standard heat load.
According to the energy certificate, we have such a large house.
Hmm...
Another project in the same development area is 2m² (22 sq ft) larger, with just under 6kW standard heat load. That one resulted in an 8kW system.
Same builder.
B
Benutzer 10018 Dec 2022 13:04Wärmepumpe.seeker schrieb:
So, a surcharge on top of a surcharge on top of another surcharge?
Suspenders, belt, and garters?
Where does the heating capacity of 7.48 kW come from, I mean that number?
We actually started with a solid 5 kW standard heating load.
According to the building permit / planning permission, we have such a large house.
Hmm...
Another project in the same development area is 2 m² (22 ft²) larger, with a standard heating load of just under 6 kW. They ended up with an 8 kW system.
Same builder. Don’t let yourself be fooled. We have 250 m² (2,690 ft²) and an 8 kW heat pump, and even that is too big. A 6 kW unit would have been sufficient.
But to be safe, have an energy consultant calculate it using the correct room temperatures and pipe lengths.
A
Alessandro8 Dec 2022 13:05Wärmepumpe.seeker schrieb:
Where does the heating capacity of 7.48 kW come from, that is the number?
We originally calculated a good 5 kW standard heating load.
No idea how the Daikin software calculates...
For me, with 4 people and your data from the heating load calculation, it suggests a 7 kW unit.
That unit has a bivalence point at -7.4°C (18.7°F), but the use of the electric heater probably won’t cost more than $50 a year.
Edit: I even calculated with a 4-hour utility company lockout 😉
The tool used to calculate the heating load in #42 is well-known and proven. It works fine. Everything else, as mentioned before, is like using suspenders with a belt.
But when you add safety margins on top of safety margins + poor planning + ERR + DAU + monovalent design –> you end up with a monster 11 kW system.
As @Alessandro wrote, design for bivalent operation. You need an appropriately sized unit for about 90% of the time. The heating element covers the remaining 10%, which doesn’t really make much difference. Even then, it’s questionable whether the heating element is needed at all. Usually, we don’t have many consecutive days of subzero temperatures, and solar gains are generally not properly considered.
It should be clear by now that this is totally pointless. The question is how to get out of this mess (if that’s still possible).
But when you add safety margins on top of safety margins + poor planning + ERR + DAU + monovalent design –> you end up with a monster 11 kW system.
As @Alessandro wrote, design for bivalent operation. You need an appropriately sized unit for about 90% of the time. The heating element covers the remaining 10%, which doesn’t really make much difference. Even then, it’s questionable whether the heating element is needed at all. Usually, we don’t have many consecutive days of subzero temperatures, and solar gains are generally not properly considered.
It should be clear by now that this is totally pointless. The question is how to get out of this mess (if that’s still possible).
Wärmepumpe.seeker schrieb:
Then completely different figures appear, suddenly an outdoor temperature of -8.6°C (17°F) is used. This was a critical point for us where I made progress. The old standard still used higher values (-12°/-14°/-16°). However, to my understanding, this no longer applies, and our contract stated that the heating system must be designed according to the standard temperature. So calculations were done using -14°, but the correct value for us would be -11.3°C (12°F). You can easily find the current values by searching for the standard outdoor temperature on Google. Therefore, the value of -8.6°C (17°F) is probably correct. Maybe you could pressure your builder by pointing out that the design was not done according to the standard and that you expect a revised plan. For us, it only affected the calculated flow temperature and pipe spacing, but perhaps that could be a starting point.
You don’t have to include the 4-hour dead time in the calculations, right?
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