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!
The standard outside temperature for our postal code area is -12°C (10°F).
If I understand correctly, the Vaillant aroTHERMplus is a monoblock system. A monoblock probably won't work because the heating coils, refrigerant lines, and screed are already installed inside the house. Everything is set up for a split unit—can it still be changed to a monoblock?
I’m confused about the term "bivalent." Some people define bivalent as the ability to use two heat sources, for example, the heat pump plus solar or an existing boiler. Then I read that the bivalence point is the outdoor temperature at which the heat pump can just barely deliver the specified output to maintain the desired indoor temperature. Below that temperature, the electric backup heater kicks in. Is that correct?
What does designing a system as bivalent mean?
And one more question about heating load: This is calculated for us at -12°C (10°F) outside. Does that mean that at -12°C (10°F) outside, we need about 5 kW to heat our house to 20/24°C (68/75°F)? Does it mean that at -3°C (27°F) we need less kW? And even less at 5°C (41°F)?
So, I admit I’m a heat pump newbie, but that’s what you’re here for ;-)
If I understand correctly, the Vaillant aroTHERMplus is a monoblock system. A monoblock probably won't work because the heating coils, refrigerant lines, and screed are already installed inside the house. Everything is set up for a split unit—can it still be changed to a monoblock?
I’m confused about the term "bivalent." Some people define bivalent as the ability to use two heat sources, for example, the heat pump plus solar or an existing boiler. Then I read that the bivalence point is the outdoor temperature at which the heat pump can just barely deliver the specified output to maintain the desired indoor temperature. Below that temperature, the electric backup heater kicks in. Is that correct?
What does designing a system as bivalent mean?
And one more question about heating load: This is calculated for us at -12°C (10°F) outside. Does that mean that at -12°C (10°F) outside, we need about 5 kW to heat our house to 20/24°C (68/75°F)? Does it mean that at -3°C (27°F) we need less kW? And even less at 5°C (41°F)?
So, I admit I’m a heat pump newbie, but that’s what you’re here for ;-)
Wärmepumpe.seeker schrieb:
I read that the bivalence point is the temperature at which the heat pump can just still deliver the specified output needed to heat the house to the desired temperature. If the outside temperature drops below that, the backup heater switches on. Is that correct?Yes, exactly. Since safety margins are included and solar gains are often neglected (even at -10°C (14°F), the sun can frequently shine during the day), the actual bivalence point is often lower in reality.
Additionally, this situation rarely occurs because your house doesn’t lose heat instantly if temperatures are that low for only a few hours at night. During the day, the temperature recovers. It is very rare for such low temperatures to persist for several days in a row.
And when it does happen, the backup heater helps. Since these conditions are so uncommon, it’s not a big issue.
Wärmepumpe.seeker schrieb:
I have another question regarding heating load: Ours is calculated for -12°C (10°F). Does this mean at -12°C (10°F) outside, we need roughly 5 kW to heat our house to 20/24°C (68/75°F)? And at -3°C (27°F) it needs less kW? Even less at 5°C (41°F)?Exactly! That’s why having a larger heat pump can be counterproductive. At 5°C (41°F), you might only need about 2 kW. But the heat pump can’t modulate that low and ends up short cycling.
Therefore, heat pumps should be sized to cover around 90% of the heating demand, not the peak 10%.
Edit: Bivalence means in this context 1. heat pump 2. backup heater (integrated in the heat pump)
Monovalent means covering all heating needs using only the heat pump.
T
Torti2022neu10 Dec 2022 14:05face26 schrieb:
Monovalent would mean covering everything with just the heat pump.Which, however, is sufficient in 95% of cases.Torti2022neu schrieb:
Which, however, is sufficient in 95% of cases.Correct – as long as the heating load is calculated properly. But as mentioned before, if both the braces and the belt are included in the calculation, it works on paper, while with the smaller one it doesn’t.
In that case, just tell the heating engineer to design a bivalent system.
Regarding the thermal insulation verification for KfW55, only the simplified building heating load is determined, not the sum of the room heating loads according to DIN EN 12831, which can differ by up to 30%. This relates to building services engineering and not thermal insulation. Additionally, it should be considered whether the KfW55 was calculated according to the old DIN standard or the current DIN 18599, and whether the thermal bridge surcharge was verified or merely assumed. The simplified method does not take individual rooms into account but only the building envelope and the standard temperature.
Monovalent heat pumps are often far superior to split systems, but German manufacturers have missed this... The key here is the stratified storage tank working in combination. The systems, especially from one manufacturer mentioned, have monovalent bivalence points between -15°C and -20°C (5°F and -4°F). The electric heater is only used as a backup in case the heat pump fails.
Our German-speaking neighbors, with well-known winter sports regions, offer corresponding studies and evaluations of systems such as stratified storage tanks.
Monovalent heat pumps are often far superior to split systems, but German manufacturers have missed this... The key here is the stratified storage tank working in combination. The systems, especially from one manufacturer mentioned, have monovalent bivalence points between -15°C and -20°C (5°F and -4°F). The electric heater is only used as a backup in case the heat pump fails.
Our German-speaking neighbors, with well-known winter sports regions, offer corresponding studies and evaluations of systems such as stratified storage tanks.
D
Daniel-Sp11 Dec 2022 01:43A well-designed heat pump and underfloor heating system does not require a buffer tank. The heat pump can feed directly into the underfloor heating.
The high flow rates of a heat pump are not always beneficial for the proper operation of a buffer tank.
Expansion vessels (ERR) should, of course, be removed in that case.
The high flow rates of a heat pump are not always beneficial for the proper operation of a buffer tank.
Expansion vessels (ERR) should, of course, be removed in that case.
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