ᐅ Air-to-Air vs. Air-to-Water Heat Pump for a KfW55 House – Importance of Cooling Function
Created on: 26 Jun 2023 14:32
N
nanella
Hello everyone,
we are currently deciding between several prefab house suppliers, and a major difference is the heating system offered. Some suppliers install an air-to-air heat pump as standard (cooling available at extra cost), while others provide an air-to-water heat pump with underfloor heating and a ventilation system with heat recovery (an air conditioning unit can be added). Geothermal or groundwater as a heat source will likely not be an option for the plot we are currently considering. It will be a KFW 55 house, initially without photovoltaics for cost reasons, but solar panels are planned to be added later.
We have already read quite a bit on the topic, but as laypeople, we find it difficult to make a decision regarding the heating system. It is important to know that we are very sensitive to heat and want to include active cooling right from the start. In the worst case, we would need to heat/cool only individual rooms.
These are the advantages and disadvantages we know so far:
In principle, this results in 3 options that we are currently considering (we were advised against underfloor heating with cooling function for the reasons mentioned):
Which option would you prefer, or do you see another solution? Do you have any ideas which option would be better in terms of running costs? Because we probably have a rather expensive plot and need to watch costs during construction, air-to-air currently sounds like the better solution to us.
We would appreciate your assessments.
we are currently deciding between several prefab house suppliers, and a major difference is the heating system offered. Some suppliers install an air-to-air heat pump as standard (cooling available at extra cost), while others provide an air-to-water heat pump with underfloor heating and a ventilation system with heat recovery (an air conditioning unit can be added). Geothermal or groundwater as a heat source will likely not be an option for the plot we are currently considering. It will be a KFW 55 house, initially without photovoltaics for cost reasons, but solar panels are planned to be added later.
We have already read quite a bit on the topic, but as laypeople, we find it difficult to make a decision regarding the heating system. It is important to know that we are very sensitive to heat and want to include active cooling right from the start. In the worst case, we would need to heat/cool only individual rooms.
These are the advantages and disadvantages we know so far:
| Heat Pump | Advantages | Disadvantages |
| Air-to-Air with Cooling Function |
|
|
| Air-to-Water with Underfloor Heating + Air Conditioning |
|
|
| Air-to-Water with Underfloor Heating with Cooling Function |
|
|
In principle, this results in 3 options that we are currently considering (we were advised against underfloor heating with cooling function for the reasons mentioned):
- Install air-to-air heat pump with cooling function
- Install air-to-water with underfloor heating, add air conditioning when photovoltaics are installed, and live with the heat until then
- Install air-to-water with underfloor heating and air conditioning, tolerate high cooling costs until photovoltaics are added
Which option would you prefer, or do you see another solution? Do you have any ideas which option would be better in terms of running costs? Because we probably have a rather expensive plot and need to watch costs during construction, air-to-air currently sounds like the better solution to us.
We would appreciate your assessments.
R
RotorMotor29 Jun 2023 14:32kati1337 schrieb:
Don’t underestimate the heat generation in a new building. The heat is generated by the computers and people, not by the new building itself.
kati1337 schrieb:
You won’t manage without air conditioning in the summer. I wouldn’t fully agree with that.
Even with underfloor cooling, a considerable amount of heat can be dissipated.
But yes, if you have two computers at 300W each, two people at 100W each, plus switches, servers, and the like, you quickly need to remove about 1kW of heat from a single room (and that’s without solar gain or other heat transfer). That’s quite a specific challenge, especially if the room is small and used for many hours at a time.
I always find it interesting that many people say air conditioning feels uncomfortable for heating in winter, yet in summer it’s suddenly pleasant to have cold air blowing on you along with the noise.
RotorMotor schrieb:
I always find it interesting that many say having an air conditioner heating in winter is very uncomfortable, but in summer it suddenly becomes pleasant to be blown with cold air and to deal with the noise?The noise is definitely a valid downside. Right now, I’m still in an old building, and the portable air conditioner is sitting on my desk, about 30cm (12 inches) away from me, which is a bit annoying. However, it’s not nearly as frustrating as being unbearably hot. You only get blown on if you stand directly in front of the unit. We even manage that in our current cramped apartment.
Proper split systems don’t make nearly as much noise as portable units (like the one buzzing here now), and they are usually mounted above the door. It should be possible to adjust the airflow so it doesn’t blow directly on you.
RotorMotor schrieb:
But yes, if you have two computers at 300W each, two people at 100W each, plus switches, servers, and so on, you quickly need to remove 1kW just from one room (and that’s without considering sunlight or other heat transfer). That’s quite a specific challenge, especially if this room is rather small and used for many hours at a time.That’s true, but that’s just how we are—and from what the original poster says, their situation is similar. That’s why I’m warning you, because we’ve already had experience with the scenario of “intensive office use in a new building.” We were very glad to have the split system in the room. RotorMotor schrieb:
The heat comes from the computers and people, not from the new building.That’s true, but the problem with the new build is that the heat has nowhere to go without my intervention. In our current home, I had no problems in the office during winter.
W
WilderSueden29 Jun 2023 15:52kati1337 schrieb:
That's true, but the problem with new builds is that heat can't escape anywhere without my intervention.That's not quite accurate. You have walls, ceilings, screed—all of these absorb heat. Plus, there is air exchange with other rooms. So, quite a bit of heat does dissipate.By the way, what kind of machines are you using? My work laptop has a 45W power adapter, so it can't draw more than that. It can do everything I need for work and is fast enough. Intensive performance tests are better run on a server anyway.
H
HeimatBauer29 Jun 2023 16:16My laptop for pushing PowerPoint also only has a 45W wall wart—my developers have workstation laptops where the power supply is heavier than the laptop itself. At the office, we have really fast machines with three monitors connected, which definitely consume a lot of power and generate heat. And the workstations can’t be reasonably relocated.
Sure, my switch is in the basement, but that doesn’t make much of a difference.
Sure, my switch is in the basement, but that doesn’t make much of a difference.
W
WilderSueden29 Jun 2023 16:40I also have 3 external monitors (so 4 in total 😀) in my office. It requires the expensive Dell docking station with its own power supply, but it’s really impressive what you can run through such a small USB-C DisplayPort. We used to have workstations as well, but we were only in the office every 5 days back then. When the sudden shift to home office happened, I didn’t want that anymore. Honestly... Marketing and sales present us as specialists for large data volumes and we do have some clients with significant data. But in practice, you usually test the code with datasets you can manage. For the large, hours-long tests, I don’t want that on my own machine blocking me.
K
KatlarOne5 Jul 2023 09:19A quick note about underfloor cooling – the additional cost depends on the system.
Last week, we looked at two systems:
- Viessmann – heat pump and ventilation system were two separate units → around 3,000€ (around $3,200) for the cooling
- Stiebel Eltron – combined unit (more like a cabinet ^^) – 500€ (around $530); sounded like it just needed a “software update.”
Now we’re facing the question again – cheaper cooling or both systems separate (so that only one needs to be replaced if something breaks, not the whole cabinet ^^).
Last week, we looked at two systems:
- Viessmann – heat pump and ventilation system were two separate units → around 3,000€ (around $3,200) for the cooling
- Stiebel Eltron – combined unit (more like a cabinet ^^) – 500€ (around $530); sounded like it just needed a “software update.”
Now we’re facing the question again – cheaper cooling or both systems separate (so that only one needs to be replaced if something breaks, not the whole cabinet ^^).
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