ᐅ Integrating Cooling into Mechanical Ventilation with Heat Recovery or Using a Separate Air Conditioning System?
Created on: 9 Oct 2018 22:13
J
junge_familie
Hello everyone,
In our future house, the two children will have their rooms under the roof. From experience, I know that it gets extremely hot there in the summer.
We want to integrate a possibility for active cooling into our house. We have already had a conversation with an HVAC technician who, based on the size of the rooms, proposed an air conditioning system with a cooling capacity of about 13 kW. The cost would be around 15,000 €.
There is also a cooling element from Zehnder (ComfoCool Q600 ST), which is significantly cheaper but only has a cooling capacity of 2.3 kW. The technician estimated that his system could lower the temperature by up to 10°C (18°F). The Zehnder unit, however, has only about 20% of that capacity. Would it even make a difference? If 20% cooling capacity means it can only cool about 2°C (4°F) down, isn’t it basically useless?
Honestly, I find it quite strange that mechanical ventilation systems with heat recovery usually don’t include proper cooling units. Until recently, I thought nearly all these systems could also cool.
Thanks for your feedback,
junge_familie
In our future house, the two children will have their rooms under the roof. From experience, I know that it gets extremely hot there in the summer.
We want to integrate a possibility for active cooling into our house. We have already had a conversation with an HVAC technician who, based on the size of the rooms, proposed an air conditioning system with a cooling capacity of about 13 kW. The cost would be around 15,000 €.
There is also a cooling element from Zehnder (ComfoCool Q600 ST), which is significantly cheaper but only has a cooling capacity of 2.3 kW. The technician estimated that his system could lower the temperature by up to 10°C (18°F). The Zehnder unit, however, has only about 20% of that capacity. Would it even make a difference? If 20% cooling capacity means it can only cool about 2°C (4°F) down, isn’t it basically useless?
- Has anyone here used this unit?
- Should we install an air conditioner in addition to the mechanical ventilation system with heat recovery?
Honestly, I find it quite strange that mechanical ventilation systems with heat recovery usually don’t include proper cooling units. Until recently, I thought nearly all these systems could also cool.
Thanks for your feedback,
junge_familie
Certainly, good insulation is important but it does not replace air conditioning.
It’s not just about temperature but also about dehumidification.
Both factors determine how the temperature is perceived in the room.
I wouldn’t want to do without air conditioning in the bedroom anymore.
It’s not just about temperature but also about dehumidification.
Both factors determine how the temperature is perceived in the room.
I wouldn’t want to do without air conditioning in the bedroom anymore.
D
Deliverer10 Oct 2018 09:35How large is the house? And how many unshaded south-facing and roof windows will there be?
If all windows have external shading, you can roughly estimate that 13 kW in a new build can cool about 400 m² (4,300 sq ft) down to a very low temperature.
I cool 140 m² (1,500 sq ft) in an older building, open all the way up to the roof, with a huge window front facing south (shaded by the roof) using 3.5 kW. That was enough even during the summer of 2018 in southern Germany for my wife to literally pull a blanket over herself at night.
So the offer is at least twice as high as needed, both in terms of price and capacity. It will definitely be enough to cool the upper floor. If the stairwell is open, enough cool air will fall downwards. I would even go so far as to say that cooling just the upper hallway with one unit would be sufficient, ideally placed at the highest point of the house.
Then it is only important to switch on the system early and let it run continuously at a lower capacity. This gives the air enough time to circulate evenly.
If you’re often away and only turn the system on once the temperature inside has already reached 28°C (82°F), this approach won’t work anymore. Then you need multiple units in the main rooms.
If you want more opinions on this, the kaelte-treffpunkt forum is a good place. But be warned – the guys there aren’t as gentle as on this forum…
If all windows have external shading, you can roughly estimate that 13 kW in a new build can cool about 400 m² (4,300 sq ft) down to a very low temperature.
I cool 140 m² (1,500 sq ft) in an older building, open all the way up to the roof, with a huge window front facing south (shaded by the roof) using 3.5 kW. That was enough even during the summer of 2018 in southern Germany for my wife to literally pull a blanket over herself at night.
So the offer is at least twice as high as needed, both in terms of price and capacity. It will definitely be enough to cool the upper floor. If the stairwell is open, enough cool air will fall downwards. I would even go so far as to say that cooling just the upper hallway with one unit would be sufficient, ideally placed at the highest point of the house.
Then it is only important to switch on the system early and let it run continuously at a lower capacity. This gives the air enough time to circulate evenly.
If you’re often away and only turn the system on once the temperature inside has already reached 28°C (82°F), this approach won’t work anymore. Then you need multiple units in the main rooms.
If you want more opinions on this, the kaelte-treffpunkt forum is a good place. But be warned – the guys there aren’t as gentle as on this forum…
No matter what you choose, avoid skylights as much as possible. They are troublesome. Even shutters don’t help much—at least not dark-colored ones—because the air gap between the window and the shutter gets extremely hot and then heats up the room. A ventilated shading system is much better! Also, for roof tiles, you might want to go for red rather than anthracite. That could probably make a 1–2°C (2–4°F) difference.
Whether you really need air conditioning also depends on the local climate. In southern German areas with muggy conditions where the air can be still for days, I wouldn’t want to do without it. But here, nights usually cool down quite a bit, there’s always some breeze, and the humidity is generally lower. With the right ventilation system (including proper shading, unlike what’s in my apartment here ), you can manage well without air conditioning. You’ll have to assess the situation where you are. But if you do need it, skip the complicated controlled ventilation systems and go for a proper air conditioner.
Whether you really need air conditioning also depends on the local climate. In southern German areas with muggy conditions where the air can be still for days, I wouldn’t want to do without it. But here, nights usually cool down quite a bit, there’s always some breeze, and the humidity is generally lower. With the right ventilation system (including proper shading, unlike what’s in my apartment here ), you can manage well without air conditioning. You’ll have to assess the situation where you are. But if you do need it, skip the complicated controlled ventilation systems and go for a proper air conditioner.
You didn’t mention anything about your roof structure! Maybe it’s not necessary?
Here, everyone probably assumes 1.5 stories with a gable roof!
Above the upper floor, we have a 22cm (9 inches) concrete ceiling, with 24cm (9.5 inches) of insulation on top, and a cold roof with a gable shape in stone gray (light gray). So, I’m not worried about the roof or the rooms below overheating.
@Alex The geothermal heat exchanger is also available for the smaller Zehnder units. However, the 30m (98 feet) of piping costs extra and isn’t cheap (it’s installed by our shell builder). The underground piping costs about 2200€ net. The alternative would be a brine heat exchanger, which is another 2000€ more expensive.
At that price, you could almost build your own air conditioning system.
Here, everyone probably assumes 1.5 stories with a gable roof!
Above the upper floor, we have a 22cm (9 inches) concrete ceiling, with 24cm (9.5 inches) of insulation on top, and a cold roof with a gable shape in stone gray (light gray). So, I’m not worried about the roof or the rooms below overheating.
@Alex The geothermal heat exchanger is also available for the smaller Zehnder units. However, the 30m (98 feet) of piping costs extra and isn’t cheap (it’s installed by our shell builder). The underground piping costs about 2200€ net. The alternative would be a brine heat exchanger, which is another 2000€ more expensive.
At that price, you could almost build your own air conditioning system.
The Comfocool mainly provides dehumidification and about a 1-degree reduction inside the house, and you can run the system continuously during the day. This can noticeably improve indoor climate. For thermal protection, shading on south-facing windows is more important. For the price of the Comfocool, you could probably get one to three split air conditioning units, which of course have a very different cooling capacity. So, the Comfocool would be nice, but probably too expensive.
We also had some heat issues in our new build this year, mainly because my self-programmed roller shutter control wasn’t working well yet, shading in the extension was still missing, the ventilation system was unregulated (running at full power around midday, fixed with a software update and timer control), and due to the lack of outdoor landscaping (no trees for shade, gravel).
Next year, I plan to install a central split AC unit, mainly to be able to dehumidify when needed in summer.
We also had some heat issues in our new build this year, mainly because my self-programmed roller shutter control wasn’t working well yet, shading in the extension was still missing, the ventilation system was unregulated (running at full power around midday, fixed with a software update and timer control), and due to the lack of outdoor landscaping (no trees for shade, gravel).
Next year, I plan to install a central split AC unit, mainly to be able to dehumidify when needed in summer.
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