ᐅ Split air conditioning system and mechanical ventilation with heat recovery
Created on: 16 Mar 2023 11:30
R
Rafaelsen
Hello everyone,
Does anyone have experience with a split air conditioning system combined with a central controlled residential ventilation system with heat recovery?
The main question is whether the controlled residential ventilation can distribute the cool air from the air conditioner and how well or poorly this works.
My idea: Because of the simplicity and short distances, I am considering a split air conditioning system with 2 indoor units.
The outdoor unit would be placed on the garage, and from there it is only about 50 cm (20 inches) through the wall into the bedroom upstairs and the living room downstairs. Power supply is also available. I want to avoid major effort and long duct runs to actively cool all rooms. The children’s rooms are not as easy to reach. It would be possible via an external duct on the outside wall, but I want to avoid that for aesthetic reasons.
The house was built in 2018 and exceeds the KfW 55 efficiency standard.
The primary energy demand is calculated at 42 kWh/m² (square meter) and the values from recent years confirm this.
We have 178 m² (1,914 square feet) of living space according to the living space ordinance and about 212 m² (2,282 square feet) of floor area. No basement and a gable roof are present, which explains the discrepancy.
Heating is provided by a ground-source heat pump with a water circuit, which is also equipped with a cooling function.
Cooling via the underfloor heating works satisfactorily and keeps the temperature around 24°C (75°F) even in midsummer.
However, it requires consistent shading and following recommendations. Once the heat has entered, it takes several days for the cooling system to lower the temperature again.
In 2022, we consumed 2,169 kWh of electricity and generated 9,408 kWh of heat for heating and domestic hot water.
The building is therefore comparatively efficient in terms of insulation.
We still want to get advice regarding the air conditioning. Both rooms are about 40 m² (430 square feet), and the question arises whether it makes sense to choose a more powerful air conditioner to have more cold air for distribution?
The controlled residential ventilation also supports this to some extent. In summer, it cools the outside air by a good 8°C (14°F).
The air volume flow is approximately 180 m³ (6,360 cubic feet) per hour on automatic setting.
Would the controlled residential ventilation noticeably distribute the cool air from the air conditioner and cool the other rooms, or would we rather get cooling zones within the house?
Thank you very much in advance.
Does anyone have experience with a split air conditioning system combined with a central controlled residential ventilation system with heat recovery?
The main question is whether the controlled residential ventilation can distribute the cool air from the air conditioner and how well or poorly this works.
My idea: Because of the simplicity and short distances, I am considering a split air conditioning system with 2 indoor units.
The outdoor unit would be placed on the garage, and from there it is only about 50 cm (20 inches) through the wall into the bedroom upstairs and the living room downstairs. Power supply is also available. I want to avoid major effort and long duct runs to actively cool all rooms. The children’s rooms are not as easy to reach. It would be possible via an external duct on the outside wall, but I want to avoid that for aesthetic reasons.
The house was built in 2018 and exceeds the KfW 55 efficiency standard.
The primary energy demand is calculated at 42 kWh/m² (square meter) and the values from recent years confirm this.
We have 178 m² (1,914 square feet) of living space according to the living space ordinance and about 212 m² (2,282 square feet) of floor area. No basement and a gable roof are present, which explains the discrepancy.
Heating is provided by a ground-source heat pump with a water circuit, which is also equipped with a cooling function.
Cooling via the underfloor heating works satisfactorily and keeps the temperature around 24°C (75°F) even in midsummer.
However, it requires consistent shading and following recommendations. Once the heat has entered, it takes several days for the cooling system to lower the temperature again.
In 2022, we consumed 2,169 kWh of electricity and generated 9,408 kWh of heat for heating and domestic hot water.
The building is therefore comparatively efficient in terms of insulation.
We still want to get advice regarding the air conditioning. Both rooms are about 40 m² (430 square feet), and the question arises whether it makes sense to choose a more powerful air conditioner to have more cold air for distribution?
The controlled residential ventilation also supports this to some extent. In summer, it cools the outside air by a good 8°C (14°F).
The air volume flow is approximately 180 m³ (6,360 cubic feet) per hour on automatic setting.
Would the controlled residential ventilation noticeably distribute the cool air from the air conditioner and cool the other rooms, or would we rather get cooling zones within the house?
Thank you very much in advance.
S
steuerlexi5 Sep 2024 09:39We already have a central cooling system integrated into our controlled residential ventilation / air-to-air heat pump. However, it doesn’t provide much cooling. It circulates 300 m³ (11,000 ft³) of air per hour. Therefore, we are considering adding a 7 kW unit to support it, which is capable of circulating 1,200 m³ (42,400 ft³) of air while cooling. I imagine this could work if it runs continuously and tries to maintain 22 degrees Celsius (72°F) in the house. That would be 3 degrees less than what the normal central cooling system can achieve. This should be feasible, right, or am I missing something?
How do you cool centrally? Using a chiller and cold water unit integrated into the mechanical ventilation with heat recovery system?
Or do you mean through the underfloor heating? That can only buffer 2-3°C (4-5°F) at most and does not dehumidify.
Air conditioning units placed in several locations can be controlled more precisely and provide better air distribution.
How large is the house? It’s better to have two 3.5 kW units rather than one 7 kW unit.
Or do you mean through the underfloor heating? That can only buffer 2-3°C (4-5°F) at most and does not dehumidify.
Air conditioning units placed in several locations can be controlled more precisely and provide better air distribution.
How large is the house? It’s better to have two 3.5 kW units rather than one 7 kW unit.
Hello,
Unfortunately, it won’t help much. The mechanical ventilation with heat recovery simply doesn’t have enough airflow to “carry the cold” (correctly put: to remove the heat).
What you could do is integrate a small air conditioner into the intake duct to dehumidify the incoming air. The real discomfort in summer is usually not the temperature but the high humidity. 25°C (77°F) inside with 65-70 percent humidity causes heavy sweating, whereas 25°C (77°F) at 45 percent humidity can actually feel quite cool.
Best regards,
Andreas
steuerlexi schrieb:
Shouldn't this work, or am I missing something?
Unfortunately, it won’t help much. The mechanical ventilation with heat recovery simply doesn’t have enough airflow to “carry the cold” (correctly put: to remove the heat).
What you could do is integrate a small air conditioner into the intake duct to dehumidify the incoming air. The real discomfort in summer is usually not the temperature but the high humidity. 25°C (77°F) inside with 65-70 percent humidity causes heavy sweating, whereas 25°C (77°F) at 45 percent humidity can actually feel quite cool.
Best regards,
Andreas
For example, this would be the option with a refrigeration unit and chilled water system.
However, there is also a dew point issue with the pipes in this setup.
Constantly cooling a flow of 300 m³ per hour (about 176 cubic feet per minute) requires significant capacity.
If it’s 30°C (86°F) or higher outside, you first need to cool it down.
I recommend multiple indoor units, either multi-split or single-split systems. This delivers noticeably more power, is more efficient, and allows for more precise control.
On very hot days, turn off the controlled ventilation system.
However, there is also a dew point issue with the pipes in this setup.
Constantly cooling a flow of 300 m³ per hour (about 176 cubic feet per minute) requires significant capacity.
If it’s 30°C (86°F) or higher outside, you first need to cool it down.
I recommend multiple indoor units, either multi-split or single-split systems. This delivers noticeably more power, is more efficient, and allows for more precise control.
On very hot days, turn off the controlled ventilation system.
S
steuerlexi5 Sep 2024 10:27rick2018 schrieb:
How do you cool centrally? Chiller and cold water system integrated into the controlled residential ventilation? Or do you mean through the underfloor heating? That can only buffer 2-3°C (4-5°F) and does not dehumidify. Air conditioners in multiple locations allow for more precise control and better distribution. How large is the house? Better to have 2 units of 3.5 kW than one 7 kW unit.The heat pump works by reversing the refrigeration cycle. We don't have underfloor heating. It is a pure air-to-air heat pump with ventilation and heat recovery. Our house is 168 m2 (1,808 sq ft) and has an open layout.
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