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.
R
RotorMotor21 Mar 2023 11:32rick2018 schrieb:
There is always a temperature difference, even if it is small.
If you have low ceilings, the effect is smaller. How significant is the effect at different ceiling heights?
rick2018 schrieb:
Another question is what your controlled mechanical ventilation system does when the outdoor air is warmer than the desired indoor temperature. Presumably, it would switch off heat recovery. This way, only air is exchanged, and no cold is transferred to the incoming air. Why would it do that?
The so-called summer bypass is of course only active when it is cooler outside than the indoor set temperature.
But even then, the effect is rather small.
P
Pitiglianio21 Mar 2023 11:35Rafaelsen schrieb:
The house was built in 2018 and exceeds the KfW 55 standard.Putting the main topic aside for a moment... You built a KfW 55 energy-efficient house and probably received a government subsidy for it?
By installing the split air conditioning units, you are changing the original conditions that your energy consultant had calculated for your energy-efficient building. However, KfW excludes any modifications to the building envelope for 10 years in their related terms. Does this apply to you?
R
Rafaelsen21 Mar 2023 11:38Pitiglianio schrieb:
Putting the main topic aside for a moment...
You built a KfW55 energy-efficient house and probably received a government grant for it?
By installing the split air conditioning units, you change the original conditions that your energy consultant calculated for your efficient build. However, KfW excludes any changes to the building envelope for 10 years according to their conditions. Does that apply to you? No, that does not apply. We exceed the standard and did not take advantage of any subsidies. At that time, KfW loans were not more favorable than those from regular banks. Repayment grants were only available from the 40 and 40+ standard onwards. It was not worth the effort for us.
Effective cooling through controlled residential ventilation only works properly at an air exchange rate of five times per hour or more. Standardly designed controlled ventilation systems are usually well below this. Therefore, neither the positive nor negative effects are significant.
The temperature near the ceiling can be calculated as: floor temperature x (1 + (0.1 x ceiling height)). Of course, insulation, solar radiation, and other factors also play a role. However, this formula is generally used.
The temperature near the ceiling can be calculated as: floor temperature x (1 + (0.1 x ceiling height)). Of course, insulation, solar radiation, and other factors also play a role. However, this formula is generally used.
RotorMotor schrieb:
The so-called summer bypass is only active when the outside air is cooler than the desired indoor temperature. rick2018 did not say anything else. The summer bypass simply disables heat recovery. It is basically a damper that prevents outside air from passing through the heat exchanger.
R
RotorMotor21 Mar 2023 11:45Dogma schrieb:
Rick2018 didn't say anything different. The summer bypass disables heat recovery because the summer bypass is nothing more than a damper that prevents outside air from flowing through the heat exchanger. Wrong, he wrote exactly the opposite.
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