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 10:23rick2018 schrieb:
Mechanical ventilation with heat recovery doesn't really distribute air. It extracts air and blows in fresh air.Usually, though, this occurs across different rooms, so there is some air exchange between rooms. But as mentioned, the energy content of air is relatively low.rick2018 schrieb:
Therefore, when cooling is running, the mechanical ventilation with heat recovery should ideally be turned off or set to a low level.Why is that? Do you also turn off the mechanical ventilation when you switch on the heating?
Mechanical ventilation with heat recovery works the same for cooling as it does for heating.
The mechanical ventilation system extracts air from the ceiling, where it is warmest.
This means the ventilation system is working against cooling. In winter, during heating, the heat recovery reduces heat loss, but if the system were off, the loss would actually be even lower.
A fan would make more sense for air distribution and mixing.
My system is different, so I don’t have these issues.
This means the ventilation system is working against cooling. In winter, during heating, the heat recovery reduces heat loss, but if the system were off, the loss would actually be even lower.
A fan would make more sense for air distribution and mixing.
My system is different, so I don’t have these issues.
R
Rafaelsen21 Mar 2023 10:33rick2018 schrieb:
A controlled ventilation system for living spaces doesn’t actually distribute air. It extracts air and supplies fresh air.
Therefore, when the cooling is running, the controlled ventilation should ideally be turned off or set to a low level. Well, it does distribute air. For example, the vents in the children's rooms are outlets, and the inlet is in the bathroom. The bedroom has both inlets and outlets due to its size.
It’s similar on the ground floor.
And the cold air from the air conditioning is recovered in the ventilation unit through the heat exchanger. This already works, and the outdoor air is cooled in summer.
I appreciate any feedback and will provide updates in the summer.
R
Rafaelsen21 Mar 2023 10:35rick2018 schrieb:
The mechanical ventilation system extracts air near the ceiling, where it is warmest.
This means the ventilation system is actually working against cooling. In winter, while the heat recovery reduces heat loss during heating, if turned off, the loss would be even smaller.
A fan would make more sense for air distribution and mixing.
My system is different, so I don’t have these issues. It should be the opposite. In summer, the warm air is then exhausted.
In our case, there is no noticeable temperature difference between the floor and the ceiling even in winter. This is probably due to our underfloor heating.
There is always a temperature difference, even if it is small. If you have low ceilings, the effect will be less noticeable. Another question is what your controlled ventilation system does when the outdoor air is warmer than the desired temperature. It will probably switch off the heat recovery, meaning only air exchange takes place and no cold is transferred to the incoming air.
R
Rafaelsen21 Mar 2023 11:28rick2018 schrieb:
There is always a temperature difference, even if it is small. If you have low ceilings, the effect is smaller. Another question is what your controlled ventilation system does when the outdoor air is warmer than the desired temperature. Presumably, it will switch off the heat recovery. This means only air is exchanged, and the cold is not transferred to the incoming air. The ceilings are quite high. The controlled ventilation system behaves similarly in automatic mode. If it is supposed to cool, the bypass opens when it is cooler outside. Otherwise, the air passes through the heat exchanger and is cooled. According to the display, this can reduce the temperature by up to 8°C (14°F). That was also the origin of the thought. If I actively cool the air, the supply air should be cooled even more by the heat exchanger. The question is by how much.
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