How can a ventilation unit be used to save electricity?
The efficiency of ventilation should be adjusted based on the need and the supply air temperature should be kept as low as possible. The ventilation is sufficient when the home smells fresh when coming in from outdoors, the air is good in the bedrooms also in the morning, and the wetrooms dry out after their use. A too low supply air temperature can cause unpleasant drafts.
A ventilation unit that is equipped with heat recovery warms up the supply air in winter by using the heat contained in the extract air (heat recovery cell) and, where required, by using a post-heating radiator. The more efficient the heat recovery of the ventilation unit is, the less energy the post-heating radiator consumes. The best way to determine the operation and efficiency of the heat recovery cell is to measure how much cooler the exhaust air is as compared to the indoor air.
If the ventilation unit blows air into the apartment that is cooler than the room temperature, the supply air is heated by using the building’s own heating system to ensure that the room temperature does not decrease. The lower the set supply air temperature, the less electricity the post-heating radiator will consume. Subsequently, less energy is required from the heating system.
In Vallox MV models that have a so-called partial bypass of the heat recovery cell, heat recovery always operates at the maximum efficiency level when the outdoor temperature is below +3°C. If the set supply air temperature is very low when the outdoor air temperature is above +3°C, the unit can let some of the heat contained in the extract air past the heat recovery cell. If all heat contained in the extract air is to be utilised in the autumn and the spring, the heat recovery cell bypass can be turned off completely. If the software version is older than 2.0 and does not include the option to turn off the bypass function, a new software version can be downloaded here. Do not forget to turn on the bypass automatics in the spring.
In Vallox SE models, heat recovery is in use when the outdoor temperature falls below the set “HR cell bypass” temperature or when the light of the post-heating button is on.
In Vallox MC models, heat recovery is in use when the outdoor temperature falls below +14°C, if the supply air temperature control is in the Auto or Off position. If the set temperature is between these two values, heat recovery is always in use. In the Auto position, the unit aims to maintain the supply air temperature at +17°C in winter. In the Off position, the post-heating resistor is always turned off and the supply air temperature is as high as the heat recovery cell is able to heat it.
If the ventilation unit has a manually operated summer/winter damper, it must be ensured that the damper is turned into the winter position in the autumn. If the unit has an automatic summer/winter damper, its operation should be checked at the beginning of the heating season.
If a so-called summer cell is used in the ventilation unit, it must be ensured that the heat recovery cell is replaced in the unit in the autumn.
The post- and additional heating radiators of Vallox MV models must never be turned off, as the unit needs them during the defrosting cycles.
If the building only has extract air ventilation, e.g., a roof fan, a house extraction fan, or natural ventilation, all of the replacement air is heated by using the apartment’s heating system.
The energy consumption of the ventilation system essentially depends on how much air is being replaced, i.e., on the efficiency of the ventilation. Ventilation can – and must be – used based on the need. When the apartment is unoccupied, the efficiency of the ventilation can be decreased even radically, but it must never be turned off completely. When the efficiency is halved, the energy consumption of the ventilation drops by more than half. When the residents are at home, the air flow specified in the ventilation plan should be used; however, it is important to boost the ventilation after saunas and showers, for example. If the ventilation unit has humidity and/or carbon dioxide sensors, they adjust the efficiency of ventilation based on the need to ensure that air is not being replaced unnecessarily. Therefore, these sensors should be kept on.
A more efficient heat recovery cell cannot be installed in an old ventilation unit, because they are larger than the old heat recovery cells. Neither can AC fans be replaced with EC fans. The amount of electricity consumed by the fans is relatively small when compared to the heating of the replacement air.
Read more about the energy consumption of ventilation in the blog (in Finnish only).
Here you can download a calculator for calculating the energy consumption of your ventilation unit