• Today, people spend most of their lives indoors, so it is very important to take care of the microclimate of the housing.
• Air quality requirements for rooms with different needs may vary. In addition, every person may also have a different comfort temperature, but it should preferably be maintained between 18°C and 22°C.
• The recommended relative humidity of air is between 40% and 60%.
• Low relative humidity can have adverse effects on the skin, airways, nasal membranes and eyes, causing irritation, and increases the ability of viruses and bacteria to spread in dry air.
• On the other hand, high relative humidity increases the likelihood of dust mites as well as water drops that cause moulding may condense on cold surfaces, such as window frames.

• The concentration of carbon dioxide (CO₂) in the room is a very important indicator of the microclimate. It is measured in parts per million or “ppm”.
• The CO₂ level in the room should not exceed 800 ppm above the outdoor air CO₂, which is 350-400 ppm.
• A CO₂ concentration of up to 1000 ppm is considered to be acceptable air quality.
• Beyond this value, oxygen is reduced in the room causing people feel tiredness, drowsiness and even headache.

• Air circulation in housing usually takes place through open doors, hallways or other gaps.
• When replacing indoor doors, it is preferable to leave a small gap under them so that even in closed condition the air between rooms can be exchanged.
• If doors are closed tightly, an overpressure condition may build in the room where air supply is provided, while the rooms with air exhaust channels will be in a low pressure condition.
• It can be felt as a resistance in the process of opening or closing the door.

• The natural ventilation exhaust channels must not be closed or fans not working 24 h a day must not be installed in front of them, as there is no air exhaust at the time, when the fan does not work and ventilation in the housing does not function.
• The same applies to natural ventilation exhaust channels in the kitchen.
• Apartments in multi-apartments, where gas cookers and heating equipment are used, should not interfere with the natural ventilation system.
• Any intervention in main structures of the building, such as reconstruction of natural ventilation without coordination or connection of a stove hood to the exhaust channel in the kitchen, is not allowed and should be regarded as arbitrary construction.

• In the case of a decentralised ventilation system, separate installations ensure air exchange in individual rooms or groups of rooms.
• There are solutions, where air supply and air exhaust are ensured by separate installations or simple fans.
• Such solutions are suitable for multi-apartment buildings, where all the dwellers of the building do not want or cannot install a joint ventilation unit.

• The plate recuperator consists of cross-shaped plates, between which isolated supply and exhaust air flows are flowing across and in parallel and their temperature equalises.
• The advantage of the plate heat exchanger recuperator is very high efficiency of separation of exhaust and supply air – up to 99.9%.
• Thus, it can be used to recover heat even from the warm air flowing out of the kitchen exhaust channel without worrying that unwanted smells will spread in other areas of housing.
• This type of recuperator does not recover the humidity in the room.
• In cases where the outdoor air is very dry, humidity levels in the room will also decrease.
• The disadvantage of a plate recuperator is the possible formation of condensate in the heat exchanger itself.
• This may occur during the winter period, when the outdoor air temperature drops below -2°C.

There are two solutions that are used to prevent condensate formation:

1. to reduce the air supply intensity and to increase the air exhaust intensity, thereby reducing the efficiency of the recuperator and reducing the supply air temperature.
2. to install an electric heater in the outdoor air supply channel and to heat outdoor air above -2°C, but this will result in additional electricity consumption.

• An aluminium plate rotor containing air flow channels is installed on bearings in the ventilation unit with a rotary heat exchanger. The exhaust air heats up the rotor and this heat is used to heat the supply air.
• In this type of equipment, supply and exhaust air are slightly mixed – 2% to 5%.
• Thus, there is a minimal possibility of transmitting odours from exhaust air to supply air.
• The rotary heat exchanger partially recovers humidity from exhaust air, which is important during the winter period when the relative humidity of the outdoor air is low.
• There is no possibility of condensate formation in the rotary heat exchanger, which eliminates the risk that the equipment may freeze.
• It should be noted that at very low outdoor temperatures the effectiveness of this type of recuperator will reduce.

• An enthalpy heat exchanger has been created to combine the good properties of a plate heat exchanger and a rotary heat exchanger.
• The enthalpy heat exchanger basically is a plastic plate heat exchanger.
• Its plates are made of a special nanomembrane, the main property of which is the recovery of humidity.
• The membrane structure is designed so that only compounds that are the size of water vapour molecules can move from one side of the membrane to the other.
• The enthalpy heat exchanger has a high energy recovery efficiency.
• Due to the nature of the recovery of humidity, the risk of freezing of the heat exchanger reduces significantly.
• Such a recuperator allows the air humidity level in the rooms to be maintained at the same time and guarantees that the supply and exhaust air flows are separated from each other.