The ABC of air conditioning
1. What should you take into consideration when selecting an air conditioner?
The following factors should be considered in the selection of an air conditioner:
A. the device can be connected to a cooling/refrigeration system
B. the system is equipped with high-quality filters
C. heat recovery is automatic, so residents do not have to mull over when to use heat recovery
D. the device is equipped with an efficient defrosting system to prevent the supply fan from freezing when the temperature drops
E. the system is quiet
F. the system has sufficient capacity to make it possible to step up ventilation
G. the re-heating system is compatible with other heating systems in place in the building
H. the central vacuum cleaner and the extractor fan can be connected to the air conditioner, enabling them to receive filtered supply air via the air conditioner
2. Heat recovery
A heat exchanger is an air conditioner component that is used to transfer heat from exhaust air to incoming air.
3. The efficiency of heat recovery
The efficiency of heat recovery refers to the amount of energy that is recovered from the exhaust air by the heat exchanger and transferred to the supply air. This efficiency is reported as a percentage. However, in a comparison of efficiencies, the system’s total energy consumption should be considered rather than just the efficiency percentage. Some systems available on the market are equipped with a preheat resistor to enable them to retain high efficiency values. This increases energy consumption even though efficiency values remain good.
4. How does the heating system influence the selection of an air conditioner? Why is it important to know what kind of radiators you have?
In winter, the heat recovery system alone isn’t sufficient to heat the incoming air and the system needs to have a re-heating functionality. Power for the re-heating system can be supplied by an electric power source or a water-circulation system. It is important to select the re-heating method on the basis of the building’s heating system because the air conditioner’s energy consumption may account for 30% of the heating energy required by the building. Installing an air conditioner that uses an electric coil as a power source is a sensible solution in buildings with electric heating. For buildings with a geothermal or district heating system, an air conditioner that can utilise the same, cheaper energy source should be selected. With KAIR systems, the water-circulation heating coil can be connected directly to a low-temperature heating system, helping to create savings.
5. Why is it important that the supply air fan is not switched off in winter?
Switching off the supply fan in cold weather is the most commonly applied antifreeze method. With KAIR air conditioners the supply fan is not switched off, as doing so would turn the air conditioning system into a mechanical extract system. As the building has no routes for supply air, the incoming air would enter through the floor structures and chimney flue. The air flowing in through the floor would also bring radon with it.
6. Pressure balance
Under Finnish building regulations, the atmospheric pressure inside the building should be slightly lower than outside to prevent damage to the building’s structures. Therefore, the volume of exhaust air should be slightly higher than the volume of supply air. If the pressure difference grows, supply air begins to flow in an uncontrolled manner, for example via the chimney flue. The central unit and the extractor fan contribute to an increasing pressure difference. A pressure balancing system helps to maintain the desired pressure difference. All KAIR systems are equipped with a pressure balance functionality, which can be connected to the central vacuum cleaner and the extractor fan via a sensor.
Cooling refers to the refrigeration of the incoming air. This is carried out either with an integrated cooling coil or a cooling unit’s evaporator. Refrigerated air is supplied to the building via the ducts used for ventilation. The cool incoming air is used to maintain a pleasant temperature in the house or flat. Refrigeration also removes moisture from the air. It is the removal of excess moisture that results in a comfortable and fresh sensation that is the objective of cooling systems. All KAIR air conditioners can be connected to a cooling system.
8. Geothermal cooling
Buildings equipped with a ground source heat pump with heating pipes installed in a vertical borehole can utilise geothermal technology for cooling. The cold liquid in the pipes is circulated via the air conditioner’s coil, which cools the supply air. It is important that the coil is inside the air conditioner and not in the duct, because water is condensed on it and from the air conditioner it can directed to a drain.
Filters play a major role in air conditioning. Air conditioners are equipped with two types of filters: pre-filters for coarse filtering, and fine-dust filters. Pre-filters are designed to prevent larger particles of dirt from entering the system and causing its components to get dirty, thereby improving the functioning of the air conditioner.
Fine-dust filters prevent particles that are harmful to human health from entering the indoor air. Both mechanical and electric fine-dust filters are available.
10. Maintenance required by air conditioners
The user is generally required to clean the air conditioner. Filters must be cleaned or replaced about four times a year. The natural ventilation system was in wide use until the 1970s.
11. Ventilation methods
Natural ventilation is based on hot air being lighter and therefore rising. In this method, air is removed from the building via flues, while supply air enters through the walls and gaps in the windows and doors. Then houses began to have central heating and a moisture barrier in their wall structures, which increased the level of insulation and prevented supply air from entering the building. With the natural ventilation method, energy is wasted. It works well in winter but not at other times of the year. In many buildings, this ventilation system has been replaced with mechanical ventilation in connection with renovation.
Mechanical ventilation began to gain a foothold in construction in the 1970s when it became apparent that natural ventilation was not efficient enough. In mechanical ventilation, fresh air was brought in via vents installed in windows and walls, while exhaust air was directed out of the building through ducts, assisted by extractor fans placed on the rooftop. This made ventilation more efficient and easier to control, while helping to prevent damage to the building caused by damp. However, the supply air is not filtered and as it is the same temperature as the outdoor air, it may cause a draught. Heating energy is also lost with the exhaust air. Such a system can be converted to a mechanical supply and extract system relatively easily.
Mechanical ventilation with heat recovery
In these systems, both supply and extract vents are equipped with fans to assist air flow. Air is directed in and out of the building via ducts. Outgoing air is extracted from rooms such as bathrooms, toilets, utility rooms and kitchens. Heat is recovered from exhaust air and transferred to incoming air. The supply air is also filtered and is post-heated in winter if necessary. The filtered supply air at a desired temperature is then directed to bedrooms, living areas and fireplace rooms.
Heat recovery systems increased in popularity in the 1980s and became mandatory in 2003 when new building regulations came into effect.