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HVAC Systems

Renesas HVAC system achieves convenience and energy efficiency by motor control and sensing technologies.

Outline

HVAC building automation system can be divided into two types: central air conditioning and individual air conditioning.

*Renesas provides semiconductor solutions.

Central Air Conditioning System

As illustrated in Figure below, in a central air conditioning system a heat source in a single location is used to circulate air, water, or steam to the various rooms, and exchange heat, in order to cool or heat each room to the specified temperature.
The chiller refrigerates water for use as a refrigerant, circulates it to the various rooms, and exchanges heat. The cooling water gradually becomes warmer, and in the cooling tower on the roof it is chilled through contact with air and then reused. Pumps are used to recirculate the water.
The heat source (boiler) is powered by gas, oil, or electricity. It heats water in a vessel to produce hot water or steam. To heat the rooms, this hot water or steam is circulated through the rooms, and heat exchange takes place.
Either a pair of two pipes or a set of four pipes can be used to circulate the cold or hot water. There are outgoing and incoming hot-water and cold-water pipes used to distribute the hot and cold water to air handling units (ACUs), fan coil units (FCUs), etc. In a two-pipe system the same pipes are used for both hot and cold water, switching from one to the other depending on the season and whether heating or cooling is required. This means heating and cooling operation cannot take place at the same time. On the other hand, if the cooling and heating coils built into the ACUs, FCUs, etc., are each equipped with their own outgoing and incoming pipes, simultaneous heating and cooling operation is possible within the same building. Such an arrangement is called a four-pipe system from the total number of pipes used.
An outdoor-air processing unit (or total heat exchanger) extracts the heat or cold from indoor air that expelled to the outside (exhaust) and transfers it to fresh air from outside, thereby minimizing the difference in temperature between the indoor air and the fresh air from outside. An ACU or air handling unit uses cold water, hot water, or steam supplied by the heat source unit to adjust the temperature and humidity of the air, which is then supplied to the rooms.
HVAC systems use air, water, or refrigerant as the medium for heat exchange. Some central air conditioning systems use a method called variable air volume (VAV), in which valves are used to adjust the volume or cool (or warm) air passing through the ducts. In a water-cooled system cold or hot water is circulated via pipes, and FCUs perform heat exchange to adjust the temperature of each room.

Central Air Conditioning System

Individual Air Conditioning System

In an individual air conditioning system refrigerant gas is circulated and exchanges heat. One typical example is a building multiple air conditioner system. The temperature can be set undependably for each room, and simultaneous heating and cooling operation are possible.
Sometimes central air conditioning and individual air conditioning are used in combination, depending on the size of the building and its purpose.

Individual Air Conditioning System

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