Types and application of air conditioning

Air conditioning, or HVAC, is an abbreviation of the word Heating, Ventilation, and Air Conditioning, which means heating and cooling, ventilation, and improving air quality to achieve comfortable conditions. These conditions are different for different users. A complete building air conditioning system must have the ability to cool, heat, humidify or dehumidify, and filter air to provide ideal conditions for occupants. This operation can be done in different ways in different equipment. For example, all operations can be performed in one compressed unit, or several separate units can be used in conjunction with each other. But in general, air conditioning systems can be run as all-water, all-air, mixed mode (water-air), and direct expansion (DX) mode. The equipment of each of these methods and their design are different from each other, and according to the conditions of the project, one can choose one of them.

In the all-air or channel air conditioning system, channels are made of galvanized sheets, which are often placed behind the walls and in the false ceiling of the building. The task of these channels is to direct the flow of cold, hot and fresh air from the air conditioner or other channel devices such as airwasher, Zent, ​​etc. to different parts of the building. All-air systems are divided into two categories: constant air volume (CAV) and variable air volume (VAV). In the CAV system, the volumetric flow rate of conditioned air is transferred to the required location in a constant and uniform manner, and to change the thermal power, the temperature of the output from the system is changed; But in the VAV system, it is possible to change the air flow to change the system capacity and the temperature of the system is considered constant.

Single zone air conditioning system is a system that is only able to provide temperature conditions suitable for one zone or zone. This system is often used in residential buildings and large stores. Among the examples of this system, we can mention rooftop air conditioning devices known as roof top package or unit package. These devices have advantages such as easy design and installation and maintenance, as well as lower initial cost than other duct ventilation systems. But since they are single zone, they are not capable of providing different temperature conditions in one set. Therefore, this system will not be suitable for places like hotels.

In the multi-zone air conditioning system with reheating terminal, it has been tried to remove the cooling coil of the zones. For this purpose, the temperature of the air conditioner (AHU) is set by the main cooling coil to the lowest temperature required by the zones, and for the zones that need a higher temperature, the heating coil corresponding to each zone is used as reheating. In some cases, heating elements are used instead of reheating coils. The main advantage of this system is the elimination of the coils placed in each zone, which leads to a reduction in the required space and also a significant reduction in the initial costs of the system. But its main disadvantage is the issue of energy waste; Because in this method, it is necessary to reduce the total temperature of the air coming out of the air conditioner to the lowest required level, and increase it again by the reheating coil for some zones.

In this method, the advantages of the previous two systems have been used. In this way, two separate and parallel paths of hot and cold air are created by using heating and cooling coils, and a branch is taken from each of these paths for each area. These branches enter a box called a mixing box and using the built-in control components, the temperature of the air coming out of it reaches the required temperature of each zone. Therefore, the waste of energy is reduced in this method.

Variable air volume air conditioning system with constant temperature is widely used in office complexes. In this method, unlike the introduced systems, the temperature of the coils is constant, and to change the thermal power, the air flow rate of each zone is changed. This flow rate change is often done by the damper and its corresponding actuator. The schematic of this system is very similar to the single zone system, with the difference that the incoming air flow to each zone passes through the VAV box before entering. This box is responsible for regulating the flow rate of the passing flow, and according to the needs of each zone, it decreases or increases the flow rate. It should be noted that the temperature of the heating and cooling coils of the air conditioner is constant and does not change.

In the pipe or all-water air conditioning system, ducting is not used, and thermal or cooling energy is transferred by piping from the heating and cooling engine room to heat distribution units such as fan coils, radiators, floor heating, unit heaters, etc. is transmitted Therefore, one of the great advantages of these systems is the increase in building space due to the elimination of large air ducts. In these systems, a heat distribution device (such as a fan coil) is considered for each zone, and all of them are connected by piping to central cooling units such as chillers and heating units such as engine room. One of the characteristics of the all-water system compared to the all-air system is the significant difference in the heat capacity of water compared to air. This means that a much smaller volume of water is needed to provide heat or cold to a certain volume of the environment. Therefore, this is why water pipes (compared to air channels) have a smaller size.

Fan coils consist of four main components, which are the body of the fan coil, cooling and heating coils, device fan, and its control system. There are different types of fan coils, among them, it can be mentioned how they are placed on the ground, ceiling, and wall, as well as surface or built-in installation. The heating coil of the system is connected to the engine room or the heating package, and the cold coil is connected to the chiller or mini chiller. After detecting the desired temperature by the thermostat, hot or cold water flow is established to the device coil and the device fan starts working. Most of the fan coils are made in two types of two tubes and four tubes. In a two-pipe fan coil, hot or cold water enters the coil from one pipe and exits from the other pipe. But in the four-tube fan coil, both coils can be fed simultaneously in all seasons. There are also three-pipe models in which the return of hot and cold water pipes is done jointly and from one pipe, but the use of these types of fan coils is much less.

Radiators, which are also known as heating, are one of the most common and well-known methods of heating, which have different types, including cast iron, steel and aluminum. Its aluminum type is due to its light weight, high thermal efficiency, better corrosion resistance, more beauty, and wider application. Radiators transfer heat to the surrounding environment by passing hot water through their internal pipes. Their performance is very similar to fan coils, with the difference that they do not have a blower fan.

Underfloor heating is a relatively new heating system that heats the air in the room without the need to install a separate heat distribution device. For this purpose, it is necessary to insulate the floor of the room and install special pipes in a spiral form and in a special order on the floor. Ceramics or parquet are often used on these pipes after concreting. The most important advantage of underfloor heating is the uniform distribution of heat throughout the room. But on the other hand, the duration of heating the desired environment is much longer than heating by radiator and fan coil. It should be noted that for the distribution of hot water in the floor heating pipes, special collectors of this system, which are equipped with a flowmeter, are used. These flowmeters balance the piping system and will result in uniformity of heat distribution.

The air-water system is created by combining two systems of all water and all air to use the advantages of these two systems to achieve a better system. Therefore, the water-air system provides the required fresh air at the same time, and its occupied volume is smaller than an all-air system. One of the subsets of this system is the channel fan coils, where the fresh air needed by the air conditioning unit first enters the fan coil and then is sent to the desired space. It should be noted that in this method, the main burden of providing heat or cooling is the responsibility of the fan coil and the air conditioning unit will only be responsible for the preheating operation.

Direct Expand system is another type of air conditioning system that is used to transfer heat between the inside and outside environment. In this system, refrigerant is used instead of water or air fluid. Therefore, the refrigerant coming out of the condenser directly enters the evaporator and absorbs heat. The pipes of this system are made entirely of copper, and since the heat exchange is done without intermediaries, there is less loss and the efficiency of this type of system will be high. Read more about what is refrigerant and types of refrigerants. Among the advantages of this system, we can mention the reduction of piping route and heat loss caused by it, lower cost of installation and operation, no need for fan and pump, increasing system efficiency, and increasing the life of parts compared to the all-water type. The types of direct expansion system are: VRF system, chiller and air conditioner, roof top package, split and split duct.