The characteristics, design methods and comparison of commonly used air-conditioning systems Part Two

2) Air treatment process of fan coil unit + fresh air air conditioning system

The fresh air and the fan coil unit supply air to the air-conditioned room respectively. In this way, even if the fan coil unit stops running, the fresh air will remain unchanged.

The fresh air is mixed at the air outlet (extrusion end) of the fan coil unit. This method does not need to set up a special fresh air outlet, which is more beneficial to the ceiling layout; when the fan coil unit is running, the fresh air is required to increase the pressure there.

The fresh air is mixed with the return air from the fan coil unit and sent to the air-conditioned room. Compared with the above two methods, the number of air changes in the room is slightly reduced; when the fan coil unit stops running, the fresh air volume is reduced.

3) Selection principle of fan coil unit Select the appropriate model according to the use requirements and layout.

According to the calculation results of cooling and heating loads, select the appropriate unit specifications. Generally, fan coil units are selected according to the cooling load in summer.

According to the cooling load of the room, select the model according to the cooling capacity at the mid-range, and check whether the heating capacity in winter can meet the heating requirements of the room.

Combined with the actual working conditions, the cooling capacity and heating capacity of the unit under standard working conditions are corrected so that the actual cooling and heating capacity of the selected unit is close to or greater than the calculated cooling and heating capacity.

Pay attention to the residual pressure value outside the unit.

Pay attention to the noise level of the unit, and choose sound-absorbing measures reasonably.

4) Water loop heat pump air conditioning system

Water loop heat pump air conditioning system is a form of full water air conditioning system.

Water ring heat pump is also called water-air heat pump, and its heat transfer medium is water. When cooling, the unit releases heat to the water in the loop to lower the air temperature; when heating, it obtains heat from the water to heat the air.

Working principle of water ring heat pump unit

When the water ring heat pump unit is running under refrigeration conditions, the built-in compressor of the water ring heat pump unit compresses the low-pressure and low-temperature refrigerant vapor into a high-temperature refrigerant gas and enters the condenser. In the condenser, the refrigerant is condensed into a high-pressure liquid through the cooling effect of water. The flow device (expansion valve) throttles and expands and then enters the evaporator, thereby cooling the air passing through the water ring heat pump unit.

When the water ring heat pump unit is running in the heating condition, the system of the unit is the same as the cooling condition. The evaporator then becomes a condenser. The unit absorbs the heat in the water through the evaporator, and releases heat from the condenser to the air passing through the water ring heat pump unit to achieve the purpose of heating the air.

Air volume and air organization

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The task of airflow organization design is to reasonably organize the flow of indoor air, so that the temperature, relative humidity, speed and cleanliness of the air in the indoor working area can better meet the process requirements and people's comfort requirements.

1. Air volume

The air supply volume of the air conditioning system should be able to eliminate the maximum residual heat and humidity in the room, which is usually calculated and determined according to the maximum indoor cooling load in summer.

1) Air supply temperature difference The air supply temperature difference is a key parameter to determine the air supply status and calculate the air supply volume. If the air supply temperature difference is selected to be large, the air supply volume will be small, and the equipment required for air treatment and air delivery will be correspondingly small, so that the initial investment and long-term operation costs can be reduced. However, if the temperature difference of the supply air is too large and the supply air volume is too small, the distribution of the indoor air distribution will be affected, and the uniformity and stability of the indoor temperature and humidity distribution will be affected.

Under comfortable conditions, the summer air temperature difference of the air conditioning system should be increased as much as possible, but should not exceed the following values: when the air supply height is less than or equal to 5m, it should not exceed 10°C;

When the air supply height is greater than 5m, the temperature shall not exceed 15°C;

When the air supply height is greater than 10m, it shall be determined according to the jet flow theory;

When the top air supply (non-diffuser) is used, the temperature difference of the air supply should be calculated and determined according to the jet flow theory.

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