Fresh air is an important condition for air conditioning unit room to ensure the air freshness in production area. Most fresh air air conditioning units use steam or high-temperature hot water as the heat source to heat the air. When the air conditioning units are running or stopping, the coil pipe is often frozen and cracked.

So, how should we prevent this phenomenon from happening?

1. The fan coil adopts the downstream design structure, even if the low-temperature air directly exchanges heat with the high-temperature inlet water of the coil, the water temperature reduction time is delayed and the coil is prevented from freezing and cracking;

2. While satisfying the heating capacity, choose the circulation process with fast flow rate to effectively reduce the circulation time of hot water in the coil. The flow rate is designed to be more than 1m/s, which makes the opening of the self-controlled hot water valve smaller and makes the flow rate in the coil reach  of 0.15m/s required for antifreeze;

3. The highest point of each group of fan coil units is provided with a manual air release valve, and the lowest point is provided with a water discharge port, which can completely empty the air and impurities inside the coil units during system debugging;

4. Set Y-type filter on the system pipeline entering the coil, and clean the Y-type filter after installation and commissioning to avoid impurities entering the coil, increase resistance and reduce flow rate;

5. When the coil is only used for heating, the heat exchange area of the coil is reduced by the design allowance, which should be no more than 5% of the calculated value. At the same time, the structure can be designed to be vertical, which can exhaust and drain water from bottom to top.

6. The new tuyere is designed with closed thermal insulation air valve, the anti-freezing switch is designed behind the coil, and the fresh air section is designed with anti-freezing electric heating after shutdown. The fresh air valve is interlocked with the fan. When the fan stops, the closed and insulated air valve is closed. When the temperature behind the coil is lower than 5℃, the antifreeze switch gives a signal, and the electric heater works. When it is heated to 10-15℃, the electric heater is turned off. Usually, in order to prevent the uneven temperature behind the coil, two anti-freezing switches are set up behind the coil of the large air volume unit of fresh air conditioning; At the same time, the antifreeze switch can also give a signal during the operation of the unit to control the opening of the hot water valve or stop the operation of the unit to prevent the coil from freezing and cracking;

7. The hot water circulating pump is designed for the system pipeline. When the system is shut down, the hot water circulating pump works to ensure the flow velocity inside the coil and prevent the coil from freezing and cracking;

8. When the fan coil unit does not work for a long time, the water inside the coil can be drained, and the equipment manager can set a three-way valve at the exhaust valve position of the coil, then connect the compressed air with a pressure of 0.16MPa, purge for 30min, and open the drain at the lowest point of the coil to completely drain the water to prevent the coil from freezing and cracking.