DCC——Dry Cooling Coil Introduction

Dry coil, also known as dry coil, is called a dry coil because its inlet water temperature is generally about 2 degrees higher than the dew point of indoor air (usually 13 ℃ for inlet water and 18 ℃ for outlet water), and there is generally no condensation water produced above this point

• Structure of dry coil: 1. Aluminum fins, which are the main heat dissipation components of dry coil, are composed of thin aluminum sheets. 2. Coils are mainly processed from copper tubes and inserted into aluminum fins. Depending on the cooling energy, they are usually divided into 2 rows of tubes/3 rows of tubes/4 rows of tubes; 3. Water collection tray, mainly used to collect and drain water, usually requires insulation at its bottom; 4. The exhaust valve is usually installed at the interface of the outlet pipe of the dry coil. When the water is first supplied, the air stored in the dry coil can be discharged by opening the exhaust valve. If the air is not discharged, the water flow cannot pass smoothly through the dry coil, and the dry coil will not have a good cooling effect. 3、 The working principle of dry coil is that DCC dry coil is a heat exchange device composed of a series of parallel arranged coils inside. Hot or cold water flows through the coil and exchanges heat with the air outside the coil, thereby changing the temperature of the air. Specifically, when cold water flows through the coil, it absorbs heat from the air, causing a decrease in air temperature; And when hot water flows through the coil, it releases heat to the air, causing the air temperature to rise.
• l The selection of dry coil should pay attention to the following points: 1. Determine the number of copper tube rows for the selected coil based on the enthalpy difference of the inlet and outlet air; 2. The air volume of a single dry coil obtained by dividing the total amount of system return air by the number of dry coil units, and the required air volume determines the windward area of the selected coil unit; Targeted training or personalized courses for HVAC enterprises. 3. The frontal wind speed of the coil is generally not greater than 2.5m/s; 4. The coil fins are made of aluminum and require blue wave treatment to prevent corrosion. 5. The water collection tray must be set up, mainly considering that when the coil is first operated with water in humid areas, the humidity in the room is high, and the coil will produce a lot of condensed water.
• l Common fault phenomena of dry coil: 1. Poor heat transfer effect: (1) The capacity of the dry coil is too small, which is caused by improper selection in the initial stage. This problem is generally caused by designers and is relatively rare in engineering practice. Usually, a smaller capacity is due to an increase in the area of the cleanroom after renovation, without a corresponding increase in the number of dry coil units, resulting in a relatively smaller cooling capacity of the dry coil units compared to the entire cleanroom. (2) The inlet air direction of the dry coil is incorrect. Generally, the airflow needs to follow the direction of the dry coil in order to achieve good heat transfer efficiency. (3) There is gas blockage in the dry coil. Before the dry coil is put into operation, the air accumulated in the coil must be removed to ensure smooth water flow and good heat transfer. 2. There is no heat exchange effect, which may be caused by the inlet and outlet valves being closed, or the electric valve losing control and closing, resulting in the water flow not being able to pass smoothly through the dry coil for cooling, or the main machine room's ice water host malfunctioning and unable to produce ice water. 3. The dry coil pipe is leaking water, and cracks may occur in the dry coil pipe during long-term operation. This may be due to incomplete flushing of the pipe in the early stage, resulting in small particles such as welding slag impacting the copper pipe of the dry coil pipe for a long time, causing cracks to occur. 4. There is abnormal noise in the dry coil, and there are small particles inside the dry coil, such as welding slag, etc. Therefore, it is necessary to thoroughly flush the system in the initial stage. Sometimes, air in the pipeline can also make abnormal noise. 5. If the bottom water tray of the dry coil does not drain, the dry coil should not have accumulated water. However, if the water temperature is too low, condensation will occur, or if there are cracks in the coil in the dry coil, water will seep into the water tray. (1) The installation slope is incorrect. This problem is mainly caused by the installation personnel, who start the installation without measuring the slope during the initial stage, resulting in difficulty in drainage. (2) The drainage pipe is blocked, which may have occurred during installation, without conducting a water test after installation, or due to the slow blockage of the bottom by some dirt during long-term use. (3) The structural problem of the dry coil itself often occurs in manufacturers. The entire water collection tray is tightly hit by the end plate iron sheets extending from both ends of the dry coil in the middle, and the accumulated water on the side facing away from the drainage pipe that is hit by the iron sheets cannot be drained smoothly.
• Daily maintenance items for dry coil: 1. Measure whether the airflow through the dry coil is unobstructed. Generally, if the airflow through the dry coil is too small, its cooling effect will be greatly reduced. Usually, the air speed through the dry coil is controlled at 1.5-2 meters per second, which can ensure a good heat transfer effect at around 1.5-2.0 meters per second. Check if there is any blockage on the windward side of the dry coil, and if there are foreign objects covering the windward side of the dry coil. Clean up foreign objects on the windward side in a timely manner. 2. Check whether the heat exchange of the dry coil is normal by touching the degree of cooling of the inlet and outlet pipes of the dry coil. The inlet water temperature is approximately 12-14 degrees Celsius and the outlet water temperature is 17-19 degrees Celsius. Setting such inlet and outlet water temperatures is mainly to ensure that the surface temperature of the dry coil is higher than the dew point temperature of the surrounding air, so as not to produce condensation. 3. Check the cleaning of the bottom water tray of the dry coil. The water tray of the dry coil should be kept drained smoothly. If the drainage is not smooth, water will accumulate at the water tray. If it accumulates too much and cannot be drained smoothly, it will overflow. 4. It is best to keep the bottom of the water tray insulated to prevent condensation from accumulating at the bottom of the chassis when the water temperature is too low. 5. Check if there is any water leakage in the inlet and outlet valves of the dry coil. Generally, after 5 years of operation, some valves may age and rust, which can easily lead to water leakage in the inlet and outlet valves. At this time, it is necessary to check and repair them in a timely manner to prevent the water leakage from becoming more serious and affecting the normal production of the workshop. 6. Check if the electric valve on the outlet pipe of the dry coil is working properly. The outlet pipe of the dry coil is generally equipped with an electric valve to control the on/off of the water circuit, in order to regulate the temperature. Usually, the following methods can be used to test electric valves to determine their quality: (1) Testing for power signals reaching the wiring terminals of the electric valve; (2) Rotate the electric knob on the upper part of the electric valve to see if it can automatically reset; (3) Send manual signals through the DDC central controller to force it to perform actions. After identifying through the above three methods, the quality of the electric valve can generally be checked. If it is found that the electric valve is broken and cannot work normally, it should be replaced in a timely manner to ensure that the electric valve can automatically control the water circuit.

Suzhou Pharma Machinery Co.,Ltd.

2025/02/05

Gino