The inspection indexes of hvac duct making machine include the following items: air volume, cooling capacity, heating capacity, cooling capacity per unit fan power, water resistance, A-level noise, condensation, condensate treatment, motor winding temperature rise, thermal insulation resistance, leakage current and grounding resistance. However, the standards for evaluating the quality of a fan coil unit in engineering mainly depend on its air volume, cooling capacity, noise and power consumption.
Problems to be noted
1. Insufficient cooling capacity of coil: this problem is one of the most complained problems at present. The main reason for this problem is that many enterprises do not have their own test methods, the parameters on the samples are copied from the samples of other manufacturers, and the thermal performance of the coil produced by themselves is poor (this is mainly caused by the fin form, tube expansion quality, production process, etc.). Therefore, it is suggested to pay attention to the testing facilities and means of the manufacturer during the project inspection. It is difficult to imagine that a manufacturer without its own testing device can produce good products.
2. Air volume: at present, we usually select fan coil according to the calculated cooling load by consulting the samples of relevant manufacturers. How to consider the air volume of coil is a problem. In the domestic market, most manufacturers only have one type of coil with three rows of tubes, but some manufacturers also provide two rows of tubes. I hold the view that it is more advantageous for most civil building air conditioning systems to choose the coil with two rows of pipes (except for high humidity situations). This is because the air volume of the products with two rows of pipes is large under the same cooling capacity, which will increase the air exchange rate of the air-conditioned room and is conducive to improving the accuracy and comfort of the air-conditioning. Under the same cooling capacity, air conditioner using small temperature difference and large air volume to supply air will achieve better air conditioning effect than the one with large temperature difference and small air volume.
3. External residual pressure: due to the current national standard for coil units in China, the parameters of air volume, cooling capacity and noise of fan coil units are tested under the condition that the external static pressure is zero. However, in actual use, a small section of air duct and air louver are often connected in front of the air outlet of the coil. In addition, some projects also have a return air box. Therefore, in actual use, it will be found that the actual air volume of the coil is less than its nominal air volume. As a result, the air volume of the room decreases, the air temperature difference increases, and the comfort of the air conditioner decreases. In order to avoid this situation, some designers select the coil according to the mid range air volume to avoid insufficient air volume, but increase the initial investment of the project. Therefore, the author suggests that when the domestic test standard has not been changed, we should give priority to the unit with residual pressure (generally 10-15pa) in coil selection.
4. Noise problem: this is a place where the gap between domestic products and foreign products is large, and it is also a key point that coil is complained about due to quality problems. The reason of this problem lies in the unreasonable configuration and matching of the motor and fan in the coil. Another reason is that the manufacturer's quality management is not strict, the assembler's sense of responsibility is not strong, resulting in instability in the aspect of product quality. Therefore, when inspecting a manufacturer's products, we should refer to the noise test report of this product (note that we must pay attention to those products we are going to order) issued by the national authoritative quality inspection department.