The outdoor condenser of the high-precision constant temperature and humidity air conditioning circulation system in the computer room is located on the outdoor platform on the north side of the 17th floor of the building, and the indoor unit is located in the central computer room on the third floor. The vertical drop is 40 meters, the horizontal distance is 100 meters, and the total refrigerant pipeline is 140 meters long. This length has exceeded the conventional requirements of high-precision constant temperature and humidity air conditioning. Generally, the vertical height difference between indoor and outdoor units should not exceed 25 meters, and the total refrigerant pipeline length should not exceed about 60 meters. With such an extra-long equipment distance, the first thing to consider is how to solve two technical problems: one is the exhaust pipe quality oil return problem; the other is the problem of starting the extra-long pipeline in winter.

    1.The solution to the problem of exhaust pipe oil return is to ensure the smooth circulation of refrigerant oil in the refrigeration system circuit and prevent the liquid refrigerant from flowing back into the exhaust pipe when the compressor is stopped. When the outdoor unit pipeline of the high-precision constant temperature and humidity air conditioner climbs up 3 floors and the vertical drop is about 10 meters, a U-shaped oil storage bend is added to the exhaust pipe, and sufficient refrigerant oil is added to the refrigeration system. When the exhaust pipe of the compressor of the indoor unit climbs vertically upward through the pipe well of the 3-17 floors, an oil storage bend is arranged every two floors. Ensure that the exhaust diameter of the refrigeration system is equipped with a standard of 28nm), and the return pipe is reduced by one gear to 19nm).
(1) There are two purposes for making the bend: First, when the refrigeration system is stopped, the oil film on the wall of the super-long and vertical exhaust pipe will flow down to the lowest end and accumulate, which will affect the normal circulation of the refrigerant oil. Moreover, when the machine is turned on next time, too much liquid refrigerant oil will also affect the normal establishment of the compressor exhaust pressure. After the oil storage bend is set, the oil film on the wall of the short-circuit pipe is collected in sections (the amount of oil is reduced), and the diameter of the bottom of the U-bend is reduced due to oil storage. When the system is running, the refrigerant flow rate here will increase, and the high flow rate is used to carry away the U-bend to buffer the vertical copper pipe weight,
which plays a buffering and decomposition role in the vertical super-long pipeline. (2) Setting of the reverse bend: A reverse U-bend is installed at the air inlet collection pipe of the condenser. Its purpose is to prevent the refrigerant liquid in the condenser from flowing back into the exhaust pipe when the compressor is stopped, affecting the next startup of the compressor.
2. Solution for winter startup of super-long pipes
    The solution to the problem of winter startup of super-long pipes is to install a one-way valve and a liquid storage tank before the refrigerant return pipe enters the indoor unit.
    In the ultra-long pipeline system, since most of the pipelines are laid outside the machine room, if the compressor stops running for too long, the refrigerant in the pipeline will slowly reach the atmospheric temperature. The coldest room in Zhengzhou in winter can reach -11℃, and the saturation pressure of the R-22 refrigerant is 1.5bar (gauge pressure). If the compressor is started, the high pressure is too low, so that the inlet pressure entering the expansion valve cannot meet the opening requirements, and the liquid supply of the evaporator is severely reduced, resulting in a decrease in the evaporation pressure of the evaporator, and a low pressure alarm appears. Over time, the refrigerant oil in the compressor crankcase will foam and be brought into the refrigeration system due to low pressure, resulting in a decrease in the lubrication effect of the compressor until the compressor is damaged.
    In order to solve this problem, a one-way valve and an 8-liter liquid storage tank are added to the ultra-long pipeline system, and the equipment is required to be installed in the machine room.
    The function of the one-way valve is to ensure that the pressure of the refrigerant in the liquid storage tank will not decrease with the low outdoor temperature when the refrigeration system is shut down for a long time. In addition, the one-way valve has another function. When the compressor is cold-started, because the pressure of the outdoor pipeline is lower than that of the liquid storage tank, the one-way valve is closed to prevent the refrigerant from flowing to the indoor unit side. In this way, the high-temperature and high-pressure refrigerant gas discharged by the compressor can quickly raise the pressure of the condenser to the ideal value. If there is no one-way valve, the refrigerant will flow to the indoor unit side while the compressor is exhausting to the outside, and the high pressure will be established much slower. The
    volume of the liquid storage tank is selected based on the displacement of the compressor of the refrigeration system, and the capacity of the liquid storage tank is calculated based on the relevant parameters of the equipment. Because the liquid storage tank is in the machine room, the temperature can be around 22°C, and the minimum pressure in the tank will not be lower than the saturated pressure value corresponding to the machine room temperature (about 8.5 bar gauge pressure). The function of the liquid storage tank is to ensure that the next time the compressor is started, the expansion valve is supplied with a satisfactory pressure and liquid volume to ensure that the evaporation pressure does not drop too low.
3. Conclusion
    After the corresponding technical modification, the performance parameters of the high-precision constant temperature and humidity air-conditioning unit are within the design requirements, the suction and exhaust pressure of the compressor operates smoothly, the refrigeration oil circulation of the compressor is normal, and the refrigeration effect does not show significant attenuation. After a period of continuous operation and testing, all high-precision constant temperature and humidity air-conditioning equipment has no quality problems, which proves the high adaptability of the high-precision constant temperature and humidity air-conditioning equipment solution to non-conventional working conditions in practice.