Basic principles of data center cooling and energy saving solutions

Basic principles of data center cooling and energy saving solutions

Each data center has its own characteristics, so there is no technical solution that can be applied to any data center. This document mainly discusses some basic principles and technical issues in data center cooling and energy saving. On this basis, each different data center can make its own energy saving plan.

　　 But this assumption has the following uncertainties:

　　 1. When the computer room air conditioner does not use variable variable (VAV) fans, the cooling efficiency of the air conditioner determines the number of feet of the dry air conditioner. As the heat density of each cabinet is greatly increased, according to the law of acquaintance (*Note 2), the efficiency of the matched refrigeration system cannot be significantly improved.

　　2. The matched refrigeration system is an additional step in the heat exchange process of the traditional data center. This step is added between the cooling water cycle of the data center and the cooling water cycle of the water-cooled unit. Therefore, increasing the supply air temperature cannot improve the cooling efficiency of the water-cooled unit and increase the natural cooling time.

　　3. According to Darcy Weissbach's theory, the length and volume of the water pipe will reduce the pressure in the water pipe, so these pipes will greatly affect the cooling efficiency of the air conditioner in the data center and reduce the time of natural cooling.

　　4. When the cold supply air and the hot return air are completely isolated, the matching refrigeration system can provide the same natural cooling time as the dry computer room air conditioner in the cold water economizer. However, the air economizer or heat exchange runner economizer cannot have the same natural cooling time. Both of these energy savers are widely used energy savers in the world.

　　Sustainable data center energy conservation improvement projects should consider the following points:

　　 1. Accurately matched refrigeration systems can be used in level 1 data centers, but adjustable fan fans must be used to meet the heat density of the server. However, it should be avoided in level 2 data centers. For example, in a data center, some cabinets have a heat load of 60%, some have 80%, and others have 30%. At this time, the air volume of the matched refrigeration system is (.603, .803 and.303), and the average efficiency of these fans is only about 25%.

　　2. When considering concurrent redundancy and non-stop maintainability, we need to consider the cooling efficiency and redundancy conditions of the air conditioner at the same time. For example, in a data center with a heat load of 120 tons, we are equipped with six 30-ton air conditioners under the N10Z redundancy standard. In contrast, when we only turned on 4 of the air conditioners, each of the 6 fully turned on only used 67% of the air supply or 30% of the energy usage. Compared with the 100% utilization rate when only 4 air conditioners are turned on, when all 6 air conditioners are fully turned on, the air delivery efficiency of all air conditioners is 45%, or each air conditioner only uses 30% air delivery efficiency. According to the law of acquaintance, we waste a lot of energy.

　　 3. The precise matching refrigeration system closely connects the refrigeration system and the cabinet, and we have to consider its redundancy performance and maintainability. We must install an independent backup matching refrigeration system or install an independent computer room air-conditioning system for emergencies.

　　4. When using closed cold aisles for cooling, in order to achieve redundancy, we must add the computer room air conditioner to the UPS. This is what we need to consider the operability and efficiency of UPS.

　　 Precisely matched refrigeration has the same energy-saving effect as isolated cold supply air/hot return air, which can reduce the waste of cold air and increase the temperature of the hot return air to improve the cooling efficiency of the air conditioner. When using inverter air conditioners and adjustable air volume fans, we can use the principle of acquaintance to save energy. In addition, we need to use natural cooling as much as possible to get the greatest energy savings. Accurately matched refrigeration and isolated cold supply air/hot return air are both ways to obtain a huge energy saving effect when using the cold water economizer. But when using an air economizer or a heat exchange runner, the method of isolating the cold supply air/hot return air has a greater advantage. In summary, whether energy saving depends on temperature difference, pipeline design, cooler and evaporator design and flow, etc., so in the end we must comprehensively examine the requirements of sustainable development and comprehensively examine Present every element.

　　 1. Classified by layout

　　 According to the different layout positions, the air conditioner terminal can be divided into room level, row level and rack level.

　　1.1 End of room air conditioner

　　The room-level air-conditioning terminal is mainly dedicated to the computer room. The setting form is to set up a dedicated air-conditioning area on one or both sides of the computer room, in which the dedicated air-conditioning terminal for the computer room is arranged. The air supply at the end of the air conditioner can be divided into two types: bottom supply and top supply. The bottom air supply method of the dedicated air conditioner for the computer room is to convey cold air from bottom to top through a static pressure box, which is currently the most commonly used air conditioner terminal method. The continuous energy-consuming operating component at the end of the room-level computer room special air conditioner is the fan. For energy conservation, mainstream manufacturers all configure the fan with a built-in controller back-tilted electronically controlled commutation motor, that is, the EC fan.

　　1.2 Inter-row air conditioner terminal

　　Inter-row air-conditioning terminals can be divided into two types: inter-row air-conditioning terminals and overhead air-conditioning terminals according to different layout positions.

　　The end of the inter-row air conditioner is arranged between the rows of the racks. The front side blows the wind horizontally to the racks, passes through the front door of the rack and cools the equipment, and then returns to the rear of the air conditioner through the rear door of the rack.

　　The heat exchange coil at the end of the overhead air conditioner is laid on the top of the rack. The hot air from the rack flows out from the rear of the rack and is cooled by the overhead air conditioner coil. The cold air returns to the air inlet of the rack.

　　 Compared with the end of the room-level air conditioner, the air transport distance at the end of the inter-row air conditioner is shorter and the required air pressure is lower. At the same time, the EC fan is equipped, which can significantly reduce the power consumption of the fan. Generally, it is necessary to adopt measures to close the cold aisle (or hot aisle) at the same time to optimize the airflow organization and reduce the loss caused by mixing.

　　1.3 End of rack air conditioner

　　The end of the rack-level air conditioner is closer to the rack heat source and closely integrated with the IT rack. The rack-level air conditioner terminal is installed on the front door or back panel of the rack to form the front door air conditioner terminal and the back panel air conditioner terminal. In order to ensure the uniformity of the air distribution at the end of the air conditioner, it is generally necessary to lay multiple DC fans on the front door or back panel of the air conditioner, and each fan has a small air volume.

　　2, classified by refrigerant

　　 According to different refrigerants, the air conditioner terminal can be divided into cold water type and heat pipe type.

　　1) Cold water type air conditioner terminal

　　The cold water type air conditioner terminal introduces cold water into the machine room, that is, the refrigerant in the heat exchange coil at the end of the air conditioner is cold water. Adopt the cold water type air conditioner terminal, because cold water enters the inside of the computer room, measures such as waterproofing, detection, alarm, and drainage must be strengthened.

　　2) Heat pipe type air conditioner terminal

The refrigerant in the heat exchange coil at the end of the heat pipe type air conditioner is freon (or other phase change working medium), and the cold water is transferred to the corresponding refrigerant through the heat exchanger, and the heat exchanger also serves as the condensation end of the refrigerant , And the heat exchange coil is its evaporating end, relying on the phase change of the refrigerant to realize heat transfer.

　　The characteristic of the heat pipe type air conditioner terminal is that the cold water does not enter the heat exchange coil of the air conditioner terminal. According to whether the refrigerant requires power, it can be divided into unpowered heat pipe type and powered heat pipe type. There is a certain height difference between the condensing end and the evaporating end of the heat pipe type air conditioner. If the density difference caused by the height difference can be used as the power of the refrigerant phase change cycle, the heat pipe type air conditioner end is an unpowered heat pipe type air conditioner end; if not, If a fluorine pump needs to be added for the transmission and distribution device, the end of the heat pipe type air conditioner is a powered heat pipe type air conditioner end. The engineering application mentioned in this article is the unpowered heat pipe type air conditioner terminal.

　　3) Air conditioning terminal classification

　　 After combining the air conditioner terminal according to the layout position and the type of refrigerant, several air conditioner terminal forms in Table 1 are obtained.