Application and analysis of energy-saving technology in data center air conditioning

With the development of economy, the rapid development of a large number of enterprises, for the http://www.aliyun.com/zixun/aggregation/14345.html "> Data processing business needs are rapidly improved, has built a lot of data centers." Data center from more than 10 years ago 100-200w⋅m-2 to today's development to 1000w⋅m-2 or even higher, the increase in engine room density makes the data center energy consumption becomes an increasingly important topic, since the Greengrid organization proposed using PUE to measure the data center energy-saving requirements, More and more domestic construction parties in the design of the data Center for the PUE value of the request, PUE is powerusageeffectiveness, is the evaluation of data center energy efficiency indicators, the data center consumes all the energy and it load use of energy ratio, pue= Data center total equipment energy consumption/IT equipment energy consumption, pue is a ratio, the closer to 1 indicates the better energy efficiency, this article will introduce some measures to improve the energy efficiency of air conditioning and reduce the energy consumption of data center in order to obtain the lower Pue value.

Cold

Data center air conditioning cold source generally has air-cooled direct evaporative air conditioning system, water-cooled direct evaporative air-conditioning system, water-cooled or air-cooled chilled water air-conditioning system, dual cooling air conditioning system and other air-conditioning systems. From the point of view of energy saving, using the data center of air-cooled system, the PUE can not be less than 1.8, usually more than 2.0, in a large scale, can set the central cooling source, energy-efficient water-cooled chilled water system is preferred. When the motor power power exceeds 500kw, 6kv or 10kv voltage can be used to power supply, which can improve the running efficiency, select the unit with high COP value, and consider the integrated performance coefficient (IPLV) of the part load of the unit. The cooling water unit adopts the frequency conversion to obtain the better partial load comprehensive performance coefficient, causes the unit the High-efficiency area to be bigger. In the case of non rated operating conditions, the variable frequency centrifugal chiller will combine the diversion vane control with the frequency conversion control, and control the compressor together. The evaporation temperature of the chiller has influence on the unit efficiency, it is estimated that the evaporation temperature is increased by 0.6 degrees and the efficiency is 1%-3%, so the higher evaporation temperature efficiency is higher than the general 7℃/12℃ efficiency.

Figure 1: Comparison of energy efficiency of different chilled water effluent temperature

If we can increase the temperature of the end air supply, we can use the higher evaporation temperature, which can make the efficiency further improved. As for the energy consumption of air-conditioning system, the energy consumption of chiller is the largest, so lowering the power consumption of chiller is very helpful to improve the efficiency of the whole air-conditioning system.

The use of water system security issues, such as the redundant design of water systems: dual-line or annular pipe, accident emergency release, water supply protection: multiple water supply and reservoir, we also need to consider, this article does not unfold.

If the water supply temperature is 12 degrees, in the outdoor wet bulb temperature of about 9 ℃, you can use the cooling tower for free refrigeration, according to the table statistics: In this temperature range, the Shanghai area full use of free refrigeration time of 2,901 hours of free refrigeration relative to the water side, and a free cooling of the wind side, refers to the use of outdoor air , can be in the outdoor enthalpy value below the indoor enthalpy value of the whole time for natural cooling, but in the data center to use the water side free refrigeration, no need to use the wind side free refrigeration, for the following reasons:

1. The use of free air cooling will occupy a large indoor space.

2 Wind side free refrigeration requires a large number of outdoor air, if the outdoor air quality is not very good will lead to a reduction in the operating life of the equipment.

3 Energy for Humidification and humidification will be very large, the use of wind-side free refrigeration energy-saving effect and these energy consumption compared to the difference is not much, at the same time will make indoor humidity control more complex.

4. Wind side free refrigeration and water side free refrigeration in the use of time overlap, so in more than a small amount of time to use the case, the use of the significance is not.

The amount of free refrigeration time determines the Pue value of the air conditioning energy consumption, and from the above can be seen in the free refrigeration by the outdoor environment is also very large, for North China and most of the Yangtze River basin, can be very good use of free refrigeration, in the Northeast and other cold areas, the use of free refrigeration longer, The energy consumption factor of air conditioner in Pue can be done about 0.2 to obtain lower pue value. It's worth it. The construction party should pay attention to the location of the data center and consider the influence of climate environment on the operation cost of data center in consideration of economic and geographical factors.

Free refrigeration and freezing mechanism cold switching

When outdoor free refrigeration does not fully meet the needs of the data center, will open refrigeration unit refrigeration, but at this time the outdoor temperature is below 15 degrees, can not meet the cooling water chiller required condensation temperature, and the use of electric heating, such as neither energy-saving, and not so large electricity to meet, at this time only need to join the system in the bypass, So that after plate heat exchanger than 15 degrees after the backwater does not return to the cooling tower but into the chiller can solve this problem, with the increase in outdoor temperature, chiller set to open, free refrigeration heat exchanger by stage off, until all turned into cold water chiller.

Heat recovery of frozen water side

Considering the characteristics of the data center year-round refrigeration, it is necessary to heat the data center, the evaporation side or the condensation side can be used heat recovery technology, such as the Telehousewest Data center in London to use the heat generated by the server to provide heating services for nearby homes. The data center and its supporting facilities construction project investment of 180 million U.S. dollars, is expected to provide the data center around 130,000 square feet of the equivalent of 9 million watts of energy, and a relative reduction of 1100 tons of carbon dioxide

Put。 The heat recovery of the evaporation side can be achieved by a simple loop of water ring. For example, when the refrigeration system water supply backwater temperature is 12-17 degrees, the winter and the transition season will be the return of chilled waters through a heat exchanger and domestic hot water supply exchange, pre-heating living quarters of hot water supply, simple take over and no impact on the system. Refrigeration units and other equipment are conventional equipment. The heat recovery of the condensation side can be achieved by selecting the Heat recovery unit, but the efficiency of the Heat recovery unit and the safety of the system are evaluated, and the efficiency and safety of the system can be ensured, which can be used as the preferred measure for heat recovery.

Air conditioner End

(1) General it room

Generally speaking, the energy consumption of the terminal (CRAC) of the data center is mainly composed of fan and electric heating, dehumidification is usually done by cooling coil, if the dehumidification requires a lower temperature, then the air will be too cold need to be hot, and then heat wasted energy, so for the air-conditioning end energy saving, First, the dehumidification system should be designed to avoid heat in low load condition. In addition to the reasonable design of air supply temperature, we can also use independent temperature and humidity control system to solve the heat, in principle, if the room can maintain positive pressure, the fresh air system can be fed into the indoor after dehumidification, and the data center in general there is no wet source, then the absolute humidity in the room can be guaranteed. (according to ASHARE2008 's latest report, the impact of equipment in the data center of the air Water content index, is absolute humidity, rather than the previous emphasis on relative humidity, as long as the dew point temperature control in 5.5°c above, the data center of the equipment can ensure safety, to avoid the harm of static electricity. Therefore, we set up a special custom precision air conditioner in it room (without electric heating and humidifier), the fresh air system uses the following function section unit to solve the fresh air dehumidification, as long as the fresh air is good to send the wind dew point temperature control, then all precision air-conditioning without electric heating and humidifier, greatly reduced the operating costs and installed costs.

In addition, we can increase the air supply temperature, generally speaking, if the air supply temperature is increased to 20 degrees, the cooling unit can achieve more than 12 degrees of water temperature, has been to improve the data center inlet temperature is the global data center design trend, because higher data center inlet temperature means more energy-saving potential, and the number of free refrigeration hours that weather conditions can support will also increase. Better energy efficiency will directly reduce energy consumption.

(2) high-density it room

With the increase of processing speed and capacity of data processing equipment, the calorific value (cold load) of communication equipment is increasing, while the cooling system has some limitations, that is, when the heat dissipation reaches above 4kw, it is difficult to solve the heat dissipation problem by using the cooling method. Here we introduce a solution, the concrete is the first completely closed hot channel, and then in the heat channel on both sides of the room set wind wall type AHU, such equipment fan energy consumption is small, the monomer refrigeration capacity and frozen water or refrigerant water completely without entering high-density room. In conventional engineering, the CDU (liquid cooling distributor) is used to solve the problem of cooling in high-density room, and the CDU has mature products and successful applications.

The article introduces the advantages of wind wall type Ahu, which aims at excavating the potential of energy saving.

1. The rupture of the chilled water pipe will have a devastating effect on the computer room if a chilled water pipe is used to enter the end of the room CDU.

2. If a heat exchanger is used, let the chilled water and refrigerant tube after exchange only refrigerant tube into high-density room, at this time the refrigerant pipe temperature is very low, although to avoid the 1th frozen water pipe rupture brought by the great danger, but the low-temperature refrigerant pipe to bring the condensate problem is to be considered.

3. There is energy loss in the way heat is exchanged.

4. Closed heat passage greatly reduces the energy loss of hot and cold air mixing.

To sum up, reduce the energy loss of heat exchange, and can improve security, for high-density room air-conditioning, but also a new means of energy-saving measures.

Green energy-saving is a trend of data center, PUE because it is a regional index requirement because of the relationship with free refrigeration time and so on, but it is very clear to use this index to measure the energy-saving situation of data center. For example, most construction parties in Shanghai will require the PUE value to be controlled within 1.6 to control the application of energy-saving technology in architectural design.

Finally, in the air-conditioning system to achieve energy-saving emission reduction and obtain a lower pue value, can be taken by the following measures.

(1) The use of water-cooled units, and to maximize the evaporation temperature and the use of inverter units.

(2) Selection of high efficiency equipment, and the use of efficient transmission and distribution system

(3) As far as possible to extend the cooling tower free refrigeration time and the use of heat recovery and other energy-saving measures.

(4) Reasonable heat and cold channel layout of the room and efficient air-conditioning terminal system.

(5) To avoid air-conditioning end because of dehumidification and cold and heat offset, the use of independent temperature and humidity air-conditioning is also a means can be used.