Applications and analysis of cooling methods for outdoor communication equipments

Along with the intensifying competition in telecommunications industry, more and more operators choose to construct communication networks with outdoor equipments to reduce CAPEX and OPEX. Cooling turns to be operators’ great concern as it is critical to ensure smooth operation of equipments in outdoor environment, especially in areas where the temperature is high. A diversity of cooling methods has been employed on outdoor communication equipments, among which, natural cooling, heat exchanger, cooling fan and thermoelectric refrigeration (TEC air conditioning) are the most commonly applied. This article is to demonstrate how to select suitable cooling modes by simulating, testing and analyzing different cooling modes.

Simulation and testing of the cooling modes

Thermal simulations of battery cabinets with and without cooling fan are shown in figure 1 and 2 (external environment temperature is 35℃). From which we can tell, without the cooling fan, the average internal temperature of the cabinet is 11℃ higher than the environment temperature as heat from sun is contained in the cabinet and can’t be dissipated effectively. While the internal is only 3℃ higher than the environment temperature when fan is employed to draw the heat of the cabinet.

Figure 1 Thermal simulation of natural cooling　　　 　  Figure 2 Thermal simulation of fan cooling

Fig.3 shows the thermal simulation of battery cabinet with TEC cooling. Which says when the environment temperature is 50℃, the average temperature of the cell’s surface temperatures is about 35℃. A quite good cooling result of 15℃ is achieved.

Figure 3　 distribution simulation of temperature of TEC cooling

• Test analysis

Test scene1: Heat dissipation comparison for of natural cooling and fan cooling

Test temperature: 20℃ ~ 26℃ (natural environment temperature),

Test equipment: Integrated outdoor cabinet, including equipment chamber and battery chamber.

Test results: as shown in figure 4.

Figure 4 Heat dissipation comparisons of natural cooling and fan cooling

According Figure 4, heat exchanging of battery cabinet with fan is remarkable faster than that of the cabinet without a fan. When the balance is reached, the temperature difference is 3℃ with fan and 8.5℃ without fan. The temperature difference may even bigger without fan when the environment temperature is higher and more heat is contained in the cabinet.

Test scene 2: heat dissipation contrast test of cooling fan and TEC air-condition,

Test temperature: 40℃ (indoor environment of high temperature),

Test equipment: Integrated outdoor cabinet, including equipment chamber and battery chamber.

Test results: as shown in figure 5.

Figure 5 Heat dissipation comparisons of fan cooling and TEC

According to figure 5, TEC air-conditioning actively cools the cabinet when the temperature is high. When the external environment temperature is 40℃, the temperature inside the cabinet is stabilized to 25℃, 15℃ lower than outdoor environment temperature. Fan cooling is passive, internal temperature of the cabinet is 44℃, 4℃ higher than external environment temperature. Therefore, TEC cooling is more suitable for the battery cabinet in high temperature environment, and also prolongs the service life of the battery.

Field test

September 2009, ZTE provided TEC battery cabinet to Pakistan operators as the battery lifespan is dramatically shortened in the high temperature of about 50℃ in cabinets with any other cooling systems. May 2010, we tested two sets of TEC battery cabinets with 12V 150AH VRLA. The test lasted for 36 consecutive hours and data was collected once an hour. The testing field and results are shown as follows:

Figure 6  device context

Figure 7 TEC cooling test

Test results: In Pakistan, the outdoor temperature is between 27℃ and 46 ℃ for 36 hours (the temperature at daytime is above 39℃), internal temperature of TEC battery cabinet maintains at 21℃ ~ 29 ℃. The highest difference between internal and external temperature is 17 ℃ and 18 ℃, which testifies the active cooling function of TEC and makes it ideal solution for high temperature application environments. The shelter is also quite useful to shed the sunshine and to protect equipments and batteries as the temperature in the shelter is 5℃ lower at 15:00) 

Recommended cooling modes in different application environments 

ZTE recommend the following cooling modes for different application environments based on field test, simulation and years of experience in overseas and domestic market.

• For areas where the average temperatures of the hottest month exceeds 30℃
  TEC cooling is recommended for battery cabinet and heat exchanger for equipment cabinet. Fan cooling is also workable for equipment cabinet when the environment is dry and clean.
• For areas where the average temperatures of the hottest month is between 26℃ and 30℃
  Fan cooling is suitable for battery cabinet. Heat exchanger and fan are optional for equipment cabinet depending on the humidity and dust level of the application environment.
• For areas where the average temperatures of the hottest month is below 25℃
  Fan cooling is optional for battery cabinet, and natural cooling will do in cool places. Heat exchanger and fan are optional for equipment cabinet depending on the humidity and dust level of the application environment.
• For areas where the average temperatures of the coldest month is below -10℃
  Battery cabinets and equipment cabinets are equipped with heating panels. However, in areas with high midday temperature and strong solar radiation, shelter is required to shed direct sunshine.