Common Cooling Solutions in IDC: Chapter 2. Water Cooled Direct Evaporative Air Conditioner System

It’s indoor air conditioner to control the temperature and humidity in IDC (Internet Data Center), and the indoor air conditioner has the characteristics of high efficiency, high sensible heat ratio, high reliability and flexibility, which can meet the requirements of increasing server heat dissipation, constant control of humidity, air filtration and other aspects in IDC.

With the stringent requirements of PUE (Power Usage Effectiveness) in different regions and the wide application of high-density servers, there are more and more new cooling solutions, increasingly developed and used in IDC, I’ll introduce the traditional and new cooling solutions in IDC in the forthcoming 7 chapters. In this chapter, we’re gonna talk about Water Cooled Direct Evaporative Air Conditioner System.

1.     Water Cooled Direct Evaporative Air Conditioner System Composition

Water Cooled Direct Evaporative Air Conditioner System is mainly composed of frame, compressor, evaporator, condenser, electronic valve, indoor fan, outdoor fan, unit control system, temperature and humidity sensor, plate heat exchanger (freon, cooling water/ ethylene glycol), etc.

After the refrigerant high temperature gas discharged from the compressor is condensed into liquid in condenser, it’s throttled and depressurized by the expansion valve to become low temperature gas-liquid mixture, and then flows into the evaporator absorbing heat and evaporating, and it returns to the compressor to complete a refrigeration cycle. At the same time, the air in the room is cooled by passing through the evaporator and the cold air is sent to the room by indoor fan.

2.     Cooling Scheme Diagram of Water Cooled & Air Cooled Condenser

The main difference between air cooled condenser and water cooled condenser is cooling method. The indoor unit of water cooled direct evaporative air conditioner system is equipped with water cooled condenser, the cooling water( or ethylene glycol) is provided by the outdoor dry cooler( or cooling tower), and the plate heat exchanger exchange heat. Cooling water( or ethylene glycol) circulation powered by pump.

3.     Applications

(1)   Compared with the Air Cooled Direct Evaporative Air Conditioner System, Water Cooled Direct Evaporative Air Conditioner System has some advantages as below:

①   It avoids the problems of long refrigerant transmission distance and difficult oil return.

②   The condensing temperature of the air conditioning unit is low to improve the refrigeration efficiency.

③   The initial investment cost is lower than that of air cooled and evaporative cooled.

④   Good cooling effect, suitable for medium and large data centers.

The temperature of the air-cooled condenser is determined by the ambient temperature. The higher the ambient temperature, the higher the condensing temperature. Generally, for air cooled condenser, the condensing temperature is 7-12℃ higher than ambient temperature, and the value of 7-12℃ is as known as temperature difference. The higher the condensing temperature, the lower the cooling efficiency of the air conditioner, so we should control the temperature difference not too large. However, if the temperature difference is too small, then the air cooled condenser will need larger heat exchanger area and air volume, and the cost will be larger too. While the temperature of water cooled condenser is determined by the wet bulb ambient temperature, the higher the wet bulb ambient temperature, the higher the condensing temperature. Generally, for water cooled condenser, the condensing temperature is 5-7℃ higher than wet bulb ambient temperature.