Yosuke Udagawa

Study on free cooling systems for data centers in Japan

A free cooling system is one effective solution for reducing the power consumption of air conditioning systems. In recent years, free cooling systems have gained the spotlight in Japan, so we have conducted a survey and simulation-based estimation toward their introduction. The estimation results have shown that the water-side economizer requires doubling the capacity of the cooling tower and consideration of the installation space and cost, while the air-side economizer increases the humidifying power, which requires the relaxation of indoor humidity specifications. According to the simulation-based comparison results, the package-type air-conditioning unit with an expanded scope of low pressure ratio control has the lowest power consumption per year.

Verification of improved air conditioning operation measures in server rooms

Improving efficiency of air conditioning in data centers involves improvement of server room operations as well as improvement of efficiency of air conditioning units. This is because server room operations significantly affect the airflow inside the room, and improper airflow results in hotspots. Hotspots result in excessive cooling, which in turn leads to increased energy needed for air conditioning. Here we will report on the experiments we conducted inside an actual server room to verify air conditioning power efficiency in order to understand the effect of measures to improve server room operations. The measures we evaluated were the separation of IT equipment intake and exhaust airflow (aisle capping[1]) and the correction of return airflow (ceiling chamber opening adjustment). Our measurements showed that aisle capping could result in 6% while correction of ceiling chamber opening in 4.1% increase in energy efficiency.

Packaged air conditioner incorporating free cooling cycle for data centers

Aiming to improve energy saving in regard to data centers, the authors have developed a high-efficiency air conditioner for use in data centers. In consideration of application to data centers, which are considered “mission-critical” facilities, development of air conditioners using a refrigerant - which have no effect on ICT equipment even in the event of leakage - has been continuing. A key feature of air conditioners for data centers is that they must provide sufficient cooling all year round, to handle the huge amount of heat generated by ICT equipment, and this is the key to energy saving. Given those circumstances, by improving compression efficiency in regard to outside environments in the low- to mid-temperature range and expanding the operational range at low pressure ratio, the authors developed a high-efficiency air conditioner [1]. Aiming to further reduce electrical power consumption, the authors developed an air conditioner whose pump cycle is juxtaposed on the conventional compression cycle. In more concrete terms, the pump cycle is configured so that low-temperature outside air (hereafter, “cold”) is imported into the refrigeration cycle via a heat exchanger (HEX) inside an outdoor unit. In the HEX, the cold is transferred to a refrigerant, which carries it into a computer room by means of a refrigerant pump. As one kind of indirect outside-air cooling method, this configuration does not degrade the quality of the air inside the computer room. Since the refrigerant pump (which consumes less power than the compressor) works when the outside air temperature is low, energy consumption is significantly reduced. In comparison with conventional air conditioners, the developed air conditioner can reduce annual power consumption by 54%, 50%, and 38% in the cases of Sapporo (Japan), New York (USA), and Austen (Texas, USA), respectively. We are sure that it will significantly contribute to reducing energy consumption of air conditioners used for data centers.