Air conditioning is normally the largest electrical load in commercial buildings, and its energy expenses can be even higher in mission critical data centers. Air conditioning and ventilation must operate 24/7 to keep suitable conditions for IT infrastructure, and there are stringent control requirements for air humidity and particles.
The data center industry is highly competitive, and energy efficiency measures can reduce operating costs significantly. However, HVAC efficiency depends on building conditions and the local climate, and each facility requires a unique approach.
Minimizing the Cooling Load on Data Center Air Conditioners
The first step to improve air conditioning efficiency is minimizing the amount heat that must be removed from the data center facility. Although the heat release from servers is unavoidable, the heat gained through the building envelope can be minimized with smart design decisions. Adequate insulation reduces heat gain, and an airtight design contributes to both energy efficiency and air quality control
The HVAC system must also offer reliable humidity control, since low and high humidity are both detrimental for data centers. Relative humidity in the range of 30% to 60% is acceptable in most applications, but ASHRAE recommends keeping relative humidity as close as possible to 50% in data center applications.
Low and high humidity are both hazardous for data centers. Low humidity increases the risk of an electrostatic discharge, while high humidity can cause condensation, leading to electrical faults or corrosion. Air conditioning systems can often control both temperature and humidity, but additional humidification or dehumidification may be necessary under some weather conditions.
Selecting Air Conditioning Equipment with a High Efficiency
After the cooling load on a data center air conditioning system has been minimized, the next step is specifying equipment that can meet this load as efficiently as possible. Air conditioning systems are available in various configurations, and the efficiency rating used changes depending on the type of equipment.
Air conditioning systems of the scale used in mission critical data centers normally use the Integrated Energy Efficiency Ratio, or IEER. This metric is weighted average or performance at full load and several part-load conditions, and it considers 15 different climate zones. Numerically, the IEER is a ratio of cooling output in BTU and energy input in watt-hours. The most efficient air conditioning systems in the market offer IEER values above 20.
A high-efficiency air conditioning unit can be complemented with other efficiency measures to boost performance at the system level. For instance, the speed of hydronic pumps and air handlers can be controlled with variable frequency drives (VFD), which is much more efficient than intermittent operation under part load. The installation can also use energy recovery ventilation (ERV), where heat and humidity are exchanged between the supply air and exhaust air to reduce HVAC loads.