How to Increase Chiller Efficiency in Your Office Building
Because chiller systems are often the choice to cool large commercial spaces, efforts to increase chiller efficiency can reduce operating costs and help keep occupants comfortable and tenants satisfied. Historically, chiller systems were not held to efficiency requirements commensurate with air-based systems. In some states, however, new standards now drive the efforts to increase chiller efficiency.
Air vs. Water
All air conditioning systems utilize some method to disperse cool air throughout a structure. In typical air-based A/C systems, heat is extracted from the air at a central evaporator coil in the air handler. Cooled air is then conveyed by blower fans through a network of supply ducts. Return ductwork simultaneously draws air out of rooms and conveys it back to the air handler. Air ductwork is by nature bulky and the size necessary to disperse the volume of cool air required by commercial buildings makes air-based systems unfeasible in many settings where large square footage, multiple stories or separated buildings are the rule.
Instead of dispersing cool air through long spans of ductwork, a chiller system utilizes the refrigeration cycle to chill water in a central unit and distributes the chilled water throughout the building in pipes. A compressor in the central unit pumps refrigerant through an evaporator coil that extracts heat. Chilled water is pumped to dedicated air handlers on individual floors that incorporate a cooling coil and fan. The blower draws warm air over the coil and pushes cool air directly into rooms.
Water carrying heat energy circulates back to the chiller through a separate line and disperses heat into outdoor air at a chiller tower. Installation of water pipes to and from the central unit on the roof to the dedicated coil and blower at each floor is less space-intensive and costly than integrating a large network of ductwork in the building. In addition to space advantages, chillers incorporate components designed for heavy industrial service with useful life exceeding 20 years.
Lower Load, Higher Efficiency
Chiller efficiency is especially advantageous where less than full output is required because the cooling load is moderate. In most climates, this may be over 90 percent of the time. Chillers adapt better to conditions of lower load, actually increasing efficiency as output demands diminish. Standard air-based A/C delivers either the same efficiency ratio at lower cooling load, or efficiency may even decline.
The Efficient Future
Requirements to increase chiller efficiency in California have become increasing stringent. Improvements of 25 percent were imposed in 2001 and the 2008 code now in effect places even greater demands to increase chiller efficiency. Three major factors impact the trends to increase chiller efficiency and may result in improvements up to 50 percent over the current 2008 requirements.
The right design. The optimum design will accommodate the unique operating conditions of the specific structure and produce optimum efficiency. One example would be incorporating variable-flow pumping system to circulate water around a large, widespread campus. Another is integrating data relating to the specific expected cooling load at the site into the selection process for chillers.
The right components. Components like pumps, motors, fans and chillers should be evaluated according to their individual, stand-alone efficiency as well as efficiency operating in a system. High-efficiency motors, pumps with improved efficiency when operating under specific expected loads and chillers that deliver optimum efficiency at both full and partial load demand are examples of appropriate considerations.
The right installation. Shortfalls in the installation process can impact chiller efficiency for the life of the system. Each installation must include a commissioning process that includes extensive testing to demonstrate that the system delivers optimum efficiency at all loads under all operating conditions.
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