HVAC system retrofits can affect local environmental concerns, principally indoor air quality (IAQ), as well as global concerns such as ozone depletion and global warming.
Most studies have found that the majority of IAQ problems are related to HVAC systems with inadequate air flow, poor maintenance, and insufficient outside air flow. When the HVAC system is identified as the cause of a problem, a system retrofit may be required to solve the problem.
Ozone depletion, one of today’s most talked-about global environmental concerns, has been traced in part to HVAC systems that use chlorofluorocarbon (CFC) or hydrochlorofluorocarbon (HCFC) refrigerants. While there currently is no requirement to remove or modify this equipment, increased costs of these refrigerants and regulations aimed at reducing emissions are encouraging many managers to consider these changes.
Older chillers can be retrofitted to utilize replacement refrigerants that are more ozone friendly. HCFC-123 is the current choice to replace CFC-11, while HFC-134a (hydrofluorocarbon) is the current choice to replace CFC-12. HCFC-123 is an interim solution, and is currently scheduled to be phased out starting in 2010.
There is no compelling reason to retrofit a chiller with a new refrigerant unless major work is to be done on the unit. On the other hand, it may be more cost effective to replace the equipment if it is old and near the end of its useful life.
Reciprocating chillers and direct-expansion systems generally utilize HCFC-22, which also is scheduled to be phased out starting in 2010. Several alternative replacement refrigerants are currently undergoing testing, but no manufacturer has yet settled on a replacement.
Global warming also is becoming a concern, and agreements may be adopted to reduce carbon dioxide emissions by reducing the burning of fossil fuels. Refrigerants have a direct global-warming impact, as well as an indirect impact because of the energy their systems consume. Thus, any overall system efficiency improvement also will reduce carbon dioxide emissions.
There are several choices for new or replacement chillers. Centrifugal and rotary screw chillers utilizing HCFC-123 or HCFC-22 are available from several manufacturers.
Another option is to utilize double-effect absorption chillers, either steam or gas-fired. These units use water and lithium bromide and have no ozone-depletion or global-warming potential. The double-effect absorbers are much more efficient than the old-fashioned single-effect absorbers.
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