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Building owners don't upgrade HVAC systems simply because they want the latest HVAC technologies; rather, they are looking to correct perceived shortcomings with existing systems. That means the jumping off point should be a comprehensive assessment of the existing system. A detailed survey and inspection of all major system components should assess age, condition, efficiency and expected remaining useful life. This should include a review of original construction drawings and maintenance and repair records. Performance testing or non-destructive testing may be warranted for major equipment components or systems, including piping and ductwork.
It is important to analyze the existing system to determine whether the system is causing comfort problems. Many HVAC systems installed in the 1950s and 1960s were only intended to provide a moderate degree of cooling. No one expected a system to provide a constant temperature year-round irrespective of outside conditions.
Since high energy costs often justify HVAC upgrades, historical energy consumption should be compared against industry benchmarks of dollars or BTUs per square foot for similar types of facilities. This comparison will show how efficient a building is and will identify possible target values for improvement. It may also indicate that, although an HVAC system is 25 or more years old, overall operating costs may be comparable to newer buildings, so that a complete system replacement may not be warranted based on energy savings. In this case, replacement of selected components might be the best approach.
For some equipment, such as centrifugal chillers, current equipment is significantly more efficient than units installed 20 or more years ago, using 30 to 40 percent less energy than older models. However, depending upon the hours of operation of the equipment, these savings alone may not justify replacement because of the high capital costs of new equipment.
Another consideration in evaluating an existing system is whether it uses an obsolete technology. Building automation systems have evolved considerably over the last 10 to 15 years. Even with systems that are functioning reasonably well, it may be difficult to get parts or to find service personnel familiar with older technologies. In addition, new systems may have capabilities that the older systems lack but that would enhance mechanical system operation and improve occupant comfort.
Compliance with codes and regulations is another key issue. Buildings built from the late '70s to the mid '80s were often designed to provide lower outside air quantities than required by current codes. Replacement of an individual HVAC system component may not necessitate compliance with the new codes; however, this may be desirable to alleviate concerns that lower outside air quantities may lead to indoor air quality problems.
A comprehensive HVAC system analysis is necessary to evaluate the impact of increasing the outside air rate. It is usually not as