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 simple as rebalancing the air handling systems to provide additional outside air. Increasing the outside air will increase heating and cooling loads, which the existing heating and cooling plant and related distribution systems may not have adequate capacity to serve.
In the event a comprehensive system replacement is to be undertaken, compliance with the current codes will likely be required. HVAC upgrades must be carefully evaluated to determine the full extent of code-required upgrades; this work could make the project significantly more expensive than originally expected.
Consider one owner who was contemplating a major building renovation, including mechanical system upgrades. The existing water-cooled air-conditioning units on each floor were not sized to handle the quantities of outside air currently required. Although the equipment was in fair condition and could likely have continued to operate for several years, the owner elected to replace the units so the building would meet the new ventilation standard, as well as to avoid future disruption if replacement was required after the building was fully occupied. As a result, other system components, such as cooling towers and pumps, also had to be replaced.
Environmental regulations may influence HVAC upgrades. In 1996, the Clean Air Act mandated a ban on the manufacture of CFC (chlorofluorocarbon) refrigerants, which were used in virtually all large chillers produced up until the early ’90s. Some CFC refrigerants are still relatively widely available on a recycled basis; others are scarce or are very expensive. An owner with a CFC chiller should consider refrigerant issues in deciding whether to replace the equipment.
The Right Approach
After the system assessment is completed, a key question is whether the major problems can be addressed by replacing components or if there are inherent limitations in the system that cannot be rectified without a major system renovation or replacement.
A major advantage to a systems approach is that it makes it possible to redesign and optimize the HVAC system. For example, a new HVAC system may be able to utilize smaller ductwork than that which presently exists. In an office building with a congested ceiling plenum – where additional space is needed for distribution of data cabling or new fire sprinkler systems – this may be a significant benefit. It may also be possible to design a new system to correct inherent comfort problems with an existing system, such as limited ability to control temperatures on a localized basis.
A variation of the systems approach is to combine HVAC system upgrades with other building upgrades, such as lighting retrofits. Upgrading existing lighting systems to more energy efficient lamps and ballasts will reduce the cooling load for many facilities. This may enable new HVAC systems to be downsized, with a corresponding reduction in installation costs as well as operating costs.
Future building uses must be considered as part of every HVAC upgrade project. For example, if a single-tenant building with one operating schedule is to be converted to a multi-tenant building with a wide variety of schedules and cooling requirements, the new use may require multiple smaller systems. Changing to a different use type, such as from retail to office, will also have major implications for equipment size and configuration because of different ventilation, load and control requirements.
Even with replacement of individual system components, future uses must be considered. For example, with replacement of a cooling tower dedicated to a central chilled water plant, it may be desirable to install additional capacity that can be utilized to serve individual tenant supplemental cooling equipment.
Potential Pitfalls
HVAC upgrades often have significant implications for other building systems. Changing the HVAC system will often require major electrical distribution modifications. If the electrical distribution system consists of obsolete equipment that can not be expanded or if it does not meet current codes, significant additional upgrades to the electrical system may be required, at substantial cost.
Operations and maintenance requirements will often be affected by HVAC upgrades. Usually, maintenance requirements will initially decrease when new systems are installed. However, sometimes operations and maintenance requirements of a new system may require major changes in practices or personnel. Existing operating personnel may not have the skills to operate and maintain the new systems, or may not have the required licenses from the local jurisdiction. This may necessitate some combination of training, hiring or outsourcing. Similar issues may arise for service contractors. Even if the firm that worked on the original systems did a good job, it is important to verify that they have the skills and experience to maintain the new system.
Physical building constraints will almost always have a major influence on HVAC upgrades. A new HVAC system may require more equipment room space or vertical shaft space for ductwork or piping, or may require additional space in other locations that must be taken away from occupied areas. This may have a significant impact on the functionality of the space or may reduce rental income.
A primary consideration prior to undertaking any building upgrades is the potential disruption to occupancy. For HVAC systems, major upgrades may take some or all of the system out of service for an extended period. Unless the building is unoccupied, this may not be a realistic course of action. Often, partial system replacements can be engineered and phased so that work is limited to unoccupied portions of a facility or only occurs during nights and weekends when the facility is not occupied. However, to accomplish this, the existing system must be carefully evaluated to reuse as much of it as possible, particularly within occupied spaces.
Project planning should also consider seasonal heating and cooling requirements. Ideally, replacement of heating equipment should occur during the cooling season and vice versa. If this is not possible, large central systems with multiple units serving a common load may be able to run most of the time with a portion of the units operational so that equipment can be replaced one unit at a time. Project schedules must also consider manufacturer lead times, which can be four months or longer for major equipment such as large chillers or boilers.
An HVAC upgrade project is a significant business decision requiring a major capital investment. The results of an engineering assessment may suggest that a complete system replacement or major upgrade is the best course of action but if an acceptable return on investment cannot be demonstrated to the owner, this approach will frequently not be approved. The rationale for an upgrade may not always be direct savings in energy or operating costs, but may also include improved marketability or higher lease rates for rental property if the upgrade helps to reposition the property along with other functional and aesthetic renovations. Intangible considerations such as improved occupant comfort or higher occupant productivity should also be taken into account. Given the magnitude of the financial impact and the long life of the equipment involved, it is advisable to seek the services of a qualified engineering professional to help guide the evaluation and planning process.
