Building owners don’t upgrade HVAC systems simply because they want the latest HVAC technologies; rather, they seek to correct perceived deficiencies with existing systems. That means the starting point must 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 the original construction plans and maintenance and repair records. Performance testing or non-destructive testing can be guaranteed for major components or equipment systems, including piping and ducting.
It is important to analyze the existing system to determine if 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 throughout the year, regardless of outside conditions.
Since high energy costs often justify HVAC upgrades, historical energy consumption should be compared to industry benchmarks of dollars or BTUs per square foot for similar facility types. This comparison will show how efficient a building is and identify potential target values for improvement. It may also indicate that even though an HVAC system is 25 years or older, overall operating costs may be comparable to newer buildings, so a full 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, today’s 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 on the hours of operation of the equipment, these savings alone may not justify replacement due to the high capital costs of new equipment.
Another consideration when evaluating an existing system is whether it uses outdated technology. Building automation systems have evolved considerably in the last 10 to 15 years. Even with systems that work reasonably well, it can be difficult to obtain parts or find service personnel familiar with older technologies. In addition, new systems may have capabilities that older systems lack, but that would improve mechanical system performance and improve occupant comfort.
Compliance with codes and regulations is another key issue. Buildings constructed from the late 1970s to the mid-1980s were often designed to provide lower amounts of outdoor air than required by current codes. Replacement of an individual HVAC system component may not require compliance with the new codes; however, this may be desirable to alleviate concerns that lower amounts of outdoor air can lead to indoor air quality problems.
A comprehensive analysis of the HVAC system is necessary to assess the impact of increasing the outside air rate. It’s usually not as simple as rebalancing air handling systems to provide additional outside air. Increased 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 of a complete system replacement, current code compliance will likely be required. HVAC upgrades must be carefully evaluated to determine the full scope of the upgrades required by the code; this work could make the project significantly more expensive than originally expected.
Consider an 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 amounts of outside air currently required. Although the equipment was in good condition and could probably have continued to operate for several years, the owner chose to replace the units to bring the building up to the new ventilation standard, as well as to prevent future outages if replacement was required after the building was built. totally busy. As a result, other system components such as cooling towers and pumps also had to be replaced.
Environmental regulations can 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 refrigerators produced until the early 1990s. Some CFC refrigerants are still relatively available in recycled form; others are scarce or very expensive. An owner with a CFC chiller must consider refrigerant issues when deciding whether to replace the equipment.
The right approach
Once the system assessment is complete, a key question is whether the major issues can be addressed by replacing components or whether there are inherent limitations in the system that cannot be corrected without a major system refurbishment or replacement.
A great advantage of a systems approach is that it makes it possible to redesign and optimize the HVAC system. For example, a new HVAC system may use smaller ducts than currently exist. In an office building with a congested ceiling plenum, where additional space is needed for data cable routing or new fire sprinkler systems, this can be a significant benefit. It may also be possible to design a new system to correct comfort problems inherent in an existing system, such as limited ability to control temperatures locally.
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 can allow new HVAC systems to be downsized, with a corresponding reduction in installation and operating costs.
Future building uses should be considered as part of every HVAC upgrade project. For example, if a single-tenant building with one operating hours is to be converted to a multi-tenant building with a wide variety of hours and cooling requirements, the new use may require multiple smaller systems. Switching to a different type of use, such as retail to office, will also have significant implications for equipment size and configuration due to different ventilation, loading and control requirements.
Even with the replacement of individual system components, future uses must be considered. For example, with the replacement of a dedicated cooling tower at a central chilled water plant, it may be desirable to install additional capacity that can be used to service individual tenant supplemental cooling equipment.
HVAC upgrades often have significant implications for other building systems. Changing the HVAC system will often require major modifications to the electrical distribution. If the electrical distribution system consists of obsolete equipment that cannot be expanded or if it does not meet current codes, significant additional upgrades to the electrical system may be required, at considerable cost.
Operation and maintenance requirements will often be affected by HVAC upgrades. Typically, maintenance requirements will initially decrease when new systems are installed. However, sometimes the operation and maintenance requirements of a new system may require significant 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 require some combination of training, hiring, or outsourcing. Similar problems can arise for service contractors. Even if the company that worked on the original systems did a good job, it’s important to check that they have the skills and experience to maintain the new system.
The physical constraints of the building will almost always have a big influence on HVAC upgrades. A new HVAC system may require more space in the equipment room or vertical axis space for ductwork or piping, or it may require additional space in other locations that must be removed from occupied areas. This can have a significant impact on the functionality of the space or can reduce rental income.
A primary consideration before undertaking any building improvement is the potential interruption of occupancy. For HVAC systems, major upgrades can take part or all of the system out of service for an extended period of time. Unless the building is unoccupied, this may not be a realistic course of action. Partial system replacements can often be designed and staggered so that work is limited to unoccupied portions of a facility or only performed on nights and weekends when the facility is not occupied. However, to achieve this, the existing system must be carefully evaluated to reuse as much as possible, particularly within occupied spaces.
Project planning must 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 several units serving a common load can be operated most of the time with a portion of the units running, 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 more for major equipment such as chillers or large boilers.
An HVAC upgrade project is a major business decision that requires a large capital investment. The results of an engineering evaluation 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 often not be approved. The justification 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 the rental property if the upgrade helps reposition the property in conjunction with other functional upgrades and aesthetic. Intangible considerations such as increased occupant comfort or increased occupant productivity must 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.