Retrofits: Opportunities & Challenges
There’s more room for mystery and surprise in the early phases, but retrofit projects still contain a unique advantage or two for the thoughtful engineer and owner.
Retrofit projects are opportunities to renew the life of a building and the utilities within that building.
Many engineers enjoy retrofit projects. However, the work can be both challenging and frustrating depending on the scope of the project. Just as with new building design, the HVAC engineer needs to consider and evaluate various system options so that the owner can make an informed decision about how to spend their funds.
Building HVAC retrofits involving existing ductwork that is inaccessible can create challenges in many buildings, especially in health care facilities. New industry fan selection criteria will make this even more of a challenge to select fans that have sufficient — yet not too much — “safety” factor in the pressure loss calculations. The financial risks involved for the engineer, contractor, and owner in retrofit projects can be greater than in new facility designs.
Retrofit projects in today’s world of “green” focus and energy improvement awareness become even more challenging. Historical buildings that must maintain the original architectural features both inside and outside can create unique challenges for the HVAC engineer tasked with updating systems to meet current codes and standards for ventilation, temperature, and humidity control.
DESIGN CRITERIA and CONSIDERATION
The first phase of a retrofit project includes determining the design criteria and project scope. ASRHAE Standards 55 (comfort), 62 (ventilation), and 90 (energy) are standards that are necessary to evaluate when a building undergoes a retrofit. Obviously, the building envelope becomes a focal point when these standards are considered due to rising concerns with comfort and moisture migration and infiltration through the building envelope. Buildings in seismic zones require a greater level of code analysis to determine applicability and assess existing structural design and condition.
Fairly new systems such as VRF, underfloor air distribution, displacement ventilation, and chilled beams are worth considering in retrofit buildings. These systems require integration among all of the architectural and engineering disciplines.
The 2016 ASHRAE Handbook — HVAC Systems and Equipment gives some good guidance on any HVAC project saying, “The design engineer is responsible for considering various systems and equipment and recommending one or more system options that will meet the project goals and perform as desired.”
Determining the system and equipment options in a retrofit project must take into consideration many of the same criteria as a new building. Accessibility and space constraints due to existing systems and utilities that will remain in place are generally the biggest challenge. Staging of the retrofit project based on occupancy that may or may not be relocated is a logistics challenge. Rigging and access to remove demolished system components and bringing in new product components and equipment adds additional complexity in most cases. Some products such as fans may need to be shipped in sections and assembled in place in lieu of being built as one piece in the factory. This all takes coordination and certainly additional cost.
RISKS OF UNKNOWNS
One of the good things about retrofits is that there is not only sometimes history of the existing HVAC performance, but there is also the opportunity to physically observe the installation in an as-built condition. In addition, the current building owner and facility staff can be consulted for valuable insights regarding performance and problems.
However, in many retrofit projects, the existing HVAC system usually can’t be fully observed due to limited access to the system components above inaccessible ceilings. Evaluation of the ductwork and piping systems and equipment in a retrofit project can disclose conditions that may require serious remediation that could take the entire original budget of a project. Discovering asbestos insulation on piping, ductwork, or equipment may have a huge impact on the project budget.
Assuming that the existing HVAC system and equipment will continue to function adequately can be shortsighted and create issues later in the building lifecycle which would be better dealt with at the time of the retrofit.
The scope of some retrofit renovations is only intended to update the architectural aesthetics, whereas other retrofit projects are more extensive and possibly a total gut/rehab. In a gut/rehab, the building is essentially completely stripped down to the structure and rebuilt with interior walls, ceilings, HVAC systems, and utilities. In a gut/rehab project, the unknowns are minimized, so that the HVAC system can be coordinated with existing structure, and the main concern becomes coordination with the structural engineer to understand weight limits and possible seismic constraint coordination and equipment vibration concerns.
In the “good ol’ days,” many years ago, the bid drawings issued by consulting engineers could almost be used as the as-built drawings when the installation was complete. The reason for this is somewhat a function of the the way it was done back when consulting firms took more time to actually do the detailed “drafting” and detailed layouts of the ductwork, piping, and equipment. The old drawings were almost a work of art as were the installations.
Not to give too much credit to those good ol’ days, since the reality is many of the systems in the buildings and the complexity of the buildings were much less involved than they are today. In many designs today, the coordination of each piping, duct, and equipment layout is not drawn exactly as it must be installed for a variety of reasons, not the least of which includes lower engineer fees for the engineers by the owner. This leaves part of the existing conditions discovery up to the contractor as part of their scope of work as they start demolition. This has pros and cons as an approach to a retrofit project from the owner’s point of view.
The use of true as-builts is a great idea, but it takes a lot of time and care to verify the accuracy. As-builts for years were part of the contract requirements that the contractor had to do as part of their duties, and full payment was not given to them until the engineering team took the time to go out and verify that the as-builts were indeed accurate. The building owner paid both the engineer and the contractor for this level of service as well. Then through the life of a building, as changes were made, many building owners actually required that any modifications made would then be updated on the record as-builts. This was and is still sometimes done by some facility owners and government agencies.
Turning the clock forward many years with the development of computerized drawings and BIM, the as-built drawings of the old days are not the same. There are debates on whether BIM is appropriate for all projects, especially retrofit projects. It really depends on whether or not a facility owner will indeed utilize the BIM documentation.
In the ideal facility, the owner would have all the exact equipment data on file as well as maintenance records. However, the normal reality is that the complexity of locating, accessing, and reading simple equipment and motor nameplates is a challenge due to the condition of older painted nameplates. Rooftop equipment may have nameplates with paint that has been destroyed over time thanks to UV rays, if the etched nameplates available today were not used.
Without reliable as-builts, the engineer doing a retrofit is left with a lot of work to investigate as best as possible the current conditions of an HVAC system. This is not an easy task, especially in a health care or hospital facility with many more HVAC and other engineering system components to squeeze into limited space in the ceilings.
CASE IN POINT — HOSPITAL RETROFITS
Every type of building retrofit project presents its own challenges for the HVAC engineer, but a hospital’s 24/7 nature, regulatory environment, and security criteria can affect retrofit construction more than other types of facilities. In addition, there are contamination control protocols in most hospitals when access above ceilings is required.
Building space isolation with differential air pressure control and physical barriers is a major concern, especially if asbestos or other contaminants such as dust and odor control are considered. In health care, the standards have changed through the years on ventilation rates and comfort conditions.
Rated walls are not always marked on old plans, so identifying where fire, smoke, and combination fire/smoke dampers are and their physical condition is a huge challenge in hospital retrofits.
The engineer investigating the existing condition must review existing documents and talk to facility managers to identify existing conditions as much as possible without interrupting the occupants and patients. Looking above ceilings for existing conditions is a trial and error approach (e.g., lift a ceiling tile out to take a look and then realize that the ladder must be moved to a different location to get the real view needed). Cameras can be helpful in documenting with photos the above ceiling conditions so that the access can be limited. Some health care facility owners require a bleach to be sprayed at the ceiling tile opening or a portable HEPA filter unit to be used to try to capture any dust that may fall out of the ceiling during the investigation above ceilings. This adds complexity and time to the process.
Retrofits that involve old air handlers that may have been improperly maintained open a discussion on maintainability and accessibility to the components like filters, motor bearings for lubrication, coils, drain pans, and dampers. There may be insufficient space for proper maintainability of new equipment. Old field-fabricated custom units may have good housings and the internal components may just need to be replaced. Other times, new and smaller packaged units may be the better choice in lieu of reusing existing equipment that has reached or exceeded the life expectancy based on how it was maintained.
Some basics tips for retrofit HVAC projects include but are not limited to the following.
Clearly document the scope of the project for both design and construction.
Discuss the scope of the project with the code official Authority Having Jurisdiction (AHJ).
Have extensive discussion with the facility manager regarding existing conditions and HVAC system operation.
Review and verify the accuracy of all documents that are used to document existing conditions for bidding purpose for demolition and coordination of new work with existing work to remain.
Allow a generous contingency in the budget for conditions that are unknown, along with methods for the owner to negotiate changes with the contractor if needed during construction.
There is no doubt retrofit projects are challenging in different ways than new facility design projects. The HVAC engineer has a huge responsibility to help the owner understand the options in the HVAC systems. Retrofit projects can cost a lot in design fees for the investigation phase and construction phase. The risk of dealing with the unknowns should be minimized, but more than likely that risk will never be eliminated, thus requiring contingencies in both the engineering and construction budgets.