Engineering in K-12 schools: HVAC systems

03/17/2014


CSE: Do you find it more challenging to retrofit HVAC systems on older buildings than installing on new?

Najafi: Existing facilities do pose a retrofit challenge that adds another level of complexity compared to new building design, especially in the arena of coordinating with limited passageways (for equipment replacement) and hidden obstructions, but there are advantages that can be employed with some of these older, mass-based school structures that support lower differential temperature approaches, such as in radiant heating and cooling.

Hedman: Retrofitting older buildings is more challenging due to the existing structure. Systems in older schools were mostly designed for heating and ventilation only. Schools that are being retrofitted are now designed to incorporate air conditioning throughout. Existing ductwork cannot be used because it was sized for lower airflows (based on heating load) and not necessarily insulated. Therefore, as a design engineer on a retrofit project, we need to coordinate with the existing structure and architecture to incorporate larger ductwork.

Jefferson: Dealing with existing space limitations in older buildings can be a challenge. Too often though, designers don’t look at why it’s a challenge to retrofit these buildings. Most of these buildings didn’t use centralized, forced-air systems originally, so putting one in place today is going to create headaches. Instead, we look at the original design team’s approach, which typically involved steam or hot water piping (but no cooling). Thermodynamically, water or refrigerant is so much better than air for heat transfer, so we can move small piping around a building in much more compact spaces than what a ducted, air-based system would use. We still need to introduce ventilation air, but that system is usually much easier to accommodate than a centralized forced-air HVAC system.

Roy: It is almost always easier to design from a clean sheet than to try to integrate with existing systems. However, the relative ease isn’t necessarily a function of the building’s age. Many times, it’s easier to work with older buildings because they were built much more soundly and the existing MEP systems are generally much simpler. Whether gutting the existing and starting from scratch with an empty shell or retaining some or all of the existing systems, older (pre-1950s) systems are generally better documented, when original drawings are available, and it is easier to determine whether they are still viable or should be scrapped. Many times, there is greater pressure to reuse systems that are 1970s and 1980s vintage because they appear to be in functional condition, whether their operational efficiency justifies reuse or not. Most times, it is safe to say operation efficiencies trump functional conditions in determining whether to remove older systems. Also, code issues such as refrigeration availability and ozone depletion potential (ODP) calculations drive the elimination of older systems. However, project construction budgets many times require maintaining old, inefficient equipment. This is where the greatest challenges come up with retrofitting or renovating existing building systems: establishing capacity and condition, whether HVAC or electrical, when the budget doesn’t allow upgrading. Most times, it is easier to determine the capacity and condition of existing HVAC than existing electrical infrastructure. However, the challenge is always the same to establish the condition of concealed distribution systems like ductwork, piping, conduit, and wiring. If these distribution systems have to remain, they limit design options to less than optimal solutions.

Hammelman: It is more of a challenge to retrofit HVAC systems within older facilities, especially those built between 1950 and 1980, over retrofitting newer buildings. Often the buildings were not planned or designed to account for air conditioning, and now owners want to incorporate it. These facilities also possess environmental issues ranging from asbestos-containing materials to lead paint, which need to be remediated prior to construction, or they may not have adequate/existing electrical infrastructure and structural capacity to support the new HVAC equipment without significant upgrades and additional costs.


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