By Tony Kuracek
When it comes to indoor air quality, it would be ideal if we had a crystal ball to predict future threats and opportunities. However, there are trend indicators gaining traction out of necessity that may shed some light on some areas of focus for the remainder of 2025 and beyond. Three standout areas are (1) seeking alternative air sources needed for pressure gradients and air changes per hour; (2) system designs that are more easily convertible for pressure gradients and (3) construction practices that limit room leakage for better pressure gradient, as well as cost and performance efficiency.
Nationwide events spur innovation
Nationwide events such as forest fires, chemical spills and naturally occurring weather phenomena have found a weak link in the provisions of indoor air quality where outside air has been the tool used for both pressure gradients and fresh air. These occurrences that threaten outdoor air quality have shown that OA is not always clean air. Areas that require AC/HR and pressure gradients need an alternative air source and, perhaps, a differently designed airflow system.
Modern HVAC designs featuring an alternative air source, especially in areas that require strict pressure gradients provided by clean fresh air such as pressure gradient rooms for medical, laboratories and clean rooms, are areas that will benefit from this design. The alternative air source could be from other areas in the building that have already been filtered and tempered, or dedicated sources designed specifically for and used only in emergency situations.
The Covid Pandemic brought to light the potential need for an exponential increase in the number of negative isolation rooms during pandemic emergencies. This conversion of positive gradient rooms to negative took a lot of work and in many cases additional temporary HVAC equipment. Temporary exhaust ductwork run down hallways with temporary fans located outside in courtyards were common sights at most hospitals. Typical isolation rooms are designed to be positive, which means more supply air than exhaust air and systems that reflect that design.
If we think of a room as a balloon that has small holes, the pressure in the balloon blows out of the holes but enough air stays in the balloon to keep it inflated. A continuous amount of air is blown into the balloon to keep it inflated to the same size or pressure and over time a complete air change in the balloon occurs. This analogy exemplifies a positive gradient room. To convert to a negative gradient room, there has to be more exhaust than supply. The leakage areas do not change but the flow of air is reversed, and there is more exhaust than supply. A new paradigm in the future design of gradient rooms to achieve positive or negative pressures with just a change of system performance settings is almost certain in order to meet the needs of future similar emergencies.
Reducing costs through minimizing leakage
In the example of a balloon, the holes in the balloon represent both designed and unintended leakage areas in gradient rooms. Doors, pass-throughs and lab hoods are all designed areas of leakage. The more holes there are, the more offset between supply and exhaust airflow is needed. That means more energy costs to both temper the supply air and more energy to run bigger system fans. One way to reduce energy costs is to minimize unintended leakage therefore reducing the amount of offset needed to make the design pressure gradient. This requires a collaborative effort in room construction. Starting with the basic room construction, walls will need to be sealed to the floor and roof deck. All mechanical and electrical penetration through the walls will need to be sealed. Room tightness testing will measure the room leakage until an allowable leakage rate, specified by the engineer, is met.
A case study in reducing costs
In Albuquerque New Mexico, an architect engineer design team was tasked with reducing the mechanical operating costs for several hospitals. The first hospital started with an emphasis on trying to reduce operating room leakage. Positive pressure smoke tests were done to find leaks and seal them. The resulting work yielded OR offsets between supply and exhaust of about 2000 cfm to achieve room pressure. After a period of a year, the operating expenses were the lowest in all of its other hospitals to date.
The second hospital had an extreme effort placed on room tightness testing based on square footage of surface area of the ORs. With the allowable leakage rate met, the offset for these, almost identical ORs with the first hospital, was about 200 cfm. A significant reduction in leakage and energy costs. Hospitals since then, by this design team, have become even more efficient in their operations by insuring minimal leakage rates.
These are but a few predictions based on past events and needs; there are sure to be more as current trends evolve to predict more of what the future may require.
Tony Kocurek is SMACNA’s immediate past president and owner of Energy Balance & Integration, LLC in Albuquerque, New Mexico. Kocurek serves as an officer of SMACNA New Mexico and an appointed trustee of the Local 49 Sheet Metal Workers JATC, Health and Welfare Board, and Defined Pension Board.
