As published by Consulting-Specifying Engineer

If you remember back to what your high school locker room was like, one of the first things to come to mind is probably the smell or what we would call bad indoor air quality. There were likely many things contributing to that smell, one of which was the heating, ventilation and air conditioning design.

The IAQ in sports training and fitness facilities can vary greatly depending on a facility’s age and level of competition among other factors. Retail fitness (strip mall spin or aerobics studios) and youth sports are more often going to have bare minimum HVAC systems resulting in fair to poor IAQ. As you can imagine, the IAQ expectations are much higher in professional and NCAA Power Five conference sports facilities.

ASHRAE Standard 62.1: Ventilation for Acceptable Indoor Air Quality dictates that locker room ventilation is exhaust driven and training spaces are outside air driven. The minimum exhaust rate for locker rooms is 0.5 cubic feet per minute per square foot. The minimum OA rate for training spaces is 20 CFM/person with area rates ranging between 0.06 and 0.18 cfm/square foot depending on the occupancy category. Makeup air for locker room exhaust is not required to be 100% OA, so transfer air from adjacent spaces can be used as makeup. Retail fitness and youth sports facility designs are often first cost driven and will use the minimum requirements to stay within budget.

Typical systems designed to meet minimum ventilation requirements will include overhead exhaust grilles, either duct- or ceiling-mounted, connected to a constant volume exhaust fan for locker room ventilation. Locker room makeup air is often handled by wall or ceiling mounted transfer grilles with the primary conditioning coming from a recirculating type air handling unit. Training areas will most times be served by a recirculating type air handling unit providing code minimum OA. MERV 8 filters, the industry-accepted minimum, are often used in the air handling units with both the air handlers and exhaust fans cycling off at night when the building is unoccupied.

Some easily overlooked design considerations on budget driven projects — or any project for that matter — that negatively impact IAQ are building pressurization and mixing of different air classes. A building air balance calculation should be performed and OA flow adjusted to ensure a positive building pressure at all times.

If a building is allowed to operate negatively pressurized (i.e., more exhaust air than OA), then air will be pulled in through doors and cracks in the building envelope. This air is unfiltered and unconditioned which could both negatively impact IAQ and energy usage. Mixing of different air classes is regulated by code and should be avoided except under certain conditions as detailed in the code.

For example, air from a locker room (Air Class 2) returned to an air handler is prohibited from being mixed with air from offices spaces (Air Class 1) before being redistributed to spaces with an Air Class of 1. When designing to meet higher IAQ expectations, these pressurization and air class concerns are often inherently improved by the system types and strategies used.

Improving on baseline IAQ

Meeting client IAQ expectations in professional, NCAA Power Five conference and similar high-end sports and training facilities requires going above and beyond the minimums that code dictates. In an ideal world where cost and operations could be ignored, this would mean using 100% OA at a constant rate, which not only meets the space loads but gives great air turnover while exhausting all air supplied except what is needed for building pressurization.

The OA could even be cleaned before entering the building using HEPA filters and the latest contaminant-killing technologies. Certainty at this point the resulting IAQ could be as good if not better than the air quality outdoors.

However, the first cost, operating cost and maintenance required would be enough to take any client’s breath away. To avoid blowing budgets, a balance must be made between the client’s IAQ expectations, energy use and cost. There is also a point of diminishing return, where only marginal increases in IAQ are achieved, but cost and energy usage for those increases remain high as the graphic below illustrates.

As most IAQ strategies are implemented, there is an increase in cost and energy/carbon dioxide (known as CO₂). At a certain point, strategies may yield marginal IAQ improvements but still have a high cost and increase to energy/CO₂ (see Figure 1 below).

Figure 1: Graph showing as most IAQ strategies are implemented there is an increase in cost and energy/CO2. At a certain point, strategies may yield marginal IAQ improvements but still have a high cost and increase to energy/CO2.

Some current strategies that strike a good balance between IAQ, energy use and cost include things like increasing ventilation rates, 100% OA air handlers with energy recovery, source capture, contaminant separation, building automation systems, increasing filtration and commissioning.

Figure 2: Section view of lockers with a field constructed exhaust plenum for source capture of contaminants in different locker compartments.

The list below highlights ways to improve IAQ with a primary focus on sports training and fitness facilities and is not intended to be an exhaustive list.

• Increasing the exhaust rates and OA rates is one of the first things to consider when looking to improve IAQ. How much to increase ventilation rates varies depending on numerous factors including, but not limited to, system types, energy goals, how spaces will be used and other strategies being used to improve IAQ.
• Using 100% OA air handling units not only improves IAQ, but also simplifies many of the air balance and control pitfalls that are detrimental to IAQ. These units typically serve a dual purpose by both ventilating the spaces and conditioning the space with the same 100% OA supply air. The same unit should also be used to exhaust the spaces to allow for relatively easy energy exchange between the OA and exhaust air streams using an energy recovery device such as an enthalpy wheel, fixed plate or similar. This reduces energy usage by pretreating the OA before it is mechanically heated or cooled. Like the above, the airflow rates should be weighed against multiple factors including what is needed to meet space loads and what will provide adequate air turnover depending on how the space will be used and the contaminants generated within the space.
• Ventilation reduction control strategies should be considered to ensure maximum OA is provided only when the spaces served require it. Care should be taken to ensure ventilation rates do not fall below code minimum requirements at any point. Setting a minimum fan airflow setpoint, using an inline fan if connecting to a larger modulating system, or incorporating exhaust air terminal boxes can help maintain minimum requirements. When using a 100% OA air handling unit to serve a training space, exhaust/return air bypass dampers could be used to allow the unit to use recirculated air to condition the space during unoccupied/low-occupancy periods.
• Integrating source capture strategies into locker designs is becoming more popular and is a good way to remove contaminants before they enter the occupied space. A common way of accomplishing this is by providing opening(s) in the back side of the lockers, then field constructing an airtight exhaust plenum behind that the lockers will seal against. The exhaust plenum is then exhausted by ducts dropping into the top of the plenum, which in turn pulls air through the lockers like Figure 2. This method has some inherent challenges, such as ensuring the exhaust plenum behind the lockers is sealed properly and how to balance the airflow through the lockers. There are other methods to consider, including fully ducting to each locker exhaust opening or using small integral fans on the locker openings but these methods also come with their own set of challenges. Coordination with the project architect, locker vendor and others is necessary to provide effective solutions that perform as intended.

• A good passive method of improving IAQ is contaminant separation by having a dedicated dirty changing vestibule or mud room. This mud room is where athletes go directly after a workout or event to remove soiled uniforms, cleats and other gear. Ideally, the mud room is adjacent to the laundry area, so the soiled uniforms and equipment do not have to be transferred throughout the facility to be cleaned. Additionally, placing showers between the mud room and locker room would encourage athletes to shower before entering the clean locker room. The locker room IAQ benefits from this type of setup by preventing dirty uniforms and equipment from polluting the locker space, where athletes store their clean clothes and generally spend time between activities.
• Building automation systems offer several ways to improve IAQ while minimizing energy usage. Widely used options include ways to monitor occupancy such as CO₂ and occupancy sensors, which allow ventilation systems to activate or increase ventilation only when people are present. Also, airflow measuring stations on OA and exhaust systems ensure anticipated amounts of ventilation are actively being provided while helping with troubleshooting issues that could lead to excessive energy usage. Airflow measuring stations are a great way to ensure a building is positively pressurized by adding alarms if airflows are outside predetermined limits.
• Another BAS control strategy that may not be widely used but is easily implemented even with existing systems is a preoccupancy purge cycle. Most ventilation systems cycle off at night or when a building is not occupied. A preoccupancy purge would simply involve turning the ventilation system on a set time before the building being occupied to help remove and dilute any contaminants that may have built up while the system was off. One last BAS strategy that can be used is providing an easy method for building operators to manually control ventilation on bad environmental days such of when there is wildfire smoke or smog.
• Providing increased filtration is a well-known way of improving IAQ. In many facilities, providing MERV 13 filters in air handling units has become the expectation. Including MERV 8 filters upstream of the more expensive MERV 13 filters help prolong their life.
• Commissioning ventilation systems and HVAC systems in general is critical to knowing the installed system operates as the design intended. Related is having a quality test and balance of all systems done and verified at the completion of construction and before a buildings occupancy. Skipping these steps could leave a building under-ventilated, and also over-ventilated, leading to excessive energy use and space temperature and humidity control issues.
• Quality testing and balancing of ventilation systems ensures proper air pressure relationships between spaces are maintained in addition to verifying an overall positive building pressure. Maintaining proper air pressure relationships between spaces helps minimize the impact adjacent spaces can have on one another regarding IAQ. Figure 3 is an example of the expected air pressure relationships between spaces in a sports training facility.
• Another passive way of improving IAQ is locating exhaust intakes in wet areas when those wet areas like shower rooms and restrooms are open to lockers rooms. The wet area exhaust intakes should be sized for most, if not all, the open area exhaust needs. This will promote good air turnover in the wet areas, helping to dry them out. Also with this arrangement, air will move from the locker room (cleaner) to the wet area (less clean), which should help contain any smells generated in the wet area.
• Cleaning and disinfecting surfaces in these facility types is important to occupant health but also can impact IAQ. The use of surface disinfectants with adverse air quality effects should be avoided if possible, but especially when spaces are occupied or immediately before occupancy.

Figure 3: Floor plan showing the different space air pressure relationships in a sporting training facility.

The above strategies for improving IAQ are frequently used in projects that cater to professional or collegiate athletes. However, any of these strategies can be scaled to fit most sports and fitness training facilities while keeping an eye on the budget. For example, 100% OA units can be paired with more cost-effective packed rooftop units or variable refrigerant flow systems. Properly planning for increased filtration at the start of a project can help keep impacts to cost down.

Commissioning, sometimes required by code, can be easily tailored to fit any project and even targeted at specific IAQ goals within a project. As these strategies continue to become more widely adopted across all facility types, the relative cost should come down making way for new technology to emerge.

New strategies to improve IAQ

Like any new technology going into buildings, the goal should be to improve the occupant and operator experience while reducing energy use. The same goes for new IAQ technology. Some newer technologies already on the market but not widely adopted include equipment disinfecting cabinets. These are cabinets where athletes put their equipment immediately after a workout to both disinfect and dry using ultraviolet lights or ozone among other systems.

Source-capture locker exhaust systems, while currently in use, have room to improve. Better locker design and integration with the building ventilation systems could improve the source capture effectiveness. BAS technology is quickly evolving in ways to improve building IAQ.

Tying the BAS to locally installed ambient air quality sensors or open-source OA quality data to implement real time optimization techniques can prevent intake of OA to a building that is worse than the target IAQ. One possibility is when OA quality sensors pickup wildfire smoke nearby, the BAS could then in real-time engage a smoke mitigation mode to minimize smoke intake to a building. Alternately when in metropolitan areas, a BAS could be tied to various information sources available via the internet that track OA quality and adjust ventilation accordingly.

Creating digital twins is an emerging technology that will revolutionize how buildings are designed and operated. A digital twin is an exact virtual model of a physical building where all the building systems, indoor conditions and outdoor conditions can be manipulated and analyzed for optimal performance throughout the entirety of a building’s life cycle, from design to decommissioning. A digital twin could be used to analyze what the optimal building system design is for the best IAQ. After a building is built, the digital twin could be updated as any given condition changes to help an operator make IAQ related decisions. A digital twin could be used to analyze and make decisions related to just about every aspect of a building with IAQ being only one of them.

Some of these new technologies like disinfecting cabinets require no real integration with other building systems and can even be easily used in existing facilities. Other technology requires more upfront coordination in a building’s design but can be paired with existing strategies to both improve IAQ and save energy.