At a glance
- Ventilation systems should be tailored to a client’s IAQ goals.
- When you evaluate strategies to improve IAQ, look for ways to lessen the impact on energy use.
- In addition to HVAC design, building architecture and operations can also impact IAQ.
If you remember what your high school locker room looked like, one of the first things to come to mind is probably the smell—in other words, bad IAQ. Many things probably contributed to that smell, including the design of the building’s HVAC system.
IAQ in sports and fitness facilities can vary greatly depending on a facility’s age, the level of competition practiced there, and other factors. Retail fitness and youth sports facilities often have bare-minimum HVAC systems, which results in fair to poor IAQ. The IAQ expectations are much higher in professional and 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 (CFM) per square foot. The minimum outdoor air 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 percent outdoor air, so transfer air from adjacent spaces can be used as makeup. Retail fitness and youth sports facility designs are often cost driven and use the minimum requirements to stay within budget.
Typical systems designed to meet minimum ventilation requirements include overhead exhaust grills, 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 grills with the primary conditioning coming from a recirculating-air-handling unit. Training areas are typically served by a recirculating-air-handling unit that provides code-minimum outdoor air. 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 that negatively impact IAQ are building pressurization and mixing of air classes. A building air balance calculation should be performed and outdoor air flow adjusted to ensure positive building pressure at all times.
If a building is allowed to operate negatively pressurized—in other words, more exhaust air than outdoor air—air is pulled in through doors and cracks in the building envelope. This air is unfiltered and unconditioned, which could negatively impact IAQ and energy use. Mixing of air classes is regulated by code and should be avoided except under certain conditions detailed in the code.
For example, air from a locker room (Air Class 2) returned to an air handler can’t be mixed with air from office spaces (Air Class 1) before being redistributed to spaces with an Air Class of 1. When you design to meet higher IAQ expectations, pressurization and air class concerns are inherently improved by the system types and strategies you use.
Improving baseline IAQ
Meeting client IAQ expectations in professional conference and high-end sports and training facilities requires going above and beyond the minimum dictated by code. In an ideal world where cost and operations could be ignored, this means using 100 percent outdoor air at a constant rate, which not only meets the space loads but gives great air turnover while exhausting all air supplied except what’s needed for building pressurization.
The outdoor air could even be cleaned before it is brought into the building using HEPA filters and the latest contaminant-killing technologies. The resulting IAQ could be as good as if not better than the air quality outdoors.
The 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 use for those increases remains high (Figure 1).
As most IAQ strategies are implemented, there is an increase in cost, energy, and CO2. At a certain point, strategies may yield marginal IAQ improvements but still have a high cost and increase to energy and CO2 (Figure 2).
Figure 1: At a certain point, IAQ strategies may yield marginal IAQ improvements but still have a high cost and increase to energy and CO2.
Some strategies that strike a good balance between IAQ, energy use, and cost include increasing ventilation rates, 100 percent outdoor-air handlers with energy recovery, source capture, contaminant separation, building automation systems, increasing filtration, and commissioning.
The following list highlights ways to improve IAQ with a primary focus on sports and fitness facilities. This list isn’t exhaustive.
- Increasing the exhaust and outdoor air rates is one of the first things to consider when looking to improve IAQ. How much to increase ventilation rates varies depending on system types, energy goals, how spaces will be used, and other strategies to improve IAQ.
- Using 100 percent outdoor-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 and conditioning a space with the same 100 percent outdoor supply air. The same unit should also be used to exhaust spaces to allow for relatively easy energy exchange between the outdoor air and exhaust airstreams using an energy recovery device such as an enthalpy wheel or fixed plate. This reduces energy use by treating the outdoor air before it is mechanically heated or cooled. 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 within it.
- Ventilation reduction control strategies should be considered to ensure maximum outdoor air is provided only when the spaces served require it. Care should be taken to ensure ventilation rates do not fall below code minimum requirements. Setting a minimum fan airflow setpoint, using an inline fan if you connect to a larger modulating system, or incorporating exhaust-air terminal boxes can help maintain minimum requirements. When a 100 percent outdoor-air-handling unit serves a training space, exhaust/return air bypass dampers could allow the unit to use recirculated air to condition the space during unoccupied or low-occupancy periods.
- Integrating source capture strategies in locker designs is becoming more popular and is a good way to remove contaminants before they enter an occupied space. A common method is to provide openings on the back side of lockers, then construct an airtight exhaust plenum behind that the lockers 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 (Figure 2). This method has some inherent challenges, such as ensuring the exhaust plenum behind the lockers is sealed properly and determining how to balance the airflow through the lockers. There are other methods to consider, including fully ducting each locker exhaust opening or using small integral fans on the locker openings, but these methods also come with challenges. Coordination with the project architect, locker vendor, and others is necessary to provide effective solutions that perform as intended.
Figure 2: Integrating source capture strategies in locker designs is becoming more popular and is a good way to remove contaminants before they enter an occupied space.
- A good passive method of improving IAQ is contaminant separation using a dedicated dirty changing vestibule or mudroom. This mudroom is where athletes go directly after a workout or event to remove soiled uniforms, cleats, and other gear. Ideally, the mudroom is adjacent to the laundry area, so the soiled uniforms and equipment do not have to be transferred through the facility to be cleaned. Additionally, placing showers between the mudroom and locker room encourages athletes to shower before entering the clean locker room. The locker room IAQ benefits from this setup by preventing dirty uniforms and equipment from polluting the locker space, where athletes store their clean clothes and spend time between activities.
- Building automation systems offer several ways to improve IAQ while minimizing energy use, including ways to monitor occupancy, such as CO2 and occupancy sensors, which allow ventilation systems to activate or increase ventilation only when people are present. Airflow measuring stations on outdoor air and exhaust systems ensure anticipated amounts of ventilation are actively provided while helping troubleshoot issues that could lead to excessive energy use. Airflow measuring stations are a great way to ensure a building is positively pressurized by adding alarms if airflows are outside predetermined limits.
- Another building automation control strategy is a preoccupancy purge cycle. Most ventilation systems cycle off at night or when a building is not occupied. A preoccupancy purge involves turning on the ventilation system at a set time before the building is occupied to help remove and dilute contaminants that built up while the system was off. Another strategy is to provide 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. Installing MERV 8 filters upstream of the more expensive MERV 13 filters helps prolong their life.
- Commissioning ventilation and HVAC systems is critical to knowing the installed system operates as the design intended. Quality testing and system balancing at the completion of construction and before building occupancy is also helpful. Skipping these steps could leave a building under- or overventilated, leading to excessive energy use and space temperature and humidity control issues.
- Quality testing and balancing ventilation systems ensures proper air-pressure relationships between spaces are maintained and verifies positive building pressure. Maintaining proper air pressure 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 facility.
Figure 3: Expected air-pressure relationships between spaces in a sports facility.
- Another passive way to improve IAQ is to locate exhaust intakes in wet areas like showers and bathrooms when they are open to locker rooms. The wet area exhaust intakes should be sized for most, if not all, the open area exhaust needs. This promotes good air turnover in the wet area, and the air moves from the locker room to the wet area, which helps contain smells generated in the wet area.
- Cleaning and disinfecting surfaces is important to occupant health and also impacts IAQ. Avoid using surface disinfectants with adverse air quality effects if possible, especially when spaces are occupied or immediately before occupancy.
These strategies for improving IAQ are frequently used in projects that cater to professional or collegiate athletes, but they can also be scaled to fit most sports and fitness training facilities. For example, 100 percent outdoor-air units can be paired with cost-effective packed-rooftop units or variable refrigerant flow systems. Properly planning for increased filtration at the start of a project can help keep costs down.
Commissioning, sometimes required by code, can be easily tailored to fit any project and even targeted at specific IAQ goals. As these strategies become more widely adopted across all facility types, the relative cost should come down, making way for new technology.
New strategies to improve IAQ
Like any new technology for buildings, the goal should be to improve the occupant and operator experience while reducing energy use. The same goes for new IAQ technology. One technology already on the market but not widely adopted is equipment-disinfecting cabinets, where athletes put their equipment immediately after a workout to both disinfect and dry using ultraviolet lights or ozone.
Source-capture locker exhaust systems have room for improvement. Better locker design and integration with a building ventilation system could improve source capture effectiveness. Building automation system technology is quickly evolving to improve building IAQ.
Tying a building automation system to locally installed ambient-air-quality sensors or open-source outdoor-air-quality data to implement real-time optimization techniques can prevent intake of outdoor air to a building that is worse than the target IAQ. For example, if outdoor-air-quality sensors pick up wildfire smoke, the system could engage a smoke-mitigation mode to minimize smoke intake to a building. In metropolitan areas, a building automation system could be tied to information sources on the internet that track outdoor-air quality and adjust ventilation accordingly.
Digital twins are 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 the building’s systems, indoor conditions, and outdoor conditions can be manipulated and analyzed for optimal performance through the building’s life cycle, from design to decommissioning. A digital twin could be used to analyze the optimal building system design for the best IAQ. It could be updated for condition changes to help an operator make IAQ-related decisions and used to analyze and make decisions related to just about every aspect of a building.
Some new technologies, like disinfecting cabinets, require no real integration with other building systems and can be easily used in existing facilities. Others require more up-front coordination in a building’s design but can be paired with existing strategies to both improve IAQ and save energy.
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