Indoor Pool Air Quality Requires an Integrated Approach

Blog by: Keith Coursin, President of Desert Aire Corp.

In the last few years there has been a major breakthrough in understanding how to better maintain the indoor air quality of pool facilities.

For too long those that planned, designed, built and operated the facilities treated HVAC systems, building structures, water loops, energy consumption and event programming independently. Rarely was an effort made to integrate these elements to create the best and lasting indoor pool for all stakeholders. The status quo needed to change, and thankfully it has. The integrated approach is now the way to go.

Here’s a brief overview of the integrated approach to designing an HVAC system for today’s natatorium.

New uses, new demands

The many ways people use natatoriums, indoor pools, water parks and aquatic centers continues to change. 

Mixing competitive and recreational uses, water park features like spray pads, varying water temperatures according to use and the age of swimmers, are a few of these changes. The range of how people use indoor pools places new and evolving demands on HVAC systems. 

The expanded scope – it’s the principle

On top of the new demands on HVAC systems comes an expanded scope. HVAC engineers strive to design systems that provide great indoor air quality and to keep the fun going in a safe and efficient manner. These HVAC design goals must reconcile the intensive tasks of dehumidifying the space, heating and cooling the interior, heating pool water, and meeting outdoor air requirements.

The expanded scope comes from the powerful role controlling air temperature and humidity has been found to have not only on indoor air quality and the comfort of swimmers, but also on energy efficiency and the useful life of building equipment as well as buildings themselves.

The expanded scope includes protecting the health of swimmers, divers, coaches and spectators; promoting the long term-structural integrity of the building and supporting systems; and conserving energy, water and water treatment resources. 

For HVAC engineers who must convert all of these imperatives into design goals the integrated, sustainable approach has become an absolute necessity.

Help in hitting the targets 

CDC LogoFortunately, today’s design engineers have access to a range of problem-solving equipment technologies and strategies. These technologies and strategies complement resources made available by professional associations and engineering societies; and the goals manifest in building codes and standards. 

The Model Aquatic Health Code (MAHC), published by the Centers for Disease Control and Prevention (CDC), is a more recent addition to the resources available to those professionals designing indoor pools and their HVAC systems. The MAHC builds on the resources and guidance provided by the American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (ASHRAE).

As part of bringing together knowledge and best practices, the MAHC states the design, construction and installation of indoor aquatic facility air handling systems shall comply with local codes as well as the proven ASHRAE standard 62.1 2013, Ventilation for Acceptable Indoor Air Quality. 

Staying balanced

Pool Cleaning ASHRAE recommends maintaining the natatorium air temperature at two to four degrees above the pool water temperature but not above the comfort threshold of 86 degrees F.  This seeks to balance HVAC equipment sizing and the energy costs associated with maintaining conditions in the pool space and water. The warmer air temperature will help make swimmers not feel as cold when leaving a pool.

It’s very important when the planning process for a new or remodeled facility is underway that the pool owner communicates to the engineer the desired operating set points of the HVAC system.

Similarly, it’s important the engineer communicate to the pool operator the importance of maintaining conditions in the natatorium to design set points. If water temperature is raised to  86 degrees F while other factors are kept the same, the evaporation rate of water from the pool surface will increase significantly. HVAC equipment including the dehumidification system will now be significantly undersized to handle the warmer pool water. 

ASHRAE recommends that the relative humidity in a natatorium be maintained at between 50% to 60% relative humidity. Lower relative humidity increases operation costs due to increased evaporation and it can lead to swimmer discomfort due to evaporative cooling from their bodies when exiting the pool. Higher relative humidity increases the risk to the building structure.

Loading up

Indoor Aquatic CenterFor indoor pools, loads are the amount of heat energy or moisture that HVAC systems must add or remove from spaces to hit target set points. The heating load is the amount of heat energy that must be added to maintain a target temperature. Cooling load is the amount of heat energy that must be removed. Moisture load is the amount of moisture that needs to be removed to attain a target relative humidity level. 

The heating, cooling and moisture loads of a natatorium are the products of seasonal variations in outdoor air temperature and humidity, solar gains and losses as well as the presence of spectators and bleacher areas.

To calculate heating, cooling and moisture loads to specify and size HVAC equipment, these loads are expressed as sensible and latent. Sensible heat loads are the heat swimmers and building users feel on their bodies and are temperatures that can be measured by a thermometer. Latent heat loads are the energy and heat stored in humidity, a product of its change from liquid to gas. These two components when combined provide the total system rating HVAC systems must be designed to remove.

A pool room that does not maintain the proper temperature of its air and pool water along with setting the correct relative humidity range can quickly overwhelm even the best HVAC equipment.

Don’t go with the airflow

To minimize evaporation, one of the recent changes in natatorium design is moving away from designing HVAC ductwork and grilles that aim airflow at pool water surfaces. HVAC equipment is now configured to pull air across pool water surfaces at less than 30 feet per minute. 

If operators of pools with water at 82 degrees F and air at 84 degrees F increase the airflow across the pool water from 30 feet per minute to 125 feet per minute, the evaporative load on the HVAC system increases by 40%. This again means the HVAC system and dehumidification equipment will be under designed.

Where is the airflow directed? To eliminate condensation as a problem and an additional load factor, all of the air supply should be aimed at exterior walls and windows and not at the pool. 

Indoor air quality and outdoor air

Indoor Pool ExitLocal building ventilation codes protect public health and safety by providing minimum safeguards and standards for ventilation. Most codes have a set amount of outside air that must be brought into the pool area with factors based on the pool surface area, the swimmer drip area, and spectator areas. 

Most local codes are based on ASHRAE Standard 62.1, the industry accepted ventilation code for indoor air quality, which defines the minimum volume of outdoor air to be introduced into the indoor pool enclosure. 

This volume is generally only a small percentage of the total air volume required by a dehumidification system to maintain the space humidity. Proper interpretation can also enhance energy conservation by reducing the volume of outdoor air required to the minimum required by code.

Note the ASHRAE standard treats the different areas of an indoor pool separately. These defined areas include the pool and wet deck, the remaining floor area and the spectator areas. 

Condensation & building integrity

While the design of the building does not fall under the responsibility of the HVAC engineer, it is a key HVAC system component. The engineer and the architect must be in communication on building features and construction materials that will influence the size and capacity of the HVAC system. This includes the quality and quantity of the doors and windows in the natatorium, and controlling humidity within the entire structure with proper vapor barriers. Nowhere is this communication more important than the area of condensation and building integrity.

Condensation control is essential to maintain building integrity. The dew point for a natatorium is fairly high. That means anytime a window or door has a temperature below dew point then condensation will form. Over time, if condensation is allowed to form, the acidic content of the condensation can destroy key building features. These at-risk features include doors, windows and pool room fixtures. 

A vapor barrier is a material or film that prevents moisture migration or penetration. Moisture will travel from high moisture content air to low moisture content air. Because of the high moisture load inside a pool room, the vapor barrier in a pool facility is required to be on the inside of the structure in all North American locations.  

If the facility is in a cold climate and the temperature outside is below freezing and a proper vapor barrier is not installed, moisture will be present inside the wall cavity. This moisture will condense inside the wall cavity. Once condensation occurs inside the wall cavity the remaining insulation value is lost and the problem will get worse. Condensation inside the wall cavity may also prompt decay or mold to the building structure.

Natatoriums should be maintained at a negative air pressure (0.05 to 0.15 in. of water) relative to the outdoors and adjacent areas of the building. This prevents the formation of condensation in the wall and ceiling spaces and prevents the dispersal of chloramines, other noxious fumes, and moisture to other occupied rooms in the building. 

To promote the negative pressurization function of the HVAC system, the natatorium must be separated from adjacent spaces by effective partitions and air barriers. These include tightly gasketed doors and sealed cracks in the frames of doors and windows.

Equipment considerations

To achieve integration objectives and additional benefits, HVAC equipment should be selected and sized to go beyond temperature and humidity control and not just to meet ventilation codes. 

The expanded system can attain benefits that include maximizing energy recovery, integration with chloramine source capture systems and heating pool water.

Before start-up

A design that includes an integrated approach for the HVAC system in the natatorium should include commissioning. Commissioning encompasses a set of techniques and procedures to check, inspect and test each operational component of the system to confirm everything is working together as planned.

The equipment startup and commissioning process should include training of the natatorium staff. The facilities and maintenance staff should have a basic understanding of the HVAC systems and equipment. Other personnel, such as aquatic directors and lifeguards, should be advised of the design conditions of the pool room and the importance of maintaining these conditions. 

To conclude, the overarching goal in designing and managing HVAC systems is sustainability: ensuring indoor pool facilities continue to fulfill the purposes for which they were built in a safe and cost-effective manner. The integrated approach goes a long way to making that happen.

Keith Coursin is the President of Desert Aire Corp, a Milwaukee-based manufacturer of commercial and industrial humidity and climate control systems. Desert Aire systems provide healthy and comfortable indoor environments while saving energy in a variety of settings including indoor pool facilities, indoor water parks, ice rinks, schools and universities, rec and fitness centers, indoor farms, office and retail buildings, and water treatment plants. Keith has participated in key indoor pool industry efforts including development of the CDC’s Model Aquatic Health Code as well as ANSI/ACCA standards detailed in HVAC Design for Swimming Pools & Spas (Manual SPS). To reach Keith Coursin directly, email Keith@desert-aire.com. For more information on Desert Aire’s indoor climate control solutions, visit desert-aire.com.

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