Introduction to Controlling Humidity in Natatoriums

Twenty years ago, humidity control for an indoor swimming pool was to bring in outside air while pushing the warm humid air outside with large exhaust fans. This process only worked effectively when the outside air temperature was cool and dry enough to allow for humidity control. This type of system is not only ineffective, but it is the most expensive to operate in a pool enclosure because it cannot consistently maintain the required 50-60% RH humidity levels. When compared to conventional ventilation or "waste ventilation" systems, recycling and dehumidifying pool enclosure air with a mechanical dehumidifier can save 50-75% on energy costs, maintain the 50-60% RH required by ASHRAE, and provide 100% room heating, air conditioning and pool heating.

Humidity control in an indoor pool enclosure is a complex endeavor involving many parties and disciplines. EPS, Inc. has taken a very unique approach to high humidity envelopes. As a design/engineering and consulting firm, our primary focus is on the initial design of the structure (for new construction). We believe preventing problems at the design stage is considerably less expensive than correcting problems which occur "downstream".

In order to ensure the pool enclosure is protected from damage that can be caused by excessive humidity and condensation, the building envelope must be designed to perform to a much higher standard than structures intended for other uses. For a successful application of dehumidifiers, it is crucial that all of the parties involved, from architects to builder to mechanical contracting firms be aware of the importance of the preventive measures that are taken in the planning stages BEFORE applying dehumidification systems to the equation.

Preventing Condensation

Preventing condensation is perhaps the most important purpose of all for dehumidifying an indoor pool enclosure. If condensation forms in or on wood, plaster, or other porous materials, it can cause warping, rot, mold, mildew, rust or simply saturate the material until it loses its integrity.
Condensation, by nature, is aggressive and will attack many materials by leaching the minerals out of the surface it forms on. Condensation, if allowed to form on ferrous materials, will cause accelerated oxidation of the surface of the metal. If left unchecked, condensation will ultimate compromise the structural integrity of all metal components and eventually lead to the failure of those components.

Building considerations such as fenestration, moisture migration, doors/windows/ skylights and other openings, exposed structural surfaces, insulation, ventilation, vapor barriers, ductwork, and mechanical space requirements are critical aspects in the design and engineering of each residential/commercial project that must be addressed in the design and planning stages of the project.

Dew Point Temperature

As you cool air, it cannot hold the same amount of moisture. At some point, that air will become saturated and moisture will begin to condense out of the air onto any adjacent surface. When it condenses, at that point it is called "Dew Point Temperature". For example, take a cold can of pop and place it outside on a 90 degree day. What happens? It begins to sweat, or in our terms it has reached its "Dew Point Temperature". The Design Objective for pool enclosures is to ensure that no surface within the pool enclosure or within the structural members reaches "Dew Point" and cause moisture to condense.

Designing a Clean, Healthy, Stable Environment

At EPS, we believe a successful project starts with good design. The objective for designing mechanical air handling systems for pools is to ensure that no surface within the pool enclosure or within the structural members of the building will reach "Dew Point" and cause moisture to condense. The DRY-AIR Dehumidifier helps to accomplish this objective by reducing the relative humidity in the pool enclosure and therefore, effectively reducing the Dew Point Temperature.

Air distribution also plays a key role in preventing surfaces from reaching DEW POINT temperature. There are surfaces, in particular glass surfaces such as windows, door walls and skylights that will reach Dew Point Temperature even with reduced humidity levels affected by the dehumidifier. For these surfaces, the objective is to completely blanket the area with warm dry air supplied by the dehumidifier, thereby increasing the surface temperature to a point above the temperature at which moisture will condense.

EPS forms a "partnership" with each client. As we interface with architects, engineers, building and mechanical firms, we provide the necessary services to include Design Guidelines, project engineering for the air delivery system, and technical competency in high humidity envelopes that focuses on and addresses all of these issues.

Each DRY-AIR Dehumidification system is sized and built to exceed all ASHRAE requirements and ensures maximizing energy and cost savings. You have a complete resource for assistance in the building, planning, design stages, and engineering of the system for your application.

Designing & Engineering Dehumidification Systems for a Pool Room

Sizing of all dehumidification systems is based on the basic following information. It is important to understand the geographics and demographics for your design  temperatures/conditions. Warmer climates will have a greater cooling load, especially if bringing in large amount of Outside Air. Colder climates will have a higher heating load. It is also important to understand the building materials required for maximum protection and prevention of condensation.

The following information is needed to properly engineer your system:

• Type of facility (commercial, residential, school, medical facility)
• Size of room in square feet
• Size of pool(s) and size of spa in square feet
• Design conditions: Air, pool and/or spa temperature to be maintained
• Type of construction: 2x4, 2x6, concrete block, steel framed, manufactured enclosure, etc.
• The amount of glass (windows, skylights, door walls) within the structure
• Sensible calculations (heat loss/heat gain)
• Will a pool cover be used?

EPS will cover many of these pertinent building areas with each customer:

1. Insulation- R/Value of the building materials and insulation
2. Sensible Calculations
3. Acceptable Materials used for interior finishes
4. Vapor Barriers and why they are required
5. Skylights
6. Recessed Top Hat/Can Lighting
7. Negative Pressure
8. Outside Air Requirements if applicable
9. Windows & Skylights must be addressed
10. Air delivery system-Duct work
11. Air turnovers required
12. Temperature settings (water and air) and how they affect your operation and costs
13. Humidity settings
14. Pool Covers (best way to cut costs)
15. Chlorine & pH balance, problems with automated chemical feeders
16. Mechanical Space Required

If this is an existing facility or retrofit please call us for more information, please call us for our Retrofit Questionnaire.

Pool Room environments should be designed and maintained as a separate environment from the rest of the commercial or residential structure. Because pool rooms operate at a much high integrity level than non-pool related environments, certain precautions should be taken at the planning and designing stages. Humidity and chlorine can cause serious problems for areas (i.e. commercial -- work-out/fitness areas with equipment, residential – living areas) that are not related to pool room and are not protected by dehumidification, vapor barriers, etc.

Indoor pools are treated much the same way you would treat your home. Pool rooms require year round conditioning to prevent condensation, mold, mildew, rot, warping and an overall deterioration of the structure. With new construction, the type of building materials used, the amount and type of glass, insulation, heat gain/heat loss, windows, pool covers, will be taken into consideration when designing the system. The air delivery system will also play a critical role in the overall protection, operation and energy costs associated with indoor pools. The complete environmental control package is a SEPARATE system from office or home systems.

The Design Guidelines are in PDF format, are printable and can be shared with all involved in your project. This information has been gathered over the years from a variety of resources, building professionals, pool contractors, architects-engineers, mechanical contractors, ASHRAE, ACCA, and is not expressly the opinion of EPS. Providing of these guidelines does not negate your own research into building materials and preventive measures for your indoor pools; they are provided as an additional resource to ongoing research.

EPS does not assume responsibility or liability of any nature with respect to consulting services, or make any warranty with respect to the services provided by outside consultants, engineers, architects or HVAC-mechanical firms providing installation. By receiving design assistance from EPS, you waive all claims against EPS and release EPS from any liability for any errors, omissions, or negligence arising out of or connected with the services of the architect or engineer. EPS will not be deemed a principal, agent, partner, or joint venture with respect to any project. In no event shall EPS be liable to any party for fees and costs to be reimbursed for design or consulting services.