Humidity Control Technology

Design Manual
Video Segments

Step-by-step design advice
in 30 short video segments

Design Manual
Downloads

Our complete Natatorium
Design Manual in PDF format

Design Checklist

A helpful 9-point natatorium
design checklist

Online Design Manual

Humidity Control Technology

  • How to Remove Moisture
  • Refrigeration Based Dehumidifiers
  • Chilled with Reheat Air Handler
  • Outdoor Air Ventilation Systems

Humidity Control Technology Bookmark and Share

How to Remove Moisture

Engineers typically consider one of three approaches to ventilate a natatorium. It is important to understand the capabilities and limitations of each approach in order to select the best system for the application. Seresco manufactures all three styles of unit and will help you evaluate what is right for your application. Energy consumption, geographic location, budget and desired control of space conditions are among some of the key decision making criteria.

Refrigeration Based Dehumidifiers

Refrigeration based dehumidifiers are by far the most common and popular method of removing moisture from the space. These are the NE Series style unit built by Seresco. The units are designed and developed specifically for dehumidifying indoor pools. They offer year round humidity control at the lowest operating costs.

The Energy Cycle

A major benefit of this approach is year round humidity control with low operating costs. These systems use both sides of the refrigeration cycle (evaporator and condenser) simultaneously. Contrast this to traditional air conditioning units that use only the evaporator and dump condenser heat outdoors. These units use the evaporator to dehumidify (and cool when needed) but also put heat back into the pool or back into the process air. This approach is unique to the natatorium industry. The system can be simultaneously dehumidifying (cooling) the air and then reheating it (and/or the pool water) to deliver dehumidified and reheated air to the space, and warm water to the pool. Not a single BTU on either side of the refrigeration cycle is wasted. COPs are close to 8 and EERs greater than 25!

Figure 3 and 4 illustrate schematically how warm humid air passes through the dehumidifying coil and is cooled to below its dew point. Once air is cooled below its dew point, moisture condenses out of the air. Depending on the space temperature requirements the hot gas from the compressor can be used to reheat the air or be rejected to an outdoor condenser. Compressor hot gas can also be used to heat the pool water. Figure 4 shows an example of these components in a vertical unit.

Packaged Mechanical Refrigeration System
Figure 3 - Packaged Mechanical Refrigeration Systems
Vertical Dehumidifier
Figure 4 - Vertical Dehumidifier

Chilled with Reheat Air Handler

These units are not very common and generally only found on applications that have abundant chilled water year round and installing a refrigerant based system proves problematic. The dehumidification process of these systems is essentially the same as with compressorized systems. The chilled water supply temperature must be low enough to cool the air below its dew point at the chilled water coil and condense moisture out of the air. Reheat is required for most of the year. Systems that cannot use captured condenser heat for reheating air require the operation of a heating coil while the chilled water coil is in use. If reclaimed heat is not available for reheat, this approach does not meet most energy codes. This approach is not recommended if chilled water is not available year round.

Outdoor Air Ventilation Systems

While not technically a dehumidifier, because only outdoor air is used, this approach is considered in areas that are dry and/or cool outdoors year round. Solutions can be a very basic, from a single pass of outdoor air that is introduced at one end of the space and exhausted at the other to a more sophisticated system that has variable outdoor air and heat recovery. The single pass system is rare due to the prohibitive operating costs.

A more typical approach is the Seresco NV series style ventilation unit. These units provide ventilation air, heat recovery, heating and also have 100% outdoor air modes for milder weather. It is important to note that the space conditions may not be maintained in summer as the outdoor air may not be dry enough.

The outdoor ventilation style units have several attractive features if your facility is located in a suitable geographic area. They have a lower first cost than a refrigerant based approach and are also considerably simpler units. With heat recovery between the exhaust air and outdoor air streams and controls that properly sequence the outdoor air, this can be a very attractive means to ventilate a natatorium.

There is a misconception that because these systems provide more outdoor air than a refrigeration based unit that the spaces as a result will have much better air quality. This is not correct.  The airside design requirements are the same for a Natatorium regardless of which solution is chosen. Supply air CFM, minimum outdoor air CFM and minimum exhaust air CFM requirements are identical for all systems.

Some manufacturers promote more outdoor air than codes require in order to ensure good IAQ. Seresco does not recommended this approach because it increases building operating costs and still may not have any such impact on the space if the air distribution is not done correctly. A better solution is to stick with the ASHRAE guidelines and ensure the air distribution is correct.

System comparisons and features are highlighted in table 4. Note: The table assumes all units are designed with the same airside characteristics.

Table 4 - System Comparison

Refrigeration

Chilled Water

Outdoor Air Ventilation

Operating Cost

Lowest

Highest

Medium

First Cost

Highest

Medium

Lowest

Year round humidity control

Yes

Yes

Weather dependant

Meets/exceeds Energy Standard 90.1

Yes

No

No

Dehumidification energy recovery

Yes

No

No

Heat recovery on Exhaust and Outdoor air

Option

Option

Option

Free summertime AC

Yes

Yes

No

Free summertime pool water heating

Yes

No

No