By Ralph Kittler
A myriad of new energy-reduction and environmentally friendly dehumidification technologies have been introduced to the indoor swimming pool market in the last 10 years. These innovations not only provide significant advancements in system performance and reliability, but also considerably reduce operating expenses. These systems also provide natatorium owners/operators a quick return on investment (ROI), which has prompted more facilities to consider upgrading their existing dehumidification equipment even before its useful lifecycle is over. For new construction projects, these systems can potentially save hundreds of thousands of dollars over the equipment’s lifecycle.
Today, a natatorium design team that is simply considering a basic dehumidification unit could still be looking at a system with significantly upgraded components and features compared to what was available even five years ago. Therefore, before considering adding features and options to the base model, designers should evaluate the higher upfront capital cost with the energy savings over the product’s lifecycle.
The dehumidification equipment innovations discussed below are not budget busters and can potentially provide a quick ROI. In fact, many manufacturers include the following features in their base model.
The introduction of direct-drive plenum fans with variable-frequency drives (VFDs) is one example of a new energy-saving technology. These fans deliver air more efficiently than centrifugal-style fans, which are common in traditional dehumidification systems. In comparison, the direct-drive approach provides greater efficiencies with significant energy reductions and less maintenance. While this technology has existed for many years, it was only recently introduced to the dehumidification industry.
Before this, state-of-the-art was the age-old concept of fan belts connecting the fan motor to the blower, a method which needs regular adjustments and belt replacements. Conversely, the direct-drive method connects the motor directly to the fan shaft, thus eliminating friction, noise, maintenance and power transfer inefficiencies.
When VFDs are added to the mix there is further potential for greater efficiencies with the ability to ramp fan speed up or down, which also adds more flexibility for air balancing. Another potential advantage is the ability to ramp down the plenum fan speed during off-peak hours when less overall supply airflow might be a consideration.
A direct-drive plenum fan with VFD can reduce fan motor energy consumption by as much as 15 per cent. Considering the fans on an aquatic facility’s dehumidification equipment operate 24-7, energy savings over the equipment’s lifecycle can be significant. The payback is instantaneous since this technology is comparable in price to belt-driven systems.
Energy recovery: Using exhaust air to preheat outdoor air
All commercial buildings must bring in outdoor air as mandated by local building codes. These codes are generally based on the recommended values from American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) Standard-62, Ventilation for Acceptable Indoor Air Quality (IAQ).
In the winter, heating cold outdoor air to at least 26.6 C (80 F) just to get it neutral to the indoor air temperature can be expensive. ASHRAE also recommends that an indoor pool’s exhaust air be used to keep the space at a slight negative pressure to assure potentially destructive indoor air, which contains moisture and often chemicals, is not accelerated through the natatorium’s walls or doors leading to other non-pool areas in the building. Therefore, the volume of exhaust air must always exceed the amount of outdoor air. Fortunately for natatorium operators, humid and warm exhaust air is extremely energy rich and ideal for energy recovery, allowing it to be used to preheat the code-required outdoor air.
Energy recovery from exhaust air to outdoor air is an option available from some dehumidifier manufacturers. The exhaust air is warm (minimum 26.6 C [80 F]) and its energy can be recovered and used to preheat the incoming outdoor air, via heat exchangers. Using recovered heat from the exhaust air can cut outdoor air heating costs by 50 to 75 per cent.
Additionally, preheating outdoor air minimizes potential for condensation inside equipment in cold climates. Introducing freezing cold outdoor air into a dehumidifier could theoretically generate snow inside the unit.
The ROI for this type of dehumidification system is often only a few months and rarely more than a few years, which makes it a cost-effective investment for most natatoriums. When considering which form of heat recovery to use, it is important to consider performance, longevity and impact on equipment size. At a minimum, the heat recovery device used to extract heat from the chemically laden exhaust air should be provided with the best possible corrosion protection coatings.
Remotely located exhaust fans can also be outfitted with heat transfer coils that are piped to the dehumidifier. Designers and operators should always consider exhaust air as an energy source for heat recovery.