Print full article

Energy-saving technological advancements renew interest in outdoor air ventilation systems

Dedicated-duty, direct-drive fans

Aa-Direct Drive Plenum Fans v.1
Direct-drive plenum fans with variable frequency drives (VFDs) are an example of an emerging technology being used for dehumidifiers that is now also making outdoor air-based ventilation-only systems (OAVOS) more attractive efficiency-wise.

The introduction of dedicated-duty, direct-drive exhaust fans and direct-drive plenum fans with variable frequency drives (VFDs) is another example of an emerging technology being used for dehumidifiers that is now also making an OAVOS more attractive efficiency-wise.

The dedicated-duty approach only operates as many fans as needed compared to systems with two large fans operating at full airflows. The supply fans deliver a constant volume of air 24-7; however, since the amount of outdoor air needed varies with weather conditions, this approach ramps up and down the amount of exhaust fans in use in concert with the amount of outdoor air needed to control the indoor space conditions. This also dramatically reduces energy use by the fans.

A-Direct Drive Plenum Fans
Plenum fans are different in that they deliver air more efficiently than centrifugal-style fans, which are typically found in traditional dehumidifiers.

Plenum fans are different in that they deliver air more efficiently than centrifugal-style fans, which are typically found in traditional dehumidifiers. Compared to traditional belt-driven fans, the direct-driven approach provides greater efficiencies with significant energy reductions and reduced maintenance.

A direct-drive plenum fan with VFDs can amount to as much as 15 per cent in fan motor energy reduction. Considering OAVOS supply fans operate 24-7, the savings over the equipment’s lifecycle are significant. The payback is instantaneous since direct-drive plenum fans with VFDs are comparable in price to belt-driven systems.

For example, a 906-CMM (32,000-CFM) OAVOS operating 24-7 with an electricity rate at 0.095 cents per kWh, direct-drive plenum fans would save approximately $3,200 annually versus using a belt-driven, centrifugal blower. When adding the on-demand exhaust fan operation to the savings, a natatorium would be looking at approximately $6,000 to $8,000 in fan energy savings compared to using older technology. This is a substantial sum over a 20-year period.

While this technology has been available for years, it was only recently introduced into the indoor pool HVAC market and still not all manufacturers offer them. The age-old concept of fan belts connecting the fan motor to the blower requires more maintenance such as regular adjustments and fan belt replacements. Conversely, the direct-drive method connects the motor directly to the fan shaft, thus minimizing maintenance and noise, as well as friction and power transfer inefficiencies associated with belt drives.

When VFDs are added to direct-drive technology there is potential for even more efficiency with the ability of ramping up or down the fan speed. Adjusting the fan speed via a VFD also adds more flexibility for air balancing.

Another potential advantage VFDs offer is the ability to ramp down the plenum fan speed during off-peak hours when less overall supply airflow might be a consideration.

Remote monitoring for optimum dehumidifier performance

Technological improvements do not deliver their full savings unless they operate at optimal performance levels for which they were designed. Like all technology, controls, dampers, fans, and sensors on an OAVOS need oversight and fine-tuning for minimizing operating costs, while maximizing efficiency and air comfort.

A factory-trained technician should ideally be servicing and adjusting the system a few times a year to assure parameters such as RH, temperature, and other operating conditions are within an efficient range.

The aforementioned outdoor air modulation, for example, is critical to a natatorium’s air comfort and energy usage. A facility operator who is not aware that outdoor air and humidity were being inefficiently controlled could result in compromised air comfort. Further, less efficient use of fans, air modulation, or space heaters can cost a facility hundreds or even thousands of dollars in energy costs before it is discovered.

The expense of periodic maintenance checks by a factory-trained technician might seem high enough that facility operators may be inclined to let things slide, especially for facilities with limited budgets. This is not the best approach since the risk of higher operating costs and repairs makes a proper service and maintenance program a good investment. Thanks to recent technological advancements, support has never been better and service costs have been dramatically reduced. Manufacturers have developed an on-board monitor/control microprocessor that can send all of the OAVOS vital operating statistics to their factory via the Internet. These manufacturers offer a free daily monitoring service and even have smartphone applications where an authorized user can access a unit’s current and historical performance statistics from a remote location. The manufacturer can alert the facility operator of any issues and help the local service contractor set-up and adjust the unit to ensure optimum performance. In the event of an alarm, troubleshooting can be assisted by a factory engineer, which ensures a quick resolution to any problem.

An OAVOS can be a viable option if the geographical climate delivers acceptable conditions. Only proper computer modelling will provide the information upfront whether or not this is an approach an operator can consider. Advancements in technology have dramatically reduced the operating costs while providing excellent cold weather space condition control. However, knowing how the facility will perform in the warmer weather is a vital part of making an informed decision as to what approach a facility operator would like to consider for conditioning a natatorium.

The modern dehumidifier’s advantage is precise space temperature and humidity control. These systems mix outdoor air—as well as recirculated indoor air—that is mechanically cooled and dehumidified to provide optimal indoor air comfort year-round.
Using refrigerants and compressors, much like modern air-conditioning, but on a larger scale, indoor pool dehumidifiers maintain a cool coil that wrings the moisture out of the air as it passes through to maintain an optimal 50 per cent relative humidity (RH). If the space needs cooling, the refrigeration cycle also provides air conditioning.
These systems also use the compressor waste heat to contribute to space heating to provide considerable energy savings.



Kittler_HeadshotRalph Kittler, P.Eng., is co-founder and vice-president of sales and marketing of Seresco USA in Decatur, Ga., a subsidiary of Seresco Technologies Inc., an Ottawa-based manufacturer of natatorium dehumidifiers and outdoor air ventilation only systems (OAVOS). He has 25 years of experience in the heating, ventilation, and air conditioning (HVAC) industry and a degree in mechanical engineering from Lakehead University in Thunder Bay, Ont. Kittler recently produced a free ‘Professional Development Hour’ (PDH) video available at, which targets the continuing education requirements for engineers, but also serves as an invaluable primer of indoor pool design and operation basics for facility managers. He can be reached via e-mail at

Leave a Comment


Your email address will not be published.