June 21, 2018
By Eric Cournoyer
When to service a dehumidifier and who to call are probably two of the most critical decisions that must be made for an aquatic facility, whether it is a huge indoor waterpark or just a small indoor pool.
Most indoor pools in Canada rely on a mechanical dehumidifier to keep the environment comfortable for occupants. Typically, dehumidifiers maintain a 50 to 60 per cent relative humidity (RH). In most cases, a dehumidifier (depending on the model) will also heat and cool the space, and possibly use waste heat from the compressor to provide free pool water heating.
Although dehumidifiers provide air conditioning, they are quite different from conventional air conditioners and, therefore, should not be serviced in the same manner. For example, air conditioning systems are typically serviced every six months, or one year at the most. However, an authorized service technician should check a natatorium dehumidifier at least every three months.
A dehumidifier provides total control over the indoor space, as opposed to just cooling it. Therefore, most malfunctions are noticeable to patrons and management, such as fog or condensation on the windows, uncomfortable temperature/humidity, and stuffy breathing conditions. Unusual vibrations/noises from the dehumidifier or supply ductwork may also occur, while pool odours in the facility’s non-pool areas may be noticeable.
Fog and condensation typically indicate insufficient airflow to the windows to condition them with dry, warm air. This is especially common during the winter when the dew point temperature of exterior wall glass drops too low—due to insufficient airflow—the humid air inside the facility condenses on the glass.
An uncharacteristically uncomfortable temperature or high humidity in the natatorium might point to dehumidifier problems. Air media filters inside the unit could be clogged if they are not periodically changed. Dampers that control exhaust or outdoor air intake could also be skewed.
Like most mechanical equipment, an unusual sound or vibration generally means there is a problem. Therefore, it is a good idea for facility managers to become familiar with the routine sounds of a mechanical room. Then, a daily or weekly inspection can detect any recent audible noise variation or vibration. If the operating sound is different from the norm, then it could indicate a malfunction or a potential problem.
In some cases, modern dehumidifiers may have web browser-based communication centres that can send e-mail or smartphone alarms/alerts when operating conditions degrade. If available, facility managers should use this interface access.
Pool odours beyond the pool area, such as in the facility’s lobby, offices, or other rooms could indicate the natatorium is no longer under the necessary negative building pressure. Unlike most commercial buildings, a natatorium is designed to operate at a negative pressure, which means more air is exhausted than is delivered to the space via outdoor air and return air (i.e. more pool air is drawn out than what is being pushed in). To check the building’s pressure, a facility manager can perform a simple test, which involves slightly opening the natatorium’s entrance doors and holding a tissue near the opening to see if it is drawn into or away from the building. If the tissue is drawn in, it confirms a negative pressure. (For this test to work, however, it is important to make sure the locker room doors are closed.)
Dehumidifiers also have several dampers for airflow. Dampers control incoming outdoor air into the dehumidifier or return air. These dampers can become inoperable from possible ice formation, stuck open or closed from poor periodic maintenance, or just improperly adjusted by local contractors or facility staff that does not understand their function.
If there is an issue with an aquatic facility’s dehumidifier, it is important the facility manager knows who to call for service. Most heating, ventilation, and air conditioning (HVAC) service contractors are qualified in air conditioning, but may have little experience or education on commercial dehumidifiers, which, as mentioned earlier, are quite different from air conditioners despite the similar tasks they perform. More specifically, it is the control strategy and the dehumidifying equipment’s objectives that are unique.
For example, dehumidifiers have adjustable slide-gates for controlling outdoor airflow and dampers for diverting return air away from the cooling (dehumidification) coil. This control and operational strategy’s objective is maintaining a comfortable 45 to 55 per cent RH, not an uncomfortable 10, 20, or 30 per cent RH, which can happen when too much moisture is removed. There are many air balancing adjustments that were most likely part of the facility’s post-construction commissioning process. Sometimes, local HVAC service contractors close or improperly adjust these balancing dampers because they are inexperienced with dehumidifiers.
Keeping the coils and filters clean is important as well. If they become dirty, it affects the static pressure of the system, which results in restricted airflow. In this case, outdoor air dampers can be mistakenly adjusted, whereby opening them more to increase the airflow; however, this increases energy costs. Further, when filters are replaced, or coils are eventually cleaned, the additional airflow created by the previously opened dampers can adversely affect the space’s set point temperature and RH.
The dehumidifier’s free pool water heating system (if it is part of the dehumidifier design) is another common service call. In many cases, it is inadvertently turned off during the filter backwash process by facility maintenance staff or service contractors who then forget to turn it back on. An air pocket that develops in the piping can be another common occurrence. Should this happen, the pump will lose water pressure (i.e. prime). When the low water flow alarm is ignored, sometimes due to excessive alarm incidents, the system automatically switches to the backup conventional pool heater (which is not free), resulting in an energy bill shock that could go unnoticed for months.
When a local contractor services a commercial dehumidifier, aquatic facility managers should check to see if the following components have been itemized and inspected for functionality on the invoice.
Other problems such as heat rejection can result from the aforementioned differences between air conditioners and dehumidifiers. While air conditioning equipment typically only rejects heat to one source, such as an outdoor condenser, dehumidifiers can reject heat in multiple ways. Instead of wastefully dumping the heat outside, dehumidifiers can divert waste heat from compressors to warm the water, preheat outdoor air, or even reheat the air downstream from the cooling coil by using a heat exchanger. In the latter instance, the cooling coil’s temperature (between 7.2 and 10 C [45 and 50 F]) condenses moisture out of the air. Distributing air at this temperature into the pool environment would make wet bathers extremely uncomfortable. Therefore, it is mixed with return air in an efficient method, reheating the natatorium’s supply air to a comfortable 27.7 C (82 F), or any temperature specified by the facility’s design. Outdoor air can also be preheated using return air in a heat exchange process, right before it is exhausted.
|Top six maintenance items on a routine dehumidifier service call|
|When a local contractor services a commercial dehumidifier, aquatic facility managers should check to see if the following components have been itemized and inspected for functionality on the invoice.
Since local contractors may not have the necessary experience to maintain a dehumidifier, many manufacturers offer different tiers of factory service, such as a quarterly equipment checkup and air filter replacement, which can also be combined with a full annual inspection. In the first option, a local contractor would facilitate filter replacement, which is a common practice for all types of HVAC equipment. However, during the maintenance call, factory service technicians can access the unit remotely (if it is equipped with a web browser-based access system) and guide the contractor via telephone to perform a technical operations checkup. The contractor would also photograph each dehumidifier compartment for historical reference, which the manufacturer keeps on file. Pictorial and historical references help future troubleshooting. If an issue beyond the contractor’s routine capabilities is detected, a regional factory representative can perform an on-site visit to fix the problem.
The web browser-based communications feature, which is now available on many dehumidification system brands, emphasizes the importance of never disconnecting the unit from the Internet. Doing so severs the line of communication, alarms, and notifications between the unit and the factory, which will ultimately impede the troubleshooting process when service is required.
Before calling a service company when environmental conditions appear to be degrading, the facility manager should review what the temperature set points are for the pool water and interior space, along with the RH for which the natatorium was designed. The design engineer, mechanical contractor, or dehumidifier manufacturer should have the data if it is missing on site. Adjusting water or interior temperatures away from the designed set points of the facility, even by a degree or two, can skew the conditions of the indoor environment. Further, activities performed in the facility, which may not have been considered in the original design, such as senior swims with warmer water, or large spectator-attended swim meets, can also alter the indoor conditions.
|Top three signs of a malfunctioning dehumidifier|
Like any mechanical equipment, dehumidifiers have a life expectancy that can range between 10 and 20 years, possibly even longer depending on the periodic maintenance it has received and how well the pool’s water chemistry has been maintained (balanced). Sometimes it is more economical to replace an older dehumidifier, especially if it continually requires extensive maintenance.
Ongoing refrigerant leaks and repairs are probably the most common reason for replacement. Refrigerant leaks are infrequent for systems that are properly maintained and operated. However, leaks are not impossible and they may occur over the lifetime of the equipment. More importantly, if leaks are frequent, they should be meticulously recorded. Multiple leaks that occur in the same year could indicate the end of the system’s lifecycle and the need for a major renovation.
Another reason for replacement is R-22 refrigerant, which was commonly used by manufacturers from 1980 until 2010. This refrigerant (R-22) is a hydrochlorofluorocarbon (HCFC), which was banned internationally from manufactured units in 2010. Due to the refrigerant’s ozone-depleting potential, it will be phased out completely by 2020. The refrigerant has steadily risen to unaffordable prices due to a continuing demand and a dwindling supply. An R-22-based dehumidifier, which can potentially contain hundreds of pounds of refrigerant, would incur a devastating replacement and repair costs in the tens of thousands of dollars.
Instead of risking a budget-busting repair and other liabilities associated with refrigerants, it is better to replace the dehumidifier with a unit using a reduced amount of refrigerant. Like most mechanical dehumidifiers, these units still have a refrigeration circuit for condensing moisture out of the return air stream; however, for heat rejection, they use propylene glycol, which is environmentally friendly and can reduce the volume of refrigerant to a small fraction of what a conventional dehumidifier uses. A propylene glycol leak is unlikely to happen, but should one occur, it is less costly to repair and has low impact to the environment.
A dehumidifier may work perfectly fine, but the natatorium environment can still be uncomfortable due to reasons beyond the mechanical equipment. A natatorium is a unique synergy of building envelope (design, construction, and materials), air distribution, mechanical HVAC equipment, and water chemistry. Any dysfunction of one or more of these elements will result in an uncomfortable and energy-inefficient environment.
The key to good aquatic facility management is to know the functions and set points the system was designed for, review the total operation periodically, and maintain a close relationship with the manufacturer and its authorized service technicians.
Eric Cournoyer, P.Eng., is the service manager for Dehumidified Air Services (DASV) in Montreal, a newly created service division of Dehumidified Air Solutions (DAS), which services North America’s three largest dehumidifier brands, Dectron, PoolPak, and Seresco. Cournoyer has a chemical engineering degree from the University of Ottawa and is a former director of engineering for HVAC air purification manufacturer, Circul-Aire, Montreal. Most recently, he served as process engineer at GEA Barr-Rosin in Boisbriand, Que. Cournoyer can be reached via e-mail at firstname.lastname@example.org.
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