March 1, 2011
By James Hogan
Indoor pools have always been more expensive to operate than other comparably sized buildings, because the heating, ventilating and air conditioning (HVAC) system must run continuously to control humidity and protect the building. However, technological advancements, such as new energy-efficient equipment and add-ons for existing indoor pool HVAC units, offer aquatic facility operators the potential to significantly reduce monthly operating costs.
Probably the most important technological energy-saving innovation to emerge for indoor swimming pool facilities was the mechanical dehumidifier, which hit the market in the 1970s. Previously, natatoriums attempted to control relative humidity (RH) with either conventional air-conditioning or supply/exhaust systems, or a combination of both.
Conventional air conditioning is not designed for, and therefore can not handle, the tremendous humidity loads of natatoriums. However, the technology did help somewhat prior to the development of the modern commercial dehumidifier. Another approach is the use of 100 per cent outdoor air to remove humidity. Since it takes a significant amount of energy to heat and cool that much air, this method is quite costly.
The development of the modern dehumidifier changed energy costs drastically. Instead of being exhausted, a large percentage of air is re-circulated through the dehumidifier’s refrigeration process to condense the moisture and return a drier 50-per cent RH air to the space. The heat reclaimed from the refrigeration process is used to provide free pool water heating and/or to heat the space as needed.
Over the last 30 years, mechanical dehumidification has become the HVAC system of choice for the majority of new and retrofitted natatoriums. However, there are still many remaining natatoriums that have not switched to modern dehumidification. That, combined with the fact the last decade has seen many technological innovations in energy-saving add-on equipment for new and existing dehumidifiers, offers many opportunities for natatorium owners to improve operational costs and lower energy use.
Natatoriums are significantly more complex for engineers to design efficiently compared to comparable structures, such as gymnasiums. Constant changes in localized air buoyancy present a challenge in temperature and humidity prediction. Designing an HVAC system with rule-of-thumb practices may be sufficient for conventional buildings, but may fail to meet a natatorium’s unique challenges.
Five years ago, natatorium engineers were presented with a new design tool called computation fluid dynamics (CFD), which accurately simulates air flow, temperature and relative humidity through computer modelling.
This tool is invaluable for both new construction and retrofits. Engineers use CFD to confirm airflow calculations are correct, so that any repositioning of grilles and diffusers are first tried virtually, before physical construction is completed. This allows an early confirmation of design and assurance of suitable indoor air quality (IAQ).
Besides IAQ, a CFD analysis also improves energy savings because the facility is more efficient. Therefore, CFD analyses can lead to a building’s Leadership in Energy & Efficiency Design (LEED) credits from the U.S. Green Building Council (USGBC), Washington, D.C. (For more on LEED credits, see pg. 60.)
Another common natatorium concern is the accumulation of chloramines, which are inorganic compounds that produce strong odours and can cause skin, eye and respiratory issues among bathers. Some aquatic facility operators attempt to remedy this problem by inefficiently exceeding the outdoor air levels recommended by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE).
An example of a better way to handle this issue can be found at the Nottawasaga Inn Resort, in Alliston, Ont., where chloramines built up on days with high bather loads (Pool & Spa Marketing, October 2009). During the replacement of the facility’s 20-year-old dehumidifier, the owners originally considered introducing more outdoor air, which would decrease energy efficiency and require expensive ductwork additions. Instead, operators chose a gas-phase air purification filter option for the dehumidifier, which serves as a good second line of defence against pool area odours.
In a gas-phase filter, room air is drawn through a sorptive/reactive filter material that removes gaseous contaminants such as chloramines, which pass freely through other filters. The filter media can be tested periodically for efficacy and is easily replaced when necessary.
By code, commercial natatoriums are required to bring in a certain amount of outdoor air to maintain healthy IAQ levels. Consequently, air must be exhausted to allow space for incoming air; in a natatorium environment, exhausting 27 to 30 C (80 to 86 F) air is wasteful. However, recent heat-recovery coil innovations allow for the transfer of both sensible and latent heat from the exhaust air to the incoming outdoor air. For example, on a cool Canadian day with an outdoor temperature of –12 C (10 F), outdoor air can be preheated by about 30 C before using expensive purchased energy to heat the facility to the desired 27 to 30 C range. This method can save more than C$6,000 in annual energy costs in an average-sized community centre pool.
The amount of outdoor air introduced to a facility can also be controlled by carbon dioxide (CO2) and/or air flow monitoring. For infrequent large crowds, such as those assembling at a swim meet, more outdoor air should be used to rid the space of CO2 accumulations associated with human exhalation. However, bringing in the same amounts of outdoor air during idle or limited use periods is wasteful. Therefore, CO2 monitors can determine the amount of outdoor air required to maintain healthy IAQ levels.
Another energy-efficiency choice that relates to outdoor air is whether to use an economizer. This device inhibits refrigeration and introduces 100 per cent outdoor air to an aquatic facility when outdoor ambient conditions are suitable for dehumidification and/or cooling. Use of this device is an economic consideration, since the decrease in space cooling and dehumidification costs must be compared to increases in heating costs. However, for certain projects, economizers can produce a quick payback.
Econo-purges are a variation on the economizer. Dehumidifier purge mode is popular for evacuating indoor air in 10 minutes during super-chlorination periods, when chemical odours can become overwhelming. Besides purging, this feature also makes an excellent economizer when incorporated into the dehumidifier, with an even better payback than normal economizers.
New technology in blowers and motors can also save energy and deliver short paybacks. Direct-drive blowers save energy compared to belt-drive blowers. Induction motors can easily be equipped with variable-speed drives, which can reduce energy usage when airflow demands increase. Energy-saving, electronically commutated (EC) motors can also be retrofitted into existing dehumidifiers. Both direct-drive blowers and EC motors offer both energy and maintenance savings.
An existing dehumidifier manufactured before 2005 is probably using R-22, which was declared to be an ozone-depleting refrigerant along with other hydrochlorofluorocarbons (HCFCs) and chlorofluorocarbons (CFCs) under the Montreal Protocol. Manufacturing of new equipment using R-22 ended on Dec. 31, 2009. Refrigerants allowed under the Montreal Protocol, such as R-407C and R-410A are available for new units.
Depending on use and temperature, a medium-sized commercial indoor swimming pool can evaporate 91 to 181 kg (200 to 400 lbs) of water per hour, which, over the course of one year, can amount to an entire pool fill. Dehumidifiers with water reclamation capabilities can return the water they condense out of the air stream to the pool. In some jurisdictions, where pool water reclamation is prohibited due to sanitation concerns, additional water sanitation devices, such as ultraviolet (UV) sanitizers, may be used. Otherwise, the water can be used for landscape irrigation, rather than drained into the municipal water treatment system. Consult local authorities to determine the best method for a given area.
A great source of energy savings is a properly programmed electronic dehumidifier controller. Indoor temperature, relative humidity and other variables are continually monitored and managed, and data can be communicated to most building management systems. In most cases, these systems should monitor, but not control, dehumidifiers. Not all dehumidifiers have on-board controllers, but retrofits are possible in most cases.
Energy usage can be reduced in nearly any indoor pool by upgrading or replacing its HVAC equipment. Hiring an energy consultant or a dehumidifier manufacturer for an energy audit is the first step toward saving energy with today’s modern equipment. Paybacks can be realized in as little as one year, which means the investment is paid for and reducing facility operational costs for the remaining lifecycle of the equipment.
|LOOKING FOR LEED CREDITS?|
|New dehumidifiers can also help accumulate credits when applying for Leadership in Energy & Environmental Design (LEED) certification. Several dehumidifier functions qualify for LEED credits:
Air is cooled to dehumidify it. Sensible heat in the room air is recycled from the cooling coil to the reheat coil. At times, sensible heat equal to the latent heat can also be delivered to the reheat coil.
Almost all of the heat lost from the average indoor swimming pool is through latent heat evaporation. This heat must be removed from the air in order to dehumidify it, and that heat can be returned to the pool water via the dehumidification process.
Optional domestic water pre-heaters are available to use as much of the remaining heat as possible.
James Hogan is product development engineer at indoor air quality equipment manufacturer, Dectron Internationale, (www.dectron.com), based in Roswell, Ga. In his 13 years at Dectron, Hogan has advised hundreds of natatorium building owners about IAQ and energy problems. He can be reached at (800) 676-2566.
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