Updating natatoriums for maximum occupant comfort

by jason_cramp | September 28, 2017 3:59 pm

By Ralph Kittler, P.Eng.

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The knowledge of what natatoriums require for a successful design has been upgraded dramatically in the last quarter century. Recent technological advancements and state-of-the-art engineering standards have not only made these improvements possible, but have also made significant improvements in indoor pools for spectators and swimmers.

In fact, managers of older community, high school, and private health club pools should review their facilities for energy-efficiency and environmental stewardship, as well as for optimized air distribution, to improve indoor air quality and comfort.

A case in point is the Forest Hills Public Schools Community and Aquatic Center (CAC) in Grand Rapids, Mich. Built more than 25 years ago, the CAC, a 111.5-m² (12,000-sf) natatorium, needed two aging 24-ton dehumidifiers replaced. Rather than performing a drop-in replacement, the school district saw a building and equipment retrofit opportunity to upgrade the natatorium’s indoor air quality (IAQ), while also reducing future operational costs with state-of-the-art heating, ventilation, and air conditioning (HVAC) equipment.

“The difference in air comfort and quality for spectators, not to mention the swimmers after the retrofit has been incredible,” said Kelly Swieter, CPO, aquatic supervisor, Forest Hills Public Schools.

Modernizing the facility

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The design team first looked at upgrade possibilities for the 300-seat, 223-m² (2400-sf) spectator area. One unique HVAC challenge a natatorium presents versus more conventional spaces is some occupants are wet and are wearing only swimsuits, while others—especially during competitive events—are fully clothed spectators. This presents an air comfort challenge, especially because the ideal air temperature range for swimmers is approximately 26 to 27 C (80 to 82 F). The ideal spectator temperatures, however, are considerably lower.

Three design methods were available to accommodate this challenge:

1. Provide swimmers and spectators the same air temperature from the same HVAC system;
2. Use two separate HVAC systems to supply each respective section its most ideal temperature;
3. Use separate HVAC systems that provide two supply air temperatures, and cordon off the spectator section from the pool area with glass.

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The first method is the least expensive, most commonly used 25 years ago, and the system originally used at the CAC. The third method is the least desirable, because in the process of separating the two environments, it also mutes the spectators from a swim meet’s exciting atmosphere. Therefore, the CAC design team selected the second option.

The facility’s original mechanical room location, under the spectator area, housed the two HVAC units that performed the dehumidification, cooling, and heating for the entire natatorium. Already crowded with pool equipment, there was not enough space to install two new systems to control two separate indoor environments. Instead, the design team used the original mechanical room to install the unit that would manage the spectator area, and built a new, ground-level mechanical room to house the system for the pool area.

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Pre-existing mechanical rooms in older aquatic facilities pose a series of challenges for any HVAC replacement team—specifically in terms of access. Indoor pool dehumidifiers are typically very large and, circa the ’90s, architects rarely planned for the day the equipment would need to be replaced. Therefore, many mechanical rooms only have single 813-mm (32-in.) wide or double-access pedestrian doors. While old equipment can be disassembled and carried out, older mechanical room door openings cannot accommodate today’s larger dehumidifiers.

This poses several decisions for a design team:

1. Bring in the new system by opening a wall or roof, which could potentially cost tens of thousands, if not hundreds of thousands, in envelope construction.
2. Request the manufacturer to factory-disassemble the unit (after factory assembly and testing) and deliver to the site in multiple sections that fit through pedestrian doors for on-site assembly.
3. Use a variation on the previous example, whereby gutting the old dehumidifier components, but leaving the shell in place, then requiring the new system’s manufacturer to design a new component configuration for assembly into the old shell.
4. Realizing access is problematic in retrofits, some manufacturers have recently designed modular units to fit through standard-sized pedestrian doors for integration into one unit that equals the refrigeration tonnage and cubic feet per minute (CFM) of one large unit.

The CAC design team chose the fourth option for the spectator dehumidifier. The two, 2-m (6.4-ft) long by 1.1-m (3.5-ft) wide by 0.76-m (2.5-ft) four-ton units that were specified were easily dollied through the mechanical room door. Inside, both modular units were integrated in tandem using their factory-aligned connections designed for piggybacking into one small horizontal footprint.

The new system consumes approximately 50 per cent less floor space, making the mechanical room less confined. More importantly, the eight-tons of dehumidifier capacity and revamped spectator section ductwork helped to quadruple the spectator area’s air changes per hour (ACPH) to eight. The additional air changes provide a more comfortable temperature and humidity of 24 C (76 F) and 50 per cent relative humidity (RH), versus the pool area’s 27 C (82 F) and 50 per cent RH.

Further, the modular units have their own compressor, blower, and refrigeration circuit. This configuration allows them to operate in tandem for full capacity situations at swim meets, or as a single-stage unit when few or no spectators are present, which provides significant energy savings for the facility.

Improving air comfort for swimmers

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Typically, natatoriums should operate at four-to-six ACPH; however, the CAC’s original design fell short of this goal. The fewer air changes, and the pool industry’s growing challenge of controlling chloramines for better indoor air quality, prompted the design team to tackle both issues in the retrofit.

To do this, as mentioned previously, the design team built an additional 67-m² (720-sf) mechanical room onto the side of the natatorium. Positioning the equipment at ground level inside a mechanical room, versus a rooftop installation, was more expensive, but less exposed to outdoor elements. A new mechanical room offered an energy-saving climate controlled environment, easier maintenance access—especially during winter conditions—and created an esthetic exterior to the building by concealing the equipment.

The energy-efficient, 32-ton unit dehumidifies the space to 50 per cent RH, uses compressor recovered heat for free 26 C (80 F) pool water heating, cools and heats the space to 27 C (82 F), and uses exhaust air to pre-heat the outdoor ventilation air. In the event of extreme cold weather, the natatorium can tap into the pool’s 995-MBH (thousand [British thermal units (Btus)] per hour) hot water/pool water heat exchanger for additional heating.

As per the aquatic supervisor’s request, the HVAC system now offers staff the ability to customize the environment to match a specific activity. For example, the dehumidifier’s capacity was sized larger by the design team for more demanding swim period humidity loads, such as warmer water and space temperatures for senior swimming, or cooler water and space temperatures during swim meets. Those parameters were unreachable with the original units.

Virtually eliminating chloramines

Today, chloramines and the respiratory irritation (called granulomatous pneumonitis and sometimes referred to as Lifeguard Lung) they inflict on swimmers are challenging the entire indoor pool industry. Chloramines are created from the chemical bonding formation of chlorine molecules and organic contaminates. The bond creates a heavy gas that stratifies, just above the water surface, in the swimmers’ breathing zone, making it difficult to remove even in ideal natatorium ventilation designs.

There are commercial products designed to exhaust chloramines off pool water surfaces, however. In new construction, these systems are integrated into the gutter in the pool wall and connected to an underdeck exhaust duct. In retrofit situations, they are secured to the top of the pool deck and exhausted through a flexible on-deck duct.

Since the CAC was undergoing a high-cost HVAC renovation, the design team innovatively created a dual-purpose 9.1-m (84-ft) concrete bench for swimmers along a wall nearest the pool surface. The bench’s secondary purpose was to draw chloramines from the pool surface through dozens of perforated metal openings located in the face of its masonry infrastructure. The bench’s interior plenum delivers the return air to the new mechanical room’s dehumidifier for heat recovery and exhaust via an underground concrete tunnel built as part of the project.

An additional deterrent to the accumulation of chloramines is an ultraviolet (UV) water sanitation system. When combined with the ventilation ductwork redesign, the bench and the UV system have eliminated almost all traces of chloramines in the pool area.

Ventilation redesign

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The design team replaced the existing perimeter duct system with a new, larger diameter spiral-round metal duct system. The new 1.8-m (6-ft) diameter main perimeter supply ductwork was the largest possible size for fitting through ceiling joists. This ductwork helped double the air change rate (ACH) in the room to four per hour, which complies with the four-to-six ACPH recommendations for natatorium design by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE).

Besides facilitating more air changes, the larger ductwork and additional CFMs from the new dehumidifier greatly increased much needed airflow to all areas of the facility, right down to the breathing zone of swimmers.

Another improvement was revamping the return air system to minimize air stratification at the ceiling level. The natatorium’s original two-return air duct openings were located high on the back wall of the spectator area as a value engineered measure, because the short proximity to the original mechanical room dehumidifier below required minimal ductwork and installation labour.

Consequently, the positioning of these returns drew 27 C (82 F), chemical-laden air through the spectator breathing zone. It also created air stratification throughout the pool area and, as a result, the potential for poor IAQ during high occupancy swim competitions.

This problem was resolved in the retrofit by positioning high and low return air vents in the pool area, with a 40/60 airflow ratio, respectively. The high vents are mounted in the ceiling duct located 3 m (10 ft) above the west end of the pool and another position located 9 m (30 ft) above the southwest end of the pool. The aforementioned swimmer’s bench also contributes to the increased return air design.

Energy savings and protecting the environment

Besides temperature and RH tolerances, the new dehumidifier illustrates the technological advances of the HVAC industry. It uses energy-efficient electronically commutated (EC) motors and direct-drive fans, which are approximately 15 per cent more efficient than the belt-driven fans the previous system used.

Another advantage with respect to energy-efficiency is its ability to preheat outdoor air, virtually for free, up to 10 to 15 C (50 to 60 F) using heat recovered from the return air before it is exhausted. Avoiding the need to use utility energy to heat the air—especially during the winter in subfreezing temperatures—saves the facility thousands of dollars annually in energy costs.

Perhaps the greatest technological difference between the new and old systems is the use of glycol as a substitute for refrigerants. The original HVAC equipment used approximately 227 kg (500 lbs) of refrigerant for their dehumidification/cooling circuit and heat rejection to an outdoor condenser. Refrigeration coils and soldered copper joints typically leak at least once, if not multiple times over the life of a system. Leaked refrigerant ends up in the atmosphere. The new system uses 80 per cent less refrigerant and glycol for heat rejection. Glycol is an environmentally safer liquid, and should a leak ever occur, there is no ecological damage.

That said, the CAC has reduced its liability and dependability on refrigerants, such as R-22, a hydrochlorofluorocarbon (HCFC), which is regulated by two international agreements; the Montreal Protocol and the Kyoto Protocol. In fact, this refrigerant has been banned for manufacturing in the United States after 2020,[7] and 2030 in Canada[8].

Further, the new system’s internal dehumidification refrigeration circuit is factory-sealed and tested, which eliminates the expense of on-site refrigerant-certified installers, in addition to oil migration issues.

Improving spectator comfort with a dedicated system

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The units used for the spectator section and main pool area have an onboard microprocessor and a web-based monitoring software program that allows authorized users to monitor more than 60 operating parameters via a smartphone or personal computer. Alarms are also sent if there is a malfunction.

Factory technicians can also troubleshoot performance challenges and recorded historical operating conditions via the Internet to help assist local HVAC service contractors. The facility’s building management system (BMS) also monitors the natatorium conditions.

While the previous dehumidifiers could have operated inefficiently for months between semi-annual service calls, the new systems will signal an operating problem to authorized users within seconds, which the factory can sometimes adjusted online.

Today, natatorium managers must face the fact that older HVAC equipment will eventually need to be replaced with newer systems that meet current design standards. The trade-offs must be weighed; however, the technological advancements of a new dehumidification—along with their short payback period as a result of energy savings—almost always outweigh the liability of maintaining outdated, less efficient equipment.

[10]Ralph 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.[11], an Ottawa-based manufacturer of natatorium dehumidifiers. He has 27 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 has produced a professional development hour (PDH) video (see www.serescodehumidifiers.com[12]), which targets the continuing education requirements for engineers. It also serves as a primer for facility managers interested in indoor pool design and operation basics. He can be reached via e-mail at ralphkittler@serescodehumidifiers.com[13].

Source URL: https://www.poolspamarketing.com/trade/updating-natatoriums-maximum-occupant-comfort/

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