December 1, 2010
By Christopher Chivetta
Energy-saving initiatives are at the centre of many of the decisions indoor pool owners and operators must make every day. As energy costs continue to rise, manufacturers and suppliers are marketing a wide variety of environmentally friendly products and services. With so many options available, operators can find it difficult to choose an appropriate strategy.
First and foremost, it is important for an operator to understand where his or her energy dollars are spent when it comes to indoor pool maintenance. According to a previous U.S. Department of Energy program called ‘Reduce Swimming Pool Energy Costs’ (RSPEC), indoor pools can be one of the largest energy users per square foot. RSPEC’s analysis, while several years old, still correctly identifies the major energy uses of indoor pools. Evaporation is, by far, the largest energy user, accounting for 70 per cent of the total energy load. This energy use derives primarily from the tremendous amount of heat, or energy, used during the phase when the pool water changes from a liquid to a vapour. Ventilation systems, which maintain comfortable indoor conditions for pool patrons, are the second largest energy drain, accounting for approximately 27 per cent of energy use. The remaining three per cent originates from pool circulation systems, pumps, filtration needs and auxiliary devices.
To control energy consumption in the evaporation load, it is necessary to understand the important relationship between water and air temperatures. The National Swimming Pool Foundation (NSPF) recommends pool water temperature for active swimming should range from 78 to 80 F (25 to 27 C). For general use, a water temperature ranging from 82 to 84 F (28 to 29 C) is ideal. To maintain a comfortable participant environment while keeping the evaporation rate low, the air temperature of the facility should be two to five degrees warmer than the water temperature. In addition, the relative humidity of the space should be between 40 and 60 per cent.
When designing a new facility or replacing an existing heating, ventilation or dehumidification system, it is important to determine the appropriate water and air temperature relationships, as well as the relative humidity level, to achieve ideal evaporation. A system designed for a lower water temperature will not be able to maintain adequate indoor conditions, causing it to be more costly to operate and leading to potentially poor indoor air quality (IAQ). For each two-degree rise in water temperature, the heating, ventilating and air conditioning (HVAC) system’s required capacity increases seven per cent. Similarly, a mere 10 per cent change in the relative humidity increases system demand by more than 30 per cent. For these reasons, a system designed to meet specific pool water temperature needs will operate more efficiently, while providing a safe, healthy indoor pool environment.
Another way to reduce evaporation rates is by installing a pool cover. Covers provide a barrier to reduce evaporation from the pool surface, reducing heat loss within the pool. However, while covers reduce the evaporation rate from the pool surface, they may not reduce the evaporation rate from the entire pool space. It is important to understand evaporation occurs regardless of water depth. Puddles of water that accumulate on the pool deck, play surfaces, starting blocks, diving boards or on top of the pool cover continue to evaporate and cause energy loss. When using a pool cover, operators must be careful not to submerge it or allow water to collect on top of it, as even this standing water can dramatically reduce the cover’s effectiveness.
The evaporation load is directly proportional to the amount of energy consumed. For every pound of water evaporated, the facility loses energy, a loss that adds directly to operating costs. When pool water and air temperature are lowered, evaporation load lowers. Raising the relative humidity of the space to 60 per cent also reduces the evaporation load. The use of a pool cover reduces the base evaporation rate from the pool. By maintaining temperatures, controlling the relative humidity and using a pool cover, an operator can achieve an optimized evaporation energy load.
An indoor pool’s second-largest energy user is ventilation equipment. Power use can, however, be reduced, primarily by using a dehumidification unit to condition and control the pool space. These units are designed using a specialized refrigeration cycle that switches between heating and air conditioning modes based on outdoor conditions. In addition, these units can use exhaust air to pre-heat or pre-cool outside ventilation air. The dehumidification cycle may also redirect heat from the compressor to heat pool make-up water, re-circulated pool water and domestic water. These systems are complex, but a basic understanding of the energy conservation features can be used for maximum benefit.
One recent industry trend to maximize efficiency is to incorporate a geothermal system, which transfers heat from the ground into the dehumidification system. According to a recent project at Morehead State University in Morehead, Ken., use of geothermal systems save on both initial installation and long-term operating costs. However, this option should only be considered in geographic locations with the ability to accommodate a geothermal well field.
Another efficiency maximization technique is temperature and humidity control at night or during unoccupied times. An operator should consider, for example, using a night setback temperature and relative humidity level, which reduces the evaporation rate and energy load on the ventilation system. The dehumidification unit, however, must remain on at all times to control moisture in the pool space. Turning the system off as an energy-saving solution can have adverse effects. A shut-down system can lead to high temperatures and high relative humidity, which will begin to migrate to other areas of the building and attack its structural system, resulting in significant problems.
Aside from primary control procedures for evaporation and ventilation, other strategies, which focus on pool facility operations, can also reduce energy consumption. These strategies involve auxiliary devices, such as circulation systems, lighting, filters and pool water heating.
The use of variable-speed pumps on circulation systems and play features has increased dramatically in recent years. These pumps can operate at different speeds to deliver water flow according to the operator’s needs. Operating at slower speeds reduces power consumption, energy costs and noise, all while extending the life of the equipment. The pumps are monitored by a variable-frequency drive (VFD), which controls the motor to match flow settings. Flow rates can be adjusted based on use, e.g. daily circulation, backwashing, play features, waterfalls, water slides or lazy rivers, providing flexibility and reducing energy costs. A significant number of pool pump manufacturers are now providing variable-speed pumps in their product lines as standard equipment.
The lighting system provides the atmosphere for recreational or competitive pools. It may be used throughout the day to manage ambient light levels and ensure a safe environment. Replacing existing incandescent lamps with high-efficiency compact fluorescent bulbs can save more than 50 per cent on a facility’s electrical bill. Compact fluorescent lights can last up to four times longer than incandescent bulbs, which also significantly reduces labour costs involved in light replacement. Standard ballasts and lamps can also be replaced with energy-saving electronic ballasts. T-8 or T-12 lamps can also be used to save energy. With indirect lighting systems, it may be cost efficient to replace existing fixtures with high-intensity discharge (HID) lamps to reduce electrical consumption; however, each system should be individually evaluated in order to optimize energy savings.
Pool filters are another source of potential energy savings. Filters can increase operating costs due to the amount of water used to backwash; if this process is better controlled, energy losses are reduced. While some operators backwash filters according to a set schedule, it is best to backwash only when the filter pressure gauge reaches the manufacturer’s recommended level. In addition, waiting to backwash filters for 30 minutes after circulation systems have been shut down gives the sand bed time to settle; settled sand requires half as much water to clean. If the system needs to be replaced altogether, new high-efficiency filter systems are currently on the market. When a facility reduces the amount of water used in the backwashing process, the amount of energy required to heat the make-up water when it circulates back to the pool is also reduced, allowing for greater savings and efficiency.
Heater performance should also be reviewed to determine the costs and benefits of increasing efficiency based on utility costs. For natural gas or propane sources, heaters should have efficiency ratings of at least 95 per cent. Electric heaters should have a coefficient of performance (COP) ranging from 6.0 to 8.0. Alternate pool heating systems include solar panels and ground-source heat pumps, which can, in certain cases, be used for pool water heating.
When developing and implementing cost-effective energy-conservation strategies, operators need to focus on the largest energy users first. By understanding the different energy requirements of various systems within the aquatic centre, an operator can easily optimize savings. Reviewing all aspects of an indoor pool’s operation determines if replacement of existing equipment will have long-term paybacks and benefits. For new construction, advances in current technology are available to reduce energy consumption from day one. Energy costs are predicted to rise in future years, making it crucial for operators to understand a facility’s current energy use and implement strategies today to reduce future demand.
Christopher Chivetta is president of Hastings & Chivetta Architects Inc. He can be reached via e-mail at email@example.com.
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