Weighing The Options
The annual operating cost for a typical outdoor 25-meter x 50-meter pool--including water, power, heating and pool chemicals--is about $256,000. The largest expense is natural gas at $184,400 (72 percent of total cost). Electricity is next at $40,800 (16 percent), followed by pool chemicals at $20,900 (8 percent), and finally, water usage at $9,400 (4 percent).
In just the past few years in California, the cost of natural gas has risen from an average of $0.55 per therm to almost $0.85 per therm, and the cost of electricity has jumped from $0.10 per kilowatt (kW) hour to nearly $0.15 per kW. For the sample outdoor 50-meter pool, that’s an operating cost increase of over $75,000 annually.
There is good news, however. There are basic pool-design strategies and cutting-edge energy alternatives that can maximize operating efficiency when planning a new aquatic facility, or renovating an existing one.
Starting with design, it is important to explore all options.
A cheaper, readily available, self-priming pump may operate at only 55- to 60-percent motor efficiency because it spins at a relatively high 3,450 rpm. One of the goals of energy-efficient design is to select pumps with a minimum 75-percent motor efficiency. These typically cost more and require installation at an elevation below the static water level of the pool, but a lower rpm pump motor (1,750 or 1,150 rpm) can yield up to 85-percent motor efficiency. Another benefit to low rpm pump motors is longevity, at least twice that of their harder-working counterparts.
Variable Frequency Drives
The use of variable frequency drives, or VFDs, can provide significant reductions in electrical energy use associated with electric motors operating over extended time periods. For example, in many jurisdictions, state and local health departments may mandate the sizing of pool circulation pumps for the worst possible condition. What this means is when conditions are optimal, the circulation pump is oversized for the actual design condition. In some cases, the health regulations mandate sizing of a 20-horsepower pump, when the actual design condition for 95 percent of the operating hours would only require a 15-horsepower pump.
By connecting a VFD package to the pump motor and providing a highly accurate digital flow meter with input to the VFD, the operator can set the required flow rate. Given a clean and empty pump strainer and filter, the motor can deliver the required flow rate more efficiently, and “dial down” the horsepower output to meet actual conditions. VFD packages in the 10- to 20-horsepower range cost approximately $3,000 to $5,000 and can deliver 30- to 50-percent savings on electricity.
Each time a filtration system backwashes, money is lost, not only in the water that goes down the drain, but in the cost to heat and chemically treat that same water. By specifying filtration systems with automated microprocessor control, the systems can be programmed to backwash only when necessary; for example, only when the influent (water within the filtration system) pressure is 10 psi greater than the effluent (water outside the filtration system) pressure.
Pool heaters--although similar to traditional water heating boilers--historically have been less than stellar when it comes to energy efficiency. However, since the pool water is heated directly within the heater, they can be more efficient than traditional plate and frame or tube and shell heat exchangers connected to a central boiler plant. Within the past five to 10 years, pool-heater manufacturers have greatly improved the efficiencies of their products. Pool heaters that are up to 89 percent thermal-efficient are commonly available, and careful attention should be paid to the type of pool heater being proposed by the consultant or contractor.
Studies reveal up to 40-percent savings in natural gas costs for operators that are dutiful in replacing pool blankets every evening--even indoors. At an average cost of $2.50 per square foot of water-surface area, thermal blankets can pay for themselves in six to 12 months.
In addition to design, alternative energy sources should be explored.
Passive Thermal Solar
Passive thermal solar systems produce no air emissions, and installations typically utilize the existing circulation pump to discharge water through a series of solar collectors, where a transfer of heat from the sun to the pool water occurs. Downstream of the pool filtration system, a bypass piping system routes the water into solar collectors. If the solar system provides the necessary set-point water temperature, the heater is not activated, thus reducing run time and cost for natural gas.
Non-metallic (polypropylene or EPDM) solar panels are preferred and are less expensive than the copper and glazed variety. Installation costs for this type of passive solar system (assuming suitable mounting space with proper solar orientation) run approximately $12 to $18 per square foot of solar panel. The amount of solar panel required varies by region, but an average of 80 percent of water-surface area is common. With a potential annual operating cost savings of $50,000 to $75,000 (for a 50-meter pool), and an expected full return on investment within four to six years, passive solar systems are highly attractive.
Co-Generation With Micro Turbines
Co-generation implies multiple sources of energy from a single device. For gas-powered micro turbines, recoverable electricity and heat are produced.
Gas-powered micro turbines range from 25 kW-500 kW (based upon anticipated demand). These units produce substantially greater electricity than heat. Sizing for electrical demand means that net-metering (excess generated electrical power sold back to the utility) is usually not feasible unless a renewable energy source, such as landfill or biogas, is utilized. Where heat recovery is used, these systems can be 85 percent efficient, with costs $0.005-$0.016 per kW, and maintenance intervals of 5,000 to 8,000 hours.
These systems also enjoy low NOx emissions (
Co-Generation With Fuel Cells
With co-generation's use of fuel-cell technology, electricity is generated and heat is recovered. These systems use natural gas for fuel, which is reformed into a steady stream of input hydrogen. Fuel cells are reliable, quiet and virtually pollution free. Economic advantages depend on utility rates, possible rebates and incentives.
Capital costs remain high: $1.1 to $1.2 million for systems of 200 to 250 kW power output, with payback within eight to 12 years.
Photovoltaic Electricity Generation
Photovoltaic (PV) systems convert sunlight into electricity, but no heat is generated in the process. They are simple, reliable, quiet and nonpolluting, with no moving parts.
Capital costs average $7 to $10/watt for standard, flat-mounted roof systems, which can add up to $250,000 for a 50-kW PV system--assuming rebates and incentives. Payback can be up to 40 years. Because natural gas is the largest utility cost, PV systems are less desirable than other efficiencies.
Fluctuating costs will require either scaled-back operations or adoption of energy-efficient pool-design strategies. Pool operators should embrace these technologies, recognizing that while initial capital costs may be high, the technologies can provide a worthwhile return on investment.
Randy Mendioroz is a Principal with Aquatic Design Group, a Carlsbad, Calif., consulting firm that specializes in the programming, planning, design and engineering of competitive, recreation and leisure-based aquatic facilities.