Reduce Your Pool's Energy Footprint
By Randy Mendioroz
First, the bad news: The annual operating cost for a typical outdoor 25 yard by 50 meter pool, including water, power, heating and pool chemicals, is about $307,538 per year. The largest expense is natural gas at $216,972 (71 percent of total cost). Electricity is next at $43,275 (14 percent), followed by pool chemicals at $31,698 (10 percent), and finally, water and sewer at $15,592 (5 percent).
In just the past few years in California, the cost of natural gas has risen from an average of $0.55 to more than $1 per therm, and the cost of electricity has jumped from $0.10 to up to $0.15 per kilowatt hour. For the sample outdoor 50 meter pool, that's an operating cost increase of more than $123,000 annually.
Now, the good news: There are good basic pool design strategies and cutting-edge energy alternatives that can maximize operating efficiency when planning a new aquatic facility or renovating an existing facility.
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. One more benefit to low-RPM pump motors: The longevity is at least twice that of their harder-working counterparts.
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 in practical terms is that when conditions are optimum, the circulation pump is oversized for the actual operating condition. In some cases, the health regulations mandate sizing of a 20-horsepower pump, when the actual operating 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 an accurate digital flow meter with output to the VFD, the operator can set the desired flow rate (as required by code) with the VFD software. The VFD will then adjust the horsepower output to meet actual operating conditions. VFD packages in the 10-to-20-horsepower range cost approximately $7,500 to $10,000 and can deliver 30 to 40 percent savings on electricity, producing a return on investment ranging from six to 12 months.
Every time a filtration system backwashes, money is lost not only in the water that goes down the drain, but the cost to heat and chemically treat that water. By specifying filtration systems with automated microprocessor control, the systems can be programmed to backwash only when necessary, thereby reducing water consumption, which results in cost savings for natural gas and chemicals.
In years past, pool heaters have been less than stellar when it comes to energy efficiency. However, since the pool water is heated directly within the heater, pool heaters can be more efficient than traditional condensing boilers or heat exchangers connected to a central boiler plant. 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 $3.50 per square foot of water surface area, thermal blankets can pay for themselves in six to 12 months.