On practically a daily basis during summer 2003, major newspapers in California carried articles citing closures of public swimming pools due to an inability to afford the utility costs, or justify keeping pools open.
Prospects for lower energy costs seem dim. A review of natural gas costs from 1994 to 2008 indicates the trend lines are headed in the wrong direction.
Commercial aquatic designers and builders must look for ways to reduce energy costs, or this industry in general (and our livelihoods in particular) are in serious trouble.
For example, in the past few years, natural gas in California has risen from a statewide average of 55 cents per therm to just over $1 per therm; electricity has jumped from 10 cents per kilowatt hour to nearly 15 cents per kilowatt hour. Annual utility costs for an outdoor 25-yard-by-50-meter pool in today’s dollars run approximately $270,000, and break down as follows:
- Natural gas, 68 percent ($184,426)
- Electricity, 15 percent ($40,802)
- Pool chemicals, 11 percent ($29,887)
- Water, 4 percent ($9,682)
- Sewer, 2 percent ($5,271)
What can you do when planning a new facility, or renovating an existing one, to ensure that you are not driving the aquatics-facility equivalent of a Hummer? The good news is that a number of basic, energy-efficient design strategies can be employed without resorting to exotic schemes. These include:
At times, consultants and contractors select pumps based on initial cost and availability. For example, a relatively inexpensive, readily available self-priming pump may operate at 55- to 60 percent motor efficiency. This is because the pump motor spins at 3,450 revolutions per minute. Energy-efficient designers select pumps with a minimum 75 percent motor efficiency. Pumps with these types of motor efficiencies will cost more initially, and require installation at an elevation below the static water level. However, if a lower-rpm pump motor (in the range of 1,150- to 1,750 rpm) is selected, one can achieve up to 85 percent efficiency.
In nearly every case, careful selection of pumps can provide significant operational savings. (Recently we estimated one project owner would save approximately $22,000 per year in electricity with lower-rpm motors). An additional benefit is that the longevity of the motors is two to three times that of their harder-working self-priming counterparts.
Automated Filtration Systems
Every 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 lost water. Many filtration systems incorporate manual backwash, in which the operator backwashes on a regular maintenance schedule whether needed or not. Filtration systems utilizing microprocessor-controlled backwash allow backwash only when necessary, thereby saving water, heating and chemical treatment costs.
High Thermal Efficiency Pool Heater
Pool heaters, while similar to traditional water-heating boilers, historically have been less than stellar when it comes to energy efficiency. However, because water is heated directly within the heaters, they are capable of being more efficient than traditional plate-and-frame or tube-and-shell heat exchangers connected to central boiler plants.
Within recent years, pool heater manufacturers have greatly improved performance. Heaters with thermal efficiencies ranging from 89- to 95 percent now are commonly available.
Thermal Pool Blankets
While operators may complain about the labor it takes to remove and replace covers each day, you save more utilizing a well-insulated set of thermal blankets on a pool — even indoors — than just about anything else. Studies of outdoor pools have shown up to a 40 percent savings in natural gas costs for operators who dutifully apply blankets every night. At an average capital cost of $2.50 per square foot of water surface area, blankets can pay for themselves in six to 12 months.
Variable Frequency Drives
Use of these drives can provide significant reductions in electrical energy use. For example, in many jurisdictions, state and local health departments mandate the sizing of pool circulation pumps for the worst possible condition (that is, a dirty filter and a pump strainer full of debris). What this means in practical terms is that when conditions are optimal, the circulation pump is oversized for the actual design condition. In some cases, health regulations mandate sizing of a 20hp pump when the actual design condition for 95 percent of the operating hours would only require a 15hp pump.
By connecting a VFD package to the pump motor and providing a highly accurate digital flow meter with input back to the VFD, operators can set the flow rate (as required by the health department), and the VFD controls the voltage to the pump motor based on the actual design condition.
If the filter is clean and the pump strainer empty, the pump motor does not have to work as hard to deliver the required flow rate. Similar to a dimmer switch, the VFD can “dial” the horsepower output up and down as required to meet actual conditions, which results in considerably higher motor efficiencies. VFD packages for pump motors in the 10- to 20hp range run approximately $3,000 to $5,000 (depending on motor size), and many operators have reported 30- to 50 percent electricity cost savings as a result.
Thermal Solar Pool Water Heating
Thermal solar systems produce no air emissions, and installations typically utilize the existing pool 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 (but upstream of the pool heater), a bypass piping system is installed to route the pool water into the solar collectors.
Because the pool heater is activated by low pool water temperature, if the solar system can provide the necessary set-point water temperature, the pool heater is not activated, thereby reducing the run time for the pool heater and the associated cost for natural gas.
Over the past decade, a great deal of interest in solar heating has been expressed by commercial pool operators. With utility rates spiking more recently, this interest has reached a fever pitch. Six years ago, proposing solar was an exercise in political correctness because the payback typically averaged eight to 10 years, and the average life of most systems is 12 years. However, with current natural gas prices, full return on investment now is in the four- to six-year range, which is considerably more attractive to the average pool operator.
Generally, copper and glazed solar panels are the most efficient (and expensive) of the systems available.
However, these are less than ideal for commercial aquatics facilities because of the potential for vandalism (kids love to toss rocks at and break the glazed panels). In addition, the high potential for out-of-balance water chemistry within pool water can wreak havoc within the copper piping. For instance, if the pH feed system were to malfunction and drive the pH down below 7.0, copper could precipitate out of the solar heating system and into the pool water, discoloring the pool plaster to the point where it might have to be completely replaced.
For these reasons, the use of nonmetallic solar panels (typically polypropylene or EPDM collectors) is preferred.
Installed costs for this type of passive solar system (assuming suitable mounting space with proper solar orientation is available) run approximately $12 to $18 per square foot of solar panel.
The solar panels required varies greatly by region, but an average of 80 percent of water surface area is common for all but the most sunlight-challenged spots within North America. For an outdoor 25-yard-by-50-meter pool, this translates into a requirement of approximately 10,000 square feet of solar panels, with installed costs ranging from $180,000 to $220,000.
However, with a potential annual operating cost savings of $50,000 to $75,000, passive solar can be an attractive option for many pool operators.