The Complete Guide to Saving Energy While Heating Your Pool
Heating a swimming pool in Orlando can consume a lot of energy and add up to high heating bills. You can improve your swimming pool’s heating and energy efficiency by doing the following:
Installing an energy-efficient pool heater
Gas Swimming Pool Heaters
Gas-fired pool heaters remain the most popular system for heating swimming pools. Today you can find new gas-fired heater models with much higher efficiencies than older models. Still, depending on your climate and pool use, they may not be the most energy-efficient option when compared to heat pump and solar pool heaters.
How They Work
Gas pool heaters use either natural gas or propane. As the pump circulates the pool’s water, the water drawn from the pool passes through a filter and then to the heater. The gas burns in the heater’s combustion chamber, generating heat that transfers to the water that’s returned to the pool.
They’re most efficient when heating pools for short periods of time, and they’re ideal for quickly heating pools. Therefore, gas pool heaters can be a good choice for pools that aren’t used on a regular basis. Unlike heat pump and solar pool heaters, gas pool heaters can maintain any desired temperature regardless of the weather or climate.
Heat Pump Swimming Pool Heaters
How They Work
Heat pumps use electricity to capture heat and move it from one place to another. They don’t generate heat.
As the pool pump circulates the swimming pool’s water, the water drawn from the pool passes through a filter and the heat pump heater. The heat pump heater has a fan that draws in the outside air and directs it over the evaporator coil. Liquid refrigerant within the evaporator coil absorbs the heat from the outside air and becomes a gas. The warm gas in the coil then passes through the compressor. The compressor increases the heat, creating a very hot gas that then passes through the condenser. The condenser transfers the heat from the hot gas to the cooler pool water circulating through the heater. The heated water then returns to the pool. The hot gas, as it flows through the condenser coil, returns to liquid form and back to the evaporator, where the whole process begins again.
Higher efficiency heat pump pool heaters usually use scroll compressors versus the reciprocal compressors of standard units.
Heat pump pool heaters work efficiently as long as the outside temperature remains above the 45ºF–50ºF range. The cooler the outside air they draw in, the more energy they use. However, since most people use outdoor swimming pools during warm and mild weather, this usually isn’t an issue.
Solar Swimming Pool Heaters
You can significantly reduce swimming pool heating costs by installing a solar pool heater. They’re cost competitive with both gas and heat pump pool heaters, and they have very low annual operating costs. Actually, solar pool heating is the most cost-effective use of solar energy in many climates.
How They Work
Most solar pool heating systems include the following:
- A solar collector — the device through which pool water is circulated to be heated by the sun
- A filter — removes debris before water is pumped through the collector
- A pump — circulates water through the filter and collector and back to the pool
- A flow control valve — automatic or manual device that diverts pool water through the solar collector.
Pool water is pumped through the filter and then through the solar collector(s), where it is heated before it is returned to the pool. In hot climates, the collector(s) can also be used to cool the pool during peak summer months by circulating the water through the collector(s) at night.
Some systems include sensors and an automatic or manual valve to divert water through the collector(s) when the collector temperature is sufficiently greater than the pool temperature. When the collector temperature is similar to the pool temperature, filtered water simply bypasses the collector(s) and is returned to the pool.
Solar pool collectors are made out of different materials. The type you’ll need depends on your climate and how you intend to use the collector. If you’ll only be using your pool when temperatures are above freezing, then you’ll probably only need an unglazed collector system. Unglazed collectors don’t include a glass covering (glazing). They are generally made of heavy-duty rubber or plastic treated with an ultraviolet (UV) light inhibitor to extend the life of the panels. Because of their inexpensive parts and simple design, unglazed collectors are usually less expensive than glazed collectors. These unglazed systems can even work for indoor pools in cold climates if the system is designed to drain back to the pool when not in use. Even if you have to shut the system down during cold weather, unglazed collectors may be more cost effective than installing a more expensive glazed collector system.
Glazed collector systems are generally made of copper tubing on an aluminum plate with an iron-tempered glass covering, which increases their cost. In colder weather, glazed collector systems—with heat exchangers and transfer fluids—capture solar heat more efficiently than unglazed systems. Therefore, they can be used year-round in many climates. Glazed collectors also can be used to heat domestic hot water year-round.
Both glazed and unglazed collector systems should include freeze protection if they’ll be used in colder conditions.
Swimming Pool Covers
You can significantly reduce swimming pool heating costs by using a pool cover. Below is a table showing the costs of heating pools with and without pool covers in different U.S. cities:
Use of a pool cover also can help reduce the size of a solar pool heating system, which can save money.
How They Work
Swimming pools lose energy in a variety of ways, but evaporation is by far the largest source of energy loss. Evaporating water requires tremendous amounts of energy. It only takes 1 Btu (British thermal unit) to raise 1 pound of water 1 degree, but each pound of 80ºF water that evaporates takes a whopping 1,048 Btu of heat out of the pool.
The evaporation rate from an outdoor pool varies depending on the pool’s temperature, air temperature and humidity, and the wind speed at the pool surface. The higher the pool temperature and wind speed and the lower the humidity, the greater the evaporation rate. In windy areas, you can add a windbreak—trees, shrubs, or a fence—to reduce evaporation. The windbreak needs to be high enough and close enough to the pool that it doesn’t create turbulence over the pool, which will increase evaporation. You also don’t want the windbreak to shade the pool from the sun, which helps heat it.
Indoor pools aren’t subjected to the environment, but they still can lose a lot of energy from evaporation. They even require room ventilation to control indoor humidity caused by the large amount of evaporation. The ventilated air also must be conditioned, which adds to the energy costs.
Pool covers minimize evaporation from both outdoor and indoor pools. Covering a pool when it is not in use is the single most effective means of reducing pool heating costs. Savings of 50%–70% are possible. Pool covers on indoor pools not only can reduce evaporation but also the need to ventilate indoor air and replace it with unconditioned outdoor air. You can also shut off exhaust fans when an indoor pool is covered, which saves even more energy.
Types of Pool Covers
Technically, all you really need for a pool cover is a large sheet of plastic. Plastic meets the requirement of being a vapor barrier. But a large sheet of plastic that you get from the lumber store is probably not your best choice. It will be very difficult to handle and store, it tears easily, and sunlight will deteriorate it rapidly. You can use a sheet of plastic, but it will be very inconvenient and it will probably only last 1 to 2 seasons maximum.
It’s best to use a cover designed specifically for swimming pools. They’re made of special materials, such as UV-stabilized polyethylene, polypropylene, or vinyl. They can be transparent or opaque. Covers can even be light or dark colored.
One of the lowest cost covers made specifically for swimming pools is the bubble (or solar) cover. Bubble covers are similar to bubble packing material except they use a thicker grade of plastic and have UV inhibitors.
Vinyl covers consist of a heavier material and have a longer life expectancy than bubble covers. Insulated vinyl covers are also available with a thin layer of flexible insulation sandwiched between two layers of vinyl.
Outdoor pools gain heat from the sun, absorbing 75%–85% of the solar energy striking the pool surface. This is an important contribution to the pool’s heating needs. A pool cover will decrease the solar gain contribution to some extent, depending on what type you use. A transparent bubble cover may reduce pool solar energy absorption by 5%–15 %. A completely opaque cover will reduce it by 20%–40%. You need to consider this when selecting a pool cover.
You also need to decide whether you want a manual, semi-automatic, or an automatic pool cover. You can manually pull the cover on and off, fold it, and place it somewhere out of the way. You can also purchase a pool cover reel to help manually roll up the pool cover. The reel, usually on wheels, can be rolled out of the way.
Semi-automatic covers use a motor-driven reel system. They use electrical power to roll and unroll the cover, but usually require someone to pull on the cover when unrolling, or guide the cover onto the reel when rolling up the cover. Semi-automatic covers can be built into the pool deck surrounding the pool, or can use reels on carts.
Automatic covers have permanently mounted reels that automatically cover and uncover the pool at the push of a button. They’re the most expensive option, but they’re also the most convenient.
Some pool covers fit into tracks along the sides of the pool. This prevents anything or anybody from getting into the pool. They even support the weight of several people. If liability is a concern, these are a good option to explore. They can be run manually, semi-automatically, or automatically. Safety covers are recommended for public pools, and may be required by inspectors.
How to Use a Pool Cover
Pool covers should be used during your swimming season. If you use your pool during the daytime, take off the cover just before swimming and replace the cover as soon as you’re done using the pool.
If you use your pool only at night, the effectiveness of a pool cover will depend on whether the evaporation and other losses prevented by the cover exceed the solar gain reduction caused by the cover. The type of cover and the climate affects this balance. In dry and/or windy conditions, the evaporation rate of the pool increases. Therefore, it is generally beneficial to have a transparent or bubble cover on during daylight hours. In warm, humid conditions the evaporation rate decreases. In this case, it may be more beneficial to leave the cover off during the daytime.
Other Pool Cover Benefits
Besides offering energy savings, pool covers also do the following:
- Conserve water by reducing the amount of make-up water needed by 30%–50%
- Reduce the pool’s chemical consumption by 35%–60%
- Reduce cleaning time by keeping dirt and other debris out of the pool.
Managing Swimming Pool Water Temperature for Energy Efficiency
The water temperature you desire for your swimming pool not only affects the size of the pool’s heater, but also your heating costs if use a gas or heat pump pool heater.
Pool water temperatures in Orlando typically range from 78ºF to 82ºF. The American Red Cross recommends a temperature of 78ºF for competitive swimming. This coincides with good fuel savings. However, this may be too cool for young children and the elderly, who may require a temperature of 80ºF or higher.
The energy consumption for each degree rise in temperature will cost 10%–30% more in energy costs, depending on your location. In warmer climates, this percentage is higher because of the relatively low cost of heating a pool at 78ºF.
Also, turn the temperature down or turn off the heater whenever the pool won’t be used for several days. This will save energy and money. It’s a myth that it takes more energy to heat a pool back up to a desired temperature than you save by lowering the temperature or turning off the heater.
Installing and Operating a Swimming Pool Pump for Energy Efficiency
You can save energy and maintain a comfortable swimming pool temperature by using a smaller, higher efficiency pump and by operating it less.
In a study of 120 pools by the Center for Energy Conservation at Florida Atlantic University, some pool owners saved as much as 75% of their original pumping bill when they used these energy conservation measures (see table below).
Table courtesy of Home Energy magazine. These savings represent a typical pool in Florida. The average pool pump energy bill is probably higher in Florida than in many other areas of the country because of the long swimming season. While the absolute savings here will be greater there than elsewhere, the percentage savings should apply nationwide. Note that the savings for the combination of measures are not simply the sum of savings for the individual measures. When both are implemented, the energy use is 60% of 40% of the original use-percent savings.
Sizing the Pump
The larger the pump, the greater your pumping and maintenance costs. Therefore, you want to use the smallest size pump possible for your swimming pool. To choose the right size pump, you can consult a pool supplier’s design chart. Using the chart, match the hydraulic characteristics of the pump to both the piping and the pool’s flow characteristics. For a solar pool heating system, you also need to consider the need to pump the pool’s water to and through the collector(s).
The Florida study shows that a 0.75 horsepower or smaller pump is generally sufficient for residential pools. Smaller pumps, which cost less, can be used if you decrease the pool circulation system’s hydraulic resistance by doing the following:
- Substituting a large filter (rated to at least 50% higher than the pool’s design flow rate)
- Increasing the diameter or decreasing the length of the pipes, or replacing abrupt 90-degree elbow pipes with 45-degree ones or flexible pipes.
By decreasing the pool circulation system’s hydraulic resistance, you can reduce the pump’s electricity use by up to 40%.
Operating the Pump
Pool pumps often run much longer than necessary. Circulating your pool’s water keeps the chemicals mixed and removes debris. However, as long the water circulates while chemicals are added, they should remain mixed. It’s not necessary to recirculate the water everyday to remove debris, and most debris can be removed using a skimmer or vacuum. Furthermore, longer circulation doesn’t necessarily reduce the growth of algae. Instead, using chemicals in the water and scrubbing the walls are the best methods.
Reduce your filtration time to 6 hours per day. If the water doesn’t appear clean, increase the time in half-hour increments until it does. In the Florida study, most people who reduced pumping to less than 3 hours per day were still happy with the water’s quality. On average, this saved them 60% of their electricity bill for pumping.
You can install a timer to control the pump’s cycling. If debris is a problem, use a timer that can activate the pump for many short periods each day. Running the pump continuously for, say, 3 hours leaves the other 21 hours a day for the pool to collect debris. Several short cycles keep the pool cleaner all day.
Keep the intake grates clear of debris. Clogged drains require the pump to work harder, which uses more energy. Backwash your filter appropriately. Backwashing too frequently wastes water, while not backwashing wastes energy by requiring the pump to work harder.
This information was made possible by the US Dept of Energy in the Energy Savers Tips