Solar heating options for above-ground pools

October 1, 2012

FlatMat_Heater_4525_Pool[1][1]
A solar collector for an above-ground pool should ideally be placed in close proximity to the pool; otherwise, costly energy is required to pump the water from the pool to the collector(s) and back again.
By Mitch Smith

Much has been said in recent years about the need to reduce the reliance on fossil fuels—not to mention household energy bills. In the pool industry, these conversations often focus on pool heating, which can be considered a luxury, on top of the amenity of having a pool.

However, heated pools tend to be used more which helps pool owners maximize their investment. Adding a week or two to the season, or being able to swim comfortably early in the morning or late in the evening, can dramatically improve pool owner satisfaction. The ability to increase satisfaction in the most economical and environmentally friendly way possible is a great outcome.

As consumers become more savvy about conserving energy—whether their motivation is to save money, protect natural resources, or both—energy-efficient heating options become more attractive. Pool owners do not want to spend as much money heating a pool as it costs to buy and install it in the first place.

An article posted online earlier this year asked: “Is it possible to live a green lifestyle and own a backyard pool?1” It essentially goes on to say, yes, and the first item on the list of ways pools can be eco-friendly is to use solar heat.

Solar heating devices offer an excellent way for pool owners to cut the energy consumption associated with pools and use free natural heat sources[2].

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Harnessing the sun

NS790 Solar Fish (4)[3]
Another form of solar heating is the use of isopropyl alcohol—dispensed from floating pool toys—which forms a film that acts like a solar blanket by keeping heat in the water.

Solar heating methods for above-ground pools fall into two categories: products on the water’s surface, and external devices. Using these methods together enhances the performance of each.

One factor often giving customers the idea solar heating is cumbersome, or not the right option for them, is the perception a large area attracting the sun (e.g. a roof pitched at just the right angle) is required for collectors. This may be true if solar energy is being used to heat a large pool or house, but the amount of solar energy required to make a noticeable difference in a medium-sized above-ground swimming pool, can easily be collected in a relatively small space. Some products do it using only the pool’s surface.

Solar blanket

A basic form of solar pool heating is the solar blanket. This is a sheet of bubble plastic cut to the same shape as the pool that lays on the water’s surface when the pool is not in use. During the day, energy from the sun passes through the blanket and warms the water. Day or night, the blanket prevents heat from evaporating out of the water, so whatever heat is collected (or generated by more active heating technologies, e.g. gas, heat pump or solar heater) remains in the water.

4.1.1[4]
A solar blanket prevents heat from evaporating out of the water and is a basic form of solar pool heating.

Some solar blankets come in sections held together by magnets or other mechanisms. Some pool owners find these products easier to handle and store when not in use. Whether the blanket is one large sheet or in sections, the concept is the same—passive solar energy collection has no monetary cost after the initial purchase, so the heat is essentially free.

Over the years, products have been developed allowing this solar blanket behaviour to occur while the pool is in use. Often designed to look like floating pool toys, these devices dispense isopropyl alcohol (C3H8O) into the water, which quickly finds the surface and forms a film that acts like a solar blanket, by keeping heat in the water.

Swimmers temporarily disrupt the isopropyl alcohol, but surface tension properties cause it to form the invisible blanket-like film again and again. Unlike solar blankets, there is a recurring replacement cost with the isopropyl alcohol dispensers, but it is far lower than the cost of a traditional solar blanket or operating a fossil-fuelled heater.

Solar collectors

GAME_solarpro_XD2[5]
Dome-shaped collectors use coiling tubes inside a semi-spherical receptacle and generate more heat per square metre/foot than mat-style heaters/collectors.

Moving outside the water, there are slightly more aggressive ways to harness the sun’s heat energy and deliver it to the pool. These come in various shapes and sizes and can be no more complicated than a garden hose. In fact, some pool professionals and owners have experienced a do-it-yourself version of the solar collector when they leave a garden hose out in the sun for a few hours before filling the pool. Assuming the hose has been full of water as it sits in the sun, the water will be warm when it comes out. If the hose is long enough, the water’s warmth can make a difference when added to the pool.

Essentially, this is the concept behind solar collectors, whether they are large and flat or more compact and dome-shaped.

Dome-shaped collectors have some advantages over large flat mats. For example, by coiling tubes inside a semi-spherical receptacle, the collector itself is better protected from dirt, grass clippings, small animals, and other backyard hazards. Also, because they are relatively small, dome-shaped collectors designed for above-ground pools have far less impact on the lawn or landscaping design, compared to a large mat that may lie on the ground near the pool. The dome shape allows this type of solar heater to generate more heat per square metre/foot than a mat-style heater or collectors installed on a roof or large frame for support.

Whether dome-shaped or not, a solar collector for an above-ground pool should ideally be placed in close proximity to the pool. Otherwise, costly energy is required to pump the water from the pool to the collector(s) and back again. The dome shape is quite attractive for the small pool (and small budget) market because proximity is desirable.

Solar dome technology

Over the years, solar-dome technology has been successfully used internationally and installations with multiple large domes can heat industrial buildings. Some residential versions use a dome placed in a warm attic with plumbing used to connect the dome to the pool (or the home’s water heater). A pump (the pool’s pump or one dedicated to the heater) circulates water between the solar collector and the vessel of water being heated.

The simplest version of the solar dome sits right next to the pool, using no more energy than the pool’s filtration pump to generate heat.

More elaborate solar heating systems are available for bigger pools and for customers with larger budgets. In extremely hot climates, it may be desirable to run the system at night, actually cooling the pool by circulating the water though the collectors when it is dark and cool outside. These systems are more expensive and require sensors and digital controls to fully automate the heating and cooling cycles; however, they use the same basic concepts as more affordable systems—energy from the sun is free and can be captured to increase pool water temperatures.

It is important to understand—and to make sure pool owners understand—passively generated heat cannot provide on demand heating like a gas pool heater. (See Table 1, page XX.) Solar heating technologies increase the water temperature, but, for a price, gas-fired heaters will generate more heat faster.

Above-Ground Pool Heating Reference Chart for Dome-Style Solar Heaters

Pool Volume Days Required to Heat Pool Five Degrees
Pool Dimensions Litres (Gallons) Typical 0.4 m2 (4 sf) Dome Typical 0.8 m2 (9 sf) Dome
3.6 m x 0.9 m (12 ft x 36 in.) 7,896 L (2,086 gal) 2.5 1.2
4.5 x 1.2 m (15 ft x 48 in.) 16,807 L (4,440 gal) 5.3 2.6
5.5 x 1.3 m (18 ft x 52 in.) 26,426 L (6,981gal) 8.3 4.2
7.3 x 3.6 x 0.6 m (24 x 12 x 2 ft) 29,094 L (7,686 gal) 9.1 4.6
6.4 x 1.3 m (21 ft x 52 in.) 35,015 L (9,250 gal) 11 5.5
7.3 x 1.3 m (24 ft x 52 in.) 47,246 L (12,481 gal) 14.9 7.4
9.7 x 4.8 x 1.3 m (32 x 16 ft x 52 in.) 54,373 L (14,364 gal) 17.1 8.5
9.1 x 1.3 m (30 ft x 52 in.) 71,525 L (18,895 gal) 22.5 11.2
12.5 x 5.5 m (41 x 18 ft) 102,206 L (27,000 gal) 32.1 16.1
This chart shows typical average water temperature increase for dome-style heaters. Other styles may have slightly varied results, but still only provide gradual heating. Chart courtesy GAME.

Pool heating hybrid

Heat pump pool heating technology is essentially a hybrid of passive and active heating. These systems transfer heat energy from the air to heat the water as it passes through the unit, making them more economical to operate than gas heaters. They do not generate heat directly; rather, they harness and repurpose it.

According to the U.S. Department of Energy (DOE), heat pumps are an energy-efficient way to heat a swimming pool. As the pool’s pump circulates water for filtration purposes, it also passes water through the pump’s heater. The heater has a fan drawing in outside air and directing it over an evaporator coil. Liquid refrigerant within the evaporator coil absorbs the heat from the outside air and as its temperature increases, it converts into a gas. The warm gas inside the coil then passes through a compressor. The compressor increases the heat and the gas becomes very hot as it passes through the condenser, which then transfers the heat from the hot gas to the cooler pool water as it passes through on its way back to the pool. Meanwhile, the hot gas reverts back into liquid and returns to the evaporator so the process can repeat. A heat pump heater is essentially an air-conditioner in reverse.

The DOE’s guide[6] to energy efficiency and renewable energy states heat pump pool heaters perform efficiently when the air temperature is at least 7 C (44.6 F), which is a lot cooler than most people would consider to be outdoor swimming weather. The warmer the outside air, the less energy a heat pump heater requires to warm the water. So during the swimming season, such a unit can be very efficient.

According to the DOE, heat pump pool heaters generally cost more up front than gas heaters, but their annual operating costs are dramatically lower and they tend to last longer.

As efficient as they are, however, heat pumps cannot beat solar pool heating on the score of energy consumption for pool heating. Solar heating systems use only the energy required to move the water from the heat source to the pool.

ECONOMICAL HEATING TIPS
● When adding top-off water to the pool, position the hose to sit in the sun for a while, allowing the fill water to warm up prior to adding it to the pool.
● Minimize the distance water has to travel between the heat source and the pool. Pumping water over large distances increases both installation and energy costs of running the pump.
● Cover the pool when not in use to conserve heat and water.

Combined efforts

The most effective pool heating systems combine heat collection (or active generation) with retention. In other words, no matter how heat is added to the pool water, retaining as much of it as possible by covering the pool when it’s not in use is critical if the goal is energy-conscious pool heating. This is akin to keeping doors and windows closed when the air-conditioner (or, more similarly, the furnace) is on.

Like many things, making a pool heating decision comes down to common sense. Customers need to understand what they want to accomplish, and pool professionals need to know what combination of products get the job done. When the desired outcome is an environmentally friendly, cost-effective way to increase pool water temperature by a few degrees, solar-technology is extremely efficient.

 

Smith_HeadshotMitch Smith is vice-president, specialty channel sales for GAME, a swimming pool and accessories manufacturer in Scottsdale, Ariz. He has been in the pool and spa industry for almost 30 years, having worked with Muskin, Zodiac and Vogue prior to joining GAME. Smith can be reached via e-mail at mks@game-group.com[7].

 

Endnotes:
  1. [Image]: http://poolspamarketing.com/wp-content/uploads/2012/10/FlatMat_Heater_4525_Pool1.jpg
  2. natural heat sources: http://voices.yahoo.com/can-own-eco-friendly-pool-11256232.html
  3. [Image]: http://www.poolspas.ca/wp-content/uploads/2015/05/NS790-Solar-Fish-4.jpg
  4. [Image]: http://www.poolspas.ca/wp-content/uploads/2015/05/NS100-AG-Solar-Blanket-hi-res.jpg
  5. [Image]: http://www.poolspas.ca/wp-content/uploads/2015/05/GAME_solarpro_XD2.jpg
  6. DOE’s guide: http://www.energysavers.gov
  7. mks@game-group.com: mailto:mks@game-group.com

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