Conserving Energy and Heating Your Swimming Pool With Solar Energy

7/28/2019 Conserving Energy and Heating Your Swimming Pool With Solar Energy

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Swimming pools provide a great way toexercise and beat the summer heat. Build-ing and maintaining a pool, however, alsomeans relatively high costs added to yourhouseholds budget. There are severalways that you can reduce operating andmaintenance costs, lower water consump-tion, and conserve heat if you heat yourpool. Many people heat their pools toextend the swimming season and/or to

keep it at a temperature that they are per-sonally comfortable with. This lets themenjoy the full value from their pool. Solarpool heaters are an option to heat the poolwith clean energy from the sun, and canreduce heating costs.

This fact sheet discusses options for reduc-ing the costs for operating and heatingyour pool.

Optimizing WaterFiltration andCirculation Pumping

A study by the Center forEnergy Conservation atFlorida Atlantic Univer-sity shows that pool own-ers can save energy andmaintain a comfortablyheated pool by usingsmaller and higher effi-ciency pumps, and operat-

ing pumps less each day.In this study of 120 pools,some pool owners savedas much as 75 percent oftheir original pumping bilwhen they used both con-servation measures (seetable on page 2).

Conserving Energy andHeating Your Swimming

Pool with Solar Energy

CLEARIN

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This document was produced for the U.S. Department of Energy (DOE) by the National Renewable Energy Laboratory (NREL), a DOE national laboratory.The document was produced by the Information Services Program, under the DOE Office of Energy Efficiency and Renewable Energy. The Energy Efficiencyand Renewable Energy Clearinghouse (EREC) is operated by NCI Information Systems, Inc., for NREL / DOE. The statements contained herein are based on

information known to EREC and NREL at the time of printing. No recommendation or endorsement of any product or service is implied if mentioned by EREC

Printed with a renewable-source ink on paper containing at least 50% wastepaper, including 20% postconsumer waste

DOE/GO-102000-107FS104

July 2000

Roof-mounted solar collectors are used to heat the pool below,reducing energy costs.

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Sizing the Pump Right

When a pump wears out or cant berepaired, a pool owner typically installs alarger one, thinking that bigger must bebetter. Instead, a larger pump mayincrease the costs of pumping and mainte-nance. To choose the right size pump, con-sult design charts that match the hydrauliccharacteristics of the pump to both thepiping and the pools flow characteristics.A local pool supply dealer should haveaccess to these charts.

The Florida study shows that a 0.75 horse-power or smaller pump is generally suffi-cient for residential pools. Smaller pumps,which cost less, can be used if you

decrease the pool circulation systemshydraulic resistance. This can be donethrough one or more of the followingways: substituting a large filter (rated to atleast 50 percent higher than the poolsdesign flow rate), increasing the diameteror decreasing the length of the pipes, orreplacing abrupt 90-degree elbows with45-degree elbows or flexible pipe. Thesetypes of changes can slash up to 40 per-cent off the pumps use of electricity (seetable above).

Circulating the WaterAnother way to save energy is to reducethe pumps operating time. Pool pumpsoften run much longer than necessary.Pool owners need to understand the rea-sons behind circulating the pools water.Circulating water keeps your pools chem-icals mixed. However, as long as the watercirculates while chemicals are added, theyshould remain evenly mixed with minimaldaily circulation. Secondly, circulating the

water keeps the pool free of debris bydrawing water out and through the filter.It is not necessary to recirculate the watercompletely every day to remove debrisand clean the water. One complete circula-

tion usually takes between 6 and 12 hoursper day. But this may be longer than nec-essary since most debris either floats orsinks, and can be removed with a skim-mer or vacuum. After about an hour, mostof the pumping power is wasted by circu-lating clear water and does little toimprove the waters quality.

Furthermore, longer circulation does notnecessarily reduce the growth of algae.Instead, using chemicals in the water andscrubbing the walls are the best methods.

In the Florida study, most people whoreduced pumping to less than 3 hours perday were still happy with the watersquality. On average, this saved them 60percent of their electricity bill for pump-ing. Combined with using a smaller sizepump, pool owners saved up to 75 percentof their original electricity bill for pump-ing water (see table above).

One last simple measure for saving moneyis to use an accurate timer to control thepumps cycling. Use a clock that can acti-

vate the pump for many short periodseach day if debris is a problem. Runningthe pump continuously for, say, 3 hoursleaves the other 21 hours a day for thepool to collect debris. Several short cycleskeep the pool cleaner all day.

2

In a Florida study,

most people who

reduced pumping to

less than 3 hours per

day were still happy

with the water's qual-

ity. On average, this

saved them 60 percent

of their electricity bill

for pumping.

Savings from Pump Conservation Measures

Energy Use Cost of EnergyCondition (kWh/year) ($/year) Energy Savings

Original 3000 240

Pump replacement 1800 140 40%(downsizing)

Reduced time (60%) 1200 100 60%Combination of above 720 60 75%

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 begreater there than elsewhere, the percentage savings should apply nationwide. Note that the savings for the combination of measures are notsimply the sum of savings for the individual measures. When both are implemented, the energy use is 60 percent of 40 percent of the original

use75 percent savings.


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Summary of Recommendations

Pool owners can save a great deal ofmoney by:

Choosing the smallest pump and thelargest filter suitable for their pool

Decreasing the hydraulic resistance of

the pools circulation system whereverpossible Circulating the water with the pump for

the shortest time possible (often fewerthan 3 hours)

Installing a timer.

Keep in mind, however, that all pools aredifferent. Circumstances such as specialcleaning and heating needs, climate, poolsize, and usage all affect a pools circulation,as well as the potential for saving money.

Reducing Water and Heat LossAlmost all of a pools heat lossabout 95percentoccurs at the surface, mostlythrough evaporation to the air and radia-tion to the sky. A pool cover is an effectivemeans to keep heat (and water) in a poolby reducing evaporation of water from thepool when it is not in use, and reducesradiant heat losses. Apool cover can reducewater loss by 30 to 50 percent. Each gallonof 80-degree water that evaporates removesaround 8,000 Btu from the pool. Reducing

water loss also reduces the amount ofchemical water treatment required.

Outdoor pools can gain a significantamount of heat from the sun, absorbing 75to 85 percent of the solar energy strikingthe pool surface. A bubble cover (some-times called a solar cover) is one of theleast expensive covers made specificallyfor swimming pools. Its similar to bubble-packing material except it has a thickergrade of plastic and ultraviolet (UV)inhibitors. Vinyl covers are made of a

heavier material, which extends their use.You can also get vinyl covers with a thinlayer of flexible insulation sandwichedbetween two layers of vinyl.

A transparent bubble cover may reducesolar energy absorption by 5 to 15 percent,and an opaque cover may reduce it by 20to 40 percent. However, the decrease insolar gain can be balanced or more thanoffset by the covers retention of the pools

heat, which depends on the air tempera-ture and humidity. Generally, the drierand cooler the air, the greater the heatingbenefit from covering the pool during thedaytime. Of course, a cover should alwaysbe used at night to prevent losses whenthere is no solar gain.

A cover also helps you keep the pool cleanand extend the life of the chemicals inyour pool. At a cost of 20 to 60 cents persquare foot, a pool cover may pay for itselfin 1 year. Be aware, however, that UVradiation deteriorates the cover, requiringthat you replace it every 3 to 5 years.Before you buy one, make sure the covercomes with at least a 2-year warranty. Alsofind out how easily you can place thecover over the pool, how to remove it, andhow to store it. Systems are available thatmove the cover off and on the pool with amotor or hand crank.

Covers should always be installed andused according to the manufacturersguidelines. Always consider that peoplecould use the pool unauthorized or unsu-pervised.

A windbreak around the pool can alsoreduce evaporation, and make poollounging more comfortable and private.A 7-mph wind at the pool surface can

increase heat loss by 300 percent. A wind-break could include a fence or vegetation.It needs to be high and close enough to thepool so that it effectively blocks wind frommoving across the pool surface, but doesntblock beneficial solar energy.

3

Outdoor pools can

gain a significant

amount of heat from

the sun, absorbing

75 to 85 percent of the

solar energy striking

the pool surface.

Types of Pool Covers

Insulated vinyl

Bubble/solar

Vinyl


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Heating the Pool Efficiently

If you are selecting a pool heater, ask foras energy-efficient model as you canafford. Several heat pump manufacturersmake retrofit desuperheater coils for poolheating, and several make heat pumps forpool heating. These may be cost effective

relative to natural gas heaters.

Besides that, the easiest way to saveenergy is to lower the thermostat on yourpools heater so that it heats the pool nohigher than the temperature that you feelcomfortable with. Every 1 degree reduc-tion can cut your energy usage bybetween 5 and 10 percent. Once you havelowered the thermostat, keep the remain-ing heat from escaping by using a poolcover when the pool is not in use.

Solar Pool HeatersIf you have taken steps to retain yourpools heat but are still not happy withyour heating bills, or if you plan to installa new pool, a solar pool heater may be agood investment. Such heating systemsare one of the most cost-effective applica-tions of solar energy. It is relatively simpleto integrate a solar water heater since mostpools require a pump, filter, and plumb-ing. With a solar energy system, the poolswater is pumped through the filter and

then through a solar energy collector(s)

instead of directly back to the pool. Thesun heats the water in the collector(s)before it returns to the pool.

If you add a solar heater, you may need apump larger than your present one, or aseparate, smaller pump to pump thepools water to and through the solar col-

lectors. Adding any heater, solar or other-wise, will preclude selecting the smallestpump. Nevertheless, you also may reducepumping time to help cut costs.

Unlike solar domestic water heating sys-tems, which raise a small amount of waterto a high temperature of about 140F, poolheaters raise the temperature of severalthousand gallons of water to about 80Fby circulating the water at a relatively fastrate through the collectors. This allowsmost of the solar energy falling on the col-lectors to transfer to the pool water.

Solar energy not only can be used for heat-ing residential pools but also for largercommercial and public pools. One suchapplication is the International Swim Cen-ter in Santa Clara, California. Heatersusing solar energy heat three poolsa 50-meter racing pool, a 25-yard and 17-footdeep diving well, and a 25-yard trainingpool. Nearly 13,000 square feet of flat-plate collectors heat 1.2 million gallons of

water. Since the project was completed in

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A solar pool heating system.

The easiest way to

save energy is tolower the thermostat

on your pool's heater

so that it heats the

pool no higher than

the temperature that

you feel comfortable

with.

Flow

controlvalve

Solar collectors

Conventionalpool heater

Sensor

Check valve

FilterPump FilterPumpStrainer


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February 1979, solar energy has been pro-viding 60 percent of the energy required toheat the pools. The pool used for the 1996Summer Olympics in Atlanta is heatedwith solar energy as well.

Solar collectors can also be used to coolthe pool in hot climates or during peak

summer months by circulating the waterthrough the collectors at night. The collec-tors lose heat by radiation to the night sky.

Solar Pool Collectors

Collectors for heating a pool normally donot require glazing or insulation becausethey operate during warmer months whensolar radiation and ambient temperaturesare relatively high. This allows for a sim-pler design that is usually less expensivethan collectors for domestic hot water.

Many pool collectors are made of heavy-duty rubber or plastic treated with a UVlight inhibitor to extend the life of the pan-els. The advantages of plastic collectorsare that theyre usually less expensive andweigh less than metal collectors.

Metal collectors generally are made of cop-per tubing mounted on an aluminum plate.The disadvantages of metal collectors arethat they are more susceptible to corrosionand freeze damage, and the copper tubesmay react with your pools chlorine if the

pH level falls below 7.2. Too many copperions in pool water may form dark-coloredprecipitates, which can coat the poolswalls. This discoloration can only beremoved by draining, cleaning, and repaint-ing the pool. This problem can be reducedif the pH level is always kept above 7.2.

The area needed for collectors to heat yourpool depends on many factors. A generalrule of thumb is that the collector surfacearea should equal at least one half of thepools surface area. In a relatively sunnyclimate, this additional heating helpsextend the swimming season into springand autumn. In cooler and cloudier areas,you may need to increase the collectorssurface area to equal the entire surfacearea of the pool.

Collectors can be mounted on roofs oranywhere near the pool that provides theproper exposure, orientation, and tilttoward the sun. The optimum collector

orientation is south, but west-facing orien-tations are good if the collectors surfacearea is increased to at least 75 percent ofthe pools surface area. East-facing orien-tations are marginally good. The tilt of thecollector is as important as the orientation.For heating primarily in the summer, thetilt should equal the latitude where the

pool is located minus 10 to 15 degrees.Where optimizing the tilt is not possible,for example on an existing roof with ahigh slope or on a flat roof, increasing thecollector area may be necessary to achievethe desired pool temperature.

One potential benefit of roof installation is

that it may reduce the cooling load of thebuilding that its located on, since it putsthe solar heat into the pool water andkeeps it from radiating into the attic andthe conditioned space below.

There is a company that makes a heatexchanger, which is placed in the attic, forheating pool water. This collectorabsorbs heat that builds up in the attic andtransfers it to the pool water.

Because swimming pools include a pumpand related plumbing, adding on a solarheater can be relatively simple. Unless youhave experience with plumbing and elec-trical wiring, however, have a professionalinstall your system. Often the pump circu-lates the pool water enough, but be sure itmaintains a high flow rate to keep thepanels operating at optimal efficiency.Your collector should require little mainte-nance if the pools chemical balance andfiltering system are checked regularly.

5

It is relatively simple

to integrate a solar

water heater since

most pools require a

pump, filter, and

plumbing.

For heating primarily in the summer, the tiltof a solar collector should equal the latitudewhere the pool is located minus 10 to 15degrees.

Solar Collector Orientation

Latitude minus

1015 degrees

South


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Resources

The following are sources of additional information onenergy-efficient swimming pools:

Organizations

American Solar Energy Society, Inc. (ASES)2400 Central Avenue, G-1

Boulder, CO 80301Phone: (303) 443-3130; Fax: (303) 443-3212Email: [email protected] site: http://www.ases.org/

ASES is a nonprofit educational organization that encouragesthe use of solar energy technologies.

Florida Conservation Foundation (FCF)1251 B Miller Ave.Winter Park, FL 32789Phone: (407) 644-5377E-mail: [email protected] site: http://sundial.sundial.net/~florida/

Its mission is to provide accurate and authoritative informa-tion accessible to the public, and innovative ideas on solvingenvironmental problems.

Florida Solar Energy Center (FSEC)1679 Clearlake RoadCocoa, FL 32922Phone: (321) 638-1000; Fax: (321) 638-1010Web site: http://www.fsec.ucf.edu/

FSEC researches and develops renewable energy and energyefficiency technologies, and educates the public on the resultsof its research.

National Spa & Pool Institute (NSPI)1-800-323-3996

Web site: http://www.nspi.org/NSPI is dedicated to the safe use and enjoyment of pools, spas,and hot tubs.

Solar Energy Industries Association (SEIA)1616 H Street, NW, 8th Floor, Washington, DC 20006Phone: (202) 628-7979; Fax: (202) 628-7779Web site: http://www.seia.org

SEIA is the only trade association of solar energy system man-ufacturers and suppliers in the United States.

For more information about many kinds of energy efficiencyand renewable energy topics, contact:

The Energy Efficiency and Renewable Energy

Clearinghouse (EREC)P.O. Box 3048Merrifield, VA 221161-800-DOE-EREC (1-800-363-3732)E-mail: [email protected] site: http://www.eren.doe.gov/consumerinfo/

EREC provides free general and technical information to thepublic on many topics and technologies pertaining to energyefficiency and renewable energy.

Web Sites

Pool & Spa NewsWeb site: http://www.poolspanews.com/

Reducing Swimming Pool Energy Costs (RSPEC!)U.S. Department of EnergyWeb site: http://www.eren.doe.gov/rspec/

Reading List

The list is not exhaustive, nor does the mention ofany publication constitute a recommendation orendorsement.

Books and Pamphlets

Build Your Own Solar Water Heater, D. Root, FCF (seeResources), 1985, 25 pp.

Designing and Installing Commercial Pool Heating Systems,D. Root; FSEC (see Resources), 1984, c200 pp. Availablefor purchase from FSEC.

The Homeowners Handbook of Solar Water Heating Systems,B. Keisling; Rodale Press, 35 E. Minor St., Emmaus, PA18049, 1983, 246 pp.

How to Design and Build a Solar Swimming Pool Heater, F.deWinter, Copper Development Association, 1975, 47pp. Available from ASES (see Resources).

Solar Heat for Swimming Pools, D. Root; FCF (seeResources), 1982, 68 pp.

Solar Heating for Swimming Pools, FCF (see Resources),1251 B Miller Ave., Winter Park, FL 32789, 1982, 68 pp.

Solar Heating of Swimming Pools: A Question and Answer

Primer, C.J. Cromer; FSEC (see Resources), 1997, 4 pp.Solar Water and Pool Heating Design and Installation Man-ual, D. Root; FSEC (see Resources), 1982, c500 pp. Avail-able for purchase from FSEC.

Articles

Efficient Design: Constructing an Energy-Efficient PoolCan Save Homeowners Plenty of Money, R. Messengerand S. Hayes; Pool & Spa News 26(3): 136, 142, 180, Janu-ary 26, 1987.

Running Pump Less Often is More Efficient, R. Mes-senger and S. Hayes; Pool & Spa News 25(21): 142, 144,

186, November 3, 1986.Solar Pool Heaters: The Simplest Use of Active SolarEnergy. K. Sheinkopf; Solar Today 11(6): 22, November 1,1997.

Solar Pool Heating, A Question and Answer Primer,C. Cromer, Solar Today 9(3): pp 32-34, May/June, 1995.

Swimming Pools Soak Up the Sun, D. Coughi, P.Hesse and T. Schiller,Home Energy, 13(3), pp. 37-42,May/June 1996.

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Conserving Energy and Heating Your Swimming Pool With Solar Energy