Saving with Solar Pool Heating: Page 3 of 3

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Pool Heating with Rooftop Solar Collectors
Extending the swimming season and improving your pool’s comfort with a cost-effective solar pool heating system.
Unglazed copolymer collectors
Unglazed copolymer collectors are the most common types for solar pool heating. This version comes in various colors to blend in better with the roofing material.
Pool’s mechanical system
To properly integrate a solar pool heating system, it is important to identify the components of a pool’s mechanical system.
A differential controller
A differential controller is the brains of the system, sending pool water to the collectors when heat is needed.
The controller operates a diversion valve
The controller operates a diversion valve that integrates the solar loop with the usual filtering system loop.
Flexible unglazed flat-plate collectors
Flexible unglazed flat-plate collectors require a support framework if they are mounted at an angle, and tie-downs for wind protection.
Unglazed coil-type collectors
Unglazed coil-type collectors are best plumbed in parallel to reduce friction and preserve their solar collection efficiency.
Glazed flat-plate collectors
Glazed flat-plate collectors are more expensive, but may be more appropriate in colder climates or for heating indoor pools.
Evacuated-tube collectors
Evacuated-tube collectors are more expensive, but may be more appropriate in colder climates or for heating indoor pools.
Solar pool heating systems are sized based on surface area.
Because pools lose the majority of their heat from their surface, solar pool heating systems are sized based on surface area.
Pool Heating with Rooftop Solar Collectors
Unglazed copolymer collectors
Pool’s mechanical system
A differential controller
The controller operates a diversion valve
Flexible unglazed flat-plate collectors
Unglazed coil-type collectors
Glazed flat-plate collectors
Evacuated-tube collectors
Solar pool heating systems are sized based on surface area.

Ratings. Solar pool collector manufacturers may opt to have their products certified through the Solar Rating & Certification Corporation (SRCC) OG100 protocol or through the FSEC Standard 102-10. These are the same protocols that are used to certify glazed flat-plate and evacuated-tube collectors. The program gives manufacturers an industry-recognized label for their products, and consumers can use the ratings to ensure durability and compare performance.

Pump considerations. The flow of water through pool piping is affected by the speed at which the fluid is pumped, the diameter and length of the piping, and how high water has to be lifted to the collectors. For example, a single collector made from 200 feet of coiled 3/4-inch poly pipe located 20 feet above the pool will significantly impact flow rate when compared to the same pump in a mechanical system with just a filter. When selecting collectors, consider whether the design will require more energy for pumping, or require a larger pump or even a dedicated pump specifically for the SPH system.

Cost & availability. Polymer collectors tend to be fairly affordable. Even so, homemade collectors made from materials that have been reclaimed or are readily available can reduce a pool owner’s initial investment in a SPH system. When the decision is driven by cost, be sure to also consider the lifespan of the materials being used and their effectiveness.

System Sizing

It is common to initially consider sizing an SPH system based on the volume of water in the pool. Since the system will be heating the entire pool contents, this seems a logical conclusion.

However, the reality of a pool is that it is a large thermal mass that is brought up to temperature at the beginning of the swimming season and maintained at that temperature throughout the season. While a SPH system helps bring the pool up to its operating temperature, it is typically sized to offset the heat loss that occurs once the pool water reaches the desired temperature.

Since the primary sources of pool heat loss are evaporation, radiation, and convection from the pool surface, SPH systems are sized based on the surface area of the pool, not its volume. For simplicity, the size of the collector array is expressed as a percentage of the surface area of the pool.

The recommended size of the collector array depends upon a variety of factors, including the:

  • orientation of the array with respect to true south
  • extent of shading of the array and the pool
  • desired pool temperature
  • number of months the pool is open
  • number of hours the pool is uncovered.

For a site where these factors have a minimal impact on solar production, the size of the collector array in relation to the pool surface area is illustrated in the map above. If the site is shaded or the array is oriented significantly away from true south, the size of the array should be larger.

While the thermal performance of collectors is a major consideration, SPH also requires an understanding of the function of the pool’s mechanical system and how a collector array best integrates with this system. Through proper selection and integration, a solar pool heating system can ensure that more time is spent pool-side and less time is spent worrying about paying for fuel for this luxury.

Access

Vaughan Woodruff owns Insource Renewables, a solar design/build and consulting firm in Pittsfield, Maine. A NABCEP-Certified solar heating installer, he serves on committees for NABCEP, IAPMO, and IREC, and teaches for organizations across the United States. Vaughan co-authored the NABCEP Solar Heating Installer Resource Guide with Chuck Marken.

Resources:

Florida Solar Energy Center • bit.ly/FSECPoolHeating • Consumer information and pool collector ratings

Residential Solar Pool Heating Systems: A Buyer’s Guide, Natural Resources Canadabit.ly/NRCAN_SPH

U.S. Department of Energy • bit.ly/DOESPH

Natatoriums: The Inside Story (Indoor Pools) • ASHRAE Journal • bit.ly/IndoorSPH

Solar Panels Plus • bit.ly/SPHcalc • Pool heater calculator

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