Solar Pool Heating: Open-Loop vs Closed-Loop


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In the United States alone, there are over 400,000 commercial swimming pools. Over two-thirds of those pools are heated to a comfortable swimming temperature through the burning of fossil-fuels.

In a world where fossil-fuel pool heating is a luxury we can no longer afford, Dave Sizelove, President &CEO of solar panel manufacturer Aquatherm Industries provides a comparative cost and payback analysis of two of the most popular types of systems designed to harness the sun for free heat.

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Solar Pool Heating: Open-Loop vs Closed-Loop

  1. 1. Distributed Solar Thermal:Rebirthing a Mature TechnologyPool Heating - “Open Loop” vs “Closed Loop” Dave Sizelove, President & CEO Aquatherm Industries, Inc.
  2. 2. The MarketIn the United States alone there are...• 5,000,000 In-Ground Residential Pools• 400,000 Commercial Pools Heated vs Unheated Indoor vs Outdoor Heated Unheated Outdoor Indoor 67% 33% 60% 40% Heated with natural gas... CO2 emissions = 6.6 MILLION cars (driven 12,500 miles annually)
  3. 3. The SolutionA hybrid solar pool heater consists of... ✓The most cost-effective primary heater Goal: (Solar is free heat from the sun) To engineer a “reasonable balance” ✓The existing natural gas, propane or between cost and electric pool heater for anytime heat BTU heat collection (for times when solar will not be enough) from solar. Projected Energy Savings w/ Hybrid Solar Pool Heater: Year-round Pool: 40-60% Seasonal Pool: Up to 100%
  4. 4. System Types Open Loop: Closed Loop: Direct heating with Low-Temperature Indirect heating with a heat exchanger using Unglazed Polymer Collectors Medium-Temperature or Evacuated-Tube Collectors Collectors ControllerExisting Pump & Filter Existing Heater
  5. 5. Open Loop Open Loop: Benefits Direct heating with Low-Temperature Unglazed Polymer Collectors ✓ Designed to economically raise temperatureabove large volumes of water (like a pool)10-15 F of o ambient air temperature. Collectors ✓ Specifically designed for low-temp feed/return lines. pool heating; inexpensive PVC for applications like ✓ Approx. Cost - $15-20 per sq. ft. (commercial). Considerations ‣ Controller Little or no performance when ambient is more than 25o F cooler than pool water temperature. ‣Existing Pump & Filter Existing Heater Sensitive to areas with a cool prevailing breeze. ‣ Life expectancy of 15-20 years
  6. 6. Closed Loop Closed Loop: Benefits Indirect heating with a heat exchanger usingMedium-Temperature or Evacuated-Tube Collectors ✓ Good year-roundclimates. especially in cooler, northern performance, ✓ Less sensitive to cool prevailing breezes. ✓ Life expectancy of 20-25 years. Considerations ‣ Performance losses of 17-25% due to glazing and use of a heat exchanger. ‣ Feed and return lines must be insulated copper to prevent heat loss from higher temps generated. ‣ Approx. Cost - $80-100 per sq. ft. (commercial).
  7. 7. Case Studies Annual Savings Comparison Based on D.O.E. RSPEC Program Simulations $6,725 Based on: Portland, OR $9,290 ‣ 4,000 sq. ft. indoor pool $13,360 Dallas, TX ‣ 80o F pool temperature $14,375 ‣ 82o F room temperature $9,969Washington, DC ‣ 50% room humidity $11,953 ‣ $1.00 per therm $8,516 Chicago, IL ‣ 75% efficient heater $11,421 ‣ 3,000 sq. ft solar area $11,445 Atlanta, GA $12,620 ‣ $15 / sq. ft. open loop ‣ $80 / sq. ft. closed loop Annual Average Savings Open Loop Closed Loop
  8. 8. Case Studies Comparative Payback Analysis Based on D.O.E. RSPEC Program Simulations 32.5000 Based on: 26 Open Loop Closed Loop ‣ 4,000 sq. ft. indoor poolPayback Period (in years) 27.0833 21 ‣ 80o F pool temperature 20 21.6667 19 ‣ 82o F room temperature 17 ‣ 50% room humidity 16.2500 ‣ $1.00 per therm 10.8333 ‣ 75% efficient heater ‣ 3,000 sq. ft solar area 5.4167 7 5 5 ‣ $15 / sq. ft. open loop 3 4 0 ‣ $80 / sq. ft. closed loop Portland, OR Dallas, TX Washington, DC Chicago, IL Atlanta, GA