Click the dots to the right for more systems

Direct - Differential Control

Direct, forced circulation systems are the simplest and most efficient solar water heating systems. In this variant a pump, controlled by a differential controller, circulates water from the storage tank to the solar collectors and back again. This type of system is restricted for use in climates that rarely freeze due to the potential for system damage from water freezing inside the piping and/or collector(s). These systems may feature one or more freeze protection mechanisms such as recirculation freeze protection, manual drain-down, or freeze valves.

  • Low Cost
  • High Efficiency
  • Simple Design – Differential Controller controls the pump at all times.
  • For use only in warm, southern climates
  • Freeze protection options: Recirculation, freeze valve, manual drain down

Direct Differential Control Schematic

Direct - PV Powered Pump

Direct, forced circulation systems are the simplest and most efficient solar water heating systems. In this variant a D/C pump, powered by a small PV module, circulates water from the storage tank to the solar collectors and back again. This type of system is restricted for use in climates that rarely freeze due to the potential for system damage from water freezing inside the piping and/or collector(s). These systems may feature one or more freeze protection mechanisms such as manual drain-down or freeze valves.

  • Low Cost
  • High Efficiency
  • Simple Design – Pump is on whenever PV module is producing power
  • For use only in warm, southern climates
  • Freeze protection options: freeze valve, manual drain down

Direct PV Pump Schematic

Indirect - Drainback Single Pump

Indirect, drainback systems separate the fluid in the solar collector from the potable water using a heat exchanger. In this variant the heat exchanger is integrated into the storage tank requiring only one pump to be used. Susceptibility to fluid overheating or freezing is eliminated because all of the fluid drains back to the drainback tank automatically when the controller turns the pump off. The fluid used in the solar loop is generally distilled water which avoids the need for a double-walled heat exchanger. The circulator pump in a drainback system must be more powerful than in a direct system as it must also overcome gravity head.

  • Eliminates the chance of fluid freezing or overheating
  • Uses water as the heat transfer fluid
  • Solar loop is unpressurized, simplifying the design
  • For use in all climates
  • Collector(s) and exposed piping must be sloped to drain automatically
Indirect Drainback Single Pump Schematic

Indirect - Drainback Pump Station

Indirect, drainback systems separate the fluid in the solar collector from the potable water using a heat exchanger. In this variant the heat exchanger is part of a packaged pump station unit. This variant shares the benefits of the single pump drainback system but adds value by using a plug & play pump station comprised of pre-plumbed pumps, valves, and heat exchanger. The installer simply connect the piping to the pump station unit and the system is ready to commission. Additionally the use of a pump station allows for the use of a standard storage tank (without integrated heat exchanger).

  • Eliminates the chance of fluid freezing or overheating
  • Uses water as the heat transfer fluid
  • The pump station comes preassembled, saving time and money
  • For use in all climates
  • Collector(s) and exposed piping must be sloped to drain automatically
Indirect Drainback Pump Station Schematic

Indirect - Drainback (Load Side Heat Exchanger)

Indirect, drainback systems separate the fluid in the solar collector from the potable water using a heat exchanger. This variant is suited for larger systems using a larger, atmospheric (unpressurized) storage tank for both thermal storage and drainback duties. An immersed coil heat exchanger carries potable water from the boiler and/or main storage tank heating it as it travels through the solar storage tank. Since the tank is unpressurized it can be made of thermoplastics or insulated sheet metal. Multiple heat exchangers can be placed in the tank for multiple heating duties (DHW, pool heating, space heating, etc.).

  • Eliminates the chance of fluid freezing or overheating
  • Uses water as the heat transfer fluid
  • Large, unpressurized tank provides an affordable alternative
  • For use in all climates
  • Collector(s) and exposed piping must be sloped to drain automatically
Indirect Drainback Load Side Schematic

Indirect - Glycol (Single Pump)

Indirect, glycol systems separate the fluid in the solar collector from the potable water using a heat exchanger. In this variant the heat exchanger is integrated into the storage tank requiring only one pump to be used. The heat transfer fluid is a mixture of water and propylene glycol which allows the fluid to remain liquid at extremely low temperatures. The solar loop is pressurized so the circulator pump only needs to overcome friction head loss through the pipe and collectors. Pressure relief valves and thermal expansion tanks are needed to provide protection against high pressure events.

  • Eliminates the chance of fluid freezing
  • Uses water & propylene glycol as the heat transfer fluid
  • Solar loop is pressurized allowing for smaller pumps to be used
  • For use in cold climates
  • Proper pressure regulation equipment is required

Indirect Glycol Single Pump Schematic

Indirect - Glycol (Pump Station)

Indirect, glycol systems separate the fluid in the solar collector from the potable water using a heat exchanger. This variant shares the benefits of the single pump glycol system but adds value by using a plug & play pump station comprised of pre-plumbed pumps, valves, and heat exchanger. The installer simply connect the piping to the pump station unit and the system is ready to commission. Additionally the use of a pump station allows for the use of a standard storage tank (without integrated heat exchanger).

  • Eliminates the chance of fluid freezing
  • Uses water & propylene glycol as the heat transfer fluid
  • The pump station comes preassembled, saving time and money
  • For use in cold climates
  • Proper pressure regulation equipment is required
Indirect Glycol Pump Station Schematic