Indirect Solar Water Heating System Design

Indirect solar thermal systems use a heat-transfer fluid (HTF), such as a propylene glycol solution, to safely move heat from solar collectors to a storage tank via a heat exchanger. This decouples the potable water loop from the collector circuit, making these systems ideal for freeze-prone zones, applications requiring secondary containment, or commercial projects that demand durability and redundancy. 

At the heart of AET’s indirect solutions are our OG-100 certified flat plate collectors, pre-engineered pump stations, and heat-exchange-ready storage tanks. Combined with differential temperature controllers, our designs streamline deployment and meet long-term performance targets. 

Indirect systems are ideal for: 

• Healthcare facilities
• Educational campuses
• Multifamily housing
• Military installations
• High-rise buildings
• Cold climate regions

Our indirect solar thermal systems are engineered for superior performance across diverse environments, particularly excelling in cold climates. These systems ensure continuous energy capture throughout the year while safeguarding critical components from harsh weather conditions. Designed with compliance, efficiency, and durability in mind, our solutions meet the highest industry standards, delivering both environmental benefits and cost savings.

Designed for year-round performance, our indirect systems ensure solar collection continues through winter months while protecting collectors, piping, and tank components from damage. 

AET systems are built to meet and exceed requirements for BABA (Build America, Buy America), LEED, and state-level solar thermal incentives. We support our partners with documentation and submittals to streamline code compliance and funding eligibility. 

By separating the collector and domestic loops, indirect systems reduce scaling, minimize maintenance, and allow for remote component placement, ideal for rooftops, ground arrays, or mechanical room integration. 

AET offers fully engineered systems: 

• Collectors and mounting hardware
• Pump station with integrated expansion tank, valves, and sensors
• Heat exchanger-ready thermal storage tanks
• Digital controller and safety module

Each package is sized for specific draw profiles, site constraints, and collector field layouts, ensuring the system performs as designed. 

AET indirect systems are a strategic tool in decarbonization planning. By displacing fossil-fueled water heating with renewable thermal energy, our designs directly reduce Scope 1 emissions. Systems are eligible for IRA Section 48 credits, state-level rebates, and contribute toward ESG reporting, LEED certification, and carbon neutrality goals. 

 If you’re specifying or retrofitting water heating systems in cold climates or commercial environments, our technical team can assist with system selection, layout guidance, and incentive alignment.