glycol SOLAR and other closed loop designs

These systems are what professionals call pressurized closed-active systems (closed because they use a glycol based fluid or other non-freezing medium instead of water; active and pressurized because they use pumps instead of convection or other natural principles to route the water and the glycol). We will call these systems, in this page, glycol solar...

See also:

Batch solar water heaters
Thermosyphon design
Active Solar Design
Drainback Design

Elements of Glycol solar systems

Glycol solar are the most complex solar water heating systems. They comprise 1) Solar panels, 2) an expansion tank and a storage-backup tank, 3) a pump, 4) an heat-exchanger, 5) a differential controller and obviously a set of valves and sensors to interconnect the system…

Glycol solar systems are in direct competition with drainback solar designs; both are excellent for cold climates, namely for those with extreme temperatures.

Anti-freezing

Glycol solar systems do not use water in the collectors. Potable water is pumped to the storage tank but never to the solar panels.

It’s the anti-freezing fluid (typically a mixture of water and glycol) that circulates in the solar panels and through a coil of pipe (in the storage tank). The anti-freezing/glycol supports extremely low temperatures and protects the system from damages caused by severe cold.

Antifreezing should be checked each year and changed regularly every few years (depending on temperatures and glycol quality).

Glycol Solar Expansion tank

The use of glycol or other anti-freezing fluid requires the system to have an expansion tank, designed to keep the pressure below the relief valve settings and to absorb an increased volume of water.

Glycol Solar pump and controller

Glycol solar solutions demands a controller, closely linked to the pumps and sensors. The controller is the brain of the system, and determines when the pump should be activated in order to route the anti-freezing through the panels.

Heat exchanger

Glycol solar water heaters also require an heat exchanger (to transmit the warmth of the fluid to the water); the heat exchanger can be internal (often a coil of pipe within the tank where the potable water is heated: as the hot fluid routes the coil, the heat passes from the fluid to the cooler water surrounding the coil) or external (often a mere tube within a tube, one for the circulating heated fluid and the other with the water to be heated).

Climates

Glycol solar systems are popular in regions with long-lasting subzero temperatures; they are typical and efficient solutions in these climate conditions.

Solar Panels & Glycol Solar systems

Tube solar panels are the best option for glycol solar systems (and for other thermal solar applications involving colder climates).

Other elements

Glycol solar hot water systems also include auxiliary elements: sensors, controls, valves…

The image (EERE) depicts the components of a glycol-type solar system. It doesn't show the expansion tank, a common option in these systems. It shows a flat solar panel, though today's systems use preferentially tube solar panels, a more efficient option in colder climates.