Closed-loop solar water heating systems

Closed loop systems use heat-exchangers that circulate heat-transfer fluids through the panels and feed pipes. This type of system is called a closed-loop system, because the solar exchange fluid is closed-off from the external atmosphere or isolated from the potable water through utilization of a heat exchanger.

A closed-loop system works essentially by heating solar fluid that is pumped through the solar collectors. The heated solar fluid flows through a copper or stainless steel heat exchanger located near the solar storage tank. The heat from the solar fluid transfers to the potable water within the solar storage tank. Another small circulator pump may be used to circulate the water through the potable side of the heat exchanger.

strengths

The anti-freeze heat exchange fluids can withstand freezing temperatures, allowing the system to operate during periods when there is the greatest temperature difference between cold incoming water, and temperatures reached in the solar collectors. The system can have the greatest performance benefits at this time. Also, if maintained properly, these systems will not corrode or scale the passage ways in the solar collectors and pipes. Closed-loop systems tend to have the lowest overall operating costs --other than passive systems-- and are especially adapted to work in regions with extended periods of freezing temperatures, and commercial environments that are used daily (including weekends).

A closed-loop system is a good alternative to consider if installation conditions inhibit installing a drainback system, for example because the feed and return pipes to the solar panels cannot be plumbed at an adequate slope (usually 0.25inch per 1 horizontal foot or steeper).

weaknesses

Closed-loop systems tend to have the highest installation cost associated with them. They heat water slightly less efficiently than direct open-loop systems, (but can work more and longer when it is risky to operate open-loop systems). These systems are designed to operate daily, and may overheat (releasing heat transfer fluid) if the fluid in the closed-loop does not circulate during a hot summer day --for example, when a unit is shutoff because residents leave for vacation. At these times, instructions sometimes call for panels to be covered to prevent discharges due to overheating.

Closed-loop water heating systems in the catalog

DekkaSupply.com > Solar and Radiant Hydronic Heating > Closed-Loop systems and modules