CSLB C-46 Solar ContractorSolar Thermal System InstallationHard
A solar thermal system with an open-loop drainback configuration is being designed for a commercial building. What is a critical design consideration for the collector array piping in this type of system that differs from a closed-loop system?
- AGlycol concentration must be precisely maintained for freeze protection.
- BThe system requires a pressure relief valve at the highest point of the collector array.
- CAll collector piping must have a continuous slope back to the drainback tank.
- DPiping must be rated for higher operating pressures.
Show answer & explanationAnswer & explanation
Correct answer: C. All collector piping must have a continuous slope back to the drainback tank.
In a drainback system, all collector piping must be continuously sloped back to the drainback tank to ensure complete drainage of the fluid when the pump turns off, preventing freezing and stagnation. This is a unique and critical design aspect of drainback systems.
Why the other options are wrong
- A. Drainback systems typically use plain water, not glycol, for freeze protection by draining the collectors.
- B. Drainback systems are open to atmosphere or a vented tank, so a pressure relief valve at the highest point is not typically required as it is not a pressurized system.
- D. Drainback systems typically operate at atmospheric pressure, unlike pressurized closed-loop systems.
Drainback System Piping Design
Specific requirements for collector loop piping in a solar thermal drainback system to ensure complete fluid drainage.
- All piping must be continuously sloped.
- Prevents freezing and stagnation by draining collectors when pump is off.
- Requires careful attention to eliminate sags or traps.
Memory trick: For drainback's flow, a continuous slope must show, let no water stay, let it all go!