CSLB C-46 Solar ContractorSolar Thermal System InstallationMedium
A solar thermal installer is integrating a new pumped closed-loop system with an existing domestic hot water (DHW) storage tank that has an unused heat exchanger coil. The installer must ensure that the non-potable heat transfer fluid (glycol) in the solar loop does not contaminate the potable water supply. Which of the following heat exchanger configurations is required by code for this application?
- ASingle-wall heat exchanger with a backflow preventer on the potable water supply.
- BDouble-wall vented heat exchanger with an air gap or leak detection.
- CDouble-wall unvented heat exchanger with a check valve on the potable water supply.
- DSingle-wall heat exchanger with a pressure relief valve on the solar side.
Show answer & explanationAnswer & explanation
Correct answer: B. Double-wall vented heat exchanger with an air gap or leak detection.
When a non-potable fluid (like glycol) is used in a solar thermal system to heat potable water, plumbing codes (e.g., Uniform Plumbing Code - UPC) typically require a double-wall vented heat exchanger. This design provides a positive separation between the two fluids and a means to detect leaks, preventing contamination.
Why the other options are wrong
- A. A backflow preventer protects against reverse flow but does not prevent contamination if the single wall of the heat exchanger fails.
- C. An unvented double-wall exchanger lacks the leak detection capability of a vented design, which is crucial for code compliance with non-potable fluids.
- D. A single-wall heat exchanger is generally not permitted for non-potable to potable fluid transfer due to contamination risk.
Solar DHW Heat Exchanger Code
Code requirements for heat exchangers separating non-potable solar fluids from potable water prioritize public health and safety, typically mandating double-wall vented designs.
- Prevents contamination of drinking water.
- Double-wall provides redundant separation.
- Venting or a leak detection system indicates failure of the inner wall.
Memory trick: Double walls, vented space, keeps the glycol in its place.