The Building Code regulates where a backflow preventer is required. Articles 7.6.2.1.and 7.6.2.2. require protection of potable water systems against contamination due to reversal of the normal direction of flow between a potable water system and any other system containing non-potable water or substances, where there is a direct connection between the two systems.
Consequently, a backflow prevention device is required in a solar domestic hot water (SDHW) system only where there is a direct connection between the building’s potable water make-up supply and the solar heat transfer loop containing non-potable fluids. Where a non-potable heat transfer loop is charged with potable water through a charging port that is not permanently connected to a potable water system, the temporary connection to the potable water system shall include a backflow preventer or an air gap.
Equipment forming part of a packaged system for solar heating of potable water must conform to CAN/CSA-F379.1, “Packaged Solar Domestic Hot Water Systems (Liquid-to-Liquid Heat Transfer)”. The installation of packaged systems for solar heating of potable water in residential occupancies must be in conformance with CSA F383, “Installation of Packaged Solar Domestic Hot Water Systems”. All other systems must be installed in accordance with good engineering practice and are expected to comply, where applicable, with the same practices required for package systems.
According to Clause 7.4.3.1. of CAN/CSA-F379.1, a SDHW system that utilizes a single-wall heat exchanger is required to contain a relatively harmless heat transfer fluid (which may present minor to moderate hazard) and be properly labelled. In this case, a permanent backflow prevention device would be required on the charging line between the potable water system and the heat transfer loop only if there is a permanent direct connection between the heat transfer loop and the potable water system. Otherwise, the Building Code does not require backflow prevention devices on the domestic hot or cold potable water lines. In case of a conflict between the provisions of the Building Code and the standard, the provisions of the Building Code govern.
Similarly, where a SDHW system has a double-wall heat exchanger and there is a permanent direct connection between the heat transfer loop and the potable water system, the selection of the required backflow preventer would be determined in accordance with Sentence 7.6.2.3.(1), based on the type of heat transfer fluid used and other risks.
The requirement for premise isolation would be determined based on the use and the occupancy of the entire building. In most cases, the installation of a domestic solar hot water system that has a direct connection to a potable water system, alone, would not require the premise isolation referenced in Sentence 7.6.2.6.(1). “Relatively harmless” as defined in CAN/CSA-F379.1, “Packaged Solar Domestic Hot Water Systems (Liquid-to-Liquid Heat Transfer)” as a fluid having an oral LD50 of 15 000 mg/kg or greater, in accordance with Toxicity Class 6 (relatively harmless) of the Hodge and Sterner scale. The Hodge and Sterner scale is a toxicity scale recognized by the Canadian Centre for Occupational Health and Safety that provides ratings from 1 (extremely toxic) to 6 (relatively harmless) based on the LD50 approach for oral administration. LD stands for “Lethal Dose”. LD50 is the amount of a material, given all at once, which causes the death of 50% (one half) of a group of test animals. The LD50 is one way to measure the short-term poisoning potential (acute toxicity) of a material.
Information is published in the material safety data sheets supplied with all heat-transfer fluid shipments, as required by Canadian law.