A copper coil in any steel boiler creates electrolytic corrosion, leading to early tank failure.
With a coil inside a remote boiler, two additional below grade insulated domestic water lines are required (a supply and return line that connects the coil to the water heater). This adds significant cost to the project. Any domestic hot water heating system must comply with the following rules: All domestic water piping, valves, fittings, pumps, controls and the overall installation must meet all national and state plumbing, sanitation and health codes. After installation is complete, the entire domestic waterside of the system must be pressure tested, flushed, and then sanitized according to local health department requirements. In all cases, a NSF or Board Certified anti-scald mixing valve is required by national and state codes when preheating or heating domestic water with equipment other than a conventional water heater. The valve shall be set to deliver hot water at a temperature of 120°F maximum. The two methods of preheating domestic water include: 1. A n external “ saddle mounted” or “side - arm” heat exchanger . A double walled, leak detecting tube within a tube all copper water-to- water heat exchanger is the recommended “saddle type” heat exchanger. This heat exchanger is to be mounted, close to and slightly below the level of the top of the existing water heater. Saddle heat exchangers can be installed to thermo-siphon or use a pump on the domestic waterside. Install a differential thermostat to control the small (1/25 hp) system pump. The domestic water within the water heater should be heated to 145°F in order to kill water borne Legionelle bacteria. The “hot sensor” of the control should measure the GARN® water temperature; the “cold sensor” should measure the domestic water temperature at the inlet of the heat exchange r. The sensors may be “strapped” to the pipe and covered with insulation in order to provide accurate temperature readings to the differential controller.
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Hydronic System Design Manual ©DECTRA CORPORATION - March 2013
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