Install a 3 way mixing valve to blend cooler radiant floor return water with hot supply water from the GARN® unit in order to maintain the moderate supply water temperatures (between 95°F and 130°F) required for radiant floor heating. Mixing valve brands are Paxton ESBE, Honeywell Sparco and Watts. Install mixing valve between the GARN® unit and pump so that the pump draws through the valve from the GARN®.
CONNECTION TO AN EXISTING PRESSURIZED SYSTEM
Retrofitting a GARN® WHS unit to an existing pressurized heating system requires the installation of a pressure rated flat plate heat exchanger. Contact your local GARN® dealer or DECTRA CORPORATION for sizing, availability and pricing of FlatPlate heat exchangers. Note the following and review the drawing: DO NOT connect any GARN® unit to a steam boiler or steam heating system. The water-to-water heat exchanger must have a pressure rating that is equal to or greater than the pressure rating of the existing boiler. Consider changing the system to a primary secondary system. Position the heat exchanger on the return side of the existing boiler. The GARN® unit and the heat exchanger shall NOT be installed so as to interfere with the normal delivery of heated water from the existing boiler. The GARN® unit and the heat exchanger shall be installed without changing the function of the controls or rewiring the existing boiler. A control wiring connection is permitted only if required to obtain proper operation. For instance, when a thermostat calls for heat, both the GARN® pump and the existing pump are to be powered. The electrical system of the existing boiler and GARN® pumps must be powered from a single branch circuit, without exception.
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Hydronic System Design Manual ©DECTRA CORPORATION - March 2013
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