PRESSURIZED, FIXED SUPPLY TEMP – VARIABLE SPEED PUMPING
The following piping configuration provides a fixed supply temperature via a variable speed primary pump and constant speed secondary pump. A heat exchanger separates the system ’ s primary (GARN side) from the secondary (heat distribution) side. The primary pump circulates water between the GARN unit and the heat exchanger; the secondary pump circulates water around the heat distribution piping. When the space calls for heat, controls activate both pumps.
Advantages
Disadvantages
Can be easily connected to a pressurized system. No mixing valve required. A variable speed pump will only supply as much water as necessary to maintain a set HWS temperature on the secondary side of the heat exchanger. This allows the system to take full advantage of the GARN tank ’ s thermal stratification. The heat exchanger separates the GARN from the heat distribution system, so glycol can be used.
The heat exchanger must be sized and piped properly. Notice the “ counter flow ” configuration on the heat exchanger. See discussion in in the Water to Water Flat Plate Heat Exchanger section of this manual. The strainers must be maintained and cleaned so the heat exchanger does not plug up and lose performance.
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Hydronic System Design Manual ©DECTRA CORPORATION - March 2013
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