Size the pump to provide 1 to 1.5 gpm of flow at a maximum velocity of 4 FPS through each baseboard. Individual room-by-room control is best. This is easily accomplished by using a radiant floor manifold with individual runouts to each HWBB section. If this is not possible, try to zone the system so that rooms with similar heat loss characteristics are on the same circuit.
Whenever a zone thermostat calls for heat, the pump serving that zone is to be activated.
Strictly follow the manufacturer’s installation and placement instructions.
NEW CONSTRUCTION
Determine the linear footage of wall that is available for the placement of the hot water baseboard. Divide the BTUH heat loss of the building by the available footage. Select the baseboard units that can supply the BTU’s per foot required to meet the building’s heat loss. Select the baseboard based on a supply water temperature of 140°F. If the available linear wall footage is not sufficient, adding more baseboard, selecting a more efficient baseboard, or selecting a larger GARN® unit with greater thermal storage is required.
CONVERTING AN EXISTING BASEBOARD SYSTEM
Most installers select a GARN® system that will supply 140°F water to a baseboard system. If the existing system was supplying water at a higher temperature, say 180°F, an analysis must be done to determine whether a lower supply water temperature will meet the needs of the building. The following table can be used for this purpose.
Water Temperature Correction Factors (entering air temperature = 65°F)
100 110 120 130 140 150 160 170 180 190 200 210 215 0.13 0.19 0.25 0.31 0.38 0.45 0.53 0.61 0.69 0.78 0.86 0.95 1.00
Supply Water Temperature (°F)
Correction Factor
The above table can be used to determine the difference between the BTU/HR delivered by the existing system vs. the BTU/HR that can be delivered by the GARN® system at a lower supply water temperature. A standard of 215°F is used in the industry as the basis for rating. If a baseboard is rated at 1000 BTU’s/linear foot at 215°F (contact manufacturer for output ratings), the table indicates that at 180° the exist ing baseboard can deliver 69% of the rated BTU’s or 690 BTU’s/linear ft. A GARN® system sized to use 140° water will yield 38% of the rated BTU’s or 380 BTU’s/linear ft. If the old system was sized twice as large as the actual heat loss (a common occurrence), then the sizing of the GARN® system for 140° water is correct. If more heat is required, a larger storage system or more baseboard footage will be required.
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Hydronic System Design Manual ©DECTRA CORPORATION - March 2013
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