You are to provide a snowmelt system for a 100’ x 100’ pedestrian plaza with brick pavers over a sand bed with 2” insulation under the area and on the vertical edge. Only light maintenance vehicles will be permitted in this area and it is not critical to keep the area completely clear under any conditions. Some snow accumulation will be permitted during heavy snowfalls, but it is expected that the area will be generally free of snow and ice during “normal” conditions. It rarely snows in this location if the temperature is below 20°F and the temperature never drops below -5°F. The system will have a separate heating plant and is expected to operate without supervision. The mechanical room will be at the center of one of the boundaries of the melt area with all equipment and manifolds located in the room.
Equipment Size: When you check the chart for Heat Output and Fluid Temperature for tubing in a sand bed under brick pavers you can see that at +10°F with a 10 mph wind you need approximately 100 btuh/ft². Total system output required for this system will be a minimum of 1,000,000 btu/hr. Remember that this is NET OUTPUT of the heating plant. The heating fluid will be a solution of 40% propylene-glycol and water, providing freeze protection to a temperature of approximately -10°F. Total system flow rate at a 25°F drop across the system will be about 1,000,000 (btuh req’d) / 12,500 (system flow at 25°F ΔT) x 1.10 (flow correction for 40% P-G) = 88 gpm total flow. From the same chart we can see that the average fluid temperature should be 99°F. The supply temperature is now 99°F (average fluid temp) + 12.5°F (½ of the ΔT) = 112°F
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