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Greenhouse Radiant Heating System
Heather InstasiTulio Borel
ObjectivesDesign a radiant heating system for a
greenhouse located in Atascadero, CAHot ethylene-glycol solution flowing in tubes
embedded in 20ft x 40 ft concrete foundationKeep greenhouse air around 68 °F
ProcessCalculate heat loads based on
greenhouse geometrySelect spacing and diameter of
tubing and number of coils2D conduction modelFind heat transfer, flow rate,
temperatures, pressure drop in each coil
Find total pressure dropSelect a pump, heat exchanger,
boiler, expansion tankCost estimation
2D Conduction ModelThings to consider:
Pressure dropCostEven heating
0 1 2 3 4 5 60
20
40
60
80
0.75" - 5"space
Distance from wall (in)
Surf
ace H
eat
Flu
x
(Btu
/hr*
ft^
2)
System Layout Drawing
Total System Pressure DropInclude:
Heat Exchanger Pressure Drop (2.42 lbf/in2 ) Pressure drop due to fittings (elbows & tees—
branch and line flow) (0.1196 lbf/in2)Pressure drop in each coil (3.715 lbf/in2)Pressure drop in pipe connecting mechanical
room & greenhouse (1.1494 lbf/in2)Pressure drop between boiler and heat
exchanger in mechanical room (0.028 lbf/in2)Total = 7.432 lbf/in2
Pump SelectionOperating
Point:6.368 gpm17.17 ft of
Head
Heat Exchanger SelectionNeed at least 48972 Btu/hr
heat transfer rateSEC PL/PLT 70 Heat
Exchanger produces 52208 Btu/hr
Temperature difference of 15.5 °R on boiler side
Flow Rate 3373 lbm/hr (25L/min)
Boiler SelectionUtica MGB-125J
Input Rate: 125000Btu/hrHeating Capacity:
104000Btu/hrEfficiency: 82%
Bypass flow rate: 6.683 gpm
Expansion Tank Selection
Flexcon 2.1 gallon tankTotal volume needed = 0.4098
gallons
Cost AnalysisTotal capital cost: $13172Insulation costOperating Costs
Boiler: $3321/yrPump: $19.44/yr
Present worth analysis for 15 years at 6% interest rate: $45,613
Electric system PW analysis: $85163Electric system is 86% more expensiveInsulatio
n Thicknes
s (in)
Area of Insulation
(ft^2)
Heat Transfer
Loss (Btu/hr)
Capital Cost ($)
Operating Cost in a
year ($/yr)
O.C in 15 year Life Cycle ($)
1 800 12729 856 338.2 3284
2 1600 6364 1712 169.1 1642
3 2400 4243 2568 112.7 1095
4 3200 3182 3424 84.53 821
5 4000 2546 4280 67.64 656.9
Figure 1: Insulation Cost Analysis
Questions?