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?