Question

A farmer in upstate New York (Albany, NY), wants to grow Buttercrunch Lettuce in the winter months in a greenhouse with artificial lighting.

Given:

Insulation (R-vaule): 3.0 ^oF-ft²-btu/hr

Lamps: 15 Metal Halide lamps (Surface Temperature: 417^oF, Surface area:0.167 sf, Emissivity: 0.85)

Ventilation rate: 1 change per hour (Greenhouse Volume:1680 ft²)

Average Outside Winter High: 48 ^oF

Average Outside Winter Low: 24 ^oF

Average Outside RH%: 70%

Greenhouse: Surface Area = 806 ft²

Indoor Temperature range: 60 to 65 ^oF

Indoor RH: 50-70 %

Calculate the Heat Gain from the lamps in the greenhouse

Select one:

a. 798.9 BTU/hr

b. 650.55 BTU/Hr

c. 553.1 BTU/Hr

d. 110.3 BTU/hr

e. 129.8 BTU/Hr

f. 36.87 BTU/hr

Answer 1

Heat loss by conduction Q = A(T_1 - T_0)/R Heat loss = ventilation heat + connect line/conduct line heat loss Q ventilation = L - H load + SH load S.H = ni C_pm(t_1 - t_2) m = 47.57 times 1.2 = 5.7 08 ks/hr ventilation rate 1080 ft^3/hr = 47.5 + m^3/hr t_1 = 118 degree f = 8.88 degree c t_2 = 65 degree f = 18.33 degree c S.H = 57.08 times 1.02 (18.33 - 8.88) = 550.19 kw for condensing of winter high for condensing of winter low t_1 = 24 degree f = -4.44 degree c t_2 = 18.33 degree c SH = 57.08 times 1.02 (18.33 + 4.44) = 1325 kw = 1254 Btu/hr