Assume you have a 20m x 100m greenhouse with 2.4m sidewalls, an open-gable interior roof and a roof at an 18.4 degree
angle (i.e., a typical 4â rise on 12â run roof line). You are growing plants that release into the greenhouse the equivalent
of 2500 gallons of liquid water/day-acre of growing area (in the form of water vapor). Additionally, the plants absorb
0.19 kg CO2/hr-100m2 of growing area. The ambient CO2 entering the greenhouse is 340 ppm. The outside air entering
the greenhouse through the ventilation system is 20oC and 50% RH. The greenhouse glass (R=0.8 m2-oC/W; air films NOT
included) receives 670 W/m2 of short-wave solar energy, 60% of which transmits through the glass where 30% of this
energy is absorbed within the greenhouse and used to heat the surrounding greenhouse air. You want to maintain the
following conditions: a). Inside temperature of the greenhouse no more than 10oC above ambient levels, b). CO2 inside
the greenhouse at 1200 ppm, during the 12 hours of daily sunlight, and c). the inside relative humidity at 70%.
1. (2) Determine the mass of water vapor produced in the greenhouse per second, hour, and day.
2. (2) Determine the mass flow rate of dry-air required to maintain the desired humidity ratio, W, in the greenhouse.
3. (4) Determine the mass of CO2 uptake by the plants to maintain photosynthesis per second, hour, and day.
4. (4) Using the mass flow rate of dry-air determined in (2), determine the amount of CO2 that must be added inside the
greenhouse to maintain the desired concentration of 1200 ppm.
5. (3) Determine the UA-value for the greenhouse.
6. (3) Determine the net solar energy absorbed inside the greenhouse that is available for sensible heating. Assume the
solar load is transmitting only through the roof surface area.
7. (4) Determine the mass flow rate of dry-air required to maintain the desired greenhouse air temperature.
8. (4) Assume that you want to ventilate the greenhouse at the larger of the rates determined for a water vapor balance
and energy (i.e., dry-bulb temperature) balance. At this rate, and using the CO2 generation rate determined in (4),
determine the resulting relative humidity, humidity ratio, dry-bulb temperature, and CO2.
9. (4) Plot using excel, the concentration of CO2 inside the greenhouse (in ppm) given the supply rate determined in (4),
as a function of the mass flow rate of dry-air through the greenhouse. Label the x-y axis (variable + units), use a scatter
graph, and label your legend. You are plotting CO2 concentration (y-axis) versus mass flow rate of dry-air (x-axis). You
will be graded on the accuracy of your solution and the professionalism of your plot.
Assume you have a 20m x 100m greenhouse with 2.4m sidewalls, an open-gable interior roof and a roof at an 18.4 degree
angle (i.e., a typical 4â rise on 12â run roof line). You are growing plants that release into the greenhouse the equivalent
of 2500 gallons of liquid water/day-acre of growing area (in the form of water vapor). Additionally, the plants absorb
0.19 kg CO2/hr-100m2 of growing area. The ambient CO2 entering the greenhouse is 340 ppm. The outside air entering
the greenhouse through the ventilation system is 20oC and 50% RH. The greenhouse glass (R=0.8 m2-oC/W; air films NOT
included) receives 670 W/m2 of short-wave solar energy, 60% of which transmits through the glass where 30% of this
energy is absorbed within the greenhouse and used to heat the surrounding greenhouse air. You want to maintain the
following conditions: a). Inside temperature of the greenhouse no more than 10oC above ambient levels, b). CO2 inside
the greenhouse at 1200 ppm, during the 12 hours of daily sunlight, and c). the inside relative humidity at 70%.
1. (2) Determine the mass of water vapor produced in the greenhouse per second, hour, and day.
2. (2) Determine the mass flow rate of dry-air required to maintain the desired humidity ratio, W, in the greenhouse.
3. (4) Determine the mass of CO2 uptake by the plants to maintain photosynthesis per second, hour, and day.
4. (4) Using the mass flow rate of dry-air determined in (2), determine the amount of CO2 that must be added inside the
greenhouse to maintain the desired concentration of 1200 ppm.
5. (3) Determine the UA-value for the greenhouse.
6. (3) Determine the net solar energy absorbed inside the greenhouse that is available for sensible heating. Assume the
solar load is transmitting only through the roof surface area.
7. (4) Determine the mass flow rate of dry-air required to maintain the desired greenhouse air temperature.
8. (4) Assume that you want to ventilate the greenhouse at the larger of the rates determined for a water vapor balance
and energy (i.e., dry-bulb temperature) balance. At this rate, and using the CO2 generation rate determined in (4),
determine the resulting relative humidity, humidity ratio, dry-bulb temperature, and CO2.
9. (4) Plot using excel, the concentration of CO2 inside the greenhouse (in ppm) given the supply rate determined in (4),
as a function of the mass flow rate of dry-air through the greenhouse. Label the x-y axis (variable + units), use a scatter
graph, and label your legend. You are plotting CO2 concentration (y-axis) versus mass flow rate of dry-air (x-axis). You
will be graded on the accuracy of your solution and the professionalism of your plot.
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