Sizing and Selection of Equipment
There are many factors contributing to the need for greenhouse cooling and ventilation equipment. The primary source of heat in a greenhouse is solar radiation. To reduce greenhouse temperatures, air removal is required and its rate of removal is a function of the floor area. A simplified method for sizing and selecting equipment for greenhouse temperature control is included in this brochure.
From charts 1 and 1A, locate the greenhouse size using the "equivalent width" from the formula below nd the actual length of the greenhouse.
Select the Fan-Jet(s) within the range shown. If the Fan-Jet is to be used for distributing heat, include the heat accessory kit to go with the Fan-Jet. Select the proper model of tubing according to the length of the greenhouse. Improper tube punching will not provide uniform air distribution.
SELECTING EXHAUST FANS:
Winter Ventilation: (used in conjunction with Fan-Jet) Between 1 1/2 and 2 CFM per square foot of floor area is required for winter ventilation.
Either increase the size of the Fan-Jet or reduce exhaust below the Fan-Jet CFM rating.
Summer Ventilation and Cooling: Approximately 8 CFM per square foot of floor area is required for maximum ventilation and cooling.
If fans and pads are less than 100 feet apart, adjustments must be made for air velocity.
Select the exhaust fans to provide the higher of either CFM for conditions or CFM for velocity.
SELECTING KOOL-CEL SIZE:
Kool-Cel is most efficient with air velocity of 250 fpm. Therefore, for maximum efficiency add the total exhaust selected and divide by 250 to get the square feet of pad required. Divide the square feet of pad by the available length of run to get the height of Kool-Cel required. Round off to the nearest foot.
The pads are 4" x 12" x 24", 36", 48", 60" & 72". Using the tall pad support, they may be stacked to provide 60", 72", 84", and 96" high pads, The number of Kool-Cel pads required is equal to the length of run.
Select the distribution system that matches the length of run up to 100'. (50' in PDR systems.)
Select the water pump according to the length of the distribution system. Use #15 pump for systems up to 40', #30 up to 70', and #60 up to 100'.
SELECTING INLET SIZES:
Winter Ventilation: The inlet shutter sizes for Fan-Jet systems are listed with the Fan-Jets on Page 10.
Because of non-resident management of greenhouse operations today, automatic controls become a necessity.
If simple one or two step heating or cooling is required, thermostats will satisfactorily operate the equipment. But to conserve energy, staging equipment is recommended to use minimum equipment while achieving desired temperatures.
The ACC-I has zero, one, two, or three stages of heat, one stage of circulation and four, five, six, or seven cooling/ventilation stages.
The Grotron II has two stages of heat, one for circulation and five stages of cooling/ventilation. More features are a part of the Grotron II system and are detailed on Page 19 and in Brochure C46.
A 25' x 100' greenhouse located in an area with less than 1000 feet elevation and 5000 f.c. of light. This example is based on 15 degree winter inside temperature above outside temperature and 7 degree rise from pad to fan in summer. Air flow will be end to end and, therefore, fan to pad distance is 100'.