44 CIRCULAR 740, U. S. DEPARTMENT OF AGRICULTURE 



for delivery the desired equality of volume discharged at various 

 openings may also be had by installing a deflector vane at each to 

 turn the air outward through the opening. These deflectors, or scoops, 

 are illustrated in figure 14 and also in figure 15, which is from a 

 photograph of such a deflector inside a duct. 



When the air direction is reversed periodically, the ducts should be 

 laid out somewhat as illustrated in figure 14. The ducts are at the 

 ceiling, one along each side of the room. The figure shows a pair 

 of ducts, either one of which may be used as a delivery while the other 

 acts as a return. The arrangement permits reversing the direction of 

 air movement without throwing the quantity of air entering or leaving 

 such opening out of balance. The openings and deflectors extend the 

 full width of the duct and their size is progressively larger as the 

 distance from the fan end of the duct increases. This provides for 

 uniform air volumes when the duct acts as a return. The scoops are 

 adjusted to distribute the air Uniformly when acting as a delivery. 

 The size of openings and adjustment of the deflectors should be fixed 

 for uniform distribution without provision for readjustment from 

 time to time. Openings 10 to 25 feet apart are spaced equally along 

 the duct. It is sometimes convenient to have one opening in each bay. 



DESIGN FOR 36° F. ROOMS 



Attempts to keep a room at 36° F. by merely choking down the duct 

 openings delivering 30° to 32° air inevitably result in failure, because 

 (1) some fruit adjacent to the delivery ducts will be subjected to low 

 temperature, and (2) choking down the volume of air necessary to 

 remove the field heat, and later the storage heat of respiration, results 

 in a wide range of temperatures in different parts of the room. To 

 avoid these conditions, it is necessary to recirculate sufficient air to 

 raise the temperature of the incoming air and to provide adequate 

 air movement through the stored fruit. 



Where it is desirable to refrigerate one room at 30° F. and another 

 at 36° from the same brine-spray chamber, it will be necessary to pro- 

 vide the 36° room with a damper in the main supply duct and to 

 install within the room a recirculating duct with a small fan between 

 delivery and return ducts. This arrangement will choke down the 

 supply of air at 30° and mix it with the warmer air that is recircu- 

 lated by means of the auxiliary duct and fan. Thus, the air is tem- 

 pered to 36° before leaving the delivery duct and an adequate volume 

 is circulated. 



Girders and Joists 



In designing the structural elements of a cold-storage building the 

 layout of the system of air ducts should have preliminary considera- 

 tion, so that girders extending below the ceiling may be in the direction 

 of air flow from delivery to return ducts. Wliere this is not feasible, 

 the ceiling should be so constructed that air will flow over the girders 

 between the joists. Where the ceiling is to be insulated, either the 

 insulation should be applied above the joists or the ceiling should be 

 recessed between the joists so as to leave 3 or 4 inches free space between 

 the ceiling and the lower edges of the joists (fig. 16) . 



