i88 
Journal of Agricultural Research 
Vol. XXVI, No. 4 
GREENHOUSE COMPARTMENTS - 
The installation has been enlarged so as to provide four chambers 
located in one of the greenhouses. These chambers are used for growing 
plants in sunlight, partly to measure salt absorption in the light, and 
partly to study the effect of low temperature on the hardening of plants. 
The close control of temperature in these chambers is, as before stated, 
attended with considerable difficulty, caused by sunlight and the passing 
of clouds which suddenly shut off or let on this source of heat. Fairly 
accurate control of the temperature, however, has been obtained by re¬ 
ducing the temperature somewhat below that desired and heating back 
by an electrically heated coil. There is the great danger, however, in 
the heating-back method, of desiccating the plants too much, owing to low 
relative humidity. This has been corrected somewhat by providing a 
cold-air bunker at the bottom of each chamber. Cold air from this 
bunker is mixed with the warm air of the chamber by means of a fan and 
air valve. With this arrangement, entirely satisfactory control is not 
obtainable during the summer months, owing to the high temperature of 
the greenhouse, the large amount of solar heat, and the consequent high 
rate of air changes in the chamber. 
It is believed that it is impracticable to accomplish very accurate 
temperature and humidity control during the summer months if at¬ 
tempted on a small scale. Accurate control can perhaps be economically 
obtained only when the equipment is large enough to provide for the 
necessary heat interchanges and for the control of humidity by a spray 
system. 
Typical temperature charts are illustrated in figure 4. The upper 
chart shows the variation in the greenhouse temperature, and the lower 
chart shows the temperatures maintained in one of the cold chambers 
during the same period. 
Referring to the lower chart, the numbered points are explained as 
follows: 
1. Shows the temperature in the chamber at the beginning of the 
experiment. In about one and one-half hours the temperature of the 
chamber was down to the desired point and the control equipment began 
to function. A temperature of about 23 0 F. was maintained for several 
hours to insure the satisfactory operation of the control equipment and 
the cooling of the chamber. 
2. Plants placed in the chamber. 
3. Plants placed in and removed from chamber (2 lots). 
4. Plants placed in and removed from chamber and regulator reset 
to maintain a slightly lower temperature. 
5. Plants placed, then box opened and plants allowed to thaw before 
removing. 
6. Repetition of No. 5. 
7. Plants placed, temperature regulator reset. 
8. Plants placed (2 lots), temperature regulator reset. 
9. Plants placed and removed. 
10. To this point the temperature was controlled by heating back with 
electricity. After this point the temperature was controlled by refrig¬ 
eration alone, that is, by starting and stopping the refrigerating machine 
automatically. 
11. Experiment finished and compressor stopped. 
