In fact, without storage, circulating fans would only have to run during daylight hours, thereby saving on electrical use. Air is circulated in the dryers to facilitate heat transfer from the absorber and to assure uniform drying. A typical air velocity through the lumber pile is 150 feet per minute. When this value is multiplied by the total sticker space openings, the result is the average cubic volume of air required. The drying rate in the dryer can be controlled directly by varying the relative humidity in the dryer.
Low humidities result in faster drying and lower final moisture contents than high humidities.
When the cooler outside air is subsequently heated, its relative humidity is lowered, thereby assisting drying. This loss of energy and the benefit of venting must be considered together. Excessive venting will be wasteful and will result in cool dryer temperatures and therefore slow drying. On the other hand, inadequate venting may result in very high humidities which also will result in slow drying. In general then, venting should be sufficient to lower inside humidities, but not to substantially reduce inside temperatures.