ns 4 HLMIDirriNG APPARATUS fCP SMALL TEST ROCMS August 1949 tin* * JAM 1 2 Ah ATLANTA, v No. R1752 UNITED STATES DEPARTMENT OF AGRICULTURE AGRICULTURAL RESEARCH ADMINISTRATION BUREAU OF PLANT INDUSTRY. SOILS. AND AGRICULTURAL ENGINEERING DIVISION OF FOREST PATHOLOGY MADISON 5. WISCONSIN IN COOPERATION WITH THE FOREST PRODUCTS LABORATORY FOREST SERVICE rus FOB - THEODORE C. SCIEFFER,- Pathologist and OSCA ... TORGESON,^ Engineer The wood-element hygrostat illustrated in figure 1 was devised by Torgeson for use in an experimental lumber dry kiln at the U. S. Forest Products Laboratory, Lison 5j ' r is. Because of its simplicity and sturdiness it later was in- stalled in each of two 600-cubic-foot rooms used at the L ory for accel- erated testing of the resistance of wood and v:ood products to decay by pure cultures of wood-destroying fungi. As set, the hygrostat, in conjunction with the humidifier illustrated in figure 2, maintains an average relative humidity of 70 percent with deviations of about plus and minus 2 percent. The tempera- ture of the rooms is thermostatically kept at 80° F. Over several years, no adjustment in setting on account of changes in characteristics of the hygro- stat has been needed. The reliable performance and simplicity of this hum id i- fication system should make it useful in many connections requiring humidity control within a moderately narrow range and at a level greater than that prevailing outside the space to be conditioned. It is already being used for biological work at a number of other laboratories. '._>- . novel features of the hygrostat consist of the wood element and a micro- type switch that is sensitive to a very slight movement of the element. The wood should be free of defects and have as flat a grain as possible for the flatter the grain the greater will be the dimensional change lengthwise of the element with a given change in relative humidity, and thus a correspondingly greater operating sensitivity of the hygrostat will be provided. The sapwood of hardwood species, such as maple and birch, makes a good element. The switch should be of the normally closed type. It is opened by pressure of the foot of t'.'.e wood element against a protruding contact point, and this interrupts the flow of current through the heating coil of the humidifier. It is closed again and hum id if ication is resumed as the element shrinks in response to decreasing relative humidity. No relay is required; itch, which is designed for current loads up to 1,200 watts, is simply connected in scries with the heating element of the humidifier. -Published in SCIENCE, Tug. 26, lvhT, Vol. 110. 2 -Bureau of riant Industry, Agricultural Research Administration, U. S. Depart- ment of Agriculture, in cooperation with the Forest Products Laboratory. 3 -Forest Products Laboratory, Forest Service, U. S. Department of Agriculture, in cooperation with the University of Wisconsin, . J ..• , As. hept. No* P1752 -1- riculture-h.adison The relative humidity to be maintained is controlled by the proximity of the element foot to the snitch contact point, which is regulated by adjusting the spacing between the spring bronze element supports. These supports are spread or contracted by turning the right- and left-hand thread screw in the nuts brazed to the supports. The final adjustment is arrived at by trial and error, using a wet- and dry-bulb hygrometer to indicate when the proper setting lias been made. The humidifier (fig. 2) consists of a closed 5-gallon reservoir of water that feeds through 10 mm. glass tubing into a glass evaporating pan. Heat is supplied by an open, 200-watt heating coil submerged in the pan. A sealed heating unit probably v:ould give longer service, although the open coil is remarkably durable when kept submerged. The smaller the heat output of the unit, the smaller will be the overrun in humidification resulting from lag in the response of the hygrostat. The water reservoir is filled as necessary through a half-inch hole bored in the top. A rubber stopper is inserted in the outlet tube during the filling process* Distilled water is used because of the extreme hardness of the tap water in j.iadison, although lime would not, of course, materially interfere with the operation of the apparatus if it were removed from the evaporating pan and heating unit frequently enough to prevent large accumulations. Significant stratification of relative humidity and temperature in the con- trolled rooms at the Laboratory is avoided by keeping an electric fan running at low speed in each room. From measurements made in one of the rooms during the winter, it was found that about 073 grams of water per day were evaporated in maintaining the 70- percent relative humidity. The humidifier was in operation about £.6 hours each day, which entailed a daily power consumption of about 1.16 kilowatt- hours. Corresponding summertime values were not measured, but are known to be considerably smaller. The room in this case is Trailed on three sides with double sheet-rock panels with mineral-wool insulation batting between them, and on the fourth side with unglazed tile. All conspicuous cracks and similar openings to the outside are sealed with caulking compound, a measure tiiat materially reduced the amount of humidification required. To provide a relative humidity lower than that of the outside atmosphere, some arrangement for increasing the temperature ( if this could be tolerated) or for dehumidification would, of course, be necessary. In any case, the wood-element hygrostat could be adapted to serve as the control apparatus. T.ept. Mo. R17£2 -2- SUPPORT BRACKET COUPLING Hil> EXTENSION ROD 3 C ADJUSTING KNOB TOP VIEW RIGHT AND LEFT HAND THREADS WOOD ELEMENT (END GRAIN) jj SPRING BRONZE SUPPORTS FOR ADJUSTING WOOD ELEMENT D C NUTS BRAZED TO METAL SUPPORTS SIDE VIEW ^2 SPRING BRONZE FOOT THAT OPERATES CONTACT POINT OF ELECTRIC SWITCH DOUBLE-THROW ELECTRIC SWITCH SCALE 3 INCHES J END VIEW Figure L. — Hygrostat z m l*bT) * UNIVERSITY OF FLORIDA 3 1262 08866 5020 ONE -INCH STOPPERED OPENING FOR FILLING 200 W. HEATING UNIT 10 MM. OUTLET OF GLASS TUBING THROUGH RUBBER STOPPER TO I/O V. CIRCUIT TO HYGROSTAT SWITCH O I L. 2 i 4 INCHES 2 h 80267 F SCALE Figure 2. — Humidifier.