b'PSYCHROMETRICSPSYCHROMETRIC MEASUREMENTPsychrometric measurements are done with a sling psychrometeran indispensable tool for any building scientistHANDLE and should be in every Kirby bag (named for G.K. Kirby Garden, a pioneer in building science with the Division ofSWIVELBuilding Research at the National Research Council Canada). The device is basically two thermometers swivel mounted onFRAMEa common frame so that it can be swung around in the air. WET-BULB SCALEThe bulb on one of the thermometers is wrapped in absorbent wicking (called the sock), which is wetted to saturation before the device is used.When the device is spun in the air for about one minute, both thermometers come into intimate contact with the air; the thermometer with no sock (the dry bulb) comes into thermodynamic equilibrium with theDRY-BULB SCALEsurrounding air, which provides an accurate measurement ofDRY BULBthe air temperature, called the dry-bulb temperature. As the device spins, the water in the sock evaporates until it reachesWET BULB (INSIDE SOCK)thermodynamic equilibrium with the moisture in the air, which causes evaporative cooling in the second thermometer. The amount of cooling, as measured by reduction of the wet-bulb temperature, defines the amount of evaporation that hasThe benefits of the sling psychrometer are that it provides occurred, which can be accurately correlated to the amountdirect measurement (unlike electronic devices, which rely on of moisture in the air. This is an elegant method to directlycalibration curves to correlate the electrical resistance of the measure the humidity in the air and only requires a few dropsair to humidity levels) and it doesnt require batteries or other of water and a strong wrist. The direct-measurement methodpower sources, except the aforementioned wrist. The main of this device is preferred to electronic devices, as the latterdisadvantages are that one must use a psychrometric chart do not reach equilibrium with the air as quickly and theirto process the measured results and that the device is filled instantaneous measurements may be a better indication ofwith mercury. DO NOT use this device in close quarters with the conditions where the device has been stored, rather thanhard surfaces; breaking the thermometer will release mercury the room where the measurement was taken. The accuracy ofinto the surrounding environment, and poisoning yourself or the electronic device also depends partly on battery strength. the building occupants is considered poor business practice.IRC BUILDING SCIENCES GROUP STEVE TYNE, CTRRoof Consulting Client Development Manager, Bringing theBritish ColumbiaBuilding Envelope c: 604.842.0579 Science off: 204.633.8218 BuildingsStructural Engineering s.tyne@alumicor.comALUMICOR LIMITED into Focus. Pavement Engineering VANCOUVER, BCIRC Building Sciences Group vancouver@ircgroup.com CONSULTING | ENGINEERING | DESIGN 604.295.8070WWW.ALUMICOR.COM14 BCBEC ELEMENTSA BCBEC PUBLICATION'