Section 2 Of 6 - Carl Munters

Section 2 of 6Applied Psychrometrics Psychrometric chart - your energy mapKey psychrometric variables for humidityPredicting building condensation Hot weather Cold weather Predicting moisture sorption and mold growth1

Maps help us understand where we are and howfar we have to go to our destinationLong distance. lot of effortDistance quantifiedby the map’s scaleMunters Technical Training - October 20162

Psychrometric chart helps us understand thecurrent energy state of air, and how muchwork we’ll have to do to change itLong distance. lot of effortRequired work is quantifiedby the chart’s (many) scalesMunters Technical Training - October 20163

Each axis quantifies a different property of the airWet bulb temperatureDew point temperatureHumidity ratioRelative humidityDry bulb temperatureMunters Technical Training - October 20164

Consider typical indoor conditions75 F50% Relative HumidityMunters Technical Training - October 20165

75 F Dry bulb temperatureThe temperature of theair as measured by athermometer that has adry sensing bulbMunters Technical Training - October 20166

50% Relative humidityThe amount of watervapor in the air.compared to itsmaximum capacityat that temperature.A relative (not absolute)measurement ofhumidityMunters Technical Training - October 20167

Grab your chart and plot the point - 75 F, 50% RHMunters Technical Training - October 20168

Humidity ratio 0.0092 lb/lb 65 gr/lbThe weight of watervapor in the air.compared to theweight of dry air alone(lbw lba)An “absolute”measurement ofhumidity(0.0092 lbw 1 lba) x 7000 gr/lb 65Munters Technical Training - October 20169

Dew point temperature 55 FThe temperature atwhich the vaporcontained in the airwill begin to condense.The dew point is another “absolute”measurement of humidityMunters Technical Training - October 201610

Predicting indoor condensation (hot weather)At design conditions inHampton, VA, any outdoorair sucked into the cavitiesabove ceilings is 83 F and151 gr/lb.How cold does the ceilingsurface have to be toproduce condensation?In other words.What is the dew point of air at 83 F, 151 gr/lb ? )Munters Technical Training - October 201611

Assessing mold risk - School summer vacationIn Hampton, VA, outdoor airinfiltrating into an empty schoolduring the summer time has a dewpoint of 79 F.Thermostat is reset to save energy. Ifthe AC system keeps the building at85 F, what is the probable RelativeHumidity indoors?In other words - What is the RH of airwhen the dew point is 79 F and the drybulb temperature is 85 F ?RH ?Munters Technical Training - October 201612

Mold risk on building surfaces - Hotel roomMunters Technical Training - October 201613

Using the chart to find RH at the SURFACEDew Point 19.6 CSurface 20.7 CMunters Technical Training - October 201614

Helps explain common mold growth in hotels(and underlines the importance of air-tight ductconnections)Munters Technical Training - October 201615

Predicting cold weather condensation in wallsIn Calgary, Alberta, small amountsof air are leaking outward fromthe swimming pool enclosure @85 F, 60% RH.That air will condense moisturewhen it contacts a surface with atemperature of ? .In other words, what is the dew point of air at 85 F, 60% RH ?Dew point ?Munters Technical Training - October 201616

Wet bulb temperature 62.5 FThe temperature ofthe air as measured bya thermometer with awet sensing bulb.The temperature at which waterwill begin to freely evaporate intothe air.Munters Technical Training - October 201617

Finding humidity from DB WB bulb temperatureIn Phoenix, AZ, the design dry bulbtemperature is 110 F.During hours when the outdoortemperature is that hot inPhoenix, the average wet bulbtemperature is 70 FHow much humidity is in thatoutdoor air at peak dry bulbconditions?In other words, what is the dew point, humidity ratio andrelative humidity of air at 110 F, 70 F WB ?Dew point ?Munters Technical Training - October 2016Humidity ratio ?RH ?18

Wetbulb:62.5 FRH:50%Psychrometric summary for air at 75 F, 50% RHDew point: 55 FHumidity ratio: 65 gr/lbDry bulb: 75 Munters Technical Training - October 201619

Psychrometric chart - your energy map . compared to its maximum capacity at that temperature. A relative (not absolute) measurement of humidity. Munters Technical Training - October 2016 Grab your chart and plot the point - 75 F, 50% RH 8. Munters Technical Training - October 2016