Manual J basics, CFM and duct design, psychrometric chart terms, humidity and comfort.
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- What is Manual J load calculation used for?
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To determine the heating and cooling capacity required for a building based on its structure and climate.- Name three major components of a Manual J cooling load calculation.
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External loads (solar gain, outdoor air), transmission losses through walls and roof, internal gains (people, equipment).- What does CFM stand for?
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Cubic feet per minute, a measure of volumetric airflow rate.- What is ACH in HVAC?
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Air Changes Per Hour, the number of times total air volume in a space is replaced per hour.- Define static pressure in a duct system.
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The perpendicular force air exerts on duct walls, measured in inches of water column (IWC).- What is a psychrometric chart primarily used for?
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To determine relationships between dry bulb temperature, humidity, enthalpy, and other air properties.- On a psychrometric chart, what does dry bulb temperature represent?
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The actual air temperature measured with a standard thermometer, plotted on the horizontal axis.- What is wet bulb temperature?
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The lowest temperature air can reach through evaporative cooling, measured with a wet cloth around the thermometer bulb.- Define relative humidity (RH).
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The ratio of actual water vapor pressure to saturation pressure at the same temperature, expressed as a percentage.- What is dew point?
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The temperature at which air becomes saturated and water vapor begins to condense into liquid.- Define enthalpy in psychrometrics.
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The total heat energy in air, including sensible heat and latent heat of water vapor, measured in BTU per pound of dry air.- What is sensible heat?
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Heat that increases or decreases air temperature without changing its moisture content.- What is latent heat load in HVAC?
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Heat required to evaporate or condense moisture without changing air temperature, typically from occupants and ventilation air.- What is the typical comfortable indoor relative humidity range?
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30 to 60 percent, with optimal comfort around 40 to 50 percent.- What is the typical comfortable indoor temperature range according to ASHRAE 55?
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68 to 76 degrees Fahrenheit (20 to 24 degrees Celsius) in winter, 72 to 80 degrees Fahrenheit (22 to 27 degrees Celsius) in summer.
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