Psychrometric charts can also be used to determine the value for various air properties but it is more important to understand what must be done to more from one point on the graph to another. This presentation in on the basics of psychrometrics and the primary purpose is to gain and understanding of its importance in residential housing.*All changes in the properties of air can be described graphically on a psychrometric chart. What if humidity ratio of return air equals the humidity ratio of the supply air?Operation of an Air ConditionerĪnnual Hourly Outside Air Conditions Lexington KYĪnnual Hourly Outside Air Conditions Phoenix, AZ Solving the General Equations for Air Conditioning - Sources of Errorġ2,000 Btuh / ton400 cfm /tonSensible heat fraction = 0.70Latent heat fraction = 0.30Standard Operation of an Air Conditioner Sensible Heatq (Btuh) = (cfm) (1.08) (t)(t) = q (Btuh) (cfm) (1.08)cfm lower - (t) highercfm higher - (t) lowerq lower - (t) lowerq higher - (t) higher Latent Heatq = (cfm) (4840) (w)w = humidity ratio, lb water per lb dry airSolving the General Equations for Air Conditioning Sensible Heatq = (cfm) (1.08) (t)t = temperature F Total Heatq = (cfm) (4.5) (h)q = Btuhh = enthalpy, Btu per lb dry air Ma3h3w3Energy Balancema1 h1 + ma2 h2 = ma3 h3īy Algebrah2 h3 = w2 w3 = ma1h3 h1 w3 w1 ma2 Supply air from furnacereturn air to furnaceHeating System Example Heating System Examplesupply air from furnacereturn air to furnace1) Return Air 65 F and 60%2) Supply Air 95 F and 22% Length (ft) x Width (ft) x Height (ft) = Volume (ft3)Volume (ft3) / Specific Volume (ft3/lb) = Mass of Air (lb)Mass of Air (lb) x Enthalpy Change (Btu/lb) = Heat Input (Btu)īedroom12 x 12 x 8 = 1152 ft31152 / 14.02 = 82.17 lb82.17 x 0.25 = 20.54 BtuRaise Room Temperature 1 degree FConstant Humidity Ratio Raise Room Temperature 1 degree FConstant Humidity Ratio27.31 Btu/lb27.06 Btu/lb00.25 Btu/lb Specific volume = 13.6 ft3 / lb dry airSpecific Volume Sea Level ChartDry-bulb temperature = 70 FRelative Humidity = 60%
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Sea Level ChartDry-bulb temperature = 70 FRelative humidity = 60%