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Condition Air into the Human Comfort Zone

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Condition Air into the Human Comfort Zone



Humans generally feel comfortable between temperatures of 22 °C to 27 °C and a relative humidity of 40% to 60%.


In this application, air at 35 °C and 60% relative humidity will be conditioned into the human comfort zone, with the thermodynamic process plotted on a psychrometric chart. To do this, we will



first cool the air to 14 °C (this removes some of the water from the air),


and then heat the air to 24 °C.


Additionally, we will calculate



the heat and mass of water removed in the cooling phase,


and the heat added in the heating phase.

Plot the Comfort Zone on the Psychrometric Chart


restart; with(ThermophysicalData); with(plots)


Functions for the lower and upper bounds of the human comfort zone.

lower := proc (T) options operator, arrow; Property(humidityratio, HumidAir, P = 101325, Tdb = T, R = .4) end proc:

upper := proc (T) options operator, arrow; Property(humidityratio, HumidAir, P = 101325, Tdb = T, R = .6) end proc:


Shade the human comfort zone between 22 °C and 27 °C.

comfortZone := shadebetween(lower, upper, 273.15+22 .. 273.15+27):


Plot the human comfort zone on a psychrometric chart.

plots:-display(PsychrometricChart(), comfortZone)

Plotting the Thermodynamic Cycle


Initially the air is at a temperature of 35 °C at a relative humidity of 60%

T__1 := 35+273.15:

hr__1 := ThermophysicalData:-Property(humidityratio, HumidAir, Tdb = T__1, "P" = 101325, "R" = .6)


Then, we cool the air, and calculate the temperature at saturation (that is, the temperature at which the relative humidity is 1).

T__2 := ThermophysicalData:-Property(Tdb, HumidAir, R = 1, P = 101325, humidityratio = hr__1)


hr__2 := hr__1:

We continue cooling along the saturation line until we reach 14 °C (in this process, water condenses out of the air).

T__3 := 14+273.15:

hr__3 := ThermophysicalData:-Property(humidityratio, HumidAir, Tdb = T__3, P = 101325, R = 1)


Now we heat the air until it reaches 24 °C.

T__4 := 273.15+24:

hr__4 := hr__3:

Hence the entire thermodynamic cycle can then be plotted.

route1 := pointplot([[T__1, hr__1], [T__2, hr__2]], connect = true, thickness = 4):

satLine := plot(ThermophysicalData:-Property("humidityratio", HumidAir, Tdb = T, P = 101325, R = 1), T = T__2 .. T__3, color = black, thickness = 4):

plots:-display(ThermophysicalData:-PsychrometricChart(), comfortZone, route1, route2, satLine)

Heat Changes and Water Removed over the Thermodynamic Cycle


Water removed in the cooling process (in kg water per kg dry air)



Heat removed in the cooling process (in J kg-1)

h__1 := ThermophysicalData:-Property(enthalpyperdryair, HumidAir, Tdb = T__1, P = 101325, R = .6):

h__3 := ThermophysicalData:-Property(enthalpyperdryair, HumidAir, Tdb = T__3, P = 101325, R = 1):



Heat added in the heating process (in J kg-1)

h__4 := ThermophysicalData:-Property(enthalpyperdryair, HumidAir, Tdb = T__4, P = 101325, R = .5):