# Help with Function

#### nutttom

##### New Member

The WB Function is return a #VALUE! error and I can't understand way. Here is the code:

Thank you Tom

'====================================================================================================================='
' Constants
'====================================================================================================================='

Const CONST_01 = -5674.5359
Const CONST_02 = 6.3925247
Const CONST_03 = -0.009677843
Const CONST_04 = 0.000000622157
Const CONST_05 = 2.0747825E-09
Const CONST_06 = -9.484024E-13
Const CONST_07 = 4.1635019
Const CONST_08 = -5800.2206
Const CONST_09 = 1.3914993
Const CONST_10 = -0.048640239
Const CONST_11 = 0.000041764768
Const CONST_12 = -0.000000014452093
Const CONST_13 = 6.5459673
Const CONST_14 = 6.54
Const CONST_15 = 14.526
Const CONST_16 = 0.7389
Const CONST_17 = 0.09486
Const CONST_18 = 0.4569

Const R_WATER = 18.015268
Const R_AIR = 28.964546

'1) Equation 1: Get humidity from paritial vapour pressure and saturated vapour pressure.

Function get_humidity(ByVal paritial_vapour_pressure As Variant, ByVal saturated_vapour_pressure As Variant)

get_humidity = (paritial_vapour_pressure / saturated_vapour_pressure) * 100

End Function

'5) Equation 5: Get saturated vapour pressure from dry bulb.

Function get_saturated_vapour_pressure(ByVal dry_bulb As Variant)

If dry_bulb >= 0 Then
get_saturated_vapour_pressure = (Exp(CONST_08 / (dry_bulb + 273.15) + CONST_09 + CONST_10 * (dry_bulb + 273.15) + CONST_11 * (dry_bulb + 273.15) ^ 2 + CONST_12 * (dry_bulb + 273.15) ^ 3 + CONST_13 * Log((dry_bulb + 273.15)))) / 1000
Else:
get_saturated_vapour_pressure = (Exp(CONST_01 / (dry_bulb + 273.15) + CONST_02 + CONST_03 * (dry_bulb + 273.15) + CONST_04 * (dry_bulb + 273.15) ^ 2 + CONST_05 * (dry_bulb + 273.15) ^ 3 + CONST_06 * (dry_bulb + 273.15) ^ 4 + CONST_07 * Log((dry_bulb + 273.15)))) / 1000
End If

End Function

'6) Equation 6: Get humidity ratio from dry bulb vapour pressure and pressure.

Function get_humidity_ratio(ByVal dry_bulb_vapour_pressure As Variant, ByVal pressure As Variant)

get_humidity_ratio = R_WATER / R_AIR * dry_bulb_vapour_pressure / (pressure - dry_bulb_vapour_pressure)

End Function

'7) Equation 7: Get moisture content from wet buld, humidity ratio and dry bulb.

Function get_moisture_content(ByVal wet_bulb As Variant, ByVal humidity_ratio As Variant, ByVal dry_bulb As Variant)

If dry_bulb <= 0 Then
get_moisture_content = ((2830 - 0.24 * wet_bulb) * humidity_ratio - 1.006 * (dry_bulb - wet_bulb)) / (2830 + 1.86 * dry_bulb - 2.1 * wet_bulb)
Else:
get_moisture_content = ((2501 - 2.326 * wet_bulb) * humidity_ratio - 1.006 * (dry_bulb - wet_bulb)) / (2501 + 1.86 * dry_bulb - 4.186 * wet_bulb)

End If

End Function

'8) Equation 8: Get dry bulb vapour pressure from wet bulb.
Function get_dry_bulb_vapour_pressure(ByVal wet_bulb As Variant)

If (wet_bulb + 273.15) >= 0 Then
get_dry_bulb_vapour_pressure = Exp(CONST_08 / (wet_bulb + 273.15) + CONST_09 + CONST_10 * (wet_bulb + 273.15) + CONST_11 * (wet_bulb + 273.15) ^ 2 + CONST_12 * (wet_bulb + 273.15) ^ 3 + CONST_13 * Log((wet_bulb + 273.15))) / 1000
Else:
get_dry_bulb_vapour_pressure = Exp(CONST_01 / (wet_bulb + 273.15) + CONST_02 + CONST_03 * (wet_bulb + 273.15) + CONST_04 * (wet_bulb + 273.15) ^ 2 + CONST_05 * (wet_bulb + 273.15) ^ 3 + CONST_06 * (wet_bulb + 273.15) ^ 4 + CONST_07 * Log((wet_bulb + 273.15))) / 1000
End If

End Function

'9) Equation 9: Get partial vapour pressure from pressure and moisture content.

Function get_partial_vapour_pressure(ByVal pressure As Variant, ByVal moisture_content As Variant)

get_partial_vapour_pressure = (pressure * moisture_content) / (0.621945 + moisture_content)

End Function

'10) Equation 10: Get enthalpy from dry bulb and moisture content.

Function get_enthalpy(ByVal dry_bulb As Variant, ByVal moisture_content As Variant)

get_enthalpy = 1.006 * dry_bulb + moisture_content * (2501 + 1.86 * dry_bulb)

End Function

'11) Equation 11: Get pressure from altitude.

Function get_pressure(ByVal altitude As Variant):

get_pressure = 101.325 * (1 - 0.0000225577 * altitude) ^ 5.2559

End Function

'12) Equation 12: Get specific volume from dry bulb, moisture content and pressure.

Function get_specific_volume(ByVal dry_bulb As Variant, ByVal moisture_content As Variant, ByVal pressure As Variant):

get_specific_volume = (0.287042 * (dry_bulb + 273.15)) * (1 + 1.607858 * moisture_content) / pressure

End Function

'13) Equation 13: Get dew point temperature from partial vapour pressure.

Function get_dew_point_temperature(ByVal partial_vapour_pressure As Variant)

If dry_bulb <= 93 And dry_bulb >= 0 Then

get_dew_point_temperature = 6.54 + 14.526 * Log(partial_vapour_pressure) + 0.7389 * Log(partial_vapour_pressure) * Log(partial_vapour_pressure) + 0.09486 * Log(partial_vapour_pressure) ^ 3 + 0.4569 * partial_vapour_pressure ^ 0.1984

ElseIf dry_bulb < 0 Then

get_dew_point_temperature = 6.09 + 12.608 * Log(partial_vapour_pressure) + 0.4959 * Log(partial_vapour_pressure) * Log(partial_vapour_pressure)

Else
get_dew_point_temperature = "Error"

End If

End Function

Function hum_acc(ByVal humidity As Variant, ByVal humidity_loop As Variant)

If (humidity / humidity_loop) < 1.1 And (humidity / humidity_loop) > 0.9 Then

hum_acc = True

Else

hum_acc = False

End If

End Function

Function WB(ByVal altitude As Variant, ByVal dry_bulb As Variant, ByVal humidity As Variant) As Variant

Dim wet_bulb As Variant
Dim wb_loop As Variant
Dim saturated_vapour_pressure As Variant
Dim pressure As Variant
Dim dry_bulb_vapour_pressure As Variant
Dim humidity_ratio As Variant
Dim moisture_content As Variant
Dim partial_vapour_pressure As Variant
Dim hum_ok As Boolean

wb_loop = 0.001
wet_bulb = dry_bulb

Do

wet_bulb = wet_bulb - wb_loop
saturated_vapour_pressure = get_saturated_vapour_pressure(dry_bulb)
pressure = get_pressure(altitude)
dry_bulb_vapour_pressure = get_dry_bulb_vapour_pressure(wet_bulb)
humidity_ratio = get_humidity_ratio(dry_bulb_vapour_pressure, pressure)
moisture_content = get_moisture_content(wet_bulb, humidity_ratio, dry_bulb)
partial_vapour_pressure = get_partial_vapour_pressure(pressure, moisture_content)

humidity_loop = get_humidity(paritial_vapour_pressure, saturated_vapour_pressure)

hum_ok = hum_acc(humidity, humidity_loop)

Loop Until hum_ok = True

WB = 1000

End Function

### Excel Facts

What does custom number format of ;;; mean?
Three semi-colons will hide the value in the cell. Although most people use white font instead.

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