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Psychrometric Properties
This excel addin can be used to calculate all of the psychrometric properties of air by giving two properties of air as input. Dry bulb temperature is compulsory, whereas the second property can vary depending on what user has on air of his interest. User has two ways to use these functions.
Pressure and Unit Settings
The pressure used for psychrometric calculations is 1 atm (101325 Pa). This is the default value. But this can be changed using following function.
where input variable "Pressure" is the desired pressure value for psychrometric calculations for the excel sheet. This also can be done using "Use the guided excel function filler" method, which is much more convenient.
The input variable Type accepts 0 for SI unit system and 1 for IP unit system.
Please make sure to check for underlying pressure and unit system in the excel sheet if the results from other psychrometric functions seem to be incorrect. You can change it by clicking on "Units" button in "PSYCHROMETRY" ribbon. Then there will be message indicating the pressure and the unit system used for calculation as illustrated above.
Use the guided excel function filler
This method is the easiest way to use psychrometric chart. In this method, you will be guided, therefore no or least amount of knowledge is required about the functions or the variable used in the functions. Most of them will be filled by the guided system. You have to follow simple steps described below to utilise the power of the guided function filler.
After the installation of Psychrometric Chart addin, there is a new tab coming in to place at your ribbon called "Psychrometry". Navigate to the "Psychrometry" tab first as illustrated in figure.
First you have to select the cell where you have to insert the function. Make sure not to be in typing mode (don't double click on the cell, just select it) at the cell. Then goto "Functions" menu.
This will show all the available functions in the psychrometric chart addin. This figure illustrates on how to use psychrometric chart to calculate specific enthalpy for air for given dry bulb temperature and relative humidity. Click on "Known Relative Humidity"
Psychrometry Tab > Functions > Specific Enthalpy > Known Relative Humidity.
Then specific enthalpy function will be added with some input variables filled in to that cell as shown.
Now you can assign the relevant cell for dry bulb temperature and relative humidity. All you have to do is double click on "Drybulb" word in the cell function which will select the whole word and then click on the relevant cell for drybulb temperature. It will replace the selected word with the cell reference. Follow the same steps for relative humidity.
Click here to get additional information about the function and its input variables.
In the same manner, you can calculate Wetbulb temperature, Dew point temperature, Relative Humidity,Humidity ratio, Specific Volume, Degree of Saturation. Saturation pressure only requires the dry bulb temperature. It also can be used via the guided menu system in the psychrometric chart.
Functions
Psychrometric excel addin has few different functions to get psychrometric properties of air. All the functions listed below have same number of input arguments, first one being the drybulb temperature, second one being the type of the 2nd property of the air, and the third one being the value of the third property of air. Default units system for inputs and outputs is SI. Check unit conversion dialog for the list of SI and IP units used in each category. Saturation Pressure function is the only function in psychrometric properties chart which only has one input argument which is the temperature in SI units or IP units as selected by the excel sheet.
| Function Name | Description |
|---|---|
| SpecificEnthalpy | Returns specific enthalpy of a given point in a psychrometric chart |
| SpecificVolume | Returns specific volume of a given point in a psychrometric chart |
| Wetbulb | Returns wet bulb temperature of a given point in a psychrometric chart |
| RelativeHumidity | Returns relative humidity of a given point in a psychrometric chart (Range - [0,1]) |
| HumidityRatio | Returns humidity ratio of a given point in a psychrometric chart [ kg/kg ] |
| DegreeofSaturation | Returns degreeof saturation of a given point in a psychrometric chart |
| SaturationPressure | Returns saturation pressure for a specified temperature |
| Input Variable | Value |
|---|---|
| Drybulb | Inputs drybulb temperature (use Celsius for SI unit system, Fahrenheit for IP unit system) |
| PropertyType |
Inputs the type of second property of air. Following values are accepeted.
|
| SecondProperty | Inputs the value of second property. Please check unit conversion dialog for list of SI units or IP units used for this input for specified categories. |
Examples
Following examples are based on a drybulb temperature of 26 celsius degrees.
For a known relative humidity of 65%
For a known wet bulb temperature of 22°C
For a known relative humidity of 65%
For a known wet bulb temperature of 22°C
For a known relative humidity of 65%
For a known humidity ratio of 0.01 kg/kg
For a known wet bulb temperature of 22°C
For a known humidity ratio of 0.01 kg/kg
For a known relative humidity of 65%
For a known wet bulb temperature of 22°C
For a known relative humidity of 65%
For a known wet bulb temperature of 22°C
Process Line Properties
Functions are introduced to calculate resultant point properties of processes in a psychrometric chart. All these functions can be used with the excel menu guided function filler as explained here for the psychrometric functions
Process results for a sensible heat ratio
A user can calculate resultant point's psychrometric properties for a given process. This function requires following details of the process.
- Starting point's drybulb temperature
- Starting point's humidity ratio
- Sensible heat ratio
- Total specific enthalpy change between starting and resultant point
This function has two sub functions. They are,
- Process line temperature
- Process line humidity ratio
All the above mentioned functions have four input variables. The functions are illustrated below.
To get temperature of the resultant point
To get humidity ratio of the resultant point
| Input Variable | Value |
|---|---|
| T1 | Temperature of the starting point of the process |
| W1 | Humidity ratio of the starting point of the process |
| SHR | Sensible heat ratio of the process |
| Delta_E | Specific enthalpy change from the process |
All input and output variable used in here can be used with SI units (Default) or IP units as specified by the excel sheet. Navigate here for examples.
Adiabatic mixing process
Function explained in this section can be used to calculate resultant point's psychrometric properties for a adiabatic mixing process of two streams. This also can be used with the guided excel function filler explained here.
To get mixture's temperature
To get mixture's humidity ratio
Following input variables are used in functions
| Input Variable | Description |
|---|---|
| T1 | Temperature of first air stream |
| W1 | Humidity ratio of first air stream |
| M1 | Mass flow rate of first air stream |
| T2 | Temperature of second air stream |
| W2 | Humidity ratio of second air stream |
| M2 | Mass flow rate of first air stream |
All the input and output variable used in here can be used with SI units (Default) or IP units as specified by the excel sheet. Navigate here for examples.
Sensible heat ratio calculation
This function can be used to determine the sensible heat ratio of a process in a psychrometric chart. Users can use excel guided function filler to use this function easily in excel environment.
Variables used in this function are described below.
| Input Variable | Description |
|---|---|
| T1 | Temperature of first point in psychrometric chart |
| W1 | Humidity ratio of first point in psychrometric chart |
| T2 | Temperature of second point in psychrometric chart |
| W2 | Humidity ratio of second point in psychrometric chart |
Examples
Following examples are based on a process line with an initial starting point of 26°C and 60% relative humidity. The sensible heat ratio used is 0.4 and enthalpy change is 28 kJ/kg. (Humidity ratio corresponding to 26°C and 60% relative humidity is 0.012638).
Following examples are based on adiabatic mixing with one air stream having 26°C, 0.012 humidity ratio and 0.1 kg/s mass flow rate. The second stream is having 29°C and 0.015 humidity ratio and 0.3 kg/s mass flow rate.
Following examples is based on a process, starting point with 26°C and 0.012 humidity ratio and ending point with 28°C and 0.015 humidity ratio.
Thermal Comfort
Predicted Mean Vote (PMV) and Percentage of People Dissatisfied (PPD) are two most renowned measures of thermal comfort. They are used in standard settings, and to obtain certifications like LEED. This excel addin is empowered to calculate PMV and PPD without a hassle and quickly.
Predicted Mean Vote
Predicted Mean Vote calculation requires few input parameters. This function also can be used with excel guided function filler. Format of the function to be used by manual function insertion is shown below. You can use unit conversion to conert "met" units to W/m2 for metabolic rate and external work or "clo" units to m2K/W values which are used as input variables for this function.
Following table describes variables used in this function.
| Input Variable | Description |
|---|---|
| AirTemperature | Temperature of the air in Celsius (Default unit) |
| MeanRadiantTemperature | Mean radiant temperature of air in Celsius (Default unit) |
| RelativeVelocity | Relative velocity of air in m/s (Default unit) |
| RH | Relative humidity of air (Range 0 to 1) |
| Clothing | Clothing level of the people in m2K/W (Default unit) |
| MetabolicRate | Metabolic rate of people in W/m2 (Default unit) |
| ExternalWork | External work in W/m2 (Default unit) |
Percentage of People Dissatisfied
Percentage of people dissatisfied has a single input variable. That is the Predicted Mean Vote value. So using this function is straightforward.
Examples
Following examples are based on a scenario with 26°C as the air temperature and mean radiant air temperature. Relative velocity is 0.7 m/s and relative humidity is 60%. Clothing level is 1 clo. Metabolic rate is 1 met and external work is 0 W/m2.
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