Psychrometer table

Table to calculate the relative humidity using a double thermometer psychrometer with the interpolation of the two measurements (wet bulb temperature and difference in °C with the dry bulb temperature).

This work created by Itieffe represents a fundamental resource for those involved in the field of air conditioning, thermal engineering or in any sector in which the control of the relative humidity of the air is of crucial importance. The psychrometer is an instrument used to carry out the indirect measurement of the relative humidity of the air through two temperatures (dry and wet bulb), a fundamental quantity for the design and monitoring of air conditioning systems, heating, ventilation and applications industrial.

Relative humidity is a measurement of the moisture in the air compared to the maximum amount of moisture the air can hold at a given temperature. This quantity is essential to ensure the comfort of building occupants, preserve the quality of industrial materials and products and regulate production processes in various sectors.

This table is a reference tool that allows you to easily determine the relative humidity of the air based on measurements taken with a psychrometer. This table contains data that combines air temperature with wet bulb temperature (measured by the psychrometer) to calculate percent relative humidity.

During this paper we will explore various aspects related to the use of the table including:

  1. Operating principle of the psychrometer: we will understand how the psychrometer works and how it measures the wet bulb temperature, one of the fundamental components for calculating relative humidity.
  2. Interpretation of the table: We'll walk you through how to read and interpret the table, explaining how to use temperature readings to determine relative humidity.

The objective of this paper is to provide operators and experts in the field of air conditioning and thermal engineering with a clear and informative resource to understand and correctly apply the data identified in the table for the measurement and control of relative air humidity . We hope this guide can be of help to anyone who wishes to improve indoor environmental quality or effectively manage air conditions in various contexts.

Psychrometer table

Table for calculating the relative humidity with the use of a double thermometer psychrometer by interpolating the two measurements (wet bulb temperature and difference in ° C with the dry bulb temperature).

Classic precision psychrometer with mechanical winding fan by means of a key that allows the air to touch both thermometers, both the naked one and the one covered with gauze. The difference of the two temperatures, using the table, gives the relative humidity value.

Instructions for using the table

How to proceed to carry out the reading:

in the first column you must look for the temperature indicated by the thermometer with the suitably moistened gauze (Wet bulb temperature) while in the first line (Temperature difference with the dry bulb thermometer) you must find the temperature difference between the two thermometers. The intersection of the values ​​indicates: the relative humidity in percentage sought (ur%).

Let's take an example

In the first column we consider the value measured by a wet bulb thermometer = 21 ° C;

Our dry bulb measurement is = 25 ° C;

The difference between the two temperatures will be = 25 - 21 = 4 ° C

Intersecting table 2i with 4, a relative humidity of 68% is obtained  

Let's take a second example by varying only the dry bulb temperature.

Wet bulb = 21 ° C

Dry bulb = 24 ° C

Difference 3 ° C

Result obtained = ur 75%

As can be seen as the differential between the two temperatures decreases, the relative humidity increases and vice versa as it increases, it decreases.

To see what effect temperature and humidity can have on the human body, please refer to the program: "Heat index"

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Psychrometer table

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