EXAMPLES OF AIR MIXING PROCESS

Examples of Air Mixing

The following examples illustrate use of the psychrometric chart to plot values and determine conditions in a ventilating system. The examples also show how to obtain the same results by calculation. Example A requires only Chart No. 1. Example B requires both Charts No. 1 and 2, since the outdoor air temperature is in the range of Chart No. 2.

EXAMPLE A:

Plotting values where only Chart No. 1 (below Figure) is required.

Figure A

In this example:

1. A fixed quantity of two-thirds return air and one-third outdoor air is used.

2. The return air condition is 24°C dry bulb and 17°C wet bulb.

3. Outdoor air condition is 2°C dry bulb and 40% RH.

To find the mixed air conditions at design:

1. Plot the return air (RA) condition (Point A) and outdoor air (OA) condition (Point B).

2. Connect the two points with a straight line.

3. Calculate the mixed air dry-bulb temperature:

            (2/3 x 75) + (1/3 x 36) = 16.5°C dry bulb

4. The mixed air conditions are read from the point at which the line, drawn in Step 2, intersects the 16.5°C dry-bulb line (Point C).

EXAMPLE B:

Plotting values when both Chart No. 1 and Chart No. 2 are required.

In this example, a ventilating system (as shown in below image) is used to illustrate, how to plot data on Chart No. 2 and transfer values to Chart No. 1.

Figure B

 Chart No. 2 is similar to Chart No. 1, except that it covers the -40°C to 10°C temperature range. This is the temperature range immediately below that of Chart No. 1. Note that there is an overlap of temperatures between 0°C and 10°C. The overlap is important when transferring values from one chart to another.

        This example illustrates mixing two different air conditions with no change in total heat (enthalpy). Any changes in the total heat required to satisfy space conditions are made by heating, cooling, humidification, or dehumidification after air is mixed.

        In this example:

        1. A fixed quantity of two-thirds return air and one-third outdoor air is used.

        2. The return air condition is 24°C dry-bulb and 17°C wet-bulb.

        3. Outdoor air conditions is -12°C dry-bulb and 50% RH.

        To find the mixed air condition:

        1. Plot the outdoor air (OA) condition on Chart No. 2, as shown in below image.

Figure C

            2. Plot the return air (RA) condition on Chart No. 1, as shown in below image.

Figure D

3. Calculate the mixed air enthalpy as follows:

    a. For the return air, project a line parallel to the enthalpy line from Point A to the enthalpy scale on above image. The value is 47.5 kilojoules per kilogram of dry air.

    b. For the outdoor air, project a line parallel to the enthalpy line from Point B to the enthalpy scale on Figure 8. The value is -10.5 kilojoules per kilogram of dry air.

    c. Using the determined values, calculate the mixed air enthalpy:

    (2/3 x 47.5) + (1/3 x -10.5) = 28.2 kilojoules per kilogram of dry air.

4. Calculate the mixed air moisture content as follows:

    a. For the return air, project a line from Point A horizontally to the moisture content scale on Figure D. The value is 9.4 grams of moisture per kilogram of dry air.

    b. For the outdoor air, project a line from Point B horizontally to the moisture content scale on Figure C. The value is 0.7 grams of moisture per kilogram of dry air. Also, project this value on to Chart No. 1 as shown in Figure D.

    c. Using the determined values, calculate the mixed air moisture content:

    (2/3 x 9.4) + (1/3 x 0.7) = 6.5 grams of moisture per kilogram of dry air.

5. Using the enthalpy value of 28.2 kJ/kg and the moisture content value of 6.5g, plot the mixed iair conditions, Point C, on Chart No. 1, Figure D, by drawing a horizontal line across the chart at the 6.5g moisture content level and a diagonal line parallel to the enthalpy lines starting at the 28.2 kilojoules per kilogram of dry air enthalpy point. Point C yields 12°C dry-bulb and 9.5°C wet-bulb temperature.

6. Read the other conditions for the mixed air (MA) from Chart No. 1 as needed.

                         In the current period of a dangerous atmospheric deviation, outrageous temperature conditions have turned into the new ordinary. Hot spots are becoming more blazing and more moist, and cold spots are getting cooler and freezing. Under such conditions, a HVAC (Heating, Ventilating, and Air Conditioning) framework for associations, private ventures, vehicles, and inns turns into a need than an extravagance. 

                    In Air Handling System, air definition results from ill-advised blending of air inside the given chamber. This outcome is trouble in working the Air Handler as well as running the unit actually and keeping up with Indoor air quality. In winter the issue is considerably more genuine, with freeze up curls also caused Freeze Stat outings and detecting blunders. Lately issues is considerably more genuine since the ventilation prerequisite ordered by ASHRAE Standard is calling for siphoning all the more natural air inside the structure.

Throughout the long term, structures subsequent to building dislike existing framework causing weighty energy spillage with low productivity. In cases, valuable molding was utilized since existing hotness move loops neglected to moderate gathering the necessary limit. Air Control has analyzed many such cases, some were trying to fix some had simple admittance to air separation arrangements. Many cases old blending gadgets were taken out clearing a path to new Air Mixers which gave better blending as well as saved energy bills with no moving parts.

               An excellent air blender doesn't permit air stratification because of unmixed air, as its braiders blend air at a reliable speed, accordingly taking out possibilities of having unmixed air in the Plenum. Air stratification indiactes, the layering of air because of which much electrical and mechanical energy is squandered to conquer its impact. Gauges say that a normal of 20% of energy is squandered due to air stratification. Consequently, it's judicious to have an air mixer that has an extraordinary control instrument for weighty blending while, simultaneously, having acoustical media to impede commotion emerging from the machine.

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