What is the purpose of a PUD? problems with planned unit development.
Contents
Psychrometric chart is one of the chart that is commonly used in solving HVAC problems. The properties of air such as wet bulb temperature, dry bulb temperature, dew point temperature, relative humidity, humidity ratio, specific enthalphy and specific volume are shown on this chart.
A psychrometric chart for a given location can tell you information about temperature (wet bulb and dry bulb) and humidity (relative and absolute). … Psychrometric charts show temperature vs. humidity, and can be used to express human thermal comfort, design strategies, and energy requirements for those strategies.
While this method is not accurate enough for laboratory calculations, it is useful for field calculations using the psychrometric chart, where extreme accuracy is not of prime importance. On most psychrometric charts space is limited so that only the total heat content of the air is shown.
a psychrometric process that involves the increase or decrease in the temperature of air without changing its humidity ratio. Example: passing moist air over a room space heater and of kiln air over the heating coils.
Hence partial vapour pressure is not shown on psychrometric chart.
What is the range of DBT on the psychrometric chart usually used? Explanation: Generally, the temperature range of dry bulb temperature lines on the psychrometric chart is from -6 to 45°C. These lines are drawn with a difference of every 5°C of DBT.
Vapor pressure is measured in units of mercury. For this specific graph, it is measured in inches of mercury. The dew point is represented on the chart by Point 3. The dew point is measured vertically and usually measured in degrees Fahrenheit or degrees Celsius, on this chart it is measured in Fahrenheit.
One of the major applications of the Psychrometric Chart is in air conditioning, and we find that most humans feel comfortable when the temperature is between 22°C and 27°C, and the relative humidity φ between 40% and 60%. This defines the “comfort zone” which is portrayed on the Psychrometric Chart as shown below.
- Find the annual mean temperature, Tav. …
- Find the thermal neutrality (Tn) …
- Find the lower (L) and upper (U) limits of Tn. …
- Find the SET slope expressions. …
- Find the base line intercepts for L and U from the SET slope expressions.
A Psychrometric chart graphically represents the thermodynamic properties of moist air. Standard psychrometric charts are bounded by the dry-bulb temperature line (abscissa) and the vapour pressure or humidity ratio (ordinate). The Left Hand Side of the psychrometric chart is bounded by the saturation line.
Adiabatic humidification injects water (not steam) directly into the air using a spray mechanism or wetted medium, and the heat from the surrounding air causes the water to evaporate. So instead of sliding up the vertical dry bulb temperature line on the psychrometric chart, we move diagonally up the wet bulb line.
- Dry Bulb (DB) Temperature Lines: The dry bulb temperature scale is shown along the base of the shoe shaped psychrometric chart forming the sole. …
- Moisture Content: …
- Wet Bulb (WB) Temperature Lines: …
- Dew Point (DP) Temperature Lines:
Psychrometric charts are complex graphs that can be used to assess the physical and thermodynamic properties of gas-vapour mixtures at a constant pressure. They are often used to assess the properties of moist air.
Take a ruler and draw a vertical line at the dry bulb temperature of 70 and draw a horizontal line where the dew point is 50. The point where these two lines intersect is known as a ‘state point’. Plot the state point and you can also read the rel- ative humidity, wet bulb, enthalpy, vapor pressure and humidity ratio.
Concept: Every psychometric chart includes vertical lines that represent the dry bulb temperatures, diagonals line represents wet bulb temperature and curved lines represent relative humidity.
Sensible Heat Factor – The ratio of sensible to total heat. Alignment Circle – Located at 24°C DB and 50% RH and used in conjunction with the sensible heat factor to plot the various air conditioning process lines. Kilograms of Dry Air – The basis for all psychrometric calculations.
Willis Carrier is known as the Father of Air Conditioning. He also invented the psychrometric chart. It was a result of his research studying the effects of heat and humidity on heat and cooling comfort.
Concept: Every psychometric chart includes. vertical lines that represent the constant dry bulb temperatures, The diagonal lines that represent wet bulb temperature and enthalpy. curved lines that represent relative humidity.
Knowing both the dry-bulb temperature (DBT) and wet-bulb temperature (WBT), one can determine the relative humidity (RH) from the psychrometric chart appropriate to the air pressure.
Psychrometry is the study of the properties of mixtures of air and water vapor. Curved lines represent relative humidity.
Explanation: Psychrometric chart has DBT on the x-axis and sp. Humidity on the y-axis. So, if a process is going down on the chart, then there is a decrease in relative as well as specific humidity. So, the vertical line with an arrow downwards denotes dehumidification process.
The dew point is the temperature the air needs to be cooled to (at constant pressure) in order to achieve a relative humidity (RH) of 100%. … The higher the dew point rises, the greater the amount of moisture in the air. This directly affects how “comfortable” it will feel outside.
The higher the dewpoint is, the more moisture that is in the air. The higher the dewpoint is above 65 F, the stickier it will feel outside (feels like you have to breathe in a bunch of moisture with each breath). 75 F or above dewpoint, the air really feels sticky and humid.
However, when the air is already saturated with water vapor (as it is when humidity levels rise to 70 percent and higher), sweat can’t evaporate. So instead of cooling down, you just feel hotter and stickier. At that point, the body is forced to resort to other means to try to cool off.
On the vertical line corresponding to the temperature of 20°C, we go up until we reach the 60% HR curve. Moving to the right until the end of the diagram we find the absolute humidity vertical line. This give us the information that our air contains 8.77 g of water vapor.
You can install the package as a plug-in in Microsoft Excel. Once installed, if you click on ‘insert function’ and select the ‘user-defined’ category. You can find a list of the available psychrometric functions: With this fantastic plug-in installed, plotting a psychrometric chart is straightforward.
The Dry Bulb Temperature refers basically to the ambient air temperature. It is called “Dry Bulb” because the air temperature is indicated by a thermometer not affected by the moisture of the air.
Relative humidity can be changed in two ways. One is by adding or subtracting water vapor. The second is by changing the air’s temperature.
The Comfort Chart is a tool that helps operators determine how well air-handling equipment is providing thermal comfort for the building occupants or for a process within the facility.
Humans generally feel comfortable between temperatures of 22 °C to 27 °C and a relative humidity of 40% to 60%.
Psychrometric chart is one of the chart that is commonly used in solving HVAC problems. The properties of air such as wet bulb temperature, dry bulb temperature, dew point temperature, relative humidity, humidity ratio, specific enthalphy and specific volume are shown on this chart.