Hvac Wet Bulb Chart

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.

Hvac wet bulb chart.

Other properties are calculated using equations and tables from ashrae 2009 fundamentals and 2008 hvac systems and equipment. Temperature of the ordinary air measured by the thermometer when it is covered by wet cloth or wick is called as the wet bulb temperature commonly referred to as wbt. It is a reference point on a chart that allows us to know what the correct superheat a piston evaporator should have. This will be your target superheat.

Once you determine the indoor wet. Wet bulb is the temperature at which moisture evaporates. The temperature of the air measured by the ordinary thermometer is called as the dry bulb temperature of air commonly referred as dbt. In the chart above you can see that a 62 8 degree wet bulb mass of air contains approximately 28 4 btus per lb.

Go to your superheat table look for your outdoor drybulb and indoor wetbulb temperature where they intersect. The dbt and wbt of the air are measured by a special thermometer called sling thermometer. Dry bulb temperature dbt 2. Using wet bulb return air temperature the wet bulb return air temperature method is the most accurate superheat method.

The outdoor dry bulb temperature will affect how well the system can reject heat to the outdoor air. The more humid it is inside the higher the wb will be. The indoor wet bulb reading reflects the total heat of the air and therefore the total loading on the indoor coil both sensible and latent. The wet bulb dew point and apparatus dew point are iterated using a curve fitted enhancement factor.

The dry bulb wet bulb and dew point temperatures are important to determine the state of humid air. Intersect the 2 numbers on the chart shown on the next slide that will give you the amount of superheat you need using superheat table. The knowledge of only two of these values is enough to determine the state of the moist air including the content of water vapor and the sensible and latent energy enthalpy in the air. In the case of the outdoor air there s no latent heat involved.

Psychrometric chart is one of the chart that is commonly used in solving hvac problems. The tricky part is reading at this extreme level of resolution because 28 4 vs. Equation of state is p v r t 1 bm v cm v. A psychrometric chart contains a lot of information packed in an odd shaped graph.

28 6 can make a significant difference when it is multiplied out over a large air mass. Wet bulb temperature wbt 3. The psychrometric chart highlights seven properties of air. While the unit is operating measure the dry bulb temperature at the condensing unit.

You can measure the wet bulb with a thermometer with a tiny wet sock around it.