(My notation differs slightly from ASHRAE's.) Vertical lines indicate constant dry bulb temperature (Figure 2). The amount of moisture in the air, called relative humidity, cannot be determined from the dry bulb temperature alone. The wet bulb temperature is always lower than the dry bulb temperature but will be identical with 100% relative humidity (the air is at the saturation line). The dry bulb temperature scale is located at the base of the chart. The dry-bulb temperature (air temperature) decreases from the entering to the exiting side during most of the schedule. The greater the wet bulb depression, the greater the felt effect is on the discharge air temperature. ASTM standard E 337-02 (2007) reviews in great detail the wet- and dry-bulb technique. Dry bulb temperature. The term dry-bulb is customarily added to temperature to distinguish it from wet-bulb and dew point temperature. 2. Full details can be found in Chapter 6 of the ASHRAE Fundamentals handbook. 0.4% Summer Design Dry Bulb and coincident Wet Bulb Temps mean that the summer temperatures in an year for that location will exceed this design value about 0.4% of the time. This is the difference between daily maximum and minimum dry- or wet-bulb temperatures, respectively, averaged over all days where the maximum daily dry-bulb temperature exceeds the 5% monthly design dry-bulb temperature. reflects the cooling effect of evaporating water. Mean daily dry- and wet-bulb temperature ranges coincident with the 5% monthly design dry-bulb temperature. This is known as temperature drop across the load, or TDAL. Dry bulb temperature is the temperature of air that does not take into consideration any moisture content. The wet-bulb temperature (temperature of a wetted thermometer) does not change from the entering to the exiting side after the kiln is warmed. According to this Dry bulb temperature is given in weather reports. MCDB Mean coincident dry bulb temperature, °F MCWB Mean coincident wet bulb temperature, °F MCWS Mean coincident wind speed, mph PCWD Prevailing coincident wind direction, °, 0 = North, 90 = East Design conditions for DALLAS/FORT WORTH INT AP, TX, USA Aug Sep Oct Nov Dec % Jul Sep Oct Apr May % Jan Jul Nov Apr n=5 years The Wet Bulb/Dry Bulb Technology (psychrometer) Introduction Wet- and dry-bulb temperature measurement is a commonly used and widely accepted technique for controlling relative humidity in environmental chambers. The dry-bulb temperature is the temperature indicated by a thermometer exposed to the air in a place sheltered from direct solar radiation. The dry bulb temperature is the ambient air temperature that is measured by regular thermometers, while the wet bulb temperature is measured by thermometers that are wrapped in wetted wicks. 99.6% Winter Design Dry Bulb Temp means that the outdoor temperature that your locations stays above for 99.6% of all the hours in the year, based on a 30-year average. If, for example, the dry-bulb temperature was 60°F and wet-bulb was 50°F, we can plot these on the chart as shown in Figure 4-16 and find the relative humidity to be 50%. If the temperature were 70°F and wet bulb still 50°F the relative humidity would be down at about 20%. The conversion between wet-bulb and dry-bulb temperatures is surprisingly non-trivial. Dew Point Temperature - T dp The Dew Point is the temperature at which water vapor starts to condense out of the air (the temperature at which air becomes completely saturated). An ordinary thermometer placed indoors or outdoors will measure the dry bulb temperature. Wet bulb temperature . By definition, wet-bulb temperature is the lowest temperature a portion of air can acquire by evaporative cooling only. It includes a dry-bulb thermometer, a wet-bulb thermometer and a psychrometric chart - a graph that plots the relationships between the dry and wet-bulb temperature, relative humidity, and dew point at constant pressure. is the air temperature determined by an ordinary thermometer.