Dew point temperature chart pdf DEW POINT: Temperature at which moisture will condense on the surface. The horizontal lines represent Dew Point temperatures. A new humidity chart DEW POINT TEMPERATURE - °F Chart by: HANDS DOWN SOFTWARE, www. • Determine the dew point temperature. 2 238. Why is dew point temperature a useful parameter? Dewpoint temperature is a useful parameter in many industrial humidity applications. 80 70. 10 Reading Your Psychrometric Chart Dew Point Temperature: T of air at which water vapor begins to condense given a certain P and water vapor content – T at which air becomes completely saturated dew-point temperatures at 20 psig, R-401A begins to boil at 11°F and does not become a saturated vapor until it reaches pressure (21°F – 11°F = 10°F). This is illustrated in the following graph. 05 27. 2 105. No coating should be applied unless surface temperature is 62°F Fillable and printable Dew Point Temperature Chart Template 2025. 1: 38. 2. com 1. File Type: pdf . 1: Dew Point Temperature. 41 8. EXAMPLE : If air temperature is 21°C and relative humidity is 65%, the dew point Calculate dew point temperature using the following formula? Plot your results for temperature, relative humidity, and dew point temperature on the graph below. 55+0. 086902 E–01 D = –3. 48%. Title: Microsoft PowerPoint - Dew Point and 2 Dew Point Temperature Chart Template free download. Note: When the partial pressure of water vapour (p v) is equal to the pressure (p s) corresponding to saturation temperature, then the water vapour is in the saturated condition and the air PSIA) dew point temperature of 7 °C (44. 6 101: 240. 53 12. , the saturation temperature of water corresponding to the vapor pressure. Download free printable Dew Point Temperature Chart Template samples in PDF, Word and Excel formats File Type: pdf . As Simply search online for a “dew point table” from a reputable source. 53 4. 1 1. 51789 E+00 B = –8. And for pressure, the atmospheric pressure, partial pressure of water vapor, and saturated vapor pressure. 6 . Pages: 1 Page(s) Dew Point Calculation Sample Chart. 09 -4. The 13°C dry bulb temperature is also known as the dew point temperature where air condenses into liquid water. It displays the properties of air: dry bulb temperature (vertical lines), wet bulb temperature (lines sloping gently downward to the right), dew point temperature (horizontal lines), and relative humidity (the curves on the chart). If you have ever wondered "what is dew point?" or how to calculate relative humidity in certain conditions, then this calculator is for you! Dew Point and RH Table - Free download as PDF File (. The chart the temperature below which water condenses out of air - this is known as the dew-point the coldest temperature you can achieve through evaporative cooling - this is known as the wet-bulb temperature Both quantities can be calculated with Maple 2016's ThermophysicalData package, and visualized on a psychrometric chart. Dew Point Temperature - T dp. We may need to use protractor and set square to draw this line WET BULB TEMPERATURE - °F 20 30 100 110 160 180 190 PSYCHROMETRIC CHART FOR HVAC ANALYSIS (at sea level) Air–Conditioning Formulas and Conversion Factors Atmospheric pressure = 29. It is an industrial de . 4 C dew point corresponds to 1. To simplify how to calculate the dew point, we are going to look at the dew point formula, simple-to-use calculator, and chart of dew points at different temperatures and Sontag’s Pressure Dew-Point Chart in PDF. 921" Hg. 2. 6 Saturation Pressure-Temperature Data for R404A (psig)* Temp (°F) Pressure Temp (°C) Temp (°F) Pressure Temp (°C) Temp (°F) A few definitions •When the air contains little water, this lapse rate is known as the dry adiabatic lapse rate: the rate of temperature decrease is 9. 3-48; 1. The Dew Point is the temperature where water vapor starts to condense out of the air (the temperature at which air becomes completely saturated). e, o F. Below this temperature, dew or frost forms. 921 inches of Mercury Linric Company Psychrometric Chart, www. This is a classic gas to liquid conversion. EXAMPLE: If air temperature is 21°C and relative humidity is 65%, the dew You can use this dew point calculator to determine the dew point temperature (T dew) according to the temperature of the air (T) and the relative humidity (RH). 4 C dew point air and replacing it with 19 C dew point air will mean you are removing some of the moisture from the air inside. Vapor: Liquid: Vapor Liquid: Vapor Liquid: Vapor-49; 0. 354309 E–01 X o = 2. 749023 E+00 Because both pressure and temperature appear in the reduced form in the equation, the same constants can be used for either SI or mirror dew points to those obtained using two automated instruments: the Ametek 241 CE II and the Michell Condumax II. 33 5. 8 °C/km (5. •If the air is saturated ♦ How much is RH? ♦ What is the air T? •The dew point is a measure of the water vapor content in the atmosphere. Dry‐Bulb = 22°C Difference = 4°C Dew Point = _____ 2. The curve forming the top edge of the chart is called the begins to boil it forms bubbles i the liquid. If air temperature is 70°F and relative humidity is 65% the dew point is 57° F. 2 1. 60 50. So, if you find the dry bulb temperature and the relative humidity now, you can easily calculate the dew point at which that same air will reach Calculator and equations for the apparatus dew point temperature and by-pass factor of an air handling unit. 85 0. Use the graph to state the relationship between air temperature and relative humidity. 5 to 277. container, the temperature of the water is the dew point temperature. 00 0. • Record the temperature of water while ice is slowly added. 90 0. 65 24. 6. The dew point lines traverse the chart as horizontal lines. 1 31 31 Temp ºC 30-13. 31 -13. 80 0. Fig. e. The dew point temperatures were predicted slightly higher in all calculations than the other methods, more at lower dry bulb temperature conditions. 39 13. 9 22. 6: 10. 5 1. Conversely, lower dew points can also be uncomfortable, causing skin irritation and cracking, as well as drying out a person's airways. Dew point is the temperature at which water evaporates from the surface of a coating. handsdownsoftware. 14 28. So flushing out 23. In simple terms, the dew point is the temperature at which the air can no longer hold all of its water These tables calculate Dew Point and Relative Humidity based on the observed wet bulb and dry bulb temperatures and the elevation at the site of the observation. Created Date: Dew Point Chart - Free download as PDF File (. 53558 E–05 Density of the Saturated Liquid d f /D c = a 0 + a 1 z + a 2 z2 + a 3 z3 + a 4 z4 A 23. Above this temperature the moisture stays in the air. 7 MB; pdf) Go to the Weather - Temp, RH, and Dew Point Tables page of the Fire Behavior Field Reference Guide (PMS 437) Citation dew point; dry-bulb temperature; elevation PRESSURE-TEMPERATURE CHART at SEA LEVEL DEW POINT. Agar lebih jelas dalam memahaminya, yuks kita bahas satu persatu dari ke tujuh parameter udara yang tadi disebutkan di atas : 1. Relative humidity (%) and dew point temperature (degC) are used in the calculation of relative humidity. The difference is the superheat of the suction gas อุณหภูมิน ้าค้าง (Dp-dew point temp. Dew point = Temperature at which condensation occurs Condensation is created as a function of relative humidity and air temperature. 521484 E+00 B = –6. The dew point temperature in Los Angeles has a smaller range; rarely going above 60°F or below 25°F. The Dew Point is the temperature at which water vapor starts to condense out of the air, The Psychrometric Chart provides a graphic relationship of the state or condition of the air at any particular time. An instrument that could measure relative Dew Point Temperature, td % Moisture by Volume (%MV) The % Moisture by Volume can be defined in a least two ways: The dew point temperature scale is located along the same curved portion of the chart as the wet bulb temperature scale. Relative humidity: RH is an expression of the moisture content of a given atmosphere as Dew point temperature screen This screen (Fig. 55 0. 8 -4. 6 1. 1 DEW POINT SCALE DEGREES °F °C TO GRAINS PER POUND DEWPOINT DEWPOINT DEWPOINT R404A Pressure-Temperature Chart Liquid. 18 29. ทฎพัฎดภตด•ฐฐฎชฐฝฉบพ 1. 05 152 147 142 137 133 129 124 120 117 113 109 106 103 99 96 93 90 88 85 82 80 If the dew point is 30°F (-1. 4 2; 35. 93 16. 50 0. When the temperature cools to the dew point, fog or dew can occur, and the Dew-Point Temperature Relative Humidity Humidity Ratio Enthalpy If any two of the above properties are known, the Psychrometric Chart can be used to find the remainingPsychrometric Chart can be used to find the remaining properties 5. The US Occupational Safety and Health Administration recommends that indoor air temperatures be maintained between 68-76°F with a relative humidity of 20-60%. Pressure Dewpoint chart (sontag) Dewpoint (°Cdp) Pressure (barg) -100 -90 -80 -70 -60 the dew-point temperature also increases. 20 0. Psychrometric Chart Dew Point Chart 1. No coatings should be applied unless surface temperature Heat Index ChartHeat Index Chart Classification Extremely Hot Very Hot Hot Very Warm Heat Index/Apparent Temperature ≥130°F 105°F - 129°F 90°F - 104°F The dew point is the temperature, at which if the air were cooled to that value, the relative humidity would be 100%. Just to the right of the Y-axis, find the line with the dew point measurement in degrees Fahrenheit or Celsius. PDF | Climate factors such as dew point temperature, relative humidity and atmospheric temperature may be crucial for the spread of tuberculosis. 77 Temperatures must be maintained during curing. 440004 E+00 E = –3. Temperature must be maintained during curing, or Temperature should be steady and falling, but never rising. This document provides a chart and instructions for calculating dew point based on ambient air temperature and Look on the right side of the chart to find the vertical dew point line. 45 0. 4 %âãÏÓ 383 0 obj > endobj xref 383 28 0000000016 00000 n 0000001255 00000 n 0000001399 00000 n 0000001817 00000 n 0000002201 00000 n 0000002752 00000 n 0000004072 00000 n 0000004504 00000 n 0000005610 00000 n 0000006810 00000 n 0000009539 00000 n 0000012899 00000 n 0000016227 00000 n 0000019434 00000 n 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 115 120 125 130 135 140 145 150 155 160 DRY BULB TEMPERATURE - °F Linric Company Psychrometric Chart, www. 0 . 117T)*x)**14 T = temperature DEW POINT: Temperature at which moisture will condense on the surface. 3 0. It is often used to measure dryness in applications such as plastics and compressed-air drying, where the relative humidity is typically below 10%RH. 58 PSIA) and corresponding ‘Dew Point’. com. 7-44. 3. Example: A 0° F atmospheric dew point con-verts to a +47° F pressure dew point at 100 psig. Take a close look at the annual dew point temperature for your regional climate. 6-17. 40 50 60 70 80 PDF | Simple and precise methods for accurate calculation of wet –bulb temperature and dew-point temperatures are presented in the paper. xls), PDF File (. 007T)*x)**3 + ((15. ) When the temperature of a In this IAQA Tech Tip video from the Indoor Air Quality Association (http://iaqa. 32 23. 0 × 105 Pa in the temperature range from 195. 7 33. When using Airtable’s PDF psychrometric chart, there are some formational aspects to be aware of. Example: For an air temperature of +20 ° C and relative Dew point is the temperature at which moisture will condense on a surface. MATERIALS Referring to Figure 21, air at state point 1 (65°C dry bulb temperature and 57°C wet bulb temperature) experiences a temperature drop of 3°C as it passes through the 1. 36 20. This chart provides information to calculate relative humidity and dew point from dry bulb temperature measurements. At a fairly low relative humidity of 40% the dew point chart shows dew point is 5. • Observe the formation of condensation. 8 . 9 × 105 and 106. What this tells you is that dew point does not change as the dry bulb temperature varies. 3 — High temperatures, 50 to 250F Chart No. Namely, the dew point is a temperature at which moisture in the air starts to condensate on the surface (forming dew). APPROXIMATE PRESSURE CONTROL SETTINGS Pressure - Pounds Per Square Inch Gauge APPLICATION TEMPERATURE R°)ANGE ( F EVAPORATOR T°)D ( F REFRIGERANT 2a2 1A3 44705 Onut ItOnu ItOnu ItOnu I Beverage Cooler Floral Cooler 355 to 38 11466713335286568 As you can see, at 20 degrees (a fairly normal temperature in the UK), the dew point chart shows that variances in humidity in the property makes a huge difference on dew point. 38 °F/1,000 ft). Input parameters required for calculation of psychrometric properties are wet- and dry-bulb temperatures, dew point and dry-bulb temperatures and relative humidity and dry-bulb temperature. (3. 5 . On the other side of the vertical line where you located dew point is the scale for vapor pressure expressed in inches of mercury The saturated vapor condition is referred to as the dew point. Determine the properties of the air at state point 2 and compare them with those at state point 1. Anytime outside air is brought into a storage space and the dew point temperature (absolute humidity or moisture content) the graphs of Figure 1 and Figure 3 that the relative humidity is a useless and even misleading scale for indicating moisture level above 212°F. In addition, the specific humidity Psychrometric chart, Diagram psikometrik, Cara membaca psychrometric chart Dew Point Temperature, Relative Humidity, Humidity Ratio, Specific Entalpy dan Spesific Volume. 1 — Normal temperatures, 32 to 100F Chart No. 2 51: 107. Dry Bulb Temperature (DB) Dew Point Temperature from Dry and Wet Bulb Temperatures 0 5 10 15 20 25 30 35 40 Dry Bulb Temperature (degC) D e w P o i n t T e m p e r a t u r e (d e g C) Wet Bulb Temperature (degC) The Enoineerino ToolBox . 4 1. 9; 0. 10106 E+03 D = 0. We can define humid or moist air conditions using the temperature and pressure parameters like wet bulb temperature, dry bulb, and dew point temperature. For other pressures, relevant corrections have to be applied. Temperature must be Temp. However, at a higher relative humidity of 70% Fillable and printable Dew Point Temperature Chart Template 2025. 5. 4. 5 PSIA) When we compress the gas isothermally to 4 bars (58 PSIA), the vapor pressure increases linearly As a result, the vapor pressure would be 40 hPa (0. 16 30. Properties of AirProperties of Air Dew point can be approximated in temp range ‐40 to 50 deg C by T ‐ D = (14. So, if we want the room condition to be at 23°C and temp f)1400 1425 1450 1475 1500 1525 1550 1575 1600 1625 1650 1675 1700 1725 1750 1775 1800 1825 1850 1875 1900 % C + 0. [1] When this occurs through the Chart No. No coatings should be applied unless surface is a minimum of 5 degrees above this point. Linde Gas & Equipment Inc. IRS Tax Forms. 25 0. 9°C which is a very low temperature. If the air is flowing Wet bulb temperature: The temperature registered by a thermometer whose bulb is covered by a wetted wick and exposed to a current of rapidly moving air Dew point temperature: The temperature at which condensation of moisture begins when the air is cooled. org), you'll learn how to use a psychrometric chart in order to calculate th From the above chart, given that the dry bulb temperature is 24°C and the wet bulb temperature is 18°C, at around 55% relative humidity, the moisture contain is 10. com PSYCHROMETRIC CHART BAROMETRIC PRESSURE 29. Lines representing Wet Bulb temperatures are the straight diagonal lines sloping downward from left to right. 114T)*x + ((2. A high dew point temperature corresponds to high H2O content. If the temperature of the storage unit is 75°F (24° C) and the relative humidity is 35%, the intersection of the two shows the dew point of the area to be 45°F (7°C). 7) is intentionally organized in sequence after the saturation line and wet bulb temperature so that the learner can connect the previously learned Experimental measurements of dew points for five synthetic natural gas (SNG) mixtures between 1. 3 . 75 0. 6 °F) and total pressure of 1 bar (14. Dew-point temperature T dp: The temperature at which condensation begins when the air is cooled at constant pressure (i. Pressure-temperature charts for non-azeotropic refrigerant blends will normally list both bubble- and dew-point values so that subcooling and superheat measurements can be easily Temp-humidity meters From dry bulb temperature and relative humidity measurements, temperature-humidity meters such as the Fluke 971 can calculate wet bulb temperature and dew point temperature, psychrometric points that are essential for HVAC evalu-ations and diagnostics. Fill, sign and download Dew Point Temperature Chart Template online on Handypdf. One axis of the chart shows relative humidity levels, and the other shows temperature levels, both typically in 5 percent/degree increments. 91 KB . txt) or read online for free. 9+0. Dew point is expressed as a temperature. 2-m wide stack of lumber. However, horizontal lines indicate equal dew point Simplified psychrometric chart for temperatures and relative humidities. Use the left y-axis as the DEW POINT CALCULATION CHART RELATIVE AMBIENT AIR TEMPERATURE - FAHRENHEIT HUMIDITY 20° 30° 40° 50° 60° 70° 80° 90° 100° 110° 120° 90% 18 28 37 47 57 67 77 87 97 107 117 85% 17 26 36 45 55 65 75 84 95 104 113 DEW POINT: Temperature at which moisture will condense on surface. 69%. 25 grams. 5+0. Input | Find, read and cite all the research you need Dew point temperature (DP): The temperature to which air must be cooled before condensation of its moisture will begin. 11°C), the air contains 24 grains you get the point. 67 19. 10 0. Size: 57. Locate the inlet & outlet points in the chart and draw a line through it which represents the SHF. 83549 E+01 C = –9. OBJECTIVES In this experiment, you will • Compare room temperature to the temperature of air next to a can of ice water. ) ความชื้นสัมพัทธ์ (RH) คือสัดส่วนของปริมาณ Dry bulb (Tdb) / Dew point (Tdp) / RH (%) / Psychrometric chart Figure 1. 12°C. First, the properties of air indicated in the chart are calculated at standard atmospheric pressure. The document describes a Mellcon dew point apparatus, which is a simple and economical system for measuring the dew point temperature of T HE CHART Figure 1 shows a typical psychrometric chart. The saturated vapor condition is referred to as the dew point. 8. pdf), Text File (. Physical Properties Chemical Formula CH 2 F 2 /CHF 2 CF 3 /CH 2 FCF 3 (dew point), p g: A = 7. 16, which was recently offered as an alternative empirical equation in calculating dew point temperature, 191 is also shown in Table 10. Such a chart is very useful to visualize the changes undergone by a mixture of air and water vapor as the air is conditioned. 66 11. 87 14. • To determine the effects of pressure reduction on dew point: On the vertical temperature scale . Extend the line and locate ADP at the intersection on saturation line. 70 0. 750000 E+00 C = –5. Dew Point – At this temperature, moisture starts condensing from the air. 60 0. 4 — Normal temperature at 5,000 feet above sea level, 32 to 120F Chart No. 21 KB . Relative Humidity, % 100 90 80 70 60 50 40 30 20. • Wet bulbis very closely related to enthalpy, or the total heat in RH & DP Chart - Free download as Excel Spreadsheet (. wEngineeringT00180Kcorn . Created Date: Example: Read the air temperature in the left hand column and the humidity at the top of the chart. Subtract saturation temperature (from Step 2) from suction gas temperature (from Step 3). 96 0. 4 kg of water vapor per 100 kg of dry air. You can calculate the dew point in three simple steps: Select the temperature unit between A convenient, precise and customizable psychrometric chart & calculator tool for HVAC engineers. If you’re having trouble seeing the lines on the This dew point calculator can be used to explore the relationship between dew point, temperature, and relative humidity, without the need for a dew point chart. 35 0. 58 7. This means that the dew point is the temperature at which dew will begin Dew Point Temperature - T dp. 2 . 4. •The temperature decreases with the dry adiabatic lapse rate, Lines of constant wet bulb temperatures run diagonally from the upper left to the lower right in the Psychrometric Chart. Dry Bulb temperatures are shown on the chart as vertical lines. It is also shown on Figure 1. 865265 E+00 F = –7. 40. 5 — Normal temperature at 7,500 feet above sea level, 32 to 120F Chart No. 7. At saturation, dew point temperature equals wet bulb temperature equals dry bulb temperature, and the RH dew point versus ppm. 40 50 60 70 80 %PDF-1. at right, locate the dew point of the higher pressure and follow the horizontal line The temperature at which condensation first occurs is the dew point temperature. The psychrometric calculator will assist you in estimating the properties of moist air. 9 1 1. No coatings should be applied unless the surface temperature is a minimum of 5°F above this point. The temperature at which the water vapor in gas then condenses is dependent on the absolute moisture content and pressure of the gas. Imagine a room full of vapor and dew drops forming on the furniture. This is the dew point temperature. 4 . Size: 41. 7 . Burr Ridge, IL 60527 The dew point is the temperature where air becomes saturated with water vapor. 82 17. PT charts for the zeotropic blends list two columns next to each temperature: one for the saturated liquid (bubble point) and the other for the saturated vapor (dew point). HOW TO CALCULATE THE DEW POINT: Starting at the recorded %Relative Humidity reading in the left (green) column, scroll directly across to the correct cell under the Ambient Air Temperature must be maintained during curing, or Temperature should be steady and falling, but never rising. if the dew-point temperature is close to the dry air temperature - the relative humidity is high Dew point has always been difficult to calculate. 95 0. 40 0. 18°C. 3 1. 30 SENSIBLE HEAT RATIO = Qs / Qt SENSIBLE HEAT RATIO = Qs / Qt WET BULB, DEW POINT, SATURATION TEMP - °C. This | Find, read and cite all the research you Hydrocarbon dew point in natural gas is an important quality parameter, stipulated in contractual specifications and enforced throughout the supply chain, from producers through transmission and distribution companies to final end users. 1 can be used alone when no freezing DEW-POINT-CALCULATION-CHARTenglish - Free download as PDF File (. 74 15. Measure suction gas temperature on the line at the expansion valve bulb’s remote location. 7000 High Grove Blvd. 1. 3 VAPOR PRESSURE - INCHES OF MERCURY-20 0 10 20 25 30 35 40 45 50 55 60 65 70 75 80 85 DEW POINT - °F The dew point of a given body of air is the temperature to which it must be cooled to become saturated with water vapor. As a sample of air is cooled, its RH climbs until it reaches 100% RH (saturated air). Accurately monitoring hydrocarbon dew point temperature in natural gas is therefore vital if the integrity The results of using Equation 10. 88 26. 2 — Low temperatures, –40 to 50F Chart No. HEAT EXHAUSTION HEAT OR STROKE Dew point is the temperature at which Relative Humidity (RH) in your space is at 100% so that the moisture will start condensing out of the air. Methods of Measurement This is the dew point temperature. linric. 9 . Dry‐Bulb = 6°C Wet‐Bulb = 2°C Dew Point = _____ For the time represented by the graph, did the air temperature ever equal the dew point temperature and how do you know? Graph it! Graph the relationships below. 3. 33%. Support IP and SI units. 65 0. It lists dry bulb temperatures from 5 to 40 degrees Celsius across the top and depression of wet bulb temperatures from 1 to 10 degrees Celsius DEW-POINT TEMPERATURE Constant-presssure cooling of moist air and the dew-point temperature on the T-s diagram of water. [Show full abstract] wet-bulb and adiabatic-saturation temperatures is shown to decrease with increasing wet-bulb temperature and vanish altogether at the boiling point. 7 34. at sea level 1 BTU = Amount of heat required to raise (or lower) the temperature of one pound of water 1°F 1 ton of refrigeration = 12,000 Btu/hr = 200 throughout the entire range of temperature, pressure, and density presented in these tables. Two different manual chilled mirror dew points were measured: an iridescent ring dew point, which occurs first as the temperature is lowered, and the droplet dew point, which occurs several degrees cooler. Constants for vapor pressure of saturated vapor (dew point), p g: A = –1. Note that in this case the cooling of the mixture takes place shown on a psychrometric chart. 82 10. 8 kg of water vapor per 100 kg of dry air, whereas a 19 C dew point corresponds to 1. Step 6. 2 Theory Definition of dew point: The dew-point temperature is the temperature to which the air must be cooled to reach saturation (assuming air pressure remains the same). 3 K and nine SNG + water The dew-point temperature can easily be calculated from the relative humidity and temperature. Dew point is also considered in general aviation The dew point temperature scale is located along the same curved portion of the chart as the wet bulb temperature scale. £ÿÿP$bØ8T³ T- 2/XýñëÏ?ÿýæeÓ^¼¯ìÔr¦I dã±^m" i î('îÝ Q € @mæ9 3Ñg&"/6L]åEÆéé¼ê‹ê«¾èsõã •¦h ;Î öÚŸI„YûÚ˸ÙÍó Dew Point •The temperature to which the air has to be cooled (with no change in the air pressure or water content) for saturation to occur. The figures in the middle of the chart show the dew point at particular temperature and humidity combinations. This temperature indicates the pressure dew point. This temperature depends on the pressure and water content of the air. When the air is cooled below the dew point, its moisture capacity is reduced and airborne water vapor will condense to form liquid water known as dew. Use temperature-pressure chart to determine saturation temperature at observed suction pressure. Pages: 1 Page(s) Related Categories. 3-45 1: 34. For the time represented by the graph, did the air temperature ever equal the dew point temperature and how do you know? 2°C.