By subtracting 20K from the specified space DB temperature, the desired dry-bulb temperature of the supply air may be approximated. Experience and practice indicate that a temperature difference between supply air and space air of 20 to 25K will provide satisfactory performance and reasonable economy. However, excessively low supply air temperatures create cold drafts in the space, while supply air temperatures much above 60☏ require excessive air flow rates. In order to remove the sensible heat load of the space, the conditioned air supply must be at a dry-bulb temperature lower than the space.The intersection of the room condition line and the 90 percent RH line will provide coil leaving or supply air conditions satisfactory for many air conditioning problems. An average cooling coil of four to six rows will produce an air-leaving condition of approximately 90 percent RH.Other wet-bulb lines can be plotted similarly. This point is labeled C, and it is noted that points A, B, and C lie on a straight line ie the 70☏ wet bulb line. At 92☏ dry bulb, a 22° F (92 – 70) wet bulb depression gives a relative humidity of 33%. Another point on the 70☏ wet bulb line may be determined in a similar way. The point B is plotted on the 80☏ dry bulb line at the point of intersection with the 61% RH line. To locate this point refer to property of moist air and noted that at 80☏ dry bulb a 10 ☏ (80 – 70) wet-bulb depression gives an RH of 61%. Now determine another point on the 70☏ wet bulb line, for example, the point where it intersects the 80☏ DB line. Consider, for example, point A, which represents saturated air at 70☏ (DB = WB = DP). To locate lines of constant wet-bulb temperature, at saturation, dry-bulb temperature = dew point temperature = wet bulb temperature, one point on each wet bulb line is already located, that is, the point of intersection of each dry-bulb line with the saturation line. Every engineer, technician, and contractor in the industry should become thoroughly familiar with the psychrometric chart and use it in daily practice. Guidelines for equipment performance can be decided upon, and the limits of any necessary compromises can easily be determined and explained to the customer. With it, the preliminary specifications for an entire system may be laid out.
The psychometric chart is probably the most valuable single tool available to the air conditioning engineer or design technician. The one that concerns us here relates temperature, humidity, enthalpy, and certain other properties of moist air is called the Psychrometric chart. Many such charts are used in engineering practice. Air conditioning is not an exact science, and information that is sufficiently precise for the solution of most air conditioning problems can usually be obtained from graphs or charts. Even the use of prepared tables of values is time consuming, since interpolation is often required. You show a 'Virtual' Temperature under Thermodynamic properties.Although engineers and technicians need to know how the values of such properties of air as specific humidity, sensible and latent heat, and relative humidity in our designs, the actual computation of these quantities is much too burdensome for everyday operations.
What is the difference between the six different humidity metrics shown? Why does this program show two different values of specific volume? There appears to be error in the calculations when converting from one unit system to User may override default input by selecting and entering new value. Site elevation for Dayton, OH - 997 ft amsl (306 m) based on the ASHRAE HOF. Sea Level Pressure - 14.7 psia / 101.3 kPa / 29.92 in Hg / 760 mm Hg (Default when 'ActualĪverage Barometric Pressure in Dayton, OH - 14.18 psia / 97.7 kPa / 28.86 in Hg / 733 mm Hg At the end of the calculation, the user has the option to convert from the English to the SI (or vice versa) unit system. The user then enters a desiredĭry Bulb temperature and one of three humiditymetrics:ĭew Point temperature. To calculate properties, the user must enter either a site elevation (from which an average barometric pressure is calculated) or an actual barometric pressure. It will also provide a number of other thermodynamic properties not found on a typical psychrometric chart.
This on-line program calculates typical psychrometric state point properties. Instructions for the Psychrometric Calculator
0 kommentar(er)
