Balancing of a Water and Air System (PDF

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106 industry for many years. They reasonably meet the need to obtain test data close to the tower design conditions, while not imposing such stringent limits on the test conditions as to severely limit the opportunities for obtaining a test. Similarly, the instrumentation and procedures set forth in the test parameters are the culmination of many years experience in testing cooling towers of all sizes and configurations. They have been shown to give consistent and repeatable results. Performance Test The objective of this test is to determine a performance factor (P.F.) for the tower that is constant at all heat load conditions and all entering (W) wet bulb conditions that may occur. The performance factor (P.F.) will be used to determine the performance of the tower at the design conditions. Following is an outline of the analysis that establishes this test procedure, according to applicable cooling tower factors and how they operate: • Water flow GPM and airflow across the tower are constant. • At constant heat load, the approach will decrease as the entering WB increases. Approach is defined as the difference between the temperature of the water leaving the tower and the wet bulb temperature of the air entering the tower. • Evaporation takes place in a tower but has no effect on the cooling of the water. It is simply a conversion of air sensible heat to latent heat. • For standard cooling towers, the heat rejected per ton of refrigeration is 15,000 BTU/Hr. (3 GPM with a 10º∆T) • At any point of test, the water, air, and fill arrangement combine to allow the air to remove a given percentage of the theoretical heat available to it. This percentage, called the Performance Factor (P.F.), will remain constant at any entering WB temperature and heat load as long as the GPM (Vs), CFM (Vs), and fill do not change. Test Procedure During the test procedure, the following data is recorded with the same intervals and no greater deviations than outlined in 13.3.3: • Water temperature entering the tower. • Water temperature leaving the tower. • WB temperature of the air entering the tower (use table 11 to convert to enthalpy H2). • WB temperature of the air leaving the tower (use table 11 to convert to enthalpy H3). • Water flow rate GPM. 106
107 BTUH = GPM X 60 X 8.337 X ∆T of the water Tons = GPM X ∆T of the water / 30 GPM = BTUH / 60 X 8.337 X ∆T of the water GPM = (Tons X 30) / ∆T of the water GPM = (Air Density X CFM X ∆ Enthalpy h1-h2) / (8.337 X Water ∆T) . CFM = (GPM X 8.337 X Water ∆T) / (Air Density X ∆ Enthalpy h1-h2) Example 12: Find the tons of a cooling tower with an entering water temperature of 90º and a leaving water temperature of 80º and a 145 gpm. Solution 1 • GPM x 60 X 8.337 X ∆T of the water = BTUH • BTUH / 15,000 = Tons • 145 gpm X 60 X 8.337 X 10º ∆T = 725,319 btuh • 725,319 btuh / 15,000 = 48.35 tons Solution 2 • GPM X ∆T of the water / 30 = tons • (145 gpm X 10º ∆T) / 30 = 48.33 tons Example 13: Find the GPM of a cooling tower with an entering water temperature of 90º and a leaving water temperature of 80º and a entering air temperature of 95º dry bulb and 67º wet bulb, leaving air temperature of 92º dry bulb and 84º wet bulb and a 10,167 CFM. Solution 1 • GPM = (Air Density X CFM X ∆ Enthalpy h1-h2) / (8.337 X Water ∆T) • Air density of 92º dry bulb and 84º wet bulb is 0.071 • Enthalpy of 92º dry bulb and 84º wet bulb is 48.13 • Enthalpy of 95º dry bulb and 67º wet bulb is 31.38 • Water ∆T is 10º • (0.071 X 10,167 X 16.75) / (8.337 X 10) = 12,091.10 / 83.37 = 145.02 gpm Analysis of the Test Data 107
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Balancing of a water and air system
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3 8 TBA (Testing, Balancing and Adj
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5 Air Balancing Multiple Hood syste
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7 87 Series Loop 88 One pipe main 9
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9 Testing and Balancing HVAC A syst
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11 13. Filter frame properly instal
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13 13. Measure and record all requi
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15 15 Example 3: Find the nearest s
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17 For traverses taken in round duc
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19 Flat Oval Duct Traverses For fie
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21 Balancing Devices Volume Dampers
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23 Turning Vanes Turning vanes (Fig
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25 Balancing the VAV System The gen
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27 maximum out-side air damper for
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29 determines how much energy is in
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31 the water removing capacity of a
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33 Table 8A Dry Bulb on left, Wet B
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35 60 58 56 54 52 50 48 46 44 42 40
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37 Foot³ per 1lb Altitude 0 Feet A
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39 Table 9 C Air Density at 29.29
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41 41 Wet-Bulb (F) .0 .1 .2 .3 .4 .
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43 Table 11A Enthalpy at saturation
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45 Table 11 C Enthalpy at saturatio
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47 Wet bulb temperature____________
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49 and replacement should be shut o
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51 duct may be great; the balancing
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53 Design below the 250°F limit (A
Page 55 and 56: 55 Differential Pressure Gauges The
Page 57 and 58: 57 Venturi The venturi is a device
Page 59 and 60: 59 Pressure Total pressure Velocity
Page 61 and 62: 61 Table 1 shows that if the coil i
Page 63 and 64: 63 adjustment of these devices is n
Page 65 and 66: 65 Grouting Motor and lubrication N
Page 67 and 68: 67 For every outside temperature ot
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Page 71 and 72: 71 2. Turn the pump off 3. Close th
Page 73 and 74: 73 Net positive suction head availa
Page 75 and 76: 75 All automatic control valves mus
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Page 79 and 80: 79 4. Read and record the actual pu
Page 81 and 82: 81 13. Record the coils design and
Page 83 and 84: 83 Air Control Air is always presen
Page 85 and 86: 85 • allow draining of all or par
Page 87 and 88: 87 Valves have linear throttling ch
Page 89 and 90: 89 to all the terminals down the li
Page 91 and 92: 91 Pump Circuits Primary-Secondary
Page 93 and 94: 93 • Evaporator: • the design a
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Page 97 and 98: 97 Condenser • the design and act
Page 99 and 100: 99 • Each reading of liquid tempe
Page 101 and 102: 101 • Design and actual entering
Page 103 and 104: 103 differs from the average by mor
Page 105: 105 • Orifice plate • Turbine m
Page 109 and 110: 109 Lam = lbs. of air per minute th
Page 111 and 112: 111 When dry bulb temperature measu
Page 113 and 114: 113 GPM = FPM X Gallons per foot FP
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