Balancing of a Water and Air System (PDF

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110 Cold-water temperatures should not be taken in the tower basin or by bleeding water from the basin or outlet pipe since temperature gradients of several degrees may exist in the basin and the suction piping extending from the tower to the pump. Only after the water is well-mixed by the pump can one be assured the measured temperature is representative of the true cold water temperature leaving the tower. Many cooling tower systems have an automatic or manual bypass arrangement (Figure 13.4) used to control temperatures in the cooling loop by diverting hot water from the cooling tower riser into the cold water line leaving the tower or into the tower basin. Where such a bypass line exists, it is imperative it be shut The cold-water temperatures should be measured on the discharge side of the system circulating pump (Figures 13.1 8z 13.2). If the temperature of the cold water leaving the pump is being measured through a bleed test valve (as shown in Figure 13.3), the average temperature must be corrected for the heat added by the pump and the valve. The test valve must be sufficiently opened to provide adequate quantities to establish accurate temperature measurements. Cold-water temperatures should not be taken in the tower basin or by bleeding water from the basin or outlet pipe since temperature gradients of several degrees may exist in the basin and the suction piping extending from the tower to the pump. Only after the water is well-mixed by the pump can one be assured the measured temperature is representative of the true cold water temperature leaving the tower. Many cooling tower systems have an automatic or manual bypass arrangement (Figure 13.4) used to control temperatures in the cooling loop by diverting hot water from the cooling tower riser into the cold water line leaving the tower or into the tower basin. Where such a bypass line exists, it is imperative it be shut with a liquid of high thermal conductivity (oil or water). Inlet Air Temperature Measurements The wet bulb temperature of the air entering the cooling tower is a required measurement on all tests. Similarly, the dry bulb temperature of the entering air stream is required on forced draft (blow through) towers to determine the density of the air entering the fan(s). Wet bulb temperature must be measured with mechanically aspirated psychrometer. Mount the psychrometer on tripods or other support devices so they remain stationary for the duration of the test. A sufficient number of instruments, located within four feet of the cooling tower air inlet(s), shall be employed to ensure that the test average is an accurate representation of the true average inlet wet bulb temperature. See Figures 13.5 and 13.6 for typical situations. 110
111 When dry bulb temperature measurement of the inlet air is made on forced draft (blow through) type towers for the purpose of density determination, a measurement accuracy of 2°F to 5°F (1ºC-2ºC) for the average inlet dry bulb temperature is usually satisfactory. In most cases this can be achieved by means of a single psychrometer situated at a representative location along an air inlet face. Water Flow Rate Measurement As specified in the test code, water flow rates may be measured by any of several procedures and devices. Since the circulating water, flow rate is one of, if not the single, most important test parameter; take considerable care to ensure it is measured accurately. Install the flow measurement station in a straight section of pipe with the proper distances between it and any upstream or down stream fittings. Specific recommendations for various flow measurement devices can be obtained from the manufacturer. In pipes smaller than 8 inches (200 mm), the preferred measurement device is a venturi, flow nozzle, or orifice plate. Alternatively, a calibrated turbine meter may be used. For pipes 9 inches (225 mm) and larger, any of the aforementioned devices 111
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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
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55 Differential Pressure Gauges The
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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
Page 69 and 70: 69 4. Identify the riser with the h
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
Page 77 and 78: 77 77
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
Page 95 and 96: 95 95
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 and 106: 105 • Orifice plate • Turbine m
Page 107 and 108: 107 BTUH = GPM X 60 X 8.337 X ∆T
Page 109: 109 Lam = lbs. of air per minute th
Page 113 and 114: 113 GPM = FPM X Gallons per foot FP
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