Balancing of a Water and Air System (PDF

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62 Flow Tolerance and Balance Procedure The design procedure rests on a design flow rate and an allowable flow tolerance. The designer must define both the terminal’s flow rates and feasible flow tolerance, remembering that the cost of balancing rises with tightened flow tolerance. Any overflow increases pumping cost, and any flow decrease reduces the maximum heating or cooling at design conditions. WATER-SIDE BALANCING Waterside balancing adjustments should be made with a thorough understanding of piping friction loss calculations and measured system pressure losses. It is good practice to show expected losses of pipes, fittings, and terminals and expected pressures in operation on schematic system drawings. The waterside should tested by direct flow measurement. This method is accurate because it deals with system flow as a function of differential pressures, and avoids compounding errors introduced by temperature difference procedures. Measuring flow at each terminal enables proportional balancing and, ultimately, matching pump head and flow to actual system requirements by trimming the pump impeller or reducing pump motor power. Often, reducing pump-operating cost will pay for the cost of waterside balancing. Equipment Proper equipment selection and preplanning are needed to successfully balance hydronic systems. Circumstances sometimes dictate that flow, temperature, and pressure be measured. The designer should specify the water flow balancing devices for installation during construction and testing during hydronic system balancing. The devices may consist of all or some of the following: • Flow meters (ultrasonic stations, turbines, venturi, orifice plate, multiported pitot tubes, and flow indicators) • Manometers, ultrasonic digital meters, and differential pressure gages (analog or digital) • Portable digital meter to measure flow and pressure drop • Portable pyrometers to measure temperature differentials when test wells are not provided • Test pressure taps, pressure gages, thermometers, and wells. • Balancing valve with a factory-rated flow coefficient Cv, a flow versus handle position and pressure drop table, or a slide rule flow calculator • Dynamic balancing valves or flow-limiting valves (for pre-balanced systems only); field 62
63 adjustment of these devices is not normally required or possible • Pumps with factory-certified pump curves • Components used as flow meters (terminal coils, chillers, heat exchangers, or control valves if using manufacturer’s factory certified flow versus pressure drop curves); not recommended as a replacement for metering stations Record Keeping Balancing requires accurate record keeping while making field measurements. Dated and signed field test reports help the designer or customer in work approval, and the owner has a valuable reference when documenting future changes. Sizing Balancing Valves A balancing valve is placed in the system to adjust water flow to a terminal, branch, zone, riser, or main. It should be located on the leaving side of the hydronic branch. General branch layout is from takeoff to entering service valve, then to the coil, control valve, and balancing/service valve. Pressure is thereby left on the coil, helping keep dissolved air in solution and preventing false balance problems resulting from air bind. A common valve sizing method is to select for line size; however, balancing valves should be selected to pass design flows when near or at their fully open position with 12 in. of water minimum pressure drop. Larger P is recommended for accurate pressure readings. Many balancing valves and measuring meters give an accuracy of ±5% of range down to a pressure drop of 12 in. of water with the balancing valve wide open. Too large of a balancing valve pressure drop will affect the performance and flow characteristic of the control valve. Too small a pressure drop will affect its flow measurement accuracy as it is closed to balance the system. Equation (2) may be used to determine the flow coefficient Cv for a balancing valve or to size a control valve. The flow coefficient CV is defined as the number of gallons of water per minute that flows through a wide-open valve with a pressure drop of 1 psi at 60°F. This is shown as {CV = Q X √ (SF / ∆P)} (2) Q = CV / √ (SF / ∆P) Where CV = flow coefficient at 1 psi drop Q = design flow for terminal or valve, gpm ∆P = pressure drop, psi ∆H = pressure drop, ft of water 63
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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
Page 11 and 12: 11 13. Filter frame properly instal
Page 13 and 14: 13 13. Measure and record all requi
Page 15 and 16: 15 15 Example 3: Find the nearest s
Page 17 and 18: 17 For traverses taken in round duc
Page 19 and 20: 19 Flat Oval Duct Traverses For fie
Page 21 and 22: 21 Balancing Devices Volume Dampers
Page 23 and 24: 23 Turning Vanes Turning vanes (Fig
Page 25 and 26: 25 Balancing the VAV System The gen
Page 27 and 28: 27 maximum out-side air damper for
Page 29 and 30: 29 determines how much energy is in
Page 31 and 32: 31 the water removing capacity of a
Page 33 and 34: 33 Table 8A Dry Bulb on left, Wet B
Page 35 and 36: 35 60 58 56 54 52 50 48 46 44 42 40
Page 37 and 38: 37 Foot³ per 1lb Altitude 0 Feet A
Page 39 and 40: 39 Table 9 C Air Density at 29.29
Page 41 and 42: 41 41 Wet-Bulb (F) .0 .1 .2 .3 .4 .
Page 43 and 44: 43 Table 11A Enthalpy at saturation
Page 45 and 46: 45 Table 11 C Enthalpy at saturatio
Page 47 and 48: 47 Wet bulb temperature____________
Page 49 and 50: 49 and replacement should be shut o
Page 51 and 52: 51 duct may be great; the balancing
Page 53 and 54: 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: 61 Table 1 shows that if the coil i
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 and 110: 109 Lam = lbs. of air per minute th
Page 111 and 112: 111 When dry bulb temperature measu
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113 GPM = FPM X Gallons per foot FP
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