Control Valve Authority and Pressure Independent …

1 Control Valve Authority and yPressure Independent SystemsTA Hydronic CollegeTA Hydronic College Hailey differential controllers? Controllability in ATC valves Energy SavingsEnergy Savings Retrofit-ability How to use Dp controllers?How to use Dp controllers? How does it work Where do they go Balancing the systemBalancing the systemHow TA/Victaulic can help Hydronic College SeminarsHydronic College Seminars TA Select 4 Engineering Services Center2 Why Differential Pressure Control ? Control valves work with improved Authority , therefore their performance is improved Reducing pump head and keep high controllability in the system Control valves are Pressure relieved, so low force (= lower cost) actuators can be used Noisein Control valves is reduced or removed completely Circuits are Pressure Independent modules. Which means: That the changesin other parts of the system do not affect the circuit Large plants can bebalanced module by moduleindependently Large plants can be balanced module by module independently New modules can be added to the system without rebalancing3 Differential Pressure Variationsg seasonthis loadHeatingHeating2qP 100%120%of heatingor below t80%100%PowerDp piping58%40%60%80%Thermal plant load [%]% at 20%40%60%50 % load0%20%0%50%100% 150% 200%easons loadThermal plant load [%]

2 0%20%0%20% 40% 60% 80% 100%load4% sebelow this20 % flowAt constant supply water temperature4% of at or CoolingCooling68% Pressure drops are reducedto 4% of their design LoopSet value UDisturbancesx =U - x0 - 10 volts0-100%k2k30-100%0-100%k4k5xSensorTe rminalControllerActuatorValveRoomxFlowPo weroutputLiftSignalk1x = controlled valueFlowin%Heatoutputin%Heatoutputin%Po wer output %Power output %Flow in%10090807060 Flowin%1009080706010090807060 Heat output in %=+Heatoutputin%pp5040302010 Lift h in %50403020105040302010=+Flowin%Lift h in %500 10203040506070901008000 10203040506070901008000 102030405060709010080 Flow in %Terminal unit characteristicControl Valve characteristicControl Valve Authorityflow design and openfully Valve ControlPP shutfully Valve ControlP Thth it ( )flthhqppVHThe Authority ( ) formulates how much the differential Pressure builds up on the Control orifice of a Control Valve when it is closing100%50%~35%pVBal ValveHCis closing~15%Its value indicates how effectively the Control Valve can reduce the flow while it is Control Valve Authority (Variable Flow)Constantas soon as the Valve Cv is chosen ( pV).

3 HtflllCtlflow design and openfully Valve ControlPP shutfully valveControlP ViblddflithiiVariable,depends on flows in the piping, thus also on the opening of all the other Control valves . In a variableflow distribution, thth itft lliibl7the Authority of a Control Valve is of Valve CharacteristicThe lower the Authority , the larger the p variations on the Control Valve , the larger distortion of the Valve characteristic 8090100ow %Unstable Control BadFair toGoodExcellent0102030 0 102030405060708090100 Control Valve with Lift % minimumLowest acceptable value8 Equal-percentage characteristic (EQM)Variable Authority of 2-way Control ValvesAuthority in design conditions: 5/(5+7) = at half-load: = 5/(5+7+ *21) = !Low flow (halfload)Low flow (half-load) *21 ft in excessin the Valve at half-loadftPump head5 ft in the valve7 ft in the circuitH: 33 fVSP does not allow to compensate for all local 9p7 ft in the circuitDp variations in the plantControl Valve SizingControl valves are commercially available with Cv liiditthRd ivalues increasing according to the Reynard series:Cv.

4 Flow to a FCU of 29gpm p5psiand2psiinCv:11Cv:1120Cv:112010 Flow to a FCU of 29 gpm, p 5 psi and 2 psi in connecting pipes. the commercially available Control valves create a design pV of:pVHCv:11 pV [psi]7 :1120 pV [psi] :112010 pV [psi] in between H [psi]14 H [psi] H [psi] :Conclusion: Control valves are generally of Dp Variations p variations distort the characteristic of the Control Valve the nonlinear characteristic of the terminal unit is no longer compensated90100 Power output in %90100 Power output in %90100 Power output in %H x 10607080 Design607080H x 4 Design607080H x 4 Design304050 Valvecharacteristic:304050 Valvecharacteristic:304050 Valvecharacteristic:01020 Control Valve liftValve characteristic:EQM = R = 25 Rangeabilityarea of thecontrol valve0102030 Control Valve liftValve characteristic:EQM = R = 2501020 Control Valve liftValve characteristic:EQM = R = 2511010 20 30 40 50 60 70 80 90 1000010 20 30 40 50 60 70 80 90 1000010 20 30 40 50 60 70 80 90 1000ON/OFF controlNoiseSound Pressure level [dB]CavitatinggvalveRULE OF THUMBRULE OF THUMB :Static Pressure at the inlet of the Valve should be at least twice the Pressure pdrop in the of Control ValvesAccording to its design, each Valve has a required actuation close-off force or torquethat depends on: Tension of the return spring, if any, Friction with o-rings and seals, Differential Pressure applied on the Control Valve /actuator combination has a certainEach Control Valve /actuator combination has a certain close-off differential pressure13 Agreed?

5 The differential Pressure across Control valves must not vary too Valve AuthorityTo achieve good Control it s recommended to fulfill two rules on Authority : 1. Size the Control Valve with a Cv with design p that min H Hp H pV pC ppipe pBVRule no 1:Rule no 2: p piping pV pC+ ppipe+ pSTADor pV H pV ( ppiping+ pC)/3or pV H15 design min Control by Correct Control Valve SizingIDEAIDEAH p circuit: 7 ftIDEAIDEAE nsure designauthority of at least minimumon inallcontrol valves in theworst Hin allcontrol valves in the flowdesign andopen fully valveControl p piping: 33 ftHPflow design and openfully Valve Controlmin Rule no 1:Rule no 2:Rule no 1:For obtaining a design Authority of : p in Control Valve must be HRule no 2:For obtaining a minimum Authority of : p in Control Valve must be HSince p circuit = 7 ft, p in Control Valve must be 7 ftFinal pump head=40+7=47 ftSince p piping + circuit = 33 + 7 = 40 ft, p in Control Valve must be ft (40/3)Final pump head=40+ ft16 Final pump head 40 7 47 ft design= 7/14 = but min= 7/47 = pump head 40 ft design= = and min= = Control with Reduced Pumping EnergyH p circuit: 7 ft H p riser: 2 ftHead (ft) ft8% savings inControl Valve sizing with Dp Control : p piping: 31 ft5049 ft8% savings in Pump HeadFor obtaining a design Authority of and min of : p in Control Valve must be H and of stabilized pSince pcircuit=7ft45 Since p circuit = 7 ft, p in Control Valve must be 7 ftFinal stabilized p = 7 + 7 + 2 = 16 ft =7/14 = 0 design= 7/14 = and min7/16 = pump head= 31 + min p of DpC (2 ft) + 2 + 7 + 7 = 49 ftFlowHow Does it Work ?

6 +Measuring valveFlowmeasurement+ P HDifferential--DifferentialpressureStabi lizationDp controller18Dp Controller PositionDepending on project structure, Dp Control will be applied:On risersOn branchesOn Control valvesOn risers, On branches,On Control Plant Could Have it All20 Find the best Dp Control , decompose the plant into modules21into modulesDp Control (1)Dp Control on each Control valveParameters:On-off or modulating controlor22Dp in pipes; length of branchesMaterial costDp Control (2)Dp Control on branchesParameters:On-off or modulating control23Dp in pipes; length of branchesMaterial costKey 2 Take away ..Using differential Pressure controllers is theUsing differential Pressure controllers is the most cost effective method to insure a minimum stabilized Control Valve authorityDp Controllers can reduce your operating costMaintain Control of what gets installed in your design by including in your spec minimum Control Valve Authority 0 25 to be verifiedcontrol Valve Authority to be verified during submittal process24 Tour Anderson / VictaulicFree Services Offered Seminars for PDHsSeminars for PDHs TA Select 4 ~ Engineering Support Center Engineering Support Center25 Thank you for your attention !

7 Thank you for your attention !26