Pressure independent balancing and control valve (PIBCV) AB-QM

Transcription

1 Pressure independent balancing and control valve (PIBCV) AB-M Description AB-M valve is an automatic balancing valve - flow limiter. Typical applications are: Automatic (adjustable) flow limitation on terminal units (fan-coils, chilled ceilings, Air-handling units..) or branches. It is recommended to be used only in constant flow systems. Benefits: Exact and pressure independent flow limitation allows no overflow at partial conditions to keep Δt on terminal units as high as designed. The AB-M is able to control the temperature at low loads and is equally stable all through the range. All changes in the available differential pressure are corrected by the pressure controller part of the valve. Therefore, less disturbances for temperature control and further less movements from actuator. AB-M offers full flexibility of adjustment AB-M valves can be set to a precise design value they allow full control over the real conditions in the system. Due to the membrane design the valves are less susceptible to blockage. Always the right flow, so no complaints from end users or excessive energy consumption Because the AB valve covers two functions: Balancing & Control, the installation costs are halved Test plugs allow optimisation of the pump head. 100 % built in control valve authority allows lower pump head than traditional setup, thus minimizing energy consumption. AB-M valve equipped with an actuator is a control valve with full authority and automatic balancing valve - flow limiter. Typical applications are: Temperature control and permanent automatic balancing on terminal units (fan-coils, chilled ceilings, Air-handling units..). Because of the automatic flow limiting function, commissioning costs are nonexistent. Easy adjustability allows late change of design flows without high costs. Plug and Play even when installation is not yet completely finished. For example when some floors are already occupied while construction is still going on at other floors, the occupied floors are already fully functional and balanced. Simplifications: Flow limitation is achieved by setting the valve to required flow - Set & Forget. Flow is the only parameter to be considered, so easy and fast valve selection. Easy troubleshooting No control ratio calculation No authority calculation Commissioning is a matter of adjusting the valve without using specialised equipment or highly educated staff. Compact design allows instalment where only limited space is available, for example in standalone fan-coils. DH-SMT/SI VD.A2.W /2008 1

2 Applications - variable flow systems Air handling unit (AHU) / fan coil (FCU) An AB-M with an actuator can be used as a combined flow limiter and control valve with full authority for an AHU (Air Handling Unit). The AB-M ensures the required flow on every AHU and simplifies the hydronic balancing of the system. Because of the integrated differential pressure controller the control valve always has 100 % authority which means that partial load in the system has no influence on temperature regulation as it will have with normal control valves. By installing AB-M the whole system is divided in independent control loop zones not influencing each other. The flow setting is very simple. Just set the required flow for the AHU direct at the AB-M. There is no special method needed for balancing the whole systems. This means a lot of savings in working hours. Not to forget the combination of several functions in one valve body means less valves and installation work. For temperature control AB-M can be equipped with different actuators (on/off, 3-point, 0-10 Volt) as required. Chilled ceiling AB-M in systems with chilled ceilings are used to achieve the required flow in the system and to control the temperature. An AB-M is installed at every chilled ceiling limiting the flow. The integrated control valve is used for temperature control by mounting an actuator. Different types of actuators can be used. 2 VD.A2.W /2008 DH-SMT/SI

3 Ordering AB-M AB-M with meas. nipples Size max. (gpm) Ex. thread connection Code No. ½ 4.0 ¾ - NPSM 003Z0312 ¾ NPSM 003Z ¼ - NPSM 003Z ¼ ½ - NPSM 003Z0315 Accessories - Fittings Code No. Size NPT (male) Sweat 1/2" 003Z Z0292 3/4 " 003Z Z0293 1" 003Z Z /4" 003Z Z0295 Combinations AB-M XT with electrical actuators Valve type Stroke (in) TWA-Z** ABNM-Z AMV 110NL/AME 110NL AMI F V Recommended ordering code numbers (for details refer to data sheets for these actuators) 082F1094 Thermal actuator 24 V (0-10 V) 082F1072 Adapter for AB-M (M30 x 1.5) 082H8056 AMV 110 NL / 24 V, 24 s/mm, 3-point control 082H8057 AME 110 NL/24 V, 24 s/mm, 0-10 V 082H8048 AMI 140 / 24 V, 12 s/mm, 2-point control Size ½, ¾ 0.16 ü ü ü ü Size 1, 1 ¼ 0.2 û* û* ü ü * up to 80 % of max ** Please be aware that only this type of TWA actuator is to be used with AB-M Closing pressure for all actuators: 87 psi. Technical data Size 1/2 3/ /4 Ranges max. (100%) (recomm. lowest setting is 20% of max.) (gpm) Diff. pressure range (p1 - p3) psi psi Control valve s characteristic Max. working pressure Linear 300 psi Flow medium Water and water mixuers with secondary coolants (like glycols) for heating and cooling closed (oxigen tight) Medium temperature ( F) Stroke (inch) Connection actuator (metric) M30 x 1.5 Material In the water Valve bodies Membranes and O - rings Springs Cone (Pc) Seat (Pc) Cone (Cv) Seat (Cv) Screw Flat gasket Sealing agent (only for valves with test plugs) Brass (CuZn36Pb2 - CW 602N) EPDM W.Nr ,W.Nr W.Nr EPDM CuZn36Pb2 - CW 602N CuZn36Pb2 - CW 602N Stainless Steel (A2) NBR Dimethacrylate Ester Out of the water Plastic parts Insert parts and outer screws POM CuZn36Pb2 - CW 602N; W.Nr ; W.Nr DH-SMT/SI VD.A2.W /2008 3

4 Operation principle The AB-M is a control valve combined with a differential pressure controller. The differential pressure controller maintains a constant pressure over the control valve independent of varying conditions in the installation. Because of this construction the flow is automatically limited to a specified value and the control valve has an authority of 100 %. Flow limitation If you have a constant differential pressure across an orifice with a known resistance (c v value) you can determine the flow with the formula: = c v Δp Because the AB-M limits the differential pressure (Δp) across the control valve to a constant level it follows that the flow through the AB-M is also limited. To function properly the AB-M needs a pressure difference of at least 2.32 psi. By limiting the stroke of the control valve, the maximal flow through the valve can be adjusted. If the c v -value of the control valve is halved, the flow is also halved. Because the AB-M has a nearly linear chracteristic to have half the flow you need half the stroke (see figure). STROKE 100% 80% 50% 50% 80% c v,k 100% Authority The valve authority can be defined as: The resistance across the fully opened control valve, divided by the total resistance in the system (valve, pipes, heat exchanger etc.). A = R valve R + R valve system Usually the authority should be 0.3 (30 %) as high as possible to guarantee sufficient control quality. The resistance in the sytem is variable because it depends on the flow. If the flow is reduced, the resistance in the system also drops. Normally the control valve would have to compensate for this by closing even further, thus causing a distortion in the valve characteristic. Because the AB-M has a built in differential pressure controller that keeps the differential pressure across the control valve constant, the effect of this decrease is compensated. It is therefore possible to assume that R system is zero. The formula then becomes: R A = R valve valve =1 ( 100% ) The AB-M therefore always automatically ensures 100 % authority which provides stable control and therefore increase confort and saves time consuming calculations to check the valve authority. As an example we take two valves in a normal HVAC system (page 5), one close to the pump (position 1) and the most distant valve (position 2). Both valves have the same differential pressure potential (the pump head) but the pressure drops between: - Control valve (abbreviation as CV), - balancing valve (abbreviation as BV) and - other elements (abbreviation as OT; such as pipe, terminal units ect.) are distributed differently. With the valve closer to the pump the pressure drop in the pipes (OT) is much smaller. The differential pressure controller used as BV ensures however that the working conditions for both CV are the same. If we look at a situation where we need only 20 %, can see that the pressure drop in the pipes (OT) becomes smaller when the flow is decreasing. This effect is much bigger for the distant valve because the pressure drop in the pipes (OT) is bigger to begin with. The differential pressure controller (BV) compensates for the difference and ensures identical working conditions for both control valves across the total range. If you compare that with a situation with traditional BV you can see that, because the BV is static and doesn t react to the system conditions, the pressure drop across the CV increases significantly which puts the CV to a challenge to provide comfort and stable temperature control. 4 VD.A2.W /2008 DH-SMT/SI

5 Operation principle position 2 position 1 P P position 1 position 2 P P position 1 position 2 CV CV BV CV CV BV BV OT BV OT 20% of design flow OT flow 20% of design flow flow 20% of design flow OT flow 20% of design flow flow pressure drop in a system with AB-M pressure drop in a system with traditional valve set (manual balancing valve + control valve) DH-SMT/SI VD.A2.W /2008 5

6 Stuffing box 2. Spindle 3. Plastic ring 4. Control valve s cone 5. Membrane 6. Main spring 7. Hollow cone (pressure controller) 8. Vulcanized seat (pressure controller) P1 P2 P3 P1-P3 P2-P3 Function: The AB-M valve consists of two parts: 1. Differential pressure controller 2. Control valve 1. Differential pressure controller BV The differential pressure controller maintains a constant differential pressure across the control valve.the pressure difference (p2-p3) on the membrane is balanced with the force of the spring. Whenever the differential pressure across the control valve changes (due to a change in available pressure, or movement of the control valve) the hollow cone is displaced to a new position which brings a new equilibrium and therefore keeps the differential pressure at a constant level. 2. Control valve CV The control valve has a linear characteristic. It features a stroke limitation function that allows adjustment of the c v value. The percentage marked on the scale equals the percentage of 100 % flow marked on the pointer. Changing the stroke limitation is done by lifting the blocking mechanism and turning the top of the valve to the desired position, showed on the scale as a percentage. A blocking mechanism automatically prevents unwanted changing of the setting. 6 VD.A2.W /2008 DH-SMT/SI

7 Pump optimising / Trouble shooting Blue Red P2-P3 Pump optimization const = const const = const P1 P2 P3 P2-P3 2.3 psi 2.9 psi P1 - P3 P2 - P3 P1-P3 The AB-M features test plugs that allow measuring of the pressure difference (p2-p3) across the control valve. If the pressure difference exceeds certain value it means the differential pressure controller is operational and the flow limitation is achieved. The measuring function can be used to verify if enough pressure difference is available and thus verify the flow. It can also be used to optimize the pump head. The pump head can be decreased until no more than the minimal required pressure is available on the most distant valve (in terms of hydronic). This optimal point is to be found when proportionality between pump head and measured differential pressure cease to exist. Presetting The calculated flow can be adjusted easily without using special tools. To change the presetting: - Remove the blue protective cap or the mounted actuator. - Raise the grey plastic ring and turn to the new presetting. - Release the white plastic ring and the presetting is locked. Red The presetting scale indicates a values from 100 % flow to 0 % closed. Counter clock wise turning would increase the flow value while clock wise would decrease it. When valve is set to 80 % or more the red ring becomes visible. If the valve is a 1/2 then the max flow = 4 gpm =100 % presetting. To set a flow of 2.4 gpm you have to set: 2.4/4 = 60 %. Red Danfoss recomends a presetting/flow from 20 % to 100 %. Factory presetting is 100 %. DH-SMT/SI VD.A2.W /2008 7

8 Service For the service shut off function, it is recommended to install the valve in the supply water pipe. The valve features a service function that allows changing of the stuffing box (code 065F0006) under water pressure. Valves are equipped with plastic shut-off mechanism that is to be used for isolating function up to 14.5 psi differential pressure. When closing against higher differential pressure please use accessory - shut-off & protection piece (003Z0230) or set the value to 0 %. Unwanted change of the setting is provided by locking ring (code 003Z0236) which is inserted in the groove below the scale. The locking ring would not allow one to lift the grey plastic ring thus no change of the setting is possible. Dimensions TWA-Z AMV / AME / AMI L1* L2 L3 H1 H2 H3 H4 Type ANSI/ASME Weight in B (lb) AB-M 1/ ¾ - NPSM 1.06 AB-M 3/ NPSM 1.43 AB-M ¼ - NPSM 3.20 AB-M 11/ ½ - NPSM 4.87 L 1 * - dimensions depending on connection type 8 VD.A2.W /2008 DH-SMT/SI