ROTARY PRESSURE INDEPENDENT CONTROL VALVE TECHNICAL MANUAL

Transcription

1 ROTARY PRESSURE INDEPENDENT CONTROL VALVE TECHNICAL MANUAL

2 Introduction The EVOPICV-R Rotary Pressure Independent Control Valve EVOPICV-R is a combined constant flow limiter and rotary characterised control valve, giving full authority equal percentage temperature control valve. Application Examples The EVOPICV-R is suitable for use in variable and constant temperature systems and may be used as constant flow limiter in constant volume systems (without an actuator head) or as a true PICV in variable volume systems. Typical applications of the EVOPICV-R include Fan coils Chilled Beams Heater Batteries Small Air Handling units Heat Recovery Units Over-door Heaters Features and Benefits Features A wide range of actuators suitable for many applications High precision equal percentage ball gives maximum flow control under all conditions The EVOPICV-R shuts off fully leak tight due to the ball valve element Benefits Reduces capital outlay by eliminating the need for separate terminal balancing valves, temperature control valves, branch and mains balancing valves, and system differential pressure control valves. The valve has been designed to be easily close coupled to the terminal unit, even on 40mm centres Selection is simple as no authority calculations are needed. Late design changes and changes of use are more easily accommodated. Reduces circuit interactivity. Commissioning is simplified as no costly proportional balance is required. Controllability is improved due to the equal percentage characteristic. User comfort maximised by ensuring every temperature control valve has full authority. Call us on +44 (0) or visit 2

3 Call us on +44 (0) or visit Valve Specifications Sectional View - DN15/DN20 15 Very Low Low High Part Number PE81VL.04 PE81L.04 PE81H.04 Nominal [l/s] Max Flow l/h] 324 (396) 630 (770) 900 (1100) Nominal Min Flow [l/s] [l/h] Accuracy [0.2-4 Bar] ±10% ±10% ±10% Accuracy includes linearity and hysteresis. Start Up ΔP [kpa] Max Working ΔP [kpa] Working Pressure PN Min Temp [ C] Max Temp [ C] Connections Rp ["] 1/2 1/2 1/2 Connections are parallel BSP to BS-EN

4 Material Specification Body Forging DZR Brass CW602N 2 Cartridge Body Brass CW614N 3 Cartridge Seat Brass CW614N 4 Cartridge Spring Stainless Steel AISI Diaphragm EPDM 6 Ball Brass CW617N 7 Stem Brass CW614N 8 Stem O-Rings Viton Call us on +44 (0) or visit 4

5 Call us on +44 (0) or visit Dimensions No Actuator Dimension A B C D DN BEKR24 Actuator Dimension A B C D DN BELR24A Actuator Dimension A B C D DN

6 Valve Operation The EVOPICV-R pressure independent control valve consists of two main functional groups: 1. Differential pressure regulator 2. Characterised Ball valve for flow regulation and temperature control Pressure Regulator P2 Flow & Temperature Control P1 P3 B A 1. Differential Pressure Regulator The differential pressure regulator is the heart of the pressure independent control valve, by keeping a constant differential pressure across the valve seats constant flow and full authority temperature control can be achieved. Incoming pressure P1 is transmitted to the top face of the diaphragm, outgoing pressure P3 is transmitted to the underside of this same diaphragm. A constant effective differential pressure is maintained between P2 and P3. As P1 increases relative to P3 it acts on the diaphragm closing the shutter (A) against a seat (B) thereby lowering the effective differential pressure. As P1 decreases relative to P3 the diaphragm acts to open the shutter (A) from the seat (B) thus increasing the effective differential pressure. The diaphragm acts against a spring in order to balance the pressure control and stop the diaphragm oscillating. Functional Schematic Call us on +44 (0) or visit 6

7 Call us on +44 (0) or visit 2. Flow Rate Limitation and Temperature Control The temperature control element of the valve consists of an oblique pattern globe valve the differential pressure (P2-P3) across which is held constant by the differential pressure regulator. The authority (n) of a valve can be calculated from the pressure drops across that valve compared with the local system. In this case written as n P a P a P b In the case of a Pressure Independent Control Valve the system P b is close to 0 meaning that the authority is very close to 1. Flow rate limitation and modulating flow control are both achieved using a single characterised port in the ball element of the valve. As the differential pressure across this characterised port is held constant by the pressure regulator flow rate is now only a function of the cross sectional area of this port. As the ball closes against the Teflon seat a portion of the port is occluded, the characterised port has been designed such that the rate of change of area as the ball closes produces an equal percentage characteristic. Maximum flow rate limitation is achieved by limiting the position to which the ball may open. This can be achieved in two ways, firstly by means of a mechanical adaptor or more commonly by limiting the maximum opening position of the attached actuator. Modulating flow rate control is achieved by positioning the ball between the fully closed position and the point at which the design flow rate is achieved, in other the words the point at which the maximum opening position of the actuator is reached. Drawing showing how characterised ball is occluded by Teflon seat

8 Flow Control Figure A. Figure A. describes the general flow performance of the valve as the differential pressure changes. It can be seen that before the start-up pressure is achieved the flow rate increases almost as a fixed orifice valve. Once the start-up pressure has been achieved the valve controls the flow within a proportional band around the set point range. Values stated for the start-up pressure are calculated with the valve in the fully open position as the lowest differential pressure at which the valve will give a constant flow (±10% of nominal). It can be observed that as the valve is regulated to lower flow rates that the start-up pressure decreases. It can also be seen that once the working differential pressure range has been exceeded that the flow rate begins to rise out of the tolerance bands, however this happens at a much lower rate than a fixed orifice valve would exhibit. It should be noted that for a particular pressure a range of flows (within ± 10% of the nominal) can be produced depending on if the pressure is rising or falling. This hysteresis effect is typical of all dynamic balancing valves due to the internal tolerances of the pressure regulator. When designing the pipe system the start-up pressure should be used as the nominal resistance of the valve for pump sizing purposes. The proportional band of the valve accounts for both linearity and hysteresis effects. When deciding on tolerances for witnessing the proportional band (± 10%) of the valve should be taken in to account, we would suggest a tolerance of 0%, +20% is used. Call us on +44 (0) or visit 8

9 Call us on +44 (0) or visit PE81VL.04 - Flow Performance PE81L.04 - Flow Performance PE81H.04 - Flow Performance

10 Flow Rate [Kv/Kvmax] Flow Rate [Kv/Kvmax] Flow Rate [Kv/Kvmax] Power Output Temperature Control The valve characteristic is a measure of the rate at which the valve controls flow in relation to its opening position, authority is a measure of how well a valve performs in relation to its characteristic curve when in use. Exact curve depends on ΔT Flow Rate [Kv/Kv max ] Figure A. Coil Power Output Power output through a coil is related to water flow rate but it can be seen from figure A. that this relation ship is not linear. Figure A. shows that as flow increases the power output tends towards some maximum value. It can also be seen that power output increases rapidly from 0-50% of water flow and thereafter the rate of increase of power output decreases. The steepness of this curve is typically dependant on the temperature difference induced in the heating or cooling media (ΔT). Valve Characterisation Curves Stroke [H/H max ] Figure B. ON/OFF, Quick Acting Curve Stroke [H/H max ] Figure C. Linear Curve Stroke [H/H max ] Figure D. Equal Percentage Curve Call us on +44 (0) or visit 10

11 Power Output Power Output Power Output Call us on +44 (0) or visit Figure B. describes an ON/OFF or quick acting valve characteristic, it can be seen that flow rate increases rapidly until 30% of the valve stroke and then slowly thereafter. Figure C. describes a Linear valve characteristic, flow rate increases in direct linear proportion to the valve stroke. Figure D. describes an Equal Percentage (modified logarithmic) valve characteristic. It can be seen that flow rate increases slowly until the valve stroke is approximately 70% and thereafter flow rate increases rapidly. It is generally desirable that the power output of a coil is linear in relation to the valve stoke as this results in the most easily controllable situation. System Response Curves Stroke [H/H max ] Stroke [H/H max ] Stroke [H/H max ] Figure E. (Fig A. + Fig B.) Figure F. (Fig A. + Fig C.) Figure G. (Fig A. + Fig D.) Figure E. describes the system response (power output of a coil vs. valve stroke) when a quick acting or ON/OFF valve is used. It can be observed that the power output rises to over 95% before the valve is more than 20% open. Figure F. describes the system response when a linear valve is used, it can be seen that power output rises quickly for the first 50% of valve stroke and thereafter the rate of change decreases. It can also be seen that 95% of the power output is achieved with a valve stroke of approximately 80%. Figure G. describes the system response when an equal percentage valve is used, it can be observed that power output increases linearly with increasing valve stroke. From the above graphs it can be seen that the equal percentage characteristic gives the most desirable system response. It should be noted that in any practical system the valve characteristic and coil characteristics may not be 100% matched but an equal percentage characteristic valve will always give a more linear response than any other profile. The characteristic curves of the EVOPICV-R valves are shown overleaf.

12 Characterisation of the regulating ball. The diagram below shows the free area of passage at various opening positions, it can be seen that as the ball opens up to 50% open only a very small area of passage is presented. As the ball opens to 75% a much greater area of passage is formed until at 100% open the full area of passage is presented. This rate of change of area of passage is the factor which governs the valve characteristic. The characterised slot is laser cut directly into the ball, this allows the characterisation profile to be very precise and repeatable. 0% Open 25% Open 75% Open 100% Open Open % Open 81VL 81L 81H 0% % % % % % % % % % % Flow Rate at Each Position Call us on +44 (0) or visit 12

13 Call us on +44 (0) or visit PE81VL.04 - Characteristic Curves % 80.00% [%] Kv/KvMax 60.00% 40.00% 20.00% 0.00% 0% 20% 40% 60% 80% 100% [%] H/H Max PE81L.04 - Characteristic Curves % 80.00% [%] Kv/KvMax 60.00% 40.00% 20.00% 0.00% 0% 20% 40% 60% 80% 100% PE81H.04 Characteristic Curves % [%] H/H Max [%] Kv/KvMax 80.00% 60.00% 40.00% 20.00% 0.00% 0% 20% 40% 60% 80% 100% [%] H/H Max

14 Actuators The EVOPICV-R has been designed with an ISO standard mounting arrangement that can accommodate actuators with both ISO4 and ISO5 mounting pads. This means that almost any type of rotary valve actuator may be used with the valve so long as the minimum torque requirements are met. A wide range of actuators are available from Marflow for the EVOPICV-R valves, split into three functional types. 3 Point floating (Raise/Lower, Drive Open/Drive Close Actuators) 0-10v Proportional Actuators Programmable Multifunction Actuators BELR24A-MF Factory Setting Range Control Type 0-10v v Characteristic Linear 3 Point Operating Voltage [V] AC/DC 24v ±20% Open/Close Operating Power [W] 2 Quiesent Power [W] 1.2 Wiring [VA] 3.5 Actuating Torque [Nm] 5 Angle Of Rotation [ ] 90 Feedback [V] 2-10v v Run Time [s] Operating Temperature [ C] Fluid Temperature [ C] 5-80 Max Relative Humidity [%] 95 IP Rating 54 Cable Type 4 x 0.75 mm² Cable Length [mm] 1000 Housing Colour Orange Dimensions H/W/L [mm] 84/71/182 Input Resistance [kω] 100 Common Black 1 Live Red 2 Control White 3 Feedback Orange 5 Call us on +44 (0) or visit 14

15 Call us on +44 (0) or visit BEKR24 Control Type 3 Point Characteristic Linear Operating Voltage [V] AC/DC 24v ±20% Operating Power [W] 1 Quiesent Power [W] 0.2 Wiring [VA] 2 Actuating Torque [Nm] 5 Angle Of Rotation [ ] 90 Run Time [s] 90 Operating Temperature [ C] 0-50 Fluid Temperature [ C] Max Relative Humidity [%] 95 IP Rating 54 Cable Type 3 x 0.75 mm² Cable Length [mm] 1000 Housing Colour Orange Dimensions H/W/L [mm] 84/71/160 Common Black 1 Close Red 2 Open White 3 BEKR24 Control Type 3 Point Characteristic Linear Operating Voltage [V] AC/DC 24v ±20% Operating Power [W] 0.5 Quiesent Power [W] 0.2 Wiring [VA] 1 Actuating Torque [Nm] 2 Angle Of Rotation [ ] 90 Run Time [s] 75 Operating Temperature [ C] Fluid Temperature [ C] 5-80 Max Relative Humidity [%] 95 IP Rating 54 Cable Type 3 x 0.75 mm² Cable Length [mm] 1000 Housing Colour Orange Dimensions H/W/L [mm] 34/56/164 Common Black 1 Close Red 2 Open White 3

16 Wiring diagram, 3-Point actuators. Wiring diagram, 0-10v actuator. Setting Maximum Flow Rate To set the selected flow, follow these steps: Maximum flow rate limitation to a particular design flow rate can be achieved in practice by the following methods Mechanical setting device and manual flow measurement A mechanical device (TBR) may be fitted to the valve in order to limit the maximum opening position of the valve. A flow measurement device should also be installed. The valve should be opened manually until the deign flow rate is measured on the flow measurement device, once this is achieved then the manual regulating device can be locked in position. Manually limiting the drive time or scaling the control voltage in each BMS controller (not recommended). Using the control curves for each valve the drive time (or control voltage) for a particular flow rate can be calculated. This drive time or control voltage can then be programmed into each building management system controller. e.g. A valve is selected and the design flow rate required equates to an open position of 60 degrees (90 degrees being fully open). The actuator selected has a drive time of 90 second (or 1 second per degree) it can be calculated that the drive time required to achieve design flow is 60 seconds. This is the drive time that should be programmed into the BMS controller. Using a programmable actuator The programmable actuator internally scales its drive time to provide a particular design flow rate. The actuator can be delivered pre-programmed but is also settable on site using the programming tool. In order to program the actuator the opening percentage for a particular valve should be calculated, the example below shows the procedure for this calculation. Once the opening position has been determined the programming tool can be used program this into the actuator. Call us on +44 (0) or visit 16

17 Call us on +44 (0) or visit If desired the programming tool can also be used in concert with a flow measurement device. Whist reading from the flow measuring device the programming tool can be used to drive the valve to any position form 0 100%, when the desired flow reading is achieved the programming tool can be used to set this opening percentage in the actuator. It should be noted that the setting scale on the programming device is a linear percentage (i.e % 0% = 0 50 = % = 90 ) however because the the valve characteristic follows a square function the percentage setting must be calculated from the square root of the ratio of design flow over maximum valve flow. For Example; A design flow rate of 0.05 l/s is required and a PEB81VL.04 (Maximum Nominal Flow 0.1 l/s) has been selected, the percentage setting is calculated as follows. Using a remote commissioning capable BMS control strategy By using a remote commissioning capable BMS controller the design flow rate can be directly programmed into the BMS controller. For more information on remote commissioning and controlling the valve in this way please see our dedicated remote commissioning documentation.

18 Flushing and Media Quality It is expected that the system to which the EVOPICV-R is fitted be pre cleaned and flushed in accordance to the standards and principles detailed in the BSRIA guide Pre commission cleaning of pipework systems (BG29/2011) and the water quality maintained to standards as detailed in BSRIA guide Water treatment for building service systems. Please ensure the compatibility of any cleaning agents and water treatments with the materials listed at the front of this datasheet. It should be noted that because the pressure independent valve will limit flow to a pre-set value regardless of the differential pressure, the valve should not be forward flushed when mounted in the flow connection. It is recommended that if the terminal units need to be flushed that the system is flushed to drain whilst bypassing the EVOPICV-R. On systems where the water quality is not known or is known to be poor it is recommend that a strainer is fitted to protect the EVOPICV-R. Verification In order to verify that a particular valve is within its working range the differential pressure can be measured across the installed pressure test points, if this pressure is between the upper and lower differential pressure limits (20kPa and 400kPa) the valve is within it operational range. Note: flow rate cannot be measured across the EVOPICV-R using the incorporated test points as due to the internal function of the valve the KV is not fixed. If flow measurement is required a separate orifice plate or venturi should be installed downstream. Before onsite verification commences it should be ensured that; The circulation pump has been correctly sized. The circulation pumps are operating in constant pressure or proportional pressure mode. The system has been flushed and treated. The system is free of air. Any local strainers are clean and have remained clean for at least 24hrs of pump operation. All actuators are driven fully open. CIBSE Commissioning Code W (2010) covers the verification of PICVs in section W7.7.3 Summated flow measurement at the branch and sub mains. Since each of the EVOPICV-R valves give a constant flow the expected flow at the branch or sub mains measuring station will be the sum of all the expected flows down stream of that measuring station. If the measured flow is within ±10% of the expected flow then it can be said that all the PICV valves are functioning correctly. Further problem solving can be carried out if necessary by means of either direct flow measurement at the terminal units or by the Marflow Single Station Balancing method. Direct flow measurement at the terminal units. The flow rate can be verified by direct flow measurement at each terminal unit if it is thought necessary however it would be more usual to measure the flow rate at 10% of the terminal units and only investigate further if discrepancies are found. Optimisation When the verification stage is complete the system can be optimised for energy usage by reducing the pump speed. In order to do this the index loop must be identified, this will be the Pressure independent valve that has the lowest differential pressure across it. When the index loop has been identified the pump speed may be lowered until the pressure drop across the index PICV is equal to or just above 1.5 times the start-up pressure for that valve. This will ensure excess energy is not used in circulating water around the system. Call us on +44 (0) or visit 18

19 Call us on +44 (0) or visit Reference Terminal Unit Schematics PICV Constant Flow Regulator Flow Mounted, Variable Volume System with local flow measurement Filterball Isolating Strainer Flow Measurement Valve Return Mounted, Variable Volume System Isolation Valve Coil/Heat Emitter 3 Port Control Valve Return Mounted, Constant Volume System

20 Marflow Hydronics Limited Britannia House Austin Way Hamstead Industrial Estate Birmingham, England B42 1DU XLIT-EVOPICVR-04/12 Tel Fax Errors and Omissions Excepted, Marflow reserve the right to change specification at any time