Flow Measurements for Chilled Water Plant (CWP)

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1 APMP 2018 TCFF Workshop, 23 Nov 2018 Flow Measurements for Chilled Water Plant (CWP) Dr LUO Rongmo, A*STAR 1

2 1. Standards and regulations for Green Buildings of Singapore 2. Flow measurement for Chilled Water Plant (CWP) 3. Installation effect on flow measurement 4. Case study 2

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4 BCA 2005 Green building rating system promotes the adoption of green building design and technologies that improve energy efficiency and reduce the impact of building on the environment 2006 Environmental sustainability in buildings 2009 at least 80% of the buildings in Singapore to be green by A global leader in green buildings with special expertise in the tropics and sub-tropics, enabling sustainable development and quality living BCA Super Low Energy (SLE) Programme Super Low Energy Building (SLEB) Zero Energy Building (ZEB) 4

5 BCA Green Mark Non Residential Buildings Residential Buildings Schools Healthcare Facilities Healthier Workplaces Office Interior Landed Houses Infrastructure District Restaurants Supermarket Data Centres Retail Laboratories 5

6 Energy Efficiency Water Efficiency Site/Project Development & Management (Building Management & Operation for existing buildings) Good Indoor Environmental Quality & Environmental Protection Innovation Remark: Water and air flow measurement is very important to calculate and evaluate the Green Mark criteria. 6

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10 W = m h W: Energy quantity m Mass flow rate Δh: Enthalpy h = Cp θ ) ( T inlet T Specific heat capacity ( outlet ) BTU Meter T inlet PRT T outlet Calculator PRT Flow meter 10

11 Green Mark recommend the use of full bore magnetic flow meter. (A Full Bore meter is a circular meter where, when the flow passes by filling the entire bore area, the meter can measure the average velocity inside the meter. Naturally the accuracy of a full bore meter is always much better than any other type.) In the event that a magnetic flow meter installation is not feasible, a clamp-on ultrasonic flow meter (UFM) is the next best technology to achieve long term accuracy, repeatability and reliability of the water flow measurement. 11

12 Q = U i π 4 D k B Coil to generate magnetic field Ui = (v x B) L where: Ui: induced voltage (vector) B: induction (vector) L : length of conductor moving through a magnetic field, and V: its velocity (vector) K: non-dimensional constant 12

13 Effect of temperature on magnetization (thermoelectric effect) This effect stems from the temperature-dependent permeability characteristics of the magnetizable core. While the relationship between the permeability of a magnetizable material and temperature is generally known, consideration has heretofore not been given to this factor in flowmeter circuit arrangements to correct for fluctuations in excitation current or to produce a constant magnetic field independent of these temperature effects. Temperature changes affecting the fluid density and viscosity, and the diameter of the flow element (Jan Gersl, and Libor Lojek, EURAMET project No. 1046, 2011) Copyright 2016 All rights reserved 13

14 Q = V * A Where: V is the water velocity A is the cross area of meter L&X : the direct and lateral (along the pipe axis and in the flowing liquid ) distances between the two transducers V: velocity T12 and T21: transit times in each direction. 14

15 Comparison between PTB and NMIJ on DN200 UFM. (Cordova et al., 2015, Flow Measurement and Instrumentation) 15

16 Temperature changes affect the fluid density and viscosity, and the diameter of the flow element It need in-situ water temperature compensation on flow measurement. 16

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18 A velocity profile describes how fast a fluid is flowing at different points across the pipe. If there was no friction at all the fluid would all move at the same velocity like a solid plug. However, the pipe wall creates friction and a thin layer of fluid next to the pipe wall does not move. The further away from the pipe wall the fluid is, the less friction there is and so the fluid moves at increasingly higher velocities. This means that the highest velocity occurs at the centre of the pipe i.e. at the furthest point from the pipe walls. 18

19 Meter station piping installation configuration is one of a number of effects that may adversely impact meter accuracy. Some piping configurations can distort the flow stream and produce flow measurement bias errors (i.e., offsets in the meter output) of up to several percent of reading. Valves, elbows, or tees placed upstream of a flow meter are just some of the piping elements that can distort the flow stream. 19

20 One bend As well as creating an asymmetric velocity profile, flow around a bend can create a secondary flow. 20

21 Two bends Two bends in different planes cause a distorted profile and a single vortex also known as swirl. Swirl can take well over 100 pipe diameters to decay; in fact there have been cases where swirl has persisted for over 500 hundred pipe diameters before the profile returns to acceptably close to ideal. Swirl tends to affect meters more than asymmetry causing your meter to potentially over or under read significantly. 21

22 The effect a flow disturbance, such as swirl, has on an ultrasonic flow meter is dependent on the path design. As a general rule, the more paths the less of error there will be as you get a better average of the velocity profile. However, the more paths you have the more you will need to pay for your meter. (Cordova et al., 2015, Flow Measurement and Instrumentation) 22

23 There is another solution and that is to use either a flow conditioner or a flow straightener. Flow conditioners are, generally speaking plates with holes in them and come in various designs. They can remove swirl and asymmetry from the flow. Flow straighteners on the other hand are usually tube bundles and are capable of removing swirl but not asymmetry A straightener will reduce the amount of straight pipe needed by removing swirl but in turn it will increase the pressure losses. A flow conditioner will give even greater pressure losses but will remove both swirl and asymmetry. 23

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27 Batch no Totalizer Totalizer for EMF in for UFM 5 mins in 5 mins m3 m3 Error Error (%) =(V,EMF- V,UMF)/V,EMF x % 27

28 Set-up of old CWP before SS591 launched On-site calibration requirement. Clamped-on UFM s measurement accuracy compared with in-line flowmeters. 28

29 Accurate flow measurement is important to implement Green Mark. Challenges are still facing for calibration and on-site verification of chilled water flow meter in CWPs. c Chilled water temperature effect, Installation effect (space constraint), Flow meter size effect (on-site verification). c 29

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