Airflow and Contaminant Simulation with CONTAM

Transcription

1 Arflow and Contamnant Smulaton wth CONTAM George Walton, NIST CHAMPS Developers Workshop Syracuse Unversty June 19, 2006

2 Network Analogy Electrc Ppe, Duct & Ar Wre Ppe, Duct, or Openng Juncton Juncton or Room Battery Pump or Fan Voltage, V Pressure, P Current, I Mass flow, F

3 Network Analogy

4 Network Soluton (steady state) I by conservaton at each juncton, j I j, = 0 or wth j F j = 0, = V / R ( ) j, j, j or F = C P n j, j j, Solve smultaneous equatons for all V or P

5 Solve Smultaneous Non-lnear Equatons by Newton-Raphson teraton Relable soluton Atken s method (1982) under-relaxaton (1992) trust regon (1997) Speed for large networks skylne (or profle) (1987) equaton reorderng (1997) conjugate gradent (1997)

6 Transent Conservaton of Mass t m F F j j = +, m = mass of ar n zone ( ) t t t m R T PV t t m 1 deal gas: mrt PV =

7 Bernoull's Equaton Flow along a streamlne (wthn each arflow path) s governed by Bernoull's equaton: 2 2 ρ u 1 ρ u2 P = P ρ g z1 P2 + + ρ g z2 2 2 where P = total pressure drop between ponts 1 and 2 P 1, P 2 = entry and ext statc pressures u 1, u 2 = entry and ext veloctes ρ = ar densty g = acceleraton of gravty (9.81 m/s 2 ) z 1, z 2 = entry and ext elevatons.

8 Lmtatons We assume quescent zones Infltraton Sgnfcant flow veloctes wll mpact: * Resstance to flow n the zone * Flow coeffcent vares wth geometry * Momentum effects * Wnd pressure Pressure losses at duct junctons * Loss coeffcent C vares wth flow * Momentum negatve loss terms

9 User Interface Essental for: Complex Problems General Use

10 From Network Analogy to Interface

11 Draw Walls, Defne Zones

12 Add Flow Paths

13 Add a Duct

14 From Network Analogy to Interface

15 Case Study (~1997)

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17 Bgger and More Complex Buldngs

18 Contamnants The transent conservaton of speces mass n a control volume s: (mass of speces α n c.v. at tme t+ t ) = (mass speces α n c.v. at tme t ) + t (rate of speces α gan rate of speces α loss) t t j j j j j j t t t C R C F C m G C F t VC VC δ α α α β β α β α α α α α κ η ρ ρ , ) (1 All contamnant concentratons can be determned by solvng a set of smultaneous lnear equatons.

19 Contamnant Smulaton Test Case

20 Contamnant Test Case Results Scheduled steady source Flow rate = 1/2 ACH per zone Tme step = 15 mn.

21 Contamnant Test Case Results Scheduled burst source Flow rate = 1/2 ACH per zone Tme step = 15 mn.

22 Lmtatons Works well f tme step > mxng tme of the zone. Tradtonal ar dffuson systems desgned to mx the ar, but mxng tme s on the order of several mnutes. * Transent contamnant convecton s poorly modeled. * Even systems desgned to mx sometmes don t. Many contamnant modelng features could be added. * Detaled flter model * Adsorpton desorpton models * Complex chemcal reactons * Aerosols

23 Fast Flow Through Zone & Duct Flow = 0.2 m^3/s; Volume = 20 m^3; 36 ACH

24 1-D Flow Through Zone & Duct Velocty = 0.2 m/s; Length = 20 m

25 Notes on above sldes Mxed case: duct dvded nto two nodes 1-D smulaton: Zone by Euleran method (Patankar hybrd) Duct by Lagrangan method Good convecton 100 s transt tme Questonable dffuson coeffcents Zones requre some geometry data Implct soluton not practcal

26 Explct Soluton for Contamnants Addng cells to each zone to model convecton would greatly ncrease the number of equatons. However, the need for a good model of convecton also requres a short tme step. If the tme step s suffcently short, concentratons can be determned by an explct numercal method: NO smultaneous equatons. Stable f t < zone ar exchange tme

27 Short Tme Step (STS) Smulaton Sequence Determne boundary condtons Determne control sgnals Both of above can be set va sockets Compute arflows Compute zone concentratons Compute juncton concentratons

28 Sequental Soluton n a Duct Network Duct junctons would lkely be unstable but can be solved explctly n order.

29 Processng Control Sgnals The sequence of computaton (from known to unknown values) s determned by the drecton of the lnks. Each control node ncludes ponters to the calculaton functon and parameters, ponters to the nput values, and the computed result. The nput ponters are set at program start-up. No data s transferred durng processng.

30 CONTROLS Fan, damper, openngs, controlled by temperature, pressure, concentraton

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32 END