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Objectives

Objectives. Finish with Duct Design Review the design procedure and explain the theoretical background Diffuser Selection Answer question related to the exam. Frictional Losses. Dynamic losses. Losses associated with Changes in velocity Obstructions Bends Fittings and transitions

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Objectives

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  1. Objectives • Finish with Duct Design • Review the design procedure and explain the theoretical background • Diffuser Selection • Answer question related to the exam

  2. Frictional Losses

  3. Dynamic losses • Losses associated with • Changes in velocity • Obstructions • Bends • Fittings and transitions • Two methods • Equivalent length and loss coefficients

  4. System Characteristic

  5. Air Distribution System Design • Describe room distribution basics • Select diffusers • Supply and return duct sizing

  6. Forced driven air flowDiffusers • Grill (side wall) • diffusers • Linear diffusers • Vertical • Horizontal one side

  7. Diffusers types • Valve diffuser • swirl diffusers • ceiling diffuser • wall or ceiling • floor

  8. Diffusers • Perforated ceiling diffuser • Jet nozzle diffuser • Round conical ceiling diffuser • Square conical ceiling diffuser • Wall diffuser unit • Swirl diffuser • Floor diffuser • Auditorium diffuser • Linear slot diffuser • DV diffuser • External louvre • Smoke damper • http://www.titus-hvac.com/techzone/ • http://www.halton.com/halton/cms.nsf/www/diffusers

  9. Low mixing Diffusers Displacement ventilation

  10. V = maximum volumetric flow rate (m3/s, ft3/min) Qtot = total design load (W, BTU/hr) Qsen = sensible design load (W,BTU/hr) ρ = air density (kg/m3, lbm/ft3) Δt = temperature difference between supply and return air (°C, °F) Δh = enthalpy difference between supply and return air (J/kg, BTU/lbm) Diffuser Selection Procedure • Select and locate diffusers, divide airflow amongst diffusers

  11. Find Characteristic Length (L)

  12. Indicator of Air DistributionQuality • ADPI = air distribution performance index • Fraction of locations that meet criteria: • -3 °F < EDT < 2 °F or -1.5 °C < EDT < 1 °C • Where, EDT = effective draft temperature • Function of V and Δt (Eqn 18.1) • EDT=(tlocal-taverage)-M(Vlocal-Vaverage) , M=7 °C/(m/s) ADPI considers ONLY thermal comfort (not IAQ)

  13. Ideal and Reasonable Throws

  14. Diffuser testing

  15. ADPI

  16. Select Register • Pick throw, volumetric flow from register catalog • Check noise, pressure drop http://www.titus-hvac.com/ecatalog/subcategory.aspx?refid=186 http://www.nailor.com/ http://www.price-hvac.com/

  17. Summary of Diffuser Design Procedure • Find Q sensible total for the space • Select type and number of diffusers • Find V for each diffuser • Find characteristic length • Select the diffuser from the manufacturer data

  18. Reading asignement • Chapter 18 • 18.1-18.4 (including 18.4)

  19. Review for the Exam • Should be able to do all calculations associated with lectures as well as HWs (except HW4b) • Questions/problems may deal with context • i.e. Explain how thermal conductivity influences fin efficiency? Holding all other parameters equal, how important is increasing the thermal conductivity?...

  20. Psychrometrics and Processes (7 & 8) • Know all parameters and their location/orientation on a psychrometric chart • Be able to look up conversions of parameters on a psychrometric chart and with calculations • Use protractor to calculate SHR and ΔW/Δh • Plot processes on a chart for real buildings • List what is held constant for different processes • Everything we talked about AHU and distribution: VAV, CAV , Dual Duct, Fan-coil, Heat recovery, …

  21. Direct Contact (10) • Describe how a cooling tower works • How evaporative cooler works • Understand the Psychrometrics of chapter 10 …..

  22. Cycles (3), Refrigerants (4) • Describe Carnot cycle and components • Understand constant variables for each component • List, describe, and calculate (in)efficiencies • Use figures, refrigerant tables and equations for different substances • List important parameters for refrigerant selection/differentiation

  23. Heat Exchangers (11) • Differentiate types • Calculate NTU, ε, cr, R, P, F, m, UA, etc. • Broad analysis • Which m is larger, which Δt is larger? • Within and between heat exchangers • Calculate and compare different thermal resistances • Describe influence of key factors • Integrate different parameters/resistances • Manipulate UA equation • Describe differences/parameters of relevance for wet heat exchangers

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