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 Two methods Equivalent length and loss coefficients

System Characteristic

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

Forced driven air flow Diffusers »Linear diffusers »Grill (side wall) » diffusers »Horizontal one side »Vertical

Diffusers types »swirl diffusers »wall or ceiling »floor »Valve diffuser »ceiling diffuser

Diffusers » » »Perforated ceiling diffuser»Jet nozzle diffuser »Square conical ceiling diffuser »Round conical ceiling diffuser »Wall diffuser unit»Swirl diffuser »Floor diffuser »Auditorium diffuser »DV diffuser »External louvre »Smoke damper »Linear slot diffuser

Low mixing Diffusers Displacement ventilation

Diffuser Selection Procedure Select and locate diffusers, divide airflow amongst diffusers V = maximum volumetric flow rate (m 3 /s, ft 3 /min) Q tot = total design load (W, BTU/hr) Q sen = sensible design load (W, BTU/hr ) ρ = air density (kg/m 3, lbm/ft 3 ) Δt = temperature difference between supply and return air (°C, °F) Δh = enthalpy difference between supply and return air (J/kg, BTU/lbm)

Find Characteristic Length (L)

Indicator of Air Distribution Quality 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=(t local -t average )-M(V local -V average ), M=7 °C/(m/s) ADPI considers ONLY thermal comfort (not IAQ)

Ideal and Reasonable Throws

Diffuser testing

ADPI

Select Register Pick throw, volumetric flow from register catalog Check noise, pressure drop

Summary of Diffuser Design Procedure 1)Find Q sensible total for the space 2)Select type and number of diffusers 3)Find V for each diffuser 4)Find characteristic length 5)Select the diffuser from the manufacturer data

Reading asignement Chapter (including 18.4)

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?...

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, …

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

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

Heat Exchangers (11) Differentiate types Calculate NTU, ε, c r, 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