1. Objectives Analyze Rotary Heat Exchangers
Use Psychometric chart
- Start Air Distribution Systems
- Diffuser selection

2. Sensible and Enthalpy Wheels

3. Example of Dual Wheel System

4. Psychrometrics of sensible and enthalpy wheel
Example NMS Building HVAC system:
Fans
Enthalpy wheel
Exhaust air
Sensible wheel D A C B 1 2
Return air
form building
Fresh air
Hot and
fresh air to
building
Filters 7
Preheater 6 5 4 3
Heating coil
Cooling coil
Cool and
fresh air to
building

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

6. Designing Room Airflow
Very complex problem
Pumped flow, buoyant flow (or mixed flow)
What non-dimensional parameters govern each regime?
Archimedes number = Ar = gβLΔT/v2
L = characteristic length (m, ft)
g = acceleration due to gravity (m/s2, ft/min2)
T = absolute temperature (K, °R)
β = 1/T (1/K, 1/ °R)
v = kinematic viscosity (m2/s, ft2/min)

7. Computational Fluid Dynamics

8. CFD in Air Distribution Design
Contaminant concentration in a kitchen

9. Buoyancy driven flow: Example of airflow in a stairway
Heater (radiator)

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

11. Diffusers types Valve diffuser swirl diffusers ceiling diffuser
wall or ceiling
floor

12. Low mixing Diffusers Displacement ventilation

15. 18.7

16. Diffuser Selection Procedure
Select and locate diffusers, divide airflow amongst diffusers
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)

17. Find Characteristic Length (L)

18. 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=(tlocal-taverage)-M(Vlocal-Vaverage) , M=7 °C/(m/s)
ADPI considers ONLY thermal comfort (not IAQ)

19. Ideal and Reasonable Throws

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

21. 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

22. Example 18.3 Qtot = 38.4 kBTU/hr Δh = 9.5 BTU/lbma
Note omission in text

23. Reading asignement
Chapter 18
(including 18.2)