DC MACHINE-Motoring and generation, Armature circuit equation
Cem 350 hvac air side systems 10-2016
1. Air Conditioning & Refrigeration:
CEM 350 Facility Systems Design
Air-Side Systems
2. Contents
• Fundamental HVAC Concepts
• Air Handling Units
• Air System Basics
• Fan-duct systems
• Fan modulation & combinations
• Year-round operation & economizers
• Fan energy use & outdoor air
3. Fundamental HVAC Concepts
• Five subsystems or loops of HVAC
• Air-side
• Chilled water
• Refrigeration equipment
• Heat rejection
• Controls
4. 33 o
C, 28 o
C
27 o
C33 o
C
25 o
C
Conditioned space
5. 13 o
C 13 o
C
33 o
C, 28 o
C
27 o
C33 o
C
25 o
C
Air side system
6. 13 o
C 13 o
C
12 o
C
7 o
C
33 o
C, 28 o
C
7 o
C
12 o
C
27 o
C33 o
C
25 o
C
Chilled water
system
7. 13 o
C 13 o
C
12 o
C
7 o
C 3 o
C
38 o
C
49 o
C
10 o
C
33 o
C, 28 o
C
7 o
C
12 o
C
27 o
C33 o
C
25 o
C
Refrigeration
equipment
8. 13 o
C 13 o
C
12 o
C
7 o
C 3 o
C
38 o
C
49 o
C
10 o
C
35 o
C
29 o
C
33 o
C, 28 o
C
7 o
C
12 o
C
29 o
C
35 o
C
27 o
C33 o
C
25 o
C
Heat rejection
9. 13 o
C 13 o
C
12 o
C
7 o
C 3 o
C
38 o
C
49 o
C
10 o
C
35 o
C
29 o
C
33 o
C, 28 o
C
7 o
C
12 o
C
29 o
C
35 o
C
27 o
C33 o
C
25 o
C
Control Loop
14. Air Handling Units
• Terminal unit or device
• Such as fan coil units, VAV boxes
• Air handling unit (AHU)
• Primary equipment of the air system
• Handle & condition the air, control it to a required
state, and transport it
• Basic components:
• Supply fan, water cooling coil, filters, mixing box,
dampers, controls & outer casing
• A return or relief fan is optional, so as a humidifier
15. Air Handling Units
• Types of AHUs:
• Horizontal or vertical
• Draw-through or blow through
• Factory-fabricated and field built-up
• Rooftop and indoor
• Make-up (primary) air
• Recirculating
16.
17.
18. Air Handling Units
• Package units
• A self-contained air conditioner
• Equipped with a DX (direct expansion) coil
• “Air handler”: the portion inside that handles air
• Rooftop package units
• Gas heating / electric cooling
• Electric heating / electric cooling
• Heat pump system
19.
20. Air Handling Units
• Indoor package units
• Factory-assembly unit installed in a fan room or
machinery room
• Floor-mounted or ceiling-mounted
• Cooling, cooling/heating, heat pump
• Heat rejection:
• Connected to an air-cooled condenser, OR
• Water-cooled condenser
• Split package units
• Indoor air handler + outdoor condensing unit
21. Air Handling Units
• Rating conditions & minimum performance
• ARI and ASHRAE standards
• Rating indices:
• Energy efficiency ratio (EER)
• Seasonal EER
• Integrated part-load value (IPLV)
• Heating seasonal performance factor (HSPF)
22. Air Handling Units
• Coils
• Indirect contact heat exchangers
• Heat transfer between air flowing over the coil and
water, refrigerant, steam or brine insider the coil
• Fins: extended (secondary) surfaces
• Fin spacing and density
• Water circuits
• Number of water flow passages
23. Air Handling Units
• Direct expansion (DX) coil
• Refrigerant is fed (e.g. R-22 and R-134a)
• Air and refrigerant flow:
• Usually counterflow and cross flow
• Typical evaporating temperature = 3-10 o
C
• Condensate drain pan (to collect condensation)
• Performance factors:
• Face velocity, heat transfer coefficients, air-side
pressure drop, physical size
24. Air Handling Units
• Water cooling coils - dry-wet coil
• Chilled water flowing at 4-10 o
C
• Brine or glycol-water at 1-4 o
C
• Temperature rise (typical) = 7-14 o
C
• Water cooling coils - dry coil
• Sensible cooling (dry); no condensation
• Poorer heat transfer coefficient
• Steam heating coil
27. Air Handling Units
• Air filters
• Air cleaning and filtration
• Operating performance:
• Efficiency or effectiveness of dust removal
• Dust holding capacity
• Initial & final pressure drop
• Service life
• Types: low-, medium-, and high-efficiency filters
+ carbon activated filters
28. Air Handling Units
• Test methods of air filters
• Weight arrestance test
• For low-efficiency air filters
• Atmospheric dust spot efficiency
• For medium-efficiency air filters
• DOP (dioctyl phthalate) penetration and efficiency
test
• For high-efficiency air filters
• HEPA (high-efficiency particle air)
• ULPA (ultra-low penetration air)
30. Air Handling Units
• Humidifiers
• Steam humidifiers
• Air washers
• Selection of AHUs
• Face velocity < 3 m/s to prevent entrained droplets
• Proper size of the equipment (energy efficiency)
• Medium-efficiency filter >50% dust spot eff.:
improve IAQ, prevent smudging & discoloring
• Air economizer: save energy
33. Air-side Components
• EcoAdvisor: Energy Trainer for Energy
Managers: HAVC Module 1 [AV 697 E19]
• HVAC components
• Distribution equipment
• Air-side components
• Dampers, filters, coils, fans, ducts and plenums, terminal
units, diffusers, humidifiers, dehumidifiers
34.
35. Air System Basics
• Fan-duct systems
• Flow resistance R, pressure drop Δp and volume flow
rate V
• Duct sections in series:
• Duct sections in parallel:
2
VRp ⋅=∆
o
ns RRRR +++= 21
np RRRR
1111
21
+++=
36. Air System Basics
• Fan-duct systems
• Terminology
• Primary air (conditioned air or makeup air)
• Secondary air (induced space air, plenum air, or
recirculating air)
• Transfer air (indoor air that moves from an adjacent
area)
• System curve: volume flow vs pressure loss
• System operating point
37. Air System Basics
• Fan Laws
• Speed (n)
• Volume flow (V)
• Total pressure loss (Δp )
• Air density (ρ)
• For air systems that are
geometrically &
dynamically similar:
(D = impeller diameter)
38. Air System Basics
• System effect Δpts
• Its additional total pressure loss caused by uneven
or non-uniform velocity profile at the fan inlet, or
at duct fittings after fan outlet
• Due to the actual inlet and outlet connections as
compared with the total pressure loss of the fan test
unit during laboratory ratings
Inlet Outlet
40. Air System Basics
• Modulation of air systems
• Constant volume system
• Volume flow rate remains constant; supply temperature
is raised during part load
• Variable-air-volume (VAV) system
• Volume flow rate is reduced to match part load
operation
• Modulation curve
42. Air System Basics
• Fan modulation methods
• Damper (vary the opening of the air flow passage)
• Waste energy
• Inlet vanes (opening & angle of inlet vanes)
• Low cost; less efficient than following types
• Inlet cone (peripheral area of fan impeller)
• Inexpensive; for backward curved centrifugal fan
• Blade pitch (blade angle of axial fan)
• Fan speed (using adjustable frequency drives)
• Most energy-efficient; but more expensive
44. Air System Basics
• Fan combinations in AHUs
• Supply and exhaust fan/barometric damper
• Used when no return duct or low return pressure loss
• Barometric relief damper: to prevent excessive high
space pressure
• Suitable for systems w/ no air economizer mode & a
low pressure drop in return system
46. Air System Basics
• Fan combinations in AHUs
• Supply and relief fan
• Relief fan to prevent excessive high space pressure
• Usually operated in air economizer mode
• Outdoor air damper is fully opened; recirculating
damper closed
• Suitable when pressure drop of return system < 75 Pa,
or there is a considerable pressure drop in relief or
exhaust flow passage
48. Air System Basics
• Fan combinations in AHUs
• Supply and return fan
• Return fan at the upstream of the junction of return,
recirculating and exhaust flow passage (ru)
• Has similar characteristics as supply+relief fan, but a
higher total pressure at junction “ru”
• Careful selection of return fan is needed to avoid
excessive pressure in the duct system
• Suitable when pressure drop of return system > 150 Pa,
or those requiring a negative space pressure
50. Air System Basics
• Year-round operation of a VAV system
• Region I: Refrigeration/evaporative cooling
• Enthalpy of outdoor > that of recirculating air
• Region II: Free cooling & refrigeration
• Enthalpy of outdoor ≤ that of recirculating air
• Region III: Free cooling, evaporative cooling &
refrigeration
• Enthalpy of outdoor ≤ that of recirculating air
• Region VI: Winter heating
52. Year-round operation
Region I: Refrigeration/evaporative cooling
Region II: Free cooling & refrigeration
Region III: Free cooling, evaporative cooling & refrigeration
Region VI: Winter heating
53. Air System Basics
• Economizer
• A device consisting of dampers and control that
uses free cooling capacity of either outdoor air or
evaporatively cooled water from cooling tower
instead of mechanical refrigeration
• Air economizer:
• Enthalpy-based
• Temperature-based
• Water economizer
54. Air System Basics
• Fan energy use
• For each l/s air
supplied:
• For system using
separate outdoor
ventilation:
mf
syp
sl
W
ηη ⋅⋅
∆
=
1000/
mf
sy
SO
p
R
sl
W
ηη ⋅⋅
∆
+=
1000
)1(
/
,
55. Air System Basics
• Outdoor ventilation air supply
• Aims
• Provide acceptable indoor air quality
• Achieve energy efficiency in the system
• ASHRAE Standard 62-2001 (IAQ standard)
• Demand-based outdoor ventilation air control
using CO2 as an indicator
• CO2 concentration < 800-1,000 ppm
• A specific indoor air contaminant can also be used
56. Air System Basics
• Outdoor ventilation air supply
• Minimum outdoor air control
• Type I: uses a CO2 or mixed gas sensor + DDC
controller to control the volume flow rate of outdoor air
• The best one but can be expensive
• Type II: uses a CO2 or mixed gas sensor + DDC
controller to control the ratio of the openings between
outdoor and recirculating dampers
• Suitable for VAV system
57. Air System Basics
• Outdoor ventilation air supply
• Minimum outdoor air control (cont’d)
• Type III: uses a flow sensor or a pressure sensor + DDC
controller to control the dampers to provide nearly
constant volume outdoor air intake
• More complicated & may cause energy waste
• Type IV: adjust the opening of outdoor damper
manually to provide constant volume outdoor air
• Mainly used for constant-volume systems
