2015 x472 class 03 - distribution systems

X472 HVAC System Design
Considerations
Class 3 – Distribution Systems
Todd Gottshall, PE
Western Allied
Redwood City, CA
Reinhard Seidl, PE
Taylor Engineering
Alameda, CA
Fall 2015
Mark Hydeman, PE
Continual
San Francisco, CA

2
General
 Contact Information
Reinhard: rseidl@taylor-engineering.com
Mark: mhydeman@continual.net
Todd: tgottshall@westernallied.com
 Text
• None
 Slides
• download from web before class
• Log in to Box at https://app.box.com/login
• Username: x472student@gmail.com
• Password: x472_student (case sensitive)

3
Course Outline
Date Class Topic Teacher
9/02/2015 1. Introduction / Systems Overview / walkthrough RS
9/09/2015 2. Generation Systems TG
9/16/2015 3. Distribution Systems RS
9/23/2015 4. Central Plants TG
9/30/2015 5. System Selection 1 - class exercises RS
10/07/2015 6. Specialty Building types (High rise, Lab, Hospital,
Data center)
TG
10/14/2015 7. System Selection 2 - class exercises RS
10/21/2015 8. Construction codes and Project delivery methods TG
10/28/2015 9. 2013 T24 and LEED v4 MH
11/04/2015 10. Life-Cycle Cost Analysis and exam hand-out TG
There are three instructors for this class. Todd Gottshall (TG), Reinhard Seidl (RS)
and Mark Hydeman (MH). The schedule below shows what topics will be covered by
who, and in what order.

4
Birds Eye View of Systems
 Single Story – tilt-up
• Single zone rooftop AC
• Split units, VRV
 Two-Story
• Single zone rooftop AC
• Multi-zone rooftop AC
 3-8 Story
• Centralized systems
• Dual Duct
• VAV RH
 High-rise
• Floor-by-floor
• Built-up Systems
• Condenser loops, tenant heat
pumps
 Campus Systems
• Central plant, airside/water
side economizers, thermal
energy storage
• Cogeneration
 Specialty Systems
• Hotel
• Library
• Laboratory
• Underfloor
• Natural Ventilation
• Direct/Indirect
• Cascading cooling towers

5
Overview
 Non-campus distribution systems
(air and water)
 Central plant types and distribution
systems

6
Distribution Systems
 Single zone
 Zoned, but constant volume
 VVT
 VAV Reheat
 Dual Duct (single fan, dual fan)
 DOAS (Dedicated Outside Air System) with
auxiliary cool/heat from
• Fancoil, WSHP, Induction unit, Radiant
 Displacement
 UFAD
 Natural Ventilation

7
Small packaged unit layout
VVT
System

8
Single Zone
 Why choose single zone ?
• Cheap
• Simple
• Provides fairly good temperature zones
 Why Not ?
• Doesn’t work well for multi-story buildings
because of multiple shafts

9
 Single zone
 VVT
 VAV Reheat
 Displacement
 UFAD

11
Single Zone
 Why choose CV reheat ?
• May be needed for pressurization
• Used to be a common system because
controls hadn’t been developed
• Can be used in DOAS systems (dedicated
outside air) such as induction unit systems
 Why Not ?
• Very energy inefficient when used other
than for DOAS

12
 Single zone
 VVT
 VAV Reheat
 Displacement
 UFAD

13
VVT System Requires a Bypass
 If we vary airflow on a constant volume unit we have too
little airflow on a constant volume system = frozen unit
Frozen
compressor,
suction line
Frozen
evaporator

14
VVT System
 Until very recently, could not get
systems with low tonnage (< 10 tons
or so) with variable speed drive
 Had to use bypass damper instead
 Note: recently, thanks to “digital
scroll”, small tonnage VAV units have
started to appear.

15
VVT System
 New 2013 T24 requires small tonnage
units to be multi-stage
 See http://www.energy.ca.gov/title24/2013standards/index.html
 Prescriptive requirements section
140.4.m (fan speed control) and
section 140.4.e.5 (compressor stages)
as part of economizer requirements

19
VVT System
 Why choose VVT ?
• Better control than constant volume single zone, but
not as good as “real” VAV
• Flexible zoning
• Zoning can change with churn
• Fits into tighter ceiling space than dual duct
 Why Not ?
• Users sometimes misunderstand what they’re getting
– comfort will never equal a VAV reheat or Dual Duct
system
• Cannot zone across very different load patterns
(example: can’t use one package unit with VVT to
cover an East and a North exposure)

20
 Single zone
 VVT
 VAV Reheat
 Displacement
 UFAD

21
Recap of Distribution
Systems
VAV Reheat System – expensive application for this building

22
Systems
VAV Reheat System – good application for multi-story Reheat System
double pipe run

23
Systems
VAV Reheat System – good application VAV RH
System AC

24
Systems
VAV Reheat System – good application Reheat
System

25
Variable Air Volume with
Reheat

26
VAV Reheat
 Why choose VAV Reheat ?
• Good control for multiple floors
• Flexible
• Fits into tighter ceiling space than dual duct
 Why Not ?
• More expensive than single zone
• Re-heats
• Typically less energy efficient than dual duct

27
Air Terminal Unit (CAV or
VAV Box)
AFS=Automatic Flow Station
Works on same principle as Pitot tube
Damper controls typically pneumatic,
Electronic (stand-alone) or DDC (networked)

29
VAV Reheat
 Problem with reheat ?
• Just that. Reheat means destroying energy:
• First cool the air
• Then heat it back up
• You pay 2x
• Code (CA Title 24) limits the amount of reheat you can
do (see section on dual max control T24, 140.4.d)
 What alternatives ?
• Use fan-powered terminals
• Provide heating by heating space air, not primary
supply air (in some ways, this is what a good dual duct
design does)

30
VAV Box Minimums (from
Title-24)
 Reheat, T24 allows maximum of (with
DDC control):
• 20% of design cooling airflow
• ventilation requirements (see below)
 Ventilation Minimum Requirement =
Maximum of:
• 0.15 CFM/square foot
• 15 CFM/person

31
Fan-powered box
ensures constant
volume
Series Fan-Powered VAV
Box

32
Parallel Fan-Powered VAV
Box

33
VAV Reheat
 Series fan-powered
• Constant volume system
• Fan has to run when occupied
• Reduces central system fan static somewhat
 Parallel fan-powered
• System works with or without fan
• Fan comes on only for heating
• More energy efficient than series type

34
VAV w/ Parallel Fan-
Powered Boxes

35
VAV w/ Series Fan-Powered
Boxes

36
 Single zone
 VVT
 VAV Reheat
 Displacement
 UFAD

37
Dual-Duct VAV
Dual Duct Dual Fan System Dual
Duct
System

38
Dual-Duct VAV
 Why choose dual duct ?
• More energy efficient (no reheat)
• Good zoning
 Why Not ?
• On systems with lots of outside air (school,
assembly), benefit of not re-heating is lost
• May not fit in ceiling space
• Depending on labor rates, may be more expensive
than reheat system
• More rooftop equipment

42
Dual-Duct VAV Box
DD terminals often feature a mixing
plenum at the outlet to prevent cold
air going one way, and hot air going
the other way
DD is harder to
route through a
building than a
VAV reheat
system!

43
 Single zone
 VVT
 VAV Reheat
 Displacement
 UFAD

44
DOAS Systems
Induction / Fancoil Unit System
High rise
Induction

45
Induction Units and Fancoil
Units
Note: when laying out
piping, consider the
H/W ratio of the building
to figure out whether it
is more cost effective to
run multiple risers with
short branches, or
fewer risers with longer
branches.
It’s easy to figure out,
just make a
spreadsheet with linear
feet of piping.
This is equally true for
VAV reheat piping
loops, and condenser
water loops for
WSHP’s.
One building facade Piping option 1 Piping option 2 ….. Piping option x

46
DOAS: Floor-by-floor units
One mech. Room per floor, one large heat pump
Boiler for
VAV
Reheat
Elevator
machine
room unit
Cooling
Towers
Makeup Air
Handler

47
DOAS
 Why choose DOAS system ?
• Small ductwork, small OA air handlers
• Easy calculation/control of ventilation
requirements
• Flexible
 Why Not ?
• Fairly expensive (many terminal units or
radiant panels)
• No airside economizer (big hit for Bay Area,
small hit for Florida)

48
DOAS: Induction Units
 Why choose Induction units/chilled beams ?
• No fan (no electrical at all in pneumatic control option)
• Small zones, individual control
• Low noise
 Why Not ?
• Very expensive (see article from May 2013)
• High static on DOAS fans (although much better in modern
chilled beam design) and constant volume, leading to high
annual fan power
• Noise (also better on modern designs)
• Older vertical units: high maintenance/hard to clean, loss of
capacity when carpet particles in coil reduce or eliminate
induction

49
DOAS: Induction Systems
Actually a re-cooling system, not
re-heating system: in winter,
outside air handler provides hot air
(hot enough for all zones). The
overheated zones are re-cooled
by the induction units.

50
DOAS: Induction Units
Nozzles at
base of unit

51
Induction units are often a maintenance problem, because when dirt accumulates in the coil,
there is very little static pressure from the induction effect. Unless coils stay clean, induced air
volume is reduced over time, until the units don’t cool effectively.

52
Chilled beams : passive and active (essentially, induction units)

53
Chilled beams : passive and active (essentially, induction units)

54
DOAS: Fancoil Unit
Unlike induction units, fancoils actively push air through the cooling coil and
have much more “motive force” to ensure that coil flow remains as designed.

55
DOAS: Fancoil units
 Why choose Fancoil units ?
• Flexible
• High local capacity
 Why Not ?
• Fairly expensive
• No airside economizer
• Possible leaks (for IDF/Data rooms)

56
DOAS: Fancoil Unit
High Internal loads,
quiet operation:
Chilled-water fancoil
Note spring isolation
hangers

57
DOAS: WSHP
 Why choose water-source heat pumps ?
• Flexible
• High local capacity
• Cool/heat on one circuit (uninsulated condenser water)
• Lower first cost than fancoil system
• Recover heat during simultaneous heating and cooling
 Why Not ?
• More expensive units (each has its own compressor)
• More maintenance intensive than fancoils
• Noisier than fancoils
• No airside economizer

58
DOAS: WSHP
Like fancoils, WSHP units can handle localized loads. They use condenser water (for heating and
cooling) instead of chilled water and hot water.

59
DOAS: WSHP
Unlike fancoils, WSHP units are harder to maintain, since they have many more parts – in particular,
they contain a compressor (often 207V or 480V) and a condenser, plus a control panel.
A fancoil contains just a fan (usually 120V) and a coil.

60
DOAS: Radiant Systems
 Why choose Radiant Systems ?
• Quiet (No noise)
• Energy efficient
• High comfort level
 Why Not ?
• Can be expensive (panels much more so than in-floor
piping)
• Fairly limited capacity (this determines cost – if
additional systems are needed to augment capacity,
then overall solution becomes expensive)
• Controllability: slow reaction (Panels faster than floor)
• Architectural integration

61
PEX tubing typically used
for radiant heating / cooling
systems. Poured into slab

62
Zoning works by providing
a piping header that feeds
several loops with control
valves.
Exterior areas may have
denser pipe spacing, and
different zoning than
interior zones.
As with underfloor (UFAD)
systems, zones tend to be
quite large.

63
Zoning – note large zones
Distribution
header

64
Zoning works by providing
a piping header that feeds
several loops with control
valves.
Shown on the left is a
distribution header for one
zone, the individual pipes
are equipped with circuit
setters.
The entire heater will have
one temperature control
valve.

65
Distribution header in wall – note insulation of pipes
in the wall cavity.

66
Zoning detail

67
 Why choose Radiant Panel Systems ?
• Faster response than in-floor
• Point loads (conference room, corner office)
 Why Not ?
• Very expensive
• Cold water above dewpoint limits capacity
(cooling applications)
• Architectural integration

68
Radiant panels – models abound
Products

69
 Single zone
 VVT
 VAV Reheat
 DOAS (Dedicated Outside Air System)
with auxiliary cool/heat from
 Displacement
 UFAD

70
Displacement Ventilation
Low entry of air through very slow (read large) supply opening
Displacement

71
Displacement Ventilation
As air rises, it creates a natural
convection draft that pulls in cool
air from below. Cool air “finds its
own way to the load”

72
Displacement Systems
 Why choose Displacement Systems ?
• Work in large areas without duct distribution
• Handle the load where it occurs
• Natural stratification
 Why Not ?
• Small spaces
Individual drops (for duct from overhead) per space
Large supply openings
• High loads (can’t supply air very cold because of
discomfort).
• No Heating!

73
Displacement systems
Displacement outlet integrated into seats for theatre applications

74
Displacement systems
Displacement for wall / corner / sill applications

75
 Single zone
 VVT
 VAV Reheat
 Displacement
 UFAD

76
Underfloor Air Distribution
Systems
Air distributed in plenum underfloor instead of through ducts overhead.
Outlets

77
Systems
Air distributed in plenum underfloor instead of through ducts overhead.
Outlets

78
Systems
Weaknesses : Unknown effects: Note: our experience by now shows that stratification works less
well than expected, that the air warms up under the floor, reducing the low DT and extended
economizer use, and that air distribution suffers from leakage in the real world.
Return Air Grille
Raised Access Floor
Return Air Plenum
Ceiling
Tset
Qoccupied
Qstratified
CFM, Tsupply
Treturn

79
Systems
0
1
2
3
4
5
6
7
8
9
10
11
69 70 71 72 73 74 75 76 77 78 79 80 81 82
Room Temperature, °F
Height,ft
1.0 CFM/sq. ft
0.6 CFM/sq. ft
About the same
temperature at t’stat
despite 40% less air
Stratification aids lower air volume

80
Systems
Weaknesses : Construction issues

81
Systems
Weaknesses : Accessibility for underfloor terminals

82
Systems
Weaknesses : Accessibility for
underfloor terminals
Terminals are fancoils or fan-
powered terminals for high-load
exterior spaces, and are ducted
like regular fancoils

83
Systems
Weaknesses : underfloor distribution
Despite the pressurized plenum, it becomes
necessary to run underfloor “air highways” to
direct the air and counter effects of large
swirls, turbulence and the like, that cause
“mysterious” temperature fluctuations.
These are especially hard to seal unless
made just like ducts.

84
Systems
Underfloor terminals : fancoils … and floor diffusers

85
Systems
 Why choose UFAD Systems ?
• Work in large areas without duct distribution
• Handle the load where it occurs
• Natural stratification
• Low fan pressures, lower DT, better economizer use
 Why Not ?
• Small spaces
• Large floor plates (air heats up underfloor)
• Sealing of plenum is difficult, leads to problems for
operation

86
 Single zone
 VVT
 VAV Reheat
 Displacement
 UFAD

87
Natural Ventilation
Despite being many thousands of
years old, natural ventilation is now
in its infancy again.
Wind tunnel studies and/or CFD
calculations are usually required to
make buildings work in the design
phase.
Experiences from the real world are
beginning to increase, but are still
only a small fraction of commercial
buildings.

88
Natural Ventilation
To determine the
shape of the building
overhangs for
shading, and location
for wind, you have to
start “from scratch”

89
Natural Ventilation
Every aspect of the building
geometry affects airflows.
Thus, the architect is now as much
a mechanical designer as the
mechanical engineer – the shape of
the building, the walls, the windows,
all make up the mechanical system.
The mechanical engineer has to
review items such as windows as
part of the mechanical submittal
process !

90
Natural Ventilation
Orinda multi-purpose building, model and wind tunnel testing to determine correct opening sizes,
directions and flows.

92
Natural Ventilation

93
Natural Ventilation

94
Natural Ventilation

95
Natural Ventilation

96
Natural Ventilation
Study prevailing winds, not just weather to design the building.

97
Natural Ventilation
Good reference:
CIBSE AM10 : 2005
Introduction to Natural Ventilation

98
Natural Ventilation
 Why choose Natural Ventilation Systems ?
• Energy Efficient
• Environmentally responsible
 Why Not ?
• Complex, small reservoir of practical expertise
• Expensive (wind tunnel, CFD)
• Hard to fix if design flaws occur
• Requires whole new paradigm of coordination
between engineering team members

2015 x472 class 03 - distribution systems

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2015 x472 class 03 - distribution systems