THE MODERN
HVAC SYSTEM
J. Michael Carson P.E.
Senior Mechanical Engineer
Purdue University
HVAC Systems
Btu
Ton
Heat Gain & Heat
Loss
Air Handling Unit
Fan
Air Distribution
Preheat Coil
Cooling Coil
Reheat Coil
Double Duct
Diffuser
Grille
Register
Constant Volume
VAV
DOAS
Chilled Beam
UFAD
1
HVAC Systems
2
HVAC Systems
Physical Sciences have a long
history of discovery
Galileo
Fahrenheit
Celsius
Carrier
Fulton
Watt
3
HVAC Systems
Leading to today’s HVAC Engineer
Their work is based on energy transfer
The energy they transfer is
HEAT
4
HVAC Systems
Heat is always moving
Flows from higher energy (something hot)
to lower energy (something cold)
5
HVAC Systems
BTU (BRITISH THERMAL UNIT)
How we measure heat in America
1 BTU = 1 lb of water 1°F
6
HVAC Systems
QUIZ #1
If it takes one hour
to heat 1 lb of water
1°F the heat transfer
rate would be …
Circle your answer
1 Btu/Hr
1 BTH
1 BTUH
Being well read
engineers understand
Ralph Waldo Emerson
“A foolish consistency is the hobgoblin of little minds”
7
HVAC Systems
QUIZ #1
This helps you understand
the HVAC engineer
“A foolish consistency is the hobgoblin of little minds”
8
HVAC Systems
QUIZ #2
What was a favorite treat
Washington and Jefferson
served summer visitors?
How could they eat ice cream in the summer of 1700’s?
9
HVAC Systems
ICE HARVESTING
10
HVAC Systems
QUIZ #3 When one ton of ice melts in one day
(24 hours) what do we call the heat
absorbed by that ice each hour?
1 Ton
1 Ton = 12,000 Btu/Hr
11
HVAC Systems
QUIZ #4
Is there such a thing as one ton of heat?
No
Now what did Emerson say?
12
HVAC Systems
HEAT GAIN & LOSS CALCULATION
What makes heat?
Lights
People
Equipment
Walls & Windows
Solar
THE BACKBONE OF HVAC DESIGN
How do we get rid of the heat?
13
HVAC Systems
AHU (AIR HANDLING UNIT)
Fan, Cooling coil, Ductwork, Filters, Diffusers & grilles, Condensing unit, etc.
Originally installed in special rooms
1950s more people wanted AC
What did we do if we had multiple rooms?
14
HVAC Systems
1950S MULTIPLE AHUS
ADVANTAGES
DISADVANTAGES
• Everybody gets AC
• Exterior appearance
• Maintenance
• Noise
• Floor space
HOW WE REMOVED THE PROBLEMS
15
HVAC Systems
1960 CENTRAL STATION AHU
ADVANTAGES
DISADVANTAGES
• Serves many rooms
• Noise is isolated
• Localized
maintenance, few
pieces of equipment
• One zone
• No outside air
16
HVAC Systems
1960 CENTRAL STATION AHU
Energy Tips
1. No more OA than necessary
ADVANTAGES
DISADVANTAGES
•
•
•
•
• One zone
• Air can’t get back
to the AHU
Serves many rooms
Noise is isolated
Low maintenance
Fresh air
17
HVAC Systems
1963 CENTRAL STATION AHU
Energy Tips
1. No more OA than necessary
2. Fan operation
ADVANTAGES
DISADVANTAGES
•
•
•
•
•
• One zone
• Cools in winter
Serves many rooms
Noise is isolated
Low maintenance
Fresh air
Pressure Control
18
HVAC Systems
1965 AHU W/ ECONOMIZER
Energy Tips
1. No more OA than necessary
2. Fan operation
3. Economizer operation
4. Damper operation
ADVANTAGES
DISADVANTAGES
•
•
•
•
•
•
• One zone
Serves many rooms
Noise is isolated
Low maintenance
Fresh air
Pressure Control
Economizer
19
HVAC Systems
1966 DOUBLE DUCT
Energy Tips
1. No more OA than necessary
2. Fan operation
3. Economizer operation
4. Damper operation
5. Remove simultaneous
heating and cooling
ADVANTAGES
•
•
•
•
•
•
•
DISADVANTAGES
Serves many rooms • Uses a lot of
energy
Noise is isolated
Low maintenance
Fresh air
Economizer
Room level control
Flexible
OIL EMBARGO!!
20
HVAC Systems
1975 SHUT-OFF VAV
ADVANTAGES
•
•
•
•
•
•
•
DISADVANTAGES
Serves many rooms • Poor air quality
Noise is isolated
• Poor humidity
Low maintenance
control
Fresh air
• Poor temperature
Pressure Control
control
Economizer
Saves Money
SICK BUILDING SYNDROME!!
21
HVAC Systems
1980S VAV WITH REHEAT
ADVANTAGES
•
•
•
•
•
•
•
DISADVANTAGES
Serves many rooms • No good speed
Noise is isolated
control (mechanical)
Low maintenance
Fresh air
Pressure Control
Economizer
1990S VFD!!!!
Saves Money
HOW
DO THEY WORK?
22
HVAC Systems
VFD OPERATION
30 Hz
45 Hz
60 Hz
60 Hz
23
HVAC Systems
VFD OPERATION
30 Hz
45 Hz
60 Hz
60 Hz
24
HVAC Systems
VFD OPERATION
30 Hz
45 Hz
60 Hz
60 Hz
25
HVAC Systems
30 Hz
45 Hz
60 Hz
60 Hz
26
HVAC Systems
1990S VAV REHEAT VFD
BEEN THE
20 YEARS
WHAT
WORKHORSE FOR
IS ON THE HORIZON?
DOAS
27
HVAC Systems
DOAS
28
HVAC Systems
DOAS
29
HVAC Systems
DOAS
ADVANTAGES
DISADVANTAGES
• Small AHU
• Small ductwork
• Less energy??
• FCUs or other room
level system
OFFICES, DORMS, ETC.
CHILLED BEAMS
30
HVAC Systems
CHILLED BEAMS
HOW
DO THEY WORK?
31
HVAC Systems
CHILLED BEAMS
32
HVAC Systems
CHILLED BEAMS
33
HVAC Systems
CHILLED BEAMS
ADVANTAGES
DISADVANTAGES
• Small AHU
• Small ductwork
• Can take many
chilled beams
• Careful temp control
UFAD
34
HVAC Systems
UFAD
35
UFAD
36
HVAC Systems
UFAD
ADVANTAGES
• Small AHU
• Small ductwork
• Less energy??
DISADVANTAGES
• Careful construction
details
• Careful temp control
37
THE END OF THE
MODERN HVAC SYSTEM
J. Michael Carson P.E.
Senior Mechanical Engineer
Purdue University