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1. Introduction to HVAC Systems
Gayner Engineers
Mechanical and Electrical Engineers

2. What Does HVAC Stands for?
H = Heating
V = Ventilation
AC = Air Conditioning
A HVAC System is typically an
Environmental Controls System,
which may include controls of
temperature, humidity, and air flow,
of a space.

3. Why is it Important to understand
HVAC Systems as a Construction
Professional?
• HVAC Systems can cost from 10% to 25% of the total construction
budget.
• HVAC Systems take up more space than other trades – Impact
trade coordination, Net usable sq.ft. of the Building, and Sequence
of Installation
• HVAC Systems are essential requirements for certain type of
buildings, such as Laboratories, Hospital, Vivariums, Data Centers,
etc.
• Performance of the HVAC systems will impact the long term
operating cost of a building – Energy Efficiency, Maintenance Cost,
and life expectancy
• Essential Element in LEED Projects
• You need to know how to deal with your Mechanical-Sub!

4. Process of Designing a HVAC
System
• Perform Cooling / Heating Load Calculation
• System Selection – Centralized vs. Decentralized, Mechanical
Cooling vs. Natural Ventilation, VAV vs. Chilled Beams, Air Cooled
vs. Water Cooled, etc.
• Equipment Selection – Air Handling Units, VAV Boxes, Fans,
Chilled Beams, Diffusers, Pumps, Heat Exchangers, etc.
• System and Equipment Layout and Preliminary Spatial
Coordination – Mechanical Room Sizes, Roof Equipment Layout,
Shaft Layout, Ductwork Distribution System, Pipe Routing, etc.
• Detailed Design – Detailed Trade Coordination, Control System
Design, Support Details, etc.

5. Cooling Options
• Natural Ventilation
- Used in Stanford SEQ 2 Buildings
Design criteria and user expectations
need to be defined up front
• Evaporative Cooling
- Used in commercial kitchens, CDC
Housing buildings,
• Refrigeration System
- the most widely used cooling means
Many Options Available
- Refrigerant Selection:

6. Refrigeration Option
Packaged Refrigeration Rooftop
Air Conditioning Unit
•Self-contained refrigeration &
Air Handling System
•From 1-1/2 up to 250 Ton
•Pros: No chilled water piping,
Lower First Cost
•Cons: Lower Energy Efficiency,
Shorter Life Expectancy,
Higher Maintenance Cost,
Not flexible for future Remodel

7. Refrigeration Option
Air Cooled Condensing Unit
w/ Split DX Coil Air Handler
• Outdoor and Indoor Units
• From 1-1/2 up to 250 Ton
• Continuous Cooling Load requirement
Applications – Telecom Room, Elect Room,
• Larger Units usually used in situations where
Large packaged AC units don’t fit or indoor
air handlers are required
• Pros: No chilled water piping,
Less Costly than Chilled Water Systems
• Cons: Lower Energy Efficiency,
Less precise Temperature Controls,
Higher Maintenance Cost,
Not flexible for future Remodel

8. Refrigeration Option
Air Cooled Electric Chiller
• Require chilled water pumps for circulation
• From 5 up to 250 Ton
• Usually used in medium size project s, where
a central chilled water plant is too expensive
• Pros: Allow for more precise temperature
controls and Less maintenance
• Cons: Less energy efficient when compared to
water cooled system, potential acoustical
issue, require chilled water pumps
Pump Air Cooled Chiller
Load

9. Refrigeration Option
Water Cooled Electric Chiller
Up to 4,000 Ton
Needs Cooling Tower, Condenser water Pumps,
Chilled Water Pumps
Pros: Reliable, Energy Efficient, Long Life Expectancy,
Large Capacity, Excellent unloading performance
Cons: Higher First Cost, Require a dedicated space for
installation,

10. Refrigeration Option
Site Chilled Water Distribution System
Campus Environment: Central Chilled Water
Plant and Campus Wide Chilled Water
Distribution System – Stanford, UC Davis,
UC Merced, UCSF, etc.
Use pre-insulated PVC or Ductile Iron Pipes or
Concrete encased
Pros: Minimize maintenance Cost, Energy Efficient,
Maximize Diversity Factor, Less power requirement
for individual buildings, Less spatial requirement for
individual building
Cons: Higher First Cost, additional site work

11. Other Cooling Options
• Evaporative Condensing Chillers
Efficiency in between air cooled and water
Cooled, lot more costly than air cooled and
You have deal with water treatment
• Absorption Chillers – Stanford Central Plant,
UCSF, San Francisco General Hospital,
Always see them with Cogen Plant together
Due to the availability of Waste Heat
• Ice or Thermo Storage System – Stanford
Does not Save Energy but reduce Demand
Charges

12. Heating Options
• Gas Fired Radiant Heating
1. Used in warehouse, garages, outdoor patios, etc.
2. Not as comfortable
3. Combustion air provision
Gas Fired Force Air Heating
1. Rough Temperature Controls for
smaller units – can cause
overheating
2. Stainless Steel Heat Exchanger
Required for 100% outside air
application
3. Unit Heaters – Noisy, needs to
deal with the flue

13. Heating Options
• Heating Hot Water Force Air Heating
1. Hot water produced by hydronic boilers
2. Boiler Construction, Types: Fired Tube, Water
Tube, Copper Fin, stainless steel fire vertical
tube, condensing type, etc.
3. Piping distribution system transport water to
heating hot water coils
4. Coils at Air Handling Units or zone terminals
5. Precise Temperature Controls
6. Higher Cost
7. Most Commonly used heating system in
larger institutional buildings, such as labs and
hospitals

14. Heating Options
• Hydronic Radiant Heating
1. Plastic flexible Tubing underneath floor
2. Lower operating water temperature
3. Most comfortable heating method but
with slower response time
4. Cannot be used for lab or hospital type of
occupancies
5. Great for residential or commercial
6. Can be used at ceiling panels

15. Heating Options
• Steam Heating
1. Either by Steam Boilers or Site Steam Distribution
System
2. Costly Construction
3. Higher system losses
4. Expansion and Contraction – Stress Analysis
5. Higher than 15 psi operating pressure and 10
boiler hp requires 24 hours Boiler Attendance

16. Centralized vs. Decentralized
• Centralized VAV System vs. Single Zone Packaged Units
vs.

17. Centralized VAV with Reheat
• Most Popular Centralized HVAC System in California and rest
of the country for Institutional buildings

18. Single Zone Package AC Unit
Why Choose Single Zone Units?
•Cheap – Great for single Story commercial buildings
•Simple – limited controls
•No Mechanical Piping involved – easy to build
Why Not?
•Doesn’t work well for Multi-Story Buildings
•High Maintenance Cost
•Not precise in temperature control
•Limited filtration options
•Not Flexible for Future Remodel

19. Variable Air Volume Reheat
Why Choose a VAV w/ Reheat System?
•Great for Multiple Floor application
•Much Better Temperature Controls
•Flexible for Remodel
•Lower Maintenance Cost
•More Energy efficient than Single Zone
Why Not?
•Higher Cost – More sheet metal, expensive
equipment,
•Energy inefficient if Controls not Done properly
•Mechanical Piping in ceiling
•More complicated controls than Single Zone

20. Hybrid – Dedicated Outside Air
System with local Cool/Heat
Generally consists of a dedicated 100% Outside air unit with pre-heat
or/and pre-cool and zone level heating or cooling terminals
•Four Piped or Two-piped Fan Coil Units - Potential acoustical issue,
electrical connection, maintenance access
•Water Source Heat Pump System - Don’t see this very often now due to
Energy inefficient and Maintenance!
•Chilled Beams – Stanford LKC
•Ceiling Radiant Cooling / Heating System – Low Cooling Capacity,
Potential Condensation on Surface
What is not Working?
•Higher Cost – Chilled Beam can cost up $80 per sq.ft.
•No Air Side Economizer - Big Deal in Bay Area
•Much More Mechanical Piping in ceiling
•Less Flexible than VAV Reheat

21. Chilled Beams
Summary
•Four Piped for Exterior zone and Two-piped
units for interior cooling only zones
•Requires Precise Selection & Engineering
•Passive and Active Type
•Very low noise level
•Does not work for Hospital in CA
Truth about Chilled Beams
•Does not Save much energy unless you can
produce chilled water without running the
chiller
•Does not save money due to additional
piping and more costly equipment
•Might not work for high occupant density
areas, such as conference rooms
•Lab Application? Use it wisely
•Great for projects with low ceiling clearance

22. Other Distribution Systems
Underfloor Air Distribution System
•Great for Open Office
•Flooring Contractor’s involvement
•VAV controls - Expensive
•Very Flexible for Future Reconfiguration of
Space
•Energy efficient
•Can’t use it for Labs or Hospitals
Displacement Ventilation
•Can be applied for Labs and Hospitals
•High First Cost
•Need wall space at perimeter walls
•Interior zone might require 55 degree
overhead system while the DV is supplying air
at 63 degree – separate system
•Need Preheating when outside air is below
63 degree for 100% outside air system – not
good in Bay Area

23. Other Distribution Systems
Natural Ventilation
•Energy Efficient
•Environmentally Responsible
•Complex Controls
•Hard to Fix if it doesn’t work
•Expensive in Engineering and Time
Consuming – CFD Simulation
•Predicted Performance might be different
than reality
•Occupants need to accept adjusted building
performance
•Requires new Paradigm of A/E Design
Approach

24. Air Handling UnitsSummary
• Custom vs. Commercial Grade Units
• Dimensions determined by Cooling CFM
• Lab or Hospital requires Final Filters
• Direct Drive Plenum Fans are standard
• Double-walled construction with min. 2”
insulation is standard specification
• Stainless Steel trim for coastal and 100%
Outside Air application
• Cu/Cu Coil or Coated Coil - $$$$$$
• Seismic Certification under 2007 CBC
• Acoustical Performance – Very Important
Trade Coordination items
• Support – Concrete Curb, Pad, or Steel
• Electrical Power Connections –
Disconnect Switch, VFDs, & Controls
• Need to be pressure tested if come in
sections
• Submittal Review Process – Don’t drop
the ball!

25. Ductwork SystemsSummary
• Based on SMACNA Pressure Classification:
1. Low Pressure: 2” w.c. or lower
2. Medium Pressure: 3 to 6” w.c.
3. High Pressure: 10” w.c. or higher
• General Supply, Return, and Exhaust: Gal. Steel
• Wet or Biomedical Fume Hood Exhaust: Stainless Steel
316L all welded (min. 18 ga for welded ducts)
• Chemistry or worst: Teflon Coated Pre-fabricated Steel
or Shop Coated Steel
• Other Material: PVC coated, Fiberglass, aluminum
• Specify min. 18 ga. For exposed roof mounted ducts
• Round Duct is cheaper, quieter, and more efficient than
Rectangular Ducts
• AlumFlex - D-B Contractor’s Special
• Bracing required if larger than 6 sq.ft. cross section
• External Insulation for Labs and Hospitals
Trade Coordination items
• Riser Support, true shaft space, FSD access at shaft
• Ceiling Clearance – Flange dimensions

26. Piping SystemsSummary
• Copper up to 2-1/2” & Steel from 3” or larger:
1. Copper: Brazed for 2-1/2” or larger, Type L or K
2. Steel Pipe: Sch 40 welded or Grooved – Heating Hot Water
System, Chilled Water System
3. Welded Steel for Steam & CR, Sch 80 for CR Lines
• New Bracing Requirements Under CBC 2007
• Stainless Steel Pipes for Clean Steam or BioTech Application
• Grooved joints great for Seismic – Specify high Temp EPDM
gaskets for heating hot water application
• Use Ball valves up to 2-1/2” and Butterfly Valves for 3” and
Larger - Specify high Temp gasket for Heating hot water Sys.
• Heavy Duty Ball Valves can be used for Steam and CR; Gate
Valves for 2-1/2” or larger for Steam and Condensate –
Stanford use Gate valves for all sizes
• Provide air vents at high point for air relief
Trade Coordination items
1. Riser Support, trapeze Support for Multi-trades, etc.
2. Ceiling Clearance – Coupling and insulation dimensions