HVAC Systems and Equipment Notes

HVAC Systems and Equipment

Overview

• HVAC systems maintain safe and comfortable environments using heat transfer equipment, components, distribution, subsystems, and accessories.
  • Essential function: Maintaining thermal comfort.
• Key elements:
  1. Equipment
  2. Components
  3. Accessories
  4. Distribution

Cooling System

• Goals:
  • Reject heat.
  • Minimize heat gain.
• Loads:
  • Internal Heat Gain
  • Ventilation Load
  • Envelope Load
  • Solar Load

Heating System

• Goal:
  • Minimize heat loss.
• Loads:
  • Ventilation Load
  • Envelope Load
  • Heat Generation.

HVAC System Classification

• Classified by:
  • System size and number of buildings/spaces served.
  • Heat transfer medium between equipment and conditioned space.
• Primary System Types:
  1. Local HVAC Systems
  2. Central HVAC Systems
• Heat Transfer Mediums:
  1. Air (using ducts, fans, coils)
  2. Water (using pipes, pumps, chillers, boilers)

Local HVAC Systems

• Types:
  • Local Heating Systems
  • Local Cooling Systems
  • Local Ventilation Systems
  • Local Air-conditioning Systems
• Examples:
  • Window Air Conditioner
  • Unitary Air-conditioner
  • Split Systems
  • Packaged Rooftop Air-conditioner
  • DX Packaged Units (e.g., PTAC, PTHP)
    *Mini-Split System

Central HVAC Systems

• Types:
  • All-Air Systems
    • Single Zone
    • Multizone
    • Terminal Reheat
    • Dual Duct
    • Variable Air Volume (VAV)
  • Air-Water Systems
    • Fan Coil Units
    • Induction Units
  • All-Water Systems
    • Fan Coil Units
    • Water-source Heat Pumps
    • Heating and Cooling Panels

Air System Types

• Described by:
  • Air Volume and Temperature
  • Number of HVAC Zones
• Air Volume & Temperature Control:
  • Constant Volume (CV): Temperature varies, volume constant. Formula: $Q_s = 1.1 \times CFM \times deltaT$
  • Variable Air Volume (VAV): Volume varies, temperature usually constant.
• Number of HVAC Zones:
  • Single Zone (SZ): One unit serves one zone.
  • Multizone (MZ): One unit serves multiple zones.

HVAC Zones

• Definition: A space or group of spaces with similar heat loss/gain characteristics controlled by one HVAC system.
• Zoning Factors:
  • Exposure: Space orientation/grouping.
  • Internal Loads: People, electrical, equipment.
  • Application: Space use and schedule.
  • Budget!

Large AC Systems

• Chilled Water System (Hydronic System):
  • Utilizes a chiller to provide cold water for cooling.

System Components

• Equipment Examples:
  • Boilers
  • Chillers
  • Cooling Towers
  • Coils
• Component Examples:
  • Fans
  • Pumps
  • Compressors
  • Evaporators
• Distribution System Types:
  • Ductwork (Air) & Diffusers
  • Piping (Water) & Terminals
• Accessories Examples:
  • Temperature controls
  • Valves
  • Dampers
  • Filters

Other Equipment

• Exhaust Systems, Exhaust Fans, Exhaust Hoods
• Makeup Air Units
• Unit Heaters (Natural gas, Electric resistance)
• Radiant Heaters (Natural gas, Electric resistance)

HVAC System Selection Factors

• Preference of Building Owner
• Budget (Initial cost, Operational cost, Maintenance/Replacement)
• Size and Shape of Building
• Function of Building
• Comfort requirements
• Number of tenants
• After-hours usage
• Architectural Limitations
• Ease of Operation and Maintenance
• Time Available for Construction

General Considerations

• Cost (First cost, energy cost, maintenance cost)
• Life Expectancy
• Maintenance
• Controllability
• Acoustics
• Adaptability
• Physical Requirements
• Efficiency