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VAV Box · 02/07/2025

Introduction to VAV Box and VAV System

This document provides only the basic concepts and scope—serving as definitions—for topics related to VAV Box products and VAV systems

Introduction to VAV Box and VAV System

Author: Starduct Academy Team Published: 2025

This document provides only the basic concepts and scope—serving as definitions—for topics related to VAV Box products and VAV systems. It is intended as an introduction and a guide for further study by sales engineers and MEP engineers who are beginning to explore VAV technology.

Table of Contents

  1. Introduction to VAV Box
  2. Comparison: VAV System vs. VRV System
  3. Steps to Begin Designing a VAV System
  4. Classification and Applications of VAV Boxes
  5. Technical Specifications and Design Standards
  6. Ductwork Design for VAV Systems
  7. Airflow, Pressure Calculations, and VAV Selection
  8. Integration with Other Systems
  9. Installation, Testing, and Commissioning
  10. DDC Device Selection and System Control
  11. Maintenance of VAV Systems
  12. AI, IoT, and Smart Building Applications
  13. Comparison with Other HVAC Solutions
  14. Case Study – Real-World VAV System Design
  15. Summary of Investment Efficiency

1. Introduction to VAV Box

A VAV (Variable Air Volume) Box is a key component in central HVAC systems. It adjusts the supply airflow to each space based on actual demand. Common types include:

  • Single Duct
  • Dual Duct
  • Fan Powered
  • Reheat
  • VAV Diffuser

VAV systems optimize energy use, ensure thermal comfort, and maintain indoor air quality.

2. VAV vs. VRV Systems

  • VAV System: Uses a central AHU and VAV Boxes to regulate airflow. Ideal for large-scale projects with lower investment and energy costs.
  • VRV System: Suitable for small to medium buildings. Higher investment but easier to operate.
Criteria VAV System VRV System
Initial Cost Lower Higher
Electricity Cost Lower (efficient AHU) Higher
Maintenance Lower (simpler structure) Higher

AHU Heat Sources:

  • Chiller (Water/Air Cooled)
  • Heat Pump
  • Boiler
  • DX Coil

Choose the appropriate heat source based on project type.

3. Steps to Design a VAV System

  • Survey thermal loads and zone layout
  • Define main AHU and number of VAV Boxes
  • Create schematic diagrams and select VAV types
  • Calculate airflow and pressure loss
  • Choose controllers and sensors

Advanced topics include sensor selection, BMS integration, and energy simulation.

4. VAV Box Types and Applications

  • Single Duct VAV: Common in offices and meeting rooms
  • Fan Powered VAV: Includes fan for stable airflow
  • Reheat VAV: Includes electric/hot water coil for precise temperature control
  • VAV Diffuser: Ceiling-mounted, adjusts airflow at outlet

Safety for Reheat VAV:

  • Overheat protection: temperature limit sensor
  • No-airflow protection: airflow sensor to shut off heater

5. Technical Specs and Standards

  • Complies with AHRI 880, ASHRAE 62.1, 90.1
  • Sound-insulated materials, galvanized or aluminum casing
  • Strict control of noise and pressure loss

6. Ductwork Design for VAV

  • Calculate airflow per zone
  • Select duct size to minimize pressure loss
  • Optimize layout for balanced air distribution

7. Airflow, Pressure, and VAV Selection

  • Airflow (CFM) = thermal load / ΔT
  • Calculate pressure to select suitable AHU
  • Use software like HAP or Trace 700 for accurate design

8. Integration with Other Systems

  • BMS, CO₂, temperature, humidity sensors
  • AHU, chillers, heat exchangers
  • Coordinated operation ensures energy savings and IAQ

9. Installation, Testing, and Commissioning

  • Install per drawings, verify sensor connections
  • Calibrate Vmin/Vmax for each box
  • Test operation with AHU

10. DDC Device Selection and Control

  • Brands: Belimo, Siemens, Johnson
  • Multi-level control: zone → floor → central
  • Redundancy: dual power supply, dual network

11. Maintenance

  • Clean sensors, check actuators
  • Verify BMS connections
  • Plan regular inspections

12. AI, IoT, and Smart Building Integration

  • AI learns user behavior
  • IoT enables remote cloud connectivity
  • Integrates with smart management platforms

13. Comparison with Other HVAC Solutions

Criteria VAV VRV FCU
Investment Medium High Low
Electricity Low Medium High
Maintenance Low High Medium
IAQ Efficiency High Medium Low
Lifespan 15–20 yrs 10–15 yrs 7–10 yrs

14. Case Study – Real-World VAV System

  • Project: 5-story office, 1,000 m²/floor
  • Design: 1 AHU (80,000 CMH) + 40 VAV Boxes
  • Results:
    • 30% lower investment than VRV
    • 20% lower operating cost

15. Investment Efficiency Summary

Criteria VAV VRV
Investment 4.2 billion VND 6.5 billion VND
Electricity 300 million/year 360 million/year
Maintenance 100 million/year 200 million/year
Payback Period 4.1 years 8.5 years

Conclusion:

VAV systems offer long-term cost advantages, durability, and superior air quality control for large buildings.

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