This website requires certain cookies to work and uses other cookies to help you have the best experience. By visiting this website, certain cookies have already been set, which you may delete and block. By closing this message or continuing to use our site, you agree to the use of cookies. Visit our updated privacy and cookie policy to learn more.
This Website Uses Cookies
By closing this message or continuing to use our site, you agree to our cookie policy. Learn More
This website requires certain cookies to work and uses other cookies to help you have the best experience. By visiting this website, certain cookies have already been set, which you may delete and block. By closing this message or continuing to use our site, you agree to the use of cookies. Visit our updated privacy and cookie policy to learn more.
ES Magazine logo
search
cart
facebook twitter linkedin youtube
  • Sign In
  • Create Account
  • Sign Out
  • My Account
ES Magazine logo
  • Home
  • Magazine
    • Current Issue
    • Digital Edition
    • Ad Index
  • Products
  • News
  • Sectors
    • Colleges/ Universities
    • Commercial
    • Government/ Institutional
    • Health Care
    • Hospitality
    • K-12
    • Mission Critical
  • Topics
    • Building Automation
    • Cooling & Chillers
    • Design/ Construction Process
    • Heating & Boilers
    • IAQ
    • Life Safety
    • Motors & Drives
    • Pumps & Flow Controls
    • Retrofits
    • Ventilation
  • Columns
    • Back2Basics
    • Building Automation Column
    • Case In Point
    • Commissioning
    • Editor's Note
    • Facility Files
    • IAQ: A Physician's View
    • Tomorrow's Environment
  • Multimedia
    • Videos
    • Podcasts
    • Webinars
    • Video Spotlights
    • Interactive Spotlights
    • Sneak Peek Spotlight
    • White Paper eBlast
    • Case Study eBlasts
  • Resources
    • eNewsletters
    • Continuing Education
    • White Papers
    • Industry Events
    • ES Store
    • Classifieds
    • Custom Content & Marketing Services
    • Market Research
  • Today's Boiler
    • Today’s Boiler Digital Edition
  • Directory
    • SourceBook
    • Take a Tour
  • Contact
    • Contact Us
    • Advertise
Home » Commissioning Fan-Powered VAV Terminal Units
ColumnsCommercial HVACCommissioningHVAC Design/Construction ProcessVentilation

Commissioning Fan-Powered VAV Terminal Units

Don’t just focus on the large equipment. Keep in mind the small systems and their variety of configurations.

Figure 1. Commissioning Fan-Powered VAV Terminal Units

FIGURE 1. SERIES SUPPLY AIR REHEAT

Figure 2. Commissioning Fan-Powered VAV Terminal Units

FIGURE 2. PARALLEL SUPPLY AIR REHEAT

Figure 3. Commissioning Fan-Powered VAV Terminal Units

FIGURE 2. PARALLEL RETURN AIR REHEAT

Figure 1. Commissioning Fan-Powered VAV Terminal Units
Figure 2. Commissioning Fan-Powered VAV Terminal Units
Figure 3. Commissioning Fan-Powered VAV Terminal Units
December 7, 2016
Rebecca T. Ellis, P.E.
KEYWORDS air handling systems
Reprints
No Comments

This month, I begin a few columns about technical commissioning issues. It is intriguing to me that some of the most common and “simplest” HVAC equipment can be some of the trickiest to get right. This may not be so much because they are actually tricky, but more because we do not take them seriously enough.

Commissioning professionals focus a great deal of attention on a project’s few large and complex central systems, such as boiler plants, chiller plants, air handling units, and energy recovery equipment. This is how it should be, but there are plenty of things to keep in mind and to stay on top of with the many small and simple systems. Failing to optimize the scores or hundreds of terminal units in a building can add up to significant energy and performance issues.

A case in point is fan-powered VAV boxes (FP-VAVs). The first thing for the commissioning professional to keep in mind is that some people do not realize there are two fundamentally different types of FP-VAVs, i.e., series and parallel. For the many who understand that much, there are far fewer who realize that parallel FP-VAVs can be provided with their reheat coils upstream in the return air intake or downstream in the discharge air duct. Please refer to Figures 1, 2, and 3 for schematic depictions of each of these varieties.

During the design phase, the commissioning professional needs to make sure it is clearly understood which of the three varieties is being specified. After that, the sequence of operation needs to align with the features and capabilities of that variety. For example, in most cases:

  • Series box fans are intended to run continuously whenever the space needs to heated, cooled, or ventilated.

  • Parallel box fans with supply air reheat only need to be energized for heating when the central AHU is off.

  • Parallel box fans with return air reheat need to operate whenever the zone is calling for heat, regardless of the status of the central air handler.

During the construction phase submittal review process, it is critical to confirm that the submitted FP-VAVs are of the type intended by the design engineers. After that, the controls contractor needs to submit a graphics package which illustrates the actual configuration of the FP-VAVs and the specified control sequences. Many controls manufacturers have standard “canned” sequences of operation for FP-VAVs, which may or may not be what the design engineers have customized for a particular project. This potential disconnect needs to be revealed and corrected on paper before it is programmed into all of the terminal units and then discovered during commissioning testing. ES

es-subscribe

Recent Articles by Rebecca T. Ellis, P.E.

Prioritizing the Design Portion of Design-Build

Are Your As-Built Drawing Markups Appropriately Marked Up?

Trend Analysis for Effectiveness and Efficiency — Part 3

A Deeper Dive into Trend Analysis

Trend Analysis is a Valuable Commissioning Tool

Rebeccaellis_200

Rebecca is president of Questions & Solutions Engineering, Inc. She can be reached at rteesmag@qseng.com

Related Articles

VAV Reheat Terminal Unit Controls

VAV Reheat Terminal Unit Controls, Part 2

Automated Terminal Unit Performance Monitoring

Commissioning Hydronic Unit Heaters

Related Directories

Universal Fan & Blower Ltd.

ZOO Fans

Twin City Fan Companies Ltd.

Continental Fan Canada Inc.

You must login or register in order to post a comment.

Report Abusive Comment

Subscribe For Free!
  • Print & Digital Edition Subscriptions
  • eNewsletters
  • Online Registration
  • Subscription Customer Service

More Videos

Popular Stories

Dynamic Data Center Workloads Require a Dynamic Cooling Solution

Dynamic Data Center Workloads Require a Dynamic Cooling Solution

Protecting Pharmacists

Protecting Pharmacists: New USP 800 Standards Focus on Safety in Handling Hazardous Drugs

The Dangers of Neglecting Regular Boiler Maintenance

The Dangers of Neglecting Regular Boiler Maintenance

A2L Nov 2019 Figure 1

A2L Refrigerants: Safely Addressing Flammability Concerns

Jeff Edwards

Jeffrey W. Edwards Presented with ASPE Award of Merit

ES-20toWatch-winners250


Todays boiler

Events

December 30, 2030

Webinar Sponsorship Information

For webinar sponsorship information, visit www.bnpevents.com/webinars or email webinars@bnpmedia.com.

View All Submit An Event

Poll

Favorite Engineered Systems columns

Which Engineered Systems column is your favorite:
View Results Poll Archive

Products

The Green Energy Management Book

The Green Energy Management Book

Learn from our experts how to evaluate job opportunities, market your services, sell a Walk-through Survey, target areas for an Energy Audit, calculate energy savings, do retrofit work, and win continuing contracts for retrofit work.

See More Products

ES Kohler webinar


ES_2018Top10States_360

Engineered Systems Magazine

Engineered Systems December 2019

2019 December

Check out the December 2019 edition of Engineered Systems: Discussion of the "next generation" of building controls, the health impact of indoor particulate matter, evidence-based decision-making in the built environment and much more!
View More Create Account
  • Resources
    • ES Glossary
    • HVAC glossary
    • New Products
    • Mechanical Group
    • Partners
    • List Rental
    • Privacy Policy
    • Survey And Sample
  • Want More
    • Connect
  • Contact

Copyright ©2019. All Rights Reserved BNP Media.

Design, CMS, Hosting & Web Development :: ePublishing