flexiblefullpage -
Currently Reading

Small-Duct, High-Velocity HVAC: What It Is and Why It Pairs Well With Modular Homes

Advertisement
billboard -
Construction

Small-Duct, High-Velocity HVAC: What It Is and Why It Pairs Well With Modular Homes

Modular home manufacturers, builders, and owners now have many choices when it comes to indoor climate systems, but small-duct, high-velocity (SDHV) systems may be the perfect fit for these types of homes


By Ashton Gavelek, Unico March 14, 2023
Small duct high velocity HVAC systems
The smaller, modular components of SDHV systems mean they can easily be integrated into the structural components at a home manufacturer’s factory. Image: courtesy robin-clouet.fr | stock.adobe.com

Modular housing has come a long way since the first double-section off-site constructed home built to a local housing code appeared in 1958. Heating, ventilation, and air conditioning (HVAC) technology has also made great strides in energy efficiency, indoor air quality (IAQ), and indoor comfort in the past sixty years. Modular homemakers, builders, and owners now have many choices when it comes to indoor climate systems, but small duct high velocity (SDHV) systems may be the perfect fit for these types of homes. This article will examine how the design aspects of SDHV systems are particularly well-suited to modular homes. 

As the name indicates, small-duct high-velocity HVAC uses a smaller duct system than traditional forced air systems. Because smaller ducting results in reduced air volume, it must deliver that air at a greater speed. SDHV systems operate under higher static pressure than conventional systems, with an average of 1.5-inches water column, and deliver air at a speed of 1,000 to 2,000 feet per minute (FPM) at each terminating register, called an outlet. This air delivery method relies on aspiration rather than traditional HVAC’s “dump and throw” approach. It has its own advantages in terms of energy efficiency and end-user comfort. 

SDHV System Components

SDHV systems are made up of the following components: 

The air handling unit (AHU) — typically consists of a blower, a cooling coil, and/or heat pump coil. In those parts of the country where boilers are used as the primary heat source, a hot water coil is often substituted for the heat pump coil to provide central heating. These separate components, or modules, can be connected vertically or horizontally. SDHV AHUs are smaller than their traditional counterparts and fit into much tighter spaces. 

Main duct, or plenum — SDHV plenum can come in the following sizing and constructions: insulated round (7-inch or 9-inch inner diameter), low-profile rectangular (3.5-inches high by 14.5-inches wide), or square (6.5-inch by 6.5-inch) sheet metal or pre-formed fiberglass. Because the SDHV main supply plenum is ¼ the size of a similarly sized large duct system, 12 tons of SDHV can fit in the same physical space as 3 tons of a conventional AC system. 

Supply duct or tubing — SDHV systems use flexible supply tubing with a 4-inch OD and a 2-inch ID core for air delivery. These connect to the main plenum and weave through the smallest of cavities in the host structure, delivering air to various rooms. 


From left to right: Examples of a Unico air handler, plenum, and supply duct. 
From left to right: Examples of a Unico air handler, plenum, and supply duct. 
Image courtesy Unico

Terminating registers or outlets — Unlike the rectangular registers used by conventional HVAC, SDHV systems terminate in round (5-inch OD, 2-inch ID) or slotted (9-inch by 1-inch outer dimensions with a 0.5-inch by 7-inch inner opening). These outlets can be situated in walls, ceilings, or floors, come in various finishes and constructions, and can be painted, stained, or wallpapered to match any décor. 

Return air system — The only aspect that SDHV shares with a conventional system is the fact that its return air side can be either singular or multiple by room. 

Outdoor unit — While some SDHV manufacturers do offer outdoor units, most often varying types of heat pumps, most SDHV systems are compatible with major manufactured brands of outdoor compressors, condensers, chillers, and heat pumps (air, water, or geothermal). This provides builders, subcontractors, and end users with control over their preferred method. 

SDHV Compared With Conventional Systems

SDHV systems offer end users many benefits over their conventional counterparts when it comes to home design and aesthetics, comfort, energy efficiency, and indoor air quality (IAQ), namely: 

  • SDHV components take up far less physical space than traditional HVAC systems, eliminating the need for bulwarks, soffits, or other duct concealments. Consequently, the aesthetic impact on the home is minimal, and the system virtually disappears into its décor. 

air handling unit that's been installed above the ceiling of a home's top floor bedroom
The above image is from a custom home case study and shows an air handling unit that's been installed above the ceiling of the home's top floor bedroom.
Image courtesy Unico

  • SDHV cooling and heat pump coils are two times the thickness of traditional HVAC coils. This means they remove more moisture (i.e., relative humidity) in cooling mode and produce hotter temperatures in heating mode. Therefore, occupants are more comfortable at higher thermostat settings in the summer and lower thermostat settings in the winter, significantly reducing energy usage in both seasons. 
  • Independent studies have demonstrated that an SDHV system with a 14 SEER consumed 22 percent less energy than a conventional 22 SEER system. Additionally, due to its tight duct construction and smaller surface area, SDHV systems have virtually 0 percent leakage and thermal loss of less than 3 percent capacity. By comparison, a traditional HVAC system with four times more surface area typically experiences thermal losses upwards of 10 percent of capacity. 
  • SDHV’s humidity removal not only boosts efficiency and overall comfort but also reduces mold growth risks and other allergens’ issues. Also, the tight nature of the ductwork greatly reduces the introduction of hair, dust particles, or other allergens, and SDHV systems are compatible with most major IAQ add-ons, such as filters, purifiers, etc., for further air treatment. 
  • When installed properly, SDHV systems are quieter than their traditional counterparts. And the aspiration air delivery method employed by SDHV provides even temperatures from floor to ceiling, with no drafts or hot and cold spots. 

Unico's small duct high velocity hvac system
Image courtesy Unico

Advantages of SDHV Systems in Modular Homes

SDHV systems offer particular advantages to manufacturers and builders of modular homes, as well. Those include: 

  • All sales and equipment logistics can be direct from the SDHV manufacturer to the modular home factory and job site, bypassing any existing distribution channels they may have. This removes markups at the distributor and contractor levels and establishes a one-to-one relationship between the two entities. 
  • Major SDHV makers should be able to provide the modular home factory with the critical requirements for system integration: appropriate heating and cooling load calculations for proper sizing of the indoor comfort system; a system duct design with AHU placement, plenum, and supply layouts; and a material list for all needed equipment. They should also be able to provide in-factory installation assistance, at least for initial projects and until a standardized process is established. 
  • The smaller, modular components of SDHV systems mean they can easily be integrated into the structural components at a home manufacturer’s factory. In many modular applications, the low-profile duct (3.5-inches x 14.5-inches) can be installed in the interstitial space between modules to supply conditioned air to each module above and below the duct. 
  • The SDHV maker should also be available onsite for final supply duct and outlet hookups, installation of outdoor equipment, and commissioning to ensure a system is operating properly. Onsite, when the second-floor module is set atop the first floor, connecting the SDHV outlets should take a single, properly trained laborer less than an hour. 
  • A mutual relationship with an SDHV manufacturer allows modular home sellers to offer their clientele a complete home package that can be sold at a higher premium than their product lines that leave the HVAC system to the builder, their subcontractors, or the end-user themselves. 

The design features that make SDHV systems so attractive for retrofitting older or historically significant homes built before the advent of modern central air systems or custom-built homes whose design elements and aesthetics would be significantly impacted by traditional ductwork are ideally suited to the modular home process and can be a win-win for both manufacturers.


Ashton Gavelek is the marketing brand manager for Unico, Inc., maker of The Unico System small-duct high-velocity HVAC system. Established in 1985, the manufacturer is a NAHB's Building Systems Council member.

Related Stories

Custom Builder

Floodproof on a Floodplain

An impressive addition to the IDEA Home series, the NEWLOOK Experience Home is a master class in engineering and creative design, with builder Michael Freiburger out-thinking an exceptionally tricky lot

Custom Builder

3 Questions Answered About Reliable Energy in Home Construction

Energy expert Bryan Cordill makes a case for why and how propane is an answer to growing concerns about reliability and resilience in home construction 

Business

PERC Highlights Sustainability and Efficiency at IBS with 'Clean Build Conversations'

Hear from industry standouts Matt Blashaw and Anthony Carrino at this hour-long Show Village event

Custom Builder

Telling a Story That Preserves the Past

Custom builder and historic restoration and preservation expert Brent Hull walks us through the careful details of his Pennsylvania Farmhouse project

Business

Defining Outdoor Living in 2024

Residential experts weigh in on outdoor living trends in new report

Construction

How to Air Seal the Garage

A poorly sealed wall or ceiling between the garage and the main house can let harmful fumes into the living space

Business

Taking Advantage of Incentives Through Weatherization

Industry insider Kristen Lewis walks us through the basics and benefits of weatherization

Custom Builder

2023: A Year of Case Studies

A look back at the custom homes and craftsman details we spotlighted last year

Business

November Data: Custom Architects Weigh In, New Construction Trends, Contractor Confidence, and Material Price Changes

We've collected highlights from a number of data reports published throughout the industry in November

Business

Choosing Humanism, History, and Beauty Over Modernism

Celebrated architect Laurence Booth, whose career spans half a century, shares insights on modernism's flaws, the characteristics of beauty, his design process, and more

Advertisement
boombox1 -
Advertisement
boombox2 -
Advertisement
boombox3 -
Advertisement
native1 -

More in Category

Custom Builder

Floodproof on a Floodplain

An impressive addition to the IDEA Home series, the NEWLOOK Experience Home is a master class in engineering and creative design, with builder Michael Freiburger out-thinking an exceptionally tricky lot

Custom Builder

3 Questions Answered About Reliable Energy in Home Construction

Energy expert Bryan Cordill makes a case for why and how propane is an answer to growing concerns about reliability and resilience in home construction 

boombox4 -
Business

PERC Highlights Sustainability and Efficiency at IBS with 'Clean Build Conversations'

Hear from industry standouts Matt Blashaw and Anthony Carrino at this hour-long Show Village event

Custom Builder

Telling a Story That Preserves the Past

Custom builder and historic restoration and preservation expert Brent Hull walks us through the careful details of his Pennsylvania Farmhouse project

boombox4 -
Advertisement
native2 -
Advertisement
halfpage1 -