Bottom Access Control Unit: Offering Options for Controls in Tight Spaces

Architects and engineers continue to find many different ways to amaze us by creating beautiful buildings with their designs and innovative concepts. It does not matter if they are designing a building for new construction or retrofitting an existing space, the end result is usually extraordinary and makes the mind wonder how it was created. Often times, the finished designs of the architects and engineers can present unique challenges for the HVAC manufacturer to address by thinking outside-of-the-box to find a solution. Fortunately, Titus is filled with a knowledgeable support staff of experienced industry professionals that are accustomed to meeting challenges like this head-on.

A common problem that we have encountered through the years is with providing alternative control options for terminal units. This issue is especially relevant when dealing with reduced ceiling plenum space. As architects and engineers become more creative with their designs, reduced ceiling plenum space is often an area affected in building construction designs. As a result, there are instances when side-mounted control enclosures are not considered a viable solution for some of these applications. The ever-growing need for another control option prompted us to make the Bottom Control Enclosure as a standard option rather than continue offering it as a special option. This option provides the ability to access the controls of the terminal unit from the bottom, which is important in certain applications which have restricted space to the sides of the terminal units.

Important factors such as maintenance, programming and installation should all be easier if using this option in restricted ceiling plenum spaces. Buildings are designed to be permanent fixtures, yet their systems at some point will need to be checked. Those responsible for the maintaining, programming and installing will now have an easier time accessing the unit if the control box is mounted in a more convenient location rather than one that is mounted in a restricted one.

Presently, this option is available for the ESV and TFS terminal units. The Bottom Control Enclosure has been available since January 2012. We hope this option provides a solution for you and your clients when this situation arises.


Please direct questions toward Titus Communications (communications@titus-hvac.com) and/or Titus' TU/UFAD Product Manager Derrick Smith (dsmith@titus-hvac.com). 

A Modular Air Handler: Configuring to Match Your Exact Needs

Modularity and Flexibility

Selecting an air-handling unit (AHU) to meet the precise needs of a new construction or retrofit project can be difficult. It is important to choose an air-handling solution that meets requirements. In many cases, the engineer or contractor is forced by availability or other considerations to choose one that is oversized. While this may seem acceptable, on closer inspection, this is a less-than-efficient solution. The AHU either leads to energy consumption that is too high, or fails to perform adequately.

Revolution TFX is a concept in AHU design that is based on modularity. It gives engineers the ability to configure an air-distribution solution that matches the needs of the building and its occupants. The Revolution TFX system includes a wide variety of fans, coils, filters, and other options. In addition, many cabinet options and accessories are offered.

With an airflow range of up to 30,000 cubic feet per minute (CFM), Revolution TFX is highly suitable for healthcare, education, government and commercial applications. Jobs can be new construction or retrofit.

Selecting the Correct Fan for Variable Air Volume

With a number of fan options, Revolution TFX allows engineers to choose the most efficient fan for delivery of design and minimum CFM needs. Both are important elements in the overall delivery of air. Variable speed drives, discharge dampers, inlet vanes, etc., are also essential. Typically, the most efficiency is gained by choosing the biggest fan that will also deliver the necessary “turn down” in overall system modulation. Revolution TFX comes with a number of fan options to meet the CFM requirements of the space or spaces in question. The fan and fan motor can be housed in the fan segment of an AHU. This can be done for supply, return and/or exhaust applications. 

While a single fan is adequate for the required system design, systems can be configured with dual fans. In this event, the two fans can use the 50/50 principle, in which they operate together and share the load. This allows you to get more airflow in a smaller cabinet size. A dual-fan configuration can also use a 100/100 principle, wherein a single fan operates and the second fan exists as a backup. If the operational fan fails, this configuration ensures full capacity/airflow until repairs can be made. This is often called for in the case of critical applications such as with some healthcare facilities.

Noise Reduction, Flexibility and Efficiency

According to AMCA guidelines, DWDI fans require straight ducting runs and other considerations, which can increase the overall footprint and impose other design constraints. By using an SWSI Plenum solution, architects and engineers are given greater design flexibility. SWSI Plenum fans allow multiple duct takeoffs from the unit. The openings can be tailored to almost any duct configuration. This means units can be installed in smaller mechanical rooms.

Selecting the correct coil is key to providing the best range of heating and cooling to meet the specific needs of the application. The Revolution TFX system allows for coil options that provide optimum balance without incurring the additional expense of high air-pressure drops. The system can be configured with heating coils that use either hot ware or steam. Cooling coils are available for chilled water, chilled brine, and refrigerant.

Staggered coil options are available for Revolution TFX units. This configuration can increase overall coil face area and allow for greater CFM without increasing cabinet size. This means a reduced footprint while maintaining, or even increasing, overall efficiency. Revolution TFX can include heating coil options that are either gas-fired or electric. In the latter case, a remote control panel can be chosen. Electric heaters are offered in staged or modulating heat to better match project requirements.

The available Multizone (MZ) section is flexible. The MZ can be utilized to provide a multizone installation with multiple zone dampers or ordered without dampers to serve a dual-duct system.

Significant Energy Savings through Recovery

Revolution TFX offers energy recovery wheels that can improve overall system performance by preconditioning the outdoor air supply using adjacent exhaust and outside air streams to transfer heat and humidity. HVAC efficiency can be improved by up to 40%, and dehumidification capacity improved up to 75%. This provides a significant energy-saving advantage as well as a meaningful contribution to the overall energy-efficiency of the building as a whole. The energy recovery wheels used in Revolution TFX systems are available for horizontal or vertical mounting, depending on the overall system design.

Air Filters, Economizers and Mixing Boxes

Revolution TFX units can be configured to accommodate various types of filters, depending on the application. These include angled, flat, rigid, and bag filters. IT can be configured with filters -- ranging from MERV 1 to 14 -- depending on project requirements. The system also offers a range of economizers and mixing boxes, depending on the specific needs of the application. Because different buildings have different occupancy and equipment schedules, and therefore different requirements when it comes to economizers and mixing boxes, the Revolution TFX system will accommodate a complete range of options.

Building pressurization is a key element in building operation that affects overall comfort, air quality and energy efficiency. For this reason, Revolution TFX units are configurable to offer different solutions. For example, full-return economizers, dedicated exhaust economizers, dampers, inlet plenums, etc., to better control building pressure.

One System, Multiple Options

The Revolution TFX system offers a multitude of configuration options to architects, engineers and contractors. A solution can be configured that meets all of the required technical standards, plus the degree of occupant comfort, quality, and efficiency that you expect from a Titus product.

Titus' engineers and representatives are always available to help designers configure units to deliver optimal benefit. 


Please direct questions toward Titus Communications (communications@titus-hvac.com) and/or Titus' AHU Product Manager Jason Letterman (jletterman@titus-hvac.com). 

FlexRight - Improving Inlet Conditions to Increase Thermal Comfort

The purpose of a heating, ventilation and air-conditioning system is to provide thermal comfort to the occupied space. The ability of an HVAC system to perform this function depends on system design, equipment, air-outlet type, and inlet conditions. Proper inlet conditions at the air outlet is perhaps the simplest and most overlooked factor. It is something that has a direct effect on the level of thermal comfort in the occupied space.

When air distribution is designed for an occupied space, the outlet velocity of the supply air from a diffuser is assumed to be uniform. This is the case when the supply-duct connection at the diffuser inlet has a sufficient amount of straight duct to ensure the supply air enters the diffuser in a uniform pattern. In reality, inlet-duct connections in the field rarely have an adequate amount of straight duct to ensure an even flow of supply air into the diffuser. For the most part, this is due to space limitations in the ceiling plenum, increased costs, and time constraints during installation. In addition, the use of flex duct as a replacement for hard duct has compounded the problem. As a result, a less than optimum duct connection at the diffuser is being used. It provides a non-uniform air pattern in the occupied space with a decrease in thermal comfort (Figure 1).

To address this problem, a simple and easy solution called the “FlexRight” is available from Titus. FlexRight is a plastic 90-degree elbow that connects the flex duct to the diffuser inlet with a gentle 90-degree transition. This eliminates the problem of kinking or improper positioning of the flex duct that is often found in the field when connected to supply diffusers (Figure 2).

FlexRight is made of 100% recycled material, UL listed, and saves energy by reducing pressure loss in the system. The universal design accommodates all flexible duct sizes and diffuser inlets from 4” to 16”. It provides a less expensive alternative to hard-duct transitions and is easy to transport as well as install. With its simple and universal design, FlexRight is a great choice for both new construction and retrofit applications.

Return grilles, and sometimes supply grilles, are specified for lay-in applications. If the grilles are to be connected to ductwork, a grille size is specified as well as the lay-in module size.


Please direct questions toward Titus Communications (communications@titus-hvac.com) and/or Titus' GRD Product Manager Mark Costello (mcostello@titus-hvac.com). 

Lay-In Grilles

Return grilles, and sometimes supply grilles, are specified for lay-in applications. If the grilles are to be connected to ductwork, a grille size is specified as well as the lay-in module size.

Most Titus grilles can be ordered in a lay-in frame style. When the size of the grille is less than “module size minus 2”,” the grille must be panel mounted. Panel mounting is welding a grille of a specific size to the rear of a panel designed to mount in a lay-in grid module. This provides a unit sized to the grid opening with a grille size for the ductwork. Using a 24”x24” lay-in frame as an example with a 12”x6” grille, you would go into the ordering software, select the appropriate model grille, and enter 12” (width) and 6” (height). Next, change the module size from “NONE,” to 24”x24”. The frame type will automatically change to “TYPE 3 - LAY-IN,” and the fastening option will change from the default “A - SCREW HOLES,” to “NONE.” You will also notice a price increase for the panel mounting.

As mentioned previously, this works for grilles with a size less than “module size minus 2”,” i.e.: a 16”x16” grille in a 24”x24” module size. But, what if the return grille specified does not have a specific size and only the module size is specified (usually indicating a non-ducted return application)? Or, you need a grille that is actually specified with a size of “module size minus 2”,” like a 22”x22” grille for a 24”x24” module?

In the order-entry software, you enter 22” (width) and 22” (height). The module-size option will not let you enter 24”x24”. The answer is simple with just a little bit of grille knowledge. All grilles have overall dimensions of size plus 1 ¾”, so a 22”x22” grille results in an overall dimension of 23 ¾” x 23 ¾”, which happens to be the overall dimension of a type 3 lay-in frame for a 24”x24” module.

Although the frame style will remain shown as “1 - SURFACE MOUNT,” the unit will work perfectly in a lay-in application. The most important thing to remember is to change the fastening option from the default “A - SCREW HOLES,” to “0 - NONE.” We have no way to remove holes from a frame after the grille has shipped, and most customers do not want visible mounting holes in the face of a lay-in product. So, if the return grille is for a non-ducted application -- or a specific grille size is not specified, only the module size – order the grille size as “module size minus 2”.” Not only will you get a full-face return that is much more aesthetically appealing, but it is cheaper!

We offer a range of panels for common lay-in grid module sizes in three different frames, but occasionally a non-standard module size or an NT frame style is required. This is not a problem, as you should simply use your Titus Contact Directory to submit the request to one of our GRD application engineers. We routinely provide NT and non-standard module frames upon request. Renderings may already be available that can help verify your customer’s product requirements. A slight up-charge is required and the special units can usually be supplied in standard lead times. 


Please direct questions toward Titus Communications (communications@titus-hvac.com) and/or Titus' GRD Product Manager Mark Costello (mcostello@titus-hvac.com). 

Liner Specifications and Standards

The choice of lining material for any air-distribution system is an important consideration for the specifying engineer. There are many options available and each material has a potential impact on project cost and thermal/acoustical performance. While the traditional lining materials in the industry have been fiberglass-based, there are other alternatives available today. These new materials have many advantages from the standpoint of physical properties as well as cost and performance. In order to successfully promote these new materials, it is helpful to have a better understanding of current industry standards and how they are applied.

There are several agencies that set standards for ductwork and equipment-lining materials. They include the American Society for Testing and Materials International (ASTM), National Fire Protection Association (NFPA) and Underwriters Laboratories Inc. (UL). While most of the standards they publish must be purchased and can be costly to acquire, it is often not necessary to know more than the title of the standard when determining whether a material is in compliance. Here are some of the most frequently referenced standards:

• ASTM C411 - Standard Test Method for Hot-Surface Performance of High-Temperature Thermal Insulation

• ASTM C518 - Standard Test Method for Steady-State Thermal Transmission Properties by Means of Heat Flow-Meter Apparatus

• ASTM C665 - Standard Specification for Mineral-Fiber Blanket Thermal Insulation for Light Frame Construction and Manufactured Housing

• ASTM C739 - Standard Specification for Cellulosic Fiber Loose-Fill Insulation

• ASTM C1071 - Standard Specification for Fibrous Glass Duct-Lining Insulation (Thermal and Sound-Absorbing Material)

• ASTM C1104 - Standard Test Method for Determining the Water Vapor Sorption of Unfaced Mineral-Fiber Insulation

• ASTM C1338 - Standard Test Method for Determining Fungi Resistance of Insulation Materials and Facings

• ASTM E84 - Standard Test Method for Surface-Burning Characteristics of Building Materials

• ASTM E96 - Standard Test Methods for Water-Vapor Transmission of Materials

• ASTM G21 - Standard Practice for Determining Resistance of Synthetic Polymeric Materials to Fungi

• ASTM G22 - Standard Practice for Determining Resistance of Plastics to Bacteria

• NFPA 90A - Standard for the Installation of Air-Conditioning and Ventilation Systems

• NFPA 90B - Standard for the Installation of Warm Air Heating and Air-Conditioning Systems

• NFPA 225 - Standard Method of Test of Surface-Burning Characteristics of Building Materials

• UL 181 - Standard for Factory-Made Air Ducts and Air Connectors

• UL 723 – Standard for Test for Surface-Burning Characteristics of Building Materials

These standards are commonly referenced in equipment specifications, and most of them only cause confusion. The first thing to note is that each of these standards is either a test method or specification. Test methods define a procedure for measuring a physical property associated with a material. These procedures are often material specific. Specifications (often simply entitled “Standard”) generally reference several acceptable test methods and set maximum or minimum limitations on the result of a test for compliance.

In order to determine compliance with a specification requirement, it is important to note whether the referenced standard is an actual specification or just a method of test. Since there is no way to comply with a test standard, the inclusion of test standards in a specification often causes confusion for vendors. Another common problem involves specification that describe a specific lining material, but reference standards that do not apply to that specific material. All of these issues can be identified and clarified by simply knowing the full titles of the referenced standards.

In addition to the aforementioned ASTM, NFPA and UL standards, there are additional industry standards published by the Air-Conditioning, Heating and Refrigeration Institute (AHRI), American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE), and U.S. Green Building Council (USGBC). Traditionally, ASHRAE publishes test standards for equipment and guidelines for environmental conditions such as ventilation, indoor-air quality and thermal comfort. AHRI concentrates mainly on equipment ratings and performance certification. USGBC publishes the Leadership in Energy and Environmental Design (LEED) standard.

Since most new construction projects will be designed with a goal toward achieving LEED certification, it is important to know what the USGBC requirements are for ductwork and equipment linings. According to the latest LEED 2009 standard, in order to achieve Indoor Environmental Quality (IEQ) Prerequisite 1, the building design must meet the minimum requirements of Sections 4 through 7 of ASHRAE Standard 62.1-2007 Ventilation for Acceptable Indoor-Air Quality. Under Section 5 ‘Systems and Equipment,’ it states that all airstream surfaces (with the exception of sheet metal surfaces and metal fasteners) shall be determined to be resistant to mold growth in accordance with a standardized test method such as those found in UL 181 or ASTM C1338. In addition, all airstream surfaces (with the exception of sheet metal surfaces and metal fasteners) shall be determined to be resistant to air erosion in accordance with the test method described in UL 181. In other words, any lining material that can meet the requirements of UL 181 is acceptable for use in any LEED-certified building.

Here are some typical questions about liner specifications and standards:

Does that mean I can put exposed dual-density fiberglass in a LEED Platinum building?

Yes, it does. However, it may not be the best choice. Many engineers are looking for alternatives to fiberglass because no one knows how that material may be treated in the future. Today, there are innovative new lining materials that can provide improved indoor-air quality with little if any increase in cost.  

What kind of ‘new liners’ are you talking about?

Titus has seized the initiative to eliminate fiberglass from many of our product lines. We currently offer our latest EcoShield liner in ½” or 1”-thickness with cloth-facing for the same price as fiberglass. This material is made from pre-consumer recycled natural cotton fibers chemically-treated to be fire-retardant and anti-microbial. The same material is also available with a scrim-reinforced foil-facing for critical environmental applications for a modest up-charge. We also offer our FibreFree liner in 3/8” or 1”-thickness. This material is called engineered polymer foam insulation (EPFI). It contains an anti-microbial agent throughout to fight mold growth and cannot absorb any moisture, making it ideal for humid climates and applications wherein moisture can cause problems.

I submitted EcoShield on a project recently, but was rejected by the engineer because I could not prove that this material meets ASTM C1071. Why does EcoShield not meet ASTM C1071?

EcoShield technically cannot meet ASTM C1071 because that standard only applies to fiberglass products. That does not mean that EcoShield is not suitable as a duct-lining material, because it may actually outperform fiberglass in the same tests. The engineer’s standard specification probably only takes into account fiberglass products and does not address the new liners available today. We suggest providing EcoShield submittal sheets, explaining the advantages and encouraging him to update his standard specification to include newer materials. So long as the lining materials meet UL 181, they should be acceptable.

With a better understanding of the industry standards, it should be easier to promote new and better lining materials to the engineering community.

Please direct questions toward Titus Communications (communications@titus-hvac.com) and/or Titus' Chief Engineer Randy Zimmerman (rzimmerman@titus-hvac.com).

Designing for Comfort per ASHRAE Standards 55 and 62.1

The goal of a room air-distribution system is to provide thermal comfort and a healthy living environment for occupants in the space. ASHRAE Standard 55-2010 Thermal Environmental Conditions for Human Occupancy and ASHRAE Standard 62.1-2010 Ventilation for Acceptable Indoor Air Quality provide designers with the guidance to optimize health and comfort in building spaces. Many codes, including LEED 2009, require compliance with these ASHRAE Standards. This article will outline the goals of these standards and illustrate how to comply with these requirements.

The occupied zone as defined by Standard 55-2010 reads: “The region normally occupied by people within a space, generally considered to be between the floor and 6 ft. level above the floor and more than 3.3. ft. from outside walls/windows or fixed heating, ventilation, or air-conditioning equipment and 1 ft. from internal wall.” The space from the interior walls inward 1 ft. serves as a mixing zone where room air is entrained into the supply-air jet and mixes to provide thermal comfort in the occupied space. When designing underfloor air-distribution (UFAD) or thermal displacement ventilation (TDV) systems, the occupied area around the outlets may be excluded to a boundary where the total air jet from the outlet contains velocities greater than 50 feet per minute (fpm). These areas may also be known as the “clear zone,” “adjacent zone,” or “near zone.”

Any design must also include an adequate supply of ventilation air to the breathing zone of the space. ASHRAE 62.1-2010 defines ventilation air as “that portion of supply air that is outdoor air, plus any recirculated air that has been treated for the purpose of maintaining acceptable indoor air quality.” The breathing zone is “the region within the occupied space between planes, 3 and 72 inches above the floor… .” We will discuss additional requirements for ventilation air later in this article.

The primary factors to be considered when determining conditions for thermal comfort in the occupied space are: 1) Temperature, 2) Air velocity, 3) Humidity, 4) Clothing insulation, and 5) Activity level of the occupants. All of these factors are interconnected when determining the general occupant comfort of a space. The ideal temperature in a space (operative temperature) is where the occupant will feel neutral to their surroundings, neither feeling any heat loss or heat gain from the space. While the range of acceptable operative temperatures may vary depending on other conditions, it is a requirement of ASHRAE 55 that the “Allowable Vertical Air Temperature Difference-Between Head (67”) and Ankles (4”) is limited to 5.4 F (3.0 C)”. Ideal air velocity in the space can vary with other factors, but, in general, the goal is to keep spatial velocities less than 50 fpm during cooling mode and less than 30 fpm during heating mode. For many years, Titus has recommended maintaining the relative humidity level in the space between 25-60%. ASHRAE 55 does not define a lower limit and requires the dew-point temperature be less than 62.2 degrees (F). Another factor affecting comfort is the clothing insulation level of the occupant. In most office environments, the Clo level for occupants is between 0.5 and 1.1, where .5 would be a person wearing no socks, sandals, short-sleeve shirt or blouse, and shorts or a skirt. The 1.1 Clo level would include long pants, socks, long-sleeve shirt, and a dress coat or sweater. The range of operative temperatures where both 0.5 and 1.1 occupants are in the same space is very narrow. The final item of consideration for design comfort is the intended activity level of the occupant in the space. In most office environments, the metabolic (MET Rate) is between 1.0 and 1.3. This includes occupants who are sedentary to casual movement about the space.

The three common methods of room air distribution used in commercial buildings in the United States are fully mixed (e.g. overhead distribution), fully stratified (e.g. displacement ventilation), and partially mixed (e.g. most underfloor air distribution systems). Since interior zones usually have adequate heat loads from occupants and equipment, in addition to few heat losses, the discussion for interior spaces will be cooling only. For the perimeter spaces, the discussion will be how to meet the requirements for heating and cooling from the same overhead outlet. Design methods for cooling an interior zone and heating a perimeter zone vary with each method.

For fully mixed systems, the pattern of the air delivered to the space must be considered when selecting an air outlet. Ceiling diffusers typically exhibit flow in a circular (radial) or cross-flow (directional) discharge air pattern. The circular pattern usually provides shorter throw, higher mixing and tends to maintain ceiling effect to low velocity before turning back on itself. This pattern is ideal for variable air volume (VAV) cooling by providing less drop and more uniform temperatures in the space. The cross-flow (directional) air pattern has longer throw, but with less induction may lose ceiling effect, creating drafts in the occupied zone. Plenum slot diffusers typically discharge air in a directional air pattern, but some are available with “spreaders” to produce a more radial discharge pattern. Sidewall grilles equipped with vertical deflectors can be adjusted from zero degree (directional pattern) to a 45-degree spread (radial pattern). So, regardless of the desired type of outlet, the air pattern can be either radial or directional to best meet the comfort requirements of the space. Proper selection for comfort can be insured by using the ADPI selection program in TEAMS.

Typically, for perimeter applications where the same outlet is being used for both heating and cooling, a linear slot diffuser or plenum slot diffuser is employed. When a fixed air pattern diffuser is used, it is typical to supply half of the air across the ceiling for cooling and half down the glass for heating. For perimeter heating, the requirements for table 6-2 of ASHRAE Standard 62.1-2010 must be considered. The intent of table 6-2 is to ensure that the ventilation air supplied to the space be delivered to the breathing zone as well. For ceiling supply of warm air with a ceiling return, the requirements for heated air are to reach a terminal air velocity of 150 feet-per-minute to within 4.5 ft. of the floor. To a terminal velocity of 150 fpm or more, air is temperature independent, which means the distance air will travel will be the same for isothermal air (catalog values), warm air and cool air. This means that during heating, ventilation air will be pushed down into the breathing zone with enough heat energy to meet Standard 55’s requirement for a temperature gradient of less than 5.4 degrees. In addition, the differential temperature between warm supply air and space temperature with a ceiling return must be 15 degrees or less. Thus, the maximum supply-air temperature for a 75-degree room would be 90 degrees. When the heating supply-air temperature exceeds the 15 degree limit, the ventilation air volume must be increased by 25%.

Choosing an auto-changeover diffuser like Dynafuser or EOS does not change the Standard 62.1 requirements, but will lower energy costs and improve comfort in the space. Delivering all the warm air down the glass during heating will save energy. With a fixed-pattern diffuser, half of the warm air will be discharged across the ceiling and with a ceiling return can be short-circuited without reaching the occupied space level. Additionally, higher comfort will be realized in the space since the heated air can be designed to deliver warm air all the way to the floor. Comfort may be increased during cooling as well, as the cool air will be projected across the ceiling eliminating the potential for drafts from the jet protected down the glass with a fixed pattern diffuser.

For partially mixed air-distribution systems (typically UFAD), the core area usually experiences even loading throughout the occupied area. The goal of partially mixed systems is to save energy by comfort-conditioning the lower occupied level in the space and allowing the upper level of the space to stratify. Occupant comfort is achieved by delivering cool conditioned air from the plenum under the floor through swirl diffusers or rectangularly shaped outlets near the occupants’ work area. Individuals can enhance their personal comfort by adjusting the damper at the outlet near their workspace. For common areas such as hallways and break rooms, outlets can be equipped with actuators that are controlled by a common thermostat located in the space.

Perimeter zones for partially mixed systems create a greater challenge, as the loads are dynamically changing due to outdoor solar and air temperature changes. A common method for perimeter zone control is locating a low-profile fan-powered terminal unit under the floor near the perimeter supplying air to linear bar grilled. The fan-powered terminal can be equipped with an electric or hydronic coil. Cool plenum air can be supplied to the outlets when cooling is required and the coil can be employed to warm the air as required during heating conditions. The design challenge is selecting outlets that will limit the throw of the air pattern so that air will not bounce off the ceiling and create drafts in the adjacent occupied area.

Energy to operate the fan terminals can be eliminated and higher comfort can be achieved on the perimeter by using the TAF-L perimeter distribution outlets. With a 6” wide custom design TAF-L bar grille located along the perimeter of the space, the modular 4’ long TAF-L-V (cooling), can be attached to provide up to 225 cfm (at 0.07” plenum pressure) per 4’ unit of cooling. The TAF-L-V damper is controlled by a space thermostat to provide cooling as required. The special arrangement of bars in the grille is designed to limit the throw from the outlet during cooling. The 4’ long TAF-L-W or TAF-L-E heating module can be attached to the TAF-L grille to supply up to 3,000 Btu heat to the perimeter. The heating units operate by combining the cool convection currents from the glass with the warm currents on the floor. The mixture is induced through the heat exchanger with warm air being discharged through the grille and up the glass. Space temperature is controlled by a room thermostat controlling the water flow or electric current flow to the electric heating element. The modular design allows the system to be custom designed for use in multiple climate regions.

A fully stratified design (typically TDFV) conditions a space by discharging cool supply air through an outlet located at floor level. This happens near or in a wall or may be centrally located in the open space. Low velocity air (<80 fpm) is discharged horizontally across the floor. Air moves with little mixing across   the floor until it contacts a heat source such as an occupant or a piece of warm equipment in the space. Cool air will mix with the radiant heat, form the source, and stratify toward the ceiling. The return is usually located at or near the ceiling. The area between the outlet and where the air speed reaches 40 fpm is the “clear zone” and should not be included in the occupied area. Titus provides units with adjustable air patterns so the clear zone can be controlled to meet project requirements for space occupancy. ASHRAE Standard 62.1 (Table 6-2) provides a 20% bonus for TDV systems. This means that ventilation air can be reduced by 20% or the 20% can be used toward the 30% required for an additional LEED IEQ credit 2.

While TDV systems typically require a separate system for heating, Titus has introduced the Plexicon heating/cooling diffuser. A standard rectangular outlet is located near or mounted in a wall that discharges cool air from the upper chamber. When heating is required, an internal baffle is moved to change the flow of air from the upper chamber into the lower chamber where it flows through a linear bar grille to satisfy heating requirements.

Regardless of which type of system you are using on your project, studies have shown that occupants whom are comfortable are more productive. Designing for comfort, keeps paying back dividends forever. 

Please direct questions toward Titus Communications (communications@titus-hvac.com) and/or Titus' Chief Engineer (Grilles & Diffusers) Jim Aswegan (jaswegan@titus-hvac.com).

UFAD Systems offer Comfort, Flexibility, and Energy Savings

Underfloor air-distribution (UFAD) systems have been used for comfort-conditioning office spaces in United States office buildings since the early 1990s. Systems were initially employed in high-tech office spaces where in addition to occupant comfort, ease of office space re-configuration (churn) was a priority for building owners. UFAD systems deliver air to occupied spaces through floor-mounted outlets supplied by conditioned air from a pressurized plenum beneath the suspended floor. 

A properly designed UFAD system takes advantage of thermal stratification. The key is to have a diffuser that rapidly mixes air without penetrating the stratification layer at the ceiling. The pressurized plenum -- the area between the slab and raised floor -- is essentially a large duct maintained at a constant pressure differential to the room above; typically between .05 and .10 in. pressure (w.g.). This pressure is maintained through the supply of conditioned air from a number of supply-duct terminations. The spacing and location of these ducts are dependent on the air supply requirement and the plenum depth which typically ranges from 12” to 24”. If zone control is desired from the underfloor plenum, it can be partitioned into separate zones. The return air for a UFAD system should be located at the ceiling or high sidewall. This allows heat from the ceiling light to be returned before it is able to mix with the occupied zone. There is also a small amount of “free cooling” due to the natural buoyancy of hot air.

Some of the concerns typically associated with these systems are humidity, dirt, spillage, and leakage. A potential problem with the higher supply temperatures used in access floor air-distribution systems is the higher potential moisture content of the 60-65˚F supply air most commonly used in these systems. The supply system must reduce relative humidity to less than 65˚F. Potential solutions are either the reheat or blending of air to achieve a 65˚F supply, 55˚F dew-point condition. System designs utilizing condenser water reheat, run-around coils (face, bypass), and other strategies can be employed to solve these potential design problems. Other options include the use of desiccant dehumidification. Although underfloor air-distribution systems are not recommended for areas with a high potential for spills such as bathrooms, cafeterias and laboratories, small spills are not a problem for most applications. Typical swirl diffusers used within the interior have a dirt/dust receptacle to catch spills and dirt from normal daily use. The dirt/dust receptacle has a basin that will hold anywhere from 4-6 fl. oz. of liquid. The dirt/dust receptacle can easily be removed and cleaned to keep dirt out of the underfloor plenum. Leakage is typically due to poor sealing or the construction quality at window/wall locations, stair landings, electrical outlets, etc. These areas have to sealed and framed so the supply air does not travel up the wall toward the return air. There can also be leakage between the floor panels which can be reduced by staggering the carpet tiles over the floor tiles. The key is to limit the number of penetrations into the raised floor which will reduce the number of areas that need to be sealed.

Since typical floor plenum pressure is less than .10 in w.g. (25 Pa), energy-efficient low-pressure fans can be used. In place of complicated and expensive duct systems required to supply air to each individual air outlet in a ceiling system, UFAD systems deliver air to building zones using a limited amount of ductwork to create an air highway.

Where a traditional overhead mixed system provides comfort-conditioned air from the floor to the ceiling, partially mixed systems like UFAD save energy by providing comfort-conditioning in the lower occupied spatial zone. They allow the upper zone to stratify.  

In the core of the building where loads are relatively constant, round (swirl) or rectangular outlets are located in the floor near the occupants. Outlets typically deliver 80-100 cfm (38-48 l/s) of conditioned air to the space. Some of the units have volume control adjustability by the occupants to increase individual comfort levels. The round swirl diffusers are typically available with an occupant adjustable flow regulator that can be either manually adjustable or by the use of a room sensor that is connected to an actuator mounted directly on the diffuser. Installation of swirl units has been made easy by replacing the mounting ring which was previously attached to the unit beneath the floor tile with spring clips to provide a press fit directly into the floor tile. A recent ASHRAE research project (RP-1373) has also provided data to show that when the height of the air plume to a terminal velocity of 50 fpm (.25 m/s) is limited to 4.5 feet (1.4 m), the air change effectiveness (ACE) is improved in the breathing zone. This research has now been recognized by ASHRAE Standard 62.1-2010 with Addenda A in Table 6-2 by allowing an Ez rating of 1.2 for these conditions. This means that the ventilation (outdoor) air supplied to the zone can be reduced by 16.7%. For LEED projects where the credit point for IEQ credit 2 is desired, this 16.7% can be used in reaching the goal of 30% increased ventilation air.

Some of the biggest challenges for underfloor design occur on the perimeter of the building where loads are higher and dynamically changing due to effects of radiation and temperature conduction on the skin of the building. Where the core of the building is mainly impacted by nearly constant heat loads, the perimeter system must accommodate swings in heat loads and heat losses that can occur in a relatively short period of time.

A common method of handling perimeter loads to locate a fan-powered terminal in the floor plenum near the perimeter. These fan-powered terminals are ducted to outlets located on the perimeter. A typical outlet would be a linear bar grille with either a boot plenum or continuously fed plenum underneath. Equipped with an option hot water or electric heating coil, the fan unit can deliver warm air in response to a space thermostat. Unfortunately, as linear grilles get longer, the mass effect of the discharge air jet projects the air higher than required. If the throw from the outlet is too long and reaches the ceiling, it may deflect downward into the space and create unwanted drafts in the interior zones. In some cases, cool air from the floor plenum is supplied to the perimeter zone through the fan-powered unit.

For LEED projects, the operational cost of energy to run a fan-powered terminal can be minimized by using ECM fan motors. ECM motors operate at an efficiency of 70% or greater. The cooler operation of an ECM motor -- and enhanced construction -- contribute to a longer life and lower life-cycle cost when compared to standard construction PSC motors. An additional benefit of an ECM motor is ability to control the fan speed during operation to provide increased energy savings and better occupant comfort in the occupied space. ECM motors can also utilize remotely controlled speed controllers (pwm) that can be controlled through a building management system.

New technology in perimeter systems can lower installed/operational costs and improve comfort along the perimeter zones. By installing a continuous bar grille along the perimeter, variable air volume (VAV) cooling and plenum heating coils can be attached as needed to condition the perimeter. These cooling and heating units are passive and do not require the use of a fan terminal. The bar grille can be connected together to provide a continuous architectural appearance around the perimeter or can be installed in sections as required for comfort conditioning. The core of the bar grille is removable from the room to provide access to the unit’s working components.

The VAV-cooling units employ an electrically actuated sliding damper, which opens and closes a series of transverse apertures to vary the volume of cool air supplied from the pressurized underfloor plenum into the space. The sliding damper opens and closes to provide the amount of conditioned air required to manage the changing conditions as directed by a room thermostat located in the occupied zone. The transverse apertures manage the supply air to allow room air to be included into the air pattern. Introducing supply air in small bundles helps in managing the projection from the outlet and prevents long throws which create drafts in the occupied space.

The heating plenums also attach to the linear bar grille. The heating plenums are passive in operation and do not require a fan-powered terminal to supply air or heat. Located parallel on the perimeter at the glass, the heating unit mixes the cool convection currents flowing down the glass with warm-air currents traveling across the floor. These mixed currents are induced into the inner chamber of the plenum and flow up through the heat exchanger. The warm current then exit the linear grille at the glass and flow upward via convection to heat the cool air in front of the glass.

The hydronic heating units have a finned-tube heat exchanger with heat supplied through a hot-water pipe and controlled by a water valve to provide the precise amount of heat required to satisfy room conditions. The electric heating units are of fin-tube construction and have an SCR control to match the changing heat requirements in the space. The ETL listed heaters can be found in 120V, 208V, 240V, and 277V supply circuits. The modular construction of the VAV-cooling and the fin-tube water or electric heating units allows the installation to match the requirements of any climate zone. Where winter conditions prevail, more heating units can be installed to meet heating needs. Where hot summer conditions prevail, additional VAV-cooling units can be employed to match the cooling requirements.

To claim maximum energy efficiency and occupant comfort, care should be taken during construction to seal all floor panels. Additional care should be taken to seal all openings through the floor either into the space or into the walls where plumbing or electrical equipment penetrates the floor plenum. Regular inspection during construction will minimize problems upon building completion and commissioning.

In recent years, the application for UFAD systems has shifted from owner-occupied high-tech facilities to a more general variety of building spaces aiming to achieve LEED certification. UFAD provides superior comfort by supplying conditioned air where it is required near the occupant. Additional occupant comfort can be achieved by installing small units in the core of the building with individually adjustable dampers controlled by the occupant. By conditioning only the occupied area and stratifying the upper zone with air supplied form the low-pressure floor plenum saves energy. Additional energy can be saved by employing a passive VAV-cooling and fin-tube heating system on the perimeter. 

For your next LEED project, take advantage of UFAD to provide lower energy (EA c1), controllability of systems for thermal comfort (IEQ c6), and thermal comfort (IEQ c7).

Please direct questions toward Titus Communications (communications@titus-hvac.com) and/or Titus' TU/UFAD Product Manager Derrick Smith (dsmith@titus-hvac.com).