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Stay in Control: Specifying building automation systems for cost savings

The Sheraton Phoenix Downtown Hotel uses a BACnet (data communication protocol for building automation and control networks) compatible building automation system (BAS) for energy savings and occupant comfort. All images courtesy Alerton

The Sheraton Phoenix Downtown Hotel uses a BACnet (data communication protocol for building automation and control networks) compatible building automation system (BAS) for energy savings and occupant comfort. All images courtesy Alerton

by Kevin Callahan

In the same way today’s mobile phones have capabilities far beyond traditional telephones, modern building automation systems (BAS) have added many benefits transcending their original roots in heating and cooling control.

Today’s BAS help facility professionals obtain greater efficiencies from numerous building systems, including:

  • lighting;
  • security/access control;
  • fire and life safety;
  • elevators and escalators;
  • irrigation; and
  • HVAC.

An appropriately equipped BAS can also meet specialized needs such as emergency and critical systems monitoring in hospitals, and tenant billing for leased spaces in office buildings.

With rising energy costs, an increasing number of building owners and operators are including BAS in new buildings, as well as in retrofits. More than half of U.S. buildings larger than 9290 m2 (100,000 sf) have a BAS installed.1 The market is forecast to grow between seven and nine percent from 2014 through 2017, for a net growth of more than 40 percent above the 2012 level, according to researchers at IHS Technology. A key driver of this “/>growth is a projected eight percent annual increase in retail electricity prices through 2020.2

Building automation systems software with an intuitive, graphical interface is simple to use and helps reduce or eliminate the need to train staff on operating the system.

Building automation systems software with an intuitive, graphical interface is simple to use and helps reduce or eliminate the need to train staff on operating the system.

Vendors now offer BAS wall units with the sophistication and elegance of smartphones.

Vendors now offer BAS wall units with the sophistication and elegance of smartphones.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

BAS benefits
Automation can reduce a building’s total energy consumption between five and 15 percent annually because of more efficient control of various building systems. Savings can surpass 30 percent annually in older or poorly maintained buildings. Additionally, a BAS can help reduce building maintenance costs by alerting facility managers when equipment is operating outside of specifications and therefore might be at risk of failure.3

The facilities management and planning department at Boston University outlines these and other BAS benefits as follows:

  • control and diagnose what is going on in buildings;
  • create a graphic representation of building settings;
  • see and fix programmatic problems quickly;
  • generate reports usable by management for tracking energy consumption and the operational status;
  • schedule and control temperature settings for increased energy savings; and
  • collect and store data on energy consumption over long periods.4

Project examples
From commercial offices and government buildings, to schools and hospitals, energy saving benefits can be achieved in virtually every type of project.

Commercial offices
Seattle’s Columbia Center is the tallest building in the Pacific Northwest, with 76 stories and 142,900 m2 (1,538,000 sf) of total floor area. A BAS integrates all the building’s HVAC systems—including 2200 heat pumps, ventilation and exhaust fans, boilers, heat exchangers, cooling towers, and circulation pumps.

The building is one of the city’s largest electricity-consumers, using approximately 111,600,000 megajoules (31,000 megawatt hours) annually. However, with an energy-efficient BAS, it consumes only about 13 percent more electricity than the next highest building electricity consumer in the city, despite having 50 percent more floor area.

Government buildings
In 2009, the state of California opened a new central utility plant in Sacramento to heat and cool many office buildings throughout the city. The 7246-m2 (78,000-sf) facility supplies chilled water and steam to 23 buildings that total 510,967 m2 (5,500,000 sf) of space. One BAS monitors and controls the central utility plant, while another BAS serves the 23 buildings. The BAS for the chiller plant enables it to operate at about half the energy use of a traditional chiller plant.

K–12 schools
At Irvington High School in Fremont, California, the local school district installed a BAS as part of a set of energy-saving actions that reduced the school’s energy consumption by approximately one-third, which equates to annual savings of about $10,000. Much of the savings result from data provided by the BAS, which allows the district to shed energy loads under a peak pricing program offered by Pacific Gas and Electric (PG&E).

Universities
Eastern Connecticut State University in Willimantic installed a BAS in the Windham Street Apartments—a 30-year old, nine-story residence hall housing 224 students. The BAS reduced the building’s annual electricity consumption by 234,000 megajoules (65 megawatt hours), for a 12 percent energy cost savings. The university achieved these savings despite also adding cooling to the building, when previously it only had heating.

Hospitals
As part of a facility expansion and upgrade project, New York University Medical Center in Manhattan retrofitted outdated building controls in 13 buildings totaling 278,710 m2 (3,000,000 sf). The new BAS enables staff to manage the campus and outlying facilities through a single system, for better energy efficiency. Additionally, trend logs generated by the system illustrate how closely actual room temperatures match the set point, which allow staff to closely control the environment for patient comfort, health, and safety.

This wall unit includes subtle light-emitting diodes (LEDs) along its bottom so users can see at a glance when the HVAC system is in heating or cooling mode.

This wall unit includes subtle light-emitting diodes (LEDs) along its bottom so users can see at a glance when the HVAC system is in heating or cooling mode.

A properly equipped building automation system allows higher education facility managers to centrally monitor and control multiple buildings across campus, including at campuses in other cities.

A properly equipped building automation system allows higher education facility managers to centrally monitor and control multiple buildings across campus, including at campuses in other cities.

 

 

 

 

 

 

 

 

 

Maximizing BAS benefits
To receive the most benefits from implementing a BAS, it is important to focus on analytics and building commissioning.

Analytics for high-performance building operations
A BAS is a powerful tool for gathering data needed to make informed decisions on energy management. To maximize its cost-saving potential, one must pay attention to the data the system is generating and to use it to make strategic energy usage choices—this is the concept of building analytics. In short, a BAS is not a tool to install then simply turn the heating, cooling, and lights on and off according to a set schedule.

Analytics is about ensuring a building’s managers have enough of the right data being collected for analysis. It is important to use analytics to ensure any BAS programs created to reduce energy—or any other objective—are actually accomplishing what was intended. An appropriately equipped BAS allows the facility staff to collect and store data so there is history to compare it to.

For example, analytics can help the facility managers ensure they are not heating and cooling the same spaces at the same time, as well as confirm lights are on for a purpose, rather than solely for convenience. Analytics provide a way to determine whether energy is being wasted, and where.

A BAS delivery agent (i.e. manufacturer, dealer, or consultant) can be a valuable resource for determining what analytics are needed to meet the building owner or operator’s specific goals.

Building commissioning
A sometimes overlooked benefit of BAS is the system can be used to simplify the commissioning process, for both new construction and building retrofits. Some BAS include programs to verify HVAC and other building systems are performing according to the design intent. The wall sensors of an advanced BAS enable technicians to access the system throughout the building to conduct tests and verify environmental conditions, without carrying separate diagnostic tools—the result is faster and more accurate performance verification. Proper building commissioning is crucial to achieve efficient building operations.

“The operating costs of a commissioned building range from eight to 20 percent below that of a non-commissioned building,” reports the U.S. Environmental Protection Agency’s (EPA’s) Building Commissioning Guidelines. Additionally, it is noted commissioning costs typically range from only 0.5 to 1.5 percent of construction costs, and reduce operating costs throughout the building’s life.5

For initial commissioning, the building systems as a whole need to be commissioned at the time of construction to ensure they are operating as designed and their integration with the BAS is correct. This helps ensure the building is operated appropriately to satisfy its occupants’ needs. As a basic example, in an office building the HVAC and lighting would need to be commissioned for controlling the indoor environment while the building is in use during standard working hours, whereas in a warehouse the utility needs would be different because the building likely is not in use at all times.

An even more critical action than initial commissioning is the periodic re-commissioning of a building to ensure the systems are still serving the occupants’ requirements. Additionally, because systems can degrade over time, it is important to tune them up for optimal performance.

The Russellville School District in Arkansas uses its building automation system to monitor food and beverage freezers and coolers in its facilities.

The Russellville School District in Arkansas uses its building automation system to monitor food and beverage freezers and coolers in its facilities.

The BAS for this Sacramento central plant enables it to operate at about half the energy use of a traditional chiller plant.

The BAS for this Sacramento central plant
enables it to operate at about half the
energy use of a traditional chiller plant.

 

 

 

 

 

 

 

 

 

Specifying a BAS
Design professionals can select from numerous BAS. Several important features to consider when choosing the system include:

  • degree of interoperability of the control module;
  • software’s ease of use;
  • security measures; and
  • usability and design style of the wall sensors.

Control module
The control module is the central processing unit of a BAS. Until the mid-1990s, the communication protocols these units used to interface with building equipment were proprietary to each manufacturer. As a result, various components would not work together unless using a single manufacturer’s equipment.

In 1987, the American Society of Heating, Refrigerating, and Air-conditioning Engineers (ASHRAE) began to actively develop a standard protocol to enable a wide range of controls and equipment to work together (i.e. interoperable). In 1995, it published that standard—known as BACnet (data communication protocol for building automation and control networks), which has since been widely adopted by BAS and building equipment manufacturers.6

“Capabilities vital to BA [building automation] applications were built into BACnet from the beginning in order to ensure the highest possible level of interoperability in an environment possibly involving multiple vendors and multiple types of building systems,” according to a report from the Institute of Electrical and Electronics Engineers (IEEE).7

Such interoperability helps ensure a BAS can adapt to emerging technologies and evolving building occupancy needs, without having to start over.

BACnet is unparalleled in providing integration of the disparate systems within a building, including HVAC, lighting, access, irrigation, utility monitoring, and metering. For example, instead of having separate systems and building occupancy schedules for a building’s lighting and HVAC systems, BACnet allows for clean integration of both systems so the scheduling is from one source.

By analogy, a BAS using BACnet is like a symphony orchestra, wherein the control module is the conductor providing direction to the numerous different building systems (i.e. individual musicians) using a common protocol (i.e. BACnet) they all understand (i.e. movements of the baton, hand gestures, and facial expressions). Although a violin is different from a trumpet, the conductor’s common direction enables them to work together to produce beautiful music.

Some BAS control modules incorporate multiple protocols (BACnet and Tridium’s Niagara Framework) for even greater interoperability than relying on a single protocol. Other protocols, like LonTalk, are also available.

Software—ease of use
Learning a new software program often involves hours of training, and/or trial and error, both of which can mean thousands of dollars in staff time. This is especially true for specialized programs such as those included with a BAS.

However, a key differentiator among BAS software is how intuitive and simple it is to learn. Although many programs now employ a graphical interface, rather than text entry alone, ease of use varies. The most sophisticated BAS software includes simple schematics clearly identifying the equipment throughout a building, and its operating status (e.g. heating, cooling). Such programs enable even novice users to readily interpret the environmental or other monitored conditions anywhere in the building, and to adjust the appropriate building system, as needed.

Another simplifying feature introduced with BAS software this year is use of HTML5. With the latest HTML format, facility professionals can access the BAS remotely from any Internet-connected device, without the time and compatibility hassles of downloading a third-party’s software plug-in. As a result of this wide system accessibility, a technician could troubleshoot a piece of equipment from the field, or a facility manager could make necessary system adjustments when traveling away from the office.

Security measures
As large online security breaches have come to light in recent years, building professionals are increasingly asking about how to secure their Internet-facing building BAS. For the building design team, three cyber security best practices will improve the security of a building automation system against unauthorized access:

  • ensure network isolation by deploying behind a firewall or on a virtual private network (VPN);
  • use the security features built into the BAS; and
  • configure the system securely by disabling guest user accounts and using strong password protection protocols.

Since BAS are networked throughout buildings (and often to the Internet) to enable remote access by facility managers, it is crucial to isolate the automation system from other internal networks, such as financial management or credit card processing. To accomplish this, the building design team should involve the client’s information technology (IT) experts early in the BAS selection process, as this is a specialized aspect of specification writing and usually requires acquisition and installation of additional hardware dedicated to protecting the building networks from both external and internal attacks. This hardware (e.g. firewalls, VPN routers) is extremely important and needs to be state-of-the art to combat the evolving means of attacking networks.

For the BAS itself, a control module with multiple Ethernet ports is an important security feature that helps to isolate the network. Such control modules physically separate the building systems from connections to outside networks. It is also important to specify a BAS that can be configured to use signed certificates for web connections to prevent ‘man-in-the-middle’ attacks when users log into the server. Beyond network connections, another security feature built into some BAS is a system that does not automatically execute code from USB thumb drives. This helps prevent a BAS user from inadvertently introducing a virus or other malware into the BAS.

Building automation systems are installed throughout the world, including in this Turkey skyscraper.

Building automation systems are installed throughout the world, including in this Turkey skyscraper.

Securely configuring the system once it is installed is important, so it is critical to ensure the BAS has a security manual that provides information on how to best accomplish this task, and then make sure the contractor follows those guidelines. Additionally, the BAS integrator should have documented the processes and procedures they followed for designing and implementing the system, which will be a crucial reference for the building owner.

Cyber-security threats change frequently, and need constant vigilance. Anyone who touches the system should be trained at a minimum in cyber-security awareness, and ideally should be certified to securely deploy vendor systems. It is also important they are aware of the building owner’s cyber security standards and practices. Building owners should also keep in mind the BAS will require maintenance, which might include patches to the operating system, and anti-virus software updates and management.

Strong cyber-security is a three-legged stool comprising:

  • manufacturers and software vendors, who continually evaluate and improve the security of products;
  • contractors and installers, who ensure their customers’ systems are properly and securely installed; and
  • end-users, who build and maintain a culture of security within their organizations through the use of cyber security best practices.

Wall sensors
As with BAS software, a key differentiator among wall sensors is how easy they are to use—important for both facility staff and building occupants. Vendors have become increasingly sophisticated with designing wall sensors. One unit introduced in 2014 was designed according to what users are accustomed to seeing with their smartphones. For example, the unit includes easy-to-interpret icons for temperature control, and clear navigation tools to see interior and exterior temperatures, relative humidity (RH), and carbon dioxide (CO2) levels. To enable building occupants to see the HVAC operating condition from across the room, the unit has color light-emitting diode (LED) lights along its bottom to indicate either heating (red) or cooling (blue).

In terms of design styling, in commercial buildings, thermostats have often been visually ‘boxy.’ Now, manufacturers are focusing on aesthetics of these units in addition to performance. Some units are designed to be sharp and crisp with a low profile to complement modern architectural styling. Building owners and occupants have even gone so far as to say such units are ‘sexy.’ At any rate, a thermostat does not necessarily need to be a clunky box hidden around a corner, but can be a sleek addition to a room or hallway.

Conclusion
A properly equipped and configured automation system can save building owners tens of thousands of dollars or more on annual energy costs. Additionally, some facility professionals use the systems to save costs in other ways. For example, in Russellville, Arkansas, the school district officials use their BAS to monitor food and beverage freezers and coolers in schools throughout the area. The system sets off an alarm if temperatures begin to go out of range, which enables the facility staff to take prompt action and thereby avoid costly and wasteful spoilage.

To maximize the cost savings, when specifying an automation system it is important to think about each component—control module, software, and wall sensors—and consider how easy they are to use, and how flexible they are to changing technologies and building user needs.

Notes
1 For more, see “Building Automation Systems” at fpl.bizenergyadvisor.com. (back to top)
2 Visit “U.S. Building Automation Market Primed for Growth,” at technology.ihs.com. (back to top)
3 See note 1. (back to top)
4 See www.bu.edu/facilities/what-we-do/buildings/building-automation/ for more. (back to top)
5 Visit “EPA Building Commissioning Guidelines” at www.epa.gov. (back to top)
6 See “BACnet overview” at www.bacnet.org. (back to top)
7 See “Communication Systems for Building Automation and Control,” by Kastner, Neugschwandtner, Soucek, and Newman, Institute of Electrical and Electronics Engineers (IEEE), at www.researchgate.net. (back to top)

Kevin Callahan is a product marketing manager for Alerton, a Honeywell business. He has 38 years of experience in the building control technologies field, including control systems design and commissioning, facilities management, and user training. Callahan can be reached at kevin.callahan@honeywell.com.

Designing for Comfort & IAQ: Air distribution per ASHRAE 55 and 62.1

Photo © BigStockPhoto/Pavel Losevsky

Photo © BigStockPhoto/Pavel Losevsky

by Jim Aswegan and David Pich, PE, LEED AP

The goal of a room air distribution system is to provide thermal comfort and a healthy living environment for occupants in the space.

American Society of Heating, Refrigerating, and Air-conditioning Engineers (ASHRAE) 55-2013, Thermal Environmental Conditions for Human Occupancy, and ASHRAE 62.1-2013, Ventilation for Acceptable Indoor Air Quality, provide designers with the guidance to optimize health and comfort in building spaces. Many codes, along with the U.S. Green Building Council’s (USGBC’s) Leadership in Energy and Environmental Design (LEED) 2009 program, require compliance with these ASHRAE Standards.

ASHRAE 55-2013 defines the occupied zone as:

the region normally occupied by people within a space, generally considered to be between the floor and [2 m] 6 ft level above the floor and more than [1 m] 3.3 ft from outside walls/windows or fixed heating, ventilation, or air-conditioning equipment and [0.3 m] 1 ft from internal walls.

The adjacent zone is any area in the occupied zone where local air velocities exceed 0.25 m/s (50 fpm) at 25 mm (1 in.) above the floor. Images courtesy Titus

The adjacent zone is any area in the occupied zone where local air velocities exceed 0.25 m/s (50 fpm) at 25 mm (1 in.) above the floor. Images courtesy Titus

The space from the interior walls inward 0.3 m 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 under-floor 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 0.25 m/second (50 fpm). These areas may also be known as the ‘clear,’ ‘adjacent,’ or ‘near’ zone.

Any design must also include an adequate supply of ventilation air to the breathing zone of the space. ASHRAE 62.1-2013 defines ventilation air as:

that portion of supply air that is outdoor air plus any re-circulated air that has been treated for the purpose of maintaining acceptable indoor air quality.

The breathing zone, on the other hand, is the region within the occupied space between 76 and 1830 mm (3 and 72 in.) above the floor.

Determining thermal comfort
The primary factors to be considered when determining conditions for thermal comfort in the occupied space are:

  • temperature;
  • air velocity;
  • humidity;
  • clothing insulation; and
  • activity level of the occupants.

All these factors are inter-connected when determining the general occupant comfort of a space. The ideal temperature (operative temperature) is where the occupant will feel neutral to his or her surrounding—feeling neither heat loss to, nor heat gain from, the space.

While the range of acceptable operative temperature may vary depending on other conditions, ASHRAE 55 requires the allowable vertical air temperature difference between head (1702 mm [67 in.]) and ankles (100 mm [4 in.]) be limited to 3 C (5.4 F). Ideal air velocity in the space can vary with other factors, but the goal is generally to keep spatial velocities less than 0.25 m/second during the cooling mode and less than 0.15 m/second (30 fpm) during the heating mode.

For many years, the authors’ company has recommended maintaining the relative humidity level in the space between 25 and 60 percent. ASHRAE 55 does not define a lower limit, and requires the dewpoint temperature be less than 16.8 C (62.2 F).

Another factor affecting comfort is the occupant’s clothing insulation level—the clo. In most office environments, occupants’ clo level is between 0.5 and 1.1, where 0.5 would be a person wearing no socks, sandals, short sleeve shirt or blouse, and shorts or skirt. The 1.1 clo level would include long pants, socks, long sleeve shirt, and dress coat or sweater. The range of operative temperature where both a 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 sedentary occupants to casual movement about the space.

The three common methods of room air distribution used in commercial buildings are:

  • fully mixed (e.g. overhead distribution);
  • partially mixed (e.g. most UFADs); and
  • fully stratified (e.g. TDV).

Since interior zones usually have adequate heat loads from occupants and equipment and few heat losses, the discussion for interior spaces will solely concern cooling. For the perimeter spaces, this article discusses 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.

With fully stratified air systems, cool supply air is typically delivered at a reduced velocity from low sidewall diffusers.

With fully stratified air systems, cool supply air is typically delivered at a reduced velocity from low sidewall diffusers.

Max Allowable Differential Hi-Res

Fully mixed
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 (i.e. radial) or cross-flow (i.e. directional) discharge air pattern. The circular pattern usually provides shorter throw and higher mixing; it 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 air pattern has longer throw, but less induction means it 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 air pattern. Sidewall grilles equipped with vertical deflectors can be adjusted from zero degree (directional pattern) to 45 degree spread (radial pattern). Regardless of the desired type of outlet, the air pattern can be either radial or directional to best meet the space’s comfort requirements.

For perimeter applications where the same outlet is being used for both heating and cooling, a linear slot diffuser or plenum slot diffuser is typically 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 62.1-2013 must be considered. The intent of table 6-2 is to ensure 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 0.76 m/second (150 fpm) to within 1.4 m (4 ½ ft) of the floor.

To a terminal velocity of 0.76 m/s or more, air is temperature-independent. This means the distance air travels will be the same for isothermal (catalog values), warm, and cool air. In other words, during heating, ventilation air will be pushed down into the breathing zone with enough heat energy to meet ASHRAE 55’s requirement for a temperature gradient of less than 3 C (5.4 F). Additionally, the differential temperature between warm supply air and space temperature with a ceiling return must be 8 C (15 F) or less. Thus, the maximum supply air temperature for a 24-C (75-F) room would be 32 C (90 F). When the heating supply air temperature exceeds the 8-C limit, the ventilation air volume for heating must be increased by 25 percent.

In a mixed air system, hot or cold supply air is delivered at relatively high velocity from ceiling-mounted diffusers.

In a mixed air system, hot or cold supply air is delivered at relatively high velocity from ceiling-mounted diffusers.

Choosing an auto-changeover diffuser does not change the ASHRAE 62.1 requirements, but will lower energy cost 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 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 as the heated air can be designed to deliver warm air all the way to the floor. Comfort may be increased during cooling as well—the cool air will be projected across the ceiling, eliminating potential for drafts from the jet projected down the glass with a fixed pattern diffuser.

For fixed pattern outlets supplying cool and warm air to the perimeter, ceiling heights of less than 3.7 m (12 ft) is desirable so outlets can be selected to provide adequate heating without excessive drafts on the floor during cooling conditions. A floor-to-ceiling wall located within 4.6 m (15 ft) of the perimeter wall will help contain the warm air distributed across the ceiling. Auto-changeover outlets have a bit more flexibility, as long as the throw for the heated air down the glass is long enough to comfort condition the space at acceptable noise levels from the outlet.

Fully mixed systems are flexible enough to accommodate air distribution challenges for most applications by providing adequate thermal comfort for cooling and heating. The systems described in this article may provide some advantages for specific applications, which will be discussed.

Fully mixed systems will provide the lowest first cost for comfort control. Architectural features can add to the cost without improving performance. For perimeter spaces, a single-duct terminal with a reheat device will be a lower first cost, but higher operating expense, than a fan-powered unit with heat. The additional operating cost may be inconsequential for moderate climate zones, but cost-prohibitive for climate zones with more severe winter conditions. Providing a separate heating source, such as baseboard radiation, is common for severe winter climate zones as well.

Partially mixed
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 to stratify. Occupant comfort is achieved by delivering cool, conditioned air from the plenum under the floor through swirl diffusers or rectangular-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 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 grilles. 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 a passive system of VAV cooling and heating perimeter distribution outlets. With a 150-mm (6-in.) wide custom design bar grille located along the perimeter of the space, a modular 1.2-m (4-ft) long sliding damper with transverse apertures (cooling) can be attached to provide up to 106 L/s (225 cfm) at 17.5 Pa (0.07-in.) plenum pressure.

When it comes to interior temperatures, an important factor affecting comfort is an offi ce is the occupant’s clothing insulation level—quantifi ed as ‘clo.’ Photo © BigStockPhoto/ Cathy Yeulet

When it comes to interior temperatures, an important factor affecting comfort is an office is the occupant’s clothing insulation level—quantified as ‘clo.’ Photo © BigStockPhoto/Cathy Yeulet

The 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. A 1.2-m long plenum with fin-tube hydronic or electric heating elements can be attached to the grill to provide up to 0.9 kW (3000 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 customized for use in multiple climate regions.

UFAD systems are ideal for applications with cabling being provided to each individual work station. Additional monies can be saved by reducing the cost to reconfigure the footprint of the work area to accommodate changes in space work requirements.

The engineer must consider supply air temperature rise in the raised floor of a UFAD system. Depending on construction, supply temperature rise can exceed 0.5 C (1 F) per 3 m (10 ft), so large floor plates generally require multiple supply air injects points, either covered by multiple air handlers per floor or under floor ductwork. Multiple floor air-handling units need more usable floor space and underfloor ductwork can limit the floor plate’s flexibility. Therefore, buildings with large floor plates are not ideal for this type of system.

UFAD systems are generally designed with low supply air pressure, which allows for fan energy savings over a more conventional fully mixed overhead system. To maintain the low-pressure design, the floor plenum needs to be clear of obstruction. Full-height walls—deck-to-deck or deck-to-ceiling—will degrade UFAD system performance. (It can be overcome, but it is not ideal.)

There are many variables in a building with a UFAD system. The floor is an additional expense but, depending on the design of the building system, there is the opportunity to shorten the floor-to-floor cost, which can provide considerable savings. Depending on the UFAD system design, first cost can be lower compared with a fully mixed system with manual diffusers, limited ductwork, and minimal testing and balancing compared to a comparable overhead system.

Maintenance should be similar to a fully mixed overhead system, if a fan-powered perimeter is employed. When a passive VAV perimeter system is used, maintenance should be less, with fewer fan-powered components to maintain.

Fully stratified
In a fully stratified design, which typically involves TDV systems, a space is conditioned by discharging cool supply air through an outlet either positioned at floor level near or in a wall or centrally located in the open space. Low-velocity air (i.e. < 0.4 m/s [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 piece of warm equipment in the space. Cool air will mix with the radiant heat from 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 0.2 m/s (40 fpm) is the ‘clear zone,’ and should not be included in the occupied area. Some manufacturers provide units with adjustable air patterns so the clear zone can be controlled to meet project requirements for space occupancy.

ASHRAE 62.1’s Table 6-2 provides the information required to calculate the minimum ventilation rates for outdoor air in the breathing zone. It offers an Ez factor for various air distribution configurations to be divided into the Table 6-1 value to ensure the minimum prescribed outdoor air reaches the breathing zone. For TDV systems, the Ez factor is 1.2—this means ventilation air can be reduced by 17 percent, or the 17 percent can be used toward the 30 percent LEED requires for an additional Indoor Environmental Quality (EQ) Credit 2, Increase Ventilation Effectiveness.

For offi ce spaces, the right air distribution system should provide both thermal comfort and a healthy working environment. Photo © BigStockPhoto/Larry Malvin

For office spaces, the right air distribution system should provide both thermal comfort and a healthy working environment. Photo © BigStockPhoto/Larry Malvin

While TDV systems typically require a separate system for heating, new systems now have the ability to heat and cool using one displacement ventilation unit. A standard rectangular outlet is located near or mounted in a wall discharging cool air from the upper chamber. When heating is required, an internal baffle moves to change the flow of air from the upper chamber to the lower chamber where it flows through a linear bar grille to satisfy heating requirements.

A TDV requires similar ductwork and distribution as a fully mixed system. First cost is generally higher because TDV is large and covers a greater area than diffusers in mixed systems. Maintenance cost should be comparable to a fully mixed system. However, since TDV generally requires floor space to place the diffuser, it is not ideal for spaces with high churn.

TDV and low-mixing UFAD system will require less ventilation air to comply with ASHRAE 62.1. These systems can utilize air-side economizers and warmer temperatures to match the warmer supply air temperatures. These combined energy-saving features help increase overall system efficiency and decrease long-term payback over a fully mixed system.

Conclusion
Regardless of which type of system is being specified on a project, studies have shown occupants who are comfortable are more productive.1 In other words, designing for comfort pays back dividends forever.

Notes
1 Examples include “Productivity and Indoor Environment,” by Derek Clements-Croome and Li Baizhan (University of Reading, Department of Construction Management and Engineering), which appeared in volume one of the 2000 Proceedings of Healthy Buildings. Another example can be found in Susan S. Lang’s “Warm Offices Linked to Higher Productivity,” from the March 2005 issue of Human Ecology.

Jim Aswegan is chief engineer at Titus, with 48 years of service. He provides applications support for engineers and participates in industry organizations including the American Society of Heating, Refrigerating, and Air-conditioning Engineers (ASHRAE), the U.S. Green Building Council (USGBC), and the Air-conditioning, Heating, and Refrigeration Institute (AHRI). Aswegan’s expertise includes grilles, registers, and diffusers (GRDs), along with terminal units and acoustics. He can be contacted via e-mail at jaswegan@titus-hvac.com.

David Pich, PE, LEED AP, is the director of HVAC technology for Titus, and has more than 18 years of experience in consulting engineering. He provides application support for engineers and, as a LEED AP, offers technical training in Titus’ consulting Engineer Seminars. Additionally, Pich supports and participates in industry organizations such as ASHRAE, USGBC, and AHRI. He can be contacted via e-mail at dpich@titus-hvac.com.

Duct construction app

The Sheet Metal and Air Conditioning Contractors’ National Association (SMACNA) has released an app for the third edition of its manual, HVAC Duct Construction Standard—Metal and Flexible. The app provides a simplified process for finding construction options for rectangular ducts with dimensions up to 3048 mm (120 in.) for applications discussed in the manual. It provides options for internal and external reinforcements. Internal options are limited to electrical metallic tubing (EMT) conduit tie rods, and external reinforcements are limited to angles. The app will provide users with a written description of the duct, as well as a visual image of it. It is intended to be used in conjunction with the manual, and is largely used for onsite work. It is available at the Apple App Store or the Google Play App Store.

Missed Opportunities with Chillers

By Paul Valenta, LEED AP

IceBank Tanks

Capturing off-peak electricity savings can be accomplished by installing a hybrid cooling system that features a chiller and thermal energy storage (TES) assemblies that use water or ice to store energy.
Photo courtesy Calmac

The HVAC system is rarely thoroughly studied or analyzed until there is a problem. In the daily activities of running a business or managing a building, HVAC is out of sight, out of mind until things get too hot or cold. Then, productivity drops and costs increase as chillers limp along with Band-Aid fixes that result in expensive after-hour service calls. Replacing the chiller with a newer version (i.e. the ‘like-for-like’ method) is all too often the chosen solution, simply because it is the quickest option. However, this can represent a missed opportunity. Continue reading

The State of HVLS Technology

Images courtesy MacroAir

Images courtesy MacroAir

by Michael Danielsson

Since the original high-volume, low-speed (HVLS) fan prototype came to market more than 15 years ago, there have been significant technology developments, functional improvements, and changing market demands, propelling such fans into the spotlight as a means to save energy—and money—on HVAC systems.

Design enhancements to the motor and blades have allowed for expanded applications from the original dairy industry and large-scale commercial applications to greater use in smaller businesses. HVLS fans impart a number of benefits to business owners and facility managers, including lower energy costs of moving air and creating a comfortable environment. Compared to traditional shop or ceiling fans, the HVLS fan is an energy-efficient air-mover that displaces masses of air from its large slow-moving blades.

In addition to being a supplement to natural ventilation or HVAC systems, HVLS fans reduce or eliminate other facility challenges. The technology helps to improve ventilation and indoor air quality (IAQ) by:

  • continuously mixing incoming fresh air;
  • eliminating condensation buildup by creating a constant state of thermal equilibrium; and
  • providing heat destratification by running in reverse to even out the temperature gradient from floor to ceiling, reducing heat loss.

While the technology can sometimes be misinterpreted as working in similar fashion as generic ceiling fans, HVLS systems are much more evolved.

An HVLS fan slowly circulates a massive amount of air downward, then outward along the floor (i.e. horizontal floor jet), and back up 360 degrees. This causes air to travel through the area in a large circular motion and at a more stabilized rate of speed, keeping all the air constantly and gently moving, rather than letting pockets of air sit stagnant.

An HVLS fan slowly circulates a massive amount of air downward, then outward along the floor (i.e. horizontal floor jet), and back up 360 degrees. This causes air to travel through the area in a large circular motion and at a more stabilized rate of speed, keeping all the air constantly and gently moving, rather than letting pockets of air sit stagnant.

360 degrees of air movement
Designed on principles of physics and aerodynamics, HVLS fans move large quantities of air downward in a large diameter column of air toward the floor. When the air column hits the floor, it changes direction and becomes a ‘floor jet,’ moving outward in all directions until it reaches the walls. At this point, it travels back up to the ceiling, returning to the area of the fan in a horizontal direction, and then getting pushed back down to the floor. This is a natural, circular path created by the huge airfoil blades of the HVLS fan.

Once the air is moving in one direction, it wants to continue moving that way. The clean lines of the airfoil-shaped blades support air movement in the same direction—so once the air flow is established, it tries to continue circulating, creating an energy-efficient way to move air. In other words, keeping the air going in the same direction, rather than diverting it in different ones, enables the system to use less energy for the same result.

Destratification can be achieved in warm or hot climates through a downward air column by running the HVLS fan in forward mode. During cooler months, running it in reverse will push the warm air that accumulates at the top of the space down to the floor without creating drafts or winds in occupied areas.

Smaller high-speed fans are incapable of producing the same air movement and temperature regulation. Slower airspeed, combined with fan blade effectiveness, means large, low-speed commercial fans are significantly more efficient and effective than small high-speed fans because the large-diameter air column travels farther.

Industry standards
Fan performance is measured using cubic meters per minute, or the measurement of volume over time. This means, the higher a fan’s m3/minute (cfm), the higher its volume or capacity.

Once HVLS fans became a staple on the HVAC market about a decade ago, performance measurements became an important indicator to differentiate the growing number of manufacturers. Performance tests conducted by the Air Movement and Control Association (AMCA) in 2006 measured ‘thrust,’ which is the lifting force the fan produces as a result of the air being pushed through it. Thrust has become a valuable measurement in determining output. Fan efficiency can then be evaluated using power consumption compared with the m3/minute output.

Design changes
Various design enhancements have improved HVLS fan performance over the years. Original designs of the HVLS fan featured 10 blades, which manufacturers still offer today. However, in some models, the number of blades has been reduced to six. This complements newer airfoil blade shapes to increase performance.

CS_November2013.inddSix-blade HVLS fans carry 40 percent less weight than the 10-blade construction, thereby lowering the torque requirement, and enabling the fan to rotate more efficiently. Since torque is a constant stress on a fan’s motor, bearings and gear, less torque also means longer fan life. Figure 1 compares the output on six- and 10-blade fans. Above and beyond requiring less fan blades, the innovation also decreased the manufacturing carbon footprint of the products.

Other add-ons or upgrades have been made to enhance performance, but there is still debate on some of their efficiencies. One of the most common features is the ‘winglet’ or curved end cap, which is intended to increase downward air velocities, stabilize air movement, eliminate turbulence, and capture air that would slip off the blade’s end.

However, a winglet built into the design of a HVLS fan’s blade may not be beneficial when affixed to its tips as it may change the natural, circular air path created by the huge airfoil blades.

One 7.3-m (24-ft) diameter HVLS fan can move about 10,619 m3/minute (375,000 cfm). With one cubic foot of air weighing 0.08 pounds, this equates to about 13,608 kg (30,000 lb) of air moving through the fan blades every minute. Once the air is moving in one direction, Newton’s First Law of Motion keeps it that way. The lines of the airfoil-shaped blades, without winglets, can support air movement in the same direction.

Due to the increased torque, winglets can potentially make the fan work harder, and possibly cause turbulence that interferes with the downward column of airflow.

To inform spacing and other installation requirements for a National Fire Protection Association (NFPA) standard, the Fire Protection Research Association Foundation initiated a comprehensive research program with two phases.

To inform spacing and other installation requirements for a National Fire Protection Association (NFPA) standard, the Fire Protection Research Association Foundation initiated a comprehensive research program with two phases.

A majority of testing during the research project used a 7.3-m (24-ft) fan. Performance data indicates the fan produced approximately 9346 m3/minute (330,000 cfm) at 63 rpm.

A majority of testing during the research project used a 7.3-m (24-ft) fan. Performance data indicates the fan produced approximately 9346 m3/minute (330,000 cfm) at 63 rpm.

 

 

 

 

 

 

 

 

 

 

Confidence in safe building design
HVLS fans can be considered a trusted system within a building’s design. In 2012, a collaborative research effort was spearheaded by AON Fire Protection Engineering. Bringing together insurance companies and HVLS manufacturers, the project resulted in updates to the National Fire Protection Association (NFPA) 13, Standard for the Installation of Sprinkler Systems, which provides guidelines to avoid obstructing sprinkler performance in commercial applications.

When installed in accordance with NFPA 13, HVLS fans do not impact the performance of early-suppression, fast-response (ESFR), and control-mode-density-area (CMDA) sprinkler systems.

Both types are typically used in high-storage and warehouse facilities, and need to work in tandem with other facility systems. ESFR sprinklers provide a high output of water from a sprinkler head to suppress a fire and are installed within ceiling spaces as to not interfere with high-piled commodities or moving machinery. CMDA systems control fire outbreaks through pre-wetting combustible commodities and controlling hot gas. The outcome further supports safety guidelines, and consumer and insurer confidence for the fan category.

CS_November2013.inddHVLS fan research conducted between 2008 and 2010 tested numerous scenarios of installation spacing, speed, and other variables of HVLS fan operation on both ESFR and CMDA sprinkler systems upon fires started within rack storage and palletized commodities.1

Installation should include a means of automatic shutdown for all HVLS fans, meaning power to the fan(s) is interrupted within 90 seconds after the first sprinkler operates. This is most commonly achieved through connecting the buildings fire suppression system to the fan control panel.

HVLS fan placement is critical for maximizing effective operations. Obstructions, such as facility structures or stacked materials, reduce the HVLS fans efficiency. To ensure un-obstructed downward and then horizontal air movement, and affect the most space, fans should be installed over open floor space.

Supplementing the HVAC systems with HVLS fans
HVLS fans are increasingly relied on to provide HVAC augmentation as the technology uses little energy. Using chapter nine of the 2012 American Society of Heating, Refrigerating, and Air-conditioning Engineer’s ASHRAE Handbook, it is possible to maintain thermal comfort at a higher temperature in an environment by increasing the air speed. Figure 2 shows the air speed required to offset temperatures above the ideal operative temperature.

As industrial and commercial buildings face increased scrutiny on energy consumption, HVLS fans can provide an advantage when used as part of an energy-efficient HVAC solution. Whether installed in an existing facility or designed into a new build, HVLS fans can help a project earn points toward Leadership in Energy and Environmental Design (LEED) certification by lowering energy consumption, creating a healthy indoor environment and air quality, and using less resources and equipment through HVAC systems. Although the number of credits earned varies based on each individual building project and type, HVLS fans can help projects earn credits under the Energy & Atmosphere (EA) and Indoor Environmental Quality (EQ) categories.

For the testing, two ignition locations were selected near the tip of the fan blade and under the fan hub. The former was selected to maximize fan effect based on fan performance data. The latter was based on observations of Phase One testing. The fan was centered between four sprinklers when sprinkler spacing was 3 x 3 m (10 x 10 ft). In the control mode density area (CMDA) sprinkler tests, where spacing was 2.4 x 3 m (8 x 10 ft), the fan was offset 0.3 m (1 ft) south of center.  [CREDIT] Photo courtesy UL LLC

For the testing, two ignition locations were selected near the tip of the fan blade and under the fan hub. The former was selected to maximize fan effect based on fan performance data. The latter was based on observations of Phase One testing. The fan was centered between four sprinklers when sprinkler spacing was 3 x 3 m (10 x 10 ft). In the control mode density area (CMDA) sprinkler tests, where spacing was 2.4 x 3 m (8 x 10 ft), the fan was offset 0.3 m (1 ft) south of center. Photos courtesy UL LLC

During the second phase of testing, a total of 10 full-scale fire tests were conducted between June and December 2010, evaluating the effect of the HVLS fans on the performance of both early-suppression, fast-response (ESFR) and control-mode-density-area (CMDA) sprinklers protecting both rack storage and palletized commodities.

During the second phase of testing, a total of 10 full-scale fire tests were conducted between June and December 2010, evaluating the effect of the HVLS fans on the performance of both early-suppression, fast-response (ESFR) and control-mode-density-area (CMDA) sprinklers protecting both rack storage and palletized commodities.

 

 

 

 

 

 

 

 

 

 

 

 

Market demands expand applications
Due to the large diameter of first-generation HVLS fans—up to 7.3 meters (24 ft) in some cases—they have traditionally been specialized for large industrial or commercial spaces. With the availability of smaller-diameter blades, small spaces now look to take advantage of the technology.

The slow-moving fans even have the ability to create a breeze in un-insulated areas such as a mobile outdoor worksite without use of air-conditioning. Within temporary structures, such as in marquee fair tents, the fans can be securely installed to a steel truss and implement air movement through crowds of people.

For more traditional building projects, HVLS fans can also be beneficial. Kaizen Martial Arts Academy in Jackson, California, is home to a 464.5-m2 (5000-sf) building where people of all ages study karate, Brazilian jiu-jitsu, and yoga. When the temperatures outside the facility rise to 26.6 C (80 F) or higher, the dojo begins to feel less like a training and fitness facility and more like a sweat lodge.

Taking less than a day to install, Kaizen’s large-diameter HVLS fan is now offering a refreshing breeze, while actually accelerating the rate of perspiration evaporating from the skin, and providing more than $1500 in annual energy savings.

This fan was installed to a steel truss during an outdoor trade show.  [CREDIT] Photo courtesy MacroAir

This fan was installed to a steel truss during an outdoor trade show. Photo courtesy MacroAir

High-end luxury
Fan systems are also offering plug-and-play packages, which simply require the power cord to be plugged in and the controls remotely connected via a standard cable connection. Since no external control panel is needed, the electrical wiring is minimized and the fan can be seamlessly integrated into the building’s aesthetics.

Next-generation HVLS fans also come with a streamlined profile, including on-board electronics packaged inside a power unit in case the fan may be more visible than in a larger warehouse or industrial space. Electronics can be pre-programed with variable frequency drives (VFD) to control the fan speed and use heat transfer of the aluminum extrusion to help cool the VFD.

With a cooler VFD, carrier frequency levels can be set outside the audible level to create a more silent fan, further integrating HVLS fans’ availability to meet the needs of diverse application demands.

Notes
1 Visit safetymatters.aonfpe.com/2011/1st-Quarter/Feature-Article.aspx. (back to top)

Michael Danielsson is engineering manager of MacroAir, a manufacturer of high-volume, low-speed (HVLS) fans found in warehouses, manufacturing plants, airplane hangars, agricultural arenas, and retail establishments. He leads the engineering department in developing innovative air movement solutions. Danielsson can be contacted by e-mail at engineering@macroairfans.com.