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| Under Floor Air distribution |
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| Under Floor Air Distribution (UFAD) system are a hybrid of displacement and mixing ventilation system and are specifically designed to mix the occupied zone*-the first 6 ft [1.8 m] of the room-allowing air to stratify** above this point. UFAD systems create a general upward flow of air in the space and like displacement ventilation, allow the system effective removal of heat, pollutant and odor. UFAD systems are often able to manage higher load than displacement ventilation while maintaining same thermal comfort and offering an increased level of occupant control.
Under Floor Air Distribution (UFAD) is an alternative to traditional overhead air distribution that delivers air from a pressurized air plenum beneath a raised access floor, relying on the natural buoyancy of air to remove heat and contaminants. |
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| Occupied Zone |
The occupied zone refers to the space in a room that begins one foot from all walls and extends from the floor to six feet above the floor. Mixing the occupied zone instead of the whole space can result in energy savings in spaces with high ceilings. |
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| **Stratification |
Stratification refers to a non-uniform temperature throughout a zone, with higher temperatures towards the ceiling and lower temperatures towards the floor. In a stratified room, return air is warmer and has a higher level of contaminants than supply air does. |
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| Air flow in ventilated spaces generally can be classified as below: |
1. Mixing (Dilution) Ventilation
2. Displacement Ventilation
3. Under Floor Air Distribution |
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| Fig.1 |
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| Mixing (Dilution Ventilation) |
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Overhead mixing ventilation (Figure 1) systems generally supply air in a manner such that the entire room air is fully mixed. The cool supply air exits the outlet at high velocity, inducing room air to provide mixing and temperature equalization. Since the entire room is fully mixed, temperature variations are small while the contaminant concentration is uniform throughout the entire room. |
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| Fig.2 |
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| Displacement Ventilation |
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Displacement ventilation systems (Figure 2) introduce air at low velocities which causes minimal induction and mixing. The system utilizes buoyancy forces (generated by heat sources such as people, lighting, computers, electrical equipment etc) in a room to move contaminants and heat from the occupied zone. By doing so, the air quality in the occupied zone is generally superior to that achieved with mixing ventilation. |
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| Fig.3 |
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| Under Floor Air Distribution |
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Under Floor Air Distribution (Fig – 3), differs from displacement ventilation systems primarily in the way the air is delivered to the space. The air is supplied at a higher velocity through smaller sized outlets typically mixing the occupied zone (6 feet above the floor) allowing air to stratify above this point. Additionally the volume and direction of the local air supply are generally under the control of the occupants, allowing the comfort conditions to be optimized. The UFAD system creates a general upward flow of air in the space which, working with the natural buoyancy of room air warmed by the heat loads, allows the effective removal of heat, pollutants and odors. Together with the room air they are removed from the space through the building exhaust or return air system located in the ceiling or at a high level. The diffusers are installed in the floor tiles of the conventional raised floor system. If the room layout is changed, the floor tiles are interchangeable and air distribution can be customized as required Since the conditioned air is supplied directly into the occupied zone, supply air temperature must be higher than mixing systems (usually 63°F or higher) to avoid a cold thermal sensation due to the low surface temperature of the raised floor. By introducing the air at slightly warmer supply air temperatures and rapidly mixing with room air, a high level of thermal comfort can be achieved. |
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| Concept And Benefits |
| Under Floor Air Distribution has following benefits: |
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| Energy Savings |
Energy savings available with UFAD systems is found in the extended economizer usage, increased chiller efficiency and decreased fan energy. UFAD uses a higher supply air temperature than overhead systems, typically 59-63ºF instead of 53-55ºF, this can have a significant impact on the economizer use in markets where humidity allows. The increased supply air temperature leads it increased return air temperature and can have a positive effect on the chiller efficiency. Finally, the reduced static pressure of UFAD systems may lead to a reduction in primary fan energy but this may be reduced by the use of local fan powered terminals. |
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| Thermal Comfort |
UFAD introduces supply air at a higher temperature than overhead systems, reducing the likelihood of a cold sensation. In addition, local air supply can be controlled by the occupants, allowing the comfort conditions to be optimized. |
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| Flexibility |
UFAD and raised flooring has been used for decades in computer rooms due to the flexibility they provide. The same benefits are captured with use in office spaces and call centers. Today’s work place typically has an abundance of cubicles and a proclivity for change. UFAD is ideally suited to this type of environment, as office reconfiguration is made easier with the ability to move floor tiles with diffusers to another location simply by unscrewing and rearranging the tiles. Since there is little or no ductwork involved this can be done by building maintenance personnel instead of an HVAC contractor. |
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| Fig. 4 |
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| Indoor Air Quality |
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Indoor Air Quality is an important issue in today’s society. A better indoor environment has been linked to increased productivity and fewer sick days by employees. UFAD is a major contributor in creating a better air quality environment. (Fig – 4) shows that concentrations of air pollutants in the occupied zone (under six feet) is lower with air distribution outlets located in the floor vs in the ceiling
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| Contaminate Air Distribution - Source: Krantz Komponenten |
| Churn |
Churn Rate is the total number of moves made within a 12-month period divided by the number of occupants in the same period (IMFA, 2002). A 1997 survey by International Facilities Management Association (IFMA) determined that, on average, 44% of occupants move per year. The cost of churn is the costs associated with these moves including modifications to HVAC, cubicles and furniture to accommodate these office renovations. HVAC changes with an overhead system are time-consuming and costly, as ductwork must be moved and work done over the ceiling. IFMA estimates the average cost of a move in a government setting is $1,340, however with a UFAD system, that figure could be reduced by more than half. With a UFAD system, there is little or no ductwork to move and changes are made simply by unscrewing and moving the floor tile and diffuser to another location and screwing it in. The ability for data and power cabling to be located in the floor further adds to the cost savings associated with churn. |
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| Leed Certification |
The use of under floor air distribution can help to achieve LEED points towards LEED certification. Many city, county and state governments provide tax incentives for building in accordance with the LEED rating system. In addition, many governments require certain LEED levels for new construction projects which are publicly funded. |
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| Applications |
| In Office Buildings |
Open plan offices are the most common applications of UFAD as they benefit the most from having a raised floor due to:
• Modular power, voice, and data
• Individual comfort control
• Reduced cost of churn |
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Fig – 5 – Diffuser installed in offices (in cubicals)
Fig – 6 – Flow can be adjusted directly at the diffuser, allowing for individual comfort control. |
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| Fig – 7 & 8 – showing diffuser arrangement |
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| In Libraries |
UFAD offers the flexibility to adapt the diffuser arrangement when library stacks are reconfigured, and presents great energy saving potential in areas with high ceilings. Additionally, the low noise levels generated by UFAD systems make them ideal for libraries. |
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| In Casinos |
Casinos are another applications to which UFAD is particularly suited. Similar to office buildings, churn is common in casinos as gaming equipment is subject to reconfiguration. The ability to quickly and cost-effectively reconfigure the HVAC system is of great benefit in these buildings. In addition, some casinos allow patrons to smoke, producing an environment rife with contaminants in a completely mixed system. A UFAD system, however, stratifies room air, leading contaminants to collect at high levels outside the breathing area. |
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| Complete UFAD Systems |
We offer the most diverse and customizable product suite in the UFAD market, from grilles and diffusers to terminals and controls, as well as a variety of accessories. |
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