Underfloor air distribution (UFAD) systems, also known as raised floor or displacement ventilation systems, are an innovative approach to heating, ventilation, and air conditioning (HVAC) in commercial buildings. Instead of traditional overhead ducting and diffusers, UFAD systems introduce conditioned air near the floor level through floor perforations or grates. This allows the system to more effectively condition occupied spaces with higher indoor air quality and enhanced thermal comfort compared to conventional overhead systems.
In this guide, we will provide an overview of UFAD system design considerations and walk through the installation process step-by-step. Our goal is to educate building owners and contractors on best practices for planning and implementing an underfloor air distribution system. By understanding both design principles and practical installation techniques, professionals can leverage the performance benefits of UFAD to create more productive and sustainable indoor environments.
UFAD Systsem Design Guide – How To Design Underfloor Air Distribution For Your Project?
This guide covers best practices for designing underfloor air distribution systems. Key considerations like thermal modeling, ventilation strategies, equipment selection and more will be discussed. Following the guidance herein will help ensure UFAD design meets project requirements and delivers optimized performance.
Step 1 – System Considerations
The first step is evaluating key aspects that will impact the UFAD design:
- Building usage and occupancy loads help determine ventilation requirements. Office spaces require less air than a computer lab, for example.
- Thermal loads from people, equipment, solar gain and more are analyzed to size the HVAC plant.
- Interior layouts, designs for future changes, and location of partitions are noted.
- Existing slabs or plans for new concrete foundations are reviewed for suitability.
Step 2 – Ventilation Strategies
Proper ventilation is crucial for indoor air quality. UFAD enables several options:
- Mixing ventilation introduces supply air near the floor to mix with the room. It requires high airflow rates.
- Displacement uses temperature differences to push warm air up and pull fresher air in. Less airflow is needed.
- Personalized combines mixing with task conditioning to supply each occupant.
- Choosing the right strategy based on code and application optimizes energy and comfort.
Step 3 – Thermal Modeling
Modeling software simulates airflow patterns, temperature variations and overall thermal performance under varying conditions. This provides:
- Sized zoning for optimal control of conditioned spaces.
- Locations and sizing of air inlets, outlets and sensors for desired ventilation.
- Insight into plenum height and openings needed for desired mixing/displacement.
Step 4 – Equipment Sizing and Selection
Based on thermal and ventilation modeling outputs:
- Air handling units with modulating controls that meet airflow specifications are selected.
- Fan materials and configurations are suitable for underfloor plenum pressures.
- Ductwork, air terminals and accessories can handle required volumes and velocities.
- Filters, coils and other components support targeted indoor conditions.
- Sensors and controls integrate mechanicals with the building automation system.
Step 5 – System Layout
A coordinated layout addresses:
- Placement of AHUs, ductwork runs and underfloor mechanical penetrations.
- Locations and types of air inlets, outlets and return openings by zone.
- Structural capacity and pedestal/support placement for full system buildout.
- Interface with ceiling systems, partitions and other interior finishes.
- Access points for installation, balancing and future maintenance/repairs.
- Coordination with other trafficked trades like electrical and plumbing.
Step 6 – Construction Documentation
All design considerations are compiled into:
- Specifications outlining all mechanical system components.
- Detailed plans showing layouts, sections and connection diagrams.
- Schedules of ductwork, equipment and control points with tags.
- Sequence of construction to ensure coordination across specialties.
- Commissioning procedures to validate performance meets objectives.
With these considerations in mind, designers can generate detailed construction documents, drawings, and schedules for the UFAD installation. Coordination between architects, engineers, and contractors is key.
UFAD System Installation Guide – How To Install Underfloor Air Distribution
This guide will outline the typical steps for installing a UFAD system based on best practices from engineering specifications and contractor experience. Following the outlined procedure helps complete the physical works safely, on schedule and in accordance with design requirements.
This guide will outline the typical steps for installing a UFAD system based on best practices from engineering specifications and contractor experience. Following the outlined procedure helps complete the physical works safely, on schedule and in accordance with design requirements.
Step 1 – Site Preparation
For new construction projects, the first order of work involves site preparation:
- Survey existing conditions and mark utilities if installing on an existing slab.
- Excavate as required and form/pour footings with appropriate slope and elevations.
- Install reinforcement and form/pour a new solid concrete slab suitable for supporting the system weight with an even tolerance of ±1/8 inch over 10 feet.
- Slab must fully cure before installing pedestals or any other construction.
Step 2 – Pedestal Layout and Installation
Pedestals elevation create the plenum space so their location/height is critical:
- Lay out pedestal positions according to engineered shop drawings, allowing for adjustments.
- Adjust placement to avoid obstructions like conduits or reinforcements in the slab.
- Securely screw or bolt pedestals through predrilled holes in slab at proper elevation.
- Repeatedly check pedestal tops are level using a laser or water level and adjust as needed.
Step 3 – Stringer and Support Installation
Providing sturdy support for floor panels:
- Lay primary T-Section stringers perpendicular to pedestals, secured to top flanges.
- Install intermediate C-Section stringers orthogonally between primaries at proper spacing.
- Add diagonal braces as specified between stringers for extra rigidity in high-traffic areas.
Step 4 – Floor Panel Installation
Panels create the working surface and air distribution pathways:
- Lay perimeter panels in place first, cutting as required and securing edges.
- Interlock full panels working inward from the edges in a pyramid pattern.
- Cut and fit remaining field panels, plugging gaps with interlocking strips or filler material.
- Secure panel joints tightly together as per manufacturers’ instructions.
Step 5 – Ductwork Installation
Routing supply and return ducts within the plenum:
- Install main trunk ducts along pedestrian-free sides of the plenum space as designed.
- Route splitter ducts to each supply air device location shown in drawings.
- Support ductwork independently of pedestals using hangers securely attached to the slab.
- Seal all joints with mastic and install manual balancing/volume control dampers.
Step 6 – Air Device Installation
Supply and return outlets provide conditioned airflow:
- Position modular linear slot diffusers or perforated panels precisely at indicated locations.
- Cut floor panels as needed and secure air devices’ mounting flanges from below.
- Install return grilles or diffusers to maintain adequate return air pathways as designed.
- Balance and adjust devices to achieve specified throw patterns/volumes.
Step 7 – Electrical and Controls Installation
Integrating all mechanical and building systems:
- Wire control wiring from air devices/sensors back to control panels as scheduled.
- Connect power feeds from AHUs to fans, dampers and other equipment as required.
- Mount and terminate low-voltage controls wiring for automated operation.
- Program sequence of operations and commission all control functions.
Step 8 – Commissioning and Startup
Validating performance meets design prior to occupancy:
- Conduct air and water balancing to achieve specified thermal/ventilation criteria.
- Test all control sequences and safeties through full-face exercises.
- Collect air/duct leakage testing to establish air tightness was achieved.
- Train facility operators on UFAD system maintenance requirements.
- Trim out space with ceilings, partitions and finishes upon confirmation.
Proper documentation throughout installation and a qualified commissioning agent ensures a smooth startup and that the UFAD system reliably conditions spaces as intended for years to come. Contact engineers or specialists with any technical questions that arise.
A well-designed UFAD system involves evaluating key factors like thermal/airflow modeling, ventilation strategies, layout optimization and coordinated construction documentation. Following this guidance enables designers to leverage the technology’s benefits through integrated, high-performing indoor environments. Contact our HVAC engineer for project-specific design assistance.