Construction of a Treated Fresh Air Unit (TFAU) is an advanced type of Fresh Air Unit designed to provide ventilation while also conditioning the incoming fresh air to meet specific indoor air quality and comfort requirements. Here is a detailed breakdown of the construction and components of a TFAU:
1. Air Intake Section
- Louvers and Grilles: These place at the air intake to prevent the entry of large debris, insects, and rainwater.
- Dampers: Motorized dampers control the amount of fresh air entering the unit. They can be adjusted based on demand or environmental conditions.
2. Filtration System
- Pre-Filters: The first line of filtration to capture large particles such as dust, pollen, and leaves.
- Fine Filters: High-efficiency particulate air (HEPA) filters or other fine filters that remove smaller particles and contaminants from the air, ensuring high indoor air quality.
- Activated Carbon Filters (Optional): Used for removing odors and gaseous pollutants.
3. Heat Exchanger (Energy Recovery Ventilator)
- Plate Heat Exchanger or Rotary Wheel: This component transfers heat between the incoming fresh air and the outgoing exhaust air, recovering energy and improving efficiency. In colder climates, it can pre-heat the incoming air, and in hotter climates, it can pre-cool the air.
- Desiccant Coating (Optional): In some systems, a desiccant coating on the heat exchanger helps with humidity control by transferring moisture between the air streams.
4. Cooling Coil
- Chilled Water Coil or DX Coil: Cools the incoming air to the desired temperature. The chilled water coil uses chilled water from a central chiller plant, while the DX (Direct Expansion) coil uses refrigerant directly.
- Condensate Drain Pan: Collects and drains away the condensate formed during the cooling process to prevent water accumulation and mold growth.
5. Heating Coil
- Hot Water Coil or Electric Heater: Heats the incoming air to the desired temperature. The hot water coil uses hot water from a central boiler plant, while the electric heater uses electrical resistance for heating.
6. Humidification and Dehumidification
- Humidifier: Adds moisture to the incoming air if the indoor humidity level is too low. Common types include steam humidifiers and ultrasonic humidifiers.
- Dehumidifier: Removes moisture from the incoming air if the indoor humidity level is too high. This is often integrated with the cooling coil, where the coil itself acts as a dehumidifier by condensing moisture out of the air.
7. Fans and Blowers
- Supply Fan: Ensures the conditioned air is adequately distributed throughout the building’s ductwork. The fan speed can be controlled using variable frequency drives (VFDs) for energy efficiency and precise control.
- Exhaust Fan (Optional): Works in tandem with the supply fan to expel stale indoor air, helping to maintain balanced ventilation and pressure inside the building.
8. Sensors and Controls
- Temperature Sensors: Monitor the temperature of the incoming and outgoing air to ensure it is conditioned to the desired level.
- Humidity Sensors: Measure the humidity levels to ensure proper humidification or dehumidification.
- CO2 Sensors (Optional): Monitor indoor CO2 levels to adjust ventilation rates and maintain good indoor air quality.
- Control System: An integrated control system (often part of a Building Management System, BMS) manages all the components, ensuring they work together efficiently to maintain desired indoor conditions.
9. Casing and Insulation
- Casing: The outer structure of the TFAU, typically made of galvanized steel or aluminum, providing structural support and protection for internal components.
- Insulation: Thermal and acoustic insulation use within the casing to prevent heat loss/gain and to reduce noise levels.
10. Duct Connections
- Supply Duct: Connects the TFAU to the building’s supply air distribution system.
- Return/Exhaust Duct: Connects the TFAU to the building’s return air system, allowing for the extraction of stale air.
11. Maintenance Access
- Access Panels: Removable panels or doors that allow for easy access to internal components for inspection, cleaning, and maintenance.
Summary
A Treated Fresh Air Unit (TFAU) is a sophisticated system designed to not only bring fresh air into a building but also to condition it to meet specific indoor environmental requirements. The main components and their functions are:
- Air Intake Section: Controls and protects the incoming air.
- Filtration System: Ensures high indoor air quality by removing particulates and contaminants.
- Heat Exchanger: Recovers energy from the exhaust air to improve efficiency.
- Cooling and Heating Coils: Condition the air to the desired temperature.
- Humidification and Dehumidification: Manage moisture levels for comfort and health.
- Fans and Blowers: Distribute air through the building’s ductwork.
- Sensors and Controls: Monitor and regulate system performance.
- Casing and Insulation: Provide structural integrity and thermal/acoustic protection.
- Duct Connections: Integrate the TFAU with the building’s HVAC system.
- Maintenance Access: Facilitate easy maintenance and servicing.
By incorporating these components, a TFAU ensures that fresh air adequately treats, providing a comfortable, healthy, and energy-efficient indoor environment.
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