Air Handling Unit Design For A 5 Story Building

Designing an Air Handling Unit (AHU) system for a five-story building involves careful consideration of various factors, including the building's purpose, occupancy, and specific HVAC requirements. Here’s a structured approach to designing an AHU system for such a facility:

1. Project Overview

Building Type: Identify whether it’s residential, commercial, or mixed-use.

Occupancy: Determine the expected number of occupants and activities in each area.

Climate Zone: Consider the local climate, which affects heating, cooling, and ventilation needs.

2. Load Calculation

Thermal Load Assessment: Calculate heating and cooling loads using methods like Manual J or software tools. This includes:

External Loads: Heat gain/loss through walls, windows, roofs, and doors.

Internal Loads: Heat from occupants, equipment, lighting, and processes.

Ventilation Requirements: Determine the required fresh air intake based on occupancy and ASHRAE standards, ensuring adequate indoor air quality.

3. AHU Sizing

Airflow Requirements: Calculate the required airflow (CFM) for each floor based on load calculations and ventilation needs.

Total Airflow Calculation: For a five-story building, the total airflow can be estimated by summing the airflow requirements for each floor.

4. AHU Configuration

Type of AHU: Choose between:

Modular Units: For flexibility and ease of maintenance.

Packaged Units: For space-saving solutions.

Components:

Filters: Use pre-filters and HEPA filters for air purification.

Coils: Select appropriate heating and cooling coils based on load calculations.

Fans: Choose energy-efficient fans (e.g., centrifugal fans) with appropriate static pressure capabilities.

Dampers: Include outside air dampers and return air dampers for balanced airflow.

5. Distribution System

Duct Design:

Duct Sizing: Use duct sizing methods to ensure adequate airflow to each floor and room.

Layout: Design a duct layout that minimizes bends and pressure drops.

Terminal Units: Consider using VAV (Variable Air Volume) boxes or FCUs (Fan Coil Units) for individual room control.

6. Control System

Building Management System (BMS): Integrate a BMS for monitoring and controlling the AHUs, including:

Temperature Control: Setpoints for different areas of the building.

Humidity Control: For spaces requiring specific humidity levels (like laboratories).

CO2 Sensors: For demand-controlled ventilation.

7. Energy Efficiency

Energy Recovery: Consider energy recovery ventilators (ERVs) to pre-condition incoming air.

Variable Frequency Drives (VFDs): Use VFDs on fans to optimize energy use based on demand.

High-Efficiency Components: Select high-efficiency motors, coils, and filters to reduce energy consumption.

8. Compliance and Standards

Building Codes: Ensure design complies with local building codes and regulations.

ASHRAE Guidelines: Follow ASHRAE standards for ventilation and indoor air quality.

9. Maintenance Considerations

Accessibility: Design AHU placement for easy access for maintenance and filter changes.

Maintenance Schedule: Establish a maintenance program for regular inspections and servicing.

Example Specification

Airflow Requirement: 2000 CFM per floor (total of 10,000 CFM for 5 floors).

Filter Type: MERV 13 pre-filters and HEPA filters.

Heating/Cooling Coils: Sized for a total load of 150,000 BTU/hr.

Fan Type: Centrifugal fan with VFD.