Industrial Process HVAC

Industrial process HVAC systems serve manufacturing operations where environmental control directly impacts product quality, process efficiency, worker safety, and production output. These systems integrate thermal management, contamination control, and ventilation with production processes.

Process Cooling Loads

Industrial cooling loads differ fundamentally from comfort cooling due to high sensible heat ratios, concentrated heat sources, and continuous operation requirements.

Load Characteristics

Process equipment generates substantial sensible heat with minimal latent gains:

Heat generation from industrial processes follows the relationship:

Q = P × (1 - η) × Fu

Where:

• Q = Heat to space (W)
• P = Equipment power input (W)
• η = Process efficiency (fraction)
• Fu = Usage factor (accounts for simultaneous operation)

Cooling Strategies

Process cooling employs multiple approaches based on load magnitude and distribution:

Direct Space Cooling provides general temperature control through overhead air distribution. Supply air temperatures range from 50-60°F with high air change rates of 10-20 ACH for moderate load densities below 1000 W/m².

Spot Cooling Systems deliver concentrated cooling to specific workstations or equipment zones. These systems use flexible ductwork and high-velocity diffusers to provide 500-2000 CFM directly where needed, with supply temperatures 15-25°F below ambient.

Evaporative Cooling offers economical cooling in dry climates (outdoor dewpoint below 65°F). Direct evaporative cooling reduces dry-bulb temperature by 15-25°F while adding moisture. Indirect evaporative cooling provides temperature reduction without humidity increase.

Radiant Cooling Panels address high overhead radiant loads from furnaces, ovens, and hot processes. Chilled panel surface temperatures of 55-65°F absorb radiant heat while maintaining air temperature 5-10°F higher.

Process Heating Requirements

Industrial heating maintains process temperatures, prevents condensation, and ensures product quality during manufacturing.

Heating Load Components

Industrial heating loads include:

Fabric Heat Loss through walls, roof, and floor follows standard transmission calculations but with extended operating hours and typically higher indoor temperatures (65-75°F in manufacturing areas).

Infiltration and Ventilation represent major heating loads in manufacturing facilities with large door openings, exhaust systems, and poor building tightness. Ventilation heating loads are calculated:

Q_vent = 1.08 × CFM × (T_in - T_out)

Process Requirements include maintaining minimum temperatures for material handling, preventing condensation on equipment, and supporting specific process needs (paint curing, material drying).

Heating System Types

Unit Heaters provide zoned heating using gas-fired or hot water units with capacities from 30,000 to 400,000 BTU/hr. These suspend from ceilings with horizontal or vertical discharge, achieving 80-95% efficiency.

Radiant Tube Heaters deliver infrared heating at high bay heights (20-40 ft) with minimal air stratification. Gas-fired tubes operate at 600-1200°F surface temperature, providing 60-80% of heat as radiation. Radiant efficiency increases with mounting height and decreases with air velocity.

Make-up Air Units replace exhausted air with heated fresh air. These systems integrate heating coils (gas-fired burners or hot water/steam coils), filtration, and supply fans. Typical capacities range from 1,000-50,000 CFM with heating outputs of 100,000-5,000,000 BTU/hr.

Destratification Systems recirculate warm ceiling air downward using large-diameter, low-speed fans (8-24 ft diameter). These systems recover 15-30% of heating energy by reducing temperature stratification in high-bay spaces.

Manufacturing HVAC Systems

Manufacturing HVAC systems balance production requirements with worker comfort and energy efficiency.

System Selection Criteria

System selection depends on:

Load Density and Distribution determines whether central or distributed systems prove more effective. Centralized systems serve loads below 500 W/m², while distributed spot cooling addresses higher densities.

Contaminant Generation influences air distribution patterns and filtration requirements. Clean assembly areas use overhead distribution with MERV 8-13 filters. Dirty operations employ displacement ventilation with source capture.

Operating Schedule affects system design and control strategies. Continuous processes require redundant equipment and 24/7 operation. Batch processes benefit from setback during non-production periods.

Thermal Environment Requirements range from basic temperature control (±5°F) to precision control (±1°F) depending on product sensitivity.

Air Distribution Methods

Overhead Distribution supplies conditioned air from ceiling-mounted diffusers at 10-30 ft heights. High-throw diffusers with velocities of 500-1500 FPM provide coverage up to 40 ft radius. This approach suits general manufacturing with moderate contamination.

Displacement Ventilation introduces low-velocity air (30-50 FPM) at floor level, allowing thermal plumes to carry contaminants upward for high-level exhaust. Supply air temperatures are maintained 5-7°F below space temperature. This method achieves ventilation effectiveness of 1.5-2.0 compared to 1.0 for overhead mixing.

Local Supply Systems deliver conditioned air directly to workstations through flexible connections. Each station receives 100-500 CFM based on load. This approach maximizes efficiency in facilities with sparse occupancy and isolated processes.

Industrial Ventilation

Industrial ventilation removes airborne contaminants, controls heat, and provides fresh air to manufacturing spaces.

Ventilation Principles

Source Capture removes contaminants at generation points using local exhaust ventilation. Capture velocity requirements depend on contaminant type and generation characteristics:

Dilution Ventilation reduces contaminant concentration through mixing with clean air. Required ventilation rate follows:

CFM = (403 × Q) / (TLV × SG)

Where:

• Q = Contaminant generation rate (pints/min for liquids)
• TLV = Threshold limit value (ppm)
• SG = Specific gravity

General Ventilation provides background air changes for heat removal and air quality maintenance. Manufacturing areas typically require 4-8 ACH for general ventilation, with higher rates (10-15 ACH) for processes generating heat or odors.

Exhaust System Design

Hood Design captures contaminants through enclosure, capture velocity, and proper positioning. Enclosing hoods require lower airflow (100-200 CFM/ft² of opening) than exterior hoods (150-500 CFM based on proximity).

Duct Sizing maintains transport velocity to prevent contaminant settling:

Fan Selection accounts for system pressure drop and material characteristics. Backward-inclined and pressure-blower fans handle clean air streams. Radial-blade fans convey particulate-laden air.

Heat Recovery Systems

Industrial facilities offer substantial heat recovery opportunities due to high exhaust volumes, elevated exhaust temperatures, and continuous operation.

Recovery Potential

Heat recovery potential depends on exhaust characteristics:

Recoverable Heat = 1.08 × CFM × (T_exhaust - T_outdoor) × η

Where η represents heat exchanger effectiveness (0.50-0.85 depending on type).

Process exhaust streams provide recovery opportunities:

Heat Recovery Equipment

Run-Around Loops transfer heat between spatially separated exhaust and supply air streams using glycol solution circulated through coils. These systems achieve 45-65% effectiveness with no cross-contamination and operate at temperature differentials of 20-80°F.

Air-to-Air Heat Exchangers recover heat through plate-frame, heat pipe, or rotating wheel designs:

• Plate-frame exchangers achieve 50-75% effectiveness, handling exhaust temperatures up to 500°F with complete separation between air streams.

• Heat pipes provide 45-65% effectiveness with passive operation using refrigerant phase change. These units tilt 5-10° to ensure condensate return.

• Rotating wheels (enthalpy wheels) recover both sensible and latent heat at 70-85% effectiveness but require energy-efficient operation scheduling.

Exhaust Air Heat Pumps extract heat from exhaust air at 60-80°F to provide heating at 90-120°F. These systems achieve COPs of 3.0-4.5 when temperature lifts remain below 40°F.

Cleanroom Manufacturing HVAC

Cleanroom manufacturing HVAC maintains particle counts, temperature, humidity, and pressurization for semiconductor, pharmaceutical, and precision assembly operations.

Classification and Requirements

ISO cleanroom classifications specify maximum particle concentrations:

System Configuration

Unidirectional Flow (laminar flow) supplies filtered air through entire ceiling or wall area at 90 FPM, creating piston-like airflow that sweeps particles downward. This approach achieves ISO 3-5 classifications.

Non-Unidirectional Flow supplies filtered air through ceiling diffusers covering 15-30% of ceiling area at high air change rates. This turbulent mixing approach suits ISO 6-8 classifications.

Recirculation Systems minimize energy consumption by recirculating 80-95% of supply air through HEPA filtration. Outside air provides 5-20% of supply for pressurization and ventilation.

Pressurization Control

Cleanrooms maintain positive pressure of 0.02-0.05 in. w.g. relative to adjacent spaces. Pressure cascades from cleanest to dirtiest areas in 0.01-0.02 in. w.g. increments.

Differential pressure controllers modulate outside air dampers or return/exhaust dampers to maintain setpoints. Response time must be rapid (5-10 seconds) to prevent pressure excursions during door operation.

Environmental Control

Temperature Control maintains ±1°F in critical areas using chilled water cooling coils with 6-8 rows and close approach temperatures. Process heat loads of 300-1000 W/m² require high-capacity systems.

Humidity Control achieves ±2-3% RH through desiccant dehumidification (for dewpoints below 35°F) or chilled water dehumidification combined with reheat. Semiconductor facilities maintain 40-45% RH to prevent electrostatic discharge while avoiding condensation on cold surfaces.

Vibration Isolation prevents transmission of mechanical system vibration to process areas. Spring isolators, inertia bases, and flexible connections isolate equipment from structure. Vibration criteria (VC-A through VC-E) specify allowable amplitudes from 50-4000 μm/sec RMS.

Components

• Process Cooling Loads
• Process Heating Requirements
• Spot Cooling Applications
• Process Exhaust Ventilation
• Contaminant Specific Exhaust
• Dilution Ventilation Industrial
• General Ventilation Rates
• Heat Stress Management
• Evaporative Cooling Industrial
• Radiant Cooling Industrial
• Air Curtains Thermal Barriers
• Destratification Fans
• High Volume Low Speed Fans
• Compressed Air Systems
• Compressed Air Dryers
• Desiccant Dryers Compressed Air
• Refrigerated Dryers Compressed Air
• Heat Of Compression Drying