The process mandates 100 % fresh air with no recirculation, zoned independent temperature control, explosion-proof equipment, and remote centralized control.

The system comprises four sub-systems: a 100 % fresh-air air-cooled direct-expansion (DX) air-conditioning system as the core temperature-control loop, an explosion-proof axial-fan process exhaust system for air replacement, an air-compressor waste-heat recovery ventilation loop for energy-saving auxiliary heating, and a mechanical ventilation system for the power-distribution and windowless rooms.

Summer cooling load totals 425.18 kW (envelope 10.54 kW + indoor heat sources 41.04 kW + fresh-air load 373.60 kW), with a 10 %–15 % safety margin reserved. A detailed scheme comparison contrasts an air-cooled heat-pump water system (initial 600–700 RMB/kW, annual cost 170,000 RMB) against a variable-frequency DX AHU (initial 800–950 RMB/kW, annual cost 163,000 RMB). Seasonal operating modes — summer full-cooling, winter on-demand heating with waste-heat recovery, and transition-season fresh-air-only ventilation — minimize annual energy consumption while meeting military explosion-safety standards.

I. Project Overview

1.1 Project Brief

This project is a specialized design for the process air conditioning and ventilation system of a military-industry factory building. The building contains three core process rooms: the Preparation Room, the Weighing Room, and the Operation Room, together with a power-distribution room and windowless auxiliary rooms. The factory has a uniform ceiling height of 7.2 m and belongs to a military precision production area. The process requires that indoor air must not be recirculated, that each zone be independently temperature-controlled, that equipment be explosion-proof, and that remote centralized control be supported.

The system entirely adopts a 100% fresh-air mode: cooling in summer; heating in winter / transition seasons started and stopped on demand. Air-conditioning outdoor units are placed on the roof, with top-supply airflow distribution, supplemented by independent explosion-proof exhaust, air-compressor waste-heat recovery, and auxiliary mechanical ventilation systems.

1.2 Room Dimensions, Air Volumes, and Diffuser Configuration

1.3 Building-Envelope Thermal Parameters

• Roof heat-transfer coefficient: K = 0.40 W/(m²·°C)

• Exterior wall heat-transfer coefficient: K = 0.50 W/(m²·°C)

• Exterior window heat-transfer coefficient: K = 2.7 W/(m²·°C)

1.4 Summer Cooling Load Calculation

1.4.1 Calculation Basis Parameters

• Meteorological parameters: summer outdoor dry-bulb 33.2 °C, wet-bulb 25.9 °C, outdoor air enthalpy 79.8 kJ/kg;

• Indoor process design parameters: 25 °C, relative humidity 50 %, indoor air enthalpy 50.3 kJ/kg;

• Air density taken as 1.2 kg/m³;

• Total fresh-air-system cooling load = building-envelope heat-transfer load + indoor equipment / personnel / lighting load + fresh-air treatment load;

• Exterior windows, equipment heat dissipation, and number of personnel are routine estimated values for military-industry factory buildings; they may be precisely corrected at the construction-drawing stage based on equipment drawings.

1.4.2 Preparation Room / Weighing Room Cooling Load Calculation (the two rooms have identical parameters)

• Single-room floor area: 11.4 × 6.3 = 71.82 m²; fresh-air volume 4,000 m³/h

• Building-envelope load: 1.73 kW

• Indoor heat sources (lighting + process equipment + operators): 3.13 kW

• Fresh-air treatment load: 39.3 kW

• Single-room total cooling load = 1.73 + 3.13 + 39.3 = 44.16 kW

1.4.3 Operation Room Cooling Load Calculation

• Floor area: 11.4 × 48 = 547.2 m²; fresh-air volume 30,000 m³/h

• Building-envelope load: 7.08 kW

• Indoor heat sources (large-area lighting + multiple process equipment + operators): 34.78 kW

• Fresh-air treatment load: 295.0 kW

• Operation Room total cooling load = 7.08 + 34.78 + 295.0 = 336.86 kW

1.4.4 Whole-Factory Cooling Load Summary

Note: Unit selection reserves a 10 %–15 % safety margin to cope with extreme high temperatures and incremental equipment heat dissipation.

II. Design Basis and Design Principles

2.1 Design Basis

• GB 50019-2015 Design Code for Heating, Ventilation and Air Conditioning of Industrial Buildings

• GB 50243-2016 Code for Acceptance of Construction Quality of Ventilation and Air Conditioning Works

• GB 51245-2017 Unified Standard for Energy Efficiency Design of Industrial Buildings

• Special Environmental Safety Specification for Military Precision Production Workshops

• Building dimensions and process production environment requirements provided by the client

2.2 Core Design Principles

• Process safety first: 100 % fresh air with no return air, eliminating the recirculation and accumulation of production exhaust gases and dust; exhaust equipment adopts explosion-proof type, meeting the explosion-safety requirements of military-industry factory buildings.

• Zoned independent control: Three independent air-conditioning and exhaust systems for the Preparation, Weighing, and Operation Rooms — non-interfering, individually startable/stoppable, and individually temperature-adjustable.

• Energy-saving operation design: Seasonal switchover recovery of air-compressor waste heat; transition seasons fully utilize fresh air for natural cooling, reducing annual operating electricity cost.

• Integrated simplified system: Air-cooled direct-expansion 100 % fresh-air units are selected, eliminating the entire chilled-water plant room and water-system equipment, reducing equipment count and lowering failure rates.

• Local + remote dual control: Fans come standard with RS485 communication, supporting local manual start/stop and centralized remote monitoring and control at the central control room, making O&M management convenient.

III. Overall System Architecture Design

The entire system is divided into four independent sub-systems:

1. Process 100 % fresh-air air-cooled direct-expansion air-conditioning system (core temperature-control system)

2. Explosion-proof axial-fan process exhaust system (air replacement)

3. Air-compressor waste-heat recovery ventilation system (energy-saving auxiliary)

4. Auxiliary room mechanical ventilation system (power-distribution room, windowless rooms)

3.1 Process Fresh-Air Air-Conditioning System Description

• Zoning: The Preparation Room, Weighing Room, and Operation Room are each equipped with one independent 100 % fresh-air air-cooled direct-expansion air-handling unit — 3 units in total.

• System simplification advantage: No chilled-water host, chilled-water pumps, cooling-water pumps, cooling tower, plate heat exchanger, expansion tank, water separator/collector, water pipes, insulation, valves, or water-treatment equipment are required; the whole unit is an integrated assembly, greatly reducing investment in equipment, piping, and civil machine-room construction.

• Equipment installation location: All units are placed on the factory roof, with ducts routed downward into the interior.

• Air-supply form: Top supply air; Φ400 mm swirl diffusers are installed at the ends of the supply-air ducts, providing uniform, dead-angle-free airflow that does not disturb precision weighing operations.

• Operation mode: Cooling throughout the summer; in winter and spring/autumn transition seasons, started and stopped on demand according to workshop temperature.

3.2 Explosion-Proof Exhaust System Design

• Each process room is independently equipped with an explosion-proof axial exhaust fan that operates in linkage with the air-conditioning unit, maintaining slight positive pressure in the workshop and promptly exhausting process waste heat and exhaust gases.

• Fan control configuration: comes with local manual start/stop button; equipped with RS485 industrial communication interface; local / remote changeover switch provided, allowing free switching between the two control modes.

• Explosion-proof rating meets the explosion-safety standard for military production factory buildings.

IV. Detailed System Configuration by Zone

4.1 Preparation Room Configuration

• Air-conditioning host: 1 × 100 % fresh-air air-cooled direct-expansion unit, rated air volume 4,000 m³/h, matched to the 44.16 kW cooling load with reserved selection margin.

• Supply-air terminals: 3 × Φ400 mm swirl top-supply diffusers.

• Exhaust equipment: Independent explosion-proof axial exhaust fan, local / remote dual control, RS485 communication.

• Operation logic: Continuous fresh-air cooling and ventilation in summer; opened on demand in winter / transition seasons.

4.2 Weighing Room Configuration

• Air-conditioning host: 1 × 100 % fresh-air air-cooled direct-expansion unit, rated air volume 4,000 m³/h, matched to the 44.16 kW cooling load.

• Supply-air terminals: 3 × Φ400 mm swirl top-supply diffusers; gentle top-supply airflow avoids air-impact disturbance to weighing precision.

• Exhaust equipment: Independent explosion-proof axial fan with independent ductwork, eliminating cross-airflow with other rooms.

• Control requirements: Same as the Preparation Room; supports centralized remote monitoring and adjustment.

4.3 Operation Room Configuration

• Air-conditioning host: 1 × large-volume 100 % fresh-air air-cooled direct-expansion unit, rated air volume 30,000 m³/h, matched to the 336.86 kW total cooling load.

• Supply-air terminals: 16 × Φ400 mm swirl diffusers evenly arranged on the roof, full coverage of the large space.

• Exhaust system: Multi-point explosion-proof axial exhaust, balanced removal of waste heat and production exhaust gases from the large-area workshop.

• Applicable scenario: Core production area with many personnel and dense process equipment.

V. Scheme Comparison

Site Conditions

• No suitable host room, roof can accommodate many outdoor units → direct-expansion scheme may be preferred.

• Roof space tight, centralized cold source needed → water system preferred.

O&M Staffing

• No dedicated HVAC O&M staff → DX system is simple, DX AHU preferred.

• O&M team available, capable of water treatment and pipe maintenance → water system more suitable.

Initial Investment and Operating Cost

Project Scale

• Small-to-medium projects: DX AHU has an economic advantage — saves plant room, pumps, water-circuit construction; simple maintenance; very suitable for foreign-aid, workshop, and fresh-air unit projects.

• Large projects: air-cooled heat-pump water system — multiple-host group control, unit cooling cost decreases, standby possible.

Operation Mode

• Intermittent operation, much part-load time: DX variable-frequency advantage obvious — no pump no-load loss.

• Year-round continuous 24 h full-load operation: large water-system host at full load has high COP; long-term electricity cost lower.

5.2 Power-Distribution Room Mechanical Ventilation System

• Exhaust air volume: calculated separately based on the heat dissipation of the high/low-voltage switchgear and transformer equipment.

• Ventilation form: mechanical exhaust + exterior-wall natural make-up air louver.

• Function: continuously removes electrical-equipment heat, controls the power-distribution room temperature, and avoids high-temperature-induced electrical faults.

5.3 Windowless Auxiliary Room Exhaust System

• Windowless sealed storage and auxiliary rooms in the factory are uniformly fitted with ceiling exhaust fans, with a design air-change rate of 4–6 ACH; continuously replacing indoor moisture and odors, preventing mold and stale air in sealed spaces.

VI. Equipment Selection and System Advantage Analysis

6.1 Core Advantages of the 100 % Fresh-Air Air-Cooled Direct-Expansion Unit

• Extreme system simplicity: Eliminates the entire water-system equipment — no water-pipe leakage or freezing risk; civil works require no refrigeration plant room.

• 100 % fresh-air treatment: All outdoor fresh air, no return-air cross-contamination, suitable for military-industry clean-production requirements.

• Roof-mounted integrated installation: The whole unit is rainproof and sun-resistant, suitable for outdoor temperature-difference climates.

• Integrated assembly: The unit integrates the cooling section, filter section, and supply-air fan; factory-tested as a whole machine; on-site installation workload greatly reduced.

6.2 Unit Main Features — High-Purification Design

6.3 Unit Main Features — ④ Remote Monitoring, Convenient Maintenance

VII. Seasonal System Operating Conditions

7.1 Summer Operating Condition

The 100 % fresh-air direct-expansion units are fully operational, cooling and dehumidifying the high-temperature outdoor air; explosion-proof exhaust in each room runs simultaneously; air-compressor exhaust valves are fully open, and waste heat is discharged directly outdoors; power-distribution room and windowless room exhaust operates 24 hours a day, ensuring constant workshop temperature.

7.2 Winter Operating Condition

Air-conditioning units are started and stopped on demand for heating according to the measured workshop temperature; air-compressor exhaust valves are adjusted to recover equipment waste heat for supplementary heating, reducing the air-conditioning heating load; all ventilation and exhaust systems maintain basic air-change operation.

7.3 Spring / Autumn Transition-Season Condition

When outdoor temperature and humidity are suitable, only the exhaust system may be operated for ventilation and air replacement, with air-conditioning units started and stopped intermittently on demand; maximizing the use of outdoor fresh air to reduce annual energy consumption.

VIII. Scheme Summary

Serving clients creates value. Serving clients creates value. This scheme, targeting the precision-production process requirements of the military-industry factory building, adopts an integrated solution of zoned independent 100 % fresh-air air-cooled direct-expansion air conditioning + explosion-proof exhaust + air-compressor waste-heat recovery + auxiliary mechanical ventilation.

The scheme abandons the complex water system of the traditional chilled-water plant room: fewer pieces of equipment, simple installation, and low O&M cost. Through top-supply uniform airflow distribution and seasonal waste-heat regulation, energy-saving operation is achieved. All exhaust equipment supports local / remote dual-mode intelligent control, and the explosion-proof safety rating meets military-industry specifications.

The cooling-load calculation is based on building-envelope parameters and routine workshop heat sources; unit selection reserves ample safety margin, and can stably guarantee a year-round constant-temperature clean-production environment for the Preparation Room, Weighing Room, and Operation Room. The scheme balances safety, economy, and intelligence, and is fully adaptable to the long-term production-use needs of this military-industry factory building.