Marine HVAC System Design

Understanding Marine HVAC System Design: Principles and Applications

Marine HVAC (Heating, Ventilation, and Air Conditioning) system design represents one of the most challenging disciplines within marine engineering. Unlike their terrestrial counterparts, shipboard HVAC systems must operate reliably in constantly changing environmental conditions while contending with space constraints, corrosive salt air, vessel movement, and stringent safety regulations. For vessels operating in Atlantic Canadian waters, where temperatures can range from -25°C in winter to 30°C in summer, these systems must be exceptionally robust and versatile.

The maritime industry in Nova Scotia and throughout the Maritimes relies heavily on properly designed HVAC systems to ensure crew comfort, protect sensitive cargo, maintain equipment operating temperatures, and meet regulatory requirements. Whether designing systems for fishing vessels operating on the Grand Banks, ferries serving coastal communities, or offshore support vessels working in the North Atlantic, understanding the fundamental principles and best practices of marine HVAC design is essential for project success.

Key Components of Marine HVAC Systems

Marine HVAC systems comprise several integrated subsystems that work together to maintain optimal environmental conditions throughout a vessel. Each component must be carefully selected and specified to withstand the unique challenges of the marine environment.

Air Handling Units

Central air handling units (AHUs) form the heart of most marine HVAC installations. These units typically include supply and return fans, heating and cooling coils, filters, and damper assemblies. Marine-grade AHUs differ significantly from commercial units in several critical aspects:

• Corrosion-resistant construction: Housings are typically fabricated from marine-grade aluminium or stainless steel (316L grade minimum) with special coatings to resist salt air corrosion

• Vibration isolation: Heavy-duty isolation mounts and flexible duct connections accommodate vessel movement and reduce noise transmission

• Compact footprint: Space-efficient designs maximise capacity within limited machinery space allocations

• Drainage provisions: Enhanced condensate management systems handle the rolling and pitching motion of vessels

Chilled Water Systems

Most medium to large vessels utilise chilled water distribution systems for cooling. Typical design parameters include chilled water supply temperatures of 6-7°C with a 5°C temperature differential. System capacity calculations must account for:

• Solar heat gain through hull and superstructure (often 150-250 W/m² for exposed surfaces)

• Internal heat loads from equipment, lighting, and personnel

• Ventilation requirements and outside air loads

• Transmission losses through insulated boundaries

Chillers for marine applications typically employ scroll or screw compressors with R-410A or R-134a refrigerants. For vessels operating in Atlantic Canada, many operators specify systems with seawater-cooled condensers, taking advantage of relatively cool ocean temperatures (typically 2-18°C seasonally) to improve system efficiency.

Heating Systems

Vessels operating in Maritime waters require robust heating capabilities. Common heating methods include:

• Steam heating coils: Utilising waste heat from main engines or auxiliary boilers

• Hot water systems: Circulating water at 60-80°C through fan coil units

• Electric heating: Direct expansion units with electric resistance heating elements

• Thermal oil systems: For high-temperature applications or hazardous area classifications

Heat load calculations for vessels operating in Nova Scotia waters should account for design exterior temperatures of -25°C to -30°C, with wind chill factors significantly increasing heat loss through exposed surfaces.

Design Considerations for Atlantic Canadian Operations

Vessels operating in Atlantic Canadian waters face unique environmental challenges that must be addressed during the HVAC design phase. The combination of cold temperatures, high humidity, salt-laden air, and frequently harsh sea conditions demands careful attention to system specification and installation practices.

Cold Weather Operations

Winter operations in the Gulf of St. Lawrence, Bay of Fundy, and offshore Nova Scotia require HVAC systems capable of maintaining comfortable interior temperatures while exterior conditions may reach -30°C with substantial wind speeds. Key design considerations include:

• Freeze protection: All water-based systems must incorporate glycol solutions (typically 35-40% propylene glycol) or reliable drain-down provisions

• Air intake positioning: Fresh air intakes should be located to minimise ice accumulation and sea spray ingestion

• Defrost capabilities: Heat exchangers and coils exposed to cold air streams require automatic or manual defrost cycles

• Condensation management: Interior humidity control prevents condensation on cold surfaces, which can lead to corrosion and mould growth

Humidity and Corrosion Control

The Maritime climate presents persistent humidity challenges. Relative humidity levels commonly exceed 80% during fog events, which occur on more than 100 days annually in some coastal Nova Scotia locations. HVAC systems must address:

• Dehumidification to maintain interior relative humidity between 40-60%

• Positive pressurisation of accommodation spaces to prevent salt air infiltration

• Corrosion-resistant materials throughout all system components

• Regular maintenance provisions for filter replacement and coil cleaning

Regulatory Compliance and Classification Requirements

Marine HVAC systems must comply with numerous international and Canadian regulations. Understanding these requirements early in the design process prevents costly modifications and delays during vessel construction or refit.

Classification Society Rules

Major classification societies including Lloyd's Register, DNV, Bureau Veritas, and the American Bureau of Shipping publish detailed requirements for marine HVAC installations. Common requirements include:

• Minimum ventilation rates of 25-30 m³/h per person in accommodation spaces

• Temperature maintenance capabilities (typically 22°C ± 2°C in summer and 20°C ± 2°C in winter)

• Fire damper installations at all HVAC penetrations through fire-rated divisions

• Emergency shutdown provisions for ventilation systems serving machinery spaces

• Smoke detection and extraction capabilities in designated areas

SOLAS and Transport Canada Requirements

The International Convention for the Safety of Life at Sea (SOLAS) establishes baseline requirements for ventilation and fire safety that apply to Canadian-flagged vessels engaged in international voyages. Transport Canada's Marine Safety Directorate enforces these requirements and may impose additional standards for vessels operating in Canadian waters.

Critical SOLAS requirements affecting HVAC design include:

• Chapter II-2 fire protection requirements for ductwork materials and fire damper installations

• Ventilation system arrangements that prevent smoke spread between fire zones

• Machinery space ventilation calculations based on engine heat rejection

• Emergency ventilation shutdown capabilities from the bridge or fire control station

WorkSafeBC and Provincial Regulations

For vessels operating in Atlantic Canadian ports, provincial workplace health and safety regulations may apply to interior air quality standards during cargo operations, repair activities, or while alongside. Nova Scotia's Workplace Health and Safety Regulations specify minimum ventilation requirements and exposure limits that should inform HVAC system capacity calculations.

System Sizing and Load Calculations

Accurate load calculations form the foundation of successful marine HVAC design. Unlike building applications where steady-state conditions can be assumed, marine systems must accommodate constantly varying conditions as vessels move between operating areas and weather conditions change.

Cooling Load Components

Total cooling load calculations must account for multiple heat sources:

• Solar transmission: Calculate based on vessel orientation, glass area, and shading. South-facing surfaces may experience solar loads of 200-350 W/m² during summer months

• Conduction through boundaries: Apply appropriate U-values for insulated steel construction (typically 0.3-0.5 W/m²K for well-insulated accommodation boundaries)

• Internal gains: Personnel loads of 75-120 W sensible and 55-75 W latent per person; lighting at 10-20 W/m²; equipment loads as specified

• Ventilation loads: Based on required outside air quantities and design ambient conditions

Heating Load Components

Winter heating calculations for vessels operating in Atlantic Canadian waters should use conservative design temperatures. Recommended practice includes:

• Design exterior temperature of -25°C to -30°C for offshore Nova Scotia operations

• Wind speed assumptions of 15-20 m/s for exposed surface calculations

• Interior design temperatures of 20-22°C for accommodation spaces, 16-18°C for working spaces

• Safety factors of 15-20% to account for aging system performance and unexpected heat losses

Diversity Factors and System Efficiency

Applying appropriate diversity factors prevents oversizing while ensuring adequate capacity. Typical diversity factors for marine applications include:

• 0.85-0.90 for accommodation spaces (not all cabins occupied simultaneously at peak load)

• 0.75-0.85 for lighting and equipment loads

• 1.0 for ventilation loads (must meet minimum requirements continuously)

Ductwork Design and Distribution

Marine ductwork design requires careful attention to space constraints, noise control, and fire safety requirements. The limited overhead clearances typical of vessel construction demand creative solutions to maintain adequate airflow while preserving headroom and access for maintenance.

Duct Sizing and Velocity Limits

Recommended air velocities for marine applications balance noise control against space efficiency:

• Main supply ducts: 8-12 m/s maximum velocity

• Branch ducts to accommodation: 5-7 m/s to minimise noise generation

• Return air ducts: 6-8 m/s maximum

• Fresh air intakes: 4-6 m/s to prevent water ingestion during heavy weather

Material Selection

Ductwork materials must resist corrosion while meeting fire safety requirements:

• Galvanised steel: Suitable for interior accommodation areas with proper sealing

• Stainless steel (304 or 316): Required for machinery spaces, galleys, and areas with high humidity or chemical exposure

• Aluminium: Lightweight option for non-fire-rated applications; requires careful attention to galvanic isolation

• Fire-rated insulation: Mineral wool insulation meeting IMO Resolution A.653(16) requirements

Energy Efficiency and Sustainable Design

Rising fuel costs and environmental regulations increasingly drive demand for energy-efficient marine HVAC systems. Modern designs incorporate numerous features to reduce energy consumption while maintaining performance.

Heat Recovery Systems

Waste heat recovery from engine exhaust or jacket water cooling systems can significantly reduce heating energy requirements. For vessels operating in Atlantic Canadian waters where heating loads predominate for much of the year, heat recovery systems can provide payback periods of 2-4 years. Common configurations include:

• Exhaust gas economisers generating hot water or steam

• Jacket water heat exchangers for accommodation heating

• Charge air cooler heat recovery for domestic water heating

Variable Speed Drives

Installing variable frequency drives (VFDs) on supply and return fans, chilled water pumps, and condenser water pumps can reduce HVAC electrical consumption by 30-50% compared to constant-speed systems. The additional capital cost typically pays back within 18-36 months for vessels with high operating hours.

Smart Control Systems

Modern building automation systems adapted for marine use provide sophisticated control capabilities including demand-controlled ventilation, optimal start/stop algorithms, and integration with vessel management systems. These systems enable remote monitoring and diagnostics, reducing maintenance costs and improving system reliability.

Partner with Sangster Engineering Ltd. for Your Marine HVAC Projects

Designing effective marine HVAC systems requires deep understanding of maritime operating conditions, regulatory requirements, and the unique constraints of shipboard installations. At Sangster Engineering Ltd., our team brings decades of experience in marine engineering projects throughout Atlantic Canada and beyond.

From fishing vessels and coastal ferries to offshore support vessels and research ships, we provide comprehensive HVAC system design services including load calculations, equipment specifications, ductwork layouts, control system integration, and regulatory compliance documentation. Our familiarity with Nova Scotia's maritime industry and the specific challenges of Atlantic Canadian operations ensures practical, cost-effective solutions that perform reliably in demanding conditions.

Contact Sangster Engineering Ltd. today to discuss your marine HVAC design requirements. Whether you're building new vessels, refitting existing systems, or troubleshooting performance issues, our professional engineering team is ready to help you achieve optimal results for your maritime projects.

Partner with Sangster Engineering

At Sangster Engineering Ltd. in Amherst, Nova Scotia, we bring decades of engineering experience to every project. Serving clients across Atlantic Canada and beyond.

Contact us today to discuss your engineering needs.