Marine Laundry Facilities HVAC

Overview

Marine laundry facilities present unique HVAC challenges due to extreme heat and moisture generation in confined spaces. Shipboard laundries operate continuously with limited ventilation capacity, requiring specialized exhaust systems, aggressive moisture control, and heat recovery strategies to maintain acceptable conditions while minimizing energy consumption.

The primary HVAC concerns include managing humidity levels exceeding 70% RH, removing lint-laden exhaust air, recovering sensible and latent heat, providing adequate makeup air, and preventing condensation in adjacent compartments. Proper ventilation design prevents mold growth, protects electronic equipment, and maintains crew comfort in these high-load spaces.

Heat and Moisture Load Calculations

Sensible Heat from Equipment

Commercial washers and dryers generate substantial sensible heat loads that must be removed through ventilation:

$$Q_s = \sum_{i=1}^{n} \left( P_i \times \eta_i \times f_u \right)$$

Where:

• $Q_s$ = Total sensible heat gain (W)
• $P_i$ = Nameplate power of equipment $i$ (W)
• $\eta_i$ = Heat release efficiency (0.70-0.90 for washers, 0.40-0.60 for dryers)
• $f_u$ = Utilization factor (0.60-0.85 for marine laundries)
• $n$ = Number of equipment items

Moisture Generation Rate

Washing machines and dryers release significant moisture that must be exhausted to prevent condensation:

$$\dot{m}w = \sum{j=1}^{m} \left( C_j \times L_j \times E_j \times f_c \right)$$

Where:

• $\dot{m}_w$ = Total moisture generation rate (kg/h)
• $C_j$ = Machine capacity (kg dry laundry)
• $L_j$ = Moisture extraction per cycle (kg water/kg dry laundry)
• $E_j$ = Evaporation efficiency (0.85-0.95 for dryers)
• $f_c$ = Cycle frequency (cycles/h)
• $m$ = Number of moisture-generating equipment

Typical moisture extraction values:

• Washing machines: 0.5-0.8 kg water/kg dry laundry (residual moisture)
• Dryers: 0.4-0.7 kg water/kg dry laundry (evaporated to exhaust)

Required Exhaust Airflow

The exhaust airflow must remove both sensible heat and latent moisture:

$$\dot{V}{exh} = \max \left( \frac{Q_s}{\rho c_p \Delta T}, \frac{\dot{m}w}{\rho (\omega{exh} - \omega{supply})} \right)$$

Where:

• $\dot{V}_{exh}$ = Required exhaust airflow (m³/s)
• $\rho$ = Air density (kg/m³)
• $c_p$ = Specific heat of air (1.006 kJ/kg·K)
• $\Delta T$ = Temperature difference between exhaust and supply (K)
• $\omega_{exh}$ = Humidity ratio of exhaust air (kg water/kg dry air)
• $\omega_{supply}$ = Humidity ratio of supply air (kg water/kg dry air)

Exhaust Requirements by Equipment

Notes:

• Direct connection mandatory for dryers per NFPA 120
• Duct velocity must prevent lint settling (minimum 1500 fpm for dryer exhaust)
• Metal ducts only; no flexible ducting allowed for dryer exhaust

Marine Laundry Ventilation System

graph TB
    subgraph "Marine Laundry Facility"
        A[Supply Air<br/>Filtered, Conditioned<br/>26°C, 50% RH] --> B[Laundry Space<br/>28-32°C, 65-75% RH]

        B --> C[Washer-Extractors<br/>Hot Water 60-85°C<br/>Steam Release]
        B --> D[Tumble Dryers<br/>Exhaust Temp 65-80°C<br/>High Moisture]
        B --> E[Ironing Stations<br/>Steam 100°C<br/>Spot Exhaust]

        C --> F[General Exhaust<br/>Lower Level Capture<br/>400-600 CFM]
        D --> G[Dedicated Dryer Exhaust<br/>Direct Connection<br/>150-400 CFM per unit]
        E --> H[Steam Hood Exhaust<br/>Canopy or Slot<br/>100-150 CFM per station]

        F --> I[Lint Filter 1<br/>Mesh Screen<br/>25-50 micron]
        G --> J[Lint Filter 2<br/>High Efficiency<br/>10-25 micron]
        H --> I

        I --> K[Heat Recovery<br/>Run-Around Loop<br/>40-60% Effectiveness]
        J --> K

        K --> L[Main Exhaust Fan<br/>Centrifugal<br/>Spark Resistant]

        L --> M[Overboard Discharge<br/>Hull Penetration<br/>Weather Protection]

        N[Makeup Air Unit<br/>Tempered<br/>Heat Recovery Preheated] --> A
        K -.Heat Transfer.-> N

        O[Condensate Collection<br/>Floor Drains<br/>Bilge System] -.Moisture Removal.-> B
    end

    style D fill:#ff9999
    style G fill:#ffcc99
    style J fill:#99ccff
    style K fill:#99ff99
    style M fill:#cccccc

Lint Filtration Requirements

Filtration Stages

Primary lint separation:

• Mesh screen filters: 25-50 micron capture
• Located immediately downstream of dryer exhaust
• Cleanable design with access doors
• Inspection weekly, cleaning as needed

Secondary filtration:

• High-efficiency lint filters: 10-25 micron
• Prevents lint accumulation in heat recovery devices
• Differential pressure monitoring (replace at 1.5" w.g.)
• Critical for preventing fire hazards

Filter specifications for marine service:

• Corrosion-resistant materials (316 stainless steel)
• Vibration-resistant mounting
• Tool-free access for cleaning
• Pressure drop monitoring with alarm at 2.0" w.g.

Lint Removal System Design

Heat Recovery Strategies

Run-Around Loop Systems

Run-around loop heat recovery systems effectively recover 40-60% of exhaust heat without cross-contamination:

$$\epsilon_{ral} = \frac{\dot{Q}{recovered}}{\dot{Q}{available}} = \frac{\dot{m}{min} c_p (T{exh,in} - T_{exh,out})}{\dot{m}{min} c_p (T{exh,in} - T_{supply,in})}$$

Where:

• $\epsilon_{ral}$ = Run-around loop effectiveness (0.40-0.60)
• $\dot{Q}_{recovered}$ = Recovered heat rate (W)
• $\dot{Q}_{available}$ = Available exhaust heat (W)
• $\dot{m}_{min}$ = Minimum mass flow rate (kg/s)
• $T_{exh,in}$ = Exhaust air entering temperature (°C)
• $T_{exh,out}$ = Exhaust air leaving temperature (°C)
• $T_{supply,in}$ = Supply air entering temperature (°C)

Marine laundry heat recovery advantages:

• No cross-contamination between lint-laden exhaust and clean supply
• Coils can be located remotely (suitable for ship compartment constraints)
• Glycol solution prevents freezing (irrelevant for marine but provides corrosion protection)
• Individual coil cleaning possible without system shutdown

Heat Recovery Performance

Note: Savings assume 16 hours/day operation, 300 days/year for cruise ship laundry.

Humidity Control Strategies

Ventilation-Based Moisture Removal

Maintain laundry space humidity below 75% RH through adequate exhaust:

$$RH_{space} = \frac{\omega_{space}}{\omega_{sat}(T_{space})} \times 100%$$

Target conditions:

• Laundry space: 28-32°C, 65-75% RH maximum
• Adjacent corridors: 24-26°C, 55-65% RH maximum
• Humidity differential: Maintain negative pressure to prevent migration

Dehumidification Requirements

Supplemental dehumidification may be required when:

• Laundry operates >16 hours/day
• Ambient conditions exceed 30°C, 70% RH
• Makeup air quantity is limited by ship ventilation capacity

Desiccant dehumidification:

• Effective for high-temperature, high-humidity exhaust
• Can achieve 40-50°C dew point reduction
• Regeneration heat available from dryer exhaust

Design Standards and References

Applicable marine standards:

• IMO SOLAS Chapter II-2: Fire safety, lint control
• ANSI/ASHRAE 62.1: Ventilation for acceptable air quality
• NFPA 120: Standard for Fire Prevention and Control in Coal Mines (dryer exhaust provisions applicable)
• IEEE 45: Recommended Practice for Electrical Installations on Shipboard
• Classification society rules (ABS, DNV-GL, Lloyd’s): Ventilation and fire safety

Design exhaust rates:

• Minimum 25 ACH for laundry spaces (per classification society rules)
• Dryer exhaust per manufacturer specifications (typically 150-400 CFM per unit)
• General exhaust sufficient to maintain <75% RH

Safety considerations:

• All electrical equipment rated for high-humidity service (IP65 minimum)
• Lint filters inspected and cleaned weekly
• Dryer exhaust ducts inspected monthly for lint accumulation
• Fire dampers not permitted in dryer exhaust (per NFPA 120)
• Emergency ventilation override for fire conditions

Condensation Prevention

Critical Control Measures

Duct insulation:

• All exhaust ducts: 2" (50 mm) closed-cell insulation minimum
• Vapor barrier required on all cold surfaces
• Particular attention to hull penetrations

Pressure relationships:

• Laundry space: -5 to -10 Pa relative to corridors
• Prevents moisture migration to accommodations
• Exhaust 10-15% greater than supply

Surface temperature control:

• All surfaces maintained >5°C above dew point
• Insulation on cold water piping
• Dehumidification in equipment rooms

Related Topics:

• Galley and Laundry HVAC
• Commercial Kitchen
• Dishwashing Area
• Ships and Marine HVAC