HVAC for Warp Sizing Operations

Warp Sizing HVAC Requirements

Warp sizing applies protective coatings to warp yarns before weaving, requiring precise environmental control through three critical zones: size application, drying, and post-sizing conditioning. Each zone demands specific temperature and humidity conditions to ensure proper size adhesion, controlled moisture removal, and optimal yarn properties for weaving.

Sizing Process Environmental Zones

graph LR
    A[Raw Warp<br/>6-8% MC] --> B[Size Application<br/>70-80°F, 60-70% RH]
    B --> C[Size Box<br/>180-200°F Solution]
    C --> D[Pre-Drying<br/>160-180°F, 15-25% RH]
    D --> E[Main Drying<br/>200-250°F, 5-10% RH]
    E --> F[Cooling Zone<br/>75-85°F, 50-60% RH]
    F --> G[Sized Warp<br/>5-7% MC]

    H[Exhaust Air<br/>180-220°F] --> I[Heat Recovery]
    I --> B

Size Application Zone HVAC

The size application area requires stable conditions to maintain consistent viscosity and prevent premature drying:

Environmental Parameters:

Excessive air movement causes solution evaporation and viscosity changes. Supply air must be distributed through low-velocity diffusers positioned away from size boxes to prevent drafts across the wet yarn surface.

Sizing Dryer Ventilation

Drying chambers remove 20-40% of yarn weight as moisture, requiring substantial exhaust capacity and heat input. The moisture removal rate determines ventilation requirements:

$$\dot{m}_w = \frac{Y \cdot V \cdot \rho_y \cdot (MC_i - MC_f)}{100}$$

Where:

• $\dot{m}_w$ = moisture removal rate (lb/hr)
• $Y$ = yarn production rate (yd/min)
• $V$ = yarn linear density (yd/lb)⁻¹
• $\rho_y$ = yarn density factor
• $MC_i$ = initial moisture content (%)
• $MC_f$ = final moisture content (%)

Exhaust air requirements:

$$Q_e = \frac{\dot{m}w}{W{sa} - W_{ea}} \cdot 60$$

Where:

• $Q_e$ = exhaust air flow (cfm)
• $W_{sa}$ = supply air humidity ratio (lb/lb)
• $W_{ea}$ = exhaust air humidity ratio (lb/lb)

For a typical sizing line processing 500 yd/min of 30/1 cotton yarn with initial MC of 25% (wet sized) to final MC of 6%:

$$\dot{m}_w = \frac{500 \cdot 0.0333 \cdot 1.0 \cdot (25 - 6)}{100} = 3.17 \text{ lb/hr}$$

At supply air conditions of 200°F, 0.005 lb/lb and exhaust conditions of 0.035 lb/lb:

$$Q_e = \frac{3.17}{0.035 - 0.005} \cdot 60 = 6,340 \text{ cfm}$$

Drying Zone Configuration

Modern sizing machines employ multiple drying stages with progressive temperature increase:

Multi-Stage Drying Parameters:

High-velocity air impingement perpendicular to yarn sheet surface maximizes heat transfer. Supply air enters through nozzle arrays 2-4 inches from yarn, with exhaust collection on opposite side creating through-flow.

Heat Recovery Systems

Dryer exhaust at 180-220°F contains significant recoverable energy. ASHRAE Industrial Ventilation guidelines recommend heat recovery when exhaust temperatures exceed 150°F and runtime exceeds 4000 hours annually.

Heat Recovery Options:

1. Runaround Loops: Glycol coils in exhaust and makeup air streams, 50-60% effectiveness
2. Plate Heat Exchangers: Direct heat transfer, 60-70% effectiveness, requires filtration
3. Heat Pump Systems: Active heat transfer, 200-300% COP, highest capital cost

Recovered heat preheats makeup air or supplies space heating to adjacent preparation areas.

Post-Sizing Conditioning

After drying, sized warp must cool to handling temperature while regaining controlled moisture content for weaving flexibility:

$$MC_{target} = MC_{ambient} \pm 1%$$

Where ambient refers to weaving room conditions (65-75% RH). The cooling zone operates at:

• Temperature: 75-85°F
• Relative Humidity: 50-60%
• Residence Time: 30-60 seconds
• Air Velocity: 200-400 fpm

Supply air contacts yarn through perforated cylinders or cans, providing gentle cooling without thermal shock that could cause size cracking.

Ventilation Design Considerations

Makeup Air Calculation:

Total makeup air must balance:

• Dryer exhaust (primary load)
• Local exhaust at size boxes (fume control)
• Building infiltration
• General ventilation (8-12 ACH)

Air distribution strategy:

1. Deliver tempered makeup air to application zone
2. Allow air to flow toward drying zones
3. Exhaust from dryers and high-humidity areas
4. Maintain slight positive pressure in application zone

Filter requirements:

• Makeup air: MERV 8-10 (prevent size contamination)
• Recirculation air: MERV 13-14 (lint and fiber removal)
• Dryer exhaust: Washable screens (heavy lint loading)

Energy Optimization

Sizing operations consume 2000-4000 Btu per pound of yarn processed. Energy reduction strategies include:

1. Maximize heat recovery efficiency (target 60% minimum)
2. Optimize dryer temperature profiles (avoid excessive temperature)
3. Control makeup air based on humidity (reduce over-ventilation)
4. Use variable speed drives on dryer fans (match production rate)
5. Implement economizer cycles when outdoor conditions permit

These measures can reduce energy consumption by 25-40% compared to constant-volume, non-recovery systems while maintaining sizing quality and process reliability.

Reference: ASHRAE Handbook - HVAC Applications, Chapter 20: Textile Processing