Water Chiller selection - HVAC/R engineering | Eng-Tips

Hi all:
i am designing HVAC system for a 700 RT pharmaceutical factory. But I don't know which selection of Chiller will be optimize the energy of the factory. I am thinking about two option:
1. Select 2 Chiller with 800-900 RT to run alternately.
2. Select 2 Chiller with 500 RT to run at the same time and 1 back up Chiller.
My Water Chiller has screw compressor. Can i have your advices. Choose two chillers with different capacities, such as 300 tons and 600 tons. Switching between these different-sized chillers is more efficient than using two of the same size at a lower load. During low load periods, the smaller chiller can operate at full capacity, resulting in maximum efficiency. The building's full capacity reaches about 1% of the time in a year.

1. Introduction

Anodizing is an electrochemical process that generates significant heat due to high current passing through the electrolyte. Maintaining a stable bath temperature (18-22°C for sulfuric acid anodizing) is critical for: - Consistent anodic coating quality - Reduced chemical consumption and evaporation losses - Optimized power efficiency and reduced rectifier strain In India, where ambient temperatures can exceed 40°C in summer, an efficient cooling system is necessary. This guide provides a detailed method for calculating chiller capacity and compares air-cooled vs. water-cooled chillers for anodizing plants operating in the Indian climate.

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2. Why is a Chiller Essential for Anodizing?

Anodizing requires precise temperature control because:

1. Overheating causes poor anodizing quality – Soft, powdery, or uneven anodic layers form when the electrolyte temperature is too high.

2. High bath temperature increases acid evaporation – This leads to frequent acid replenishment and higher costs.

3. Electrolyte conductivity decreases at higher temperatures – This forces the rectifier to draw more current, increasing energy consumption.

4. Process inefficiencies increase at higher temperatures – Cooling ensures faster cycle times, lower rejection rates, and higher productivity.

3. Chiller Capacity Calculation for Anodizing (India-Specific Example)

⚠ Important Note: This calculation is an example. Always calculate based on your anodizing plant's specific production capacity and local climate conditions.

Step 1: Estimate Heat Load from the Rectifier

The rectifier is the primary source of heat in an anodizing bath. The heat load can be calculated using: Q = V × I × E

Where: - Q = Heat generated (Watts) - V = Voltage (Assume 18V for sulfuric acid anodizing) - I = Current (25,000A) - E = Efficiency factor (0.85 for anodizing)

Q = 18V × 25,000A × 0.85 = 382,500W = 382.5 kW

Step 2: Convert kW to Tons of Refrigeration (TR)

1 Ton of Refrigeration (TR) = 3.517 kW 382.5 ÷ 3.517 = 109 TR

Step 3: Consider Additional Heat Loads

In hot and humid climates like India, additional factors must be considered: - Ambient Heat Gain (10-20%) – Due to high surrounding temperatures (up to 45°C in summer). - Heat from Pumps & Agitation (5-10%) – Mixing and circulation generate extra heat. - Safety Factor (10-15%) – To accommodate peak production loads. Adding a 25% safety margin for Indian climate conditions: 109 TR × 1.25 = 136 TR

Final Chiller Requirement

A 130-140 TR chiller is recommended for a 70,000-liter anodizing tank with a 25,000A rectifier in Indian conditions.