ZNX Counterflow Evaporative Condenser

The ZNX counterflow evaporative condenser is a highly efficient heat rejection device designed for refrigeration systems in industries like food processing, chemicals, pharmaceuticals, and industrial refrigeration. It condenses refrigerants, such as ammonia or Freon, from gas to liquid by transferring heat to the atmosphere. Unlike the ZHX combined flow model, the ZNX uses a counterflow design and eliminates PVC fill, resulting in a compact structure with unique benefits for specific applications.

Working Principle
The ZNX operates on a counterflow principle, where air and water flow in opposite directions to maximize heat transfer. Here’s how it works:

– Refrigerant Flow: Hot, gaseous refrigerant enters the condensing coil, releases heat through the coil walls, and condenses into a liquid. The coil serves as the primary heat exchange surface, keeping the refrigerant in a closed loop.
– Air and Water Interaction:
– Fresh air enters through a bottom air inlet, typically drawn by axial or centrifugal fans, and flows upward.
– Spray water is distributed over the coil, flowing downward in the opposite direction of the air. As the water contacts the warm coil, it evaporates, absorbing heat from the refrigerant.
– The evaporating water mixes with the air, forming saturated hot vapor, which carries the heat away.
– Heat Exhaust and Water Recovery:
– Fans expel the hot, humid air into the atmosphere.
– A specialized drift eliminator captures water droplets from the exhaust air, minimizing water loss (typically 0.001–0.002% of circulating water flow).
– Collected water drains into a basin at the base for reuse in spraying, ensuring low water consumption.
– No-Fill Design:
– Unlike the ZHX model, which uses PVC fill to enhance heat transfer, the ZNX has no fill media.
– This allows for a larger coil, increasing the heat rejection area within a smaller footprint, improving efficiency, and simplifying maintenance.

Advantages
The ZNX’s counterflow, no-fill design offers several practical benefits:

1. Compact and Space-Saving:
   – Without PVC fill, the ZNX accommodates a larger coil without increasing the unit’s size, reducing its footprint and height.
   – Its compact design lowers transportation and installation costs, ideal for facilities with limited space.
   2. Suited for Harsh Environments:
   – The enclosed structure prevents sand, dust, or debris from entering, making it perfect for dusty or industrial settings, such as desert-based chemical plants.
   – No fill media reduces fouling risks, ensuring consistent performance in challenging conditions.
   3. High-Temperature Fluid Compatibility:
   – Traditional evaporative condensers with PVC fill can suffer from distortion under hot spray water. The ZNX avoids this, handling high-temperature refrigerants or fluids effectively.
   – Durable materials, like stainless or galvanized steel for coils and casings, resist heat and corrosion.
   4. Freeze Resistance:
   – Fill media can slow water flow, increasing freezing risks in cold climates. The ZNX’s no-fill design ensures unobstructed water flow, minimizing ice formation.
   – This makes it suitable for cold environments, such as outdoor cold storage or skating rinks.
   5. Energy and Water Efficiency:
   – The larger coil and counterflow design achieve condensing temperatures close to the wet bulb temperature (5–7°C approach), reducing compressor energy use.
   – Drift eliminators and water recirculation keep water loss low, critical for water-scarce regions.

Comparison with ZHX Combined Flow Evaporative Condenser
The ZNX differs from the ZHX combined flow evaporative condenser in several key ways:

– Flow Configuration:
– ZNX (Counterflow): Air flows upward, and water flows downward, optimizing heat transfer in a compact design.
– ZHX (Combined Flow): Air and water flow in the same direction (parallel), with PVC fill enhancing heat transfer via sensible heat conduction.
– Fill Media:
– ZNX: No PVC fill, relying on the coil for heat exchange, which simplifies maintenance and suits harsh environments.
– ZHX: Uses PVC fill to increase water-air contact, boosting efficiency but requiring fill maintenance and being less suitable for high temperatures or freezing conditions.
– Applications:
– ZNX: Ideal for dusty, high-temperature, or cold environments and space-constrained installations, like chemical plants or cold storage.
– ZHX: Better for standard conditions requiring high heat transfer, such as food processing or pharmaceutical cooling.
– Footprint and Maintenance:
– ZNX: Smaller footprint and lower maintenance due to no fill, though slightly less efficient than fill-based systems.
– ZHX: Larger footprint but offers superior heat exchange in humid climates.
– Environmental Suitability:
– ZNX: Excels in dusty or cold settings due to its enclosed, freeze-resistant design.
– ZHX: Optimized for humid climates where evaporative cooling is most effective.

Comparison with BNX Closed Circuit Cooling Tower
The ZNX also contrasts with the BNX closed circuit cooling tower from your earlier query:

– Purpose:
– ZNX: Condenses refrigerants directly for refrigeration systems.
– BNX: Cools a process fluid (e.g., water, glycol) in a closed loop for general process cooling, like HVAC or data centers.
– Design:
– ZNX: Counterflow, no-fill design with a coil for refrigerant, where spray water contacts the coil to drive evaporation.
– BNX: Counterflow, no-fill design with a coil for process fluid, kept separate from spray water to avoid contamination.
– Applications:
– ZNX: Focused on refrigeration, such as cold storage or chemical plants.
– BNX: Broader applications, including industrial processes and HVAC.
– Maintenance:
– ZNX: Simplified by no fill but requires refrigerant handling and water treatment.
– BNX: Lower maintenance for the process fluid but still needs water treatment for spray water.

Model Selection Process
The model selection process ensures the ZNX meets the system’s heat rejection needs. Here’s a clear breakdown, using the ammonia refrigeration example:

1. Determine Total Heat Rejection Capacity:
   – Calculate the total heat to be rejected, including latent heat (from refrigerant condensation) and sensible heat (from cooling the refrigerant).
   – For refrigeration: Total Heat Rejection = Compressor refrigerating capacity + Compressor shaft power.
   – Example: Total Heat Rejection = 1200 kW.
   2. Specify Design Conditions:
   – Define the condensing medium (e.g., ammonia, R717), condensing temperature (e.g., 36°C), and wet bulb temperature (e.g., 28°C).
   3. Find the Correction Coefficient (R):
   – Use a manufacturer-provided correction coefficient table for the refrigerant (e.g., R717) based on condensing and wet bulb temperatures.
   – Example: For 36°C condensing temperature and 28°C wet bulb temperature, R = 1.35.
   4. Calculate Corrected Heat Rejection Capacity:
   – Multiply the total heat rejection by the correction coefficient.
   – Example: 1200 kW × 1.35 = 1620 kW.
   5. Select the Model:
   – Choose a ZNX model with a rated heat rejection capacity equal to or greater than the corrected capacity.
   – Example: Select ZNX-1680, the smallest model with a capacity exceeding 1620 kW (based on the provided model table).

Notes:
– Rated capacities in datasheets are based on standard conditions (condensing temperature = 37°C, wet bulb temperature = 26°C).
– Operating weight includes the equipment, refrigerant, and water in the basin.
– Customization is available for non-standard requirements.
– Parameters are for reference; confirm with the manufacturer at purchase.
– Coil connection dimensions are approximate and not suitable for piping prefabrication.

Applications
The ZNX is versatile, serving industries similar to the ZHX but excelling in challenging environments:

– Food Industry: Cold storage, poultry slaughtering, fish processing, ice cream production, beer and beverage cooling, industrial ice, and skating rinks.
– Chemical and Pharmaceutical: Methanol/syngas cooling, ammonia compressor inter-cooling, distillation condensation, and gas cooling for natural gas or coke gas processes.
– Industrial Refrigeration: Large-scale refrigeration for warehouses or manufacturing.
– Specialized Environments: Dusty regions (e.g., desert chemical plants), high-temperature processes (e.g., turbine steam condensation), and cold climates (e.g., outdoor cold storage).

Potential Specifications
While specific ZNX-1680 details depend on the manufacturer, typical counterflow evaporative condenser specs include:

– Heat Rejection Capacity: 500 kW to 5 MW.
– Refrigerant: Ammonia (R717), Freon (R134a, R410A), or others.
– Flow Rates: Spray water (50–1000 m³/h, recirculated), air (10,000–500,000 m³/h).
– Fan Power: 5–75 kW, often with variable-frequency drives.
– Materials: Coils (stainless or galvanized steel), casing (fiberglass-reinforced plastic or stainless steel).
– Drift Loss: ≤0.002% of circulating water flow.
– Footprint: 2–10 m² per MW of cooling capacity.
– Noise Levels: 60–85 dB(A) at 10 meters, with low-noise options.

Consult the manufacturer’s datasheet for exact specifications.

Environmental and Economic Benefits
– Environmental:
– Saves water through drift eliminators and recirculation, ideal for water-scarce areas.
– Reduces compressor energy use with lower condensing temperatures, cutting greenhouse gas emissions.
– Prevents ammonia venting, minimizing pollution.
– Economic:
– Lowers operating costs via reduced energy, water, and maintenance needs.
– Decreases installation and transport costs due to compact design.
– Extends equipment life with durable, no-fill construction.

Limitations and Considerations
– Initial costs are higher than air-cooled condensers, though long-term savings offset this.
– Spray water requires treatment to prevent scaling or biological growth.
– Performance is best in humid climates and may decrease in very dry conditions.
– Ammonia handling requires care due to toxicity and flammability risks.

Clarification on Example Discrepancy
The provided text includes two ammonia refrigeration examples with a minor error:
– ZNX Example: Selects ZNX-1680 (>1620 kW) for a 1200 kW system with a 1.35 correction coefficient.
– ZHX Example: Selects ZHX-1765 (>1620 kW) for the same conditions but mistakenly states “1200 kW x 1.35 = 1200 kW” (should be 1620 kW).

Correction: The ZHX example calculation should be:
– 1200 kW × 1.35 = 1620 kW, leading to the selection of ZHX-1765.

The model difference (ZNX-1680 vs. ZHX-1765) likely reflects distinct model tables or capacities for the ZNX and ZHX series.

Conclusion
The ZNX counterflow evaporative condenser is a compact, efficient solution for refrigeration systems, particularly in dusty, high-temperature, or cold environments. Its no-fill design maximizes coil heat rejection, reduces maintenance, and saves space, making it ideal for food processing, chemical plants, and cold storage. Compared to the ZHX combined flow model, the ZNX excels in harsh conditions, while the ZHX offers better heat transfer in standard settings. Unlike the BNX closed circuit cooling tower, which cools process fluids, the ZNX is tailored for refrigerant condensation.