Ammonia Evaporator Used in Food Cold Storage Rooms

Ammonia Evaporator used in Food Cold Storage Rooms

The Ammonia Air Cooler serves as the core heat exchange equipment in food cold storage rooms utilizing ammonia refrigerant (R717). Its primary function is to transfer heat from within the cold storage room to the ammonia refrigeration system through forced convection. This maintains a stable, low-temperature storage environment, ensuring the freshness and safety of food products such as meat, fruits, vegetables, and dairy.

Core Components

Heat Exchange Coil (Coil)

1. Material: Primarily stainless steel 304/316L (corrosion-resistant to prevent ammonia-metal reactions that could contaminate food; easy to clean, meeting food hygiene standards);

2. Structure: Typically “finned coil” (increases heat exchange area, enhances cooling efficiency, and accommodates large-space heat dissipation requirements in cold rooms).

Forced-Air Fan

1. Type: Primarily low-noise axial fans (minimizes noise impact on food storage environment; delivers high airflow volume and stable pressure for uniform cold air distribution);

2. Protection: Motor features “IP54 or higher protection rating” (prevents condensation and moisture ingress from the refrigeration compartment, extending service life).

Defrost System

1. Necessity: In low-temperature environments, coil surfaces are prone to frost buildup (impeding heat exchange and reducing cooling efficiency), necessitating periodic defrosting;

2. Types:

- Electric defrost (suitable for small refrigeration compartments, simple control);

- Hot ammonia defrosting (suitable for large cold storage rooms, offering fast defrosting speed, energy efficiency, and preventing defrost water from contaminating food).

Housing and Protection

1. Material: The housing is made of stainless steel plate (corrosion-resistant, easy to clean, and compliant with food industry hygiene standards).

2. Sealing: Seams are strictly sealed (preventing cold air leakage, reducing energy consumption, and avoiding external moisture ingress that causes frost formation).

Typical Workflow in a Food Cold Storage Room

Taking a “large meat freezer (set temperature -20°C)” as an example, the operation process of an ammonia air cooler is as follows:

Startup Phase: The refrigeration system compressor activates, and low-temperature, low-pressure liquid ammonia passes through the throttle valve into the air cooler's finned coil.

Heat Exchange and Cooling: The axial fan of the air cooler activates, drawing warm air from the freezer (e.g., 25°C air upon entry) and directing it toward the low-temperature coil surface. The coil's liquid ammonia absorbs the air's heat, evaporating into gas while lowering the air temperature to -22°C to -25°C. This cooled air is then recirculated into the freezer, progressively reducing the internal temperature.

Frost Formation and Defrosting: After continuous operation (e.g., 8–12 hours), frost accumulates on the coil surface to a thickness of 5–10 mm, reducing heat transfer efficiency. The system automatically triggers “defrost mode”:

- For hot ammonia defrost: The fan shuts off, and high-temperature gaseous ammonia is introduced into the coils, rapidly melting the frost layer. The defrost water is drained via a channel (care must be taken to prevent dripping onto food, typically using a drip tray and drain pump);

- After defrosting completes, the system resumes normal refrigeration.

Temperature Maintenance: When the chamber temperature drops to -20°C, the thermostat triggers compressor frequency reduction or shutdown, while the evaporator fan operates at low speed. When the temperature rises to -18°C, the system restarts to maintain stable temperature.

Core Advantages of Ammonia Evaporators in Food Refrigeration

Compared to fluorocarbon evaporators (e.g., R404A, R507A), ammonia evaporators offer distinct benefits for food refrigeration:

Environmental Sustainability & Safety (Food-Grade Compatibility):

Ammonia (R717) is a natural refrigerant with ODP (Ozone Depletion Potential) = 0 and GWP (Global Warming Potential) = 0, producing no greenhouse effect. This aligns with the food industry's “green and eco-friendly” trend. Ammonia itself leaves no toxic residues (provided there are no system leaks), preventing food contamination and meeting food safety standards.

High Heat Exchange Efficiency, Low Energy Consumption:

Ammonia's latent heat (phase change heat) significantly exceeds that of fluorocarbons (e.g., ammonia's evaporation latent heat is approximately 1369 kJ/kg, R404A: approx. 207 kJ/kg). For equivalent cooling capacity, ammonia chillers require smaller coil areas and lower fan energy consumption. This makes them particularly suitable for high-load cooling demands in large food cold storage facilities (e.g., over 1000m²), reducing overall operational energy consumption by 20%–30%.

Superior Low-Temperature Adaptability:

Ammonia's low freezing point (-77.7°C) ensures stable operation in ultra-low-temperature storage environments (e.g., -40°C tuna freezers), whereas certain fluorocarbon refrigerants solidify below -30°C, rendering them unsuitable for ultra-low-temperature food preservation.

Low Maintenance Costs:

Ammonia refrigerant is cost-effective (approximately 1/5 the price of R404A), and the core components of ammonia chillers (stainless steel coils, corrosion-resistant fans) boast extended lifespans (typically 8–12 years), reducing long-term maintenance and consumable expenses for food enterprises.