Water / Glycol Evaporators for Commercial and Industrial Cold Rooms

Water / Glycol Evaporators for Commercial and Industrial Cold Rooms

Water / Glycol evaporators are suitable room coolers that can be applied to commercial and industrial cold rooms, playing a critical role in maintaining stable low temperatures (typically -40°C to 10°C) for food storage, pharmaceutical preservation, industrial process cooling, and other applications.

Cold rooms have strict demands: stable low temperatures, uniform cooling, frost resistance, and compatibility with large cooling loads (e.g., rapid cooling of fresh produce or maintaining low temperatures for high-volume frozen goods). Water/glycol evaporators meet these needs through two core features:

Antifreeze Performance: Glycol (usually ethylene glycol or propylene glycol) is mixed with water in a specific ratio (e.g., 30%–60% glycol) to lower the solution’s freezing point (e.g., 40% propylene glycol solution freezes at ~-25°C, 60% ethylene glycol at ~-45°C). This prevents the evaporator from freezing and cracking in cold room environments (a risk with pure water evaporators).

Efficient Heat Transfer: The evaporator acts as a "heat exchanger" between the cold water/glycol solution (secondary refrigerant) and the cold room air. It efficiently absorbs heat from the room air, ensuring rapid temperature reduction and stable maintenance—critical for preserving the quality of stored items (e.g., preventing food spoilage or pharmaceutical degradation).

Water/glycol evaporators do not work independently; they are part of a two-stage refrigeration system (primary refrigerant + secondary refrigerant). The entire cooling process is as follows:

Primary Refrigeration Cycle (Cooling the Solution): In the cold room’s outdoor condensing unit, the primary refrigerant (e.g., R410A, R290, environmentally friendly low-GWP refrigerants) undergoes compression (by a compressor) and condensation (releasing heat to the atmosphere). It then enters a shell-and-tube heat exchanger (or plate heat exchanger), where it absorbs heat from the water/glycol solution (cooling the solution to the target temperature, e.g., -10°C to -20°C).

Secondary Cycle (Cooling the Cold Room Air): The cooled water/glycol solution is pumped into the water/glycol evaporator (installed inside the cold room). The evaporator is equipped with fins (aluminum or copper) to expand the heat exchange area. A fan inside the evaporator forces cold room air to flow through the finned tubes:

Heat from the air is transferred to the cold water/glycol solution inside the evaporator tubes (via conduction and convection).

The cooled air is blown back into the cold room, lowering the overall temperature.

The warmed water/glycol solution returns to the shell-and-tube heat exchanger to be cooled again, repeating the cycle.

Defrosting (Critical for Low-Temperature Cold Rooms): In cold rooms below 0°C (e.g., frozen food storage at -18°C), moisture in the air will condense and freeze on the evaporator fins, forming frost. Frost blocks air flow and reduces heat exchange efficiency, so water/glycol evaporators are often equipped with defrost systems:

Hot gas defrost: Uses high-temperature refrigerant gas from the compressor to melt frost (fast, efficient, no additional energy consumption).

Electric defrost: Uses electric heating tubes on the evaporator (simple, suitable for small cold rooms, but higher energy use).

Water defrost: Sprays warm water on the evaporator (avoids temperature spikes, suitable for cold rooms storing temperature-sensitive items like pharmaceuticals).

To ensure water/glycol evaporators work efficiently in cold rooms, the following factors must be considered during design and selection:

A. Glycol Type & Concentration

Ethylene Glycol: Lower freezing point (60% concentration = -45°C) and higher thermal conductivity, but toxic (not suitable for cold rooms storing food, medicine, or in areas with personnel access). Ideal for industrial cold rooms (e.g., cooling machine tools, storing non-consumable industrial parts).

Propylene Glycol: Non-toxic, food-grade (meets FDA standards), but has a higher freezing point (60% concentration = -37°C) and slightly lower thermal conductivity. Suitable for commercial cold rooms (supermarkets, food warehouses, pharmaceutical storage).

Concentration Calculation: The glycol ratio must match the cold room’s minimum temperature (add a 5°C–10°C safety margin to avoid freezing). For example, a -18°C frozen food cold room requires at least 40% propylene glycol (freezing point -25°C).

B. Evaporator Structure & Material

Tube Material: Copper (high thermal conductivity, suitable for medium-temperature cold rooms [0°C–10°C]) or stainless steel (304/316, corrosion-resistant, ideal for low-temperature or humid cold rooms [e.g., seafood storage] to prevent rust).

Fin Material: Aluminum (lightweight, low cost, good thermal conductivity; but prone to corrosion in high-humidity environments—must be coated with anti-corrosion paint). For extremely humid cold rooms, use copper fins (more durable but higher cost).

Fin Pitch: The gap between fins affects heat exchange efficiency and frost buildup. For low-temperature cold rooms (≤0°C), choose a larger fin pitch (3–5mm) to reduce frost accumulation; for medium-temperature cold rooms (>0°C), a smaller pitch (1.5–2.5mm) increases heat exchange area.

C. Cooling Load Matching

The evaporator’s cooling capacity (in kW or kcal/h) must match the cold room’s total heat load, which includes:

Heat from stored goods: e.g., fresh produce releasing respiration heat (e.g., apples release ~50 W/ton per day) or warm goods being cooled (e.g., freezing 1 ton of meat from 25°C to -18°C requires ~300 kWh of cooling).

Heat infiltration: From door openings (e.g., frequent access by forklifts), wall insulation gaps, or solar radiation (for cold rooms with exterior walls).

Heat from equipment: Fans, lights, or defrost systems inside the cold room.

Oversized evaporators waste energy; undersized ones cannot maintain the target temperature.

D. Fan & Airflow Design

Fan Type: Use low-noise, high-efficiency axial fans (for large air volume) or centrifugal fans (for high static pressure, suitable for cold rooms with long air ducts).

Airflow Direction: Adopt "top supply, bottom return" or "side supply, side return" to ensure air circulates evenly across the entire cold room—avoid dead zones (e.g., corners where temperature is 2°C–3°C higher than the target).

Water/glycol evaporators are widely used in commercial and industrial cold rooms due to their safety and flexibility:

Commercial Cold Rooms: Supermarket refrigerated display cabinets, convenience store cold storage, restaurant food freezers, pharmaceutical pharmacies (vaccine storage at 2°C–8°C).

Industrial Cold Rooms: Large food logistics warehouses (storing frozen meat, seafood, or fruits), dairy processing plants (cooling milk to 4°C), pharmaceutical factories (bulk drug storage), and industrial process cooling (e.g., cooling plastic molds or electronic components in low-temperature workshops).