1. Why Is the Kitchen So Hot?
The heat sources in a commercial kitchen are more complex than most people imagine. Radiant heat from open flames is the primary source of sensible heat — a double-burner wok range generates heat comparable to a small industrial furnace. Steamers, ovens, and stock pots continuously release water vapor, creating a high-humidity environment. Grease and smoke from frying not only pollute the air but also carry substantial heat.
These heat sources combine to push kitchen temperatures well above 45°C during peak hours. What makes it worse is that the exhaust hood continuously extracts air, creating negative pressure in the kitchen, while hot outdoor air rushes back in through door gaps and pass-through windows. The chef stands at the stove with hot air surging in from behind and radiant heat from the burners in front — a "pincer" heat trap.
Traditional cooling methods fail in this environment. Air conditioner evaporator fins become clogged with grease, cooling capacity drops rapidly, and compressors trip repeatedly. Fans merely accelerate hot air movement, making the perceived temperature even worse.
2. How Water-Cooled Fresh Air Units Work
The approach of a water-cooled fresh air unit is completely different from air conditioning. Rather than circulating and cooling the air inside the kitchen, it introduces outdoor fresh air, cools it through a water-cooled heat exchange medium, and delivers it into the kitchen.
The core process has two steps: outdoor hot air passes through a wet cooling pad or water-cooled heat exchanger, where water evaporation absorbs heat from the air, lowering its temperature; a centrifugal fan then delivers the cooled air through ducts into the kitchen, simultaneously replacing the air extracted by the exhaust system.
This principle determines several characteristics of water-cooled fresh air units: no compressor dependency, low energy threshold; continuous fresh air introduction, improving kitchen air quality; and simultaneous make-up air and cooling, solving the negative pressure problem.
3. Core Selection Parameters
Make-up air volume must match exhaust volume. The exhaust hood's exhaust volume determines how much fresh air needs to be supplied. The industry standard is make-up air at 80% to 90% of exhaust volume, maintaining slight negative pressure in the kitchen to prevent grease spillage. Insufficient make-up air means negative pressure cannot be resolved; excessive make-up air may cause grease to backflow into the front of house.
Static pressure determines supply distance. Exhaust system negative pressure is typically 100-150 Pa. Adding duct friction loss and elbow local resistance, supply equipment static pressure should reach 300 Pa or more to penetrate the negative pressure zone. If ducts are longer or elbows more numerous, higher pressure margins are needed.
Supply air position must avoid direct blowing at stoves. Make-up air outlets should be arranged along the chef's back or to the side, avoiding direct blowing at stove flames which affects combustion efficiency. A reasonable supply position both cools and assists the exhaust hood in capturing grease.
Water and electricity consumption. The operating cost of a water-cooled fresh air unit comes primarily from water and electricity. Different models consume between 4 L/h and 50 L/h of water, with motor power from 0.32 kW to 11 kW. For restaurants operating 8 to 10 hours daily, long-term operating costs need to be calculated during selection.
4. System Coordination Is Key
A water-cooled fresh air unit is not an isolated piece of equipment — it must coordinate with the exhaust system. The exhaust side handles capture and purification, while the make-up air side handles balance and cooling. Air volumes on both sides must be calculated and matched.
A common misconception is treating the water-cooled fresh air unit as exhaust equipment. It only handles make-up air and cooling; grease purification and discharge are independently handled by the exhaust system. Each performs its own function, and only through coordination can a complete airflow loop be formed.
Another misconception is neglecting duct design. An oversized unit with unreasonable duct routing and excessive elbows will still deliver insufficient airflow at the terminal end. Reasonable design means minimizing duct length, reducing elbow count, and selecting appropriate outlet specifications.
5. Selection Advice for Kitchens of Different Scales
Small restaurants (50-100 m²). Airflow requirements are typically 4,000-8,000 m³/h, satisfiable with single-phase 220V power. Choose models with static pressure around 480 Pa for short-duct direct delivery. Water consumption controlled at 6-8 L/h keeps operating costs manageable.
Medium kitchens (100-300 m²). Airflow requirements are 8,000-15,000 m³/h, and 380V three-phase power is recommended. Static pressure needs to exceed 580 Pa to handle longer duct systems and exhaust negative pressure. Multi-outlet models can be selected for zoned air supply.
Large central kitchens or group catering cafeterias (over 300 m²). Airflow requirements exceed 15,000 m³/h, requiring high static pressure models at the 680 Pa level. Variable-frequency control is recommended to adjust make-up air volume based on exhaust system operating status, balancing energy consumption and performance.
6. Installation Notes
Water-cooled fresh air units should be installed in well-ventilated locations, avoiding direct sunlight. Sufficient space should be maintained around the air inlet to prevent hot air recirculation. The water cooling system requires connection to water supply and drainage, with maintenance space reserved during installation.
Duct connections should be well sealed to prevent air leakage affecting supply performance. Outlet positions should be reasonably arranged according to kitchen layout, ensuring coverage of the chef's main work areas.
7. Summary
Kitchen heat is not a problem solved by a single piece of equipment, but rather requires a ventilation and cooling system matched to the exhaust logic. Water-cooled fresh air units play a composite role of "make-up air plus cooling" in this system, solving both the negative pressure problem caused by exhaust and improving chef comfort.
The core selection logic is: calculate make-up air volume first, then check static pressure margin, and finally confirm supply air position. Matching the kitchen's exhaust volume and duct resistance, and selecting appropriate airflow and static pressure, allows the equipment to perform as intended.