Knowledge Base

Every summer brings the same complaint. The unit is running, air is coming out of the grille, and the cooks are still soaked. The natural response is to assume the unit is undersized and buy a bigger one. It usually does not help.

In roughly seven out of ten cases the problem has nothing to do with capacity. It sits in one of three places: the cold air never reaches the person, the capacity is being spent on water vapor instead of temperature, or the grille is aimed at the wrong spot.

Throw: cold air starts losing before it arrives

Air leaving a grille is a jet. It does not stay cold until it lands on someone; it entrains surrounding warm air as it travels, losing both velocity and temperature along the way. Engineers track two curves here — centerline velocity decay and temperature decay. In practical terms, once velocity falls to about 20 percent of its discharge value, a person standing in the stream stops feeling it.

Free jet decay is not primarily a function of distance. It is a function of outlet size. For the same airflow, a 200 by 200 millimeter grille and a 235 by 235 millimeter grille behave very differently. The smaller one discharges faster but decays sooner. The larger one feels gentler at the face but reaches farther. This is why a unit rated for eight meters of throw may deliver only three usable meters at the cooking station: the rating usually measures to a defined velocity threshold, and human perception gives up earlier than that threshold.

Real kitchens add obstacles. The exhaust hood overhead runs continuously and creates an upward induced flow that grabs a horizontal jet and lifts it. The thermal plume off the range does the same. Together they can peel the cold air away at around 1.8 meters above the floor, leaving the actual working zone — roughly 1.0 to 1.5 meters up — empty.

Which is why spot cooling should aim at the cook, not into the room. The outlet needs to sit close to working height and be adjustable in pitch. It is also why ball-joint nozzles outperform fixed louvers in kitchens: the cook moves during a shift, and the nozzle has to move with them.

Sensible heat ratio: half your capacity may be making water

Total cooling capacity splits into two parts. Sensible heat lowers temperature. Latent heat removes moisture. The sensible heat ratio, or SHR, is the sensible share of the total.

In a normal room, SHR runs around 0.75 to 0.85 because there is not much airborne moisture. A commercial kitchen is a different climate. Boiling pots, combi ovens, dish machines, wet floors and open prep tables keep relative humidity above 75 percent for most of the day; dish rooms can reach 90 percent. Under those conditions most of the machine's output goes into condensing water, and the share actually lowering temperature can fall to 0.6 or below.

Put numbers on it. A unit rated at 8,000 watts delivers about 6,400 watts of sensible cooling in a room at SHR 0.8. In a kitchen at SHR 0.6, the same unit delivers 4,800 watts. That is a one-third loss. An operator who sized the system at 250 watts per square meter is effectively getting 150, and the kitchen will not feel cool.

This is the quietest failure mode of residential units installed in kitchens. Those units are rated at 27 degrees Celsius and 50 percent relative humidity, and their evaporating temperature is set for that condition. Kitchen return air may come back at 35 degrees and 85 percent humidity, and the coil saturates almost immediately. Wet-surface heat transfer is fine in itself, but the condensate film raises air-side resistance, airflow drops, and lower airflow widens the supply-to-room temperature difference and shortens the jet. The chain compounds. Three months in, oil and dust bridging the fin gaps finishes the job — which is the mechanical reason behind "it stopped cooling after three months."

Two responses. First, design for latent load rather than floor area; kitchen systems generally need 20 to 30 percent headroom above conventional figures. Second, remove moisture at the source. Pre-treating hood make-up air, giving the dish room its own exhaust, and fitting covers on floor drains often do more than buying a larger unit.

Dew point: the real limit on supply temperature

Supply air temperature cannot be pushed arbitrarily low. It has to stay above the dew point of the air inside the unit. Otherwise condensate forms on the grille, inside the duct, or on the housing surface, and water dripping into food is a food safety incident, not an inconvenience.

Work an example. Return air at 30 degrees Celsius and 70 percent relative humidity has a dew point near 24 degrees. If that unit discharges at 22 degrees, the duct skin will sit below the surrounding dew point and it will sweat. To deliver 18 degrees, you must first reduce the moisture content of the return air — dehumidify, then cool, either in two stages or with a dedicated outdoor air unit handling the kitchen supply.

This explains a familiar argument. The operator wants 16 degrees at the grille; the supplier says it cannot be done. It is not the compressor. It is the dew point. Units advertised at 16 to 20 degrees assume either low return-air moisture or anti-sweat measures — insulated duct interiors, oversized drain pans, adequate slope. In a high-humidity kitchen, holding 18 to 22 degrees steadily is already good performance. Pushing lower buys very little; raising airflow and extending throw buys much more.

One note on condensate. Kitchen condensate volumes dwarf residential ones. An 8,000-watt unit under humid conditions can produce several liters an hour. Insufficient drain slope, undersized pans and missing traps all lead to overflow. A crude field check works well: half an hour after startup, the drain line should feel like a steady warm trickle, not an intermittent gulp.

Four field checks that narrow it down

The grille feels cold but nobody feels it. That is throw. Check mounting height, pitch angle, and whether the exhaust hood is lifting the jet. Lower the outlet or switch to an adjustable ball joint.

Strong airflow, no temperature drop. That is sensible heat ratio. Measure return air temperature and humidity first. If relative humidity is above 80 percent, do not add capacity — cut the moisture sources.

Water on the grille. That is dew point. Compare supply temperature against return-air dew point. Supply should sit at least two degrees above it.

Cool for half an hour, warm again after two. That is heat transfer. Check the evaporator fins for oil and dust, the condenser for blockage, and whether condensate is actually draining. Any one of those failing will cost you thirty percent of capacity or more.

One last principle worth applying. Budget kitchen cooling per person, not per square meter. A thirty-square-meter kitchen may only have four to six square meters of working surface that genuinely needs cooling. Concentrating capacity there uses far less power than conditioning the whole room, and the effect is immediate. Across the projects Finos has supplied, spot cooling paired with local exhaust has consistently cut electricity use by more than twenty percent compared with whole-room cooling.