This project involved the rapid cooling of food inside 200 gallon kettles so that it could be quickly placed in a freezer without introducing a large heat load to the freezer. To achieve this, liquid nitrogen was mixed into the kettles after cooking. As a result, a considerable amount of nitrogen gas had to be exhausted from the kettles to avoid saturating the kitchen space during the cooling the process due to the large liquid-to-gas expansion ratio of nitrogen.

Mechanical systems were designed to exhaust vaporized nitrogen from four cooking kettles during the cooling process. Four new exhaust fans were installed on the roof above, with ductwork routed down to the kitchen space, to remove the gaseous nitrogen from a discharge spout at each kettle with a 6” air gap. Four variable frequency drives (VFDs) were installed to allow the users to easily adjust the exhaust fan speeds based on the amount of food being cooked and nitrogen being used to cool it. Stainless steel ductwork was used to allow for proper sanitation. Three-inch insulation was installed on the exhaust ductwork to prevent condensation due to the exhaust airstream being below 0°F.  

Using an existing control panel, power and VFD control wiring was routed to roof to serve new exhaust fans. An additional conduit was routed to each exhaust fan for installation of sensor wiring by other trades.