External Supply Plenums
External plenums hung around the perimeter of exhaust only hoods are a great alternative to internal supply plenums. They do not sacrifice valuable hood containment area, can be retrofitted to almost any hood and are generally less expensive than internal plenums. Three external supply choices offered by Greenheck - Air Curtain Supply Plenum, Variable Supply Plenum, and Back Supply Plenum.
Air Curtain Supply Plenum (ASP)
The external air curtain is constructed with 304 or 430 stainless steel. Two layers of perforated panels allow for well distributed low velocity airflow at discharge. Air curtain supply plenums are available in lengths from 3 feet to 16 feet where additional lengths require hanging multiple plenums. The ASP is 14 inches wide by 10 inches high.
The external air curtain supply plenums provide spot-cooling when using tempered air, but can also keep untempered air near the hood which will save on heating/cooling loads. There are advantages over the integrated air curtain. Mounted 14-20 inches above the bottom edge of the hood or flush with a drop ceiling, external air curtain supply plenums can supply airflow at a maximum rate of 180 cfm/ft. For optimum performance, design to the recommended rate of 110/cfm/ft. In addition, external plenums can be attached to the face of ends of an exhaust only hood to create a curtain of air on all exposed sides of the hood, increasing the volume of air brought in at the hood.
Back Supply Plenum (BSP)
The back supply plenum is constructed with 304 or 430 stainless steel. A layer of perforated panel allows for well distributed low velocity airflow at discharge behind and below the cooking battery. Back supply plenums are available in lengths from 3 feet to 16 feet where additional lengths require hanging multiple plenums. The BSP is 6 inches wide and discharges 31.25 inches above the finished floor.
An effective way to introduce untempered make-up air into the kitchen is from the rear of the hood through a back supply plenum. These plenums are also ideal for heating air during the colder months since hot air will rise from its low discharge position. This plenum is mounted 31.25 inches above the finished floor and directs air flow through perforated panels behind and below the cooking equipment without affecting capture and containment, cooking surface temperature, or pilot lights. When using untempered air, utilizing low air velocities will keep the air near the hood. These plenums are 6 inches deep and stretch the entire length of the hood. They function as a backsplash panel and provide the proper clearance to limited combustibles needed in most circumstances. Back supply plenums are able to supply a minimum of 250/cfm/ft. For optimum performance, design to the recommended rate of 145 cfm/ft.
Horizontal Supply Plenum (HSP)
- Make-up air is introduced horizontally through the face of the external supply plenum via perforated panels in a manner that does not interfere with the cooking operations beneath the hood(s)
- Perforated panels are located on the face of the external supply plenum to limit the throw to within several feet of the hood(s) and maintain laminar flow.
- Easy and flexible installation
- Typically used in tempered air applications since the air will mix with the air in the surrounding space
- The HSP is 12 inches wide by 18 inches high
- The HSP is typically mounted flush with the top of the hood
Variable Supply Plenum (VSP)
The variable supply plenum is constructed with 304 or 430 stainless steel. Providing both face and air curtain supply this plenum offers versatility. A manual damper is included in the plenum to modulate airflow between the face and air curtain allowing 0 to 50 percent through the air curtain and 50 to 100 percent through the face. Variable supply plenums are available in lengths from 3 feet to 16 feet where additional lengths require hanging multiple plenums. The VSP is 12 inches wide by 18 inches high.
Variable Supply Plenums are a combination of face supply and air curtain supply. They are better suited for cooler climates where outside air can be used to cool the kitchen. More make-up air can be brought through a variable supply plenum than a face or air curtain alone, but the same limits exist for each part of the plenum, maximum 250 cfm/ft. from the face and maximum 125 cfm/ft. from the air curtain. Perforated panels should always be used to reduce air velocities and eliminate spillage from the hood. Supply rates should be designed to recommended values of 150 cfm/ft. through the face and 100 cfm/ft. through the curtain for optimum performance.