This project demonstrated the optimization potential of exhaust flow hoods and related makeup air units (MAUs), primarily in dining facilities (DFACs) located in several continental United States climate zones, by use of demand controlled ventilation (DCV) technologies. The two performance objectives were: (1) to demonstrate a minimum of 30% savings in both energy use and associated greenhouse gas (GHG) emissions, and (2) to maintain or improve occupant comfort. These objectives were accomplished primarily through the DCV technology. Energy savings were validated by monitoring energy use before and after the technology installation. Qualitative benefits, such as noise reduction, were validated through surveys of personnel working with the retrofitted systems.

The DCV technology has widespread energy savings potential. The Army alone has approximately 1,900 cafeterias, dining facilities, and various other eateries occupying more than 12 million square feet (ft²), many of which have exhaust hoods. The majority of the exhaust hoods and related MAUs are constant volume systems, some of which operate 24 hours a day regardless of activity in the facility. In Department of Defense (DoD) kitchens, exhaust flow rates range from a few thousand up to about 50,000 cubic feet per minute (CFM). Operating exhaust hood equipment in this manner wastes large quantities of energy and may result in uncomfortable working conditions.

The DCV technology operates automatically by monitoring cooking activity and by modulating exhaust airflow using temperature and opacity sensors connected to a controller and variable-frequency drives (VFD) on exhaust hood and MAU fan motors. The sensor data is passed to a controller that is programmed to increase airflow to 100% of design when active cooking is detected and to reduce the airflow typically to between 50 to 70% of design at idle conditions. These sensors measure cooking activities by sensing exhaust air temperature, infrared temperature of cooking surfaces, and/or the presence of smoke/steam.

Between 2012 and 2013, this project installed DCV systems on the main kitchen hoods in three DFACs and one food court at the following sites:

• U.S. Air Force Academy (USAFA) Preparatory School, Colorado Springs, Colorado, High Country Inn Building 5218, a DFAC with a 240-person serving capacity.
• Fort Lee, Virginia, Samuel Sharpe Dining Facility Building 18028, a large DFAC with a 5000-person serving capacity.
• Fort Carson, Colorado Springs, Colorado, James R. Wolf Dining Facility Building 1444, with a 600-person serving capacity.
• Ellsworth Air Force Base (AFB), South Dakota, Base Exchange Food Court with fast food restaurants (Burger King and Charley’s).

Table ES1 lists the energy savings achieved by the DCV systems installed on the kitchen hoods at the four sites. Before the DCV systems were installed, kitchen hood ventilation equipment was turned off at night when the dining facilities were closed approximately 75% of the time. Energy savings would be much greater at sites where kitchen hood ventilation equipment runs continuously throughout the day and night.

Table ES1. Summary of energy savings provided by DCV systems on kitchen hoods.

kWh/yr = kilowatt hours per year 
therms/yr = therms per year
MMBtu/yr = million metric British thermal units

The economics results listed in Table ES2 indicate that the cost effectiveness of the energy saving results varied from very good (savings to investment ratio [SIR] of 2.14 at Fort Lee) to poor (SIR of 0.3 at Ellsworth AFB, where installation of the technology was not economically justified). The simple payback ranged from 4.6 years (best return) to 37.2 years (worst return). Both goals of reduced GHG emission and energy reduction were reached to varying degrees. Other goals, e.g., to maintain maintenance requirements with no increase and to satisfy users, were met at all locations.

Table ES2. Economic results of installed DCV systems.

The Fort Carson facility was selected as the basis for a “typical” Army installation DFAC, in size and layout, for an Army-wide assessment of the value of installing DCV systems on DFAC kitchen hoods. The Fort Carson facility’s kitchen hood ventilation system had a much lower ventilation rate than what the system design specified. Design ventilation rates that would be more appropriate for a typical facility in combination with other information gained from the test results were used to do an economic evaluation that placed each test facility in one of the 15 climate zone cities found in the United States (Table ES3).

Table ES3. DCV control system economics when applied to U.S. climate regions.

AIRR = Adjusted Internal Rate of Return

An economic analysis to determine which size kitchen hoods were the best candidates to be fitted with DCV technology indicated that the DCV control systems were most economical when installed on main exhaust airflow hoods found in DFACs with a total motor size greater than 5 horsepower (hp) and/or exhaust volumes greater than 5,000 CFM. It appears that DCV technology is not optimally cost effective when applied to infrequently used or smaller hoods, such as those found in food service facilities located in food courts. Based on the analysis of typical energy savings, the number of facilities that could be economically retrofitted in the Army was estimated to be 378 of the 1,900 eating facilities.

Due to the size of investment for this technology, it was determined that a majority of the following parameters must be met to justify the installation cost:

• Relatively large exhaust hood (minimum of 5,000 CFM).
• Climate requiring significant heating and/or cooling of makeup air.
• Relatively long operating hours.
• Medium to high utility costs.