Demand-Controlled Ventilation for Commercial Kitchens
Commercial Kitchen Ventilation: Variable Speed Based on Heat and Smoke vs. Constant Speed Operation During Occupancy
A system for commercial kitchen exhaust fans that uses smoke and heat sensors to control the exhaust hood airflow and make-up air volume based on cooking activities.
Item ID: 155
HVAC--Sensors & Controls
Technical Advisory Group: 2009 HVAC TAG (#2)
Technical Advisory Group: 2015-1 Commercial HVAC TAG (#11)
Average TAG Rating: 3.5 out of 5
TAG Ranking Date: 03/10/2015
TAG Rating Commentary:
- I'm not clear on how this is emerging technology. It's already code in large kitchens and is in many programs already. We have found it not cost effective in small applications.
- BPA already has this measure, but there has been very little uptake. There are maintenance issues which can shut down a restaurant, and there are no non-energy benefits to counteract the maintenance issues.
- We already have a measure, but could use program help.
- I am not aware of case studies demonstrating savings, but believe the concept to be sound, a real market need, and would have some ease of implementation. Persistence of savings and maintenance issues may be present.
- My reservation is only that each installation will require a fairly sophisticated contractor to design and install, i.e, there is significant engineering time involved. This may make savings evaluation more challenging - but heck, this is like any other system.
- This one seems to be being pushed a lot by vendors. It makes sense, but I'm not sure it can be deemed.
- The technology in tests performs but there is little market uptake -- don't know if it is emerging because it is already in our programs
- This is required by CA Title 24 code for systems over 5,000cfm -- and ASHRAE. The SPEED program and the CA FoodService Technology Center have lots of case studies.
- Code requirements exist for new projects with minimum hp requirement; may be good application for existing buildings.
The Consortium for Energy Efficiency (CEE) indicates that with demand-controlled kitchen ventilation (DCKV), energy savings from kitchen supply and exhaust fans can be as much as 70%. While the energy savings are impressive, less than 1% of commercial kitchen ventilation systems have demand control. According to the American Gas Association and the U.S. Department of Energy (DOE), commercial kitchen exhaust fans in the 1 million food-service establishments in the U.S. and Canada waste more than $2 billion in energy costs each year while exhausting 3 billion cubic feet per minute (cfm) of airflow. The main problem is excess ventilation. Most exhaust fans run at constant speeds – even when the cooking equipment is idle. By contrast, demand ventilation systems vary the amount of ventilation air to more closely match the actual ventilation requirements.
Ventilation systems are integral for a safe and comfortable kitchen environment. DCKV equipment maintains comfort and indoor air quality by varying the speed of the exhaust and supply fans based on cooking activity. The DCKV system obtains continuous inputs from occupancy, temperature, and/or infrared sensors, as well as data about the amount of smoke present. Variable frequency drives (VFDs) are used to automatically adjust the amount of exhaust and ventilation airflow to meet actual requirements. Potential benefits include:
- Fan energy savings of 30% to 70%.
- Significant space heating and cooling energy savings.
- Improved comfort for kitchen employees because of reduced noise and reduced volumes of hot, cold, or humid make-up air during idle cooking periods.
- Improved fire safety because the exhaust air temperature is monitored. If the temperature approaches the fusible link temperature of the fire suppression system, an alarm sounds and/or cooking appliances are turned off. With lower air velocities, grease capture is better, which also improves fire safety.
- Improved indoor air quality because CO2 levels in the dining area can also be monitored. The exhaust and outside air levels can be adjusted to 100% if the CO2 level exceeds a specified setting.
Baseline Description: 3 hp Constant Speed Exhaust Fan for Commercial Kitchen Hood
Baseline Energy Use: 18520 kWh per year per unit
For a single 3 hp exhaust fan drive motor, the baseline input power is 2,200 watts multiplied by a 75% load divided by an efficiency of 87% at the 75% load point. The average weekly hours of operation for restaurants is 92.6 (from Table C-SC2 of the 2009 NEEA "Commercial Building Stock Assessment"), yielding about 4,800 annual operating hours. Assuming 4,800 hours of operation per year, the energy use for a baseline 3 hp kitchen exhaust fan is 9,260 kWh/yr. This annual energy use will be doubled to account for makeup air fan requirements.
Manufacturer's Energy Savings Claims:
The CEE has developed a field test protocol for DCKV savings verification studies. They have also worked with manufacturers to gather a credible body of evidence (field test reports) and operate a clearinghouse demonstrating the benefits of DCKV. The CEC indicates that fan energy savings can be as much as 70%. Space heating energy savings also occur, resulting in cost savings that might exceed the cost savings from fan energy savings. A field study at a full-service restaurant found fan energy savings of 10,000 kWh/year (valued at $800) and heating savings equivalent to 1100 therms/year of natural gas (valued at $1,000) (from: CEE ‘Commercial Kitchen DCV Reports', (CEE, 2015).
Best Estimate of Energy Savings:
"Typical" Savings: 57%
Low and High Energy Savings: 37% to 70%
Energy Savings Reliability: 6 - Approved Measure
The National Fire Prevention Association (NFPA) standards require that an exhaust hood operate at full design airflow whenever cooking activities occur under the exhaust hood. But cooking equipment is not used all at once or all of the time. Typical restaurants have a mealtime rush and low occupancy between peak periods. However, the kitchen hood exhaust and make-up air systems must be designed for the maximum load under each hood and are traditionally equipped with on/off controls, meaning that they operate constantly over the day. Energy savings are available due to system oversizing and operating schedule (EPA, 2013). The potential for energy savings is estimated by assuming the exhaust fans can run at 50% of full speed about 50% of the time (and at full speed for the remainder of the time). A fan that operates at 50% of rated speed provides about 50% of rated airflow. With this operating regime, the fan would use about 0.5 + 0.5 x (0.5)3 or 56.25% of its baseline energy use. Expected energy savings are 43.75%.
Pacific Gas and Electric (PG&E) conducted a number of DCKV case studies in California at a variety of sites, including an institutional cafeteria, a casual dining restaurant, a hotel main kitchen, supermarket, campus dining facility, and several quick-service restaurants. The average exhaust fan speed reduction was 26%, accounting for an average total fan power reduction of 57% (U.S. DOE, 2013).
A PG&E case study at the Mark Hopkins Hotel found an average exhaust and makeup fan power reduction of 62.1%. Due to variations in kitchen design and operating patterns as well as local climate, savings vary for each installation (EPA, 2013).
In addition to the fan power energy savings noted above, savings result from reduced heating and cooling loads. In a commercial kitchen, these are primarily cooling loads, which are difficult to estimate. The cooling system serving a kitchen may also serve the dining room and other spaces; it may not have heat recovery ventilators; and savings will vary significantly with climate, infiltration, and airflow between the kitchen and dining room. More data is needed to fully understand the impact on kitchen cooling loads; therefore, our estimate of total energy savings is the lower of the two in the studies referenced above and should be taken as conservative because it does not reflect cooling energy savings.
Energy Use of Emerging Technology:
7,963.6 kWh per unit per year
Energy Use of an Emerging Technology is based upon the following algorithm.
Baseline Energy Use - (Baseline Energy Use * Best Estimate of Energy Savings (either Typical savings OR the high range of savings.))
Potential number of units replaced by this technology:
According to a Navigant report for the Energy Information Administration (EIA), the estimated installed base of commercial kitchen hoods in 2015 in the U.S. is projected to be 810,000. Because the Northwest has a population that equals roughly 4% of the total U.S. population, an estimated 32,400 commercial kitchen hoods are located in the region. The percentage of hoods that are already equipped with demand-controlled ventilation is small. The U.S. DOE reports that an installed base of about 10,000 DCKV systems has been installed over the past 25 years. Assuming there are just two exhaust hoods per kitchen, an estimated 64,400 exhaust hoods are candidates for upgrading in the Northwest.
Regional Technical Potential:
0.68 TWh per year
Regional Technical Potential of an Emerging Technology is calculated as follows:
Baseline Energy Use * Estimate of Energy Savings (either Typical savings OR the high range of savings) * Technical Potential (potential number of units replaced by the Emerging Technology)
Installed first cost per: unit
Emerging Technology Unit Cost (Equipment Only): $6000.00
Emerging Technology Installation Cost (Labor, Disposal, Etc.): $0.00
Baseline Technology Unit Cost (Equipment Only): $1000.00
The installed cost for new construction is $6,000 for 3 to 8 total controlled horsepower (hp). This information was taken from the publication, “Demand Control Ventilation for Commercial Kitchen Hoods” (SCE, 2009) by Southern California Edison, and includes hood costs. For retrofit applications in a hotel, the cost can range from $20,000 to $40,000 for 30 to 35 total controlled hp. Quick-service restaurants may have retrofit costs between $8,000 and $15,000 (EPA, 2013). Note that the supply of ventilation air must be varied in accordance with the quantity of air exhausted. Energy savings (electrical or gas) may also accrue from reducing the amount of conditioned air exhausted from the kitchen.
The actual equipment cost depends on the number and size of the fans.
This is already an incentivized measure in many locations.
Simple payback, new construction (years): 5.3
Simple payback, retrofit (years): 6.3
Cost Effectiveness is calculated using baseline energy use, best estimate of typical energy savings, and first cost. It does not account for factors such as impacts on O&M costs (which could be significant if product life is greatly extended) or savings of non-electric fuels such as natural gas. Actual overall cost effectiveness could be significantly different based on these other factors.
The simple payback for retrofit applications is significantly higher than for new construction because it is much more labor intensive to install.
Demand controlled ventilation in commercial kitchens (DCKV) involves controlling the exhaust and make-up air volume of exhaust hoods based on the actual demand.
This equipment varies the speed of the fans based on the amount of heat and smoke present. This is very useful because much of the cooking equipment is typically idle for several hours every day. When equipment is idle or little ventilation is required, the fan motors slow down, reducing energy use significantly. Some of the advanced features of DCKV include:
• Variable air volume (VAV) for exhaust hoods, including applicable controls, that provide only the ventilation required, with a minimum speed of 10% to 50% of maximum.
• Make-up air that can be introduced through back wall supply and/or ceiling-mounted perforated plenums. Make-up air can, instead, be a forced air system that would also have variable frequency drive (VFD) blowers and modulating burners interlocked with the exhaust. During cooking, the speed increases as needed up to 100% until smoke and vapors are removed, keeping the ambient temperature comfortable.
• Adding side panels to hoods to promote capture.
• Replacing vane diffusers with perforated diffusers to promote capture.
The current industry practice is manually controlled fans – most are single-speed motors that are left running constantly. It is common in commercial kitchens for cooks to turn on the fans full speed when they come in in the morning, and leave the fans on until the kitchens close at night.
This technology is in the early but well-developed stage of market introduction. According to an EPA Energy Star technology profile, at least 11 DCKV suppliers exist. The Intelli-Hood® is available throughout the U.S. but has not been adopted widely in the Pacific Northwest, although this is improving. Adoption rates should greatly increase in the future due to requirements imposed under California Title 24 Building Energy Efficiency Regulations (effective January 1, 2014).
Chain restaurants are said to be aware of this technology but have not yet developed a business case for implementation (EPA, 2013). Independent restaurants and their dealers may not be aware of the technology.
With specification of a DCKV system, there is no need for a kitchen designer to take chances with a design exhaust airflow that is too low. Oversizing no longer results in excessive energy use. Benefits of noise reduction from the kitchen’s exhaust hood system include a quieter environment for restaurant customers and better communication among kitchen staff, who do not have to compete with noisy fans. Intelli-Hood’s claims include improved fire safety, increased life of ventilation systems, and improved kitchen comfort.
End User Drawbacks:
The main drawback is a higher installed cost. In addition, the controls are a little more complex than the standard installation, requiring some commissioning, user understanding, and maintenance. Equipment installers must be aware of equipment limitations. For instance, some fans have a minimum speed for safe operation; air flow velocities below 500 feet per minute (fpm) can result in deposition of grease in ducts (EPA, 2013). In addition, sensors must be placed in the proper locations to optimize exhaust fan responsiveness.
Installation of a DCKV system requires mechanical and electrical contractors to integrate several different systems, including the exhaust system, VFDs, and the building’s HVAC system (some kitchens have dedicated make-up air systems). Ensuring proper performance across the full range of possible operating conditions and fan speeds is difficult (EPA, 2013).
Operations and Maintenance Costs:
The O&M costs of DCKV systems require additional maintenance to ensure continued performance, particularly the proper operation of sensors.
The variable speed feature of DCKV should extend equipment life beyond that expected for standard constant-speed equipment. Expected life is 15 to 20 years.
• Ventilation systems that utilize only temperature sensors
• Fan controls linked to cooking equipment switches
• Custom-designed systems to serve similar functions
Reference and Citations:
Demand Control Ventilation for Commercial Kitchen Hoods
Southern California Edison
New and Underutilized Technology: Demand Control Ventilation for Commercial Kitchen Hoods
Federal Energy Management Program
Customer Advanced Technologies Program Technology Evaluation Report: Demand Ventilation Systems
Sacramento Municipal Utility District
Variable Speed Comes to the (Kitchen) 'Hood
California Energy Commission, Public Interest Energy Research
Demand Ventilation in Commercial Kitchens: Case Study: Mark Hopkins Hotel
Pacific Gas & Electric Company
Fact Sheet: Variable Speed Control for Food Service Exhaust Hood Fans
California Energy Commission, Public Interest Energy Research
Clearing the Air in Commercial Kitchens
Pacific Gas & Electric Company, Emerging Technologies Program
Kitchen Hoods Using Demand Ventilation
Commercial Kitchen DCV Reports
Consortium for Energy Efficiency
Demand Control Ventilation (DCV) for Commercial Kitchens, Webinar
U.S. Department of Energy, Better Buildings Alliance (BBA) Food Service Project Team
Schrock, et. al. ,
Demand-Controlled Ventilation for Commercial Kitchens
Technology Profile: Demand Control Kitchen Ventilation (DCKV)
U.S. EPA Energy Star Program