Energy savings for quick service restaurants.
[ILLUSTRATION OMITTED]According to the National Restaurant Association, more than 900,000 restaurants are in the United States. The energy use intensity (EUI) in the quick service restaurant (QSR) segment is significantly higher than other commercial building segments. This is mainly driven by energy-intensive cooking processes, high heat gains from cooking equipment, and limited floor space in the QSR.
To address this issue and provide strategies to achieve exemplary energy savings in QSRs, Pacific Northwest National Laboratory (PNNL), in collaboration with industrial partners, recently completed a research project and published a technical report titled "Technical Support Document: 50% Energy Savings for Quick-Service Restaurants" (referred to as TSD). (1) This article summarizes the major findings of this project. We conducted the energy saving and cost effectiveness analyses using the following steps:
* Develop a prototype building model representing a typical QSR design;
* Develop baseline buildings to comply with the minimum requirement of ANSI/ASHRAE/IESNA Standard 90.12004 in all U.S. climate zones;
* Select and optimize the energy efficiency measures (EEMs); and
* Analyze the energy savings using hourly building simulation software EnergyPlus.
Prototype Building
As shown in Figure 1, the prototype building was developed as a 2,500 [ft.sup.2] (232 [m.sup.2]) single-story building with kitchen and dining zones. Its exterior enclosure consists of wood-framed walls with exterior stucco cladding, slab-on-grade concrete floors, and flat roof with rigid insulation. The total window-to-wall ratio is 14%. These building characteristics are derived from the 2003 Commercial Buildings Energy Consumption Survey data, (2) representing the most commonly built QSRs in the U.S.
Energy Uses in Restaurant Sector
It is well documented that the total building and cooking end-use EUIs in the QSR segment are significantly higher than other commercial building segments; but two questions must be answered. How much larger are the QSRs? Have they changed over time? This section answers these questions and presents more valid EUIs for current QSR design. Some of the historical sources for EUI information can be seen in Table 3.7 of the TSD report that the food preparation (or cooking) EUIs have been estimated to vary from 123 kBtu/ [ft.sup.2] (1397 MJ/[m.sup.2]) up to 324 kBtu/[ft.sup.2] (3680 MJ/[m.sup.2]) with an average estimate of 219 kBtu/[ft.sup.2] (2487 MJ/[m.sup.2]). But how do these compare to more recent data?
[FIGURE 1 OMITTED]
Utility bills were used to estimate the total annual EUIs for three QSRs. For two of the QSRs engineering estimates also were made for the end-use. These restaurants rank at the top in regards to energy efficiency for this building sector, and they have a similar square footage compared to the prototype QSR building. Table 1 shows that for highly efficient QSRs the EUI for the total building can be as high as 1,154 kBtu/[ft.sup.2] (13 105 MJ/[m.sup.2]). The other key piece of information in Table 1 is that the percentage of energy that can be attributed to the food preparation process, including cooking and refrigeration, is estimated to be 431 kBtu/[ft.sup.2] (4895 MJ/[m.sup.2]) or 43% of the energy use in QSR 3, which is nearly double the estimate of 219 kBtu/[ft.sup.2] (2487 MJ/[m.sup.2]) from earlier studies. The question that needs to be answered is why this change has occurred over time.
The authors have determined that three key factors have been driving the EUIs significantly higher in recent years. The first factor is the heavy emphasis on drive-through windows, and that most QSRs have been working on increasing their service speed. An article (3) states that drive-through sales now account for 50% to 60% of the overall store sales in QSRs. The second factor is the expansion of menu items and associated cooking appliances. The third factor is that as construction costs have increased, the square footage allocated to the kitchen and dining areas have decreased even while the quantity of foodservice equipment has increased in the restaurants. (4)
Appliances
The kitchen appliances were organized in two categories: hooded and unhooded appliances. The hooded appliances are the primary appliances used for cooking and are located underneath the exhaust ventilation hoods. The unhooded appliances consist of other types of food preparation equipment such as ice cream machines, microwave ovens, etc.
For the baseline QSRs, commonly used cooking equipment was selected for the hooded appliances. For the low-energy QSRs, we used the best-in-class ENERGY STAR qualified appliances and California utility rebate qualified appliances to substitute the ones used in the baseline. (5,6) As shown in Table 2, the flattop grills used in the base case were replaced with double-sided (clamshell) grills and the standard deep-fat fryers were replaced with high-efficiency models.
Although the nameplate rating of the double-sided grills is larger than the flattop, the production capacity is larger in the double-sided grill. This means the efficient grills cook for a shorter period of time and can operate at a lighter duty level part of the time, resulting in energy savings.
As shown in Table 2, the efficient fryers have a marginally lower nameplate rating. However, they have significantly lower energy consumption during idle and the various cooking duties. Another EEM was to eliminate one fryer in the low-energy QSR because three efficient fryers provided sufficient production capacities.
Besides the hooded cooking appliances, the other large group of appliances is in the unhooded category. Table 3 presents the unhooded appliances, quantity, nameplate input, and usage factor during cooking. Those appliances that remained the same from the baseline to efficiency cases are not listed in Table 3.
As shown in Table 3, the coffee brewer was changed to an airpot brewer, which has a lower energy input than a standard coffee brewer. In addition, the coffee is stored in a portable, insulated carafe, which eliminates the need to have separate coffee warmers (this is the second change). The third appliance change occurred in the holding cabinets by going to a more energy-efficient model; and the fourth appliance change was with the half-size convection oven, which has a higher nameplate input, but a much lower energy use factor, resulting in an overall lower energy use for the oven.
Refrigeration
Table 4 presents the baseline and energy efficiency parameters for the smaller (nonwalk-in) refrigeration equipment, including reach-in units, under-counter units, a refrigerated prep table and ice machines.
Table 4 shows the efficiency improvements made to the reach-in refrigerator and freezer, under-counter units and the refrigerated prep table. With regard to the ice machines, there was not a direct efficiency improvement in the units themselves, but the condensers have been moved from being integral with the ice-making equipment to being mounted remotely outside of the building. One benefit this provides is that less heat is rejected to the space, which can save on cooling energy required to condition the space.
The overall power consumption of the walk-in cooler and freezers were reduced from total of 2,130 W to 1,460 W using the following measures: the insulation was increased to 5 in. (127 mm) thick from the standard 3.5 in. (89 mm) thick, evaporator fans with electronically commutated motors were used in the efficient case, along with switching to compact fluorescent lights, and strip curtains on the outer doors. Additional measures included in these savings are electronically controlled expansion valves and demand-based defrosting, and a desuperheater to recover waste refrigerant heat.
Mechanical System
Kitchen exhaust airflow is the key factor that determines the size and energy consumption of restaurant HVAC systems. High efficiency hoods and demand controlled ventilation (DCV) are two EEMs that allowed the exhaust airflow to be reduced by 60% to 75%. Table 5 shows the hood style, overall length, depth, and airflows of the hoods.
The baseline HVAC system shown in Figure 2 uses two constant air volume (CAV) packaged rooftop units (RTU); one each for the kitchen and dining zones. Since these RTUs are designed to handle a maximum of 25% of outside air when in cooling mode, they are often oversized to accommodate all of the supply air required to compensate for kitchen exhaust. This is especially true for restaurants with high kitchen exhaust. As seen in Figure 3 the high efficiency HVAC system retains two separate rooftop units for the kitchen and dining zones, but adds a dedicated outside air system (DOAS), which pretreats supply air for the whole building. This solution allows decoupling treatment of space load and outdoor air load in separate units. Now the RTUs serving the kitchen and dining room can be downsized and optimized to handle only the space load, with no need to consider the treatment of outdoor supply air required to compensate for the hoods' exhaust. As a result, the thermal comfort in the restaurant is improved at reduced energy costs. The conditioned supply air from the DOAS is supplied directly to the RTUs serving the kitchen and dining zones. Another benefit of a DOAS is that it assists the application of two other EEMs, demand-controlled ventilation and heat recovery since all outside air for the building is treated in a single unit.
The kitchen exhaust carries heat generated by the cooking equipment, and it can be used to preheat cold supply air in winter. This study investigated application of the runaround loop heat recovery system with two heat exchangers, one installed in the kitchen exhaust airstream and the other in the DOAS unit. Because of the energy penalty resulting from the increased fan and pump energy, the heat recovery EEM was found only beneficial in cold climate zones such as 5A, 6A, 6B, 7 and 8.
[FIGURE 2-3 OMITTED]
The economizer use complies with Standard 90.1-2004 and 90.1-2010 in the baseline and lower-energy buildings, respectively. The baseline DX coil efficiency meets Standard 90.1-2004; and they are listed in Table 6 along with high efficiency coils. The mechanical efficiency of fans in the advanced model is improved from 55% to 65%.
The baseline model uses a standard gas-fired water heater with a 100 gallon (379 L) storage tank. The minimum required thermal efficiency established by Standard 90.1-2004 is 80%. In the advanced cases, a single gas-fired condensing water heater with 95% thermal efficiency was selected. Besides the thermal efficiency improvement, the low-energy design recovers the waste refrigerant heat to preheat incoming city water before it is heated in the service hot water heater.
[FIGURE 4 OMITTED]
Lighting
The ambient average lighting power density (LPD) was reduced from 1.44 W/[ft.sup.2] (15.5 W/[m.sup.2]) in the baseline to 0.83 W/[ft.sup.2] (9 W/[m.sup.2]) in the low-energy case by using high performance lighting systems. Occupancy sensor control, improved lighting power management, and daylighting with dimming control further reduced consumed lighting power at different times of the day.
The lighting EEMs also include the reduced exterior lighting power levels, according to the allowances prescribed by Standard 90.1-2010. The total exterior lighting power is reduced from 4,333 W to 2,687 W. Photocells and timers were selected to further reduce exterior lighting energy during unoccupied hours and after dark.
Savings and Cost Analysis
In the TSD, energy performance of the baseline and low-energy buildings with the complete EEM package was simulated for 16 representative climate locations using EnergyPlus. Figure 4 presents the energy savings from the complete EEM package for all of the climate locations. The savings averaged 45% nationally but the savings in climate zones 7 and 8 were more than 50%. Figure 4 shows that the simple payback varied from 1.5 to 3.5 years.
Table 7 shows a more detailed breakdown of the simulation results for Houston, Baltimore, and Chicago in terms of end-use EUIs, savings percentage and simple payback period. The impact of climate zone is most evident in the variation between cooling and heating savings in these cities.
Figure 5 presents the breakdown of the savings by end-use category for all of the 16 cities analyzed in the TSD. It shows that the largest energy savings was achieved in the cooking end-use with the largest energy savings of 39% attributable to the gas cooking equipment or 45% for all of the cooking equipment. The next largest group of end-use savings is observed in the heating, cooling and fan categories, which combine for 37% of the savings. These savings are the result of various EEMs associated with the rooftop HVAC systems and also include the interactions of other measures such as the heat gain to space from the appliances or by moving the ice machines outside.
The interior and exterior lights savings accounted for 7% of the total energy savings. Although this is a relatively lower energy savings compared to some of the other end-uses categories, the costs for implementing the lighting measures is lower than the baseline lighting costs, which results in an immediate payback. Last, the hot water efficiency improvements accounted for 6% of the overall energy savings, and the refrigeration measures contributed the remaining 5% of the overall energy savings.
Considering limited budget or other design constraints, QSR designers and owners might be only interested in adopting a subset of the EEMs. Readers can refer to the TSD for the impacts of individual EEM packages and their paybacks.
Conclusions
The EUIs in quick service restaurants have dramatically increased in recent years due to their increased sales of drive-through windows, improved food quality, and reduced floor area per store. The results presented in the TSD provided new reference EUI data for code-compliant QSRs.
The complete package of EEMs demonstrated the feasibility of achieving up to 50% whole-building energy savings with short payback periods. Design teams may use this analysis directly to support design of QSRs that feature exemplary energy performance and quick paybacks on the investment in energy efficiency.
It is also crucial to understand that in a restaurant all of the major energy-using components are interrelated: the appliance selection impacts the heat load to space, the refrigeration condensers add load to the space if the condensers are in the kitchen, and the kitchen exhaust impacts the energy consumption of all the other HVAC systems in the restaurant. To achieve the energy savings in the QSR, it was not enough to simply replace components with more efficient ones, but the entire restaurant needed to be redesigned to optimize the energy using a whole-building approach.
Acknowledgments
The project was funded by the U.S. Department of Energy. The authors would also like to acknowledge the technical contributions from Don Fisher and David Zabrowski at the Food Service Technology Center, Michael Lane at Lighting Design Lab, and Rahul Athalye and Brian Thornton at PNNL.
References
(1.) Zhang, J., D.W. Schrock, et al. 2010. "Technical Support Document: 50% Energy Savings for Quick-Service Restaurants." Pacific Northwest National Laboratory. http://tinyurl.com/4zjsnhr.
(2.) CBECS. 2003 Commercial Buildings Energy Consumption Survey. Energy Information Administration.
(3.) Berta, D. 2008. "The NRN 50: grab and go." Nation's Restaurant News. Jan. 28.
(4.) Scarpa, J. 2010. "Equipment upgrades spark menu, daypart growth." Nation's Restaurant News. April 19.
(5.) ENERGY STAR. 2010. "Commercial Kitchen Package for Businesses and Operators." U.S. Environmental Protection Agency. Retrieved Sept. 2010, http://tinyurl.com/6947hr2.
(6.) FSTC. 2010. "Foodservice Equipment Rebates." Food Service Technology Center. Retrieved Sept. 2010, http://tinyurl.com/6gmbg5s.
(7.) ICC. 2009. International Mechanical Code 2009. International Code Council.
By Jian Zhang, Ph.D., Member ASHRAE; Derek Schrock, Member ASHRAE; Andrey Livchak, Member ASHRAE; Bing Liu, P.E., Member ASHRAE
Jian Zhang, Ph.D., is a research engineer and Bing Liu is project manager and principal investigator at the Pacific Northwest National Laboratory, Richland, Wash. Derek Schrock is research director at the Halton Company, Scottsville, Ky. Andrey Livchak is vice president of engineering at Halton Group Americas, Bowling Green, Ky.
Table 1: Annual end-use EUI data for QSRs with a floor area of 2,000
to 2,500 [ft.sup.2] (186 [m.sup.2] to 232 [m.sup.2]).
Estimated Annual EUIs (kBtu/[ft.sup.2])
End-Use QSR 1 QSR 2 QSR 3
(Tennessee, (Alberta, (British
U.S.) Canada) Columbia,
Canada)
Lighting -- 139.9 139.9
Cooking -- 407.4 407.4
HVAC -- 536.8 298.0
Refrigeration -- 23.9 23.9
Service Water Heater -- 46.8 46.9
Total 837.0 1,154.8 916.1
Table 2: Baseline and energy-efficient hooded appliances.
Baseline
Flattop Fryer
Grill
Quantity 2 4
Nameplate 90 122
Rating (kBtu/h)
Duty Level, Idle 0.24 0.11
Energy Input Light 0.34 0.39
(% of Medium 0.46 0.58
Nameplate) Heavy 0.65 0.94
Production 33.0 69.2
Capacity (lb/h)
Efficiency Case
Double- Double- Fryer A Fryer B
Sided Sided
Grill A Grill B
Quantity 1 1 1 2
Nameplate 96 143 120 120
Rating (kBtu/h)
Duty Level, Idle 0.14 0.11 0.04 0.03
Energy Input Light 0.28 0.27 0.16 0.16
(% of Medium 0.42 0.38 0.47 0.31
Nameplate) Heavy 0.57 0.48 0.91 0.59
Production 58.1 78.4 134.2 81.9
Capacity (lb/h)
Table 3: Baseline and energy-efficient unhooded appliances.
Baseline
Input, Use Factor
Quantity Appliance Each (kW) ([F.sub.u,idle])
1 Coffee Brewer 3.9 0.09
3 Holding Cabinets 2.5 0.35
1 Coffee Warmer 1.0 0.09
1 V2 Size Convection Oven 5.5 0.20
Efficiency Case
Input, Use Factor
Quantity Appliance Each (kW) ([F.sub.u,idle])
1 Airpot Brewer 1.75 0.09
3 Holding Cabinets 1.5 0.05
-- Coffee Warmer -- --
1 1/2 Size Convection Oven 12 0.05
Table 4: Baseline and energy-efficient refrigeration equipment.
Baseline
Input,
Quantity Type Each (kW) [F.sub.u]
1 Reach-In Refrigerator (2 Door) 1.1 0.25
1 Reach-In Freezer (1 Door) 1.2 0.41
2 Under-Counter Refrigerator 0.5 0.25
1 Under-Counter Freezer 0.8 0.41
2 Refrigerated Preparation Table 0.9 0.45
2 Ice Machine, 1,000 lb/Day 3.0 0.5
-- (Integral Condenser) -- --
Efficiency Case
Input,
Quantity Type Each (kW) [F.sub.u]
1 See Baseline 1 0.15
1 See Baseline 1 0.25
2 See Baseline 0.7 0.1
1 See Baseline 1.3 0.2
2 See Baseline 0.5 0.25
2 See Baseline 0.6 0.5
2 Remote Condenser 2.4 0.5
Table 5: Kitchen exhaust hood specifications
Length Depth
Hood Style (in.) (in.)
Baseline Two Identical Hoods Canopy 92.0 48
Efficiency Hood A for Griddles Proximity 72.5 32
Case Hood B for Fryers Proximity 59.75 32
Airflow Airflow
Hood (cfm/ft) (7) (cfm)
Baseline Two Identical Hoods 300 2,300 each
Efficiency Hood A for Griddles 180 1,088
Case Hood B for Fryers 150 747
Hood Exhaust Fan Type
Baseline Two Identical Hoods Constant Speed
Efficiency Hood A for Griddles Variable Speed (DCV)
Case Hood B for Fryers Variable Speed (DCV)
Table 6: Efficiency of packaged unitary air conditioners.
Size Category Efficiency (SEER/EER)
Baseline Efficiency Case
<65,000 Btu/h 13.0 SEER 15 SEER
65,000 ~ 135,000 Btu/h 10.1 EER 11.5 EER
135,000 ~ 240,000 Btu/h 9.5 EER 11.3 EER
240,000 ~ 300,000 Btu/h 9.3 EER 10.5 EER
Table 7: Summary of energy simulation results and simple payback
analysis.
Climate EEM EUI, kBtu/[ft.sup.2]
Zone City Package
Lighting Cooking Refrigeration
2A Baseline 57 534 87
Houston Complete 28 330 66
4A Baseline 57 534 87
Baltimore Complete 28 330 66
5A Baseline 57 534 87
Chicago Complete 28 330 66
Climate EEM EUI, kBtu/[ft.sup.2]
Zone City Package
Fan Cooling Heating SWH Total
2A Baseline 71 176 4 39 968
Houston Complete 32 81 1 14 551
4A Baseline 69 68 140 65 1,021
Baltimore Complete 32 27 40 35 557
5A Baseline 70 43 202 71 1,064
Chicago Complete 42 22 39 41 567
Average
Climate EEM Energy Simple
Zone City Package Energy Cost Payback
Saving % Saving % Years
2A Baseline -- -- --
Houston Complete 43% 43% 1.5
4A Baseline -- -- --
Baltimore Complete 45% 44% 1.6
5A Baseline -- -- --
Chicago Complete 47% 43% 3.3
Figure 5: National average end-use contribution to overall
energy savings.
Interior Lighting 4%
SWH 6%
Heating 20%
Cooling 9%
Supply Fan 6%
Exhaust Fan 2%
Refrigeration 5%
Gas Cooking 39%
Electric Cooking 6%
Exterior Lighting 3%
Note: Table made from pie chart.
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| Title Annotation: | TECHNICAL FEATURE |
|---|---|
| Author: | Zhang, Jian; Schrock, Derek; Livchak, Andrey; Liu, Bing |
| Publication: | ASHRAE Journal |
| Article Type: | Reprint |
| Geographic Code: | 1USA |
| Date: | Mar 1, 2011 |
| Words: | 3438 |
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