thermal comfort and efficiency in food service...thermal comfort and efficiency in food service...

Thermal Comfort and Efficiency in Food Service

Jason B. Greenberg, P.E. Chief Mechanical Engineer

MGN, Inc. 635 Butterfield Road, Suite 310 Oakbrook Terrace, IL 60181 (630) 627-6078 [email protected] www.mgn.engineering

Learning Objectives

• Learn what constitutes a comfortable kitchen • Design proper air distribution for kitchens • Know how make-up air temperature impacts IEQ • Understand how hood selection impacts energy usage

• How many of you design restaurants?

• How many of you design mission critical facilities?

Quick Poll:

Statistics

• 14.7 million workers • About 10% of the U.S. workforce

• Employee turnover rate is 70% • 7 out of 10 workers leave each year

• About $5,800 in lost revenue per person • Estimated $150,000 per restaurant per year

The Headlines

When It Comes to Design…

We treat servers better than restaurant workers.

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Rethinking Thermal Comfort in Food Service

Rethinking Thermal Comfort

True or False: It’s impossible to keep a kitchen comfortable.


ASHRAE Standard 55 Kitchens have: • Higher humidity • Higher radiant temperatures

• Layered clothing


ASHRAE RP-1469 – Scope • Analyzed operative temperatures

• Summer (Aug-Oct 2010) • Winter (Jan-Feb 2011)

• Over 100 restaurants • Institutional • Casual • QSR


ASHRAE RP-1469 – By Climate Zone


ASHRAE RP-1469 – Results (Operative Temperature)


ASHRAE RP-1469 – Results (PMV)

C = Cooking D = Dishwashing P = Preparation


• RP-1469 – Results • Cooking areas were the warmest with operative

temperatures close to 100°F • Warm kitchens occurred in summer and winter • Workers became acclimatized to warmer

temperatures (up to a point)


• Appliances • When will it be used? • What will it be used for? • Equipment heat gain can account for nearly 50% of

the cooling load

• Heat gain per person can be on par with fitness centers.


• Do you have enough cooling? • Kitchens operate in the 50-100 sq. ft. per ton range.

• Do you have enough airflow? • Only accurate load calculations can determine that.

• How should you distribute it? • Multiple outlets at relatively lower velocities.

Designing Airflow in the Kitchen

Designing Airflow

Designing Airflow

Do not use directional diffusers

Designing Airflow

Perforated Return Diffuser with Side Entry Plenum

• Requires shop fabrication • Can lend to Contractor

confusion and improper installation

Designing Airflow

Laminar Flow Diffuser •  Varying designs from

different manufacturers • More likely to be

installed correctly •  Top duct connection

Designing Airflow

Fabric Diffuser •  Least expensive option •  Aesthetics are a concern •  May obstruct views

Designing Airflow Example Layout •  2x4 diffusers with 4 ft.

in between •  Proximity to hoods is

of little concern •  Provides consistent

comfort throughout the space

•  Maximum outlet velocity of 200 FPM

Supply Air Plenums

Supply Air Plenums

Make-up Air Heated in winter or not tempered in summer

•  The warm air is buoyant •  About 50% of the make-up

air goes back into the kitchen

•  Needs to be included in heat gain calculations

Supply Air Plenums

Make-up Air Cooled in summer or not heated enough in winter

•  The cool air sinks to the floor

•  The cold air can cause grease to condense out of the airstream

•  Grease can accumulate on the floor

Supply Air Plenums

Make-up Air Room neutral temperature

•  Ensures proper capture and containment

•  Does not add heat to the kitchen

•  Keeps the workers comfortable

Energy Consumption

Energy Consumption Energy Use Intensity (EUI) is highest for food service at about 280 MBH/S.F.

Energy Consumption

Cooling

Envelope Lighting Equipment People Ventilation

Heating

Envelope Ventilation

Energy Consumption

Short-circuit Hood (Internally supplied make-up air) • Internal make-up air is capped at 10% of exhaust • For every 1 CFM of supply over 10% of exhaust, exhaust must be increased 1 CFM.

• Recommendation: Do not use these hoods. Little to no energy savings.

Design Example

• Two (2) 8 ft. canopy hoods – 16 ft. total

• 23% reduction in exhaust airflow

Manufacturer A Manufacturer B 4,550 CFM of exhaust 3,500 CFM of Exhaust

Design Example • Resulting Energy Savings

Sacramento Chicago Miami Cooling (kWh) 1,186 2,458 15,770 Heating (Therms) 447 1,182 0 Exhaust Fan (kWh) 3,319 Supply Fan (kWh) 975 Annual Savings* $1,368 $1,649 $1,750 *Sacramento: $0.1525/kWh & $1.19/therm, Chicago: $0.0909/kWh & $0.876/therm, Miami $0.0872/kWh

Rethinking the Design Approach

Traditional Kitchens as ancillary spaces

Modern Kitchens as mission critical

Kitchen designer specifies hoods, fans & make-up air

Mechanical Engineer specifies hoods, fans & make-up air

Heated make-up air only

Heated, tempered and cooled make-up air

Conclusions

• Operative temperatures in kitchens can be outside of ASHRAE 55. Use your best judgment on design temperatures.

• Appropriate sizing of HVAC equipment requires an understanding of how the restaurant will operate.

• Air distribution should be lower velocity with multiple outlets and no 4-way diffusers.

• Provide space neutral airflow for hood supply plenums.

• Engineers should be designing kitchen ventilation systems.

Bibliography Fisher, Don and Swierczyna, Rich. 2014. 90.1 and Designing High Performance Commercial Kitchen

Ventilation Systems. ASHRAE. Livchak, PhD, Andrey, et al. 2005. The Effect of Supply Air Systems on Kitchen Thermal Environment.

ASHRAE. Michelin Guide. 2018. How High Employee Turnover is Affecting the Restaurant Industry.

https://guide.michelin.com/us/chicago/features/restaurant-employee-turnover/news National Restaurant Association. 2018. Restaurant Industry Facts at a Glance.

https://restaurant.org/News-Research/Research/Facts-at-a-Glance Stoops, John, et al. 2013. Thermal Comfort in Commercial Kitchens (RP-1469). ASHRAE.

U.S. Energy Information Administration. 2016. 2012 Commercial Buildings Energy Consumption Survey: Energy Usage Summary. https://www.eia.gov/consumption/commercial/reports/2012/energyusage/

Questions?

[email protected]

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