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Simulated Impact of Energy Codes: Thermal Comfort in Heated-and-Ventilated-Only Warehouses

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©2018 This excerpt taken from the article of the same name which appeared in ASHRAE Journal, vol. 60, no. 12, December 2018.

By Christian Taber, Member ASHRAE, BEMP, HBDP; Donald Colliver, Ph.D., P.E., Presidential/Fellow/Life Member ASHRAE

About the Authors
Christian Taber is principal engineer-codes and standards for Big Ass Fans in Lexington, K.Y. Donald Colliver, Ph.D., P.E., is professor and director of graduate studies for Biosystems Engineering at the University of Kentucky in Lexington, K.Y.

Building energy codes and standards contain minimum requirements that provide a path to energy efficient buildings and building systems. ASHRAE/IES Standard 90.1 and the International Energy Conservation Code (IECC) are the main national building code models in the United States. Both Standard 90.1 and the IECC are updated on three-year cycles with the goal of reducing building energy consumption.

Decreased energy consumption in each update is achieved through a variety of energy conservation measures including: increased insulation levels, reduced lighting power density and reduced solar heat gain from fenestration. These measures not only save energy, they also have potential to improve thermal comfort of occupants in non-air-conditioned spaces.

So let’s examine the predicted thermal comfort level using a prototype warehouse and compare using Standard 90.1-2004, 2010 and 2016 energy efficiency levels.

The Fanger and Adaptive comfort models will be used to determine occupant thermal satisfaction. The OSHA Heat Index will also be used to evaluate frequency of high-risk hours for occupants and impacts on productivity will be examined.

Using EnergyPlus, a warehouse building model that prescriptively complied with Standard 90.1-2004, -2010, and -2016 for each of the seventeen climate zones (for a total of 51 prototypes) were simulated and the results were compiled for analysis. The simulations included the Fanger and Adaptive Comfort models to determine occupant thermal comfort levels and predict worker productivity impact. The NOAA Heat Index was also used to determine the frequency of high-risk hours for the warehouse occupants. An additional 17 models were simulated to evaluate elevated air speed impact on worker productivity.

Methods and Procedures

The modeled warehouse is approximately the same as the warehouse used by PNNL in the development of the Advanced Energy Design Guide for Small Warehouses and Self-Storage Buildings. It is 50,000 ft2 (4645 m2), has a floor-to-ceiling height of 28 ft (8.5 m) and has three thermal zones. The office zone is 2,550 ft2 (237 m2). The fine-storage zone of the warehouse is 12,450 ft2 (1157 m2). The bulk zone of the warehouse is 34,500 ft2 (3205 m2).

The warehouse occupant count was assumed to be zero in the PNNL models. Based on the internal load assumption of three operating forklifts, it was determined the number of occupants in the bulk warehouse area should be increased. Various sources were evaluated and significantly different occupant densities were noted.

Based on widely varying occupant densities, a conservative value of 5,000 ft2 (465 m2) per occupant was used to determine the number of occupants in the fine and bulk storage zones. Occupants are present from 6 a.m. until 6 p.m., with the building fully occupied from 8 a.m. to 12 p.m. and 1 p.m. to 5 p.m. The heat gain for the warehouse occupants was calculated to be 730 Btu/h per person based on an average metabolic rate of 2.0 met, heat generation of 5.4 W/ft2 (58.15 W/m2) of skin and 20 ft2 (1.84 m2) of skin.

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