Experimental Study of Thermal Comfort in an Office Environment with an Underfloor Ventilation System

Abstract

Frequent changes in arrangement in office space and the huge amount of cables brought about by the extensive use of computers make the implementation of raised flooring a necessity in modern office buildings. Under floor ventilation systems that make use of the underfloor plenum for conditioned air distribution will therefore increase in popularity as they extend the flexibility of building services and take advantage of the raised floor to accommodate the HVAC system. Previous research has revealed that the top return type underfloor system saves a significant amount of energy, as the supply air temperature can be higher than that in a ceiling-based system. However, thermal discomfort due to tempera ture non-uniformity was also reported. This paper presents the experiment results of a laboratory study of the thermal performance for a floor return (FR) type underfloor system under different heat load densities and supply air temperatures. Vertical temperature differ ences and air velocities were found to be within the com fort limits stated in major international standards. The measured predicted mean vote and predicted percent age of dissatisfied values also satisfied the ISO Standard 7730. A comfortable environment was maintained by the FR type system under a dense internal heat load and with the supply air temperature set at as high as 18°C.

Keywords

Thermal comfort Underfloor ventilation Predicted mean vote Predicted percentage of dissatisfied Air temperature Air velocity

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References

Loudermilk K. : Underfloor air distribution solutions for open office applications. ASHRAE Trans 1999;105:605-613.

Akimoto T. , Nobe T. , Tanabe S. , Kimura K. : Floor-supply displacement air-conditioning: Laboratory experiments. ASHRAE Trans 1999;105:739-751.

Bauman F. , Pecora P. , Webster T. : How Long Can You Go? Air Flow Performance of Low-Height Underfloor Plenums. Berkeley, Center for the Built Environment, NSF Industry/University Cooperative Research Center, University of California, 1999.

Bauman F. , Webster T. : Outlook for underfloor air distribution. ASHRAE J, June 2001, pp 18-25.

Chow WK , Wong LT : Experimental studies on air diffusion of a linear diffuser and associated thermal comfort indices in an air-conditioned space. Build Environ 1994;29:523-530.

Chung KC , Lee CY : Predicting air flow and thermal comfort in an indoor environment under different air diffusion models. Build Environ 1996;31:21-26.

Bauman F. , Faulkner D. , Arens EA , Fisk WJ , Johnston LP , McNeel PJ , Pih D. , Zhang H. : Air movement, ventilation, and comfort in a partitioned office space. ASHRAE Trans 1992;98: 756-780.

Matsunawa K. , Iizuka H. , Tanabe S. : Development and application of an underfloor air-conditioning system with improved outlets for a 'smart' building in Tokyo . ASHRAE Trans 1995;101:887-901.

Bauman F. , Arens EA , Tanabe S. , Zhang H. , Baharlo A. : Testing and optimizing the performance of a floor-based task conditioning System. Energy Build 1995;22:173-186.

10.

Parsons KC : Human Thermal Environments. London, Taylor & Francis, 1993.

11.

Fanger PO : Thermal Comfort. New York, McGraw-Hill , 1970.

12.

Fanger PO : Calculation of thermal comfort: Introduction of a basic comfort equation. ASHRAE Trans 1966;73:III.4.1-III.4.20.

13.

Iso 1984: International Standard 7730. Moderate Thermal Environments: Determination of the PMV and PPD Indices and Specification of the Conditions for Thermal Comfort. Geneva, International Standards Organization, 1984.

14.

ASHRAE 1992: ANSI/ASHRAE Standard 55-1992. Thermal Environmental Conditions for Human Occupancy. Atlanta, American Society of Heating, Refrigerating and Air-Conditioning Engineers, 1992.

15.

Wan MP : Comparison of Underfloor Ventilation Systems and Ceiling-Based Ventilation System in Thermal Comfort and Indoor Air Quality Aspects; MPhil thesis The Hong Kong University of Science and Technology, Hong Kong, 2002.

16.

Humphreys MA : The optimum diameter for a globe thermometer for use indoors. Ann Occup Hyg 1977;20:135-140.

17.

Tanabe S. , Kimura K. : Comparisons of ventilation performance and thermal comfort among displacement, underfloor and, ceiling based air distribution systems by experiments in a real sized office chamber. Proc ROOMVENT '96, 1996, vol 3, pp 299-306.