Elsevier

Energy and Buildings

Volume 30, Issue 2, June 1999, Pages 167-175
Energy and Buildings

Thermal comfort and energy consumption of the radiant ceiling panel system.: Comparison with the conventional all-air system

https://doi.org/10.1016/S0378-7788(98)00084-XGet rights and content

Abstract

The purpose of this study is to investigate the various characteristics of a radiant ceiling panel system and their practical application to office buildings. The radiant ceiling panel system and conventional air-conditioning system were compared in terms of thermal comfort, energy consumption, and cost. Thermal environment, along with human response, was tested by using a small meeting room equipped with radiant ceiling panels. The responses were collected by questionnaires given to the male subjects in the room. The experiment for the female subjects was conducted separately. Results show that the radiant ceiling panel system is capable of creating smaller vertical variation of air temperature and a more comfortable environment than conventional systems. When using a cooled ceiling, a small volume of supplied air creates a less draught environment, which reduced the discomfort of feeling cold in the lower part of the body. Numerical simulation of yearly energy consumption and cost estimation were conducted. Typical office rooms located on the 3rd, 4th, and 5th floor of a six-floor building in the Tokyo area were simulated. Since part of the sensible heat load is handled by radiant ceiling panels, the volume of supplied air can be reduced, leading to lower energy consumption for air transport. By using the radiant ceiling panel system in one of the three floors of the simulated building, energy consumption can be reduced by 10%. Estimated pay back time was from 1 to 17 years depending on the market price of the radiant ceiling panel.

Introduction

In Japan, a forced convection air-conditioning system, which controls room temperature by supplying cold or hot air, has been the most commonly applied to office buildings. While the system has been popular in view of merely cooling or heating rooms, some discomfort factors have been claimed. The system is likely to create uncomfortable environment caused by draught and air temperature differences between the human head and foot. Many complaints about air-conditioning systems have been claimed, especially in summer by female occupants. The required level for air-conditioning quality in office buildings has gotten higher recently. It could be possible to create an ideal thermal environment with a very expensive system that consumes large amount of energy. In reality, we need to develop a practical system that creates a more comfortable thermal environment than conventional all-air systems with lower energy consumption. One of these solutions is the radiant ceiling panel system. This system utilises a thermal radiation effect for air-conditioning with radiant panels mounted on the ceiling. The system is believed to create a superior thermal environment than conventional all-air systems. Since part of the heat load is handled by radiant ceiling panels, the volume of supplied air can be reduced, leading to lower energy costs for air transport power. The system was released into the European market recently [1].

Despite the number of advantages reported in Europe, some problems have been identified for its application in the Japanese market. The first point is the climate in Japan, which greatly differs from that of Europe. In summer, it is not only hot but also humid with the average dew point in August exceeding 22°C; in winter, it is relatively dry. Radiant ceiling panel systems in Japan definitely require dehumidification to avoid water condensation on the panels while cooling. The system also needs ventilation to maintain indoor air quality, for which an air handling unit should be incorporated. Optimal system and operating conditions must be investigated in order to reduce energy consumption 2, 3. Furthermore, if used for heating, the system allegedly causes discomfort created by the warmed ceiling panels.

The purpose of this study is to investigate various characteristics of the radiant ceiling panel system and its practical applications. This paper describes the experimental investigation of thermal comfort and the numerical simulation of energy consumption.

Section snippets

Experimental system and method

Thermal environments, along with human responses were investigated by using a meeting room equipped with radiant ceiling panels (Fig. 1). The meeting room has about 33 m2 floor area with the ceiling 2700 mm above the floor. Radiant ceiling panels cover 56% of the total ceiling area. The structure of the ceiling panel originally developed is shown in Fig. 2. The surface of the ceiling panels was cooled or heated by cold or hot water supplied into the copper pipe. Air Handling Unit (AHU) was

Numerical simulation model

To compare the energy consumption and cost efficiency of the different air-conditioning systems, typical office rooms located on the 3rd, 4th, and 5th floor of a six-floor building in Tokyo were simulated as a case study. Total area of air-conditioned space was set at 1764 m2. It was determined that about 70% of the ceiling was covered by radiant ceiling panels when the radiant ceiling panel system was applied. Calculated conditions relating to the thermal load are as follows: floor area per

Conclusions

The radiant ceiling panel system and conventional air-conditioning systems have been compared both experimentally and numerically in terms of thermal comfort, energy consumption and cost efficiency. The following conclusions have been reached:

  • 1.

    The radiant ceiling panel system creates a superior radiant environment while cooling.

  • 2.

    The system is also capable of creating a smaller vertical variation of air temperature, while heating, than a conventional system.

  • 3.

    The radiant ceiling panel system

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    Cooling ceilings—an opportunity to reduce energy costs by way of radiant cooling

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    (1993)
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