Abstract
Heat transfer coefficients are often used to describe the thermal behaviour of radiant systems and how it transfers heat between the cooled/heated surface and the room. In addition to current standards, numerous studies have been conducted to obtain the heat transfer coefficients through experiments and simulations. However, inconsistency is evident in the values or expressions suggested. Thus, this study investigated possible sources of discrepancy through an extensive literature review on articles and standards that focused on the heat transfer coefficients at the cooled/heated surface. Measurement data provided by different authors were extracted to compare both the amount of heat transfer and the actual heat transfer coefficients. Consequently, suggested values and expressions were used to predict the measurement data in other articles to examine their accuracy. Comparison of the results showed that the radiant heat transfer coefficients had a consistent value throughout the literature and had prediction error within ±20%. However, larger deviations and prediction errors were seen in the total and convective heat transfer. It was suggested that some of the sources of error may have been the calculation procedure of each heat transfer mechanism, choice of reference temperature and its measurement height/position, and room dimensions.
Highlights
Radiant systems are commonly used as a comfortable and energy efficient alternative in buildings in many countries
Comparison of the results showed that the radiant heat transfer coefficients had a consistent value throughout the literature and had prediction error within ±20%
In the detailed calculation suggested by ASHRAE [8], the differences in the hydraulic diameters resulted in an error of about 1 W/m2K at ∆T=8 K in the resulting convective heat transfer coefficient
Summary
Radiant systems are commonly used as a comfortable and energy efficient alternative in buildings in many countries. Heat transfer of radiant systems is different from that of conventional all-air systems since cooling/heating is provided by both radiation and convection from a cooled/heated surface. Heat transfer coefficients are values commonly used in calculations regarding the thermal behaviour of radiant systems, such as load calculation and dimensioning. H height of heated/cooled surface (m) hc convective heat transfer coefficient (W/m2K). Numerous investigations on the heat transfer coefficients have been carried out in previous studies, each resulting in different suggested values. Literature reviews on suggested values [1] and convective heat transfer coefficients [2, 3] have been conducted in the past. This study presents a preliminary literature review on the heat transfer coefficients for radiant cooling and heating systems, with an emphasis on measurement conditions/setup and data.
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