Natural convection from heated room surfaces

Awbi, Hazim; Hatton, A.P.

doi:10.1016/s0378-7788(99)00004-3

Cited by 180 publications

(114 citation statements)

References 8 publications

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“…This allows anthropogenic heat fluxes from building heating, metabolic processes and electric waste heat to be implicitly incorporated into the model. The convective exchange coefficient was set to 1.2, which is within the range of typical values for natural convection from internal room surfaces (Awbi and Hatton, 1999). The internal view factors were calculated assuming four-storey buildings with a layout of two rows of five rooms of equal size separated by a hallway.…”

Section: Heat Storage Estimation On the Local Scalementioning

confidence: 99%

Heat storage and anthropogenic heat flux in relation to the energy balance of a central European city centre

Offerle

Grimmond

Fortuniak

2005

Intl Journal of Climatology

191

151

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The role of net heat storage Q S and anthropogenic heat Q F are considered in the surface energy balance for a downtown area in Łódź, Poland, for a 2 year period. Eddy covariance measurements provide estimates of the turbulent heat fluxes and radiometric measurements of the net all-wave radiation. A method to determine Q S based on representative surface temperature sampling is employed and compared with results from two other models. Results show that Q S is an important flux on the scale of hours to days and that it can be more than 10 W m −2 , on average, for periods of a week or more. By incorporating Q S estimates over hourly intervals, Q F was then determined as the residual of the energy balance. Using the approach, Q F averaged 32 W m −2 from October to March (60% of available energy), and −3 W m −2 from June to August. The physically unrealistic negative values for the summer period may suggest underestimation of turbulent fluxes, but no causal factor was identified. Although energy balance closure was close to 100% throughout the year, there was weaker agreement in the winter. This is attributed to errors in estimates of Q S and variation in Q F . Results highlight the need for future investigations of the urban surface energy balance to incorporate more complete measurements and estimates of Q S .

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Section: Heat Storage Estimation On the Local Scalementioning

confidence: 99%

Heat storage and anthropogenic heat flux in relation to the energy balance of a central European city centre

Offerle

Grimmond

Fortuniak

2005

Intl Journal of Climatology

191

151

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“…As yearly simulations are required to analyze the building energy use, detailed analysis of the flow around and in the building is not possible and the calculation of convective heat transfer has to be simplified using correlations. Since the past 50 years, many researchers have studied experimentally convective heat transfer coefficients (CHTC) in order to improve the accuracy of simulations [1][2][3][4][5][6][7][8][9]. The first correlations were derived from flat plate experiments [1,2].…”

Section: Introductionmentioning

confidence: 99%

“…The first correlations were derived from flat plate experiments [1,2]. Nevertheless these correlations are not always applicable to buildings due to the scale effect and different flow characteristics: Awbi and Hatton [3] showed that the CHTC for a heated wall tends to be higher than that of isolated plates with free edges. Therefore full-scale measurements have also been performed under different conditions [3][4][5][6][7][8][9].…”

Section: Introductionmentioning

confidence: 99%

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Experimental investigation of convective heat transfer during night cooling with different ventilation systems and surface emissivities

Dréau

Heiselberg

Jensen

2013

Energy and Buildings

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a b s t r a c tNight-time ventilation is a promising approach to reduce the energy needed for cooling buildings without reducing thermal comfort. Nevertheless actual building simulation tools have showed their limits in predicting accurately the efficiency of night-time ventilation, mainly due to inappropriate models for convection. In a full-scale test room, the heat transfer was investigated during 12 h of discharge by nighttime ventilation. A total of 34 experiments have been performed, with different ventilation types (mixing and displacement), air change rates, temperature differences between the inlet air and the room, and floor emissivities. This extensive experimental study enabled a detailed analysis of the convective and radiative flow at the different surfaces of the room. The experimentally derived convective heat transfer coefficients (CHTC) have been compared to existing correlations. For mixing ventilation, existing correlations did not predict accurately the convective heat transfer at the ceiling due to differences in the experimental conditions. But the use of local parameters of the air flow showed interesting results to obtain more adaptive CHTC correlations. For displacement ventilation, the convective heat transfer was well predicted by existing correlations. Nevertheless the change of floor emissivity influenced the CHTC at the surface of interest.

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“…Awbi and Hatton [4] studied natural convection in two different enclosures. The enclosures' dimensions were 2.78 by 2.30 by 2.78 m and 1.05 by 1.01 by 1.05 m. One wall in each of the enclosure was used as a "heat sink" through an air conditioner placed in a small room next to the large enclosure.…”

Section: Introductionmentioning

confidence: 99%

Numerical Determination of Effects of Wall Temperatures on Nusselt Number and Convective Heat Transfer Coefficient in Real-Size Rooms

Açıkgöz

Kıncay

2013

Advances in Mechanical Engineering

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A modeled room was numerically heated from a wall and cooled from the opposite wall in order to create a real-room simulation. The cooled wall simulated heat loss of the room, and the heated wall simulated the heat source of enclosure. The effects of heated and cooled wall temperatures on convective heat transfer coefficient (CHTC) and Nusselt number in the enclosure were investigated numerically for two-(2D) and three-dimensional (3D) modeling states. Different hot wall and cold wall temperatures were applied in order to obtain correlations that contained characteristic length in Rayleigh numbers. Results were compared with the results of previously reported correlations that have been suggested for vertical room surfaces in enclosures. In addition, new correlations for Nusselt number and average CHTC for enclosures for isothermal boundary conditions within indicated Rayleigh number ranges were derived through solutions. Average deviations of new correlations obtained for CHTC and Nusselt number from the numerical data were found 0.73% and 1.76% for 2D study, 3.01% and 0.49% for 3D study. It was observed that the difference between the 2D and 3D solutions in terms of CHTC and Nusselt number was approximately 10%.

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Natural convection from heated room surfaces

Cited by 180 publications

References 8 publications

Heat storage and anthropogenic heat flux in relation to the energy balance of a central European city centre

Heat storage and anthropogenic heat flux in relation to the energy balance of a central European city centre

Experimental investigation of convective heat transfer during night cooling with different ventilation systems and surface emissivities

Numerical Determination of Effects of Wall Temperatures on Nusselt Number and Convective Heat Transfer Coefficient in Real-Size Rooms

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