• International Journal of Fluid Machinery and Systems
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• v.9 no.3
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• pp.229-236
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• 2016

Exergetic analysis was introduced in optimization of a rotating equilateral triangular internal cooling channel with staggered square ribs to maximize the net exergy gain. The objective function was defined as the net exergy gain considering the exergy gain by heat transfer and exergy losses by friction and heat transfer process. The flow field and heat transfer in the channel were analysed using three-dimensional Reynolds-averaged Navier-Stokes equations under the uniform temperature condition. Shear stress transport turbulence model has been selected as a turbulence closure through the turbulence model test. Computational results for the area-averaged Nusselt number were validated compared to the experimental data. Three design variables, i.e., the angle of rib, the rib pitch-to-hydraulic diameter ratio and the rib width-to-hydraulic diameter ratio, were selected for the optimization. The optimization was performed at Reynolds number, 20,000. Twenty-two design points were selected by Latin hypercube sampling, and the values of the objective function were evaluated by the RANS analysis at these points. Through optimization, the objective function value was improved by 22.6% compared to that of the reference geometry. Effects of the Reynolds number, rotation number, and buoyancy parameter on the heat transfer performance of the optimum design were also discussed.

• Journal of the Architectural Institute of Korea Structure & Construction
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• v.34 no.10
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• pp.19-26
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• 2018

The purpose of this study was to analyze characteristics and to develop estimation model of IHG(Internal Heat Gain) from appliance in domestic apartment units. To do this, it was defined the source of IHG from appliance and the calculation method through the case study of international and domestic codes. And the equipment related datum such possession, usage or not, etc were collected through field survey in apartment units, and the appliances' electricity consumption were measured separately from overall electricity consumption. Annual electricity consumption value were calculated with field survey datum and appliances' electricity consumption measurement datum, and then IHG value was calculated by applying PHPP v9 method. And it was conducted correlation analysis between IHG value and the area for exclusive use, the number of occupants, and then the IHG from applianace estimation model was deducted with regression analysis. Finally, it was analyzed the present level and of the domestic code(The Building Energy Efficiency Rating System) comparing with the value of estimation model, and the various international codes(HERS, Building America, SAP).

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.28 no.1
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• pp.9-15
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• 2014

This paper focuses on the heat gain of a lighting system, one of the most-used appliances in buildings, and its thermal effect within a low energy building. In this study, a dynamic thermal model of a lighting system is first established based on the first principle of thermodynamics. Then, thermal parameters of this model are estimated by experiments and an optimization process. Afterward, the obtained model of the system is validated by comparing simulation results to experimental one. Finally it is integrated into a low energy building model in order to quantify its thermal influence within a low energy building. As a result, heat flux of the lighting system, indoor temperature and heating energy demands of the building are obtained and compared with the results obtained by the conventional model of a lighting system. This paper helps to understand thermal dynamics of a lighting system and to further apply lighting systems for energy management of low energy buildings.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.15 no.5
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• pp.422-431
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• 2003

Theory of the building heat transfer is generally limited to the heat flux to the surfaces of windows and walls, which influences the indoor climate of a building, in the field of architectural environmental engineering. While the heat flux from the buildings to their environment has been considered in the viewpoint of urban climate, its conventional theory have been rarely examined. The purpose of this study is to propose a building-urban heat transfer model for defining the relation between the building and the urban climate by extending the building heat transfer model. In this study, the extended building heat transfer model, where response factor method is used, is established on the urban space and the indoor space by the boundary of building envelopes. Computer simulation (HASP/ACLD) is conducted on the subjected urban area by the established building-urban heat transfer model. As a result it is logically proved that the short waves of solar radiation, which interact with long Waves of radiation from the buildings and the earth, increase the urban air temperature ana buildings largely influence on the urban climate.

• Journal of the Korean Solar Energy Society
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• v.34 no.1
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• pp.39-47
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• 2014

Solar applications analysis and building energy performance depend on the quality of the solar resource data available. Unfortunately, most of the weather stations do not measure solar radiation data in Korea, as a reason many researchers have studied different solar radiation estimation models and suggested to apply them to various locations in Korea. In addition, they also studied the impact of hourly global solar radiation on energy performance of an office building by comparing the simulated building energy consumptions using four different weather files, one using measured, and three estimated solar radiation from different models, which are Cloud-cover Radiation Model (CRM), Zhang and Huang Model (ZHM), and Meteorological Radiation Model (MRM), and concluded that there was some impact on energy performance of the building due to the using different solar radiation models. However, the result cannot be applied to all other buildings since the simulated office building for that study only used limited building characteristics such as using fixed values of solar heat gain coefficient (SHGC) and window-to-wall ratio (WWR), which are significant parameters related to solar radiation that affect to the building energy consumptions. Therefore, there is a need to identify how the building energy consumption will be changed by varying these building parameters. In this study, the impact of one measured and three estimated global solar radiation on energy performance of the office building was conducted taking account of SHGC and WWR. As a result, it was identified that the impact of four different solar radiation data on energy performance of the office building was evident regardless SHGC and WWR changes, and concluded that the most suitable solar models was changed from the CRM/ZHM to the MRM as SHGC and WWR increases.

• Journal of the Korean Society for Heat Treatment
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• v.36 no.6
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• pp.402-411
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• 2023

In order to examine the effect of cementite precipitated on the steel surface on the carburizing rate, the carburizing process was carried out at various boost times to measure the mass gain and carbon flux, phase analysis and carbon concentration analysis were performed on the surface of the carburized specimen. In the case of the only boost type, the longer the boost time, the more the mass gain by the diffused carbon follows the parabolic law and tends to increase. In particular, as the boost time increased, the depth of cementite precipitation and the average size of cementite on the steel surface increased. At a boost time of 7 min, the fraction of cementite precipitated on the surface is 7.32 vol.%, and the carburizing rate of carbon into the surface (surface-carbon flux) is about 17.4% compared to the calculated value because the area of the chemical (catalyst) where the carburization reaction takes place is reduced. The measured carbon concentration profile of the carburized specimen tended to be generally lower than the carbon concentration calculated by the model without considering precipitated cementite. On the other hand, in the pulse type, the mass gain by the diffused carbon increased according to the boost time following a linear law. At a boost time of 7 min, the fraction of cementite precipitated on the surface was 3.62 vol.%, and the surface-carbon flux decreased by about 4.1% compared to the calculated value. As a result, a model for predicting the actual carbon flux was presented by applying the carburization resistace coefficient derived from the surface cementite fraction as a variable.

• Proceedings of the SAREK Conference
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• 2008.06a
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• pp.925-930
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• 2008

As office automation appliances and communication equipments are adopted in office buildings, internal heat gains increase gradually. When making simulation model, internal heat gains are usually set up with standard values or ignored. Therefore, the impact of the internal heat gains has been ignored or not been focused although it is recognised as significant contributor to heating/cooling load of buildings. This study focused on the impact of internal heat gains on curtain wall buildings. the amount and schedules of heat internal gains profiles not only affect the profiles of heating/cooling loads, but also make impact on reducing the effectiveness of high performance glazing systems. It is important to identify internal heat gains profiles before considering the installation of high performance glazing systems.

• Journal of Institute of Control, Robotics and Systems
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• v.7 no.7
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• pp.567-573
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• 2001

A real-time HVAC system is proposed which implements real-time control of thermal environment for virtual reality. It consists of a pair of hot and cold loops that serve as thermal reservoirs, and a mixing box to mix hot and cold air streams flowing if from loops. Their flow rates are controlled in real-time to meet a set temperature and flow rate. A cascade control algorithm along with gain scheduling is applied to the system and test results shows that the closed-loop response approached set values within 3 to 4 seconds.

• Journal of Biosystems Engineering
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• v.22 no.4
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• pp.459-468
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• 1997

To optimize the design and operation of a soil- air heat exchanger system, the effects of variables characterizing system design and operation on the performance of the system were analyzed by a theoretical model which included the three-dimensional transient heat conduction equation. The solution of the theoretical model was acquired by a computer program that uses Finite Difference Methods and Gauss-Seidel iteration computation, in which the time discretization scheme was an implicit difference appoximation. The computer program was validated first by comparison of the results for different grid sizes. Air outlet temperature, energy gain, and heat exchange efficiency of the system were analyzed based upon the tube diameter, tube length, tube thickness, and tube thermal diffusivity.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.29 no.10
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• pp.515-529
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• 2017

EnergyPlus, which is widely used in various fields, provides Simple Window Model, a window model that can be used practically. However, the results of building load using the model are different from those of the standard model. The main cause of the deviation by Simple Window Model was analyzed to be due to the assumption that all windows were considered as single layer. The purpose of this study is to propose a window model that improves the cause of deviation by Simple Window Model and can be easily calculated from the algebraic relations. The proposed window model solved the heat balance equation algebraically by using seven window characteristic coefficients. The coefficient relationships consisted of the heat transmission coefficient and solar heat gain coefficient as input parameters make practical use and calculation possible. As a result of comparing the deviation between each window model by implementing the dynamic analysis method, the proposed window model showed that the deviation of the total heating/cooling energy consumption was reduced to 1/3 compared to Simple Window Model for one year. Although the maximum energy consumption did not show any significant improvement, the indoor temperature evaluation showed significantly reduced deviation.