• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.12 no.1
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• pp.26-32
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• 2000

Design load calculations which depend on the thermal characteristics of the building structure such as the wall, roof, and fenestration provide the basic data for selecting an HVAC system and its equipment. Most of domestic multi-family houses include a high thermal storage layer like massive concrete structure and a floor heating structure. This study is to compare the results of the design heating load between steady state and unsteady state calculation in order to comprehend the thermal storage effect in multi-family houses. The design heating load under the steady state calculation is estimated from 5.4% to 7.8% larger than that under the unsteady state in the typical floor of a multi-family house model. The design heating load considered the safety factors like a orientation and location factor also is 21.4% to 26.5% larger than that by the unsteady state calculation. So, the safety factors for use of the practicing engineer are analyzed as the main factor of a heating plant oversizing.

• Journal of Power System Engineering
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• v.18 no.4
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• pp.23-28
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• 2014

In order to increase the performance of conventional hot water floor heating system, the bubble jet loop heat pipe for the system was developed. This experiment was conducted under next conditions : Working fluid was R-134a, charging ratio was 50%. A temperature of hot water, room temperature and flow rate were $60^{\circ}C$, $15^{\circ}C$ and 0.5~1.5 kg/min, respectively. The experimental results, show that bubble jet loop heat pipe had a high effective thermal conductivity of $4714kW/m^{\circ}C$ and a sufficient heat flux of $73W/m^2$ to heat the floor to $35^{\circ}C$ in case of the 1.5 kg/min of flow rate. So the bubble jet loop heat pipe has a possibility for appling of the floor heating system. Additionally, the visualization of bubble jet loop heat pipe was performed to understand the operating principle. Bubbles made by the narrow gap between inner tube and outer tube of evaporating part generate pulsation at liquid surface of working fluid. The pulsation had slug flow and wavy flow. So working fluid circulates in the bubble jet loop heat pipe as two phase flow pattern. And large amount of heat is transferred by the latent heat from evaporating part to condensing part.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.20 no.11
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• pp.711-717
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• 2008

Despite the fact that UFAD(Under Floor Air Distribution) systems have many benefits and are being applied in the field in increasing numbers, there is a strong need for an improved fundamental understanding of several key performance features of these systems. This study numerically investigates the effect of supplied air temperature and supplied flow rate on the performance of UFAD, especially focused on thermal comfort. Also this study has compared UFAD with conventional overhead air distribution system. In contrast to the well-mixed room air conditions of the conventional overheat system, UFAD system produces an overall floor-to-ceiling airflow pattern that takes advantage of the natural buoyancy produced by heat sources in the occupied zone and more efficiently removes heat loads and contaminants from the space. Thermal comfort parameters were evaluated by CFD approach and then PMV was computed to detect the occupants' thermal sensation. Results show that radiative mean temperature plays crucial role on the evaluating PMV. Until now, the radiative temperature has been the missing link between CFD and thermal comfort, but the present study paves the way for overcoming this weakness.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.20 no.3
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• pp.167-174
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• 2008

Cost related to building equipment accounts for about 85% of the life cycle cost of buildings. Therefore proper selection of air-conditioning system is important for reducing the overall cost of buildings. In this study, medium capacity EHP and GHP for air-conditioning a building with a floor area of 1,200 $m^2$ are compared economically. To consider all the factors of initial and operation costs effectively, an annual equal payment method is proposed. For the initial cost, cost of equipment, construction, installation, electric facility, financial subsidy and tax cut is considered. Cost of basic electricity, energy(electricity and gas), space charge, labor, insurance and repair is considered for the operation cost. Under the assumptions made in this study, overall cost of EHP is less than that of GHP, but this is not absolute and different outcome may result if different assumptions are made. This study is useful for those who are interested in choosing an air-conditioning system that costs less for mid-size buildings with simple calculations.

• Proceedings of the SAREK Conference
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• 2006.06a
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• pp.15-20
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• 2006

Despite the fact that UFAD (Under Floor Air Distribution) systems have many benefits and are being applied in the field in increasing numbers, there is a strong need for an improved fundamental understanding of several key performance features of these systems. This study numerically investigates the effect of design parameters on the performance of UFAD, especially focused on thermal comfort. The design parameters considered in this study include supplied air temperature, supplied flow rate, diffuser shape, swirl, diffuser location, and floor-to-floor height. Also this study has compared UFAD with over head system, on the point of thermal comfort by evaluating PMV using radiative mean temperature, which shows how inadequate the evaluation of thermal comfort can be when radiation is neglected. Until now, the radiative temperature has been the missing link between CFD and thermal comfort, but the present study paves the way for overcoming this weakness.

• Proceedings of the SAREK Conference
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• 2009.06a
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• pp.218-223
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• 2009

Cost related to building equipment accounts for about 85% of the life cycle cost of buildings. Therefore proper selection of air-conditioning system is important for reducing the overall cost of buildings. In this study, large capacity ice thermal storage and absorption chiller-heater for air-conditioning a building with a floor area of $9,900\;m^2$ are compared economically. For easy input and analysis, an Ms Excel VBA program has been developed. To consider all the factors of initial and operation costs effectively, an annual equal payment method is proposed. Under the assumptions made in this study, overall cost of an absorption chiller-heater is less than that of an ice thermal storage, but this is not absolute and different outcome may result if different assumptions are made. This study is useful for those who are interested in choosing an economical air-conditioning system for large-size buildings with simple calculations.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.21 no.1
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• pp.63-70
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• 2009

The air sterilization systems are investigated experimentally in this paper. The goal is to reduce bacteria, mold and viruses in office air by using a UV sterilizer installed inside a partition panel and wall-mounted unit. These systems allow occupants to turn the system on/off and to control the incoming air speed and direction. The partition air sterilization system conditions and sterilizes the air, and then delivers the clean air into the personal task area through the partition panels, which are connected to the pressurized under-floor plenum. Room air exits through the return grills mounted on the ceiling. The wall-mounted air sterilization system sterilizes the air, and then delivers the clean air to the personal task area from the wall. In this study a full-size experimental environment is established to investigate the immunization performance of these air sterilization systems. A typical office space scale is used in this study in order to find an optimal system to achieve a sterilized healthy micro-environment. Multiple system parameters, including volume flow rate and velocity of supplied air, were regulated during the experiments. The more air contact these air sterilization systems had, the better disinfection performance. Over 90% of eradication ratios were obtained by these two air sterilization systems. The results indicate that these systems can efficiently disinfect office air contamination.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.17 no.6
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• pp.505-513
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• 2005

We measured the time-dependent concentration of VOCs emitted from Ondol floor, furniture, and the wall made of various building materials. After obtaining results from the previous measurement, we developed the estimation equations of the concentration decay, and obtained the estimated graphs for the concentration decay under different air change rates and loading factor conditions by using the estimated equations. We conducted our tests by applying our measurements to real residences for 110 days in the case of furniture and for 40 days in the case of the floor. We also conducted experiments in the cases of various wall materials for 7 days which totaled 10 times. We used the GC/FID for experiments for real residences accord-ing to the specified procedures of the NIOSH 1501, and carried out experiments for wall materials according to the specified procedures of the ASTM 5116-97. When conducting experiments for wall materials, we set the temperature and relative humidity at $23^{\circ}C$ and $50\%$, respectively. We also set the air change rate and loading factor at 0.7/h and $1.617 m^2/m^3$, respectively. Our results showed that it is possible to predict proplrly the time-dependent concentration decay of VOCs by using logarithmic functions in both cases of experiments for real residences and for wall materials. Furthermore, we found that the concentration decay rate of VOCs increased rapidly as the air exchange rate increased while the concentration decay rate decreased as the loading factor increased.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.25 no.1
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• pp.14-19
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• 2013

The present study has been conducted for evaluating and comparing the performance of the underfloor air distribution system(UFAD) and the ceiling based air distribution system(CBAD) under cooling condition. Simulations and experiments were carried out for verifying the model by TRNSYS program about UFAD and CBAD. The results of simulation for various conditions of thermal load are summarized as followings. UFAD had an advantage for making thermal comfort because of lower temperature of the floor surface. Moreover, UFAD showed lower fan power about 30~50% than CBAD under the same conditions of thermal load. The energy saving rates of UFAD were increased to 17.7% in proportion to the thermal load on unoccupied zone(lighting). Ultimately, additional investigations should be done for analyzing optimized operating conditions of UFAD with considering the thermal performance of building envelop and the thermal load.

• Proceedings of the SAREK Conference
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• 2006.06a
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• pp.927-932
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• 2006

A simulation and experimental study for energy flow dynamics of floor radiant heating system were performed. The study was done under both environmental chamber and a house with several rooms. The unsteady energy analysis method using equivalent R-C circuit and radiation heat transfer analysis of enclosure analysis method with simple structured rooms were used for computer simulation. Also, first order dynamics with time delay in analyzing the return water was considered. The results of temperature changes of the simulation study are good fit with the ones of experimental one.