Mobile QR Code QR CODE : Korean Journal of Air-Conditioning and Refrigeration Engineering
Korean Journal of Air-Conditioning and Refrigeration Engineering

Korean Journal of Air-Conditioning and Refrigeration Engineering

ISO Journal TitleKorean J. Air-Cond. Refrig. Eng.
Open Access Monthly
  • ISSN : 1229-6422 (Print)
  • ISSN : 2465-7611 (Online)

외기 온도 변화가 핀-관 열교환기의 공기측 열전달계수와 마찰계수에 미치는 영향에 관한 실험적 연구 An Experimental Study on the Effect of the Air Temperature on the Air-Side Heat-Transfer Coefficient and the Friction Factor of a Fin-and-Tube Heat Exchanger

Nae-Hyun Kim ; Honggi Cho

In general, the air-side j and f factors of evaporators or condensers are obtained through single-design tests performed under air-dry and wet-bulb temperatures. Considering that the indoor or outdoor air temperatures vary significantly during the operation of an air conditioner, it is necessary to confirm that the experimentally-obtained j and f factors are widely applicable under variable air conditions. In this study, a series of tests were conducted on a two-row slit-finned heat exchanger to confirm the applicability. The results showed that, for the dry-surface condition, the changes of the tube-side water temperature, water-flow rate, and air temperature had virtually no effect on the air-side j and f factors. For the wet condition, however, the f factor was significantly affected by these changes; contrarily, the j factor is relatively independent regarding this change. The formulation of the possible reasoning is in consideration of the condensation behavior underneath the tube. The wet-surface j and f factors are larger than those of the dry surface, with a larger amount for the f factor.

수평면 전일사를 이용한 창 투과 일사량 계산 방법 Calculation Method for the Transmitted Solar Irradiance Using the Total Horizontal Irradiance

Byung-Ki Jeon ; Seung-Eun Lee ; Eui-Jong Kim

The growing global interest in energy saving is particularly evident in the building sector. The transmitted solar irradiance is an important input in the prediction of the building-energy load, but it is a value that is difficult to measure. In this paper, a calculation method, for which the total horizontal irradiance that can be easily measured is employed, for the measurement of the transmitted solar irradiance through windows is proposed. The method includes a direct and diffuse split model and a variable-transmittance model. The results of the proposed calculation model are compared with the TRNSYS-simulation results at each stage for the purpose of validation. The final results show that the CVRMSE over the year between the proposed model and the reference is less than 30 %, whereby the ASHRAE guideline was achieved.

광센서를 이용한 제상제어 방법에 대한 연구 A Study of the Defrosting Control in the Application of Photoelectric Sensors

ChangDuk Jeon

This study attempted to investigate the value of photoelectric sensors in terms of a defrost-control method. Tests were conducted in a calorimeter room under the heating with the defrost-performance test conditions described in KS C 9306. Accordingly, the photoelectric technology is a competitive defrost-control method that can precisely control the operational defrost cycle using the output voltages that are proportional to the frost height. The heating period is gradually reduced because the complex defrost-control method, for which the sensors initiate the defrosting process and the defrosting process is terminated by the time parameter, could not adjust the net defrosting time by itself. Therefore, a complex defrost-control method, for which the photoelectric sensors start the defrosting process and it is terminated by the temperature parameter, is preferred because of the adjustment of the net defrosting time. Regardless of the defrost-control method, the first defrosting cycle is activated earlier than the times that are determined in the second and third cycles and so on, because the first operation cycle can decide the characteristics of the subsequent cycle.

윈드터빈 자연환기 장치의 외기풍속 및 온도차에 따른 환기특성에 관한 실험연구 An Experimental Study on the Ventilation Characteristics of a Wind-Turbine Natural Ventilator According to the Outdoor-Wind Velocity and the Indoor/Outdoor-Temperature Difference

Dong-Hun Han ; Yeong-Sik Kim ; Hanshik Chung ; Hyomin Jeong ; Soon-Ho Choi

With the improvement of living standards, the ventilation for the mitigation of indoor or outdoor air-pollution problems has recently attracted a lot of attention. Consequently, the ventilation for the supply of outdoor fresh air into a room is treated as an important building-design factor. The ventilation is generally divided into the forced and natural types; here, the former can control the ventilation rate by using mechanical devices, but it has the disadvantages of the equipment costs, maintenance costs, and noise generation, while the latter is applied to most workshops due to the absence of noise and the low installation and maintenance costs. In this experimental study, the ventilation performance of a typical rotating-type natural ventilator, which is called a "wind turbine," was investigated with the outdoor-wind velocity and the indoor/outdoor-temperature difference. From the experiment results, it was confirmed that the temperature difference of 10℃ corresponds to the ventilation driving force with an outdoor-wind velocity of 1.0 m/s. Additionally, the intake-opening area of a building also exerts a great effect on the ventilation rates.

사무소 건축물의 건축기계설비 배관 부속자재 요율 산출 Calculation of the Attached-Piping-Material Rate for the Building Mechanical-Service System in Office Buildings

Yool Park

Currently, in comparison with other architectural estimations, the estimation work regarding building mechanical-service systems is time-consuming, and the process is continuously becoming more difficult because of the increased usage of the attached piping materials such as fittings and hangings in addition to their complicated construction processes. To improve this problem, the Korean authority provides a simple estimation method for the attached-material rate regarding the main piping material, which is the most time-consuming work in the architectural-mechanical estimation. However, to be an applicable method on construction sites, a proper conversion rate of the attached-piping material is still required for the proposed method regarding building usage and working types. Therefore, the purpose of this research is the calculation of the rate of the attached-piping materials such as the fittings and supports through the building of the mechanical-service work types of mechanical rooms, air conditioning, domestic water and hot-water supplies, and the drain-, vent-, and gas-piping work in office buildings that have been designed after 2010.

수송조건 내 포집 이산화탄소의 전달물성 예측. 1.점성 Prediction of Transport Properties for Transportation of Captured CO₂. 1. Viscosity

Won Jun Lee ; Rin Yun

In this study, the viscosity of a CO2-gas mixture was investigated for the transportation of the captured CO2-gas in pipelines and for the designing of a thermal system, both of which involve the utilization of the CO2-gas mixture. The viscosities of the CO2-gas mixture, CO2+CH4, CO2+H2S, and CO2+N2 were predicted using three different models as follows : Chung, TRAPP, and REFPROP. The predictability values of the models were validated by comparing the estimated results with the experiment data for the CO2+CH4 and CO2+N2 under high-density conditions. The Chung model showed 2.41%, which is the lowest mean deviation of the prediction among the model. Based on the Chung model, the mixture mole fractions were changed from 0.9, 0.95, and 0.97, the mixture pressure was ranged from 80 bar to 120 bar by 10 bar, and the mixture temperature was varied from 310 K to 400 K by 10 K to observe the effects of the parameters on the mixture viscosity. Considering the high mole fraction of the CO2 in the mixture, a significant variation of the mixture viscosity was observed close to the pseudo-critical temperature, and the viscosity for the CO2+H2S mixture shows the highest values compared with those of the CO2+CH4 and CO2+N2.

엑서지를 이용한 지역난방 열요금 제도 제안 Suggestion for a New Exergy-Based Heat-Tariff Assessment for a District-Heating System

Junghwan Moon ; Hoseon Yoo ; Jae-Heon Lee ; Seungjae Moon

In this study, the exergy that can be reflected in the energetic and economic values was used to assess the heat tariff of a district heating (DH) system instead of the enthalpy. It is difficult to directly apply the exergy to the current heat-charge system because of the complicated calculation; therefore, the difference between the supply and return temperatures was converted to the exergy-temperature difference for the ease of the heat-amount calculation. As a result of the exergy analysis for a DH substation, the exergy-temperature difference did not affect the surrounding temperature and pressure loss. The supply temperature and the maximum difference between the supply temperature and the return temperature exerted the main effect on the exergy-temperature difference. The new heat charge of a DH user was slightly reduced in winter compared with the previous charge, but the heat charges in the other seasons are almost the same. It is concluded from the assessment of the heat tariff for which the exergy is used that this tariff is more feasible for both DH suppliers and consumers compared with enthalpy.