• Journal of the Korean Solar Energy Society
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• 제37권1호
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• pp.71-80
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• 2017

A Data center houses a large number of server computers, storage and etc in racks. With the rapid increase of heat generation rates per rack in a data center, energy consumption rates for cooling have been increased year by year. In this study, energy conservation effects of a MOA (multi-stage outdoor air enabled) cooling system in a data center has been investigated when it is applied to 5 different locations, Korea. As results, Energy conservation effects of the MOA cooling system was achieved at about 20% to 30%. Humidifier operation time was 40 to 55 days when supply air temperature was maintained at 13, and humidity condition was kept within the allowed range even though humidifier was off. Furthermore, humidification was not needed when supply air temperature was maintained at $25^{\circ}C$. In selected 5 locations in Korea, the difference of regional climatic conditions affected no more than 5% in cooling energy consumption rates.

• Proceedings of the SAREK Conference
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• 대한설비공학회 2009년도 하계학술발표대회 논문집
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• pp.695-700
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• 2009

Maintaining an IAQ with fresh in school building is very important because the good IAQ can be possible to improve the academic performance. Since school buildings are very dense and require a lot of fresh air, the need for ERV(Energy Recovery Ventilator) has become obvious. While opening a window does provide ventilation, the building's heat and humidity will then be lost in the winter and gained in the summer, both of which are undesirable for the indoor climate and for energy efficiency. ERV technology offers an optimal solution: fresh air, better climate control and energy efficiency. However, when the outdoor air condition is favorable to control the indoor environment such as spring and autum in Korea, heat exchange in ERV would rather increase the cooling load than diminish. Economizer cycle control which using the outdoor air in controlling the indoor thermal environment has many benefit in terms of energy saving and IAQ control. In this study, the ERV with economizer cycle control will be suggested. And then the system control characteristics and energy saving effect will be analyzed through the TRSNSYS Simulation.

• Journal of Power System Engineering
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• 제18권3호
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• pp.73-78
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• 2014

Recently, Free cooling system usage has increased at many buildings in intermediate and winter season. Free cooling system is used to reduce the energy consumption of refrigeration in that season. Free cooling system is refrigeration system using cooled water. In general, this system is applied with the building having refrigeration load at all time such as a data center. In this study, energy consumption of a data center taking free cooling system in Ulsan was evaluated by the software HYSYS. the main result is as in the following : free cooling system is effective from January to April and from November to December. In case of Ulsna in 2013, using free coolng system is able to spend refrigeration energy of about 15% less than existing system. According to this result, it is appropriated that free cooling system is used in building having refrigeration load at all time such as data center.

• Journal of Bio-Environment Control
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• 제3권1호
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• pp.58-65
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• 1994

It is necessary to effective temperature and humidity management for normal growth of crops in protected cultivation during the summer season. Because the highest temperature of vinyl house inhibit normal growth of crop and decrease of crop production or marketability in summer season. Finally, the vinyl house was impossible some crop cultivation in summer season. This study was conducted to investigate effective and economic method for temperature drop in protected cultivation during the summer season. 1. In medium size vinyl house(5$\times$13$\times$3m), the effect of temperature drop appeared the highest in treatment of shading with aluminium thermal curtain＋fog system＋ventilation with fan. The effect of temperature drop was about 1$0^{\circ}C$ lower than outer air temperature and about 4$^{\circ}C$ lower than outer soil temperature. 2. The effect of temperature drop according to shading with aluminium thermal curtain＋fog system＋ventilation with fan during the highest temperature of summer season Jul., 20 to Aug., 21 was appeared about 8$^{\circ}C$ lower than outdoor above ground(1.2m) and about 7$^{\circ}C$ lower than outdoor surface ground. 3. The changes of solar radiation during a day according to shading with aluminium thermal curtain＋ventilation with fan and shading with black curtain＋ventilation with fan treatments was appeared respectively about 29.3%, 32.5% of outdoor solar radiation a fine day and respectively about 27.4%, 31.8% of outdoor solar radiation a cloudy day.

• Land and Housing Review
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• 제12권1호
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• pp.129-137
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• 2021

External shading devices are well known solar control devices that can help reduce the cooling load of commercial buildings. For this study, experiments were conducted to examine the feasibility of shading devices in reducing both the cooling and heating loads. The influence of sky radiant cooling during winter was verified for the external shading device, internal roller blind, and window. Results can be summarized as follows. The temperature difference between the inner and outer surfaces of the window with the external shading device was 11.8℃ compared to 14.6℃ for one without the external shading device. This 2.8℃ difference was due to heat exchange by sky radiation when the surface temperature of the shading device was lower than the ambient outdoor air temperature. The roller blind resulted in a lower temperature of 0.8℃ compared to the average temperature of the window's air cavity. This was due to heat exchange by sky radiation of the roller blind surfaces. Without shading devices, the outside surface temperature of the window is about 3℃ higher. The study also found that when external shading devices were installed on both the southwest and southeast sides, the outside surface temperature of the windows were lower on the southwest side than the southeast side.

• Journal of the Korea Academia-Industrial cooperation Society
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• 제18권4호
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• pp.15-20
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• 2017

Currently, residential air conditioners operate as a heat pump during winter. In this case, the outdoor heat exchanger acts as an evaporator obtaining heat from cold air. On the other hand, it acts as a condenser during summer transferring heat to hot air. The outdoor temperature changes significantly from high to low. Generally, the air-side j and f factors are obtained at a standard outdoor temperature. Therefore, the applicability of the j and f factors under different outdoor conditions needs to be checked. In this study, tests were conducted for a two-row louver finned heat exchanger changing the outdoor temperature to subzero. The effects of the tube-side brine flow rate were also checked. The results showed that air-side j and f factors were essentially constant and independent of the outdoor temperature, suggesting that an extension of j and f factors obtained under standard conditions to a low outdoor temperature is acceptable. All j and f factors agreed within 9% and 3%, respectively. Tests were also conducted by changing the coolant flow rate. Both the j and f factors did not change according to the flow rate, suggesting that the tube-side heat transfer correlation is acceptable.

• Korean Journal of Environmental Agriculture
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• 제15권2호
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• pp.223-231
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• 1996

This study was to develop the most effective cooling system which is needed to cool greenhouse during summer night for getting up early blooming of strawberry. Various cooling systems were designed and constructed to use cool air and water from an abandoned coal mine. Cooling systems built for this study included an evaporative cooling system with cooling pad, heat exchanger using small or large radiator, and cooling duct for drawing cool air from coal mine. The cooling pad, small or large radiator and cooling duct were individually tested. Also, combined cooling system was tested by operating cooling pad, small radiator, and cooling duct simultaneously. The results in this study showed that individual cooling systems such as cooling pad, small radiator, and cooling duct had about the same effect on cooling greenhouse. The combined cooling system had little better cooling effect than individual cooling system except the large radiator. The most effective cooling system for cooling of greenhouse was obtained by using a large radiator as the heat exchanger. By using a large radiator, temperature in greenhouse was dropped into about $15^{\circ}C$ when outside temperature was $23-24^{\circ}C$ during summer night.

• Journal of agriculture & life science
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• 제44권4호
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• pp.69-77
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• 2010

Fuzzy control is widely used for improving temperature control performance as controlling ventilation in greenhouse because the technique can respond more flexibly to the outside air temperature and wind speed. By pre-studied PID and normal fuzzy control this study was performed to obtain the fundamental data that can be established in better greenhouse ventilation control method. The temperature control error by the simple fuzzy control was $1.2^{\circ}C$. The accumulated operating size of the window and the number of operating were 84% and 13, respectively. These showed equivalent control performance with pre-studied result that control error. The accumulated operating size of the window and the number of operating were 75% and 12, respectively. The proposed fuzzy technique was simple control logic method compared with step and PID control methods, but it showed equivalent performance. Therefore, the proposed simple fuzzy control method could be used in micro controller of small programmable memory size and many applications.

• Transactions of the Korean Society of Mechanical Engineers B
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• 제40권2호
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• pp.85-91
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• 2016

The Positive Temperature Coefficient (PTC) is used for cabin air heating of a battery electric vehicle, which is different from conventional vehicles. Since the PTC heater consumes a large quantity of power in a parasitic manner, many valuable studies have been reported in the field of alternative heat pumps. In this study, a model for an R134a heat pump taking into account the thermal environment of the cabin was developed for a MATLAB/SIMULINK(R) platform. Component and cabin models are validated with reference values. Results show that the heat pump is more competitive for parasitic power consumption over all ambient temperature conditions. Additionally, the method of waste heat recovery to overcome disadvantages when temperatures are below zero is applied to efficiently operate the heat pump.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2011년도 춘계학술대회 초록집
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• pp.199-199
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• 2011

ATES(Aquifer Thermal Energy Storage) 열펌프 시스템은 기존의 다양한 열원 적용 시스템 대비 효율이 우수한 것으로 알려져 유럽과 미국에서 건물 냉난방 시스템으로 적용되고 있다. 특히, ATES 시스템은 기존의 냉난방 시스템 대비 경제성이 우수한 것으로 알려져 있으나 국내에서는 이에 대한 연구 결과는 전무한 실정이다. 본 연구에서는 ATES 열펌프 시스템의 실증 성능 결과를 분석하였으며, LNG 보일러와 에어컨을 사용하는 기존의 냉난방 시스템을 비교시스템으로 ATES 열펌프 시스템의 경제성 평가를 수행하였다. ATES 시스템의 연간 실증 성능 실험결과 ATES 시스템은 외기온도와 무관하게 연중 안정적인 성능을 나타내었다. 경제성 평가시에 생애주기법(Life Cycle Cost)을 적용하여 ATES 열펌프 시스템의 설치 및 운전에 필요한 총 소요비용을 산정하고, 이 결과를 바탕으로 투자회수기간법을 통해 ATES 시스템의 투자회수 기간을 산정하였다. 생애주기법 적용 시에 현재가치법을 사용하였으며, 현재가치법은 수명주기에 발생하는 모든 투자비용과 절감액을 일정한 시점을 기준으로 등가환산하는 방법을 의미한다. 현재가치법에 사용되는 현재가치는 초기비용과 현재가치계수의 곱으로 나타나는데, 여기에서 현재가치계수는 임의의 이자율로 일정기간 동안 정기적인 할부금액이 적립될 때의 현재금액을 구하기 위해 사용하는 계수를 의미한다. 전기와 LNG는 각각 2009년 7월의 (주)한국전력공사와 (주)한국가스공사의 고시요금을 적용하였다. 본 시스템은 실증 설비용량인 20RT를 대상 건물로 가정하였고, 초기투자비는 크게 공사비와 냉난방 설비 구입비로 구성되어 있으며, 기본적인 물가지표는 (사)한국물가정보(KPI)의 고시 데이터를 참조하였다. 각 시스템의 초기투자비는 ATES 시스템이 비교대상 기존 냉난방 시스템 대비 5.7배 높게 나타났다. 일일 8시간 사용기준으로 계절별 전력요금을 고려한 연간운전 비용은 ATES 시스템이 기존 시스템 대비 냉난방 시에 각각 77%와 16%를 나타내어 운전비용이 연간 절감되었고, 난방 운전 시 절감 비율이 냉방시보다 크게 나타났다. 두 시스템에 대한 생애주기비용을 산정하기 위하여 에어컨과 보일러의 기존시스템과 ATES 시스템의 가용연수를 모두 20년으로 설정하였고, 유지보수 비용은 초기투자비용의 2%로 설정하고, 할인율은 은행 예금이자를 기준으로 5%로 설정하였다. 전기와 LNG의 요금 상승률은 (사)한국물가정보를 바탕으로 각각 2%와 8%로 가정하였다. 이러한 조건에서 생애주기법을 이용한 경제성평가는 ATES 시스템의 경우 생애운전비용이 초기투자비용보다 작게 나타났으며, 기존 냉난방 시스템은 생애운전비용이 초기투자비용에 비하여 높게 나타났다. 본 연구 대상 ATES 열펌프 시스템의 실증 성능 데이터와 기존 문헌으로부터 얻은 냉난방 시스템의 성능 결과를 이용하여 생애주기 비용을 적용한 결과 ATES 시스템의 기존 시스템 대비 투자회수 기간은 6.62년으로 나타났다. 특히, 본 연구에서는 ATES 시스템이 국내 최초로 적용됨에 따라 스크린 등의 부품을 다소 고가의 제품으로 시스템에 적용하였으므로 ATES 시스템의 신뢰성과 안정성이 확보되면 초기 투자비 감소가 가능할 것으로 예상되며, 기존 시스템 대비 투자회수 기간은 더욱 감소될 수 있을 것으로 예상된다.