• Journal of Biosystems Engineering
• /
• v.27 no.6
• /
• pp.565-572
• /
• 2002

In order to control the root-zone temperature of greenhouse crops in the hydroponics at hot and cold season, heat pump system for cooling and heating was built and tested in this work. The system was air-to-water type and vapour compression type. The heating and cooling mode was selected by the four way valve. Capacity of the compressor was 3.75㎾ and heat transfer area of the evaporator and the condenser were 3.05㎡ and 0.6㎡, respectively. According to the performance test, it could supply heat of 42,360 to 64,372kJ/h depending on the water circulation rate of 600 to 1,500ℓ/h, respectively, when indoor air temperature was 10∼20$\^{C}$. COP of heat pump system was 3.0 to 4.0 in the heating mode. But, COP of the cooling mode was 1.3 to 2.1 at indoor temperature of 20∼35$\^{C}$. The feasibility test in the greenhouse the developed heating and cooling system was installed, showed that the heating cost of the developed system was only about 13% of that of the conventional heating system. The heating cost of the developed system was 367won/day(electric consumption 9.7㎾h/day), while that of the conventional system was 2,803won/day(oil consumption 7.7ℓ/day) at the same heating mode.

• Journal of the Korean Society for Geothermal and Hydrothermal Energy
• /
• v.17 no.3
• /
• pp.30-40
• /
• 2021

This paper compares the annual energy performance of four different types of air-conditioning systems in a medium-sized office building. Chiller and boiler, air-cooled VRF, ground-source VRF, and ground-source heat pump systems were selected as the systems to be compared. Specifically, the energy performance of the GSHP system and the ground-source VRF system were compared with each other and also with conventional HVAC systems including the chiller and boiler system and air-cooled VRF system. In order to evaluate and compare the energy performances of four systems for the office building, EnergyPlus, a whole-building energy simulation program, was used. The EnergyPlus simulation results show that both the GSHP and the ground-source VRF systems not only save more energy than the other two systems but also significantly reduce the electric peak demand. These make the GSHP and the VRF systems more desirable energy-efficient HVAC technologies for the utility companies and their clients. It is necessary to analyze the impact of partial load performance of ground-source heat pump and ground-source VRF on the long-term (more than 20 years) performance of ground heat exchangers and entire systems.

• Journal of Biosystems Engineering
• /
• v.43 no.4
• /
• pp.342-351
• /
• 2018

Purpose: Recently, an increasing number of farms have been cultivating shiitake mushrooms using a sawdust substrate and a cooler/heater. In this study, an attempt was made to develop an environmental control system using a heat pump for cultivating high-quality shiitake mushrooms. Methods: An environmental control system, consisting of an air-to-water type heat pump, a thermal storage tank, and a radiator in a variable opening chamber, was designed and fabricated. The system was also installed in the cultivation facility of a farm cultivating shiitake mushrooms so as to compare the proposed control system with a conventional environmental control system using a cooler-condensing unit and an electric hot water boiler. Results: The uniformity of the environment was analyzed through environment measurements taken at several positions inside the cultivation facility. It was determined that the developed environmental control system is able to control the variations in temperature and relative humidity to within 1% and 3%, respectively. In addition, a maximum temperature difference of $30^{\circ}C$ (maximum of $35^{\circ}C$, minimum of $5^{\circ}C$) and a maximum relative humidity difference of 30% (maximum of 90%, minimum of 60%) can be attained within 30 min inside the cultivation facility through the cooling of the heat pump and heating of the radiator in a variable opening chamber. Thus, the developed control system can be used to cultivate high-quality shiitake mushrooms more effectively than a conventional cooler and heater. Conclusions: In comparison with a conventional environmental control system, the developed system decreased the yield of ordinary mushrooms by 65%, and increased that of high-quality mushrooms by 217%. This corresponds to a 16% increase in gross farm income. Consequently, the developed system is expected to improve the income of shiitake mushroom cultivating farms.

• Proceedings of the KIEE Conference
• /
• 2005.07d
• /
• pp.2622-2624
• /
• 2005

화력발전소 보일러의 급수량은 유출되는 증기량에 맞추어 자동 조절된다. 유출 증기량이 변하는 상황에서도 이에 상응하는 급수량은 실시간으로 조절되어야 한다. 증기량과 급수량에 차이가 있으면 보일러의 보유 수량과 드럼의 수위가 변하게 되므로, '드림수위를 일정하게 유지하는 것'이 급수량제어의 목표라고 할 수 있다. 본 논문은 실제 운용되고 있는 설비를 대상으로 고찰한 내용이며, 급수펌프 구동력으로는 중기터빈을 사용한다. 증기터빈과 급수펌프는 같은 축으로 연결되어있으며, 급수량 조절은 급수펌프의 회전속도를 제어함으로써 이루어진다. 터빈에 사응되는 증기는, 고압과 저압 2종류이며, 저압 증기가 부족한 경우에 고압증기를 사용하는 구성으로 되어있다. 증기 밸브의 유량 특성에는 비선형성을 많이 포함하고 있었다. 이 외에도 급수펌프가 갖는 비선형성을 분석하였으며, 이 특성들을 모두 종합한 '증기터빈 속도제어기 튜닝 곡선'을 제시하였다

• Proceedings of the SAREK Conference
• /
• 2005.06a
• /
• pp.64-64
• /
• 2005

• Proceedings of the SAREK Conference
• /
• 2004.06a
• /
• pp.81-81
• /
• 2004

• 한국신재생에너지학회:학술대회논문집
• /
• 2010.11a
• /
• pp.171-171
• /
• 2010

An innovative design of a floating-buoy wave energy converter (WEC) using hydrostatic transmission (HST), named HSTWEC, is presented in this paper. The system is designed to convert ocean wave fluctuation into electricity by using the HST circuit and an electric generator. Based on the floating-buoy concept, the wave forces the sub-buoy to move up and down. Consequently, the electric power can be obtained from the generator in both the moving directions of the sub-buoy through the HST circuit as shown in Fig. 1. In order to investigate the HSTWEC operations, a mathematical model of the system is indispensible. In addition, the method to control the HSTWEC, including: pump displacement control, tension adjustment control and ballast weight control, is also discussed in this paper. Finally, the design concept as well as simulation results indicated that this HSTWEC design is an effective solution and possible to fabricate for wave energy generation.

• Proceedings of the KIPE Conference
• /
• 1997.07a
• /
• pp.141-147
• /
• 1997

The variable speed drive system of a electric motor is popular in industry due to its economical aspect and simplicity of implementation, comparing with a steam turbine or the other engine driven. For a large pumping load like a feedwater pump rated about or more than 20,000㎾, a synchronous motor could be primarily considered. In this paper, we studied the modelling of a variable speed drive system consisted with a load commutated inverter(LCI) and a brushless sailent pole rotor synchronous motor(SM) using MATLAB/SIMULINK. Simulation was performed with a small SM motor parameters.

• Journal of the Korean Society of Visualization
• /
• v.1 no.2
• /
• pp.47-51
• /
• 2003

Microfluidic chips such as lab-on-a-chip (LOC) include micro-channels for sample delivery, mixing, reaction, and separation. Pressure driven flow or electro-osmotic flow (EOF) has been usually employed to deliver bio-samples. Having some advantages of easy control, the flow characteristics of EOF in microchannels should be fully understood to effectively control the electro-osmotic pump for bio-sam-pie delivery. In this study, a micro PIV system with an epifluorescence inverted microscope and a cooled CCD was used to measure velocity fields of EOF in a glass microchannel and a PDMS microchannel. The EOF velocity fields were changed with respect to electric charge of seeding particles and microchannel materials used. The EOF has nearly uniform velocity distribution inside the microchannel when pressure gradient effect is negligible. The mean streamwise velocity is nearly proportional to the applied electric field. Glass microchannels give better repeatability in PIV results, compared with PDMS microchannels which are easy to fabricate and more suitable for PIV experiments.

• Proceedings of the KIEE Conference
• /
• 2007.04c
• /
• pp.53-55
• /
• 2007

Industrial interest in switched reluctance moor (SRM) drives has varied since 1850s. This has been primarily due to the emerging markets for variable speed drives in consumer and industrial products, such as home appliances, air conditioning, hand tools, fans, pump motor, etc. However, SRM has been plagued with the acoustic noise and vibration problem by input power of fixed section. Therefore, This paper offers electromagnetic analysis for torque ripple reduction in mechanical geometry and electric parameters. This means that the rotor pole arc and electric parameters have related to produce the active and negative torque. This analysis results are verified by the finite element method.