• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.19 no.10
• /
• pp.703-709
• /
• 2007

Much energy is used in occupying stage of the Building Life Cycle. Electric charge is one of the various factors that influence on energy use of residents. This study focused on electric charge and searched that whether electric charge affects residents' behavior of operating air conditioner and their controlled indoor climate. We surveyed three groups for field study ; A group is residents who live in a studio apartment, B group is residents who live in a university dormitory and C group is residents who live in a apartment with their family. The A and C groups are charged for electric as energy consumption they used. And the B group is students who live in a university dormitory and they are not charged for their energy consumption. We measured the time to use the air conditioner for cooling, on/off temperature of air conditioner, and room air temperature for these three groups. The result shows that consideration for electric charge affects to the residents' behavior of operating air conditioner and their acceptable thermal range.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.24 no.10
• /
• pp.711-717
• /
• 2012

A heat pump dryer for the frozen food needs to preheat the air to a certain temperature where condensation can efficiently occur. In this study, an analysis of a heat pump dryer performance with operating conditions, an analysis of supplying heat with internal and external evaporators and a warm-up experiment with the evaporators have been performed. The results showed that the external evaporator can significantly accelerate the warm-up time of the dryer, so that it can reduce power consumption greatly. The use of the external evaporator is more efficient for higher ambient temperature. In addition, it was found that COP decreases and the range of evaporating pressure for the evaporator becomes narrower as the condensing temperature of the condenser increases.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.9 no.3
• /
• pp.389-400
• /
• 1997

A thermodynamic cycle analysis is performed for refrigerator-precooled Linde-Hampson hydrogen liquefiers, including catalysts for the ortho-to-para(o-p) conversion. three different configurations of the liquefying system, depending upon the method of the o-p conversion, are selected for the analysis. After some simple and justifiable models are introduced, a general analysis program to predict the liquid yield and the figure of merit(FOM) is developed with incorporating the commercial computer code for the hydrogen properties. The discussion is focused on the effect of the two primary design parameters-the precooling temperature and the high pressrure of hydrogen. When the precooling temperature is in the range between 45 and 60 K, the optimal high pressure for the maximal liquid yield is found to be in the range between 100 to 140 bar, regardless of the o-p conversion. However, the FOM can be maximized at slightly smaller values of high pressures. It is remarkable to observe that the lower precooling temperatures are favorable since both the liquid yield and the FOM can be obtained without compressing hygrogen to extremely high pressures.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.6 no.4
• /
• pp.388-398
• /
• 1994

Computer simulation model for predicting more accurately the heat transfer performance of the evaporator and condenser which have significantly affected on the performance of air-conditioner has been suggested. In this model oil and micro-fin tube used in a actual unit are considered to simulate the more realistic case. The effects of oil and micro-fin tube on the performance of an air-conditioner have been investigated. It is found that the present model requires higher pressure than the existing model due to the characteristics of the tube considered. However, it turns out that the present model is very close to an actual cycle. As the amount of oil inside the tube increases, condensation heat transfer coefficient shows a linear decrease irrespective of a kind of oil, while evaporation heat transfer coefficient increases slightly in the oil with low viscosity and decreases exponentially in the oil with high viscosity. Pressure drop in both evaporator and condenser increases linearly irrespective of a kind of oil. It is also found that the effect of the variation of oil concentration on the magnitude of two-phase region is negligible.

• Proceedings of the SAREK Conference
• /
• 2009.06a
• /
• pp.990-995
• /
• 2009

Experimental basic study was performed to understand the characteristics of sub-cooled refrigerant using a cold heat storage system. This system was made up general vapor-compression refrigeration cycle added sub-cooler and ice storage tank. The purpose of this study are to application use of cold-heat storage systems multiplicity of fields and to understand of sub-cooling system. At the condition using ice storage system, the ice making process was operated during night time by electric power. And then, the refrigerant was sub-cooled using stored cold-heat after being discharged from the air cooling condenser during the day time. Comparing the result at general operation with the operation using sub-cooling system. This study showed the effects of the sub-cooled degree. The cooling performance was increased owing to the sub-cooling of refrigerant during day time, and the compressor consume power was a little decreased. Thus the COP was also increased owing to the sub-cooling of refrigerant.

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

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.21 no.8
• /
• pp.448-455
• /
• 2009

A performance analysis of the regenerative gas turbine system with afterfogging is carried out. Because of the high temperature at the outlet of air compressor, afterfogging has a potential of improved recuperation of exhaust heat than inlet fogging. Thermodynamic analysis model of the gas turbine system is developed by using an ideal gas assumption. Using the model, the effects of pressure ratio, water injection ratio, and ambient temperature are investigated parametrically on thermal efficiency and specific power of the cycle. The dependency of pressure ratio giving peak thermal efficiency is also investigated. The results of numerical computation for the typical cases show that the regenerative gas turbine system with afterfogging can make a notable enhancement of thermal efficiency and specific power. In addition, the peak thermal efficiency is shown to decrease almost linearly with ambient temperature.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.25 no.3
• /
• pp.131-136
• /
• 2013

The present study has conducted cycle design and control technology of a water source VRF heat pump system. Previously, study of a simultaneous heating and cooling in an air source VRF heat pump system has been conducted. However, performance data and design methods for simultaneous heating and cooling in a water source VRF heat pump system are limited in the literature, due to various system parameters and operating conditions. In this study, the operating characteristics and performances of a simultaneous heating and cooling heat pump system are carried out, in simultaneous operation modes. Control logics of an EEV are developed for flow rate control to the outdoor unit, and are verified. When the control logics are applied, the simultaneous cooling and heating performances are sufficiently achieved, and system COPs are increased by up to 23.4%.

• Journal of Biosystems Engineering
• /
• v.30 no.2 s.109
• /
• pp.110-113
• /
• 2005

Relative humidity of air In the greenhouse has to be maintained at 70 to 80 percents to provide a better growth condition of crops. To control relative humidity of air in the greenhouse, a dehumidifier functioning by refrigeration cycle was designed and manufactured in this study. And, results of its performance test in the greenhouse site were reported. The developed dehumidifier has separated condenser and evaporator in the heat exchanger part in order to increase dehumidifying capacity at a low temperature condition. When the conditions of incoming air into the dehumidifier were temperature of $15\~25^{\circ}C$ and relative humidity of $0\~95\%$, quantity of condensed water per hour, ie, dehumidification rate was $4.7\~7.0\;kg/hr$. Relative humidity difference was not greater than 5 percents at various locations in the greenhouse due to proper distributing of dehumidified air through vinyl duct. Thermal energy output from the developed dehumidifier was about 8,5000 kcal/hr that was 7 percents of maximum greenhouse heating load of 10 a.

• International Journal of Air-Conditioning and Refrigeration
• /
• v.6
• /
• pp.148-157
• /
• 1998

This study presents test results of a residential window air-conditioner using R22 and two potential alternative refrigerants, R407C and R410B. A series of performance tests has been carried out for the basic and liquid-suction heat exchange cycles in a psychometric calorimeter test facility. For R407C, the same rotary compressor was used as in the R22 system. However, compressor for the R410B system was modified to provide the similar cooling capacity. The evaporator circuit was changed to get a counter-cross flow heat exchanger to take advantage of zeotropic mixture's temperature glide, and liquid-suction heat exchange cycle was also considered to improve the system performance. Test results were compared with those for the basic R22 system. The modified system with a liquid-suction heat exchanger increased cooling capacity and energy efficiency by up to 5%.