Jae-Weon Jeong

A Study on the Subjective Response for Corrected Colour Temperature Conditions in a Specific Space

The luminous environment in a space is one of the key factors affecting the occupants work performance and mood. An illuminance value is quantitatively standardised and recommended for a specific space, but correlated colour temperature (CCT) is not. Although some studies on CCT conditions have shown that higher CCT conditions appear brighter to people than lower CCT conditions, other studies have indicated that there is no relationship between brightness perception and CCT conditions. This paper reports the results of two subjective evaluations of different CCTs on personal preferences: brightness perception, subjective impression and work performance; and describes suitable CCT conditions for a specific space and activities. One subjective evaluation (field test) was performed with four different CCT fluorescent lamps in an office space, and another (photo-image test) was performed with pictures under four different CCT conditions in an office, living room and bedroom. The results were statistically analysed for gender, preferred CCT, suitable CCT of each space and brightness sensitivity. The results showed that people preferred different CCT due to the purpose of a space, and different CCT conditions for specific activities performed in that space. The study suggests that changeable CCT lightings are better than fixed CCT for occupants in a space.

Improvement in demand-controlled ventilation simulation on multi-purposed facilities under an occupant based ventilation standard

The objective of this paper was to find an effective way of improving demand-controlled ventilation (DCV) simulation performed under an occupant based ventilation standard established in many countries. Two attractive DCV approaches, CO2–DCV and RFID–DCV, were applied to DCV simulations for a theoretical public assembly space served by a dedicated outdoor air system (DOAS) with an enthalpy recovery device. A numerical model for predicting the real-time occupant number, required ventilation amount, CO2 and formaldehyde (HCHO) concentrations under given conditions was developed using a commercial equation solver program. The current ventilation standard used in Korea was applied as a case of occupant based ventilation standards. It was found that the current standard might cause unstable DCV simulation results, especially under CO2–DCV. This is because the ventilation rate (per person) indicated in the standard is the sum of the outdoor air required to remove or dilute air contaminants generated by both occupants and the buildings themselves, and not a pure function of occupant numbers. Finally, it makes DCV control unstable when ventilation flow is regulated only by the number of occupants. In order to solve this problem, the current occupant based ventilation standard was modified as a form of ASHRAE Standard 62.1-2007 showing good applicability to various DCV approaches. It was found that this modification enhances applicability of the current ventilation standard to CO2–DCV significantly and can maintain acceptable HCHO concentrations during the entire time of operation. Fan energy reduction can also be expected from DCV operations.

Overall Heat Transfer Coefficient of a Korean Traditional Building Envelope Estimated Through Heat Flux Measurement

Abstract The objective of this research is to determine overall heat transfer coefficients (U-value) of the exterior walls, floors, and roof of a Korean traditional residence via field measurement of transient heat flow and temperature difference across each envelope. The acquired U-values are compared with other existing values and those for current residential buildings. As for the field measurement, heat flux sensors and T-type thermocouple are attached on the internal and the external surfaces of each building component. Real-time measurement data are logged for three consecutive summer days. Acquired U-values agree well with other existing values for traditional building envelopes found in the open literature, but they are higher than U-values of current buildings. From this result one may conclude that the Korean traditional building has uncompetitive thermal performance compared with todays buildings. However, the energy simulation performed in this research shows that the traditional building can provide moderate cooling load competitive to current buildings. It comes mainly from the inherent characteristic of the traditional residence including relatively high infiltration rate and reduced solar radiation penetrating the windows.

Impact of Air-side Economizer Control Considering Air Quality Index on Variable Air Volume System Performance

The objective of this study is to determine the effectiveness of a modified air-side economizer in improving indoor air quality (IAQ). An air-side economizer, which uses all outdoor air for cooling, affects the building’s IAQ depending on the outside air quality and can significantly affect the occupants’ health, leading to respiratory and heart disease. The Air Quality Index (AQI), developed by the US Environmental Protection Agency (US EPA), measures air contaminants that adversely affect human beings: PM10, PM2.5, SO2, NO2, O3, and CO. In this study, AQI is applied as a control for the operation of an air-side economizer. The simulation is analyzed, comparing the results between the differential enthalpy economizer and AQI?modified economizer. The results confirm that an AQI?modified economizer has a positive effect on IAQ. Compared to the operating differential enthalpy economizer, energy increase in an operating AQI?modified economizer is 0.65% in Shanghai and 0.8% in Seoul.

Regional Preheat Coil Capacity Estimation for Preventing Condensation in Sensible Heat or Energy Recovery Ventilators

Heat recovery ventilator and energy recovery ventilator (HRVs/ERVs) save energy load in buildings by reusing the heat from exhaust air. However, when HRVs/ERVs are operated in winter season, condensation may occur in heat exchange process causing negative influence not only on occupants but also on the performance of the system; mold and bacteria are developed through condensation causing respiratory diseases to occupants, and frosts may be developed once the condensation meets the air with the temperature under the freezing point causing the efficiency of exchangers to drop dramatically or even the breakdown of the whole system. Many methods to prevent condensation or frost have been suggested however preheating may be the simplest and the most certified method to guarantee the performance of the HRVs/ERVs systems. In this paper, variable factors for sizing the capacity of preheating coils have been verified. Also, the appropriate preheating capacity of HRVs/ERVs for different regions in Korea have been suggested based on the frost threshold temperature and the design procedure for various conditions.

Impact of Cooling Water Temperature Variation on Dehumidification Effectiveness of a Liquid Desiccant System and Feasibility of Water-side Free Cooling Application

This research is an experimental study of the liquid desiccant system performance. In the absorber, dehumidification process and sensible cooling of outdoor air takes place at the same time. The dehumidification effectiveness variation with the chilled water temperature changes in the absorber based on the experiment data collected from the liquid desiccant system operation. The liquid desiccant system used in this research dehumidifies process air and 24.5kW air-cooled chiller or 136.1kW cooling tower may provide chilled water at target temperature. Experiments were conducted on the day of peak cooling load of outdoor air in the summer season when the outdoor air was hot and humid(at Incheon, South Korea. Aug 2013). Based on the experiment data showing the dehumidification performance variation of the liquid desiccant system for the cooling water temperature, a validation of the dehumidification effectiveness values of a liquid desiccant system is compared with existing model.

A simplified model for predicting dehumidification effectiveness of a liquid desiccant system

The main purpose of this research is to propose a practical correlation returning the dehumidification effectiveness of a liquid desiccant system. From the existing literature, it was found that two desiccant solutions; lithium chloride(LiCl), and triethylene glycol (TEG) solutions are commonly used as a working fluid in two different types of absorber towers; packed bed, and spray towers. In this research, the experimental data of each absorber tower performance with two different desiccant solutions were collected from the open literature. By statistically analyzing the collected data using the 2 k factorial experiment design approach, the impact of each system operation parameters on the dehumidification effectiveness were quantitatively estimated. And then, a simplified second-order equation model was derived as a function of operation parameters showing significant impact on the dehumidification effectiveness. It was found that the operating parameters, such as inlet ambient air temperature, desiccant solution temperature, liquidto-gas ratio(L/G), inlet air relative humidity, and solution concentration have significant impact on the system dehumidification performance. The proposed model was validated by comparing the dehumidification effectiveness values predicted by both proposed model and existing models found in the existing literature.