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Introduction
My research topics are based on building physics including thermal environment, HVAC equipment, and materials and sometimes extended to the city scale.
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Publications
Publications (61)
Exergy analysis has been used in various fields to quantify the efficiency of various energy transfer processes. So far, most exergy analyses have been performed by assuming steady-state conditions both for a system of focus and its environment. However, steady-state analyses may idealize a problem too much and thereby limit what we can know about...
Two different experimental methods, namely thermal response test (TRT) and thermal performance test (TPT), have been used in the field of ground-source heat pumps (GSHPs) for different purposes. TRT is a well-established method for estimating the design parameters of ground heat exchangers (GHEs), whereas TPT has recently been adopted to examine th...
Thermal exergy analysis is typically performed under a steady-state assumption. This assumption is reasonable when the temperature difference between the environment and the system of interest is very
large; however, when the temperature difference is small, the exergetic behavior of the system becomes highly sensitive to the environmental temperat...
In the field of ground-source heat pumps (GSHPs), thermal response tests (TRTs) with constant heat rate have been conducted to estimate the design parameters of ground heat exchangers (GHEs), and thermal performance tests (TPTs) with constant inlet temperature have been conducted to examine the heat exchange performance of GHEs. These two experimen...
Ground heat exchangers are essential components of ground-source heat pump systems. One of the most-used ground heat exchanger types is a borehole heat exchanger (BHE). Many parameters, such as the building thermal loads, ground thermal properties, and BHE components, influence the required BHE length. Therefore, understanding how individual parame...
This study proposes a real-time probabilistic estimation method for determining the thermal properties of backfill used in underground power transmission lines and ground heat exchangers. The thermal properties of backfill, serving as a heat conductor between the heat source and surrounding soil, are crucial design parameters for underground transm...
The thermal resistance of a borehole heat exchanger (BHE) varies considerably depending on the position of the pipe legs. However, the pipe position cannot be fully controlled during construction because of the extreme slenderness of the BHEs. Therefore, the borehole's thermal resistance (Rb) estimated from one BHE is not representative of the enti...
Building system operation faces the challenge of reducing energy use and implementing a demand response, which can be defined as a temporary modification in energy loads affecting dynamic energy price and reliability information. The heating, ventilation, and air-conditioning (HVAC) system in buildings provides an opportunity for implementing deman...
A data-driven probabilistic model is proposed to predict the group-level thermal satisfaction of occupants subjected to a given thermal condition. This model considers the inhomogeneous variation of inter- and intra-individual thermal sensation votes (TSVs) on the basis that individual variations in TSVs are expected to be undispersed in extreme th...
As the global community seeks to reduce fossil fuel dependence, improving energy efficiency and developing an optimal operational strategy are high priorities in the building sector. Integrating thermal energy storage (TES) into building energy systems is desirable for improving energy flexibility and cost efficiency. However, an optimal control st...
Local sensitivity analysis (LSA) is widely used for evaluating the uncertainty in a model output or estimated parameters. However, it does not consider the effect of changing parameter values in the parameter space and the simultaneous change of the parameter set. Global sensitivity analysis (GSA) overcomes these limitations of LSA by adequately re...
This study extends the assessment framework proposed by Murakami et al. (1986) for the pedestrian wind environment to a fully probabilistic method by implementing Bayesian modeling. The method quantifies the uncertainties in constructed models based on the measured wind data and the results of the assessment. To model the probabilities of the daily...
In the exergy analysis of the built environment, particularly for a system with large heat capacity and low thermal conductivity, such as building envelopes, consideration of physics associated with the entropy and exergy storages is increasingly important. However, steady-state exergy analyses neglect storage-related physics. Therefore, they do no...
The development of a distributed heat pump system that utilizes several renewable energy sources to meet building heating and cooling demands was reported in this paper. We refer to this system as the multiple‐source and multiple‐use heat pump (MMHP) system. A unique sky source heat pump, ground heat exchangers, and various heat pumps are connected...
Developing effective operational strategies for commercial buildings is a high priority as the global community seeks to reduce energy usage and greenhouse gas emissions. This study aims to validate the feasibility of a model predictive control (MPC) strategy for commercial building in response to occupancy variations and time-variant electricity p...
The thermal state of the human body is closely related to thermal sensations and thermal comfort and can be estimated using a physiological human model. However, the feasibility of its prediction models in a mist-spraying environment has not been examined. The present study confirmed the applicability of existing prediction models (two-node model (...
The energy input for building operations is mainly composed of fossil fuel-based energy carriers, and therefore accounts for a large proportion of global greenhouse gas emissions. Thus, significant effort such as application of heat pumps has been focused on boosting renewable energies in building to decrease the energy demand and its related emiss...
The energy consumption of pumps for hot and chilled water circulation cannot be ignored because it can be 10-20 % of the consumption of heating, ventilating, and air conditioning (HVAC) systems. This value generally accounts for a significant proportion of the total building energy consumption. In most HVAC systems, water is usually delivered by se...
We herein report the development of a distributed heat pump system that can utilize a variety of renewable energy sources to meet different building heating and cooling demands (i.e., a multiple source and multiple use heat pump system, MMHP). In this system, a water circulating loop is used to connect ground heat exchangers, a unique sky-source he...
We present a method for constructing artificial neural network (ANN) models of the stratified chilled water thermal energy storage (TES) system and borehole heat exchanger (BHE) of a ground-source heat pump (GSHP) system to assess the feasibility of using ANNs in model predictive control (MPC) applications. In the MPC technique, prediction models a...
In energy distribution systems, thermal energy is usually transferred by a heat carrier fluid via pumps. Improper design and unreasonable control of pumping systems result in inefficient operation which accounts for a significant part of electricity consumption in the industry. The need to save energy has been sharpened the focus on improving energ...
We herein report the development of a distributed heat pump system that can utilize a variety of renewable energy sources to meet different building heating and cooling demands (i.e., a multiple source and multiple use heat pump system, MMHP). In this system, a water circulating loop is used to connect ground heat exchangers, a unique sky-source he...
In this study, an artificial neural network (ANN) was used to model the thermal performance of a novel direct-expansion solar-assisted sky-source heat pump (SSHP) during winter. The input parameters of the ANN take into account the weather conditions, water loop characteristics, and the compressor characteristics of the SSHP. The following four out...
Appropriate insulation materials, with unique physical properties and of moderate thickness, are essential for energy savings in residential buildings. However, the impact of thermal insulation on indoor thermal comfort with floor heating systems has not been studied extensively. In this study, simulations of a typical Japanese detached house were...
The presented thermal performance test (TPT) datasets were related to the research article “New perspectives in thermal performance test: Cost-effective apparatus and extended data analysis” (Choi et al., 2018), where a new TPT apparatus was developed by adding a solid-state-relay and a proportional–integral–derivative (PID) controller to a thermal...
This study investigates the heating operation performance of a multiple-source multiple-use heat pump system, consisting of a sky source heat pump, a ground heat exchanger and floor heating heat pump in an experimental facility named RE (Renewable Energy) House. The novelty of this system is that the ground thermal state is maintained by the combin...
Long-term operation of a ground-source heat pump (GSHP) under a load imbalance condition can lead to thermal build-up or depletion; consequently, this results in performance degradation. In addition, in urban areas where building densities are considerably high with building sites in close proximity to each other, thermal intrusion problems can occ...
The effective ground thermal conductivity and borehole thermal resistance constitute information needed to design a ground-source heat pump (GSHP). In situ thermal response tests (TRTs) are considered reliable to obtain these parameters, but interpreting TRT data by a deterministic approach may result in significant uncertainties in the estimates....
The effective ground thermal conductivity and borehole thermal resistance constitute information needed to design a ground-source heat pump (GSHP). In situ thermal response tests (TRTs) are considered reliable to obtain these parameters, but interpreting TRT data by a deterministic approach may result in significant uncertainties in the estimates....
In contrast to energy analysis, the analysis of exergy allows the evaluation of the quality of different energy flows and enables a comprehensive assessment of the performance of a system and its individual components by accounting for necessary exergy consumption and unnecessary consumption. While exergy analysis methods have been applied to a var...
In contrast to energy analysis, the analysis of exergy allows the evaluation of the quality of different energy flows and enables a comprehensive assessment of inefficiencies within a system and its individual components by accounting for exergy consumption. While exergy analysis methods have been applied to a variety of conventional and renewable...
Recent years have witnessed the widespread use of highly efficient energy systems as an important measure to reduce not only energy consumption but also operating costs. A ground source heat pump system has been attracting considerable attention because of its high efficiency. Although many studies have been conducted to investigate and evaluate th...
Natural ventilation is a good measure to reduce the thermal load of a building and create a good thermal environment for the occupants. To predict the ventilation performance of a building, related ventilation parameters should be estimated. However, obtaining an accurate prediction or estimation before the construction is completed is difficult be...
In contrast to energy analysis, the analysis of exergy allows the evaluation of the quality of different energy flows and enables a comprehensive assessment of inefficiencies within a system and its individual components by accounting for exergy consumption. While exergy analysis methods have been applied to a variety of conventional and renewable...
The natural ventilation rate of a room is often predicted using the tracer gas method, but obtaining an accurate prediction using this method is difficult. The effective room volume, which is estimated first, is unknown and contains significant uncertainty. Additionally, inlet velocity fluctuation, concentration sensor measurement error, concentrat...
Thermal response tests (TRTs) have been conducted to evaluate two design parameters of borehole heat exchangers (BHEs): effective thermal conductivity and borehole thermal resistance. The effect of natural convection on groundwater-filled BHE performance has been reported mainly from northern Europe. Even in a backfilled or grouted BHE, if the form...
The main drawback of renewable energy sources is the variability and intermittence in their availability; causing significant mismatches between the time of energy demand and energy production. To make these future energy sources and conversion technologies a viable solution, it is necessary to use significant levels of energy storage technologies...
To interpret thermal response tests (TRTs), analytical models that assume constant heat flux from the source are widely used because of their simplicity. However, in actual field conditions, the constant heat flux assumption is violated by the heat exchange between the above-ground TRT setup and outdoor environment. This results in perturbations in...
The approximated infinite line source (ILS) model is widely used to interpret thermal response tests (TRTs). It assumes a constant heat flux from the source. However, this assumption is violated in real field conditions by the heat exchange between the circulating fluid and the outdoor environment in an above-ground TRT setup. This results in a flu...
Thermal response tests (TRTs) are essential for reliable and accurate design of ground source heat pumps. The approximated infinite line source (ILS) model is widely used to interpret TRTs because of its simplicity. However, in actual field conditions, the constant heat flux assumption of the ILS model is violated in most cases because the above-gr...
Effective ground thermal conductivity and borehole thermal resistance, which are key parameters in the design of borehole heat exchangers (BHEs), are often determined on the basis of in-situ thermal response tests (TRTs). However, many disturbance factors can affect the accuracy of a TRT, e.g., voltage fluctuations from the power grid and oscillati...
This study measured an actual behavior of a multi-story double skin facade (DSF) in South Korea. The verification of simulation model was made against measured data, and a case study was conducted based on the verified model. Seasonal load characteristics of the DSF building were examined in comparison with the single skin facade (SSF) building, an...
The implementation of the double skin facade (DSF) has been the object of broad study in recent years. However the performance of DSF is often questionable because of the lack of experiment and monitoring data, especially regarding multi-storey DSFs.In this study, the actual behavior of a multi-storey double skin facade was measured during the heat...
In this paper, heating energy saving strategies for winter are proposed for office buildings with a multi-story double skin façade. Based on a model that was validated with measured data, two alternative operation strategies were analyzed. A model that introduces heated air in the cavity to the indoors by openable windows control(Case 2) and a mode...
In this study, the usage of cooling energy in office buildings with multi-story double-skin façades (DSF) was analyzed. A verification model was constructed by measuring the temperature of the cavity air and the surface of office buildings where DSF had been installed, and by comparing the measurement results with the results of the EnergyPlus simu...
