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Nagoya City University Graduate School
Applying CFD to Increase Air-conditioning System Life Cycle Energy Efficiency

Efficiently using limited energy resources over the long term makes it more important to optimize energy consumption versus simply cutting usage. Dr. Gyuyoung Yoon, Associate Professor at Nagoya City University, has coupled Cradle scSTREAM with an air-conditioning energy management tool to account for the impact of three-dimensional effects on total energy management.

Gyuyoung Yoon (Doctor of Engineering),
Nagoya City University Graduate School,
Associate Professor of Design and Architecture

 Energy consumption can be largely categorized into three sectors: transportation, residential and commercial, and industrial. In Japan, energy consumption in the residential and commercial building sector now consumes a third of the total energy used across the nation. Air-conditioning energy use accounts for nearly half of the energy uses from commercial sector. Because of this, optimizing the efficiency of architectural air-conditioning systems is critical to reducing total energy consumption.

 Attempts have been made in the building and architecture industry to develop air-conditioning system management and assessment tools. Some of these include CASBEE (Comprehensive Assessment System for Built Environment Efficiency), BIM (Building Information Modeling), and ZEB (net Zero Energy Building). CASBEE is a method to evaluate overall environmental performance of buildings, whereas BIM is a database for project information, such as cost, materials, drawings and documents. These tools are considered keys to improving architectural productivity. ZEB has a globe undertaking. It is based on the idea of zero total energy consumption. All these approaches emphasize total energy management instead of merely focusing on reducing energy consumption. This is important because the large portion of building energy consumption being from air-conditioning clearly underlines the need of its optimization.

School of Design and Architecture, the winner of Chubu Architecture Award and Good Lighting Award (Chikusa-ku, Nagoya)

Tackling Optimization of Air-Conditioning


 Dr. Gyuyoung Yoon, Associate Professor at Nagoya City University Graduate School, has been investigating ways to reduce building energy consumption by optimizing air-conditioning. Throughout his research exploring ways to enhance air-conditioning energy efficiency, he has investigated many different ideas including evaluation of the effectiveness of air-to-earth heat exchanger. This is a unique system that uses implementing underground pipes to provide warm air for winter and cool air for summer. Dr. Yoon also investigated the effect of dry mist, once used at the World Exposition site in Aichi, and double skin facade, which reduces energy by allowing air to circulate in the gap between two layers of exterior wall. Dr. Yoon’s latest interest is application of simulation to assess air-conditioning performance.

Managing Energy Consumption by Reviewing Life Cycle


 Due to historically slow progress made on air-conditioning optimization, the LCEM (Life Cycle Energy Management) tool was developed to simulate the annual energy consumption of an air-conditioning system. LCEM tool was developed and made public in 2006 by MLIT (Ministry of Land, Infrastructure, and Tourism) Minister’s Secretariat. LCEM tool has been used to review energy management when constructing public building since 2010 as part of a mandatory procedure.

 LCEM tool simulates the physics of the air-conditioning system, which enables users to observe the amount of energy consumed as the system operates. The tool updates the system status every hour, and users of the tool can observe its performance over time. The effects of yearly changes can be evaluated using the cumulatively collected results. Outdoor air temperature changes can also be simulated by externally calculating the thermal load and importing the load data into LCEM tool.

 One of the advantages of the LCEM tool worth noting is that it can be used through life cycle phase. The air-conditioning system can be reviewed during the planning stage by design engineers, or during test operations to check the performance during construction. For actual operation, the tool can be used to evaluate energy performance and investigate ways to improve operational efficiency.

 LCEM tool was designed to offer easy-to-use operation and offer the capability to evaluate off-peak performance. To meet the first requirement, the tool was based on spreadsheet software, as facilities engineers regularly used Microsoft Excel. The LCEM tool’s capability to evaluate off-peak performance, which varies depending on the degree of air-conditioner operation in different seasons and hours, helps to manage overall energy consumption, and accounts for part-load operation. Using LCEM tool is an innovative solution because it accounts for part-load operation, which had rarely been considered in air-conditioning system design.

 Part-load operation means the system is operating below the rated capacity (system output needed to meet a pre-determined design point usually corresponding to the worst-case indoor and outdoor environmental conditions). By accounting for the system running at part-load operation, the building design can be optimized based on part-load operation, which is actually where the air-conditioning system operates most of the time. Designing to meet a need for the worst-case design point is like choosing a freezer with enough cooling capacity to provide sufficient cooling during the hottest day. However, this condition typically only lasts for a fraction of the total time during the year. Operating appliances below their design capabilities is usually highly inefficient. To prevent this, selecting a machine with less capacity, or using several smaller machines as needed can help improve overall energy efficiency. Other options for improving efficiency during part-load operation (for example when the electrical energy consumption is 80%) include heat storage systems. Effectively combining these options and methods to accommodate part-load operation along with using the LCEM tool makes it possible to take part-load air-conditioning operation into account.

*All product and service names mentioned are registered trademarks or trademarks of their respective companies.
*Contents and specifications of products are as of August 1, 2013 and subject to change without notice. We shall not be held liable for any errors in figures and pictures, or any typographical errors.

Institute Details

 

Nagoya City University
Graduate School of Design and Architecture
Faculty Established 1996
Graduate School Established 2000
Type of University Public
Location of Head Office Mizuho-ku, Nagoya, Aichi, Japan

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