Tianzhen Hong

Comparison of energy efficiency between variable refrigerant flow systems and ground source heat pump systems

With the current movement toward net zero energy buildings, many technologies are promoted with emphasis on their superior energy efficiency. The variable refrigerant flow (VRF) and ground source heat pump (GSHP) systems are probably the most competitive technologies among these. However, there are few studies reporting the energy efficiency of VRF systems compared with GSHP systems. In this article, a preliminary comparison of energy efficiency between the air-source VRF and GSHP systems is presented. The computer simulation results show that GSHP system is more energy efficient than the air-source VRF system for conditioning a small office building in two selected US climates. In general, GSHP system is more energy efficient than the air-source VRV system, especially when the building has significant heating loads. For buildings with less heating loads, the GSHP system could still perform better than the air-source VRF system in terms of energy efficiency, but the resulting energy savings may be marginal.

EnergyPlus Run Time Analysis

EnergyPlus is a new generation building performance simulation program offering many new modeling capabilities and more accurate performance calculations integrating building components in sub-hourly time steps. However, EnergyPlus runs much slower than the current generation simulation programs. This has become a major barrier to its widespread adoption by the industry. This paper analyzed EnergyPlus run time from comprehensive perspectives to identify key issues and challenges of speeding up EnergyPlus: studying the historical trends of EnergyPlus run time based on the advancement of computers and code improvements to EnergyPlus, comparing EnergyPlus with DOE-2 to understand and quantify the run time differences, identifying key simulation settings and model features that have significant impacts on run time, and performing code profiling to identify which EnergyPlus subroutines consume the most amount of run time. This paper provides recommendations to improve EnergyPlus run time from the modeler?s perspective and adequate computing platforms. Suggestions of software code and architecture changes to improve EnergyPlus run time based on the code profiling results are also discussed.

Review of Existing Energy Retrofit Tools

xxxxx E RNEST O RLANDO L AWRENCE B ERKELEY N ATIONAL L ABORATORY Review of Existing Energy Retrofit Tools Sang Hoon Lee, Tianzhen Hong, Mary Ann Piette Department of Building Technology and Urban Systems Environmental Energy Technologies Division July 2014

Building Energy Benchmarking Between the United States and China: Methods and Challenges

Currently, buildings in the U.S. account for more than 40 % of total primary energy. In China, the same figure is 20 %. Detailed building energy analysis and benchmarking based on energy monitoring are becoming vitally important for the evaluation of energy-efficient technologies and related policy making. This paper focuses on methods and challenges in energy benchmarking of office buildings between the U.S. and China, based on the experiences and outcomes of a joint research project under the U.S.–China Clean Energy Research Center for Building Energy Efficiency (CERC-BEE). First, benchmarking methods were presented, including data analysis methods, required data, building selection criteria, and a standard data model for building energy use. Annual electricity use benchmarking was performed from a sample of selected office buildings in both countries, with the aim of identifying and understanding the main discrepancies and key driving factors. Benchmarking challenges were then summarized and discussed, and some potential solutions were proposed, including the process of building selection, data collection and clean-up, and specific analysis techniques. Recommendations were proposed for future work to improve the process and outcomes of building energy benchmarking between the two countries.

EnergyPlus Analysis Capabilities for Use in California Building Energy Efficiency Standards Development and Compliance Calculations

California has been using DOE-2 as the main building energy analysis tool in the development of building energy efficiency standards (Title 24) and the code compliance calculations. However, DOE-2.1E is a mature program that is no longer supported by LBNL on contract to the USDOE, or by any other public or private entity. With no more significant updates in the modeling capabilities of DOE-2.1E during recent years, DOE-2.1E lacks the ability to model, with the necessary accuracy, a number of building technologies that have the potential to reduce significantly the energy consumption of buildings in California. DOE-2s legacy software code makes it difficult and time consuming to add new or enhance existing modeling features in DOE-2. Therefore the USDOE proposed to develop a new tool, EnergyPlus, which is intended to replace DOE-2 as the next generation building simulation tool. EnergyPlus inherited most of the useful features from DOE-2 and BLAST, and more significantly added new modeling capabilities far beyond DOE-2, BLAST, and other simulations tools currently available. With Californias net zero energy goals for new residential buildings in 2020 and for new commercial buildings in 2030, California needs to evaluate and promote currently available best practice and emerging technologies to significantly reduce energy use of buildings for space cooling and heating, ventilating, refrigerating, lighting, and water heating. The California Energy Commission (CEC) needs to adopt a new building energy simulation program for developing and maintaining future versions of Title 24. Therefore, EnergyPlus became a good candidate to CEC for its use in developing and complying with future Title 24 upgrades. In 2004, the Pacific Gas and Electric Company contracted with Architectural Energy Corporation (AEC), Taylor Engineering, and GARD Analytics to evaluate EnergyPlus in its ability to model those energy efficiency measures specified in both the residential and nonresidential Alternative Calculation Method (ACM) of the Title-24 Standards. The AEC team identified gaps between EnergyPlus modeling capabilities and the requirements of Title 24 and ACMs. AECs evaluation was based on the 2005 version of Title 24 and ACMs and the version 1.2.1 of EnergyPlus released on October 1, 2004. AECs evaluation is useful for understanding the functionality and technical merits of EnergyPlus for implementing the performance-based compliance methods described in the ACMs. However, it did not study the performance of EnergyPlus in actually making building energy simulations for both the standard and proposed building designs, as is required for any software program to be certified by the CEC for use in doing Title-24 compliance calculations. In 2005, CEC funded LBNL to evaluate the use of EnergyPlus for compliance calculations by comparing the ACM accuracy test runs between DOE-2.1E and EnergyPlus. LBNL team identified key technical issues that must be addressed before EnergyPlus can be considered by the CEC for use in developing future Nonresidential Title-24 Standards or as an ACM tool. With Title 24 being updated to the 2008 version (which adds new requirements to the standards and ACMs), and EnergyPlus having been through several update cycles from version 1.2.1 to 2.1, it becomes crucial to review and update the previously identified gaps of EnergyPlus for use in Title 24, and more importantly to close the gaps which would help pave the way for EnergyPlus to be adopted as a Title 24 compliance ACM. With this as the key driving force, CEC funded LBNL in 2008 through this PIER (Public Interest Energy Research) project with the overall technical goal to expand development of EnergyPlus to provide for its use in Title-24 standard compliance and by CEC staff.