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National Residential Efficiency Measures Database Aimed at Reducing Risk for Residential Retrofit Industry (Fact Sheet)

Description: This technical highlight describes NREL research to develop a publicly available database of energy retrofit measures containing performance characteristics and cost estimates for nearly 3,000 measures. Researchers at the U.S. Department of Energy (DOE) National Renewable Energy Laboratory (NREL) have developed the National Residential Efficiency Measures Database, a public database that characterizes the performance and costs of common residential energy efficiency measures. The data are available for use in software programs that evaluate cost-effective retrofit measures to improve the energy efficiency of residential buildings. The database provides a single, consistent source of current data for DOE and private-sector energy audit and simulation software tools and the retrofit industry. The database will reduce risk for residential retrofit industry stakeholders by providing a central, publicly vetted source of up-to-date information.
Date: January 1, 2012
Partner: UNT Libraries Government Documents Department

NREL Delivers In-Home HVAC Efficiency Testing Solutions (Fact Sheet)

Description: Researchers at the National Renewable Energy Laboratory (NREL) have recently developed two simple in-home efficiency test methods that can be used by technicians, researchers, or interested homeowners to verify the correct operation and energy efficiency of a home's air conditioning equipment. An efficiency validation method for mini-split heat pumps (MSHPs) - highly efficient refrigerant-based air conditioning and heating systems that permit room-by-room conditioning and control - will enable building researchers to easily explore the installed performance of this class of equipment. MSHPs are very popular overseas and are gaining market share in energy efficient home upgrades throughout the United States. Yet, because MSHPs have multiple variable-speed components that work in tandem, their performance is challenging to measure in a real home. NREL researchers developed a field evaluation method including test equipment, methods, and data analysis to determine the installed performance of this equipment in occupied homes. A field test was conducted to validate the method. When testing a home's operation, it is often important to simulate occupancy within an unoccupied home. That way, the researcher will know the actual usage profiles for heat and moisture generation; this removes the uncertainty associated with real occupants. The second test method details a standardized protocol for generating heat and moisture loads, to mimic occupants and their activities by using heaters and humidifiers. Realistic heat and moisture loads can be used to drive air conditioning systems, evaluate air distribution systems, and examine building enclosure technologies. These loads are drawn from the Building America House Simulation Protocols. Proper application of the method will result in better comparison between performance of the test home and its simulated analogue. This method is also validated by field testing. These test methods are now available in two technical reports. The methods can be used widely by the building research ...
Date: January 1, 2012
Partner: UNT Libraries Government Documents Department

NREL Develops Diagnostic Test Cases to Improve Building Energy Simulation Programs (Fact Sheet)

Description: This technical highlight describes NREL research to develop a set of diagnostic test cases for building energy simulations in order to achieve more accurate energy use and savings predictions. The National Renewable Energy Laboratory (NREL) Residential and Commercial Buildings research groups developed a set of diagnostic test cases for building energy simulations. Eight test cases were developed to test surface conduction heat transfer algorithms of building envelopes in building energy simulation programs. These algorithms are used to predict energy flow through external opaque surfaces such as walls, ceilings, and floors. The test cases consist of analytical and vetted numerical heat transfer solutions that have been available for decades, which increases confidence in test results. NREL researchers adapted these solutions for comparisons with building energy simulation results. Testing the new cases with EnergyPlus identified issues with the conduction finite difference (CondFD) heat transfer algorithm in versions 5 and 6. NREL researchers resolved these issues for EnergyPlus version 7. The new test cases will help users and developers of EnergyPlus and other building energy tools to identify and fix problems associated with solid conduction heat transfer algorithms of building envelopes and their boundary conditions. In the long term, improvements to software algorithms will result in more accurate energy use and savings predictions. NREL researchers plan to document the set of test cases and make them available for future consideration by validation standards such as ASHRAE Standard 140: Standard Method of Test for the Evaluation of Building Energy Analysis Computer Programs. EnergyPlus users will also have access to the improved CondFD model in version 7 after its next scheduled release.
Date: December 1, 2011
Partner: UNT Libraries Government Documents Department

Evaluation of Humidity Control Options in Hot-Humid Climate Homes (Fact Sheet)

Description: This technical highlight describes NREL research to analyze the indoor relative humidity in three home types in the hot-humid climate zone, and examine the impacts of various dehumidification equipment and controls. As the Building America program researches construction of homes that achieve greater source energy savings over typical mid-1990s construction, proper modeling of whole-house latent loads and operation of humidity control equipment has become a high priority. Long-term high relative humidity can cause health and durability problems in homes, particularly in a hot-humid climate. In this study, researchers at the National Renewable Energy Laboratory (NREL) used the latest EnergyPlus tool equipped with the moisture capacitance model to analyze the indoor relative humidity in three home types: a Building America high-performance home; a mid-1990s reference home; and a 2006 International Energy Conservation Code (IECC)-compliant home in hot-humid climate zones. They examined the impacts of various dehumidification equipment and controls on the high-performance home where the dehumidification equipment energy use can become a much larger portion of whole-house energy consumption. The research included a number of simulated cases: thermostat reset, A/C with energy recovery ventilator, heat exchanger assisted A/C, A/C with condenser reheat, A/C with desiccant wheel dehumidifier, A/C with DX dehumidifier, A/C with energy recovery ventilator, and DX dehumidifier. Space relative humidity, thermal comfort, and whole-house source energy consumption were compared for indoor relative humidity set points of 50%, 55%, and 60%. The study revealed why similar trends of high humidity were observed in all three homes regardless of energy efficiency, and why humidity problems are not necessarily unique in the high-performance home. Thermal comfort analysis indicated that occupants are unlikely to notice indoor humidity problems. The study confirmed that supplemental dehumidification is needed to maintain space relative humidity (RH) below 60% in a hot-humid climate home. Researchers also concluded that ...
Date: December 1, 2011
Partner: UNT Libraries Government Documents Department

Improving Building Energy Simulation Programs Through Diagnostic Testing (Fact Sheet)

Description: New test procedure evaluates quality and accuracy of energy analysis tools for the residential building retrofit market. Reducing the energy use of existing homes in the United States offers significant energy-saving opportunities, which can be identified through building simulation software tools that calculate optimal packages of efficiency measures. To improve the accuracy of energy analysis for residential buildings, the National Renewable Energy Laboratory's (NREL) Buildings Research team developed the Building Energy Simulation Test for Existing Homes (BESTEST-EX), a method for diagnosing and correcting errors in building energy audit software and calibration procedures. BESTEST-EX consists of building physics and utility bill calibration test cases, which software developers can use to compare their tools simulation findings to reference results generated with state-of-the-art simulation tools. Overall, the BESTEST-EX methodology: (1) Tests software predictions of retrofit energy savings in existing homes; (2) Ensures building physics calculations and utility bill calibration procedures perform to a minimum standard; and (3) Quantifies impacts of uncertainties in input audit data and occupant behavior. BESTEST-EX is helping software developers identify and correct bugs in their software, as well as develop and test utility bill calibration procedures.
Date: February 1, 2012
Partner: UNT Libraries Government Documents Department

2011 Residential Energy Efficiency Technical Update Meeting Summary Report: Denver, Colorado - August 9-11, 2011

Description: This report provides an overview of the U.S. Department of Energy Building America program's Summer 2011 Residential Energy Efficiency Technical Update Meeting. This meeting was held on August 9-11, 2011, in Denver, Colorado, and brought together more than 290 professionals representing organizations with a vested interest in energy efficiency improvements in residential buildings.
Date: November 1, 2011
Partner: UNT Libraries Government Documents Department

NREL Evaluates Thermal Performance of Uninsulated Walls to Improve Accuracy of Building Energy Simulation Tools (Fact Sheet)

Description: NREL researchers discover ways to increase accuracy in building energy simulations tools to improve predictions of potential energy savings in homes. Uninsulated walls are typical in older U.S. homes where the wall cavities were not insulated during construction or where the insulating material has settled. Researchers at the National Renewable Energy Laboratory (NREL) are investigating ways to more accurately calculate heat transfer through building enclosures to verify the benefit of energy efficiency upgrades that reduce energy use in older homes. In this study, scientists used computational fluid dynamics (CFD) analysis to calculate the energy loss/gain through building walls and visualize different heat transfer regimes within the uninsulated cavities. The effects of ambient outdoor temperature, the radiative properties of building materials, insulation levels, and the temperature dependence of conduction through framing members were considered. The research showed that the temperature dependence of conduction through framing members dominated the differences between this study and previous results - an effect not accounted for in existing building energy simulation tools. The study provides correlations for the resistance of the uninsulated assemblies that can be implemented into building simulation tools to increase the accuracy of energy use estimates in older homes, which are currently over-predicted.
Date: March 1, 2012
Partner: UNT Libraries Government Documents Department

NREL Provides Guidance to Improve Air Mixing and Thermal Comfort in Homes (Fact Sheet)

Description: NREL research determines optimal HVAC system design for proper air mixing and thermal comfort in homes. As U.S. homes become more energy efficient, heating, ventilation, and cooling (HVAC) systems will be downsized, and the air flow volumes required to meet heating and cooling loads may be too small to maintain uniform room air mixing-which can affect thermal comfort. Researchers at the National Renewable Energy Laboratory (NREL) evaluated the performance of high sidewall air supply inlets and confirmed that these systems can achieve good air mixing and provide suitable comfort levels for occupants. Using computational fluid dynamics modeling, NREL scientists tested the performance of high sidewall supply air jets over a wide range of parameters including supply air temperature, air velocity, and inlet size. This technique uses the model output to determine how well the supply air mixes with the room air. Thermal comfort is evaluated by monitoring air temperature and velocity in more than 600,000 control volumes that make up the occupied zone of a single room. The room has an acceptable comfort level when more than 70% of the control volumes meet the comfort criteria on both air temperature and velocity. The study shows that high sidewall supply air jets achieve uniform mixing in a room, which is essential for providing acceptable comfort levels. The study also provides information required to optimize overall space conditioning system design in both heating and cooling modes.
Date: February 1, 2012
Partner: UNT Libraries Government Documents Department

NREL Tests Integrated Heat Pump Water Heater Performance in Different Climates (Fact Sheet)

Description: This technical highlight describes NREL tests to capture information about heat pump performance across a wide range of ambient conditions for five heat pump water heaters (HPWH). These water heaters have the potential to significantly reduce water heater energy use relative to traditional electric resistance water heaters. These tests have provided detailed performance data for these appliances, which have been used to evaluate the cost of saved energy as a function of climate. The performance of HPWHs is dependent on ambient air temperature and humidity and the logic controlling the heat pump and the backup resistance heaters. The laboratory tests were designed to measure each unit's performance across a range of air conditions and determine the specific logic controlling the two heat sources, which has a large effect on the comfort of the users and the energy efficiency of the system. Unlike other types of water heaters, HPWHs are both influenced by and have an effect on their surroundings. Since these effects are complex and different for virtually every house and climate region, creating an accurate HPWH model from the data gathered during the laboratory tests was a main goal of the project. Using the results from NREL's laboratory tests, such as the Coefficient of Performance (COP) curves for different air conditions as shown in Figure 1, an existing HPWH model is being modified to produce more accurate whole-house simulations. This will allow the interactions between the HPWH and the home's heating and cooling system to be evaluated in detail, for any climate region. Once these modeling capabilities are in place, a realistic cost-benefit analysis can be performed for a HPWH installation anywhere in the country. An accurate HPWH model will help to quantify the savings associated with installing a HPWH in the place of a standard electric water heater. ...
Date: January 1, 2012
Partner: UNT Libraries Government Documents Department

NREL's Field Data Repository Supports Accurate Home Energy Analysis (Fact Sheet)

Description: This fact sheet discusses NREL's work to develop a repository of research-level residential building characteristics and historical energy use data to support ongoing efforts to improve the accuracy of residential energy analysis tools and the efficiency of energy assessment processes. The objective of this project is to create a robust empirical data source to support the research goals of the Department of Energy's Building America program, which is to improve the efficiency of existing U.S. homes by 30% to 50%. Researchers can use this data source to test the accuracy of building energy simulation software and energy audit procedures, ultimately leading to more credible and less expensive energy analysis.
Date: February 1, 2012
Partner: UNT Libraries Government Documents Department

Advanced Energy Retrofit Guide: Practical Ways to Improve Energy Performance, K-12 Schools (Book)

Description: The U.S. Department of Energy developed the K-12 Advanced Energy Retrofit Guide to provide specific methodologies, information, and guidance to help energy managers and other stakeholders plan and execute energy efficiency improvements. We emphasize actionable information, practical methodologies, diverse case studies, and unbiased evaluation of the most promising retrofit measure for each building type. K-12 schools were selected as one of the highest priority building sectors, because schools affect the lives of most Americans. They also represent approximately 8% of the energy use and 10% of the floor area in commercial buildings.
Date: February 1, 2013
Partner: UNT Libraries Government Documents Department

Retail Buildings: Assessing and Reducing Plug and Process Loads in Retail Buildings (Fact Sheet)

Description: Plug and process loads (PPLs) in commercial buildings account for almost 5% of U.S. primary energy consumption. Minimizing these loads is a primary challenge in the design and operation of an energy-efficient building. PPLs are not related to general lighting, heating, ventilation, cooling, and water heating, and typically do not provide comfort to the occupants. They use an increasingly large fraction of the building energy use pie because the number and variety of electrical devices have increased along with building system efficiency. Reducing PPLs is difficult because energy efficiency opportunities and the equipment needed to address PPL energy use in retail spaces are poorly understood.
Date: April 1, 2013
Partner: UNT Libraries Government Documents Department

Office Buildings: Assessing and Reducing Plug and Process Loads in Office Buildings (Fact Sheet)

Description: Plug and process loads (PPLs) in commercial buildings account for almost 5% of U.S. primary energy consumption. Minimizing these loads is a primary challenge in the design and operation of an energy-efficient building. PPLs are not related to general lighting, heating, ventilation, cooling, and water heating, and typically do not provide comfort to the occupants. They use an increasingly large fraction of the building energy use pie because the number and variety of electrical devices have increased along with building system efficiency. Reducing PPLs is difficult because energy efficiency opportunities and the equipment needed to address PPL energy use in office spaces are poorly understood.
Date: April 1, 2013
Partner: UNT Libraries Government Documents Department