42 research outputs found
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Exterior exposed ductwork: Delivery effectiveness and efficiency
Most of California`s light commercial buildings use air transport through ductwork for thermal distribution. The same air distribution systems are often used to provide both thermal comfort and ventilation. Some air distribution ductwork is installed on rooftops, exposed directly to the outside environment. As such, there exist potential energy penalties related to externally installed ductwork. In order to evaluate the magnitude of these penalties, a case study was conducted of a one-story community college building, located in California`s Sacramento Valley. The majority of the building`s air distribution ductwork was located on the roof. Energy-related issues studied in this case included duct-related thermal losses (duct leakage and conduction), delivery effectiveness and efficiency, thermal comfort issues and the effect of a roof retrofit (additional insulation and a reflective coating). The building in this study underwent a retrofit project involving additional insulation and a highly reflective coating applied to the roof and ducts. As part of this project, methods were developed to analyze the air distribution system effectiveness independent of the introduction of outside air through an outside air damper. A simplified model was developed to predict the effectiveness and efficiency of the distribution system. The time frame of the retrofit allowed two separate three week monitoring periods. Despite the fact that the ducts started off with a conduction efficiency of 97%, the delivery efficiency was on average only 73% (with a supply side effectiveness of 78% and return effectiveness of 92%). This is due to the losses from the ducts being located on the roof. The retrofit increased the delivery efficiency to an average of 89% (with a supply side effectiveness of 90% and return effectiveness of 99%), reducing the average energy use for conditioning by 22%. The model predicted, on average, the results within 10%, or better, of measured results
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IN-SITU MEASUREMENT OF WALL THERMAL PERFORMANCE: DATAINTERPRETATION AND APPARATUS DESIGN RECOMMENDATIONS
Although the U-values of many building materials have been determined by laboratory testing, the in-situ thermal performance of walls, under either static or dynamic conditions, is not so well documented. This report examines the use of field measurements of heat flow and surface temperatures to determine the dynamic as well as static thermal performance of walls. The measurement strategies examined include both active devices, which generate their own heat fluxes on the wall surfaces, and passive devices, which rely on the weather to induce the required fluxes and temperature differences. Data obtained with both devices are analyzed with the Simplified Thermal Parameter (STP) model, which was designed to characterize a wall from flux and temperature measurements rather than from assumed material characteristics. The active measurement data are also analyzed with a modified version of the STP model that takes into account lateral heat losses. Some possible sources of error for both active and passive measurement strategies are also examined, and recommendations for both measurement strategies are given
Field trialling of a pulse airtightness tester in a range of UK homes
A new low pressure ‘quasi-steady’ pulse technique for determining the airtightness of buildings has been developed further and compared with the standard blower-door technique for field-testing a range of typical UK homes. The reported low pressure air pulse unit (APU) has gone through several development stages related to optimizing the algorithm, pressure reference and system construction. The technique, which is compact, portable and easy to use, has been tested alongside the standard blower-door technique to measure the airtightness of a range of typical UK home types. Representative of the UK housing stock, the homes mostly have low levels of airtightness, resulting in poor energy performance, poor indoor air quality and poor thermal comfort. Some of these homes have been targeted for retrofitting and a quick, low cost and simple method for accurately determining their airtightness has clear advantages for correctly predicting the benefits of any improvements. A comparison between the results given by the two techniques is presented and the field trials indicate that the latest version of the pulse technique is reliable for determining building leakage at low pressure. Repeatability of multiple APU tests in the same house is found to be within +/-5% of the mean. A test where the leakage is increased by a known amount shows the APU is able to measure the change more accurately than the blower-door test. The APU also gives convenience in practical applications, due to being more compact and portable, plus it doesn’t need to penetrate the building envelope. The field trials demonstrate the pulse test has the potential to be a feasible alternative to the standard blower-door test
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ELECTRIC CO-HEATING: A METHOD FOR EVALUATING SEASONAL HEATING EFFICIENCIES AND HEAT LOSS RATES IN DWELLINGS
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Residential Duct System Leakage: Magnitude, Impacts and Potential for Reduction
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Analysis of Errors for a Fan-Pressurization Technique for Measuring Inter-Zonal Air Leakage
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Field Measurement of the Interactions between Heat Pumps and Attic Duct Systems in Residential Buildings
Research efforts to improve residential heat-pump performance have tended to focus on laboratory and theoretical studies of the machine itself, with some limited field research having been focused on in-situ performance and installation issues. One issue that has received surprisingly little attention is the interaction between the heat pump and the duct system to which it is connected. This paper presents the results of a field study that addresses this interaction. Field performance measurements before and after sealing and insulating the duct systems were made on three heat pumps. From the pre-retrofit data it was found that reductions in heat-pump capacity due to low outdoor temperatures and/or coil frosting are accompanied by lower duct-system energy delivery efficiencies. The conduction loss reductions, and thus the delivery temperature improvements, due to adding duct insulation were found to vary widely depending on the length of the particular duct section, the thermal mass of that duct section, and the cycling characteristics of the heat-pump. In addition, it was found that the use of strip-heat back-up decreased after the retrofits, and that heat-pump cycling increased dramatically after the retrofits, which respectively increase and decrease savings due to the retrofits. Finally, normalized energy use for the three systems which were operated consistently pre- and post-retrofit showed an average reduction of 19% after retrofit, which corresponds to a chance in overall distribution-system efficiency of 24%