Cooling Energy Reduction Research Articles

A Study on Reduction of Cooling Energy in Glazed Buildings

A Study on Reduction of Cooling Energy in Glazed Buildings

Supply air temperature impact in underfloor air distribution systems under Korean climatic conditions: Energy, humidity and comfort

Underfloor air distribution (UFAD) systems have received increasing attention during the past decades due to potential advantages over conventional overhead (OH) forced air systems. Among design and operating parameters, air handling unit (AHU) supply air temperature (SAT) has significant impacts on the overall UFAD performance. In this study, the detailed whole-building energy simulation program, EnergyPlus version 6.0, was used to perform the analysis on the impact of SAT on the UFAD system performance such as energy, humidity and comfort under Korean climatic condition. It turns out that raising AHU SAT causes increased HVAC energy consumption due to heating and fan energy increase despite the cooling energy reduction. The increase in the heating energy was mainly due to the increased central AHU heating coil demand increase with the higher SAT. In addition, raised SAT elevated relative humidity in the room space during the summer season due to the fact that higher SAT set-point in the central AHU was not able to sufficiently dehumidify conditioned air compared to the lower SAT. However, the increased SAT reduced the number of hours when the occupants might feel cold during the heating season in the interior zone where the heating is not provided.

Estimation of Cooling Energy Reduction by Utilizing Cross-Ventilation in Detached Houses, within the Japanese newly introduced Energy Regulation - Evaluating Energy Consumption for Different Uses

The reduction of carbon dioxide emission due to energy consumption in the household sector is an urgent task, worldwide. As a measure to respond to the task, a new regulation has just been enforced since April 2009, in Japan. This regulation evaluates the energy performance of detached houses by estimating the primary energy consumption for different uses, namely, heating, cooling, ventilation, domestic hot water and lighting.Especially in mild or hot climates, it has been frequently claimed by practitioners that the regulation, which is heavily focused on insulation performance, is not enough and broader aspects should be equally evaluated. The effectiveness of cross ventilation in reducing cooling energy is one of these aspects. However, there have been difficulties to overcome in predicting the effectiveness of cross ventilation on cooling energy reduction. Among such difficulties are the decrease of the discharge coefficient of openings with inclined airflow, variation of the wind pressure coefficient depending on surrounding conditions, etc., occupants’ window opening behaviour and actual energy efficiency of air conditioners depending on their output and outdoor conditions. By referring to the results from experiments and observations on cross ventilation and air conditioners, the authors have proposed a solution for the Japanese new energy regulation on how to predict cooling energy consumption, taking the above factors into consideration. Even though there are still problems to be solved, the solution by the authors, shown in this paper, can be a guidepost to a more reasonable evaluation of the energy performance for cooling in buildings, as well as to a more reasonable design practice for windows and openings on the partition walls.

Energy performance of a dual airflow window under different climates

Ventilated windows have shown great potential in conserving energy in buildings and provide fresh air to improve indoor air quality. This paper reports our effort to use EnergyPlus to simulate the energy performance of a dual airflow window under different climates. Our investigation first developed a network model to account for the two-dimensional heat transfer in the window system and implemented it in EnergyPlus. The two-dimensional assumption and the modified EnergyPlus program were validated by the measured temperatures of the window and the energy demand of a test cell with the window under actual weather conditions. Then EnergyPlus was applied to analyze energy performance of a small apartment installed with the dual airflow windows in five different climate zones in China. The energy used by the apartment with blinds windows and low-e windows was also calculated for comparison. The dual airflow window can reduce heating energy of the apartment, especially in cold climate. The cooling energy reduction by the window was less important than that by shading solar radiation. The dual airflow window is recommended for colder climate. If improving air quality is a major consideration for a building, the window can be used in any climate.

Cooler tile-roofed buildings with near-infrared-reflective non-white coatings

Owners of homes with pitched roofs visible from ground level often prefer non-white roofing products for aesthetic considerations. Non-white, near-infrared-reflective architectural coatings can be applied in situ to pitched concrete or clay tile roofs to reduce tile temperature, building heat gain, and cooling power demand, while simultaneously improving the roof's appearance. Scale-model measurements of building temperature and heat-flux were combined with solar and cooling energy use data to estimate the effects of such cool-roof coatings in various California climates. Under typical conditions—e.g., 1kWm-2 summer afternoon insolation, R-11 attic insulation, no radiant barrier, and a 0.3 reduction in solar absorptance—absolute reductions in roof surface temperature, attic air temperature, and ceiling heat-flux are about 12, 6.2K, and 3.7Wm-2, respectively. For a typical 1500ft2(139m2) house with R-11 attic insulation and no radiant barrier, reducing roof absorptance by 0.3 yields whole-house peak power savings of 230W in Fresno, 210W in San Bernardino, and 210W in San Diego. The corresponding absolute and fractional cooling energy savings are 92kWhyr-1 (5%), 67kWhyr-1 (6%), and 8kWhyr-1 (1%), respectively. These savings are about half those previously reported for houses with non-tile roofs. With these assumptions, the statewide peak cooling power and annual cooling energy reductions would be 240MW and 63GWhyr-1, respectively. Statewide energy savings would reduce annual emissions from California power plants by 35kton CO2, 1.1ton NOx, and 0.86ton SOx. The economic value of cooling energy savings is well below the cost of coating a tile roof, but the simple payback times for using cool pigments in a roof tile coating are modest (5–7yr) in the warm climates of Fresno and San Bernardino.

Are the energy efficient rates (RVRs) approximate in different climatic locations for the same building with the same reform?

This paper studies the annual heating and cooling energy consumption and the variation law with the tools of characteristic temperature method (CTM) when making the same energy-saving measures on the same building under 43 different climate conditions. It can be found that for the same building, under different climate conditions, the maximal difference in annual energy consumption is up to more than 70 times and after improving building envelope, annual heating and cooling energy reductions are greatly different under various weather conditions, which illustrates that building energy consumption and its reduction is completely dependent on climate conditions; and the energy-saving potentiality and economic value with the same measures are quite different under various climatic conditions. Nevertheless, annual energy efficient rates of cooling are approximate (33.9–39.8%) for the same building with the same energy efficient measures in 43 climate conditions with quite different climatic conditions, and those of heating are also approximate (between 16.2% and 19.5%). This paper proves again the common rule that climate conditions determine energy consumption while energy efficient rates depend on the energy efficient measures.

00/00480 Cooling-energy reduction in air-conditioned offices by using night ventilation

00/00480 Cooling-energy reduction in air-conditioned offices by using night ventilation

Cooling-energy reduction in air-conditioned offices by using night ventilation

Night ventilation has been applied successfully to many passively-cooled or low-energy office buildings. This paper investigates the applicability of night ventilation in air-conditioned office buildings. A thermal and ventilation simulation model, together with suitable weather data were used to examine the potential for energy savings and/or improved internal comfort conditions by applying night ventilation cooling. It was found that natural ventilation strategies could save cooling energy in typical air-conditioned offices. However, the use of mechanical ventilation could lead to increased energy-consumption. If typical offices are modified to incorporate features assisting the application of night ventilation, then cooling energy could be saved when mechanical ventilation is used and further reduced in the case of natural ventilation. Such features would include exposed thermal mass or offices designed to ‘best practice’ guidelines, such as airtight construction and minimisation of internal and solar heat gains.

Roof solar reflectance and cooling energy use: field research results from Florida

Traditionally, architects have recognized that reflective building colors can reduce building thermal loads. Experiments in Florida have examined the impact of reflective roof coatings on air conditioning energy use in a series of tests on occupied homes. The experiments were conducted on nine residential buildings from 1991 to 1994 using a before and after test protocol where the roofs were whitened at midsummer. Measured air conditioner electrical savings in the buildings during similar pre and post-weather periods averaged 19%, ranging from a low of 2% to a high of 43%. Utility peak coincident peak savings averaged 22% with a similar range of values. Cooling energy reductions appear to depend also on initial ceiling insulation level and roof solar reflectance, air duct system location and air conditioner sizing.

Effects of Tree Shade on Home Cooling Requirements

This study was implemented to provide more information on the effects of shade trees on summer cooling energy reduction. A sample of 113 homes of similar setting and design in College Station, Texas was used. Electrical data reduced to kilowatt hours per square foot of living area were used as the dependent variable. Shade proved to be the most significant of several variables observed in reducing electrical energy usage.