Search

Closed-loop control of commercial building heating, ventilating, and air conditioning (HVAC) for demand response requires measurements used as feedback to the controllers. Demand response effectiveness is usually measured as a power deviation from baseline, but the building automation system (BAS) does not usually collect power measurements, and whole-building electric meters typically measure power at intervals of 15 min, which may be too slow for some types of demand response. Demand response strategies are sometimes focused on components of building HVAC systems, e.g., the response of supply/return fans to temperature set-point changes, but these components are usually not submetered. Fan power can be estimated from physics-based models leveraging BAS data, e.g., airflow measurements; but our ability to effectively close the loop on these estimates is not clear. In this paper, we introduce a massive dataset that contains both submetered fan power data and BAS data for several building HVAC systems during typical operation and demand response events. Through a case study we show that models leveraging BAS data alone do not provide accurate estimates of fan power during event transients, making it unlikely that closed-loop control of commercial building HVAC components for demand response would be effective using BAS data alone. This demonstrates the value of submetering HVAC components. More broadly, our dataset will enable future research bridging the gap between building control and power systems research. [ABSTRACT FROM AUTHOR]

The field performance of a low-flow internally cooled/heated liquid desiccant air conditioning (LDAC) system is investigated in this paper. The quasi-steady performance (sensible and latent heat transfer rates, coefficient of performance (COP), and uncertainties) of the LDAC system is quantified under different ambient air conditions. A major contribution of this work is a direct comparison of the transient and quasi-steady performance of the LDAC system. This paper is the first to quantify the importance of transients and shows that, for the environmental and operating conditions in this paper, transients can be neglected when estimating the energy consumption of the LDAC system. Another major contribution of this work is the development and verification of a new method that quantifies (with acceptable uncertainties) the quasi-steady performance of a LDAC system from transient field data using average data. [ABSTRACT FROM AUTHOR]

This paper focuses on the thermal and energetic behavior of a building located in the Brazilian Amazon Region, a region climatically characterized by elevated temperatures and high humidity levels, where achieving adequate thermal comfort demands a high-energy consumption due to the use of air-conditioning systems. Therefore, different energy conservation measures (ECMs) need to be evaluated to reduce the thermal load for cooling. The use of a thermal insulation material on the west wall and on the roof, and a photovoltaic (PV) system integrated as an architectural element and adapted to the roof of the building are considered. The building is simulated with the software energyplus, with its thermal behavior and energy consumption analyzed for an entire year and for a chosen design day, defined with data measured by a weather station installed close to the building. According to the evaluations carried out, it is determined that the ECMs have a direct and major influence on the reduction of the thermal load for cooling, on the reduction of the effects caused by radiation with the shading on the eaves, and the reduction of the transmittance on the surfaces that were modified in the study. In terms of energy consumption and economic feasibility, the ECMs reach an annual energy saving percentage of 74% for the building chosen as the case study, and the solutions adopted provide the return of the financial investment, proving suitable for energy saving and economically viable for regions with similar climatic characteristics. [ABSTRACT FROM AUTHOR]

In this paper, passive cooling strategies have been investigated to evaluate their effectiveness in reducing cooling thermal loads and air conditioning energy consumption for residential buildings in Kingdom of Saudi Arabia (KSA). Specifically, three passive cooling techniques have been evaluated including natural ventilation, downdraft evaporative cooling, and earth tube cooling. These passive cooling systems are applied to a prototypical KSA residential villa model with an improved building envelope. The analysis has been carried using detailed simulation tool for several cities representing different climate conditions throughout KSA. The impact of the passive cooling systems is evaluated on both energy consumption and electrical peak demand for residential villas with and without improved building envelope for five cities, representatives of various climate conditions in KSA. It is found that both natural ventilation and evaporative cooling provide a significant reduction in cooling energy use and electrical peak demand for the prototypical villa located in dry KSA climates such as that of Riyadh and Tabuk. Natural ventilation alone has reduced the cooling energy end-use by 22%, while the evaporative cooling system has resulted in 64% savings in cooling energy end-use. Moreover, the natural ventilation is found to have a high potential in all KSA climates, while evaporative cooling can be suitable only in hot and dry climates such as Riyadh and Tabuk. Finally, the analysis showed that natural ventilation provided the lowest electrical peak demand when applied into the improved envelope residential buildings in all five cities in KSA. [ABSTRACT FROM AUTHOR]

This paper describes how direct evaporative coolers can be used to improve the energy efficiency of air-cooled chillers in various operating conditions and with different strategies for staging condenser fans. These coolers are installed in front of air-cooled condensers to precool outdoor air before entering the condensers. A simulation analysis on an air-cooled chiller equipped with a direct evaporative cooler showed that when head pressure control is used, the cooler enables the condensing temperature to drop by 2.1-6.2°C, resulting in a 1.4-14.4% decrease in chiller power and a 1.3-4.6% increase in the refrigeration effect. When the chiller with the cooler operates under condensing temperature control, where condenser effectiveness is enhanced by staging all condenser fans, there is a savings in chiller power of 1.3-4.3% in some operating conditions in which the drop in compressor power exceeds the additional condenser fan power due to the pressure drop across the cooler. [ABSTRACT FROM AUTHOR]

Economic and energy-saving characteristics of cogeneration systems with microturbine and desiccant air-conditioning units are investigated on system operational planning. An optimization approach is adopted to rationally evaluate these characteristics. In this approach, on/off and rated/part load status of operation of equipment and energy flow rates are determined so as to minimize the hourly energy charge subject to satisfaction of energy demand requirements. In this optimization problem, performance characteristics of the microturbine and desiccant air-conditioning units are modeled in consideration of the influence due to ambient air temperature. Moreover, the influence due to ambient air humidity is also considered in the desiccant air-conditioning unit using the psychrometric diagram. The implementation of the numerical analysis method, discussed in this paper, to two cogeneration systems, clearly shows economic and operational benefits of using desiccant air-conditioning. [ABSTRACT FROM AUTHOR]

As unvented attics have become a more common design feature implemented by Building America partners in hot-dry climates of the United States, more attention has been focused on how this approach affects heating and cooling energy consumption. By eliminating the ridge and eave vents that circulate outside air through the attic in most new houses and by moving the insulation from the attic floor to the underside of the roof, an unvented attic becomes a semiconditioned space, creating a more benign environment for space conditioning ducts. An energy trade-off is made, however, because the additional surface area (and perhaps reduced insulation thickness) increases the building loss coefficient. Other advantages and disadvantages, unrelated to energy, must also be considered. This paper addresses the energy-related effects of unvented attics in hot-dry climates based on field testing and analysis conducted by the National Renewable Energy Laboratory. [ABSTRACT FROM AUTHOR]

As the heating, ventilating, and air conditioning (HVAC) systems accounts for a major sector of energy consumption for commercial buildings, there has been a greater demand for improving the efficiency of such systems. The air-side economizers have been developed as a class of energy-saving HVAC devices that may increase the energy efficiency by taking advantage of outdoor air during cool or cold weather. However, many economizers do not operate in the expected manner and waste even more energy than before installation, mostly due to the unreliable sensors and actuators in practice. Better control strategy is needed for optimal and robust operation. In this paper, an extremum-seeking control (ESC) based self-optimizing strategy is proposed to minimize the energy consumption, with the feedback of chilled water supply command rather than the temperature and humidity measurements. The mechanical cooling load is minimized by seeking the optimal outdoor air damper opening in real time. Such scheme does not need temperature and humidity sensors, and depends much less on the knowledge of the economizer model. Simulation was performed on a MODELICA based transient model of a single-duct air-handling unit developed with DYMOLA and AIRCONDITIONING LIBRARY. The simulation results demonstrated the potential of using ESC to achieve the minimal mechanical cooling load in a self-optimizing manner. In addition, an antiwindup ESC scheme is proposed to handle the ESC windup issue due to actuator (damper) saturation. The simulation results validated the effectiveness of the proposed antiwindup ESC. [ABSTRACT FROM AUTHOR]