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Packaged air-conditioning systems, such as rooftop units (RTUs), are widely used in small commercial buildings in the United States. Although new regulations and standards require new air-conditioning equipment to have multi-speed supply fan operation, most of the installed units employ fixed-speed supply fans. The electrical energy usage associated with constant volumetric air delivery fan systems is on the order of half the total RTU electrical energy usage because supply fans operate continuously during the occupied periods in commercial buildings for ventilation. In addition, compressors within RTUs typically feature single- or two-stage capacity controls leading to frequent unit cycling and thus, deteriorated performance in energy efficiency. This paper presents relatively comprehensive assessment results for three RTU variable-speed retrofit options: 1) retrofits of fixed-speed supply fans with variable-speed fans for single-compressor-speed units, 2) replacement of existing fixed-speed RTUs with RTUs having two-speed compressors with variable-speed supply fans and 3) retrofits of RTUs with new RTUs that incorporate variable-speed compressors and fans (indoor and outdoor). The assessment study involves parametric simulations across different building types and locations in the U.S. to understand the performance variation with respect to location and building use. Performance improvements in terms of energy efficiency, operation cost and indoor comfort delivery for the various retrofit options are demonstrated compared to conventional single-stage RTUs with constant speed supply fans. The assessment results show that all three retrofit options offer significant fan energy savings, but much smaller savings potential for compressor and condenser fan electricity consumption. The variable-speed-unit retrofit provides the highest cost savings potentials, ranging from 40 to 250 $ per rated cooling ton per year depending on the building type and location. In addition to efficiency and economic benefits, the two-stage-unit and variable-speed-unit retrofits also lead to improved indoor humidity regulation performance due to reduced unit cycling. [ABSTRACT FROM AUTHOR]

Abstract: Energy recovery ventilators (ERVs) transfer energy between the air exhausted from building and the outdoor supply air to reduce the energy consumption associated with the conditioning of ventilation air. In this paper, the applicability of ERVs with sensible and latent effectiveness values in a practical range is studied using TRNSYS simulation program. The impact of ERV on annual cooling and heating energy consumption is investigated by modeling a 10-storey office building in four American cities as representatives of major climatic conditions. The results show that heat and moisture recovery can lead to a significant reduction in the annual heating energy consumption (i.e., up to 40%, which is 5% higher than heat recovery). Also, an ERV with the capability of moisture recovery may reduce the annual cooling energy consumption by 20% provided the ERV is properly controlled. Since the un-controlled operation of ERVs during the summer may increase the cooling energy consumption, an optimum control strategy is developed and verified in the paper. This optimum control strategy depends on ERV''s latent to sensible effectiveness ratio. For instance, an ERV with equal sensible and latent effectiveness should be operated when either the outdoor enthalpy or temperature is greater than that of the indoor air. [Copyright &y& Elsevier]

Abstract: Indoor air pollutants at high concentrations in poultry houses can potentially affect workers'' health, and animal welfare and productivity. This paper presents research results of a 2-year continuous monitoring of ammonia (NH3), carbon dioxide (CO2), hydrogen sulfide (H2S), and particulate matter (PM) concentrations from to date the most comprehensive study on a single farm in two 180,000-bird high-rise (HR) and two 200,000-bird manure-belt (MB) layer hen houses located in Indiana, USA. Air was sampled at ventilation fans of the mechanically-ventilated houses. Concentrations of NH3 and CO2 were measured with photoacoustic multi-gas monitors. Concentrations of H2S and PM10 were monitored with pulsed fluorescence analyzers and Tapered Element Oscillating Microbalances (TEOM), respectively. The 2-year mean ± standard deviation concentrations at ventilation fans of the four layer hen houses were 48.9 ± 39 and 51.9 ± 40.7 ppm in HR, and 13.3 ± 9.1 and 12.9 ± 10.5 ppm in MB for NH3; 26.4 ± 17.6 and 24.9 ± 19 ppb in HR, 40.0 ± 21.1 and 41.2 ± 31.5 ppb in MB for H2S; 1755 ± 848 and 1804 ± 887 ppm in HR, and 2295 ± 871 and 2285 ± 946 ppm in MB for CO2; and 540 ± 303 and 552 ± 338 μg m−3 in HR, and 415 ± 428 and 761 ± 661 μg m−3 in MB for PM10. Compared with the MB houses, concentrations of the HR houses were higher for NH3, and lower for CO2, H2S, and PM10 (P < 0.05). High concentrations of NH3 detected in winter represent potential challenges to workers'' health and animal welfare. Variations in pollutant concentrations at the exhaust fans were affected by outdoor temperature, ventilation, bird condition, and farm operation. A new weekly variation, characterized by significantly lower PM10 concentrations on Sundays, was identified and was related to the weekly schedule of house operational activities. [Copyright &y& Elsevier]

Abstract: This paper investigates factors explaining the adoption of energy-efficient heating, cooling, window, and lighting technologies in U.S. commercial buildings. It presents multinomial logit models of technology adoption using the 2003 Commercial Buildings Energy Consumption Survey microdata set, examining, first, fundamental building components, and, second, energy-efficient adaptations. Key findings are that the choice of fundamental building components is strongly influenced by locational factors, the activities that are expected to take place in the building, and building-specific characteristics. Lighting technologies are an exception, and are poorly explained by these factors. By contrast, energy-efficient heating, cooling, window, lighting, and control adaptations appear to share common drivers, and are more likely to be adopted in newer, larger, more energy-intensive, owner-occupied buildings. These are the buildings that can best afford the up-front costs of innovation, which is often a design-intensive process. Absent policy interventions, the energy-efficient adaptations are unlikely to diffuse rapidly to the rest of the commercial building stock. [Copyright &y& Elsevier]