NREL has developed the novel concept of a desiccant enhanced evaporative air conditioner (DEVap) with the objective of combining the benefits of liquid desiccant and evaporative cooling technologies into an innovative “cooling core.” Liquid desiccant technologies have extraordinary dehumidification potential, but require an efficient cooling sink. Today’s advanced indirect evaporative coolers provide powerful and efficient cooling sinks, but are fundamentally limited by the moisture content in the air.
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Pacific Northwest National Laboratory (PNNL) with funding from the U.S. Department of Energy's Building Technologies Program (BTP) evaluated a number of control strategies that can be implemented in a controller, to improve the operational efficiency of the packaged air conditioning units. The two primary objectives of this research project are: 1) determine the magnitude of energy savings achievable by retrofitting existing packaged air conditioning units with advanced control strategies not ordinarily used for packaged units and 2) estimating what the installed cost of a replacement control with the desired features should be in various regions of the U.S. This document reports results of the study.
Miscellaneous electrical loads (MELs) are building loads that are not related to general lighting, heating, ventilation, cooling, and water heating, and typically do not provide comfort to the building occupants. MELs in commercial buildings account for almost 5% of U.S. primary energy consumption. On an individual building level, they account for approximately 25% of the total electrical load in a minimally code-compliant commercial building, and can exceed 50% in an ultra-high efficiency building such as the National Renewable Energy Laboratory's (NREL) Research Support Facility (RSF). Minimizing these loads is a primary challenge in the design and operation of an energy-efficient building. A complex array of technologies that measure and manage MELs has emerged in the marketplace. Some fall short of manufacturer performance claims, however. NREL has been actively engaged in developing an evaluation and selection process for MELs control, and is using this process to evaluate a range of technologies for active MELs management that will cap RSF plug loads. Using a control strategy to match plug load use to users' required job functions is a huge untapped potential for energy savings.
This document, developed in response to the hospitality sector’s increasing interest in using HVAC occupancy-based control (OBC) systems to reduce the energy used by unoccupied guest rooms, provides information on a technology demonstration evaluating the energy-savings potential of OBC systems produced by five manufacturers. These systems were deployed in six different hotels in three metropolitan areas and the report documents the research team’s calculation of aggregate and location-specific energy savings across four study periods, from December, 2011 to August, 2012.
This paper presents a parametric analysis using a numerical model of a new concept in desiccant and evaporative air conditioning. The concept consists of two stages: a liquid desiccant dehumidifier and a dew-point evaporative cooler. Each stage consists of stacked air channel pairs separated by a plastic sheet. In the first stage, a liquid desiccant film removes moisture from the process (supply-side) air through a membrane. An evaporatively-cooled exhaust airstream on the other side of the plastic sheet cools the desiccant. The second-stage indirect evaporative cooler sensibly cools the dried process air. We analyze the tradeoff between device size and energy efficiency. This tradeoff depends strongly on process air channel thicknesses, the ratio of first-stage to second-stage area, and the second-stage exhaust air flow rate. A sensitivity analysis reiterates the importance of the process air boundary layers and suggests a need for increasing airside heat and mass transfer enhancements.