Cooling loads must be dramatically reduced when designing net zero energy buildings or other highly efficient facilities. Advances in this area have focused primarily on reducing a building's sensible cooling loads by improving the envelope, integrating properly sized daylighting systems, reducing unwanted solar heat gains, reducing internal heat gains, and specifying cooling equipment with high nominal efficiencies. As sensible loads decrease, however, latent loads remain relatively constant, and thus become a greater fraction of the overall cooling requirement in highly efficient building designs, particularly in humid climates. This shift toward low sensible heat ratio (SHR) systems is a challenge for conventional heating, ventilating, and airconditioning (HVAC) systems. Electrically driven vapor compression systems typically dehumidify by first overcooling air below the dew-point temperature and then reheating it to an appropriate supply temperature, which requires additional energy. Another dehumidification strategy incorporates solid desiccant rotors that remove water from air more efficiently than vapor compression; however, these systems are large and increase fan energy consumption due to the increased airside pressure drop of solid desiccant rotors. A third dehumidification strategy involves high-flow liquid desiccant systems. These systems require high-maintenance mist eliminators to protect the air distribution system from corrosive desiccant droplet carryover. These are commonly used in industrial applications but rarely in commercial buildings because of the high maintenance cost. Low-flow liquid desiccant airconditioning (LDAC) technology provides an alternative solution with several potential advantages over previous dehumidification systems: This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications. Acronyms and Abbreviations AHU air handling unit ASH anti-sweat heater ASHRAE American Society of Heating, Refrigerating and AirConditioning Engineers CaCl 2 calcium chloride cfm cubic feet per minute CHP combined heat and power COP coefficient of performance DB dry bulb temperature DOE U.S. Department of Energy DP dew point temperature DX direct expansion hp horsepower HR humidity ratio HVAC heating, ventilation, and air conditioning LDAC liquid desiccant airconditioning LHR latent heat ratio LiCl lithium chloride MCBD mean coincident dry bulb temperature MRC moisture removal capacity NREL National Renewable Energy Laboratory OA outdoor air RH relative humidity RSHI regeneration specific heat input SHR sensible heat ratio TMY3 Typical Meteorological Year 3 x This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications. Nomenclature Product or process airstream Air that leaves the conditioner and will eventually be introduced into the building as supply air. The product air may go through other equipment or processes before it is introduced into the conditioned space. Regeneration speci...

NOTICEThis report was prepared as an account of work sponsored by an agency of the United States government. Neither the United States government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States government or any agency thereof. (Felts et al. 2000). Thus, RTU supply fans may provide air at rates that are much higher than those needed to meet most thermal loads, wasting the energy needed to move and heat or cool the excess air.To address this issue, some U.S. retailers have started to upgrade existing RTUs, retrofitting their constant-speed motors with stepped-or variable-speed functionality. Such retrofits may be more cost effective than replacing an entire RTU, particularly if the unit is in the middle of its lifespan. Other U.S. retailers, however, are uncomfortable pursuing this measure, as there is a lack of supporting data detailing the climate zone-specific energy savings potential associated with this upgrade. Building and portfolio energy managers have thus been unable to present a compelling business case for RTU fan motor upgrades.This study uses whole-building energy simulation to estimate the energy impact of stepped-and variable-speed RTU fan motor retrofits in the retail environment, across 16 locations in all 15 U.S. climate zones. The results allow retailers to estimate the building-level energy savings associated with this retrofit measure. This is a critical step in enabling retailers to determine whether a compelling business case can be made. Development ProcessEnergyPlus Version 6.0 (DOE 2010) was used to evaluate the whole-building energy savings associated with stepped-and variable-speed RTU fan motor retrofits as follows:1. Two prototype big-box retail EnergyPlus models were created: one with refrigeration systems and one without.2. Each prototype model was replicated across 16 locations, which encompassed all 15 U.S. climate zones, as defined by DOE (2005).3. Standard 90. 1-20041- (ASHRAE 2004a) was applied to the building envelope to create climate-specific baseline models.4. Custom sizing and control logic was used to modify a subset of the baseline models with stepped-and variable-speed RTU fan motor controls.5. EnergyPlus was used to simulate the energy performance of all models to determine the energy savings associated with these retrofits.v Results Table ES-1 through Table ES-3 present an overview of the simulation results 1 . Annual whole...

AHU air handling unit ASH anti-sweat heater CDD cooling degree day cfm cubic feet per minute COP coefficient of performance DB dry-bulb (temperature) DD design day DOAS dedicated outdoor air system DOE U.S. Department of Energy DP dew-point (temperature) DX direct expansion EER energy efficiency ratio gpm gallons per minute HR humidity ratio HVAC heating, ventilation, and air conditioning LDAC liquid desiccant air conditioning LDDX liquid desiccant direct expansion LiCl lithium chloride MCDB mean coincident dry bulb (temperature) NREL National Renewable Energy Laboratory psi pounds per square inch RH relative humidity RSHI regeneration specific heat input RTU rooftop unit scfm standard cubic feet per minute WB wet-bulb (temperature) vi This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications. Nomenclature product or process airstream Air that leaves the conditioner and will eventually be introduced into the building as supply air. The product air may go through other equipment or processes before it is introduced into the conditioned space. regeneration specific heat input The amount of thermal energy consumed by a desiccant regenerator to remove one pound of moisture from the air, in kBtu/lb (ASHRAE 2007a). The typical range of RSHI values for single stage liquid desiccant regenerators are between 1.25 and 2.1 kBtu/lb. Two stage regenerators can achieve RSHI values as low as 0.9 kBtu/lb. The RSHI does not include the energy from the regenerator's pump(s) and fan.

No abstract

Recently, the city of Boulder, CO has recently approved mandatory energy efficiency standard, called SmartRegs Program, for rental properties. Improving residential energy efficiency is a goal of the city as they strive to meet the green house gas reduction targets of the Kyoto Protocol. However, energy efficiency is typically not implemented in rental units because of a split incentive between landlords and tenants. This paper evaluates the various retrofit measures that improve rental homes energy efficiency as well as the effectiveness of SmartRegs Program. First, various energy efficiency measures are evaluated through walk-through and detailed energy audits to assess their effectiveness in improving the energy performance of rental homes. Based on the results of the energy audits and survey of various stake holders, a set of recommendations have been defined to ensure that the SmartRegs program be successfully implemented in order to improve the overall performance and quality of rental homes. Moreover, it is found that energy efficient can increase the thermal comfort levels and decrease the energy costs for tenants, increase the value of the property for landlords, and help the city meet their green house gas reduction goals.