 Lithium Bromide Chiller |
The key thermally activated technology (TAT) program areas are: Absorption chiller and heat pump technologies, solid and liquid desiccant VAQ (ventilation air quality) technologies, heat and mass transfer (energy recovery and recycling), thermal storage and thermal management technologies, advanced heat-driven power cycles (Organic Rankine Cycles, Stirling Engines) and adapting these to IES applications.
Desiccants
The desiccant activities help develop and commercialize gas-fired desiccant technology by bringing together manufacturers and users of desiccant systems; manufacturers of heating, ventilation, and air-conditioning (HVAC) systems; building designers; and the natural gas industry. Together, these stakeholders are working to accelerate the commercialization of improved integrated desiccant technology into commercial building markets, resulting in the introduction of new, marketable products under recognizable HVAC brand names.
Heat Pumps
The Program is primarily targeting two technologies: the generator absorber heat exchange (GAX) cycle heat pump and its successor, the "Hi-Cool" heat pump. The GAX heat pump is up to 40% more efficient in heating than existing technologies, requires less maintenance, and uses environmentally friendly refrigerants. The GAX heat pump provides a major jump in energy efficiency in the heating mode, but not in the cooling mode, so it is marketable primarily in the middle and northern United States. The Hi-Cool absorption heat pumps, specifically designed for improved cooling performance, are being developed for southern climates. This Hi-Cool absorption system will offer energy efficiencies that are an additional 30% or greater than those of current absorption technologies.
Advanced Thermal Recovery Cycles
New approaches and applications are needed to address situations in which more thermal energy is available than can be practically used for conventional heating and cooling functions. To capitalize more fully on an otherwise wasted energy resource, for example, thermal energy might be used to treat water or sewage on site; generate hydrogen; generate shaft power for driving pumps or blowers; or generate electricity. Many other approaches are possible as well. Organic Rankine cycle equipment is emerging from research and development laboratories. Operation of these cycles can extract heat energy from a source in the range of 250-800°F and convert it into electricity. Power system efficiency of 8-15% is expected depending on feed heater options and ambient conditions.
Heat and Mass Transfer Based Technology
Advanced heat and mass transfer innovations will focus upon significantly reducing volume, footprint and/or weight of key thermally activated technology pathways (absorption technologies, desiccant dehumidification and heat transfer, and mass transfer and thermal recovery). Energy recovery systems have taken the form of auxiliary equipment and are generally the purview of installers and not part of a well thought out integration design or strategy. These critical components to integration energy efficiency have not undergone rigorous research and development.
Projects
National Renewable Energy Laboratory (NREL)
To achieve an efficiency advantage over other power generation technologies, distributed power systems must efficiently recover and use waste heat from on-site prime movers. The goal of NREL's Thermal Conversion Project is to develop highly energy-efficient, thermally driven, heat-and-mass-transfer components that can be used to meet building end-use loads with cost, durability, and performance in line with market expectations.
Components must achieve thermal coefficients of performance (COPs) greater than 1.0 with or without waste heat, and component heat recovery efficiencies (both latent and sensible) must exceed 80%. Ventilation equipment must cost less than $1.25/cfm and effectively manage the tradeoffs between energy efficiency and indoor environmental quality (IEQ). Integrated energy systems with thermal conversion components meeting these criteria will optimize national energy density with the highest energy efficiency possible while maximizing IEQ and productivity.
 Ammonia-Water Chiller Prototype |
Rocky Research Inc., Mississippi Energies, ITT/Ambian
The objective of this project is to develop commercially viable thermally activated residential and light commercial cooling and heating appliances capable of using natural gas, propane, or on-site-generated exhaust heat as a primary energy source. This is an ammonia-water absorption system employing a cycle that recovers energy between the generator and absorber components.
Specific technical goals include the development of an air conditioner (chiller) operating at a seasonal gas fuel efficiency of 0.7 or better and a nominal chiller rating efficiency at 95°F of 0.67 or better and a heat pump with a heating performance (COP) of 1.4 or better at 47°F rating point and the capability to provide heat pumping at or below 20°F, at a cost of about $2,500 (in year 2000 dollars) for a 5-ton system.
University of Illinois at Chicago Energy Resources Center (UIC-ERC)
NREL and its subcontractors, as described in its publication "Advanced Liquid Desiccant Technology Development Study," are developing new liquid desiccant designs to achieve primary COPs of more than 1.0 and potentially approaching 2.0.
At NREL, preliminary testing of a liquid desiccant dehumidifier coupled with electric heat pump energy recovery manufactured by DryKor has revealed "excellent energy efficiency" with primary COPs up to 0.84 (and site electricity COPs up to 2.9) for inlet conditions of 86°F/70% RH. However, testing also showed that dehumidification capacity was 20%-40% lower than other thermally regenerated, desiccant-based dehumidifiers. The study indicated "auxiliary heat may be required to increase the dehumidification capacity depending on the application."
Thermally activated technologies (TAT) such as desiccant dehumidification are essential to waste heat use and the ultimate cost effectiveness of integrated energy systems (IES). Overall, per the document "Program and Peer Review for IES and TAT," NREL developments will lead to a "new class of liquid desiccant technologies with efficiency and indoor air security implications" and "better integration into IES systems."
University of Illinois at Chicago Energy Resources Center (UIC-ERC)
NREL and its subcontractors are developing high-performance/low-cost solid desiccant components, including thermally regenerated dehumidification rotors and enthalpy exchange wheels. This project, which focuses on advances to thermally regenerated dehumidification rotors (and their cassettes), resulted from an NREL April 2001 Request for Proposals providing technical support to industry for accelerating the penetration of desiccant cooling technologies into broad commercial building air-conditioning markets in which the full energy savings potential can be realized.
National Renewable Energy Laboratory (NREL)
The purpose of this project is to investigate and develop techniques for the rapid monitoring of organic contaminants present in indoor environments and to use these techniques to evaluate the contaminant removal performance of TAT used for space conditioning. The work is divided into three tasks:
- Develop a real-time sensor to detect and measure organic contaminants at concentrations typical of indoor environments.
- Develop laboratory-based methods to rapidly evaluate the contaminant removal performance of desiccant materials.
- Develop contaminant removal performance evaluation methods for full-scale TAT components.
Florida Solar Energy Center, University of Central Florida
Desiccant-based equipment has improved substantially in cost, performance, and reliability in recent years and has been used in niche markets. However, these advances have not led to desiccant equipment competing successfully in the broader buildings markets.
What is needed to successfully compete is a combined desiccant/HVAC product that can satisfy several building functions (cooling/heating, enhanced dehumidification, fresh air) and provide improved efficiency (energy savings) and indoor comfort and air quality. Also, this product must have a first cost similar to existing vapor compression dehumidification products if it is to have a substantial market penetration. Further, if such a product could use waste heat for the desorption of the desiccant, it would be more marketable and of greater benefit in reducing energy use.
The Cromer cycle desiccant-based combined system is a breakthrough product. The objective of this project is to complete the engineering effort needed to develop two manufacturing prototypes and test them for performance and energy savings.
Kathabar Inc.
The objective of this work is to design, build, and prove the performance of a thermally activated rooftop air conditioner that uses low-flow liquid desiccant technology. More specific objectives are to:
- Identify the applications in which the liquid-desiccant rooftop air conditioner will successfully compete and specify a product size (or limited range of sizes) that these applications require
- Develop a design for a rooftop air conditioner that uses the low-flow liquid-desiccant technology
- Estimate the cost to manufacture the liquid-desiccant rooftop air conditioner
- Assess the competition between the liquid-desiccant rooftop air conditioner and conventional systems
- Build and test a prototype of the liquid-desiccant rooftop air conditioner
- Attract an HVAC manufacturer to become a partner in the Phase II field demonstration of the technology.
The rooftop air conditioner developed in this project will be gas-fired. With a cooling COP greater than 1.0 and a latent cooling fraction that is much higher than conventional DX systems, the liquid-desiccant rooftop air conditioner will be an important cooling option, particularly in markets that demand better control of indoor humidity. The liquid-desiccant rooftop air conditioner, with slight modifications, can also operate on heat recovered from an on-site electrical generator. This will improve the competitiveness of building CHP systems and reduce the energy needed to cool and dehumidify the nation's commercial buildings and residences.
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