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Heat pumps provide an efficient heating method; however they suffer from sever capacity and performance degradation at low ambient conditions. This has deterred market penetration in cold climates. There is a continuing effort to find an efficient air source cold climate heat pump that maintains acceptable capacity and performance at low ambient conditions. Systematic optimization techniques provide a reliable approach for the design of such systems. This paper presents a step-bystep approach for the design optimization of cold climate heat pumps. We first start by describing the optimization problem: objective function, constraints, and design space. Then we illustrate how to perform this design optimization using an open source publicly available optimization toolbox. The response of the heat pump design was evaluated using a validated component based vapor compression model. This model was treated as a black box model within the optimization framework. Optimum designs for different system configurations are presented. These optimum results were further analyzed to understand the performance tradeoff and selection criteria. The paper ends with a discussion on the use of systematic optimization for the cold climate heat pump design. [ABSTRACT FROM AUTHOR]

The new refrigerant HFO-1234yf is being evaluated for use as a replacement for R-134a in many cooling applications. It has been proposed to use HFO-1234yf for many AC and refrigeration applications, but we show that it is not a direct replacement for higher performance refrigerants like R-410A for heating and cooling. New refrigerant compositions have been developed and are being evaluated for use in air conditioning and heat pump applications in order to reduce emissions of carbon dioxide and higher GWP gases that can contribute to global climate change. Some of these new compositions are marginally flammable, and are expected be classified by ASHRAE and ISO as "2L" refrigerants based on low burning velocity and low heats of combustion. This paper presents measured cooling and heating performance results for some of the new candidate refrigerants, and environmental impacts are modeled based on those measured results.. Some of the trade offs impacting environmental impact of the developmental refrigerants, including GWP value and energy efficiency performance will be discussed. It is shown the lower GWP fluids do not necessarily give the best environmental performance. [ABSTRACT FROM AUTHOR]

The life-cycle assessment (LCA) methodology is used in this paper to assess the environmental effects of air-handling units (AIIU) over a 20-year life cycle. This assessment is based on quantifying the consumption of resources (energy and materials,), the harmful emissions into the environment (`air; water, and soil), and the potential changes in the environment (climate change, acidification, and ozone production,). A normal AIIU, with a face velocity of 3 m/s (600 fpm), and a small AIIU, with a face velocity of 4 m/s (800 fpm), are investigated with and without two types of air-to-air energy exchangers (plate and rotating wheel). The research demonstrates the following benefits of air-to-air energy exchangers: reduced energy consumption, reduced emissions to the environment, and reduced potential harmful changes in the environment. For both of the AIIUs' studied, these benefits are several times greater than the burdens arising from the production and operation of the AIIU, where the function of the AIIU is to provide 2000 L/s (4200 cfm) of outdoor air to the building space for 2500 h/year, but not to condition this air A larger AIIU with an air-to-air energy exchanger of higher efficiency has the smallest harmful effect on the environment. [ABSTRACT FROM AUTHOR]