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Over the past decade, the use of technologies that are alternatives to the hydrofluorocarbon (HFC) direct-expansion (DX) systems for supermarket refrigeration have continued to garner interest. The market for such alternative systems has been thriving for several years in Europe and is beginning to gain some momentum in North America. One of the major unresolved issues with use of novel refrigeration systems is obtaining an accurate measurement of the energy consumption for system comparison. The motivation for having accurate energy consumption is discussed along with field results that have been published. Low-temperature systems are the main focus of the discussion due to the larger energy consumption. However, the issues discussed also pertain to medium-temperature systems. The factors necessary to formulate a proper comparison of systems are presented as well as a discussion of the need to perform testing to determine the impact of these factors. [ABSTRACT FROM AUTHOR]

This paper describes steady-state performance simulations performed on a 3-ton R-22 split heat pump in heating mode. In total, 150 steady-state points were simulated, which covers refrigerant charge levels from 70% to 130% relative to the nominal value, the outdoor temperatures at 17°F (--8.3°C), 357°F (1.7°C) and 47°F (8.3°C), indoor air flow rates from 60% to 150% of the rated air flow rate, and two types of expansion devices (fixed orifice and thermostatic expansion valve [TXV]). A charge tuning method, which is to calibrate the charge inventory model based on measurements at two operation conditions, was applied and shown to improve the system simulation accuracy significantly over an extensive range of charge levels. In addition, we discuss the effects of using a suction line accumulator in modeling a heat pump system using either a fixed orifice or thermal expansion valve. Last, we identify the issue of refrigerant mass flow mal-distribution at low charge levels and propose an improved modeling approach. [ABSTRACT FROM AUTHOR]

High energy efficiency is a target for any refrigerating plant. To date, no known survey of the practical energy efficiency of refrigerated warehouses has been made in the USA. Such a survey project was conducted by the authors and the results are presented in this paper. A total of 62 responses to a questionnaire were collected from various installations in the USA and Canada. In addition, a field investigation of 14 plants was conducted. Several aspects of the surveyed refrigeration plants, including their energy efficiency, refrigerant selection, compression stages, types of two-stage cycles, and compressor selection, are discussed in this paper. Some recommendations and conclusions are proposed based on the first-hand information surveyed and the authors' knowledge. [ABSTRACT FROM AUTHOR]

An experimental study was conducted to investigate the impacts of air-side fouling and cleaning on the performance of various condenser coils used in unitary air-conditioning systems. A total of six condenser coils with different fin geometries and depths were tested. Performance tests were conducted at three different conditions: clean-as-received, after fouling, and after cleaning. In all cases, it was observed that fouling was mostly confined to the frontal face of the heat exchanger as reported in previous investigations. The amount of deposited dust was more dependent on fin geometry for single-row heat exchangers than for double-row heat exchangers. The predominant effect of fouling was to cause a more significant increase in air-side pressure drop than degradation in heat transfer performance. For the single-row heat exchangers, the pressure drop increased by 28% to 31%, while the heat transfer performance decreased by 7% to 12% at the standard air face velocity of 1.53 m/s depending on fin shape. For the double-row heat exchangers, the pressure drop increased by 22% to 3 7%, and heat transfer performance decreased by only 4% to 5% at the same air face velocity. Once the contaminated coils were cleaned according to a manufacturer-specified cleaning procedure, the original performance of the heat exchangers was recovered almost completely. The pressure drop was restored to within 1% to 7% and the heat transfer performance could be recovered to within 1% to 5% of the originally clean heat exchangers. Therefore, it is concluded that a periodic application of .specified cleaning procedures will be effective in maintaining the thermal performance of condenser coils. [ABSTRACT FROM AUTHOR]

Most air conditioning and refrigeration systems that employ the vapor compression cycle rely on oil circulating with refrigerant to lubricate the bearings and other contact surfaces in the compressor. The lubricant acts as a sealant to reduce leakage losses during the compression process and it also helps to absorb some of the excess heat that is generated in the compression chamber. However, this oil circulation results in oil retention in various other components outside the compressor depending on the physical interaction between lubricant and refrigerant and their transport properties. Other factors, such as the geometry and orientation of connecting lines, and the system operating conditions, such as refrigerant flow rate and oil circulation ratio, also impact the oil retention. Because of oil retention, the efficiency of heat exchangers (evaporators and condensers) decreases. In addition, the oil level in the compressor reduces, which may ultimately affect its efficiency and life span. The current line sizing rules reported in the ASHRAE Handbook Refrigeration have only limited consideration of the effects of oil in the system. With the increasing development of variable-speed systems as well as future use of newer HFO refrigerants, there is a need in the industry for upgrading the line sizing recommendations, especially the connecting gas lines of unitary split systems, which consider the effects of oil retention. To develop these rules, measuring oil retention at different operating conditions is important. A test setup has been built to measure oil retention in horizontal and vertical lines of different diameters at different refrigerant and oil flow conditions. Initial results for R134a-POE32 are presented in this paper. Based on the collected data, the final goal is to build a model, which can predict oil retention in gas lines for some of the commonly used refrigerant-lubricant combinations in the HVAC&R industry. [ABSTRACT FROM AUTHOR]

Historical buildings incur diverse challenges associated with energy consumption, specifically those surrounding opportunities for potential improvements. In the U.S., space conditioning (heating, cooling and ventilation) can account for up to half of all the energy usage within a home. As a result, identification of cost-effective methods towards enhancing energy efficiency represents critical information for homeowners and businesses alike, and a measurable estimator of potential monetary investment and return. In this paper, a two-story residential home under the protection of its city's historical preservation committee is evaluated in a longitudinal study during several building renovations. This is a continuation of previous research conducted in the same location, which focused on differences in energy consumption using a fixed-speed and variable-speed heat pump system. Within this study, energy usage over a two-year period is considered, with specific building and equipment modifications divided into individual case studies. Energy consumption data is analyzed against electrical and thermal measurements, meteorological conditions, and utility recordings to establish a baseline reference for comparison across the entire study time period. These findings illustrate both the individual and composite impacts of each renovation, and performance under a variety of dynamic environmental circumstances. [ABSTRACT FROM AUTHOR]

The compressor is often considered the "heart" of a vapor compression air-conditioning system, and is also typically the largest consumer of energy within a home setting. From this designation, the selection of compressor type holds significant influence within its operational environment, including energy consumption, ease of maintenance, and generally of primary concern for a homeowner, cost. While a variable speed compressor offers greater potential for energy savings, the increase in first-cost expense should be justified by its corresponding energy savings. This paper studies the employment of both a fixed and variable speed compressor operating inside a heat pump within a residential setting. Electrical and thermal data were collected via circuit monitors and thermocouples, respectively, and observed over a wide range of ambient conditions and time periods. The home under observation is a 2-story design, constructed in the 1920's, and houses three graduate students. Data gathered in this setting is normalized against multiple parameters, and compared to real energy, cost, and overall efficiency improvements. [ABSTRACT FROM AUTHOR]

As environmental concerns and accompanying regulations grow around the world, the Heating, Ventilation, Air Conditioning, and Refrigeration (HVAC&R) industry is working to develop technologies that utilize low-global warming potential (GWP) refrigerants and remain within competitive coefficient of performance (COP) values of previous hydrofluorocarbon (HFC) systems. Carbon Dioxide (CO2) has been investigated extensively in the past 25 years as a potential substitute for HFCs in refrigeration application in mild ambient climates. In efforts to increase the efficiency of CO2 systems, researchers and industry have identified cycle modifications that are particularly beneficial in transcritical CO2 cycle application, such as expansion work recovery and economization. This paper presents an overview of the design and operation of a multi-stage transcritical CO2 cycle with two independentlycontrolled evaporators. The cycle utilizes three stages of compression with intercooling between the second and third stages, as well as flash tank economization at each evaporator, including evaporator bypass lines for vapor from the flash tank. Furthermore, the cycle was designed to allow transition between methods of expansion work recovery without the need to stop the compressors. The cycle can switch between electronic expansion valve (EXV) mode, ejector mode, and a turbomachine expander mode with the actuation of several ball valves mid-operation. The purpose of this work is to describe the theory and rationale behind system design, discuss how the test stand will be controlled, and provide instruction on the transition between expansion methods without shutting down the compressors. [ABSTRACT FROM AUTHOR]

Historical structures incur diverse challenges associated with energy consumption, specifically those surrounding opportunities for potential improvements. In the U.S., heating and cooling of spaces can account for up to half of all energy usage within a home. As a result, identification of cost-effective methods towards enhancing energy efficiency represents critical information for homeowners and businesses alike, and a measurable estimator of potential monetary investment and return. In this paper, a novel DC-powered picogrid is developed to support a local weather station adjacent to a residential home in order to optimize its energy consumption. Though regional meteorological data is readily available from numerous online cloud-services, in-situ environmental measurements afford more building-specific insights, ranging from wind direction and speed, humidity and dew-point levels, and UV and irradiance measurements. When coupled with on-site renewable energy generation such as solar and wind power, this weather data can drive real-time electrical management decisions (e.g., storing or expending battery energy, selling electricity to the grid, etc.), and also be leveraged for daily and weekly power consumption and generation forecasting. These findings illustrate the benefits of DC-powered designs, and the capability of low-cost sensors to improve residential energy administration. [ABSTRACT FROM AUTHOR]

This paper describes extensive tests performed on a 3-ton R-22 split heat pump in heating mode. The tests contain 150 steady-state performance tests, 18 cyclic tests, and 18 defrost tests. During the testing work, the refrigerant charge level was varied from 70% to 130%, relative to the nominal value; the outdoor temperature was altered by three levels at 17°F (--8.3°C), 35°F (1.7°C) and 47°F (8.3°C); indoor airflow rates ranged from 60% to 150% of the rated airflow rate; and the expansion device was switched from a fixed-orifice to a thermal expansion value. Detailed performance data from the extensive steady-state cyclic and defrost testing performed were presented and compared. [ABSTRACT FROM AUTHOR]

Research on a novel implementation of an Ericsson cycle heat pump for near ambient refrigeration applications was performed. The concept, termed a liquid-flooded Ericsson cooler (LFEC), uses liquid flooding of the compressor and expander to approach isothermal compression and expansion processes. A numerical simulation of the cycle was developed and parametric studies were performed to explore the sensitivity of the cycle to changes in various system parameters such as, pressures, heat exchanger effectiveness and working fluids. The goal of the study was to assess the viability of the technology for vending machine applications. It was found that the target cooling coefficient of performance (COP) of 1.25 could be attained if the adiabatic efficiency of the compressor and expander were 85%. [ABSTRACT FROM AUTHOR]

Dynamic models of heat pumps are useful in developing feedback controllers and fault-detection-diagnostic (FDD) studies. Several system models have been documented in the literature, but few are for centrifugal chillers. Existing publications focus on model development and validation, providing minimal detail on the numerical aspects of the solution. The solution of the PDEs that are obtained to model the heat exchangers is critical in terms of accuracy and execution speed. This paper presents the development of a centrifugal chiller system model, using the finite-volume (FV) approach for shell-and-tube heat exchangers and aspects such as mesh dependence, integration order, and step size. Sufficient and necessary mesh sizes for accurate steady-state prediction are determined for the heat exchangers. Execution speeds with integration algorithms of the first, second, and fourth order are compared for equivalent accuracy. The model is based on first principles, allowing it to be used over a wide range of operating conditions and transients. The model is validated using data from a 90-ton R-134a centrifugal chiller. [ABSTRACT FROM AUTHOR]

The growing applications of variable-speed and tandem compressors, coupled with emerging refrigerant-oil combinations, can lead to higher levels of oil retention in vaporcompression systems, especially at lower refrigerant mass flow rates. To develop better designs and mitigation strategies, it is important to have methods for accurately measuring oil circulation ratio (OCR). High levels of OCR reduce the efficiency of heat exchangers (i.e., evaporators and condensers) and cause the compressor’s oil level to reduce, which may ultimately affect its efficiency and life span. However, measuring OCR within a vapor-compression cycle is challenging due to various factors, such as the phase change of the working fluid at different locations, miscibility between the oil and refrigerant, and varying flow regimes. The objective of this study was to develop a noninvasive, in-situ method to measure OCR in real time, which involves minimal human intervention. An OCR measurement method is presented using an oil separator and a level measurement sensor. The approach has been validated with two different methods, one of which is an ASHRAE standard. The relative differences in the OCR measurement between the liquid level probe and ASHRAE standard methods are less than 12%. [ABSTRACT FROM AUTHOR]

Natural gas (NG) has been treated as one of the main sources of energy for a wide range of residential and industrial applications for more than half a century. Liquefied Natural Gas (LNG) is the most economical way to transport NG, however, the liquefaction process can be very energy-intensive, thus offering an opportunity for increased efficiency for the technology utilized in this process. Currently, the liquefaction process consists of a series of cascading refrigeration cycles with various working fluids. This paper investigates the use of novel propane chilling technology as a portion of the liquefaction process. Based on multiple studies on performance benefits achieved with an ejector-expansion device, a novel cycle architecture employing a variable-geometry ejector combined with a pump to control the ejector motive nozzle inlet state is proposed for this application. The proposed architec ture also presents a two-stage configuration to predict the performance benefit of the ejector for future application in the original three-stage evaporation process. The scaled-down test stand will be used as a proof of concept, while also aiming to validate performance benefits relative to conventional propane chilling processes. Cycle designs, thermodynamic modelling, and parametric studies are covered in this paper. Furthermore, limitations and future directions with the test setup are also discussed. [ABSTRACT FROM AUTHOR]

Within a university/industry partnership, a new air-source heat pump technology that is optimized for cold climates was designed, fabricated, and evaluated at a National Guard base in Edinburgh, IN. Two Cold Climate Heat Pumps (CCHP) were installed into two separate but nearly identical barrack buildings. Each building had two zones; allowing one half to be heated by conventional methods (natural gas furnace) and the other half to be heated by the CCHP. The performance of each CCHP was directly compared to the natural gas furnace in terms of energy, cost, and environmental impact. The field demonstration was successful in the sense that it provided a proof of concept testing within a real world environment. Significant information was gained about component-level performance, system level component integration, and controls. On the basis of the limited testing so far, a reduction in energy use as compared to a natural gas furnace has not been achieved. This document discusses these findings and presents opportunities for further improvement. Over the long term, CCHP systems have significant potential for savings on operational energy and cost when compared to traditional methods of heating, particularly in locations where natural gas is not available. [ABSTRACT FROM AUTHOR]