Edward Allan Vineyard

Superinsulation in refrigerators and freezers

The results presented here were obtained during Phase 4 of the first CRADA, which had the specific objective of determining the lifetime of superinsulations when installed in simulated refrigerator doors. The second CRADA was established to evaluate and test design concepts proposed to significantly reduce energy consumption in a refrigerator-freezer that is representative of approximately 60% of the US market. The stated goal of this CRADA is to demonstrate advanced technologies which reduce, by 50%, the 1993 National Appliance Energy Conservation Act (NAECA) standard energy consumption for a 20 ft{sup 3} (570 L) top-mount, automatic-defrost, refrigerator-freezer. For a unit this size, the goal translates to an energy consumption of 1.003 kWh/d. The general objective of the research is to facilitate the introduction of efficient appliances by demonstrating design changes that can be effectively incorporated into new products. In previous work on this project, a Phase 1 prototype refrigerator-freezer achieved an energy consumption of 1.413 kWh/d [Vineyard, et al., 1995]. Following discussions with an advisory group comprised of all the major refrigerator-freezer manufacturers, several options were considered for the Phase 2 effort, one of which was cabinet heat load reductions.

Performance Evaluation of a 4.5 kW (1.3 Refrigeration Tons) Air-Cooled Lithium Bromide/Water Hot-Water-Fired Absorption Unit

During the summer months, air-conditioning (cooling) is the single largest use of electricity in both residential and commercial buildings with the major impact on peak electric demand. Improved air-conditioning technology has by far the greatest potential impact on the electric industry compared to any other technology that uses electricity. Thermally activated absorption air-conditioning (absorption chillers) can provide overall peak load reduction and electric grid relief for summer peak demand. This paper describes an innovative absorption technology based on integrated rotating heat exchangers to enhance heat and mass transfer resulting in a potential reduction of size, cost, and weight of the “next generation” absorption units. This absorption chiller (RAC) is a 4.5 kW (1.3 refrigeration tons or RT) air-cooled lithium bromide (LiBr)/water unit powered by hot water generated using the solar energy and/or waste heat. Typically LiBr/water absorption chillers are water-cooled units which use a cooling tower to reject heat. Cooling towers require a large amount of space and increase start-up and maintenance costs. However, RAC is an air-cooled absorption chiller which requires no cooling tower. The purpose of this evaluation is to verify RAC performance by comparing the Coefficient of Performance (COP or ratio of cooling capacity to thermal energy input) and the cooling capacity results with those of the manufacturer. The performance of the RAC was tested at Oak Ridge National Laboratory (ORNL) in a controlled environment at various hot and chilled water flow rates, air handler flow rates, and ambient temperatures. Temperature probes, mass flow meters, rotational speed measuring device, pressure transducers, and a web camera mounted inside the unit were used to monitor the RAC via a web control-based data acquisition system using Automated Logic Controller (ALC). Results showed a COP and cooling capacity of approximately 0.58 and 3.7 kW respectively at 35°C (95°F) design condition for ambient temperature with 40°C (104°F) cooling water temperature. This is in close agreement with the manufacturer data of 0.60 for COP and 3.9 kW for cooling capacity. Future work will use these performance results to evaluate the potential benefits of rotating heat exchangers in making the “next-generation” absorption chillers more compact and cost effective without any significant degradation in the performance. Future studies will also evaluate the feasibility of using rotating heat exchangers in other applications.

Thermofluid Analysis of the Magnetocaloric Refrigeration

While there have been extensive studies on thermofluid characteristics of different magnetocaloric refrigeration systems, a conclusive optimization study using non-dimensional parameters which can be applied to a generic system has not been reported yet. In this study, a numerical model has been developed for optimization of active magnetic refrigerator (AMR). This model is computationally efficient and robust, making it appropriate for running the thousands of simulations required for parametric study and optimization. The governing equations have been non-dimensionalized and numerically solved using finite difference method. A parametric study on a wide range of non-dimensional numbers has been performed. While the goal of AMR systems is to improve the performance of competitive parameters including COP, cooling capacity and temperature span, new parameters called “AMR performance index-1” have been introduced in order to perform multi objective optimization and simultaneously exploit all these parameters. The multi-objective optimization is carried out for a wide range of the non-dimensional parameters. The results of this study will provide general guidelines for designing high performance AMR systems.Copyright

Design and Development of a Gas-Engine-Driven Heat Pump

Improved air-conditioning technology has the greatest potential impact on the electric industry compared to any other technology that uses electricity particularly during summer peak electric demand. Gas engine-driven units can provide overall peak load reduction and electric grid relief for summer peak demand. Peak-load conditions can lead to high electricity prices, power quality problems, and grid system inefficiencies, and even failures. Improved air-conditioning technology thus has the greatest potential impact on the electric grid compared to other technologies that use electricity. Thermally-activated systems, such as natural gas engine-driven heat pumps, can provide overall peak load reduction and electric grid relief for summer peak demand. This paper describes the development of an innovative 10 refrigeration ton (RT) natural gas engine-driven heat pump (GHP) for commercial application. The unit was tested at various Air Conditioning and Refrigeration Institute (ARI) heating and cooling conditions in a psychrometric chamber at Oak Ridge National Laboratory. The gas COP at 47°F rating condition exceeded the goal of 1.6 at both high and intermediate engine speeds. The gas COP in cooling mode also exceeded the goal of 1.2 at 95°F rating condition. In this study, principles of operation, unit performance and benefits are discussed.Copyright

Frost Growth CFD Model of an Integrated Active Desiccant Rooftop Unit

A frost growth model is incorporated into a Computational Fluid Dynamics (CFD) simulation of a heat pump by means of a user-defined function in a commercial CFD code. The transient model is applied to the outdoor section of an Integrated Active Desiccant Rooftop (IADR) unit in heating mode. IADR is a hybrid vapor compression and active desiccant unit capable of handling 100% outdoor air (dedicated outdoor air system) or as a total conditioning system, handling both outdoor air and space cooling or heating loads. The predicted increase in flow resistance and loss in heat transfer capacity due to frost build-up are compared to experimental pressure drop readings and thermal imaging. The purpose of this work is to develop a CFD model that is capable of predicting frost growth, a potentially valuable tool in evaluating the effectiveness of defrost-on-demand cycles.

Baseline, Exhaust-Fired, and Combined Operation of Desiccant Dehumidification Unit

The performance of a commercially available direct-fired desiccant dehumidification unit (DFDD) has been studied as part of a microturbine generator (MTG)-based Integrated Energy System (IES) at Oak Ridge National Laboratory (ORNL). The IES includes a second-generation air-to-water heat recovery unit (HRU) for the MTG. The focus of these tests was to study the performance of a DFDD in baseline (direct-fired with its natural gas burner) mode and to compare it with a DFDD performance in the exhaust-fired and combined modes as part of the ORNL IES, when waste heat received from the MTG was used for desiccant regeneration. The baseline tests were performed with regeneration air heated by a natural gas burner (direct-fired). The testing of the waste-heat, or exhaust-fired DFDD as part of IES involved using the exhaust gas from the HRU for regeneration air in the DFDD after hot water production in the HRU. Hot water from the HRU was used to produce chilled water in an indirect-fired (water fired) absorption chiller. The combined DFDD was the combination of natural gas burner and exhaust-fired testing. The study investigated the impact of varying the process and regeneration conditions on the latent capacity (LC) and latent coefficient of performance (LCOP) of the DFDD, as well as overall IES efficiency. The performance tests show that LC increases with increasing dew point (humidity ratio) of the process air or the increased amount of waste heat associated with increased MTG power output. In addition, baseline LC was found to be three times higher than the LC in the exhaust-fired mode of operation. LCOP in baseline operation is also almost three times higher than that obtained in the exhaust-fired mode (55.4% compared to 19%). But, at the same time, addition of the DFDD to the IES with the MTG at maximum power output increases the overall IES efficiency by 4–5%. Results of the combined tests performed at a reduced MTG power output of 15 kW (51,182 Btu/h) and their comparison with the baseline and exhaust-fired tests show that activation of the DFDD gas burner during exhaust-fired tests increases the LC over the baseline value from 91,514.9 Btu/h (25.8 kW) to 101,835.8 Btu/h (29.8 kW). The LCOP during the combined mode is less than the “baseline” LCOP, because in addition to gas input, the low-grade MTG/HRU exhaust heat input to the DFDD are also being considered. The overall IES efficiency during the combined mode is approximately 8% higher than without the DFDD integrated into the IES.© 2004 ASME

System modeling and building energy simulations of gas engine driven heat pump

To improve the system performance of a gas engine driven heat pump system, an analytical modeling and experimental study has been made by using a desiccant system in cooling operation (particularly in high-humidity operations) and suction line waste heat recovery to augment heating capacity and efficiency. The overall performance of a gas engine driven heat pump system has been simulated with a detailed vapor compression heat pump system design model. The modeling includes (1) a gas engine driven heat pump cycle without any performance improvements (suction liquid heat exchange and heat recovery) as a baseline (both in cooling and heating mode), (2) a gas engine driven heat pump cycle in cooling mode with a desiccant system regenerated by waste heat from the engine incorporated, and (3) a gas engine driven heat pump cycle in heating mode with heat recovery (recovered heat from engine). According to the system modeling results, by using the desiccant system, the sensible heat ratio can be lowered to 40%. The waste heat of the gas engine can boost the space heating efficiency by 25% at rated operating conditions. In addtion, using EnergyPlus, building energy simulations have been conducted to assess annual energy consumptions of the gas engine driven heat pump in 16 U.S. cities, and the performances are compared to a baseline unit that has a electrically driven air conditioner with the seasonal coefficient of performance of 4.1 for space cooling and a gas furnace with 90% fuel efficiency for space heating.

Development of 20 integrated energy efficiency ratio rooftop units—system modeling and building energy simulations

Based on a detailed steady-state system and component modeling, a rooftop unit system design was developed that is can achieve an integrated energy efficiency rating higher than 20. Fin-and-tube and microchannel heat exchangers were modeled using a segment-to-segment approach, and an AHRI 10-coefficient compressor map used to simulate compressor performance. The system modeling is based on a component-based modeling approach, which facilitates flexible simulation of complicated system configurations. Starting with a baseline system having integrated energy efficiency rating of 16.6, numerous technical options were extensively investigated, i.e., varying compressor sizes, heat exchanger fin densities, fin-and-tube or microchannel heat exchanger, suction line heat exchanger, desiccant wheel, tandem compressor (TD), variable-speed compressor (VS), and condenser evaporative pre-cooling; an innovative system configuration was developed by combining a tandem compression system with a variable-speed compression system. The combined system can achieve a high integrated energy efficiency ratio as well as process the outdoor ventilation air over an extensive range. The design concept for a 20-ton (70.4-kW) unit, as well as a 10-ton (35.2-kW) unit was successfully evaluated. All selected components are readily accessible on the market, and performance predictions were validated against existing rooftop unit products at the rating condition. This article illustrates a potentially cost-effective high integrated energy efficiency ratio rooftop unit design. In addtion, extensive building energy simulations were conducted using EnergyPlus to predict seasonal energy saving potentials and peak power reductions using the high integrated energy efficiency ratio rooftop unit in 16 U.S. cities in comparison to a rooftop unit with a minimum efficiency.

Review from ASHRAE Symposium, Nashville, June 1987 energy testing of refrigerators and freezers

Abstract The following papers are reviewed: 1. 1. Field and laboratory test plan for improving refrigerator/freezer energy testing procedures: W. E. Stewart Jr, University of Missouri. 2. 2. Energy use test procedures for appliances: a case study of Japanese refrigerators: A.K. Meier, Lawrence Berkeley Laboratory. 3. 3. Effects of ambient temperature and control settings on thermal performance and energy consumption of a household refrigerator-freezer: M. S. Alissi, K. J. Farley, R. J. Schoenhals and S. Ramadhyani, Purdue University.