Waste Heat Dehumidification in CO2 Booster Supermarket

Carbon dioxide (CO2) being a low Global Warming Potential (GWP) refrigerant is becoming a popular choice as an efficient refrigerant in supermarket refrigeration systems, not only in moderate climates such as Northern Europe but also in the United States. Due to its low critical temperature (31.06°C), CO2 systems also offer potential for waste heat utilization. This paper, therefore, aims to uncover this potential for the US supermarket refrigeration industry through simulation. In this process, the whole building energy modeling tool, EnergyPlus, has been used to investigate the energy consumption of a supermarket utilizing packaged rooftop air conditioning units and a transcritical CO2 booster refrigeration system. The energy impact of humidity control within the supermarket, both on the HVAC and the refrigeration systems, is investigated. Also, a desiccant system incorporating waste heat for desiccant regeneration has been analyzed. Finally, the performance of the transcritical CO2 booster refrigeration system is compared with the baseline R404A multiplex direct expansion system using bin analysis in sixteen cities from eight climate zones of the United States

Isolated Sub-Dehumidification Strategies in Large Supermarkets and Grocery Stores

The objective of this project was to determine the potential energy savings associated with reducing the relative humidity in the vicinity of refrigerated display cases in supermarkets, as compared to the widely accepted current practice of maintaining a relatively higher and uniform humidity level throughout the entire supermarket. Existing and new strategies for maintaining lower relative humidity levels near the vicinity of refrigerated display cases were analyzed to determine their effectiveness and limits of application

Suitable low Global Warming Potential (GWP) refrigerants for two-speed Heat Pumps for residential applications based on simulated performance

The next generation of heat pumps (HPs), including those intended for cold climates must transition to low-global warming potential (GWP) refrigerants to mitigate climate change. HPs must be designed to alleviate the problems of excessive discharge temperatures, low suction pressure and high-pressure ratio at low ambient conditions and insufficient heating capacity relative to the rated heating capacity. In this paper we recognize those concerns. Low global warming potential (GWP) refrigerants are screened based on the shape of their temperature-entropy (T-S) saturation boundary. Simulations of the two-stage HP with low GWP refrigerants (R32, R454B, R466A, and R452B) to replace R-410A was accomplished using the DOE/ORNL Heat Pump Design Model. Systemic inefficiency was addressed by component-level exergy analysis to refine design options. HPs with low-GWP refrigerants address issues of reducing energy consumption, lowering carbon footprint, and enabling environmental sustainability

Isolated Sub-Dehumidification Strategies in Large Supermarkets and Grocery Stores

The objective of this project was to determine the potential energy savings associated with reducing the relative humidity in the vicinity of refrigerated display cases in supermarkets, as compared to the widely accepted current practice of maintaining a relatively higher and uniform humidity level throughout the entire supermarket. Existing and new strategies for maintaining lower relative humidity levels near the vicinity of refrigerated display cases were analyzed to determine their effectiveness and limits of application

Defrost Temperature Termination in Supermarket Refrigeration Systems

The objective of this project was to determine the potential energy savings associated with implementing demand defrost strategies to defrost supermarket refrigerated display case evaporators, as compared to the widely accepted current practice of controlling display case defrost cycles with a preset timer. The defrost heater energy use of several representative display case types was evaluated. In addition, demand defrost strategies for refrigerated display cases as well as those used in residential refrigerator/freezers were evaluated. Furthermore, it is anticipated that future work will include identifying a preferred defrost strategy, with input from Retail Energy Alliance members. Based on this strategy, a demand defrost system will be designed which is suitable for supermarket refrigerated display cases. Limited field testing of the preferred defrost strategy will be performed in a supermarket environment

Manufacturing & Testing of Air-to-Refrigerant Heat Exchangers Based on 0.8mm Diameter Tubes

Recent research has shown that moving towards small tubes with diameters less than 5 mm bring significant advantages in air-to-refrigerant heat exchangers. These advantages include compactness, high airside heat transfer coefficient, reduced refrigerant charge and reduced weight. Tubes with Outer Diameter of 0.8 mm were shown to provide very high heat transfer coefficient resulting in heat exchanger with a high degree of compactness. However, using such small tube diameter comes with manufacturing and field performance challenges. Manufacturing challenges include the management of many hundreds of small tubes, tubes geometrical requirements, developing a method to ensure a specific gap between the tubes at any given point is kept, maintaining the desired geometrical shape of the complete heat exchanger and, the biggest challenge, sealing the tube to header joints. Field challenges include areas such as fouling and water drainage. This paper presents the lessons learned from manufacturing and testing of air-to-refrigerant heat exchangers that use such 0.8 mm OD tubes. Three prototypes were manufactured, the first one is made of stainless steel (SSHX), the second one is made of copper (CuHX), and these two were designed to have the same pressure drop and heat transfer performance. The third one is a larger version of the second prototype (CuHX-10kW). These prototypes are fabricated using different manufacturing techniques and lessons learned are discussed. One of the observations was that the uncertainty in tube spacing due to manufacturing has a significant impact on the performance. This points to the need for robust optimization methods in design of such heat exchangers for which the manufacturing technologies are still being developed. Hydrostatic tests as well as performance tests in a closed loop wind tunnel were conducted. Test results of three heat exchangers using air and water are discussed. The energy balances were within ±5% and uncertainties in averaged capacity were within ±3% for the three prototypes.

Compressor Calorimeter Test of R-404A Alternatives ARM-31a, D2Y-65, L-40, and R32 + R-134a Mixture using a Scroll Compressor

As a contribution to the AHRI Low-GWP Alternative Refrigerants Evaluation Program (AREP), this study compares the performance of four lower-GWP alternative refrigerants, ARM-31a, D2Y-65, L-40, and R-32 + R-134a mixture, to that of refrigerant R-404A (baseline) in a scroll compressor designed for medium temperature refrigeration applications. These comparisons were carried out via compressor calorimeter tests performed on a compressor designed for refrigerant R-404A and having a nominal rated capacity of 23,500 Btu/hr. Tests were conducted over a suction dew point temperature range of -10 F to 35 F in 5 F increments and a discharge dew point temperature range of 70 F to 140 F in 10 F increments. All the tests were performed with 20 F superheat, 40 F superheat, and 65 F suction temperature. A liquid subcooling level of 10 F to 15 F was maintained for all the test conditions. However, the cooling capacities reported in this study are normalized for 0 F subcooling. The tests showed that the compressor energy efficiency ratio (EER) and cooling capacity with all four alternative refrigerants tested are higher at higher saturation suction and saturation discharge temperature and lower at lower saturation suction and saturation discharge temperature, compared to that of R-404A. Discharge temperatures of all the alternative refrigerants were higher than that of R-404A at all test conditions

Novel gas-driven fuel cell HVAC and dehumidification prototype

Performance of a novel gas-driven, electricity-producing heating, ventilation, and air conditioning (HVAC) system with no vapor compression and no hydrofluorocarbon (HFC) refrigerant shall be discussed in the paper. The prototype was evaluated at ORNL under a Small Business Voucher (SBV) Cooperative Research and Development (CRADA) program. The target market is commercial buildings in the United States. The goal is to mitigate or eliminate grid-power for building air conditioning, coincident peak demand and associated spinning reserves, aiding in flattening of the “duck curve”. The technical goal is to transform the common packaged rooftop unit into a cost-effective distributed energy resource, opening a new range of small applications and broad markets for micro-combined cycle cooling, heating, and power with integral thermal energy storage. The test results indicate the prototype would be competitive with natural gas distributed power plants with average electrical production ranging from 45% to 60% natural gas to electricity conversion efficiency. The technology has a Primary Energy Savings Potential of 4.4 Quads, higher than any other air conditioning and heating technology

Defrost Temperature Termination in Supermarket Refrigeration Systems

The objective of this project was to determine the potential energy savings associated with implementing demand defrost strategies to defrost supermarket refrigerated display case evaporators, as compared to the widely accepted current practice of controlling display case defrost cycles with a preset timer. The defrost heater energy use of several representative display case types was evaluated. In addition, demand defrost strategies for refrigerated display cases as well as those used in residential refrigerator/freezers were evaluated. Furthermore, it is anticipated that future work will include identifying a preferred defrost strategy, with input from Retail Energy Alliance members. Based on this strategy, a demand defrost system will be designed which is suitable for supermarket refrigerated display cases. Limited field testing of the preferred defrost strategy will be performed in a supermarket environment

Compressor Calorimeter Test of R-404A Alternatives ARM-31a, D2Y-65, L-40, and R32 + R-134a Mixture using a Scroll Compressor

As a contribution to the AHRI Low-GWP Alternative Refrigerants Evaluation Program (AREP), this study compares the performance of four lower-GWP alternative refrigerants, ARM-31a, D2Y-65, L-40, and R-32 + R-134a mixture, to that of refrigerant R-404A (baseline) in a scroll compressor designed for medium temperature refrigeration applications. These comparisons were carried out via compressor calorimeter tests performed on a compressor designed for refrigerant R-404A and having a nominal rated capacity of 23,500 Btu/hr. Tests were conducted over a suction dew point temperature range of -10 F to 35 F in 5 F increments and a discharge dew point temperature range of 70 F to 140 F in 10 F increments. All the tests were performed with 20 F superheat, 40 F superheat, and 65 F suction temperature. A liquid subcooling level of 10 F to 15 F was maintained for all the test conditions. However, the cooling capacities reported in this study are normalized for 0 F subcooling. The tests showed that the compressor energy efficiency ratio (EER) and cooling capacity with all four alternative refrigerants tested are higher at higher saturation suction and saturation discharge temperature and lower at lower saturation suction and saturation discharge temperature, compared to that of R-404A. Discharge temperatures of all the alternative refrigerants were higher than that of R-404A at all test conditions