Kyle Gluesenkamp | University of Maryland, College Park (original) (raw)

Papers by Kyle Gluesenkamp

During the drying phase of a dishwasher, water evaporation and condensation phenomena take place.... more During the drying phase of a dishwasher, water evaporation and condensation phenomena take place. Some wet surfaces inside the dishwasher are above the local air dewpoint and will experience evaporation, while other surfaces are below the local air dewpoint and will experience condensation. In this study, the evaporation mass transfer resistance of a standard load used in a household dishwasher was experimentally measured. The standardized load measurements were taken in situ during a regular drying phase after the ordinary washing was complete. To determine the mass transfer resistance of condensation, a tub wall sample was cut from the interior of a commercially available dishwasher. The wall samples were tested ex-situ in a benchtop psychrometric chamber to determine the condensation heat and mass transfer coefficient. The wall samples were locally cooled using a thermoelectric module. The experimental results were compared to those from a heat and mass transfer resistance correl...

Energies

This work investigates the energy efficiency and carbon reduction potential of self-powered resid... more This work investigates the energy efficiency and carbon reduction potential of self-powered residential building heating equipment using a thermodynamic modeling approach. An integrated thermophotovoltaic power module and residential scale furnace system (40,000 Btu/h) were modeled and studied in detail to assess the influence of different design configurations on primary energy efficiency. Operational characteristics such as total power generation, electrical efficiency, and heat recovery were examined in a self-powered system configuration. A sensitivity analysis was conducted to determine the influence of the electric grid’s carbon dioxide footprint (carbon intensity) and the cost of electricity on the environmental, as well as the economic, benefit associated with the self-powered configuration. Compared with a traditional furnace powered by an electric grid at a carbon intensity of 0.5 kg CO2eq/kWhEL, the self-powered furnace was shown to decrease the annual carbon dioxide emis...

Residential dishwashers typically consume domestic hot water, heat it further with electric resis... more Residential dishwashers typically consume domestic hot water, heat it further with electric resistance heating elements, and drain the soiled heated water before each subsequent water fill. During the final rinse, the water is heated to a temperature of approximately 54.5–57.2°C (130–135°F) to heat the load and promote passive drying after the final drain event. In this work, the energy consumption, water consumption, and drying performance of a conventional dishwasher were measured under test conditions similar to U.S. energy efficiency test standards but with an unsoiled load. These measurements were considered baseline performance metrics. The dishwasher was then experimentally modified to recover heat from the drain water utilizing thermoelectric (TE) heat pump modules and a thermal storage component. The TEs were also used during the drying phase to improve the drying of the load. The novel dishwasher was operated in the laboratory under the same conditions as the baseline unit...

Water heating and dehumidification are major energy consumers in buildings. The novel semi-open a... more Water heating and dehumidification are major energy consumers in buildings. The novel semi-open absorption heat pump design utilizes the heat of absorption from the dehumidification of space for water heating. The architecture of the system consists of (1) a plate and frame membrane-based absorber, (2) a membrane-based desorber and condenser unit, (3) heat exchangers, (4) ionic liquid, and (5) a 189.3 L (50-gal) water tank. The membrane-based absorber enables heat and mass transfer between three streams: moist air, ionic liquid, and the heat transfer fluid. The heat of vapor absorption elevates the ionic liquid temperature and, in turn, heats the heat transfer fluid. In the desorber unit, the diluted ionic liquid after absorption is heated to above 150℃ and reconcentrated. The heat of condensation from the condensation of water vapor in the condenser is utilized for water heating. The dehumidification performance of the absorber directly affects the COP and heating capacity of the system. Understanding the absorber's performance at various operating conditions would allow one to optimize and design a better performing absorber. In this study, the absorber's water heating capacity and performance are evaluated for varying operating conditions. A maximum COP of 1.25 while water heating water from 18.6 to 60.2°C was achieved at a capacity of 1,010 Watts and an airflow rate of 47.19 L/s. Increasing the desorber oil mass flowrate had negligible effect on the COP. The average mass transfer resistance of the porous membrane absorber was 1.164 *10 7 m/s.

Thermal energy storage (TES) is an increasingly popular tool to level out the daily electrical de... more Thermal energy storage (TES) is an increasingly popular tool to level out the daily electrical demand and add stability to the electrical grid as more intermittent renewable energy sources are installed. TES systems can locally decouple high thermal loads from the operation of a heat pump or reduce the electrical energy demand of the heat pump by providing a more favorable temperature gradient. In addition, many policy makers and utility providers have introduced time-of-use (TOU) rate schedules for residential customers to better reflect the price of electricity generation and demand for specific times. TOU rate schedules price grid-provided electricity differently throughout the day depending on the region's climate, time of year, and electrical production portfolio. Large differences between on-peak and off-peak electrical prices may create an economic advantage for a residential customer to install a TES system. In this work, the economic and energy savings are calculated for a modeled 223 square foot residential building with water/ice-based TES using a TOU rate structure. The weather data is from Fresno County, CA, ASHRAE climate zone 3B, and a representative residential TOU utility rate structure from a utility provider in California was used. The simulation was carried out for cooling only during a week of extreme hot summer daytime temperature and the results showed that total energy consumption could be reduced by 14.5% with an 87.5% reduction in on-peak energy usage when the TES is installed. The cost of operating this system for space cooling was reduced by nearly 20% using the sample utility rate plan.

Conventional fuel-fired heating devices such as furnaces, boilers, and water heaters have fuel ef... more Conventional fuel-fired heating devices such as furnaces, boilers, and water heaters have fuel efficiency less than 100% on the basis of higher heating value. They also require electricity from the electric grid to power parasitic loads such as blowers, pumps, fans, and ignitors. The primary energy efficiency of the device accounts for both fuel used on-site and primary energy used off-site to produce electric power used by the device. This work compares conventional fuel-fired heating devices to two types of self-powered devices. A self-powered device (SPD) integrates a power cycle onboard to eliminate consumption of grid electricity. We assume that all heat rejected by the onboard power cycle is added to the process fluid, so that, compared with a conventional device, the same amount of heat is provided to the process fluid and the same amount of fuel is consumed, but grid electricity consumption is eliminated. The first SPD type is the basic one: exactly the electricity required is generated. The second type considered is the SPD with heat pump (SPD-HP), in which the power cycle generates more electricity than needed for parasitic loads, and the excess electricity is used to power a heat pump. The heat pump extracts additional heat from the ambient to boost efficiency. Both SPD and SPD-HP self-consume all the generated electricity, in contrast to combined heat and power (CHP) systems that export electricity. In this work, equations are derived to express the efficiency of three classes of heating devices: conventional (consuming grid electricity), selfpowered (consuming no grid electricity), and self-powered with heat pump. The efficiency of each is derived as a function of up to six factors: (1) the fraction of combustion heat captured, (2) the rate of parasitic power consumption, (3) the fraction of electric energy dissipated as useful heat, (4) the power cycle conversion efficiency, (5) the grid efficiency, when applicable, and (6) the heat pump COP, when applicable. Scenarios are identified in which it is possible to achieve efficiency greater than 100% on a higher heating value basis. Plausible configurations using existing technology options are outlined.

The recently introduced hydrofluoroolefin (HFO) refrigerants, including R1234yf and R1234ze(E), h... more The recently introduced hydrofluoroolefin (HFO) refrigerants, including R1234yf and R1234ze(E), have significantly lower global warming potentials (GWPs) than traditional hydrofluorocarbon (HFC) refrigerants like R410A. However, prior tests show that direct drop-in of pure R1234yf or R1234ze(E) into equipment designed for R410A results in a decrease in heat exchanger capacity and the system coefficient of performance. The primary reason is the lower in-tube heat transfer performance of R1234yf and R1234ze(E) compared with that of R410A. To address this issue, previous studies have mixed the mildly flammable HFC R32 with HFOs to improve system performance, with HFC R125 also added to suppress flammability. Previous studies selected compositions based on simple cycle analyses and did not consider modifications of the heat exchanger circuitry configuration to adapt to the new refrigerants. This study presents a novel multi-objective optimization approach to design a refrigerant composition that maximizes energy efficiency within flammability and GWP limits. The approach in this work simultaneously optimizes mixture composition and heat exchanger circuitry configuration. A case study on a rooftop unit indicates that, compared with mixture-only optimization, simultaneous optimization of mixture and heat exchanger circuitry yields a 5.9% improvement in cycle efficiency and a 48.6% reduction in refrigerant flammability with a GWP of 268. Circuitry optimization using refrigerants with different temperature glides shows that the larger the temperature glide is, the larger EER improvement is obtained. The results show that zeotropic blends with a large temperature glide are more sensitive to the refrigerant circuitry than pure refrigerants and may suffer significant performance degradation with subpar heat exchanger circuitry design. The proposed optimization approach is generally applicable to mixtures with any number of components. Using this approach to design a HVAC system can yield higher system efficiency within flammability and GWP constraints.

Air dehumidification is essential since excess moisture in the buildings causes discomfort to the... more Air dehumidification is essential since excess moisture in the buildings causes discomfort to the occupants, encourages the production of air pathogens such as mold or mildew, and causes corrosion and rotting that degrade building materials. Existing moisture removal processes are mainly focused on condensation and desiccant (liquid or solid) techniques with direct contact between air and desiccant. However, these methods are energy-intensive, or desiccant might be lost or cause corrosion in the process. The main objective of this study is to investigate an ionic liquid-based liquid desiccant absorber based on a membrane fiber bundle. A novel membrane contactor system was fabricated with a bundle of 10,000 polypropylene fibers. Each fiber has 0.3 micron outer diameter, with ionic liquid flowing inside, and air flowing outside. The fibers provide a high contact area among phases: 1.4 m 2 contact surface area in a 0.00015 m 3 volume (9,333 m 2 /m 3 ratio of surface area to volume). The ionic liquid as a sorbent has selectivity for water vapor (i.e., the ionic liquid has higher affinity for water vapor) prevents the loss of solvent in the operation due to negligible volatility, provides fast diffusion due to low viscosity compared to common ionic liquids, and has high affinity and solubility in water. The dehumidification capacity of the prototype membrane system was experimentally investigated using six modules with 10,000 fibers each. The experimental results show that the ionic-liquid based membrane system can effectively remove excess moisture from the air. The novel fiber bundle dehumidification system has a total system volume of 0.00798 m 3 (7.98 L) and active heat and mass transfer surface area of 8.4 m 2. It achieved an average dehumidification of 320 ± 25 W with a volumetric air flowrate of 3.1 m 3 /min (108 ft 3 /min).

Scientific Data, 2022

Most COVID-19 vaccines require temperature control for transportation and storage. Two types of v... more Most COVID-19 vaccines require temperature control for transportation and storage. Two types of vaccine have been developed by manufacturers (Pfizer and Moderna). Both vaccines are based on mRNA and lipid nanoparticles requiring low temperature storage. The Pfizer vaccine requires ultra-low temperature storage (−80 °C to −60 °C), while the Moderna vaccine requires −30 °C storage. However, the last stage of distribution is quite challenging, especially for rural or suburban areas, where local towns, pharmacy chains and hospitals may not have the infrastructure required to store the vaccine at the required temperature. In addition, there is limited data available to address ancillary challenges of the distribution framework for both transportation and storage stages, including safety concerns due to human exposure to large amounts of CO2 from dry-ice sublimation, issues due to the pressure increase caused by dry-ice sublimation, and the potential issue caused by non-uniform cryogenic ...

Air conditioning (A/C) systems driven by renewable energy have been studied extensively during th... more Air conditioning (A/C) systems driven by renewable energy have been studied extensively during the past decade as promising alternatives to conventional electricity-driven vapor compression A/C to alleviate stress on the grid as well as reduce CO2 emissions. Among the possible renewable energy sources to drive A/C systems, low-temperature geothermal heat (<150°C/300°F) is currently underutilized despite its abundance in the United States and the advantage of steady output. A major barrier to wider utilization is the typically long distances between geothermal sources and potential end uses. In order to overcome this barrier, an innovative two-step geothermal absorption (TSGA) system was studied. With this system, low-temperature geothermal energy is stored and transported at ambient temperature with an energy density of 349 kJ of cooling energy per kg of shipped LiBr/H2O solution, which is about five times higher than directly transporting geothermal fluid itself for space heatin...

A quasi-steady state, heat and mass transfer lumped-capacitance model was developed to predict th... more A quasi-steady state, heat and mass transfer lumped-capacitance model was developed to predict the energy consumption and drying performance of domestic dishwashers. A numerical finite element solution was applied, assuming that the following components could each be treated as a lumped thermal capacitance: dish load, tub, wash water, and air in tub. The model was used to predict the energy consumption savings of heating water using a thermoelectric heat pump that extracts heat from a thermal storage medium, and the drying performance of circulating tub air through the cold and then hot side of TE modules.

Dehumidification is a major contributor to the energy consumed by residential and commercial buil... more Dehumidification is a major contributor to the energy consumed by residential and commercial buildings. Emerging separate sensible and latent cooling (SSLC) systems can provide energy-efficient solutions to control moisture and temperature independently. In light of emerging research, a strong need has emerged to categorize and to characterize the performance of SSLC systems. The current study provides categorization and a critical review of major developments, including components, systems, processes and working media pertaining to SSLC systems. The review highlights the key features which can be used for classification, performance evaluation and steady-state capacity of SSLC systems. Finally, the study provides guidelines for further research and important performance matrixes for future developments.

To meet the growing energy consumption and mitigate climate concerns, novel energy efficient tech... more To meet the growing energy consumption and mitigate climate concerns, novel energy efficient technologies need to be developed. Water heating, dehumidification and space cooling form a significant percentage (~24%) of a typical U.S. household energy consumption and a total of 2.6 quad of primary energy consumption. In this paper, we present a novel system for combined water heating, dehumidification, and space cooling. The three processes can be achieved by one device using a novel semi-open absorption based system combined with evaporative cooling. The absorption based system absorbs water vapor from its ambient. The latent heat of absorption, released into the absorbent, is transferred into the process water that cools the absorbent. The water absorbed is later released in the desorber through heating, and the water vapor generated in the desorber is condensed and its heat of phase change is transferred to the process water in the condenser. The condensed water vapor can either be...

Clothes dryers based on thermoelectric (TE) heat pumps have the potential to save significant ene... more Clothes dryers based on thermoelectric (TE) heat pumps have the potential to save significant energy compared with the conventional electric resistance technology that is widespread today, without using any refrigerant fluid. In this work, guided by a validated system model, design and control improvements were implemented on an experimental prototype to optimize the dryer performance (duration to dry a load, and energy consumed per unit cloth mass). Starting from a fixed TE area, the physical design variables of interest were (1) the use of vented or ventless configuration, (2) the heat sink geometry, (3) the selection of blower and (4) the selection of motor used to drive drum rotation. The control variables of interest were (5) the average electrical current supplied to each bank of TEs and (6) the current profile for each bank during the drying time. By optimizing each of these choices in the model and applying the resulting design choices on the prototype, the experimentally me...

Past work has shown that thermoelectric clothes dryers are capable of much higher efficiency than... more Past work has shown that thermoelectric clothes dryers are capable of much higher efficiency than electric resistance clothes dryers. In an effort to improve performance and reduce material utilization, this work explores a new secondary loop system configuration. In this configuration, heat is transferred between air and the thermoelectric heat pumps via two water loops and two water-to-air fin-tube type heat exchangers. In this work, performance is investigated and analyzed using experimental data.

A heat pump clothes dryer (HPCD) uses a vapor compression system to dry clothes. The condenser he... more A heat pump clothes dryer (HPCD) uses a vapor compression system to dry clothes. The condenser heats air, which passes through the drum to evaporate moisture out of the clothes, and the evaporator condenses water out of the air stream. As a result, the HPCD can achieve 50% energy savings compared to a conventional electric resistance dryer. In this work we developed a physics-based, quasi-steady-state HPCD system model with detailed heat exchanger and compressor models. The system model can simulate the inherently transient HPCD drying process, to size components, and to reveal trends in key variables (e.g. compressor discharge temperature, power consumption, required drying time, etc.) The system model was calibrated using experimental data from a prototype HPCD. Air leakages, in and out, along the closed air circulation path of HPCD cause varied effects on the performance. Understanding the location, magnitude, and direction of air leakage of the heat pump clothes dryer is critica...

Part of: Thermally driven heat pumps for heating and cooling. – Ed.: Annett Kuhn – Berlin: Univer... more Part of: Thermally driven heat pumps for heating and cooling. – Ed.: Annett Kuhn – Berlin: Universitatsverlag der TU Berlin, 2013 ISBN 978-3-7983-2686-6 (print) ISBN 978-3-7983-2596-8 (online) urn:nbn:de:kobv:83-opus4-39458 [http://nbn-resolving.de/urn:nbn:de:kobv:83-opus4-39458]

Phase change materials (PCMs) with desirable phase change temperatures can be used to provide a c... more Phase change materials (PCMs) with desirable phase change temperatures can be used to provide a constant temperature thermal source or sink for diverse applications. As such, incorporating PCMs into building materials, equipment, or appliances can shift and/or reduce the energy load. The motivation of this work is to identify low-cost inorganic salt hydrate PCMs that can complement current building systems and designs, and compare them with common paraffins. In this work, we analyzed inorganic salt hydrates with phase change temperatures in the range of 5-60°C, to target both space heating and cooling applications. The properties of the salt hydrates were compared with paraffins over the same temperature range. The results showed that PCMs with a melting temperature above 20°C, salt hydrates have advantages over paraffins including higher thermal energy density (45-120 kWh/m for salt hydrates; 45-60 kWh/m for paraffins) and generally lower material energy cost (1-20 $/kWh for salt h...

A heat pump clothes dryer (HPCD) is an innovative appliance that uses a vapor compression system ... more A heat pump clothes dryer (HPCD) is an innovative appliance that uses a vapor compression system to dry clothes. Air circulates in a closed loop through the drum, so no vent is required. The condenser heats air to evaporate moisture out of the clothes, and the evaporator condenses water out of the air stream. As a result, the HPCD can achieve 50% energy savings compared to a conventional electric resistance dryer. We developed a physics-based, quasi-steady-state HPCD system model with detailed heat exchanger and compressor models. In a novel approach, we applied a heat and mass transfer effectiveness model to simulate the drying process of the clothes load in the drum. The system model is able to simulate the inherently transient HPCD drying process, to size components, and to reveal trends in key variables (e.g. compressor discharge temperature, power consumption, required drying time, etc.) The system model was calibrated using experimental data on a prototype HPCD. In the paper, ...

Space heating is a major contributor to building energy consumption especially in cold climates. ... more Space heating is a major contributor to building energy consumption especially in cold climates. Conventional gasfired furnaces are approaching thermodynamic efficiency limits, while electric heat pumps performance declines drastically at low ambient temperature. Chemisorption heat pump (CSHP) systems could be a better solution to space heating for cold climate due to their sustained capacity and efficiency at large temperature lifts. The performance of CSHP primarily depends on the working pair and cycle configuration. Most existing comparative studies of chemisorption systems in the published literature focus on refrigeration, but not many in heating applications. The few existing studies of chemisorption heat pump for heating involved too limited cycles and working pairs to represent the most promising performance of the CSHP. The goal of this study is to fill the gap through extensive performance comparison of CSHP using various salts and cycle configurations to discover the pot...

During the drying phase of a dishwasher, water evaporation and condensation phenomena take place.... more During the drying phase of a dishwasher, water evaporation and condensation phenomena take place. Some wet surfaces inside the dishwasher are above the local air dewpoint and will experience evaporation, while other surfaces are below the local air dewpoint and will experience condensation. In this study, the evaporation mass transfer resistance of a standard load used in a household dishwasher was experimentally measured. The standardized load measurements were taken in situ during a regular drying phase after the ordinary washing was complete. To determine the mass transfer resistance of condensation, a tub wall sample was cut from the interior of a commercially available dishwasher. The wall samples were tested ex-situ in a benchtop psychrometric chamber to determine the condensation heat and mass transfer coefficient. The wall samples were locally cooled using a thermoelectric module. The experimental results were compared to those from a heat and mass transfer resistance correl...

Energies

This work investigates the energy efficiency and carbon reduction potential of self-powered resid... more This work investigates the energy efficiency and carbon reduction potential of self-powered residential building heating equipment using a thermodynamic modeling approach. An integrated thermophotovoltaic power module and residential scale furnace system (40,000 Btu/h) were modeled and studied in detail to assess the influence of different design configurations on primary energy efficiency. Operational characteristics such as total power generation, electrical efficiency, and heat recovery were examined in a self-powered system configuration. A sensitivity analysis was conducted to determine the influence of the electric grid’s carbon dioxide footprint (carbon intensity) and the cost of electricity on the environmental, as well as the economic, benefit associated with the self-powered configuration. Compared with a traditional furnace powered by an electric grid at a carbon intensity of 0.5 kg CO2eq/kWhEL, the self-powered furnace was shown to decrease the annual carbon dioxide emis...

Residential dishwashers typically consume domestic hot water, heat it further with electric resis... more Residential dishwashers typically consume domestic hot water, heat it further with electric resistance heating elements, and drain the soiled heated water before each subsequent water fill. During the final rinse, the water is heated to a temperature of approximately 54.5–57.2°C (130–135°F) to heat the load and promote passive drying after the final drain event. In this work, the energy consumption, water consumption, and drying performance of a conventional dishwasher were measured under test conditions similar to U.S. energy efficiency test standards but with an unsoiled load. These measurements were considered baseline performance metrics. The dishwasher was then experimentally modified to recover heat from the drain water utilizing thermoelectric (TE) heat pump modules and a thermal storage component. The TEs were also used during the drying phase to improve the drying of the load. The novel dishwasher was operated in the laboratory under the same conditions as the baseline unit...

Water heating and dehumidification are major energy consumers in buildings. The novel semi-open a... more Water heating and dehumidification are major energy consumers in buildings. The novel semi-open absorption heat pump design utilizes the heat of absorption from the dehumidification of space for water heating. The architecture of the system consists of (1) a plate and frame membrane-based absorber, (2) a membrane-based desorber and condenser unit, (3) heat exchangers, (4) ionic liquid, and (5) a 189.3 L (50-gal) water tank. The membrane-based absorber enables heat and mass transfer between three streams: moist air, ionic liquid, and the heat transfer fluid. The heat of vapor absorption elevates the ionic liquid temperature and, in turn, heats the heat transfer fluid. In the desorber unit, the diluted ionic liquid after absorption is heated to above 150℃ and reconcentrated. The heat of condensation from the condensation of water vapor in the condenser is utilized for water heating. The dehumidification performance of the absorber directly affects the COP and heating capacity of the system. Understanding the absorber's performance at various operating conditions would allow one to optimize and design a better performing absorber. In this study, the absorber's water heating capacity and performance are evaluated for varying operating conditions. A maximum COP of 1.25 while water heating water from 18.6 to 60.2°C was achieved at a capacity of 1,010 Watts and an airflow rate of 47.19 L/s. Increasing the desorber oil mass flowrate had negligible effect on the COP. The average mass transfer resistance of the porous membrane absorber was 1.164 *10 7 m/s.

Thermal energy storage (TES) is an increasingly popular tool to level out the daily electrical de... more Thermal energy storage (TES) is an increasingly popular tool to level out the daily electrical demand and add stability to the electrical grid as more intermittent renewable energy sources are installed. TES systems can locally decouple high thermal loads from the operation of a heat pump or reduce the electrical energy demand of the heat pump by providing a more favorable temperature gradient. In addition, many policy makers and utility providers have introduced time-of-use (TOU) rate schedules for residential customers to better reflect the price of electricity generation and demand for specific times. TOU rate schedules price grid-provided electricity differently throughout the day depending on the region's climate, time of year, and electrical production portfolio. Large differences between on-peak and off-peak electrical prices may create an economic advantage for a residential customer to install a TES system. In this work, the economic and energy savings are calculated for a modeled 223 square foot residential building with water/ice-based TES using a TOU rate structure. The weather data is from Fresno County, CA, ASHRAE climate zone 3B, and a representative residential TOU utility rate structure from a utility provider in California was used. The simulation was carried out for cooling only during a week of extreme hot summer daytime temperature and the results showed that total energy consumption could be reduced by 14.5% with an 87.5% reduction in on-peak energy usage when the TES is installed. The cost of operating this system for space cooling was reduced by nearly 20% using the sample utility rate plan.

Conventional fuel-fired heating devices such as furnaces, boilers, and water heaters have fuel ef... more Conventional fuel-fired heating devices such as furnaces, boilers, and water heaters have fuel efficiency less than 100% on the basis of higher heating value. They also require electricity from the electric grid to power parasitic loads such as blowers, pumps, fans, and ignitors. The primary energy efficiency of the device accounts for both fuel used on-site and primary energy used off-site to produce electric power used by the device. This work compares conventional fuel-fired heating devices to two types of self-powered devices. A self-powered device (SPD) integrates a power cycle onboard to eliminate consumption of grid electricity. We assume that all heat rejected by the onboard power cycle is added to the process fluid, so that, compared with a conventional device, the same amount of heat is provided to the process fluid and the same amount of fuel is consumed, but grid electricity consumption is eliminated. The first SPD type is the basic one: exactly the electricity required is generated. The second type considered is the SPD with heat pump (SPD-HP), in which the power cycle generates more electricity than needed for parasitic loads, and the excess electricity is used to power a heat pump. The heat pump extracts additional heat from the ambient to boost efficiency. Both SPD and SPD-HP self-consume all the generated electricity, in contrast to combined heat and power (CHP) systems that export electricity. In this work, equations are derived to express the efficiency of three classes of heating devices: conventional (consuming grid electricity), selfpowered (consuming no grid electricity), and self-powered with heat pump. The efficiency of each is derived as a function of up to six factors: (1) the fraction of combustion heat captured, (2) the rate of parasitic power consumption, (3) the fraction of electric energy dissipated as useful heat, (4) the power cycle conversion efficiency, (5) the grid efficiency, when applicable, and (6) the heat pump COP, when applicable. Scenarios are identified in which it is possible to achieve efficiency greater than 100% on a higher heating value basis. Plausible configurations using existing technology options are outlined.

The recently introduced hydrofluoroolefin (HFO) refrigerants, including R1234yf and R1234ze(E), h... more The recently introduced hydrofluoroolefin (HFO) refrigerants, including R1234yf and R1234ze(E), have significantly lower global warming potentials (GWPs) than traditional hydrofluorocarbon (HFC) refrigerants like R410A. However, prior tests show that direct drop-in of pure R1234yf or R1234ze(E) into equipment designed for R410A results in a decrease in heat exchanger capacity and the system coefficient of performance. The primary reason is the lower in-tube heat transfer performance of R1234yf and R1234ze(E) compared with that of R410A. To address this issue, previous studies have mixed the mildly flammable HFC R32 with HFOs to improve system performance, with HFC R125 also added to suppress flammability. Previous studies selected compositions based on simple cycle analyses and did not consider modifications of the heat exchanger circuitry configuration to adapt to the new refrigerants. This study presents a novel multi-objective optimization approach to design a refrigerant composition that maximizes energy efficiency within flammability and GWP limits. The approach in this work simultaneously optimizes mixture composition and heat exchanger circuitry configuration. A case study on a rooftop unit indicates that, compared with mixture-only optimization, simultaneous optimization of mixture and heat exchanger circuitry yields a 5.9% improvement in cycle efficiency and a 48.6% reduction in refrigerant flammability with a GWP of 268. Circuitry optimization using refrigerants with different temperature glides shows that the larger the temperature glide is, the larger EER improvement is obtained. The results show that zeotropic blends with a large temperature glide are more sensitive to the refrigerant circuitry than pure refrigerants and may suffer significant performance degradation with subpar heat exchanger circuitry design. The proposed optimization approach is generally applicable to mixtures with any number of components. Using this approach to design a HVAC system can yield higher system efficiency within flammability and GWP constraints.

Air dehumidification is essential since excess moisture in the buildings causes discomfort to the... more Air dehumidification is essential since excess moisture in the buildings causes discomfort to the occupants, encourages the production of air pathogens such as mold or mildew, and causes corrosion and rotting that degrade building materials. Existing moisture removal processes are mainly focused on condensation and desiccant (liquid or solid) techniques with direct contact between air and desiccant. However, these methods are energy-intensive, or desiccant might be lost or cause corrosion in the process. The main objective of this study is to investigate an ionic liquid-based liquid desiccant absorber based on a membrane fiber bundle. A novel membrane contactor system was fabricated with a bundle of 10,000 polypropylene fibers. Each fiber has 0.3 micron outer diameter, with ionic liquid flowing inside, and air flowing outside. The fibers provide a high contact area among phases: 1.4 m 2 contact surface area in a 0.00015 m 3 volume (9,333 m 2 /m 3 ratio of surface area to volume). The ionic liquid as a sorbent has selectivity for water vapor (i.e., the ionic liquid has higher affinity for water vapor) prevents the loss of solvent in the operation due to negligible volatility, provides fast diffusion due to low viscosity compared to common ionic liquids, and has high affinity and solubility in water. The dehumidification capacity of the prototype membrane system was experimentally investigated using six modules with 10,000 fibers each. The experimental results show that the ionic-liquid based membrane system can effectively remove excess moisture from the air. The novel fiber bundle dehumidification system has a total system volume of 0.00798 m 3 (7.98 L) and active heat and mass transfer surface area of 8.4 m 2. It achieved an average dehumidification of 320 ± 25 W with a volumetric air flowrate of 3.1 m 3 /min (108 ft 3 /min).

Scientific Data, 2022

Most COVID-19 vaccines require temperature control for transportation and storage. Two types of v... more Most COVID-19 vaccines require temperature control for transportation and storage. Two types of vaccine have been developed by manufacturers (Pfizer and Moderna). Both vaccines are based on mRNA and lipid nanoparticles requiring low temperature storage. The Pfizer vaccine requires ultra-low temperature storage (−80 °C to −60 °C), while the Moderna vaccine requires −30 °C storage. However, the last stage of distribution is quite challenging, especially for rural or suburban areas, where local towns, pharmacy chains and hospitals may not have the infrastructure required to store the vaccine at the required temperature. In addition, there is limited data available to address ancillary challenges of the distribution framework for both transportation and storage stages, including safety concerns due to human exposure to large amounts of CO2 from dry-ice sublimation, issues due to the pressure increase caused by dry-ice sublimation, and the potential issue caused by non-uniform cryogenic ...

Air conditioning (A/C) systems driven by renewable energy have been studied extensively during th... more Air conditioning (A/C) systems driven by renewable energy have been studied extensively during the past decade as promising alternatives to conventional electricity-driven vapor compression A/C to alleviate stress on the grid as well as reduce CO2 emissions. Among the possible renewable energy sources to drive A/C systems, low-temperature geothermal heat (<150°C/300°F) is currently underutilized despite its abundance in the United States and the advantage of steady output. A major barrier to wider utilization is the typically long distances between geothermal sources and potential end uses. In order to overcome this barrier, an innovative two-step geothermal absorption (TSGA) system was studied. With this system, low-temperature geothermal energy is stored and transported at ambient temperature with an energy density of 349 kJ of cooling energy per kg of shipped LiBr/H2O solution, which is about five times higher than directly transporting geothermal fluid itself for space heatin...

A quasi-steady state, heat and mass transfer lumped-capacitance model was developed to predict th... more A quasi-steady state, heat and mass transfer lumped-capacitance model was developed to predict the energy consumption and drying performance of domestic dishwashers. A numerical finite element solution was applied, assuming that the following components could each be treated as a lumped thermal capacitance: dish load, tub, wash water, and air in tub. The model was used to predict the energy consumption savings of heating water using a thermoelectric heat pump that extracts heat from a thermal storage medium, and the drying performance of circulating tub air through the cold and then hot side of TE modules.

Dehumidification is a major contributor to the energy consumed by residential and commercial buil... more Dehumidification is a major contributor to the energy consumed by residential and commercial buildings. Emerging separate sensible and latent cooling (SSLC) systems can provide energy-efficient solutions to control moisture and temperature independently. In light of emerging research, a strong need has emerged to categorize and to characterize the performance of SSLC systems. The current study provides categorization and a critical review of major developments, including components, systems, processes and working media pertaining to SSLC systems. The review highlights the key features which can be used for classification, performance evaluation and steady-state capacity of SSLC systems. Finally, the study provides guidelines for further research and important performance matrixes for future developments.

To meet the growing energy consumption and mitigate climate concerns, novel energy efficient tech... more To meet the growing energy consumption and mitigate climate concerns, novel energy efficient technologies need to be developed. Water heating, dehumidification and space cooling form a significant percentage (~24%) of a typical U.S. household energy consumption and a total of 2.6 quad of primary energy consumption. In this paper, we present a novel system for combined water heating, dehumidification, and space cooling. The three processes can be achieved by one device using a novel semi-open absorption based system combined with evaporative cooling. The absorption based system absorbs water vapor from its ambient. The latent heat of absorption, released into the absorbent, is transferred into the process water that cools the absorbent. The water absorbed is later released in the desorber through heating, and the water vapor generated in the desorber is condensed and its heat of phase change is transferred to the process water in the condenser. The condensed water vapor can either be...

Clothes dryers based on thermoelectric (TE) heat pumps have the potential to save significant ene... more Clothes dryers based on thermoelectric (TE) heat pumps have the potential to save significant energy compared with the conventional electric resistance technology that is widespread today, without using any refrigerant fluid. In this work, guided by a validated system model, design and control improvements were implemented on an experimental prototype to optimize the dryer performance (duration to dry a load, and energy consumed per unit cloth mass). Starting from a fixed TE area, the physical design variables of interest were (1) the use of vented or ventless configuration, (2) the heat sink geometry, (3) the selection of blower and (4) the selection of motor used to drive drum rotation. The control variables of interest were (5) the average electrical current supplied to each bank of TEs and (6) the current profile for each bank during the drying time. By optimizing each of these choices in the model and applying the resulting design choices on the prototype, the experimentally me...

Past work has shown that thermoelectric clothes dryers are capable of much higher efficiency than... more Past work has shown that thermoelectric clothes dryers are capable of much higher efficiency than electric resistance clothes dryers. In an effort to improve performance and reduce material utilization, this work explores a new secondary loop system configuration. In this configuration, heat is transferred between air and the thermoelectric heat pumps via two water loops and two water-to-air fin-tube type heat exchangers. In this work, performance is investigated and analyzed using experimental data.

A heat pump clothes dryer (HPCD) uses a vapor compression system to dry clothes. The condenser he... more A heat pump clothes dryer (HPCD) uses a vapor compression system to dry clothes. The condenser heats air, which passes through the drum to evaporate moisture out of the clothes, and the evaporator condenses water out of the air stream. As a result, the HPCD can achieve 50% energy savings compared to a conventional electric resistance dryer. In this work we developed a physics-based, quasi-steady-state HPCD system model with detailed heat exchanger and compressor models. The system model can simulate the inherently transient HPCD drying process, to size components, and to reveal trends in key variables (e.g. compressor discharge temperature, power consumption, required drying time, etc.) The system model was calibrated using experimental data from a prototype HPCD. Air leakages, in and out, along the closed air circulation path of HPCD cause varied effects on the performance. Understanding the location, magnitude, and direction of air leakage of the heat pump clothes dryer is critica...

Part of: Thermally driven heat pumps for heating and cooling. – Ed.: Annett Kuhn – Berlin: Univer... more Part of: Thermally driven heat pumps for heating and cooling. – Ed.: Annett Kuhn – Berlin: Universitatsverlag der TU Berlin, 2013 ISBN 978-3-7983-2686-6 (print) ISBN 978-3-7983-2596-8 (online) urn:nbn:de:kobv:83-opus4-39458 [http://nbn-resolving.de/urn:nbn:de:kobv:83-opus4-39458]

Phase change materials (PCMs) with desirable phase change temperatures can be used to provide a c... more Phase change materials (PCMs) with desirable phase change temperatures can be used to provide a constant temperature thermal source or sink for diverse applications. As such, incorporating PCMs into building materials, equipment, or appliances can shift and/or reduce the energy load. The motivation of this work is to identify low-cost inorganic salt hydrate PCMs that can complement current building systems and designs, and compare them with common paraffins. In this work, we analyzed inorganic salt hydrates with phase change temperatures in the range of 5-60°C, to target both space heating and cooling applications. The properties of the salt hydrates were compared with paraffins over the same temperature range. The results showed that PCMs with a melting temperature above 20°C, salt hydrates have advantages over paraffins including higher thermal energy density (45-120 kWh/m for salt hydrates; 45-60 kWh/m for paraffins) and generally lower material energy cost (1-20 $/kWh for salt h...

A heat pump clothes dryer (HPCD) is an innovative appliance that uses a vapor compression system ... more A heat pump clothes dryer (HPCD) is an innovative appliance that uses a vapor compression system to dry clothes. Air circulates in a closed loop through the drum, so no vent is required. The condenser heats air to evaporate moisture out of the clothes, and the evaporator condenses water out of the air stream. As a result, the HPCD can achieve 50% energy savings compared to a conventional electric resistance dryer. We developed a physics-based, quasi-steady-state HPCD system model with detailed heat exchanger and compressor models. In a novel approach, we applied a heat and mass transfer effectiveness model to simulate the drying process of the clothes load in the drum. The system model is able to simulate the inherently transient HPCD drying process, to size components, and to reveal trends in key variables (e.g. compressor discharge temperature, power consumption, required drying time, etc.) The system model was calibrated using experimental data on a prototype HPCD. In the paper, ...

Space heating is a major contributor to building energy consumption especially in cold climates. ... more Space heating is a major contributor to building energy consumption especially in cold climates. Conventional gasfired furnaces are approaching thermodynamic efficiency limits, while electric heat pumps performance declines drastically at low ambient temperature. Chemisorption heat pump (CSHP) systems could be a better solution to space heating for cold climate due to their sustained capacity and efficiency at large temperature lifts. The performance of CSHP primarily depends on the working pair and cycle configuration. Most existing comparative studies of chemisorption systems in the published literature focus on refrigeration, but not many in heating applications. The few existing studies of chemisorption heat pump for heating involved too limited cycles and working pairs to represent the most promising performance of the CSHP. The goal of this study is to fill the gap through extensive performance comparison of CSHP using various salts and cycle configurations to discover the pot...