A circumstance with both heat and cold demands has emerged ubiquitously across building and urban scales. This scenario is ideally addressed by implementing a heat pump for simultaneous heat and cold production. However, ongoing challenges exist in identifying the thermodynamic effectiveness of simultaneous heat and cold production mechanisms (why) and harmonizing the time and amount of simultaneous heat and cold production with the diverse user demands (how and what). In this paper, a simultaneous heat and cold production system (SHCPS) is proposed. Three pivotal questions related to its underlying principle, design methodology, and applications are elucidated. The heat pump for simultaneous heat and cold production in this study outperforms unidirectional ones by achieving a low ratio of electricity consumption (RP) within a temperature difference of 75 degrees C between heat and cold, resulting in potential energy savings of up to 46 %. The serial-parallel configuration of the system facilitates three universal capacity sizing and operation methodologies to deal with disproportionate heat and cold production and demand: demand-based, bidirectional heat pump production-based, and balanced ratio-based strategies. In a typical supermarket scenario, the balanced ratio-based strategy can yield a 35 % occupied space reduction of storage units and attain comprehensive cost reductions in the short to medium term. The demand-based strategy holds more advantages under larger peak-to-valley electricity price ratios and in the long term. When the peak-to-valley electricity price ratio reaches 3, the investment payback period for these three strategies is within 5.2 years. The solutions to these three questions herein are anticipated to fundamentally address the practical obstacles involved in applying heat pumps for simultaneous heat and cold production, introducing novel insights into global heat and cold production patterns.

The temperature difference between evaporating and condensing side of cascade high temperature heat pump (CHTHP) can be large. However, its heating coefficient of performance (COP) is not ideal due to the performance attenuation brought by large temperature lift. If both heating and cooling sides can be utilized, the whole COP will be greatly improved. In this work, a CHTHP prototype is established, along with three application scenarios, specifically dairy processing, liquor processing, and deep dehumidification, which simultaneously have cooling and heating demands consistent with the operating range of the unit. The experimental results indicate that the CHTHP prototype can supply cooling as low as 2 degrees C and heating up to 120 degrees C with comprehensive COP over 2.58, being more than 45.8 % higher than single heating system, showing impressive performance in combined cooling and heating (CCH) for industrial processes. Through the joint investigation of heat pump and application scenarios, it is revealed that the comprehensive performance of CHTHP can surpass conventional approach of using two separate heat pumps to provide cooling and heating respectively when the ratio of heating to cooling demand is high. In addition, the performance of CCH system can be further enhanced by optimizing corresponding process parameters in different scenarios. Based on the excellent performance of CHTHP in CCH and its practical industrial applications, this work will maximize the effectiveness of high temperature heat pump in the electrificaiton of industrial thermal energy consumption.

Cascade configuration is commonly considered suitable for high temperature heat pump when there is significant temperature difference between heat source and heat supply, enabling the utilization of easily obtainable ultralow grade waste heat and providing heat for applications with high thermal demand. However, it is not advantageous in all working conditions, especially when considering various criteria. Therefore, it is important to quantitatively determined the competitive working temperature range of cascade high temperature heat pump (CHTHP) and to optimally select its working fluid pairs. In this work, 4 heat pump configurations and 289 sets of working fluid pairs are compared. The criteria for determining the competitive working temperature range include coefficient of performance (COP), cost, exergy efficiency, and total equivalent warming impact. Additionally, safety level and discharge temperature are involved when evaluating working fluids. The results indicated that cascade is optimal when temperature lift is above 70 degrees C. As temperature lift decreases, the best configurations can appear in the order of two-stage, single-stage with injection, and single-stage. The working fluid pairs collocated with R1234ze(E), R1234ze(Z), R1224yd(Z), R1233zd(E), R1336mzz(Z) show great tradeoffs among criteria, emerging as the ideal choices in different working conditions. The optimal configurations and working fluids shift towards the ones with higher COP with increasing operating hours. Finally, the rationality of evaluation method is illustrated, demonstrating that the combined weighting enhances decisions' stability and the min-max normalization improves comparability among criteria. In summary, this work provides guidance on the efficient, cost-effective, environmentally friendly, and safe use of CHTHP.

High temperature heat pump is a promising solution for efficient high temperature heat supply. However, the poor performance when it operates in large temperature lift hinders it from utilizing low temperature waste heat. To solve this problem, a cascade high temperature heat pump with economized vapor injection was established and a simulation model was developed accordingly. The tests were conducted using R134a/R245fa and R1234ze (E)/HP-1 at heat source temperature from 5 to 30 degrees C and heat sink temperature from 90 to 120 degrees C, with the coefficient of performance (COP) varying in the range of 1.72-2.73 and 1.77-2.75, respectively. The COP about 2.20 was achieved with R1234ze(E)/HP-1 at optimal intermediate temperature and optimal economized vapor injection pressure when the temperature lift is 100 degrees C. In the simulated case study, the heat pump water boiler based on the experimental prototype decreases CO2 emission by 62.8 % compared to electric boiler. Moreover, using low GWP working fluids reduces 1.32 x 104 kg direct CO2 emission in TEWI. Under the current technological, pricing, and operational condition, it takes 16 years for heat pump to have economic benefit over electric boiler, but this duration can be shortened with reduced initial cost, improved COP, and increased operating hours and electricity price. In summary, this work presented a high -efficient, environmentally friendly, and economically viable cascade high temperature heat pump system which has potential to utilize the abundant environmental heat source and deliver high temperature heat, being an alternative to the conventional heat generation equipment such as boilers.

The unreasonable energy consumption will lead to the shortage of resource and the damage of environment. Among large manufacturing countries, industry is the sector with the largest energy consumption, and its energy use transformation has received extensive attention. The high temperature heat pump which can meet the industrial heat demand is essential to promote the clean and electrification of industrial energy consumption. The establishment of high temperature heat pump mainly focuses on two aspects: cycle configuration and working fluid.In cycle configuration, compression, absorption, and hybrid compression-absorption high temperature heat pumps are sorted out; the working temperature range of the heat pump in each study is extracted; the heat source temperature and temperature lift in different cycle configurations are summarized; and a selection guideline of cycle configurations according to the condition of heat source and users’ temperature demand is provided. As for working fluids, their evolution process is sorted out; the suitable working temperature region is analyzed according to their characteristics, and the screening principles of working fluids are summarized. Finally, the application scenarios of high temperature heat pump are prospected. Besides being used in industrial processes, it can also be involved in Carnot batteries to achieve the storage and conversion of electricity-heat-electricity.

High-temperature heat pump (HTHP) for industrial heating is regarded as effective solution to control down CO2 emissions significantly, however there are still limited solutions to provide heat pumps with large scale and high temperature lift, especially it is difficult to adopt low-GWP refrigerants in HTHP and ensure efficient heating. Due to the excellent thermodynamic properties and environment friendly behavior, the application of natural working fluids in HTHP is an inevitable choice. Based on literature review and our previous research work, it is found that water could be the best working fluid in various HTHP systems. With water as refrigerant, high temperature heat pump could yield 100 degrees C temperature lift with satisfied COP values, the system could be closed cycle, combined closed and open systems, and even hybrid vapor compression and absorption systems.

Small-scale desalination devices driven by solar energy is a promising solution for freshwater in remote off-grid islands where centralized energy supplies are hardly accessible. However, the low water yield and unstable operation caused by energy inefficiency and salt precipitation are tricky problems. To provide a reliable fresh-water supply, a desalination device with high water yield and no salt precipitation is the main target of this work. A three-stage photothermal membrane distillation module with free-flow evaporation channel was fabricated and a model was developed accordingly. Upon varying flow patterns and flow rates, the effects of different flow configurations on water production and salt concentration were observed and discussed. It is revealed that the feed from the bottom to the top stage in series connection at a flow rate of 28 ml h-1 can achieve a water production rate of 2.23 kg m-2 h-1 and a solar energy utilization efficiency as high as 147.9 % without salt precipitation. This work showed a competitive water production among all the previously reported small-scale solar membrane distillation devices. Besides, the flowing design is effective in preventing salt precipitation. A strong potential in providing qualified household freshwater with salinity rejection over 99 % on remote islands was indicated.