Mechanical Compression Heat Pump Research Articles

Two-phase ejector enhanced carbon dioxide transcritical heat pump for cold climate

Among the solutions to current energy efficiency and climate change issues, the use of natural refrigerants in mechanical compression heat pumps is an important measure for an effective response. However, the heat pump’s performance decline as the ambient temperature drops is well known. The use of the two-phase ejector under these conditions can be a simple and easy to implement way to address this problem.In this respect, a thermodynamics model to simulate a CO2 transcritical heat pump cycle integrating a two-phase ejector is first presented. The modeling allows implicit adjustments of the ejector geometry with varying operating conditions, to adapt its operation in the cycle for maximised overall efficiency. The interaction between the main cycle components is highlighted and one can clearly see that the optimal operation of the cycle does not necessarily coincide with that of its components.For the simulated ejector conditions, the results show the importance of maintaining a particular entrainment ratio (0.5–0.65) in order to avoid mass balance issues in the separator. With lower Tevap, an enhanced ejector efficiency is achieved by striking a balance between decreased entrainment and improved compression ratios. The results clearly show the need to control the ejector geometry in order to meet capacity variations. Thus, decreasing Tevap (from 5 °C to −20 °C), needs to reduce the throat and the mixing diameters by 36% and 22% respectively.Cycle simulations show a definite advantage with the ejector use in terms of COP and heating capacity for low evaporator temperatures. In this case, the compression ratio of the ejector improves, resulting in a higher compressor pressure suction, compared to the conventional cycle. Thus, at optimal gas cooler pressure and for an evaporator temperature of −20 °C, gas cooler and evaporator capacities as well as the cycle COP improve by 14%, 23% and 9% respectively. These improvements are associated with a slight increase in the compressor work (≈4%).

Techno‐economic analysis of a novel hybrid heat pump system to recover waste heat and condensate from the low‐temperature boiler exhaust gas

This paper is based on the proposal of a new waste heat recovery (WHR) system, which can be utilized to heat the boiler return water, boiler supply air, and building heating air. The system is the combination of an indirect contact condensing unit (IDCCU), a mechanical compression heat pump, and two air preheaters. The system is modeled on the basis of mass and energy balance and then thermodynamically analyzed. Improved performance results were obtained in the form of an increase in the boiler's energy efficiency of about 10.47%, with 4.87% increase in exergy efficiency. The coefficient of performance (COP) of the heat pump was increased from 1.23 to 1.45 by the addition of an air heater in the conventional heat pump. The exergy destruction in each component is calculated. Sensitivity analysis was performed to check the influence of different operating parameters on the performance of the WHR system and boiler. It can be observed from the results that for a specific refrigerant temperature and a calculated amount of mass, flow rate can maximize the condensation efficiency of IDCCU by decreasing the flue gas temperature, while the use of the air heater can further reduce the flue gas temperature, and a stream of hot air can be utilized for space heating. A comparison is made with the other system on a performance basis. The results shows a clear difference in efficiencies and profit earned.

Investigation on humidification dehumidification desalination system coupled with heat pump

In this paper, a mechanical compression heat pump was coupled into the water-heated humidification dehumidification (HDH) desalination system, in which the condenser is applied to heat the seawater while the evaporator is considered to recover the carried heat from the discharged brine. In view of the integration mechanisms between the desalination unit and heat pump, mathematical models based on mass and energy equilibrium are built. Performance of the combined system, including the water production and gained-output-ratio (GOR), at the design conditions are first obtained. Moreover, the relevant influences from the prescribed critical parameters on the performance of the desalination system are simulated and analyzed. The simulation results show that the best performance of the coupled HDH desalination system, appearing as 82.12 kgh−1 for the water production and 5.14 for the GOR, is acquired at the balance condition of the dehumidifier. Two fully coupled cases, in which the heater or cooler is no longer required, when the air mass flow rate is located at 0.17 kgs−1 and 0.35 kgs−1, are found. During the influence analysis, a best value of pressure ratio, PR = 4, is found due to a highest value of GOR as 5.14 although the relevant value of water production is attained as 106.53 kgh−1 when the pressure ratio is fixed at 5. Furthermore, it is also observed that a lower value of the pinch temperature difference for the condenser, higher values of effectiveness both for the humidification and dehumidification, are effective to elevate the water production and the corresponding thermal efficiency.

An innovative trigeneration system using biogas as renewable energy

Abstract One of the ways to decrease the global primary energy consumption and the corresponding greenhouse gas emissions is the application of the combined cooling, heating and power generation technologies, known as trigeneration system. In this research an innovative trigeneration system, composed by an absorption heat pump, a mechanical compression heat pump, a steam plant, and a heat recovery plant is developed. The low temperature heat produced by absorption chiller is sent to a mechanical compression heat pump, that receives process water at low temperature from the heat recovery plant and bring it to higher temperatures. The trigeneration system is fed by biogas, a renewable energy. A design and a simulation of the system are developed by ChemCad 6.3® software. The plant produces 925 kW of electrical energy, 2523 kW of thermal energy and 473 kW of cooling energy, by the combustion of 3280 kW of biogas. Primary energy rate (P.E.R.) is equal 1.04 and a sensitivity analysis is carried out to evaluate the effect of cooling capacity, produced electrical energy and process water temperature. The first has a negative effect, while other parameters have a positive effect on P.E.R. Compared to a cogeneration system, the trigeneration plant produces the 28% higher of power and the 40% lower of carbon dioxide emissions. An economic analysis shows that the plant is economically feasible only considering economic incentives obtained by the use of heat pumps and steam plant at high efficiency. Saving 6431 t·a− 1 corresponding to 658000 EUR·a− 1 of incentives, the plant has a net present value (N.P.V.) and a pay back period (P.B.P.) respectively equal to 371000 EUR and 4 year. Future works should optimize the process considering cost and energetic efficiency as the two objective functions.

Comparative study of indirect photovoltaic thermal solar-assisted heat pump systems for industrial applications

In this paper, a comparative study of indirect photovoltaic thermal solar-assisted heat pump systems for water heating in industry is presented. The solutions to achieve a system with a steam ejector heat pump and a system with a mechanical compression heat pump integrated in a paper mill are proposed. The mathematical models are developed and used to evaluate the performance of these systems for the Bacau, Romania climatic conditions. A numerical study highlights the energy, exergy and economic efficiency of each system for the different operating hot water temperatures supplied. The obtained results show that an increase in the hot water temperature leads to a decrease in the energy, exergy and economic performance and that in an industrial company with continuous operation, the best solution is a photovoltaic thermal system with a steam ejector heat pump.

Research and development on heat pump systems in Mexico using geothermal energy

Extensive research and development work on heat pumps operating on geothermal and waste energy has been carried out by Instituto de Investigaciones Electricas, Mexico. Systems include (i) mechanical compression; (ii) absorption – one- and two-stage and double absorption; (iii) heat transformers, and (iv) hybrid, heat pump systems. Specific work and results are described on three applications: (a) a mechanical compression heat pump commissioned for brine purification and operating on low-pressure geothermal steam in Los Azufres geothermal field; (b) a cooling and refrigeration ammonia/water absorption heat pump operating on low-enthalpy geothermal energy and tested in Los Azufres and Cerro Prieto geothermal fields, and (c) an absorption heat transformer tested extensively to evaluate the performance of ternary solutions as working fluids.

703 マイクロガスタービン・コージェネレーションシステムの評価研究(マイクロガスタービンシステムの熱力学的特性)(OS.11 マイクロガスタービンと分散電源)

Distributed cogeneration systems, which supply both electric power and heat, offer many advantages over conventional central power stations for reducing the primary energy consumption. Micro gas turbines (μGT) have recently been developed as an electric power generation device for small-scale cogeneration systems. This paper reports the energy saving capability assessment based on the simulation of the annual fuel consumption in a micro gas turbine cogeneration system (μGT-CGS) including a boiler, a mechanical compression heat pump unit and an absorption chiller unit. Assuming the installation into three types of buildings (office, hotel and residence), the annual energy saving and the power supply fraction of the μGT-CGS are assessed. The results show that the advantage of the μGT-CGS significantly increases when the efficiency of μGT reaches 40%.

Optimal performance of a geothermal heat-engine-driven heat-pump system

A geothermal heat-powered, low-temperature Rankine cycle is suitable for the operation of a conventional mechanical compression heat-pump cycle in providing heating and cooling loads. This system is analyzed using a finite-time thermodynamic approach. The only irreversibilities are associated with heat transfer between the system and surrounding thermal reservoirs.

Irreversibility analysis of a water-to-water mechanical-compression heat pump

The thermodynamic irreversibility sources of a steady-flow, vapor-compression, water-to-water heat pump are analyzed. The three main components in the system (condenser, evaporator, and reciprocating compressor) are considered in detail. The heat transfers and mass flows in these three components are analyzed on the basis of energy- and mass-balance theories. The irreversibilities due to heat transfer across a finite temperature difference and mass flow across a finite pressure drop in each component are calculated according to the second law of thermodynamics. An experimental heat pump using R-22 is used as a test system for applying the analysis. Pressure, temperature, mass-flow rate, and power-consumption data are used to evaluate the irreversibilities of the system operating in steady state. Optimization of the water-flow rate in both the condenser and evaporator has been determined for this system to minimize the power consumption for a given load and inlet water temperature. The results show that an increase in the heat-transfer coefficient for the heat exchangers, even with an increase in pressure drop, will decrease the irreversible loss substantially.