Experimental study of operating characteristics of compression/absorption high-temperature hybrid heat pump using waste heat

This research describes the development of a compression/absorption hybrid heat pump system that utilizes a mixture of NH₃ and H₂O as a working fluid. The heat pump cycle is based on a hybrid combination of vapor compression cycle and absorption cycle. The system consists of major components of two-stage compressors, absorbers, and a desorber. There are also auxiliary parts like a desuperheater, solution heat exchangers, a solution pump, a rectifier, and a liquid/vapor separator to support stable operation of the heat pump. This compression/absorption hybrid heat pump provides many advantages of performance over conventional vapor compression heat pumps including a large temperature glide, an improved temperature lift, a flexible operating range, and greater capacity control. These benefits are optimized by changing the composition of the mixture. In this study, the effect of the composition on the operating characteristics of the compression/absorption hybrid heat pump was experimentally observed.     

Heat transfer enhancement in a small pipe by spinodal decomposition of a low viscosity,liquid–liquid,strongly non-regular mixture

We report experimental evidence of a 20–40 % enhancement of the effective heat transfer coefficient for laminar flow of a partially miscible binary liquid–liquid mixture in a small diameter horizontal tube that obtains when phase separation occurs in the tube. A mixture of acetone–hexadecane is quenched into the two-phase region so as to induce spinodal decomposition. The heat transfer rate is enhanced by self-induced convective effects sustained by the free energy liberated during phase separation. The experimental heat transfer coefficients obtained when separation occurs are compared to the corresponding values predicted for flow of a hypothetic mixture with identical properties but undergoing separation. For such comparison, the energy balance equation must carefully take into account both the sensible heat and the excess enthalpy difference between the inlet and the outlet streams because our liquid–liquid binary mixture is a very asymmetric system with large excess enthalpies. The non-ideal mixture thermodynamic properties needed for the energy balance are obtained by an empirical procedure from the experimental data available in the literature for our mixture. The experimental setup and calculation procedure is tested by experiments performed using single-phase water flow and single-phase mixture flow (above the critical point). The convective heat transfer augmentation that results in the presence of liquid–liquid phase separation may be exploited in the cooling or heating of small scale systems where turbulent convection cannot be achieved.     

Performance assessment of a liquid‐phase separation refrigeration cycle

Absorption refrigeration cycles are alternatives to conventional vapor‐compression cycles in which the energy required for refrigeration is provided by heat instead of mechanical work. In this paper, a novel refrigeration cycle utilizing the immiscible liquid‐phase separation behavior is simulated and analyzed using Aspen simulator. The two conjugate liquids adopted in this work are triethylamine (solute) and water (solvent). This binary system has a low critical solution temperature of 18 °C. The thermophysical properties of the binary mixture are generated using the universal functional activity coefficient (UNIFAC) and the nonrandom two‐liquid (NRTL) models. The phase splitting phenomenon at the generator temperature is predicted by both models. However, in comparison with the available experimental data for the same binary mixture, NRTL model gives better predictions for the flow rates and compositions of the material streams. Heat duties of the evaporator, absorber, and generator and the power consumption of the solution pump have been calculated using UNIFAC and NRTL models. The cycle COP that plays a major role in determining the cycle economical viability has been predicted for different operating conditions using the two models. Simulation results show that, for a waste heat reservoir at 60 °C and using NRTL model, the COP is about 2.0. Second law analysis conducted for all cycle components of the cycle shows that about 42% of the total exergy destructed occurs in the generator. Finally, the liquid‐phase separation refrigeration cycle is predicted to be a promising cycle in the near future because of hardware and energy savings. Copyright © 2011 John Wiley & Sons, Ltd.     

Optimum performance of a heat engine‐driven combined vapour compression–absorption–ejector heat pump

Optimum performance of an endoreversible heat engine‐driven heat pump cycle, based on a combination of an absorption cycle with a vapour and ejector compression cycles is investigated. This combination increases the performance of the conventional ejector and absorption cycles and provides high performance for heating. The analysis show that the combined heat pump cycle has a significant increase in system performance over the heat engine‐driven vapour compression or absorption heat pump cycle and heat engine‐driven combined vapour compression and absorption heat pump cycle. Copyright © 2000 John Wiley & Sons, Ltd.     

Mass and energy storage analysis of an absorption heat pump with simulated time dependent generator heat input

This communication presents an assessment of the feasibility of energy storage via refrigerant mass storage within an absorption cycle heat pump with simulated time dependent generator heat input. The system consists of storage volumes with the condenser and absorber of the conventional absorption cycle heat pump to store liquid refrigerant, weak and strong solutions during the generation period, which are required for the heat pump operation during the generation off period. A time dependent mass and energy storage analysis based on mass and energy balance equations for various components of the heat pump system has been carried out to evaluate energy storage concentration and storage efficiency for combined and separate storage schemes for the weak and strong solutions. Two possible performance modes, viz constant pumping ratio or the constant flow of the strong solution from the absorber to the generator have been analysed: the latter is preferable over the former from a practical point of view. Numerical computer simulation has been made for a typical winter day in Melbourne (Australia) with the desired heating load specified. It is found that the concept of refrigerant storage within the absorption cycle heat pump is technically feasible for efficient space heating. The energy storage concentration in the condenser store is slighly higher while that in absorber store is slightly lower for the separate storage mode as compared to the combined storage. However, the combined storage has an advantage of less storage volume and hence is more cost effective than separate storage and the disadvantage of limited system operation due to the decrease of solution concentrations.     

Numerical simulation and performance assessment of a low capacity solar assisted absorption heat pump coupled with a sub-floor system

A prototype low capacity (10 kW) single stage Li–Br absorption heat pump (AHP), suitable for residential and small building applications has been developed as a collaborative result between various European research institutes and industries. The primary heat source for the AHP is supplied from flat plate solar collectors and the hot/chilled water from the unit is delivered to a floor heating/cooling system. In this paper we present the simulation results and an overview of the performance assessment of the complete system. The calculations were performed for two building types (high and low thermal mass), three climatic conditions, with different types of solar collectors and hot water storage tank sizes and different control systems for the operation of the installation. The simulations were performed using the thermal simulation code TRNSYS. The estimated energy savings against a conventional cooling system using a compression type heat pump was found to be in the range of 20–27%.     

Simulation of an absorption heat pump solar heating and cooling system

An absorption heat pump (AHP) is a heat driven heat pump utilizing the absorption process. A continuous, liquid absorbent AHP with chemical storage is modeled using mass and energy balances and assuming mass transfer equilibrium. This model is used with the TRNSYS program [5] to simulate the performance of an AHP in a residential solar-driven heating and cooling system. The effects of collector area for an AHP using the NaSCN---NH₃ chemical system are investigated for the Columbia, MO, Madison, WI, and Fort Worth, TX climates. The AHP system is compared to a conventional solar heating and cooling system and the effects of heat exchanger effectiveness, storage mass, additional thermal capacitance and alternative control strategies are studied for the Columbia climate.     

A novel latent heat storage for solar space heating systems: Refrigerant storage

This paper proposes a novel latent heat storage which is applicable to solar space heating systems. The device is similar to an absorption refrigerator and stores liquid refrigerant which is subsequently evaporated to release the latent heat. It will recover the energy in a heat pump mode for application to solar space heating systems which are seen to be more cost effective—and hence to have a better market potential—than space cooling systems.     

Valorisation of low-temperature heat: Impact of the heat sink on performance and economics

Low-grade heat is available everywhere; consequently, the valorisation of this heat seems to be attractive in terms of economics. However, irrespective of the form of energy which is produced, any valorisation comes along with the production of another stream of waste heat with even lower value. The dumping of this reject heat often turns out to be the issue which determines cost.This presentation will elaborate on the influence of the heat sink temperature both on conversion efficiency and cost. It first will give a frame on a very generic level. It is easy to reproduce the well-known fact that the change in COP of a compression heat pump with heat sink or source temperatures is in the order of some %/K. The same order of magnitude holds for all generic cycles with one important exception: the influence of the heat sink temperature on the COP of a thermally driven cooling machine is about twice the impact of the other temperatures. In addition, simple equations to account for the cost of heat exchange are presented. They show that heat pumps, be it work driven or heat driven, exhibit the best efficiency-to-cost ratio.In order to leave the generic level, a more detailed analysis is given for an absorption cooling system. It is confirmed that the impact of the heat sink temperature on capacity and COP is significantly larger than that of the other temperatures; in the nominal point a rise in heat sink temperature reduces the cooling capacity by over 10%/K.Finally, the influence of the humidity of the ambient air on performance is presented in a first order approach, also.     

A new concept in gas-fired heat pump reversed rectification heat pump

The reversed rectification heat pump (RRHP) is a novel type of absorption heat pump developed at Laboratoire des sciences du génie chimique (LSGC) in the research group of Professor Le Goff. The distinctive characteristic of the RRHP is that both the separator and the absorber are multi-stage gas contacting units of a type commonly used in the process industry and each composed of the multi-stage contactor, an evaporator and a condenser. The separator is a conventional rectification unit in which the working fluid is separated into a rich and a lean phase which are recombined in the absorber. The absorption is an exact reversal of the rectification, both units having inverted flow diagrams; for this reason the absorption is refered to as reversed rectification. This heat pump can produce simultanious heat and cold and provides significant primary energy savings and reduction of harmful environmental effects.     

A comparative study of solar assisted heat pump systems for canadian locations

The feasibility of solar assisted heat pump systems for space heating and domestic hot water preheating in Canada is examined by simulating the performance of these systems on a computer using the program WATSUN. Simulations are carried out using meteorological data for seven representative Canadian cities, two different building types, and six types of system configurations. For the solar assisted heat pump system, twenty year life cycle cost comparisons are made with two reference systems, namely a conventional resistance heating system and an air-to-air heat pump system, based on current economic parameters and projected escalation scenarios for electricity rates.Results of the study show that the solar assisted heat pump systems conserve significant amounts of energy over resistance heating and heat pump systems. On the life cycle unit cost basis, solar assisted heat pump systems costs are relatively insensitive to location, but the dependence on building types is substantial with multiplex dwellings showing the least cost. Liquid based dual source solar assisted heat pump systems are found to be cost effective over resistance heating (but not over an air-to-air heat pump system) at some of the locations for multiplex units. They are not cost effective for single family dwellings at the present time.     

太阳能制冷与供暖系统的设计与比较

根据上海的气候条件，以上海地区某写字楼为对象，提出4种太阳能驱动的溴化锂吸收式与电动蒸汽压缩式热泵联合制冷与供暖系统。这4种系统分别由热管式真空管集热器或抛物面槽形聚光集热器，单效或双效溴化锂吸收式制冷机，以及风冷热泵或水源热泵构成。分析比较这4种系统的节能型和经济性的结果表明，采用抛物面槽形聚光集热器＋双效溴化锂吸收式制冷机＋风冷热泵组成的系统，同时具备较好的节能性与经济性，一次能源利用率可降低约50％。     

Heating with wind: Economics of heat pumps and variable renewables

With the growth of wind and solar energy in electricity supply, the electrification of space and water heating is becoming a promising decarbonization option. In turn, such electrification may help the power system integration of variable renewables, for two reasons: thermal storage could provide low-cost flexibility, and heat demand is seasonally correlated with wind power. However, temporal fluctuations in heat demand may also imply new challenges for the power system. This study assesses the economic characteristics of electric heat pumps and wind energy and studies their interaction on wholesale electricity markets. Using a numerical electricity market model, we estimate the economic value of wind energy and the economic cost of powering heat pumps. We find that, just as expanding wind energy depresses its €/MWh_el value, adopting heat pumps increases their €/MWh_el cost. This rise can be mitigated by synergistic effects with wind power, “system-friendly” heat pump technology, and thermal storage. Furthermore, heat pumps raise the wind market value, but this effect vanishes if accounting for the additional wind energy needed to serve the heat pump load. Thermal storage facilitates the system integration of wind power but competes with other flexibility options. For an efficient adoption of heat pumps and thermal storage, we argue that retail tariffs for heat pump customers should reflect their underlying economic cost.     

Economic feasibility of heat pumps in distillation to reduce energy use

An i-butane/n-butane mixture was selected to analyze several distillation assisted heat pump processes when compared to conventional distillation. This conventional process, along with top vapour recompression, bottom flashing and absorption heat pumps, were simulated using the HYSYS software platform, in order to determine economically the best alternative.Distillation with both top vapour recompression and bottom flashing heat pumps allows reduction of operation (energy) costs by 33% and 32%, respectively. This improves the economic potential (incorporating capital costs) by 9% and 10%, respectively. Due to the large steam consumption, when compared to the conventional case, the absorption heat pump is not suitable for this system.     

Turbulent direct-contact heat transfer between two immiscible fluids

Heat transfer between two immiscible liquid phases in turbulent flow is of great interest in improving the residence time, compactness, and energy cost of cooling and heating processes. The high-efficiency vortex (HEV) device used here as a direct-contact heat exchanger (DCHE) is a generic multifunctional exchanger/reactor in which wall tabs generate longitudinal vortices responsible for convective radial transfer that enhance macro-mixing, phase dispersion and fast temperature homogenization in the flow.The experiments reported here concern a continuous flow of water in which an immiscible mineral oil is injected. The inlet water temperature ranges from 11 to 13 °C, and the inlet oil temperature from 40 to 48 °C; the flow Reynolds number varies between 7500 and 15 000. An algebraic one-dimensional thermal model accounting for the axial evolution of the phase temperatures coupled with drop breakup is developed and validated by the experimental thermal results in the DCHE. This model requires knowledge of the turbulent field in single-phase conditions; it can be adapted to other flow geometries and can be used as a sizing tool for engineering design.Despite the phase separation at the outlet, the DCHE is more efficient than a double-jacketed heat exchanger in terms of global Nusselt number. In addition, the HEV heat exchanger is energetically less costly than the other DCHE for the same heat-transfer capacity.     

Wood chip drying with an absorption heat pump

This paper presents the thermal and economic analysis of a mobile wood chip drying process. The dryer was subjected to different operating conditions, which were studied in order to determine the optimal characteristics of the dryer in terms of energy consumption. In addition, the impact of the exterior climatic conditions on the dryer's performance was also evaluated. The performance of the dryer coupled with an absorption heat pump was modeled in steady-state conditions under different operating parameters. Finally the system's energy performance was compared to the performance of two other systems (a wood burning furnace and a waste-heat recovery system). The results demonstrate that single-stage absorption heat pumps are only interesting when the set point temperature of the drying air is below 60 °C. Otherwise, a two-stage absorption heat pump must be used. In terms of energy and financially, this type of drying is very costly. Of the three processes that were studied, heat recovery systems proved to be the most energy efficient and economic solution.     

Heat pump use in milk pasteurization: an energy analysis

This study investigates the applicability of heat pumps to milk pasteurization for cheese production and to compare the results with classical pasteurization systems. The experiments are conducted in a liquid‐to‐liquid vapour compression heat pump system and a milk‐to‐milk plate heat exchanger is used as an economizer. The experiments are also conducted in a double jacket boiler system and a plate pasteurization system, which are classical milk pasteurization systems. The results for the three systems are compared and the advantages/disadvantages of using heat pump for milk pasteurization instead of classical systems are determined. It is found that the heat pump consumes less energy than the other two classical systems. Copyright © 2004 John Wiley & Sons, Ltd.     

First and second law analysis of a solar assisted heat pump based heating system

We propose a model for the heating system of an ecological building whose main energy source is solar radiation. The most important component of the heating system is a vapour compression heat pump. Both the first law and the second law were used to analyse the heat pump operation. The state parameters and the process quantities were evaluated by using, as input, the building thermal load. The second law analysis emphasised that most of the exergy losses occur during compression and condensation. Preliminary results show that the photovoltaic array can provide all the energy required to drive the heat pump compressor, if an appropriate electrical energy storage system is provided.     

Heat pump assisted distillation. V: A feasibility study on absorption heat pump assisted distillation systems

The problems in matching a heat driven absorption heat pump to a distillation process in heat pump assisted distillation are discussed. The performance of an absorption system is a function of the temperatures in the evaporator, the condenser, the absorber and the generator and the ratio of the mass flow rate in the secondary circuit to the mass flow rate in the primary circuit. In absorption systems design choices are limited by the Gibbs phase rule. Plots are given of the coefficient of performance against the temperatures of the top and bottom products and also against the energy saved.     

LiBr-H_2O太阳能吸收式热泵海参干燥系统应用分析

提出以LiBr-H2O为工质对的太阳能吸收式热泵海参干燥系统,介绍此系统的组成及工作流程。LiBr-H2O太阳能吸收式热泵应用于干燥过程可以降低能耗,绿色环保。对其应用前景进行分析,同时提出该系统在推广应用方面的限制因素,对太阳能吸收式热泵海参干燥装置设计及推广具有参考价值。