Operating Conditions Of Heat Pumps Research Articles

Integrating energy efficiency and health safety in building design: A multi-objective optimization approach to minimize virus transmission risk

This study aims to develop an integrated design strategy for an office building in Tehran, optimizing energy efficiency and minimizing virus infection risk, addressing global challenges such as energy conservation and virus transmission. A multi-objective optimization model is developed to identify optimal design parameters for energy performance and infection risk reduction. Environmentally sustainable materials and energy-efficient equipment, such as solar panels, high-efficiency heat pump systems, and advanced air filtration techniques, are employed. The modified Wells-Riley Risk Model calculates infection risk, while energy efficiency is formulated based on the technologies used. Results showcase a significant 14% increase in energy efficiency and a 46% decrease in infection risk compared to traditional building designs, demonstrating the effectiveness of the proposed integrated approach. The optimal design parameters include ventilation rate, the number of solar panels, hot water pipe diameter, and heat pump condenser temperature. This study presents a practical, sustainable solution for designing office buildings that actively address pressing global concerns while fostering healthier, energy-efficient environments. The novelty of this research lies in the development of a multi-objective optimization model that synergizes infection control and energy efficiency, accounting for real equipment parameters and providing a new paradigm for HVAC design. This integrated strategy optimizes decision variables like ventilation rate, filtration level, solar panels, and heat pump operating conditions, offering a comprehensive approach to co-optimize infection control and energy performance.

Pinch point variation in the gas cooler of the CO2 heat pump water heater: An experimental and simulation comparative study

The carbon dioxide heat pump operation is strongly impacted by the presence of the pinch point within the gas cooler. The existing findings regarding the pinch point need to be verified due to the deficiencies of the simulation method. Given this, an experimental and simulation comparative study is performed. The pinch point variation characteristics and its connection with the heat pump operation are elucidated. The limitations and accuracy of the simulation model are revealed. The location and number of the pinch point are at most four scenarios. One locates at inside. Two locate at inside and cold end, respectively. One locates at cold end. One locates at hot end. The hot end pinch point is difficult to occur for actual heat pump operating conditions. As the carbon dioxide pressure rises, the pinch point temperature difference first grows slightly and then drops. The experiments demonstrated that the actual best operation of the carbon dioxide heat pump corresponds to one inside pinch point rather than two. The simulation model cannot reproduce this phenomenon well. The accuracy of the simulation model can be greatly improved in case the pinch point location is known, and it is acceptable from the perspective of meeting the engineering permissible error. This study may contribute to a better understanding of the pinch point variation. Moreover, it may play a reference role in the building and optimization of the gas cooler model.

Design and commissioning of an experimental facility for performance evaluation of pure and mixed refrigerants

The recent regulations about fluorinated greenhouse gases introduce a rapid phase-down of traditional, environmentally harmful refrigerants. Consequently, new working fluids are continuously appearing on the market, leading to the need of testing them to analyse their performance before making an ultimate choice. In the present paper, a test rig built to carry out experimental studies on different refrigerant in a drop-in application is described and first results for the set-up commissioning are commented. The experimental campaign was carried out in typical water-to-water heat pump operating conditions, varying the cold water temperature at evaporator inlet from 10 °C to 20 °C, with a step of 2.5 °C, and hot water temperature at condenser inlet from 30 °C to 50 °C, with a step of 10 °C and the compressor shaft rotational frequency from 30 Hz to 80 Hz, with a step of 10 Hz. The first findings demonstrate that the experimental results of some key performance parameters, namely heating capacity, COP and compressor volumetric efficiency, agree well with open literature trends, allowing to state that the experimental facility was correctly designed and can be used to deep the analysis on performance assessment of new refrigerants in a drop-in application.

A hybrid PV/T solar evaporator using CO2: Numerical heat transfer model and simulation results

This paper investigates a new geometry of hybrid photovoltaic/thermal (PV/T) solar collector used as an evaporator in a CO2 transcritical heat pump system. The solar absorber plate embeds monocrystalline silicon PV cells producing electricity and a stainless steel sheet to improve heat transfer with respect to standard back sheets. A serpentine stainless steel tube is bonded to the back of this solar absorber plate and two-phase CO2 flows inside this heat exchanger.A semi-transient numerical model is proposed to assess the thermal and electrical performances of the evaporator under given weather parameters and heat pump operating conditions. The 2-D, transient thermal diffusion equation is combined with a 1-D, steady state, compressible, two-phase flow model to compute the temperature distribution of the solar absorber plate along with the pressure, velocity, density and enthalpy field of the CO2 in the serpentine tube. A special model based on the straight fin analytical model accounting for the circumferential temperature gradient around the tubes is developed to combine the absorber plate and the heat exchanger models.The simulation results show an overall mean temperature reduction of the solar absorber plate operating at an electrical maximum power point of more than 25 °C with respect to a standard PV collector. Reducing the plate temperature leads to an additional production of 34 W of electrical power exceeding the maximum power specified under the test conditions of IEC 60904-3 international standard. In the simulated conditions, 1.028 kW of thermal power is also extracted and can be used in heating applications. The electrical efficiency increases from 14.1% for a standard solar PV collector to 16.0% for the suggested evaporator design. Finally, an overall efficiency combining both the electricity and heat production of 72.3% is achieved.

Microscopic observation of frost behaviors at the early stage of frost formation on hydrophobic surfaces

Microscopic seed behavior in the early stage of frost formation was experimentally observed with different fin surface contact angles from bare to superhydrophobicity under air-source heat pump operating conditions. The seed average height, radius, number, and frost density at the early stage of frost were analyzed. As the surface contact angle increased, the seed average height and number increased, while the seed radius and frost density decreased. A correlation with a Fourier number was proposed from the measured data. With the correlation, the large and small frost retardation effect regions were identified.

Experimental investigation of frost retardation for superhydrophobic surface using a luminance meter

We experimentally investigated the phenomena of frost retardation in terms of the heat exchanger fins with various water contact angles under normal air-source heat-pump operating conditions. We first introduced a new experimental method using a luminance meter, which measured the light intensity from the surface, and determined the phase-change time, for quantitatively defining the frost stages. The phenomena of frost retardation was analyzed for 10 samples with different water contact angles (75°–160°) at different refrigerant temperatures. When the refrigerant temperature was −10°C or −12°C, the effect of frost retardation increased remarkably with superhydrophobic surfaces. However, when the refrigerant temperature was −8°C, the effect of superhydrophobicity diminished at water contact angles greater than 150°.

Performance Estimation and Optimal Operation of a CO2 Heat Pump Water Heating System

The daily performance of a CO2 heat pump water heating system with a hot water storage tank is affected by the history of daily hot water demand and heat pump operating conditions. To attain the maximum system performance, it is important to estimate the daily changes in the system performance values accurately in relation to those in hot water demand and heat pump operating conditions, and determine the operating conditions optimally based on the estimation. In this paper, neural network models are used for this estimation, and the values of model parameters are identified by a global optimization method. In addition, the outlet water temperature for during operation and the inlet water temperature for shutdown are determined to maximize the system efficiency subject to a lower limit for the volume of unused hot water. The validity and effectiveness of this approach are ascertained by a numerical study using a simulated hot water demand.

C222 CO_2ヒートポンプ給湯システムにおける運転条件の最適化 : 給湯需要量の確定条件下における検討(OS-13:ヒートポンプの高性能化)

The daily performance of a CO_2 heat pump water heating system with a hot water storage tank is affected by the history of daily hot water demand and heat pump operating conditions. It is important to estimate the values of daily performance criteria accurately under daily changes in hot water demand and operating conditions for optimal operation. In previous papers, a neural network model has been proposed for this estimation, and it has turned out that the estimated values of daily performance criteria have high accuracy. In this paper, this model is applied to determination of operating conditions to attain the optimal system performance under certain hot water demand. The validity and effectiveness of this approach are ascertained by a numerical study using a simulated hot water demand.

1314 CO_2ヒートポンプ給湯システムにおける性能日変化の推定(ヒートポンプ運転条件決定の拡張)(GS-8 動力エネルギーシステム)

1314 CO_2ヒートポンプ給湯システムにおける性能日変化の推定(ヒートポンプ運転条件決定の拡張)(GS-8 動力エネルギーシステム)

Refrigeration systems with minimized refrigerant charge: System design and performance

Independently of the choice of refrigerant, environmental and/or safety issues can be minimized by reducing leakage and the amount of refrigerant charge in heat pump or refrigeration systems, preferably both. In the investigation reported here, a laboratory test rig was built, simulating a water-to-water heat pump with a heating capacity of 5 kW. The system was designed to minimize the charge of refrigerant mainly by use of minichannel aluminium heat exchangers and a compact system design. It was shown that the system could be run with 200 g of propane at typical domestic heat pump operating conditions without reduction in the heating coefficient of performance (COP1) compared with a traditional design. Additional charge reduction is possible by selecting proper compressor lubrication oils or by employing a compressor simply using less lubrication oil.

Effects of Evaporator Frosting on the Performance of an Air-to-Air Heat Pump

This paper shows the development and use of a transient model for evaluating frost formation on a parallel-plate heat pump evaporator. A frost formation model is derived by applying the equations of conservation of mass, momentum, and energy, as well as empirical correlations, to calculate the growth and densification of the frost layer. The frost formation model is validated by comparison with experimental results. The frost formation model is then incorporated into the evaporator subroutine of an existing heat pump model to calculate performance losses due to frosting as a function of weather conditions and time of operation since the last evaporator defrost. Performance loss calculation includes the effect of air pressure drop through the evaporator and the reduction in evaporator temperature caused by the growth of the frost layer. The results show frost formation parameters and heat pump COP as a function of time and ambient conditions. It is determined that there is a range of ambient temperatures and humidities in which frosting effects are most severe, and this range is explored to calculate heat pump operating conditions. The heat pump analysis results are expected to be useful in predicting optimum defrosting conditions, and to evaluate alternative methods for defrosting.

A heat exchanger model for mixtures and pure refrigerant cycle simulations

This paper describes a heat exchanger simulation developed for transient and steady state cycle simulations of mixtures and pure components. The simulation focuses on air to refrigerant condensers and evaporators found in residential heat pumps. The refrigerant differential momentum, continuity, species and energy equations are solved for these components and the steady state results are verified experimentally. Ten different heat transfer correlations for condensation and evaporation are evaluated to determine which best reproduces experimental data. Of those tested Jung and Radermacher's (1989, Int. J. Heat Mass Transfer 32 2435–2446) heat transfer correlation worked the best for evaporation while Dobson et al.'s (1994, ACRC Project 37) correlation worked the best for condensation. The experimentally determined capacity of four cross flow heat exchangers operating as condensers and evaporators with four different refrigerants is compared to the simulation results. The capacities predicted by the simulation agreed with the experimental results within ±8.0%. Furthermore, the simulation is used to quantify the effects of using a zeotropic mixture, R-407C, with cross, parallel and counter flow heat exchangers. As compared to a typical cross flow heat exchanger at typical heat pump operating conditions, the simulation predits that a pure parallel flow heat exchanger can decrease capacity by as much as 8.3% while a pure counter flow heat exchanger can increase performance by up to 4.4%.

Model-based Optimizing Control of a Water-to-Water Heat Pump Unit

This paper outlines the basic principles of on-line model-based steady-state optimizing control of continuous processes, and illustrates how this control approach can be used to optimize the operating conditions of heat pumps. The multilayer approach of hierarchical control theory is used to synthesise the control structure, and the control objectives are decomposed into regulatory and optimizing control tasks. The optimization problem in the optimizing control system is solved within an infeasible path nonlinear programming approach, where the performance criterion, the adaptive steady-state process model, and the operational feasibility constraints are solved simultaneously using a sequential quadratic programming (SQP) algorithm. An on-line model-based optimizing control algorithm is implemented on a personal computer and used to minimize the energy consumption of an experimental water-to-water electric-motor driven heat pump unit. During a period of steady process operation, process data is gathered and used to update parameters in the steady-state heat pump model. The updated process model is then used to calculate new set-points for the regulatory control system that minimize the total electric power input to the heat pump unit while not violating the operational feasibility constraints. The various energy losses in the heat pump unit are shown to verify the ability of the optimizing control system to conserve energy.

Effect of the design variables on the energy performance and size parameters of a heat transformer based on the system acetone/H2/2-propanol

A high-temperature chemical heat pump based on the system acetone/H2/2-propanol for waste heat recovery was studied. Two reversible catalytic chemical reactions are involved in this system. The waste heat (at 333–353 K) is recovered by means of the endothermic liquid-phase dehydrogenation of 2-propanol, and is upgraded at high temperature (453–473 K) by the reverse reaction, the exothermic gaseous-phase hydrogenation of acetone. In this process, a fraction of the recovered waste heat is removed at low temperature (303 K), to carry out the separation by vapour rectification between acetone and 2-propanol. A mathematical model was developed, that permits the study of the effect of the heat pump operating conditions on the energetic performance (COP), exergetic efficiency and size parameters. Also, this model allows the estimation the optimal range for the system control variables. Under these conditions, the energy and size parameters have been calculated on a basis of 0.32 MW upgraded heat.