Optimal Heat Pump Research Articles

An analytical solution to optimal heat pump integration

Heat pump integration has a large potential for reducing carbon emissions and operating costs of industrial processes. The Break-even COP method determines the maximum economically- or environmentally feasible heat pump temperature and the level of process heat electrification under specified economic conditions. However, this method fails to capture the optimal heat pump temperature and the possible emissions- and costs reduction in sensible heat processes. The present work introduces an analytical equation based on the Lorenz efficiency approach to determine the optimal heat pump sink temperature, maximizing the operating costs savings or the emission savings. Furthermore, it advances the break-even method to account for heat pumps with a temperature glide by applying a Lorenz efficiency approach. The method is applied to a spray-drier case study, showing a reduction on operation costs of 7.8 % and emissions by 11.9 % by a partial process electrification of 32 %. A parameter study is conducted, underscoring the importance of accurate predictions of the Lorenz efficiency factor and the electricity-to-fuel price and emissions ratios in heat pump integration studies.

The impact of heat pump load flexibility on its process integration and economics

The conventional methodology of heat pump integration has found application in various industries, including cheese production, spray drying, milk evaporation systems, brewing, and meat processing. While several approaches have been developed for optimizing direct and indirect heat recovery in non-continuous industrial processes, the optimal integration of heat pumps in non-continuous processes remains a challenge.This paper introduces a systematic methodology that leverages extensive datasets of time-resolved industrial process data to determine the optimal heat pump integration and the level of heat pump load flexibility that maximizes the economic benefit. Thus, the work establishes a connection between the domain of Process Integration and heat pump load flexibility. Additionally, the study provides insights on the requirements for load flexibility during the design phase of the heat pump, offering an estimation on the need for research on heat pump flexibility.The findings indicate the presence of a load flexibility threshold in the examined case study, beyond which additional load flexibility yields diminishing returns. Furthermore, the study shows that different heat pump integration parameters are chosen based on the heat pump’s capability for load flexibility. Within the investigated case, a heat pump with a minimum load of 55% increases the net present value by 19.3% compared to a load inflexible heat pump.

Increasing heat pump adoption: analysing multiple perspectives on preparing homes for heat pumps in the UK

Heat pumps are a solution for decarbonising home heating in the UK. However, the readiness of UK homes for heat pumps is an area of concern regarding the policies aimed at increasing heat pump adoption. This work combines multiple perspectives in evaluating the technical readiness of homes with the market readiness of installers and homeowners to proceed with installing heat pumps. The effectiveness of past heating and energy efficiency policies in the UK are reviewed, along with building regulations, incentives to promote energy efficiency and the effectiveness of heat pump technology in heating homes. Current policies support the cost of a heat pump but home improvements to make homes ‘heat pump-ready’ can be necessary to achieve optimal heat pump system performance.This paper suggests the UK will face three major challenges. First, analysis highlights an ‘eligibility-readiness gap’ describing the difference between homes ‘eligible’ (50%) for the Government’s Boiler Upgrade Scheme—a subsidy for heat pump installations—and the likely level of homes that are heat pump-ready (11%) for successful heat pump installations. Second, semi-structured interviews with heat pump installers identified gaps in capacity to deliver the necessary works to make homes heat pump-ready. As small or medium enterprises, the majority of installers do not currently see adding home improvement services to their existing business model as beneficial. All installers highlighted the need for Government to address the cost of electricity relative to gas. Third, a national survey of homeowners in England with gas boilers (n = 1,021) revealed low awareness of the necessary work to make homes heat pump-ready and low willingness to spend money on them unless supported by Government. This paper shows that the processes and costs involved in making homes heat pump-ready before successful design and installation are underappreciated by homeowners, inadequately served by industry, and insufficiently supported by Government.

Electrification of amine-based CO2 capture utilizing heat pumps

Capturing CO2 is necessary to abate the climate crisis. Amine CO2 capture is the most mature technology but suffers from high thermal energy consumption for solvent regeneration. Heat pumps are a proven technology with which to electrify industrial processes. This study investigates an integrated heat pump system used to electrify an amine CO2 capture unit for a biogas upgrading process using aqueous monoethanolamine. The study evaluates the potential of such integrated systems through the overall energy consumption at varied stripper pressures between 0.313 to 1.813 bara and includes a techno-economic analysis to determine the levelized cost. The most optimal heat pump scenario utilizes a vacuum operated stripper at 0.513 bara and reduces the overall energy consumption by 68 % compared to a classical amine scrubbing unit. The techno-economic analysis shows that the levelized costs for biogas upgrading per MWh of produced biomethane may be reduced by up to 33 % from 47 €/MWh to 31 €/MWh by implementing heat pump electrification systems and a vacuum operated stripper compared to a scenario using natural gas.

Large size heat pumps advanced cost functions introducing the impact of design COP on capital costs

Power-to-heat technologies offer low-carbon heat and integrate electricity and heating sectors. Moreover, high-temperature heat pumps can supply process heat for industries, like food, and feed early district heating networks. However, their viability is often jeopardized by high capital costs. Fluid selection affects variable and capital (TCI) costs, impacting the Coefficient of Performance (COP) and equipment sizing. Therefore, identifying the best fluid and estimating capital costs with simple and reliable cost functions are crucial for assessing heat pump market opportunities. This paper presents a multi-objective optimization, based on a detailed technoeconomic model, to find the optimal heat pump solution for different applications. Moreover, the proposed Pareto analysis is employed to derive new cost functions considering the working fluid, source/supply temperatures, and the impact of design COP on TCI, with a formulation facilitating understanding and quantification of each factor. This methodology promotes heat pump adoption in industrial electrification, especially for high-temperature applications, potentially replacing natural gas boilers. Three case studies demonstrate the robustness of the approach to assessing capital costs, showing low deviation (<8%) between the detailed technoeconomic model and the fast-to-applicate new cost functions. The innovative cost functions ensure easy but accurate assessments, fostering confidence in transitioning to heat pump solutions.

Heat pump integration in non-continuous industrial processes by Dynamic Pinch Analysis Targeting

A key strategy for the transition towards a low-carbon economy is the electrification of industrial heat. Heat pumps can recover and upgrade excess or waste heat. They present a highly efficient component to decarbonize process heating. In Pinch Analysis, most approaches to design the heat recovery system as well as the utility system are based on a single operating point or a couple of operating point. In the past, this was due to the lack of temporally detailed process data. However, the available process data is expected to increase drastically by the use of transient process simulation models. Thus, a method is needed which interprets the data correctly and assists with design choices.This study proposes a methodology for the design and sizing of a heat pump based on the simulated annual process data of an industrial process. Three approaches are explored: (1) the conventional approach for heat pump integration by application of the Time Average Model (TAM), (2) an approach that investigates the optimal heat pump parameters for each data point by the principles of Pinch Analysis and mathematical optimization and (3) an optimization method, which considers the entire annual process data as well as thermo-economic objectives such as net present value (NPV) and internal rate of return (IRR).The new methodology compared to the conventional TAM approach is able to design a 33 % smaller heat pump, which reduces the annual operating cost by an additional 2.2 %. The NPV and IRR are more than tripled.

Modeling and investigation of the performance of a solar-assisted ground-coupled CO2 heat pump for space and water heating

The rise in the popularity of heat pumps should be accompanied by the increase in the utilization of environmentally-safe working fluids. To push for wider uptake of hybrid heat pump systems that use natural working fluids, information about their performance and operating characteristics should be made available. This study models a CO2 solar-assisted ground-coupled heat pump (SAGCHP) system and investigates its performance for space and water heating. Sensitivity analysis, parametric study, and long-term performance simulation were implemented, with the system’s seasonal performance factor (SPF), levelized cost of heating (LCOH), and ground temperature change (GTC) considered as performance indicators. It was seen that ensuring a good combination of design and operating specifications can result in an SPF (∼3.5) and LCOH (0.184 USD/kWh) that are comparable with those of SAGCHP systems that use conventional working fluids. The heat pump’s high-side pressure and output temperature exhibited notable effects on all the performance indicators. Below the optimal operating pressure, a 5% increase in the heat pump’s high-side pressure brought about a ∼7–10% improvement to the SPF, a ∼3–5% reduction to the LCOH, and a ∼6–10% increase to the GTC. Reducing the output temperature by 5% increased the SPF by ∼7–8%, decreased the LCOH by ∼3%, and increased the GTC by ∼6%. Parametric studies identified the presence of optimal heat pump discharge pressure and heat source circulation rate that should be used for operations. Long-term simulation shows that managing the GTC ensures the longevity of the system. Rather than oversizing the borehole heat exchangers (BHEs), it is more practical to reduce ground temperature decline by increasing the BHE spacing or by adding solar collectors.

Uncertainty-based optimal energy retrofit methodology for building heat electrification with enhanced energy flexibility and climate adaptability

To reach net zero emissions by 2050, the UK government relies heavily on heat degasification in buildings by using heat pump technology. However, existing buildings may have terminal radiators that require a higher operating temperature than what heat pumps typically provide. Increasing the size of radiators and thermally insulating building envelopes could be a potential solution, but the feasibility of these practices is uncertain due to space constraints and high retrofit costs. This study investigates the feasibility and potential benefits of incorporating air-source heat pumps into existing gas boiler heating systems to meet heating demands. The proposed probabilistic optimal air-source heat pump design method enhances energy flexibility and climate adaptability, taking into account a wide range of uncertainty sources and multiple flexibility services (e.g., energy and ancillary services). Heating systems of three educational buildings at the University of Cambridge are used as a testbed to assess and validate the effectiveness of the proposed method, under future climate scenarios and projected decreases in heating demand due to climate change. Results indicate that the best retrofit alternative of the hybrid heating system reduces carbon emissions by 88%, total costs by 54% over its lifespan, and has an average payback period of around 3 years. Air-source heat pumps can meet the majority of the heating demand (around 80%) with gas boilers used for “top-up” heating during high demand. Furthermore, air-source heat pumps' design capacity can fulfil future cooling demand even if retrofit optimization is initially focused on meeting heating needs.

MILP design optimization of heat pump systems in German residential buildings

Heat pump systems are a key technology to decarbonize the building sector by electrifying the heat supply. Especially in refurbishments, heat pump systems compete against less cost intensive technologies such as gas boilers. To motivate homeowners to invest in heat pumps instead of gas boilers and thus, increase heat pumps’ market penetration, heat pump systems have to become more economical. In Europe, common heat pump system design standards use static rules and neglect system interdependencies to design a system ensuring energy supply as the main objective. However, the literature shows great potential to optimize the system design economically by including system dynamics and interdependencies between different components already in the design process. Therefore, we propose a mixed-integer linear program as a mathematical optimization framework to determine the economical optimal heat pump system design for a single-family house. Both design and operation of all components are optimized simultaneously considering system dynamics and component interdependencies. By optimizing the system, we reduce investment costs significantly about 45% in comparison to normative standards, while maintaining security of supply and not increasing electrical energy consumption. To further accelerate the building sector decarbonization, extension of operation optimization is highly recommended.

Effects of market and climatic conditions over a gas turbine combined cycle integrated with a Heat Pump for inlet cooling

The growing need of dispatchable units, capable to balance the variable renewable energy electrical production leads to the development of strategies aimed at increasing power plants operational flexibility and global efficiency in part-load operation. A highly efficient heat pump (integrated in a conventional natural gas combined cycle is here proposed as a flexibility enhancement solution. Such concept, applied to power oriented combined cycle, allows to modify the compressor intake temperature with a consequent increase of the power production. While this operation for open cycle gas turbine is beneficial also to electric efficiency, combined cycles’ efficiency is less sensitive to the temperature variation and thus more influenced by the auxiliary consumption. The selection of the proper heat pump size for the proposed layout was based on an optimization process considering both combined cycle and heat pump off-design performance. After a statistical analysis of climatic data and their correlations with energy market condition for the six Italian price zones, the models developed were applied to assess the thermoeconomic potential of the proposed layout. This work highlights how a proper optimization process influences both revenues and size optimization and to highlight how such integrated system can be selected at its best considering typical market and climatic frames. The ratio between the air-cooled heat pump electrical consumption and the electrical combined cycle capacity that maximize power production increase was found to be 1/100. This finding can be extended to the others world Humid subtropical climate and Mediterranean hot summer climates zones. It is underlined how electrical market conditions could jeopardize the installation profits even under favourable climatic potential reducing the optimal economic heat pump size. Using off-design curves and optimization algorithm in performing coupling analysis appears to be more effective, with respect to simplified calculations under unfavourable economic and climate conditions.

Performance assessment of optimized heat pump water heaters using low-GWP refrigerants for high- and low-temperature applications

In this study, performance improvements of optimized heat pump water heaters (HPWHs) employing low global warming potential refrigerants are numerically evaluated against the performance of the conventional R-410A HPWH. A simulation model for HPWHs is developed and validated based on experimental results obtained in the R-410A and R-32 HPWHs. The performances of the HPWHs employing R-32, R-446A, and L-41b are simulated considering for high-temperature applications (HTAs) and low-temperature applications (LTAs) based on EN 14511. The heat exchanger design parameters of the HPWHs are optimized for achieving the maximum coefficient of performance (COP) for each alternative refrigerant. The optimized L-41b HPWH exhibits the highest COP, and the COP improvements thereof are 6.3% and 4.6% in the HTA and LTA conditions, respectively, compared with those of the R-410A HPWH. Moreover, the total equivalent warming impacts of the optimized HPWHs employing the alternative refrigerants are 5.9–9.9% lower than those of the R-410A HPWH.

Control of Heat Pumps with CO2 Emission Intensity Forecasts

An optimized heat pump control for building heating was developed for minimizing CO 2 emissions from related electrical power generation. The control is using weather and CO 2 emission forecasts as inputs to a Model Predictive Control (MPC)—a multivariate control algorithm using a dynamic process model, constraints and a cost function to be minimized. In a simulation study, the control was applied using weather and power grid conditions during a full-year period in 2017–2018 for the power bidding zone DK2 (East, Denmark). Two scenarios were studied; one with a family house and one with an office building. The buildings were dimensioned based on standards and building codes/regulations. The main results are measured as the CO 2 emission savings relative to a classical thermostatic control. Note that this only measures the gain achieved using the MPC control, that is, the energy flexibility, not the absolute savings. The results show that around 16% of savings could have been achieved during the period in well-insulated new buildings with floor heating. Further, a sensitivity analysis was carried out to evaluate the effect of various building properties, for example, level of insulation and thermal capacity. Danish building codes from 1977 and forward were used as benchmarks for insulation levels. It was shown that both insulation and thermal mass influence the achievable flexibility savings, especially for floor heating. Buildings that comply with building codes later than 1979 could provide flexibility emission savings of around 10%, while buildings that comply with earlier codes provided savings in the range of 0–5% depending on the heating system and thermal mass.

Modelling the two-phase flow of propane in a capillary tube: Determination of the two-phase viscosity based on detailed experiments

Abstract Capillary tubes are widely used as throttle device in small heat pumps. A reliable and predictive capillary model within an overall heat pump model can reveal the design potential of the capillary towards an optimized heat pump operation. A flow model is presented that predicts the single and two-phase flow of propane through a straight copper capillary tube of 1.1799 mm inner diameter and 1 m length that evokes a pressure drop. An extensive and precise experimental database is generated by thorough experiments also providing refined specifications of the inner diameter and roughness of the capillary tube. Experiments are carried out for inlet pressures of 16-25 bar, mass flows of 13.5-18 kgh − 1 (3430-4573 kgm − 2 s − 1 ) and subcoolings of 5-9 K. Based on the generated experimental database, multiple common two-phase viscosity correlations are evaluated within the flow model. A proposed modified two-phase viscosity correlation results in the best fit of experimental and predicted the flow of propane through the capillary with a mean relative error of only 4 %.

Pulse vacuum pretreatment technology and neural network optimization in drying of tilapia fillets with heat pump

Low-temperature (20 ~ 40°C) heat pump drying technology for food products has advantages over conventional high temperature (45 ~ 90°C) hot air drying but requires proper pretreatment to ensure high-quality drying products. Subsequently, experimental investigations were carried out for drying of tilapia fillets with heat pump and at different pulse vacuum pretreatment parameters including vacuum cycle rate, cycle number, vacuum pressure, and concentration of trehalose impregnation liquid. The quality of the completed drying product was then evaluated and compared by eight quality indexes containing whiteness, ratio of water loss to solid content increase rate during osmosis dehydration (dehydration efficiency index, DEI), Ca2+-ATPase (adenosine triphosphatase) activity, rehydration rate, hardness, elasticity, glueyness, and chewiness. These indexes are thus generalized into one comprehensive score based on the effective weight of each index on the product quality and analysis of the fuzzy hierarchy process. The experimental measurements were applied to examine the effect of the pretreatment parameters on the product quality indexes and comprehensive score. Accordingly, an artificial neural network model has been developed to train and achieve the optimal pretreatment parameters based on the maximum product quality comprehensive score. The obtained optimal pretreatment parameters have been validated with the measurements. Ultimately, the optimal heat pump drying process is significant and can be applied to an actual application for different food product dryings. Practical applications Heat pump technology is one of the prospective processing methods for the drying of tilapia fillets. However, the relative low-temperature heat pump drying process would increase the drying time and thus deteriorates the risk of food product. To cope with this, a high efficient pretreatment method needs to be designed and applied. Correspondingly, in the project described by this paper, extensive measurements were designed and carried out on the product drying with a heat pump. Consequently, a fuzzy hierarchy process was applied to process the relevant experimental data and generate a comprehensive score for each test. Ultimately, an artificial neural network model has been developed to train and achieve the optimal pretreatment parameters. The optimal heat pump drying process is significant and can be applied to an actual application for different food product dryings.

Optimal design and operation of a central domestic hot water heat pump system for a group of dwellings employing low temperature waste heat as a source

In this work, a study of an energy recovery system from a low-grade temperature source based on heat pumps for domestic hot water is done. The main components of the system are a pre-heating heat exchanger, an optimized heat pump for domestic hot water production, and a variable-volume storage tank. A model has been developed in TRNSYS to analyse the best configuration and control strategy of the system in order to satisfy the profile demands of 10, 20, and 30 multifamily houses, which are considered as a representative target market for this type of application. From this analysis, the influence of the design/sizing parameters on the system CO2 emissions has been obtained and a design criterium for their minimization has been supplied. Finally, a sensitivity analysis based on different net and heat source temperatures has been done in order to estimate the generalizability of the proposed solution. The obtained results show that this kind of system, with the proper design, sizing, and operation, offers potential CO2 emissions reductions by a factor of almost five compared to a conventional gas boiler system but a bad system selection could reduce this potential benefit up to 25%.

Experimental investigation of the thermal dispersion coefficient under forced groundwater flow for designing an optimal groundwater heat pump (GWHP) system

Mechanical thermal dispersion has often been neglected or underestimated in the simulation of heat transport in porous media, e.g., by using zero or the default value in simulators, or by using the scaling law for solute dispersivity as a thermal dispersivity value. However, large amounts of water usually injected in groundwater heat pump (GWHP) systems may increase the groundwater flow velocity much faster than natural flow and thus change the importance of mechanical dispersion in heat transport. In this study, to investigate the effects of water injection on the flow field, thermal dispersion coefficient, and associated heat transport process, a laboratory experiment using two different heat sources as tracers was performed at various background flow velocities (Re < 0.52). The analysis results from analytical and numerical models indicate that injected water increases both flow velocities and thermal dispersion coefficients, especially near the injection well, and thus makes the effect of mechanical dispersion on heat transport very important even at low background flow velocity. This result was also found in the field-based modeling results, but the radius of hydraulic and thermal effects was larger. In particular, thermal dispersivity on a field scale is known to increase depending on the scale of measurement and the degree of aquifer heterogeneity. Therefore, to ensure the efficiency and sustainability in field applications such as GWHP systems, it is necessary to evaluate site-specific thermal dispersivity through field experiments.

Optimal heat pump integration in industrial processes

Among the options for industrial waste heat recovery and reuse which are currently discussed, heat pumping receives far less attention than other technologies (e.g. organic rankine cycles). This, in particular, can be linked to a lack of comprehensive methods for optimal design of industrial heat pump and refrigeration systems, which must take into account technical insights, mathematical principles and state-of-the-art features. Such methods could serve in a twofold manner: (1) in providing a foundation for analysis of heat pump economic and energetic saving potentials in different industries, and further (2) in giving directions for experimentalists and equipment manufacturers to adapt and develop heat pump equipment to better fit the process needs.This work presents a novel heat pump synthesis method embedded in a computational framework to provide a basis for such analysis. The superstructure-based approach is solved in a decomposition solution strategy based on mathematical programming. Heat pump features are incorporated in a comprehensive way while considering technical limitations and providing a set of solutions to allow expert-based decision making at the final stage.Benchmarking is completed by applying the method on a set of literature cases which yields improved-cost solutions between 5% and 30% compared to those reported previously. An extended version of one case is presented considering fluid selection, heat exchanger network (HEN) cost estimations, and technical constraints. The extended case highlights a trade-off between energy efficiency and system complexity expressed in number of compression stages, gas- and sub-cooling. This is especially evident when comparing the solutions with 3 and 5 compression stages causing an increase of the COP from 2.9 to 3.1 at 3% increase in total annualized costs (TAC).

In-depth analysis of the performance of hybrid desiccant cooling system incorporated with an electric heat pump

Aiming for improvement of the cooling performance, the hybrid desiccant cooling system (HDCS) is investigated and compared with a reference desiccant cooling system (RDCS). By replacing a sensible wheel of the RDCS with a heat pump, the HDCS is expected to increase the energy efficiency as well as to improve the system compactness. The cooling cycle is simulated and its results are compared with those of the RDCS. The analysis showed that specific cooling power of the HDCS increases from that of RDCS, promising the miniaturization of the system. Also, COP of HDCS was found to overtake the COP of RDCS in a particular range of heat pump capacity. For analysis of total energy consumption, a new parameter, Rv, the ratio of the primary energy factor of electrical energy to the primary energy factor of thermal energy was introduced. In the range of Rv (=5–10) such as from the CHP plants, the optimal heat pump capacity was estimated when the heat pump occupies 30–40% of the total cooling output of the HDCS. With the optimal configuration, the total energy consumption of HDCS reduces by 20–30% and the cooling capacity of HDCS increases by 40–60%, compared to RDCS.

Demand response optimized heat pump control for service sector buildings

With an increasing amount of volatile renewable electrical energy, the balancing of demand and supply becomes more and more demanding. Demand response is one of the emerging tools in this new landscape. Targeting service sector buildings, we investigated a tariff driven demand response model as a means to shave electrical peak loads and thus reducing grid balancing energy. In this paper is presented a software framework for load shifting which uses a tariff signal for the electric energy as minimization target. The framework can be used both on top of an existing building management system to shift heat generation towards low-tariff times, as well as to simulate load shifting for different buildings, heat pumps and storage configurations. Its modular architecture allows us to easily replace optimizers, weather data providers or building management system adapters. Our results show that even with the current TOU tariff system, up to 34 % of cost savings and up to 20 % reduction in energy consumption can be achieved. With Sub-MPC, a modified MPC optimizer, we could reduce computing times by a factor 50, while only slightly affecting the quality of the optimization.

Annual Performances of Reversible Air Source Heat Pumps for Space Conditioning

The paper presents the results obtained by a numerical simulation of a heating and cooling system based on a reversible air-to-water electric heat pump and electric resistances as back-up. According to the procedure suggested by the current standards EN 14825 and UNI/TS 11300-4, by using the bin method the influence of outdoor conditions and of the typology of heat pump installed has been investigated by determining the value assumed by the seasonal coefficient of performance (SCOPon), the seasonal efficiency ratio (SEER) and the annual performance factor (APF). The numerical results allow discussing the rules for an optimal heat pump sizing in a fixed site.