Heat Recovery Unit Research Articles

Towards an Efficient Multi-Generation System Providing Power, Cooling, Heating, and Freshwater for Residential Buildings Operated with Solar-Driven ORC

In buildings, multi-generation systems are a promising technology that can replace discrete traditional energy production methods. A multi-generation system makes it possible to efficiently produce electricity, cooling, heating, and freshwater simultaneously. This study involved the numerical analysis of a modified proposed novel solar-driven multi-generation system (MGS-II) integrated with the Organic Rankine Cycle (ORC), Humidification–Dehumidification Desalination System (HDH), and Desiccant Cooling System (DCS) by using heat recovery and thermal energy storage (TES) units. In addition, a comparison study with the basic multi-generation system (MGS-I) is performed. The proposed system is designed to supply electricity, air conditioning, domestic heating, and fresh water to small/medium-sized buildings. How operating conditions affect system productivity and performance metrics have been investigated. The results show that the proposed multi-generation system (MGS-II) can produce electrical power, space cooling, domestic heating and fresh water while maintaining comfortable conditions inside the conditioned space. Moreover, the MGS-II outperforms the MGS-I system, and the maximum MGS-II system productivity; electricity production (\({W_{net}^{\bullet}}\)), freshwater (\({m_{fresh}^{\bullet} }\)), space cooling (\({Q_{cooling}^{\bullet} }\)), and domestic heating (\({Q_{heating}^{\bullet} }\)) are 102.3 kW, 141.5 kg/h, 20.77 kW, and 225 kW, respectively. In addition, the highest total gained output ratio (TGOR), specific total gained energy (STG), and specific total gained energy equivalent price (STGP) of the MGS-II system are 0.6303, 3.824 kWh/m2, and 0.149 USD/m2, respectively. The accepted ranges of comfortable space-supplied air conditions (temperature and humidity) are 15.5–18.2 °C and 9.2–12.00 gv/kga for both systems, MGS-I and MGS-II. Finally, the current system (MGS-II) has the maximum of the system’s performance indicators and productivity (TGOR and \({{\overset{.}{m}}_{fresh} }\)) compared with the other reported systems.

The thermal performance and applicability analysis of the composite ventilation system with heat recovery in ultra-low energy buildings

By analyzing the energy transfer process of building ventilators with heat recovery, a novel building ventilator with exhaust air heat pump enhanced by pump-driven loop heat pipe system was proposed and experimentally compared with the dual-loop heat pump and traditional heat pump system. During the test, the thermal performance of the prototype under three different operating modes was comprehensively studied, and then the energy-saving potential and applicability of the heat recovery units in the ultra-low energy buildings (ULEBs) were analyzed by using the DEST and MATLAB tools. Results showed that compared with the heat pump system, the composite system presented the highest energy efficiency ratio (EER) in the whole year, at 12.6 for winter and 4.8 for summer conditions, respectively. What's more, the energy recovered by the composite system is in line with the fresh air load, which can solve the problem of energy recovery attenuation of traditional ventilators in cold climate conditions. In addition, the composite system had great applicability in ULEBs, and the energy-saving ratio was 35.3% and 14.5% in Harbin and Kunming, respectively. Future works are to improve the performance of the pump-driven loop heat pipe and heat pump unit under all operating conditions for better adaptability of the ventilators.

Simulation of a desiccant air-conditioning system integrated with dew-point indirect evaporative cooler for a school building

In this study, a desiccant based air-conditioning system supported by a dew-point indirect evaporative cooler, a direct evaporative cooler, two heat recovery units was investigated during a complete cooling season for air-conditioning of a school building located in Adana, Turkey. A mathematical model of the air-conditioning system was developed by deriving new equations for modelling two key components of the system, namely desiccant wheel and dew-point indirect evaporative cooler using the available correlations and experimental data. Effectiveness of desiccant wheel and dew-point evaporative cooler, heat transfer rates realized in the main system components, the thermal energy requirement to drive the system and cooling performance of the system are investigated thoroughly. The effect of desired building indoor air temperature and mixing ratio of exhaust air on the operation and performance of the system was detailed. The results show that it is possible to obtain desired comfort conditions within the building during complete cooling season with the air-conditioning system considered. The monthly average thermal COP is maximum in October with 0.78 and minimum in July with 0.22. The seasonal thermal COP of the system is 0.43.

Deep learning optimization and techno-environmental analysis of a solar-driven multigeneration system for producing sustainable hydrogen and electricity: A case study of SanFrancisco

In general, solar-driven systems have substantial heat loss; so that brought designers to consider organic Rankine cycle for heat recovery. However, it still wastes amount of energy in the organic Rankine cycle's condensers. In this context, the present study proposes a novel multigeneration system with the aim of hydrogen and cooling load production, as well as power generation using heat recovery units by considering environmental impacts. The present solar-driven system comprises two power cycles, thermoelectric generator, hydrogen production unit, and absorption chiller subsystem. Performance assessment of the system in terms of energy, exergy, economic, and environmental was executed using a developed programming code, based on a mathematical model. The model's functions were parametrically investigated by considering the most effective parameters. The time-consuming optimization process caused a machine learning optimization procedure to be employed. After optimization, the exergy efficiency, total cost rate, and hydrogen production rate of 13.05%, 101.4 $/h, and 5.15 kg/h were obtained, respectively. For optimized case, the environmental analysis showed that the amount of CO2 emission reduction rate was resulted in 203.2 kg/h, which is 70 kg/h more than the result of base case. San Francisco, as a case study, was investigated to be considered for the potential of implementing the proposed system. As a result, the hydrogen production rate of 5.94 kg/h and net power generation of 1001 kW were acquired at peak.

A Thermal-hydraulic assessment of condensing tube bank heat exchangers for heat and water recovery from flue gas

Condensing heat exchangers are capable of recovering a significant amount of latent heat at temperatures below 100 °C from the flue gas of combustion-based heating systems due to the presence of water vapor in their exhaust streams. However, the condensation of acids along with water vapor creates a highly-corrosive environment in these heat exchangers. As such, a large majority of these heat exchangers are made from corrosion-resistant alloys, such as stainless steel. Polymer-based materials are cost-effective and have great corrosion-resistant properties. Since the performance parameters of a heat and water recovery unit depend on the size and compactness of their heat exchangers, it is challenging to compare the overall performance of stainless-steel condensing heat exchangers with polymeric ones based on the data available in the literature. The main goal of the present study is to develop and assess the thermal–hydraulic performance of a proof-of-concept condensing heat exchanger made of fluorinated ethylene propylene compared to the same condensing heat exchanger made of stainless steel for heat and water recovery from flue gas. For this purpose, an in-depth parametric study is conducted experimentally to evaluate the water recovery efficiency, total heat recovery rate, and pressure drop in the flow paths. The results revealed that the water recovery efficiency of the unit with a specific size, declines when the mass flow rate of the gas increases, although it enhances the total heat recovery of the unit. Moreover, increasing the volumetric flow rate of the heat transfer fluid flow slightly increases the total heat recovery of the stainless-steel condensing heat exchanger, but has a negligible impact on the total heat recovery rate of the polymer-based heat exchanger. Increasing the humidity ratio of the flue gas or the inlet temperature of heat transfer fluid does not have any significant effect on the flue gas pressure drop. These findings are significantly important and novel as they unlock the potential of using polymer-based materials with thermally conductive additives for latent heat recovery from flue gas.

Performance and design analyses of various configurations of dew point evaporative cooling-based desiccant air-conditioning (DAC) systems for hot and humid conditions

Thermally driven desiccant- and evaporative cooling-based technologies are promising greener and cheaper alternatives to compressor-based systems due to the separate handling of latent and sensible loads. Desiccant air-conditioning (DAC) systems comprise a desiccant dehumidifier, a sensible cooling unit, a heat source for regeneration, and a heat recovery unit. These components of a DAC system can be arranged in various ways to give different configurations with varying advantages and disadvantages. In this study, five configurations of thermally driven desiccant dehumidifier- and dew point evaporative cooling (DPEC)-based DAC systems were investigated. Seven evaluation criteria namely regeneration temperature, desiccant moisture removal capacity, COPt, DPEC L/H, heat exchanger UA, system size, and fan power requirement were employed. Results show that the standard cycle in ventilation mode offers the highest COPt despite having the highest regeneration temperature. Recirculation of the return room air can operate at a significantly lower regeneration temperature at the expense of larger equipment size and much lower COPt. DAC with an internally cooled dehumidification can operate at low regeneration temperature at the expense of higher fan power and slightly lower COPt. Dividing the dehumidification process into two stages can offer operation at moderately lower regeneration temperature without severely affecting the other criteria. This study can serve as a guide for the selection of an appropriate DAC configuration for space cooling depending on the objective criteria and the resources available.

An innovative four-objective dragonfly-inspired optimization algorithm for an efficient, green, and cost-effective waste heat recovery from SOFC

This work proposes a novel yet practical dragonfly optimization algorithm that addresses four competing objectives simultaneously. The proposed algorithm is applied to a hybrid system driven by the solid oxide fuel cell (SOFC) integrated with waste heat recovery units. A function-fitting neural network is developed to combine the thermodynamic model of the system with the dragonfly algorithm to mitigate the calculation time. According to the optimization outcomes, the optimum parameters create significantly more power and have a greater exergy efficiency and reduced product costs and CO2 emissions compared to the design condition. The sensitivity analysis reveals that while the turbine inlet temperatures of power cycles are ineffective, the fuel utilization factor and the current density significantly impact performance indicators. The scatter distribution indicates that the fuel cell temperature and steam-to-carbon ratio should be kept at their lowest bound. The Sankey graph shows that the fuel cell and afterburner are the main sources of irreversibility. According to the chord diagram, the SOFC unit with a cost rate of 13.2 $/h accounts for more than 29% of the overall cost. Finally, under ideal conditions, the flue gas condensation process produces an additional 94.22 kW of power and 760,056 L/day of drinkable water.

Organic Rankine Cycle as the Waste Heat Recovery Unit of Solid Oxide Fuel Cell: A Novel System Design for the Electric Vehicle Charging Stations Using Batteries as a Backup/Storage Unit

The novelty of this study is to suggest a novel design for electric vehicle charging stations using fuel cell technology. The proposed system benefits from the Organic Rankine Cycle (ORC) to utilize the exhaust energy of the Solid Oxide Fuel Cell (SOFC) stacks in addition to the Lithium-Ion battery to improve the efficiency by partial-load operation of the stacks at night. The study is supported by the thermodynamic analysis to obtain the characteristics of the system in each state point. To analyze the operation of the system during the partial-load operation, the dynamic performance of the system was developed during the day. Furthermore, the environmental impacts of the system were evaluated considering eighteen parameters using a life-cycle assessment (LCA). LCA results also revealed the effects of different fuels and working fluids for the SOFC stacks and ORC, respectively. Results show that the combination of SOFC and ORC units can generate 264.02 kWh with the respective overall energy and exergy efficiencies of 48.96% and 48.51%. The suggested 264.02 kWh contributes to global warming (kg CO2 eq) by 5.17 × 105, 8.36 × 104, 2.5 × 105, 1.98 × 105, and 6.79 × 104 using methane, bio-methanol, natural gas, biogas, and hydrogen as the fuel of the SOFC stacks.

Recovery of waste heat from proton exchange membrane fuel cells – A review

This work discusses the novel application of proton exchange membrane fuel cells (PEMFC) in the transport sector as well as portable applications. This kind of fuel cell produces a considerable quantity of heat while in operation. This quantity of heat is about 45–60% of entire energy composition of the hydrogen that is introduced into the cell. A correctly built cooling system must be used to efficiently eliminate produced heat from the stack to extend the stack's life and preserve its efficiency throughout its entire lifespan. Using appropriate thermal management techniques coupled with exploiting possibilities for fuel cell heat recovery may significantly improve size, cost, etc., while also reducing its total energy consumption. It is possible to collect and utilise the heat produced by PEMFC in other applications. A thorough analysis of heat recovery possibilities in this type of fuel cells is presented in this investigation. Similarly, the study further touched on the need for experimental studies into waste heat recovery from proton exchange membrane fuel cells as most of the recent work being championed are modelling based and does not really present a real life scenario of the system investigated. The need for investigations into the environmental performance of the waste heat recovery unit coupled to the proton exchange fuel cell system is also another important research direction that must be considered in future studies. Finally most of the studies on waste heat recovery from fuel cells have largely employed the use of organic Rankine cycle but other types of thermodynamic cycles like Kalina cycle is however recommended for further investigations due to their range of operation hence making them suitable for low and high temperature proton exchange membrane fuel cells.

Environmental and exergoeconomic assessments of a novel biomass gasification based solid oxide fuel cell and heat engine hybrid energy system

ABSTRACT Recently, the exploitation of renewable energies and technologies in order to reduce the restrictions of fossil fuels is the attention of energy managers and engineers. Additionally, energy production cycles based on solid oxide fuel cells (SOFCs) are known for their versatility in fuel intake. In this regard, in the current article the thermodynamic-conceptual assessment of a novel combined energy system (CES) based on biomass gasification is developed. The proposed CES is comprised of four main units: a biomass gasification unit, a reformer fuel cell unit (based on SOFC), a waste heat recovery unit (WHRU), and an ignition engine (homogeneous charge compression type). The biomass gasification unit is considered as a fuel supply unit of proposed energy process. A larger fraction of CES electricity is produced through the fuel cell unit. Moreover, additional electric power is produced through the ignition engine (IE) unit. The combustible fuel for IE unit is obtained during the chemical reactions of the fuel cell unit. Further, the WHRU is responsible for the heat recovery of the fuel cell and IE units, which balances the thermal power of the process. Embedding of a unit to recover the heat of the fuel cell units and the engine can be improving the performance of the cycle. The main goal of the article is to provide a thermodynamic-conceptual evaluation of the system considering energy, exergy, exergoeconomic, and environmental analysis to achieve a comprehensive feasibility study. According to the energy analysis, it was determined that the considered CES can produce around 1.09 MW of electricity and 0.36 MW of heat. Additionally, the values obtained for electrical and total energy efficiencies were 50.5% and 68.7%, respectively. The total exergy destroyed by the considered process and the total exergy efficiency were yielded as nearly 1.1 MW and 51.6%, respectively. Besides that, the specific cost rates of electric power yielded by fuel cell and IE units were almost 8.81 and 10.04 USD/GJ, indicating that the electric power produced through the fuel cell unit is a cheaper method. Moreover, compared to petroleum and coal-driven plants, the considered CES can reduce the amount of emitted CO2 by nearly 47.7% and 62.4%, respectively.

Development and monitoring of the MEED high efficient shower heat recovery unit

In well isolated dwellings especially with multiple residents domestic hot water (DHW) accounts often for more than 50% of the energy consumption.Currently there exist shower heat recovery units which recover 40 - 70 percent of the heat in the shower water. This efficiency can drop due to fouling of the heat exchanger, which is often not accessible. Further this is a component efficiency. The system efficiency also depends on the cooling down of the shower water due to evaporation and conduction losses to wall and floor tiles. During renovation it is often practically only possible to preheat the cold water port of the thermostat with the shower heat recovery unit. The cold water feed to the boiler would then not be preheated. In apartments it is not possible to install the highly efficient pipe-in-pipe heat exchangers as they have to be installed on the floor below the bathroom. Which only leaves shower tray heat recovery units which are in the lower range of the mentioned efficiency. In practice therefore during renovation shower heat recovery is not often applied.To address these problems a new patented concept for shower heat recovery has been developed. The Multi Energy Efficient Shower cabin (MEED) involves an insulated shower cabin (tray and walls) which is closed to minimize evaporation losses. The hot shower water is pumped up and flows over an integrated helix heat exchanger. This heat exchanger is able to extract 82% of the heat and is accessible for cleaning. In the shower cabin also an electrical 10 liter 6 kW boiler is integrated, so all cold water is preheated and directly hot water is provided which minimalizes pipeline losses. The MEED has enough capacity to shower endlessly. The MEED has been installed in existing social rental housing, private housing and in hotels. First monitoring results indicate a system efficiency of more than 70%. Aside the shower the MEED is able to provide all DHW, which makes a storage vessel superfluous. This is provides important space gain in smaller dwellings.

Numerical analysis of heat and mass transfer in micropolar nanofluids flow through lid driven cavity: Finite volume approach

In this article, the heat and mass transfer mechanism of micropolar nanofluid embedded with Buoyancy force and magnetic field across an enclosure has been analyzed. Mass, energy, and momentum equations are required to construct the mathematical model to evaluate the efficacy of thermal performance of nanoparticles.The motivation for this study is to improve heat and mass transfer efficiency in heat transfer equipment and heat recovery units in industrial and engineering processes. Given the signification of dimensional analysis, 2D model is set up in their dimensionless context. In addition, the finite volume approach (FVM) is employed for numerical simulations. The thermophoresis and Brownian motion parameters has been considered for the temperature field, as proven via simulation. As a result of the random mobility of nanoparticles, more heat is emitted inside the enclosure. Furthermore, mass diffusivity and Schmidt number are inversely related,so that mass diffusion inside the cavity is faster for small values of Schmidt number. Additionally, it is discovered that a high vortex viscosity parameter produces a weak concentration field and has significant behavior when thermophoresis parameter and Reynolds number are significant. The simulations are captured in graphical form, and their results are explained in detail.

Risk Assessment of Delay for CEMS and WHRU Installation Project on Plant Shutdown at Central Processing Gas Gundih

This paper addresses a risk assessment of delay for installation of Continuous Emission Monitoring System and Waste Heat Recovery Unit as an effort to fulfil compliance with the Regulation of the State Minister of the Environment Number 13 of 2009 concerning Quality Standards for Emissions from Immovable Sources for Oil and Gas Businesses and Activities. The installation of the unit consists of three steps, pre-shutdown, window shutdown and post shutdown. In accordance with Gas Sale Agreement, that the entire period of normal maintenance work that causes gas to not flow, should not be more than 15 (fifteen) days every year. The planning and implementation of maintenance is very important by utilizing the condition of the window shutdown to avoid material and non-material losses. Reviewing the vulnerability of this project, it is necessary to conduct research that assesses the level of risk of project delays using the ISO 31000:2018 risk management concept approach, through identification of risk variables from several literature studies, risk analysis through Group Discussion Forums, and risk management efforts to reduce risk of delays in the installation project. From the risk identification, 30 risk variables that affect project delays consist of 2 High categories, 3 Medium to High categories, 15 Medium categories, 6 Low to Medium categories and 4 Low categories. The Risk Treatment carried out in the high and Medium to high categories resulted in 9 mandatory RCOs to reduce delays and 1 RCO to speed up the implementation schedule from 19 days to 13 days and earn a profit of $615,000 because the process of selling gas to consumers can be accelerated by 2 days.

Comprehensive Carbon Emission and Economic Analysis on Nearly Zero-Energy Buildings in Different Regions of China

Considering the comprehensive effect of building carbon emissions, cost savings is of great significance in nearly-zero-energy buildings (NZEBs). Previous research mostly focused on studying the impact of technical measures in pilot projects. The characteristics of different cities or climate zones have only been considered in a few studies, and the selection of cities is often limited. At times, only one city is considered in each climate zone. Therefore, this study selected 15 cities to better cover climate zone characteristics according to the variation in weather and solar radiation conditions. A pilot NZEB project was chosen as the research subject, in which the energy consumption was monitored and compared across different categories using simulated values by EnergyPlus software. Various NZEB technologies were considered, such as the high-performance building envelope, the fresh air heat recovery unit (FAHRU), demand-controlled ventilation (DCV), a high-efficiency HVAC and lighting system, daylighting, and photovoltaic (PV). The simulated carbon emission intensities in severe cold, cold, and hot summer and cold winter (HSCW) climate zones were 21.97 kgCO2/m2, 19.60 kgCO2/m2, and 15.40 kgCO2/m2, respectively. The combined use of various NZEB technologies resulted in incremental costs of 998.86 CNY/m2, 870.61 CNY/m2, and 656.58 CNY/m2. The results indicated that the HSCW region had the best carbon emission reduction potential and cost-effectiveness when adopting NZEB strategies. Although the incremental cost of passive strategies produced by the envelope system is higher than active strategies produced by the HVAC system and lighting system, the effect of reducing the building’s heating load is a primary and urgent concern. The findings may provide a reference for similar buildings in different climate zones worldwide.

Climate change mitigation technologies detection and evaluation: case of buildings

PurposeThe building and construction industry has a significant potential to reduce adverse climate change effects. There are plans to improve the natural resource use and greenhouse gas emissions caused by the buildings by choosing energy-efficient technologies, renewable energy sources and sustainable architectural and constructional elements. This study systematically reviews the patent data for climate change mitigation technologies related to buildings, aiming to detect their relative importance and evaluate each technology in the Y02B network.Design/methodology/approachThe applied approach covers the process of (1) selecting high-impact technology, (2) collecting patent data from the USPTO database, (3) creating a citation frequency matrix using cooperative patent classification codes, (4) linking high-impact patents with analytical network process method, (5) limiting centrality of identifying core technologies from indicators and (6) creating a technology network map with social network analysis.FindingsThe study results show that energy-saving control techniques, energy-efficient lighting devices, end-user electricity consumption, management technologies and systems that convert solar energy into electrical energy are core solutions that reduce the effects of climate change. In addition, solutions that will support core technologies and whose effects are expected to increase in the coming years are energy-efficient heating, ventilating and air conditioning systems, smart grid integration, hybrid renewable energy systems, fuel cells, free cooling and heat recovery units and glazing technologies.Originality/valueMost of the studies on patent analysis have failed to demonstrate any convincing evidence down to the lowest component groups of an entire technology network. The applied approach considers and evaluates each component included in a technology network from a holistic perspective.

Horizontal Shower Heat Exchanger as an Effective Domestic Hot Water Heating Alternative

Wastewater has significant potential as a source of clean energy. This energy can be used both within external sewer networks and on the scale of individual residential buildings, and the use of shower heat exchangers appears to be the most reasonable solution. However, in the case of Poland, the problem is still the unwillingness of society to use this type of solution, caused mainly by the lack of space for the installation of vertical drain water heat recovery (DWHR) units and the low efficiency of horizontal units. In response to this issue, the efficiency of a new compact shower heat exchanger designed to be mounted below the shower tray, as well as its linear counterpart, was investigated under various operating conditions. In addition, the financial efficiency of using the compact DWHR unit with average water consumption for showering was evaluated. For this purpose, discount methods were used to estimate the financial efficiency of investments. The study showed that the compact shower heat exchanger has higher efficiency than its linear counterpart. Depending on the temperature of cold water and the flow rate of both media through the heat exchanger, it achieves efficiencies ranging from 22.43% to 31.82%, while the efficiency of the linear DWHR unit did not exceed 23.03% in the study. The financial analysis showed that its use is particularly beneficial when the building uses an electric hot water heater. The investment’s sensitivity to changes in the independent variables is small in this case, even with low water consumption per shower. The only exceptions are investment outlays. Therefore, the compact DWHR unit is a clean energy device, which in many cases is financially viable.

A framework of data modeling and artificial intelligence for environmental-friendly energy system: Application of Kalina cycle improved with fuel cell and thermoelectric module

Geothermal energy-driven systems with integrated waste heat recovery units such as the use of fuel cells and thermoelectric module can help to improve the renewable energy contribution in the energy mix. Data-driven optimization can improve their economic and environmental performance and their macro-projection can help in the achievement of net-zero plans. This article extends the use of a framework containing the usage of data modeling and artificial intelligence to conduct different optimization scenarios of the geothermal-driven energy system. It includes the improvement of the economic, exergetic, energetic, and environmental performance through the development of various optimization scenarios. This is done through the development of an extensive thermodynamic model and validation based upon energy, exergy, economic, and environmental evaluations. Different machine learning techniques are adapted for digital twinning of the six performance indicators as a function of nine design variables including operational, source, and economic variables. It is shown that the artificial neural network offers the best statistical fit as compared to the other machine learning techniques including RMSE: 0.1768, R2:0.9999, MSE:0.0312, and MAE:0.1107 for the total work output. Energy-efficient design has yielded a total work output of 1044.86 kW, with a first law efficiency of 0.3322. The economic design offers the lowest cost of electricity at only 34.004 $/hr. The sensitivity analysis has shown that the following parameters are the most sensitivity: turbine inlet temperature (18.19%) and pressure (18.23%), geothermal inlet temperature (16.34%) and pressure (18.00%), and the ammonia water concentration at the inlet of separator (15.96%).

INVESTIGATION OF MODES JOINT OPERATION OF HEAT UTILIZERS AND BOILER UNITS

Given the share of energy consumption by powerful industrial enterprises in the overall balance of world consumption, it can be shown that at this stage of technology development, primary energy is not used efficiently enough, turning more into unused heat. Increasing the use of secondary energy resources reduces the consumption of primary resources, the cost of which is constantly growing, and solves the problem of improving the environmental situation in the locations of large enterprises. Thermal secondary energy losses are reduced by installing tail heating surfaces, such as economizers and air heaters.
 The operation of the boiler unit is characterized by changes in its basic parameters over time, largely depending on the degree of load on the boiler. The degree of loading of the economizer affects the efficiency of its work. Determining the parameters of joint operation of heat recovery units and the boiler unit with changes in heat capacity will determine the most rational modes of operation of the system in terms of fuel economy.
 The aim of the study is to determine the characteristic indicators of joint operation of the boiler unit at different degrees of its load, with heat recovery units installed in the required amount to determine the most efficient modes of operation of the system.
 Economizers have the lowest thermal efficiency at a load of about 40% of the boiler power, and the highest at rated load. The results of calculations of the joint operation of the boiler unit with heat recovery units show significant changes in the possible cooling temperature of the combustion products behind the boiler when the boiler load changes. Using the above technique, it is possible to determine such a combination of the number of utilizers and different distribution of combustion products between them, at which the optimal gas temperature can be achieved for each specific mode of operation of the installation.

Economical heat recovery dynamic control and business model for supermarket refrigeration system coupled with district heating system

Large amounts of waste heat during the cooling process of supermarket refrigeration systems (SRS) would be released. A heat recovery strategy potentially contributes to reducing the supermarket’s heating costs related to buying heat from a district heating system (DHS). This paper explores the techno-economic feasibility of heat recovery for a real SRS integrated with a heat recovery unit (HRU) in terms of designing a dynamic heat recovery control (HRC) and business models. A cost-effective HRC is firstly developed for HRU to optimally manipulate the amount of heat recovered, thereby minimizing the real-time heat recovery cost. Furthermore, the business models of heat recovery under a long-term operation are proposed based on two transactional strategies between the SRS and DHS. A field test of the dynamic heat recovery for a remote SRS in Copenhagen Nordhavn area is conducted which demonstrates the proposed HRC algorithm can have a benefit of 0.49€ from a 3-h heat recovery operation. Moreover, the one-year operation of the SRS is also simulated which proves the developed two business models of heat recovery can achieve significant savings of 93% and 41% in energy costs.

Effects of number of objective functions on the optimization of a hybrid building integrated photovoltaic/thermal-heat recovery wheel unit

The present study examines the effect of the number of objective functions on the optimal performance of an exhaust air heat recovery unit including a building integrated photovoltaic/thermal unit (BIPV-T) and a heat recovery wheel (HRW). The unit is able to precool/preheat the outdoor air and generate electricity. Four objective functions are introduced to optimize the performance of the system from energy, energy, economic and environmental perspectives and all the possible single-objective, two-objective, three-objective and four-objective optimizations are conducted and the results are compared. Seven geometrical and operating variables consisting of the width, depth, and length of the BIPV-T channel, air mass flow rate, and rotational speed, length, and depth of the HRW unit are chosen as the decision parameters. The outcomes revealed that if a designer expects the examined unit to supply the entire energy and exergy required by building and the production of extra energy and exergy is worthless, then the optimization of unit performance based on the maximization of the amount of undischarged CO2 (Scenario 2) will be the best and the most effective scenario for the single-objective optimization of the unit.