Domestic Hot Water Production Research Articles

Design and optimization of a geothermal absorption cooling system in a tropical climate

The electricity required for air conditioning is soaring worldwide. Absorption chillers represent an alternative to classical vapor compression systems, using heat instead of electricity. However, absorption chillers powered by renewable geothermal heat have received little attention so far. This paper introduces a system using a hot geothermal fluid (typically in the range of 80–110 °C) to produce cooling through a single-effect absorption chiller, and Domestic Hot Water (DHW) through a heat exchanger. It considers a hotel located in Martinique, a French Caribbean island. The electric consumption of every subsystem has been thoroughly estimated. The originality of this paper is twice: i) the system is modelled in TRNSYS software considering dynamic conditions, ii) the system undergoes surrogate modelling and multi-objective optimization to minimize both the cost and the CO2 content of the delivered thermal energy. Several scenarios are considered, depending upon the geothermal temperature, mass flow rate, well remoteness, and demand size. The studied system appears to be systematically more expensive than a combination of a classical vapor compression chiller and a boiler for DHW. However, it can significantly decrease the CO2 content of the provided energy, especially in an island where most electricity is generated from fossil fuels. The proximity of the geothermal well and the use of the warm water leaving the absorption generator (here for DHW production) appear to be key factors for system relevance, along with a hotter geothermal fluid (e.g., 110 °C instead of 80 °C).

Water–Energy–Nutrients Nexus of Urban Environments

The objective of this article is to deepen knowledge about the existing connections, at the level of urban environments, between energy, water, and nutrients (or food). Energy and basic resources—water and food—are closely interconnected, which is why the water–energy–food nexus constitutes the essential integrated approach to ensuring the sustainable development of humanity. This nexus is also valid in urban environments and can be adapted for buildings, interconnecting, in this case, water, energy, and nutrients. This article is a literature review in this area, intending to highlight the strong connections between water, energy, and nutrients at the level of buildings, integrating the results obtained in different studies and showing the global importance of this nexus. The water–energy relationship in buildings is already well known in terms of the production of domestic hot water or building pumping, for example, but it turns out that it goes far beyond this interrelationship, also having implications for public networks. Regarding the water–nutrients nexus in urban environments, it can play an important role in terms of food security for humanity, especially regarding the possibility of recovering phosphorus in buildings.

Performance analysis of a novel façade-based building integrated photovoltaic-thermal system with phase change material for domestic hot water

Since the current contribution of solar thermal energy to the amount of energy consumed for domestic hot water in buildings worldwide is very low (8.4 %, approximately), the potential of this renewable energy to meet the demand for domestic hot water is quite significant. In this context, this paper presents a new façade-based building integrated photovoltaic-thermal system with phase change material which has been patented recently. It is a modular device for installation on façades and roofs, enabling the production of domestic hot water and electricity using solar energy. The main novelty of the system lies in the use of a photovoltaic glass sheet, which improves the building’s aesthetics and facilitates the architectural integration of this type of devices. Thus, a photovoltaic glass is used for the production of electricity, a phase change material for heat storage and a water-phase change material exchanger for the production of domestic hot water. The design and verification stages of the system were developed for a case study under typical usage conditions. Two dimensional numerical models of five different configurations (of the energy harvesting and storage module and two dimensional and three dimensional numerical models of the finned exchanger were carried out to simulate the charge and discharge processes. The most suitable configuration of the system, characterised by a 12 mm vacuum gap and a low emissivity of the absorber, was able to meet the requirements in terms of water flow rate and supply temperature (45 °C) for a shower time of 5 min.

ANN-LSTM-A Water Consumption Prediction Based on Attention Mechanism Enhancement

To reduce the energy consumption of domestic hot water (DHW) production, it is necessary to reasonably select a water supply plan through early predictions of DHW consumption to optimize energy consumption. However, the fluctuations and intermittence of DHW consumption bring great challenges to the prediction of water consumption. In this paper, an ANN-LSTM-A water quantity prediction model based on attention mechanism (AM) enhancement is improved. The model includes an input layer, an AM layer, a hidden layer, and an output layer. Based on the combination of artificial neural network (ANN) and long short-term memory (LSTM) models, an AM is incorporated to address the issue of the traditional ANN model having difficulty capturing the long-term dependencies, such as lags and trends in time series, to improve the accuracy of the DHW consumption prediction. Through comparative experiments, it was found that the root mean square error of the ANN-LSTM-A model was 15.4%, 13.2%, and 13.2% lower than those of the ANN, LSTM, and ANN-LSTM models, respectively. The corresponding mean absolute error was 17.9%, 11.5%, and 8% lower than those of the ANN, LSTM, and ANN-LSTM models, respectively. The results showed that the proposed ANN-LSTM-A model yielded better performances in predicting DHW consumption than the ANN, LSTM, and ANN-LSTM models. This work provides an effective reference for the reasonable selection of the water supply plan and optimization of energy consumption.

Energy, exergy, and exergoeconomic analyses of an air source transcritical CO2 heat pump for simultaneous domestic hot water and space heating

The transcritical CO2 heat pump system experiences significant throttling losses in space heating operation due to the higher temperature of returning water. This paper presents an energy, exergy, and exergoeconomic analyses of an air source transcritical CO2 heat pump integrating a tri-partite gas cooler, which is an effective method to match CO2 temperature glide with water for simultaneous domestic hot water and space heating (DHW+SH) production. A pinch point-based numerical model is developed to find the optimal discharge pressure. This validated model is then utilized to investigate the impacts of water inlet temperature and ambient temperature. Two configurations are examined: one with only DHW supply and the other with DHW+SH supply. The results indicate that combining SH with DHW enhances COP by 7.5% with a 7.9% reduction in discharge pressure at 10 °C ambient temperature and 10 °C water inlet temperature. At a water temperature of 10 °C, exergy efficiency improves by 4%. The compressor accounts for 54%–60% of the total exergy loss. The DHW+SH system exhibits an average exergy destruction reduction of 7.6%. With each 5 °C rise in ambient temperature, the DHW+SH system’s total exergy destruction cost rate decreases on average 7.7% compared to the DHW system. Furthermore, the combined exergy destruction cost rate of GC2 and GC3 in DHW+SH is significantly lower (by 48.2%) than only GC3 in DHW. The exergoeconomic factors of the compressor, gas cooler 2, and gas cooler 3 emphasize the need to decrease their costs to enhance cost-effectiveness.

Energy, exergy, environment and techno-economic analysis of hybrid solar-biomass systems for space heating and hot water supply: Case study of a Hammam building

The main goal of this study is to assess the thermodynamic performance, environmental benefits and economic feasibility of using a new hybrid solar-biomass system (HSBS) for the production of domestic hot water at 60 °C and for the provision of space heating via an underfloor heating system in a Hammam building located in Marrakesh-Morocco. The HSBSs consists of small biomass pellet boilers in combination with three types of solar thermal systems (evacuated tube, flat plate and parabolic trough collectors). A TRNSYS simulation model of a biomass heating system was developed and validated against experimental data. Performance comparisons of the biomass system with various optimal HSBSs were then conducted, and their results evaluated in terms of energy, exergy, environmental, and economic perspectives. Comparisons between various collectors’ technology revealed that the optimum collector areas of 204 m2, 224 m2 and 300 m2 are responsible for the lowest Levelized Cost of Heat (LCOH) corresponding to about 0.0755 $/kWh, 0.0696 $/kWh and 0.0642 $/kWh when using PTC, FPC and ETC, respectively. Furthermore, the optimal HSBS with evacuated tube collectors is the most effective configuration with a solar fraction of 57 %, and a total life-cycle saving cost of 0.509 M$ for a total annual heat demand of 533 MWh. Moreover, the total energy and exergy efficiencies are calculated equal to 40 % and 3.9 %, respectively. The payback period is found to be around 4.9 years, the levelized cost of heat 0.0642 $/kWh, while the annual CO2 avoidance amounts to 656 tons.

Management of domestic hot water system based on the example of a gas-fired instantaneous water heater

Purpose: The aim of the study was to present the actual efficiency of a gas-fired instantaneous water heater for the production of domestic hot water. Design/methodology/approach: The object of the study was a gas-fired instantaneous domestic hot water heater located in a flat in Krakow. Measurements with a suitable device were carried out for three basic variants of hot water preparation, defined as showering, washing hands and washing dishes. Findings: The tests and analyses carried out have revealed that the current efficiency (average efficiency based on 3 measurements – 77.61%) differs radically from that indicated on the water heater data sheet. Such a drop in efficiency may be caused e.g. by fouling of the surface of the heat exchanger on the flue gas side and scaling of the exchanger on the heated side. Research limitations/implications: The tests proved that the heater did not reach its nominal efficiency during the tests, but on the other hand, simulations of different intensities and durations of water consumption did not drastically change the efficiency of hot water preparation. Practical implications: Regular cleaning of the exchanger would probably reduce the difference between the efficiency declared by the manufacturer and the one achieved during the tests. A clean heater will also ensure a sufficiently low level of carbon monoxide in the flue gas, which has a real impact on the safety of the appliance. Social implications: The values obtained from the measurements for each operating mode can help occupants understand how to prepare water most efficiently with this particular appliance, which will have a real impact on the bills they pay. The user will be provided with information on what percentage of energy they use from the volume of gas burned. Originality/value: Gas-fired instantaneous water heaters provide an efficient and energy-saving solution, especially in situations where the demand for hot water is low, and immediate access to it is crucial. Keywords: hot water, hot water management, gas-fired instantaneous water heater. Category of the paper: Research paper.

Simple solutions first—energy savings for domestic hot water through flow restrictors

Domestic hot water production is the second most important energy use in the European residential sector, nowadays accounting for 14% of the sector’s total final energy consumption. Despite its importance, the energy efficiency improvement rates for domestic hot water are lower than for other residential energy services, hence calling for energy-saving measures. One key measure is to install flow restrictors. Their advantages are the low upfront cost, easy installation, and suitability for integration into energy efficiency programs. Focusing on flow restrictors, this paper presents different methods for quantifying the energy savings using ex-ante and ex-post approaches: deemed savings (DES), dedicated measurements (DMs), and monthly and yearly billing analysis (SMBA and ABA). These methods were tested using information based on measurements (water flow, temperatures), historical billing analysis, a survey among inhabitants, and interviews with field experts. While measurements made at individual faucets or showerheads show significant water savings (20% and 33% respectively), energy savings associated with hot water production in the boiler (final energy) are significantly lower (around 10%) but far from being negligible. The main reasons for the difference are thermal losses related to hot water distribution in central heating systems, usages not affected by flow restrictors, and inhabitants removing them. We conclude that flow restrictors offer promising potential for short- to medium-term implementation. Given the simplicity of this solution, we recommend including it systematically in energy efficiency programs, as well as implementing a ban on fixtures with flow rates beyond a predefined level.

Artificial neural network model for predicting CO2 heat pump behaviour in domestic hot water and space heating systems

The natural refrigerant, CO2, possesses thermophysical properties that make it highly suitable for domestic hot water (DHW) production using heat pump technology. In this study, the development and validation of an artificial neural network (ANN) model that enables efficient design and control of a CO2 heat pump is presented. The study employs experimental data from a CO2 heat pump with a nominal heat capacity of 8 kW. The fully instrumented rig includes the heat pump and a pump rig designed to generate system temperatures representative of various space heat and DHW demands. A comprehensive dataset was generated through systematic variation of inlet temperatures and setpoints. The ANN provides predictions for outlet temperatures, heat production, and electricity consumption utilizing inlet flow rates, temperatures, and setpoints as inputs. These predictions are important for condition monitoring or in a smart operation management framework that determines optimal schedules for the machine.

The benefits of a recuperative layout of an ORC-based unit fed by a solar-assisted reservoir operating as a micro-cogeneration plant

Organic Rankine Cycle -based microcogeneration systems that exploit solar sources to generate electricity and domestic hot water simultaneously are promising solutions for reducing CO2 emissions in the residential energy-intensive sector. Such systems can be assisted by thermal energy storage reservoirs in which water is heated by solar energy and cooled by the direct use of thermal energy for domestic hot water production and acting as heat source of the power plant. An interesting plant layout optimisation involves the adoption of a recuperative heat exchanger to preheat the working fluid before it enters the heat recovery vapour generator, which is fed with the same working fluid leaving the expander. Despite the positive effect of recuperative heat exchanger adoption on the efficiency of the entire plant, the impact on electrical energy production at this microscale is not straightforward to assess as the heat source is represented by the water inside the reservoir and it is not a continuous high- or medium-temperature stream. The lack of experimental analyses in the literature on these applications makes this a debatable question.Thus, to fill this gap and quantitatively assess the benefits introduced by the adoption of a recuperative stage, a wide experimental comparison between recuperative and not-recuperative Organic Rankine Cycle-based power unit layout was performed. To support the experimental analysis, a comprehensive theoretical model of the Organic Rankine Cycle-based plant was developed and validated against experimental data.The experimental campaign demonstrated that the recuperative Organic Rankine Cycle-based unit required a lower working fluid flow rate for a given expander inlet temperature and pressure ratio. Consequently, a higher electrical power can be produced, requiring lower thermal power from a heat source. The reduction in the thermal power absorbed from the heat source, produced by a higher temperature incoming working fluid entering the Heat Recovery Vapor Generator, had a positive effect, allowing a longer-in-time working condition with a higher conversion efficiency intrinsically produced by the recuperative heat exchanger. Considering the annual electricity consumption of 2700 kWh of a family living in a city in central Italy, the contribution given by the recuperative Organic Rankine Cycle plant operating with a reservoir fed by 15 m2 of flat solar panels was 330 kWh, whereas without the recuperative stage, the production was 240 kWh. The cost of electricity saved justified the adoption of a recuperative heat exchanger.

Analysis of the performance and operation of a photovoltaic-battery heat pump system based on field measurement data

Photovoltaic-heat pump (PV-HP) combinations with battery and energy management systems are becoming increasingly popular due to their ability to increase the autarchy and utilization of self-generated PV electricity. This trend is driven by the ongoing electrification of the heating sector and the growing disparity between growing electricity costs and reducing feed-in tariffs in Germany. Smart control strategies can be employed to control and optimize the heat pump operation to achieve higher self-consumption of PV electricity. This work presents the evaluation results of a smart-grid ready controlled PV-HP-battery system in a single-family household in Germany, using 1-minute-high-resolution field measurement data. Within 12 months evaluation period, a self-consumption of 43 % was determined. The solar fraction of the HP amounts to 36 %, enabled also due to higher set temperatures for space heating and domestic hot water production. Accordingly, the SPF decreases by 4.0 % the space heating and by 5.7 % in the domestic hot water mode. The combined seasonal performance factor for the heat pump system increases from 4.2 to 6.7, when only considering the electricity taken from the grid and disregarding the locally generated electricity supplied from photovoltaic and battery units.

Achieving Net Zero Carbon Performance in a French Apartment Building?

Containing global warming to 1.5 °C implies staying on a given carbon budget and therefore being able to design net zero carbon buildings by 2050. A case study corresponding to a French residential building is used to assess the feasibility of achieving this target. Starting from an actual construction built in 2016, various improvement measures are studied: lowering heating energy needs, implementing bio-sourced materials and renewable energy systems (geothermal heat pump, solar domestic hot water production, and photovoltaic electricity production). Dynamic thermal simulation is used to evaluate energy consumption and overheating risk in hot periods. Greenhouse gas emissions are quantified using a consequential life cycle assessment approach, considering that during a transition period, exporting electricity avoids impacts corresponding to marginal production on the grid. Avoided impacts decrease and become zero when the grid is ultimately “decarbonized”. From this point, the building should be net zero emissions, but there remain unavoidable emissions. Residual GhG (greenhouse gas) emissions account for 5.6 kgCO2 eq/m2 annually. The possibility of offsetting these emissions is investigated, considering sequestration in forests or vegetation systems. A net zero emission level can be achieved, but on a national level, it would require that the whole sequestration potential of forest growth be devoted to offset emissions of new construction. A circular economy for construction products and equipment and considering water use will be needed to further decrease environmental impacts.

4E evaluations of salt hydrate-based solar thermochemical heat transformer system used for domestic hot water production

A critical step toward the widespread use of renewables is the development of effective energy storage technology. An impressive solution for energy storage and heat upgrade is the salt hydrate-based solar thermochemical heat transformer (THT). The article aims at the temperature lift effects of pressurization-assisted THT systems employing different salts to fulfill the heat requirements of domestic hot water (DHW) generation. To grasp the sustainability of the GJ-level THT systems, energy, exergy, economic, and environmental (4E) assessments are performed under various working conditions. Results manifest that the majority of THT systems enable discharging temperatures (Tdis) to surpass 65 °C, matching regular DHW production. Tdis can be further boosted by the two-stage pressurization whereas at the expense of lowering thermodynamic properties. The SrBr2-based system almost exhibits the best 4E performances with a Tdis of 74.3 °C, although its levelized energy cost (LEC) of 0.1162 $/kWh is slightly higher than that of the LiOH-based system (0.1147 $/kWh). Both systems yield great useable heat, up to 11,667 MJ and 11,140 MJ, respectively, with maximum exergy efficiency of 89.16 % and 63.41 %. Albeit capable of generating higher temperature DHW (≥90 °C), the useable heat and thermodynamic performances of the FeCl2 and CaCl2 based systems are unsatisfactory. By contrast, the K2CO3 and LiOH based systems render higher temperature DHW while ensuring acceptable thermodynamic properties and useable heat. Targeting the regular and higher temperature DHW productions, the lowest CO2 emissions are separately achieved by the SrBr2 and LiCl based systems, i.e., 15 kg/MWh and 56.2 kg/MWh; and the former shows the slowest growth rate in carbon emission with increased Tdis. Augmenting solar irradiation and duration contributes to reducing LEC, and the ideal operating conditions in thermo-economic performance may differ from system to system.

Rational Use of Energy in Sport Centers to Achieving Net Zero—The SAVE Project (Part B: Indoor Sports Hall)

Sports centers are significant energy consumers. This article outlines the engineering design for a comprehensive energy performance upgrade of the indoor sports hall in Arkalochori, Greece, and presents the projected results. The indoor sports hall constitutes a major sport facility on the mainland of Crete, hosting a broad cluster of sport municipal activities and the official basketball games of the local team in the 2nd national category. Having been constructed in the mid-1990s, the facility exhibits very low thermal performance, with considerably high U-factors for all constructive elements (from 4 to 5 W/m2∙K), still use of diesel oil for indoor space heating and domestic heat water production, and ineffective old lamps and luminaries covering the lighting needs of the facility. The energy performance upgrade of the indoor sports hall was studied, and the following passive and active measures were considered: Opaque-surfaces’ thermal insulation and openings’ replacement, stone wool panels, installation of heat pumps for indoor space conditioning, removal of diesel oil for any end use, production of domestic hot water from a novel solar-combi system, upgrade of lighting equipment, installation of solar tubes on the main sports hall roof for natural lighting as well as of a photovoltaic system for covering the remaining electricity consumption. With the proposed interventions, the studied building becomes a zero-energy facility. The payback period of the investment was calculated at 26 years on the basis of the avoided energy cost. This work was funded by the “NESOI” Horizon 2020 project and received the public award “Islands Gamechanger” competition of the NESOI project and the Clean Energy for EU Islands initiative.

Development of map-based models for the performance characterization in a new prototype of Dual Source Heat Pump

This paper presents the development of accurate map-based models for characterizing a new Dual Source Heat Pump prototype. This unit includes three braze plate heat exchangers and a round tube fin heat exchanger, allowing the unit to select different operating modes such as heat pump, chiller, and domestic hot water production using as source the ground or air. Therefore, due to the hybrid typology of this unit and the possibility of reversing the cycle, this work covers the main heat pump and refrigeration equipment technologies currently available on the market (air source and ground source units). The modeling strategy selected has been to provide several polynomial expressions to predict the performance of these units, i.e., compressor energy consumption and condenser and evaporator capacities. This approach allows obtaining accurate, compact, and easy-to-implement models for developing dynamic models of more complex systems where this type of unit – the heat pump – is an integrated part of the system. Currently, a clear example of this modeling strategy can be found in characterizing one of the main components installed in these machines, the compressor. The AHRI-540 standard specifies a polynomial model as a function of evaporating and condensing temperatures. In this sense, for the characterization of heat pumps, the polynomials developed depend only on the unit’s external variables, so they can be useful in many scenarios, obtaining direct feedback on the heat pump performance when developing a dynamic model to optimize system control strategies or to develop techno-economic studies. In this case, the hybrid typology of this unit makes it particularly relevant to optimize the control to manage the type of source to be used (air or ground), allowing the development of a more efficient and sustainable technology by selecting the most adequate source in terms of performance. This study focuses on obtaining the polynomial expressions that minimize the number of terms while simultaneously minimizing prediction error. By carefully selecting the most significant terms and suitable transformations in the characterized variables, the goal is to prevent overfitting, minimize potential extrapolation or interpolation errors and obtain polynomial expressions that can be fitted with small experimental samples. For this purpose, a detailed model implemented in a commercial software for heat pump characterization has been used, with which a large number of simulation results were generated. These simulation results include a fine meshing working map of the unit that allowed us to analyze the relationships between the characterized and external variables.

Experimental study on operating characteristics and control strategy of CO2 heat pump in circulating heating mode

The CO2 heat pump is a promising low carbon technology for domestic hot water production due to its potential heating advantages and the natural properties of CO2. However, the change pattern of operational parameters, heating time, and energy efficiency of CO2 heat pump in circulating heating mode remains to be fully revealed. Meanwhile, the matching control strategies to improve the system performance have not been developed. Firstly, we experimentally revealed the operating characteristics of CO2 heat pump in circulating heating mode. Results demonstrated that it is quite challenging to simultaneously maintain the lower input power, shorter heating time, and higher coefficient of performance (COP) without taking control measures. It is found that the circulating heating process could be divided into stable and upward periods, depending on the water temperature at the inlet of gas cooler. The deterioration of the system performance appears during the upward period, where the instantaneous COP drops from 4.1 to 3.1. This is because input power rises, while the heating capacity drops as the water temperature at the inlet of gas cooler increases. Secondly, we experimentally developed a matching control strategy to improve the system performance during the upward period. The control method is the correlation of optimal electronic expansion valve opening, and the regulation frequency is regulating for 1 °C per rise of the water temperature at the inlet of gas cooler. As a result, the overall COP increased by 3.71%, and the overall input power reduced by 3.74% while the heating time remained constant.

Experimental investigation, modeling and in-situ monitoring of a gas-driven absorption heat pump in Belgium

This work describes the methodology used to realize a performance analysis of an ammonia-water condensing gas absorption heat pump. This heat pump shows a nominal heating output of 18,9 kW for an outdoor temperature of 7 °C and a delivery temperature of 35 °C, and it is designed for domestic hot water and heating production. The experimental results obtained in the laboratory are contrasted with those obtained from the monitoring of two residential facilities in the northern part of Belgium. Experimental tests were carried out in a climatic chamber to emulate different outdoor climatic conditions based on a combination of the EN 12309 requirements and typical Belgium weather data. Measurements of gas consumption, electrical consumption, water flows, and temperatures were collected to compute performance indicators. On the other hand, the monitoring data was analyzed and contrasted with the experimental results to evaluate the field systems’ performance; the problems found and modifications made are described and discussed. The results show that the performance of the systems is highly dependent on the coupling with other appliances, on the operating conditions and control of the system, resulting in penalties that can be considerable depending on the configuration used. An empirical model calibrated with experimental data is proposed, as well as a penalization factor calibrated with the monitoring data. The results presented evidence the differences found between the studied facilities, highlighting the main role of proper installation and control not to diminish the main performance indicators.

Managing energy performance through heat pumps. Success drivers and barriers in residential sector

Abstract Despite the increasing interest in modern solutions for energy performance improvement in residential sector, a gap persists between literature development and current implementation practices on domestic heating and cooling through heat pumps technology. Homeowners are encouraged to manage their energy-related issues in a systematic manner to ensure continual improvement of energy efficiency. This paper attempts to explore the drivers and obstacles to the use of heat pumps system for domestic heating, cooling, and hot water production in the residential sector, in order to improve dwellings’ energy performance and reduce the carbon footprint. The study uses a regression model with a sample of 389 participants from Romania and shows that the availability of energy plans, voluntary association in an energy community, and mixed funding exert a positive influence, whereas bureaucracy, poor energy efficiency-related information, and fiscal incentives exert a negative influence on the intention of adopting heat pumps technology by homeowners.

Energy-Efficient Solutions: A Multi-Criteria Decision Aid Tool to Achieve the Targets of the European EPDB Directive

The building and construction sector has a significant impact on the CO2 emissions and pollutants released into the atmosphere, which contribute to climate change. The EPDB Directive mandates the achievement of minimum energy class E for all residential buildings by 2030 and energy class D by 2033. Particularly, in Italy, about 86% of the existing building stock predates the enactment of any energy laws or regulations, making it imperative to apply the energy efficiency interventions. This paper provides a support decision tool for the identification of the standardized interventions in the building envelope, the air conditioning system, and domestic hot water production. This study is focused on a specific construction period class (1976–1990) in six different climatic zones. The methodological approach is based on a cataloguing phase and the definition of ante operam energy classes as well as on case study identification, energy requalification intervention identification, solution simulations, and cost estimation. By simulating the standardized interventions for each climatic zone, a range of possible combinations is identified. The most advantageous ones are determined based on a cost–benefit analysis considering the potential class jump achieved. The research result is a matrix of energy efficiency interventions that is applicable to each climatic zone and can be extended to the existing housing stock.

Experimental Study on the Feasibility of Quick Startup of Instant Heat Pump Water Heaters Based on Active Control of Heat Sink Flow Step

The influence of flow step ratio (FSR) on the startup characteristics of instant heat pump water heaters (IHPWHs) with natural mixture M (R744/R290 (12/88)) under nominal conditions was studied experimentally to verify the feasibility of a new quick startup method. The results show that the FSR had a marked effect on the startup time of system performance parameters. Under the optimal FSR of 0.6, the shortest system startup time and available hot water supply time were 700 s and 250 s, respectively, which were markedly shorter than those in the conventional startup. Therefore, rapid startup of the system and rapid production of usable domestic hot water can be realized by controlling the flow step. The influence of flow step on the variation trend of system performance parameters was obviously different, and there was no slow warming section for the heat sink outlet temperature (HSOT) under three FSRs. The HSOT, heating capacity, and high pressure side pressures had the maximum values in the quick startup, and the maximum values were obviously affected by the FSR. The FSR had no marked effect on the minimum suction pressure. The refrigerant pressures and refrigerant temperatures fluctuated markedly in both rapid and conventional starts.