22 research outputs found

    Development of an energy digital twin from a hotel supervision system using building energy modelling

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    In this work, the utilization of the supervision system of a five-story hotel located in Northern Italy as tool to calibrate and validate a building energy model (BEM) is evaluated. The BEM is created using the TRNSYS simulation environment with the aim to develop a digital twin, to study the energy consumption of the building-HVAC system. The procedure for the supervision system preparation and the data analysis procedure is presented. The digital twin is then used to compare two control strategies for the thermostats’ control during summer to increase the energy efficiency of the building-HVAC system, and to use the heat storage properties of the building envelope to shift and shave the peaks of power demands. Control rules that allow a better match between electrical energy demand and availability, developed, and tested using the BEM, are pursued with the final goal to prepare the inclusion of the hotel in a smart grid. The building is modelled using TRNSYS Type 56 as a multi-zone building, with 96 thermal zones while the building monitoring is performed during the summer season from June to October 2022

    Subcooling with AC and adiabatic gas cooling for energy efficiency improvement: field tests and modelling of CO2 booster systems

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    In the last decade several plant configurations and components have been proposed to increase the efficiency of CO2 refrigeration systems. Among these, subcooling is considered a simple but effective solution, together with the employment of adiabatic cooling systems at the gas cooler. In this work, a fully instrumented CO2 booster plant installed in a supermarket is considered, to compare parallel compression, subcooling and adiabatic cooling. Subcooling is performed taking advantage of chilled water available from the HVAC system. The experimental data are used to validate a model for the comparison on a yearly basis. Parallel compression and subcooling show to be almost equivalent in terms of yearly energy use, while the adiabatic cooling system gives the best performance. Comparisons reveal that the subcooler cooling capacity should be chosen carefully to avoid oversizing, while the influence of the EER for the chiller appears quite small. Subcooling performed at the expense of an HVAC plant shows to be an interesting solution, while a great benefit was experienced with the employment of an adiabatic gas cooler

    Analysis of different control strategies for improved performance at off design operation in a CO2 heat pump water heater

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    A commercial heat pump water heater using CO2 as refrigerant is considered in this work. A theoretical model was first validated via experimental data, and then tested to evaluate various operations. A fundamental and well-known parameter for optimizing the system performance is controlling the high stage pressure. In this work, a logic control was derived to maximize performance even under off-design conditions. Poor stratification, or improper sizing of the water system may lead to compressor outlet temperature too high, which should be limited to avoid problems with lubricants. Usually, the maximum compressor discharge temperature is 140 °C and, to control this temperature, this work proposes and compares three different control logic, acting on the back pressure valve or on the internal heat exchanger (IHX) with the aim of gaining efficiency and reducing the operating cost

    Effects of different moisture sorption curves on hygrothermal simulations of timber buildings

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    Building energy simulations are a key tool to design high performance buildings capable of facing the future challenges and to help reaching the emissions reduction targets. Currently, thermal properties of materials used in most building energy simulations are assumed to be constant and not dependent of moisture content and temperature. Heat and moisture dynamic transfer models allow to simulate building envelope performance considering thermal resistance reduction due to moisture effects. These models are generally considered more accurate than the heat transfer models and they could be used to simulate the heat transfer (increased by water vapour storage) and the moisture buffering effect on the indoor environment. For the simulation to be performed, hygrothermal material properties should be known as functions of moisture content. Nevertheless, hygrothermal material properties are rarely available and correlations from the literature have to be used. In this study, the moisture storage curves of CLT, OSB and two types of wood fibre insulation have been measured with a dynamic vapour sorption analyser. The other hygrothermal properties are estimated from values measured in previous studies or taken from the literature. The simulations of two small single room buildings in four Italian locations are performed with the software EnergyPlus, considering an ideal HVAC system, to calculate the heating and cooling needs of the building. The HAMT (heat and moisture transfer) module of EnergyPlus is used. With the results presented in this study, it is possible to evaluate how an approximated curve affects the results of a whole-building simulation in terms of wall average water content, indoor air relative humidity and heating/cooling loads

    Geographical and temporal distribution of SARS-CoV-2 clades in the WHO European Region, January to June 2020

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    We show the distribution of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) genetic clades over time and between countries and outline potential genomic surveillance objectives. We applied three genomic nomenclature systems to all sequence data from the World Health Organization European Region available until 10 July 2020. We highlight the importance of real-time sequencing and data dissemination in a pandemic situation, compare the nomenclatures and lay a foundation for future European genomic surveillance of SARS-CoV-2

    Demand side management through latent thermal storage in HVAC systems coupled with commercial refrigeration units

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    The electrical energy demand of an HVAC plant can be better managed by using latent thermal energy storage when time-of-use tariffs or peak tariffs are in force, in a view of Demand Side Management of the electrical grid. Nonetheless, air conditioning systems show a marked use of electrical power during the day, and the peak in the cooling load mostly corresponds to the lowest performance of the chiller due to outdoor conditions, thus giving rise to a marked peak in electricity use. An HVAC plant of a supermarket is supplied with an ice thermal energy storage, with the main aim of shaving the peak in electrical power use. The latent thermal storage is charged at night-time by employing the CO2 commercial refrigeration system of the supermarket, which is considerably part-loaded during the shop closing time. During daytime, the thermal storage can be operated in replacement of or in parallel to a reversible heat pump, operating as a water chiller for air conditioning. The same heat pump operates at wintertime for heating purposes, in parallel with heat recovery from the CO2 commercial refrigeration plant. A model of the whole system is presented, and possible solutions are shown for demand side management purposes

    Influence of cooling load profile on the prediction of energy use in commercial refrigeration p

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    The cooling load of a commercial refrigeration system is affected by the operating conditions of the refrigerated display cabinets and cold rooms, mainly through their mutual interactions with the indoor environment in terms of temperature and humidity. In this paper, the effects of cooling load profiles in the prediction of the annual energy use are investigated, comparing constant and simplified load functions to a more realistic simulation-based approach. The latter is made using a calibrated hourly model of the whole commercial refrigeration system, which includes a transcritical CO2 booster system with its control rules and the simulation of the display cabinets and cold rooms. These user-defined components are implemented in the TRNSYS environment and linked to the dynamic building simulation. The analysis is performed for different system configurations and weather conditions. The results show that the load profile affects the comparison in terms of energy effectiveness among different system configurations, and should be considered for a fair assessmen

    Multiyear hygrothermal performance simulation of historic building envelopes

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    The objective of this work is to quantify the effects of the short-term climate change with a multiyear (MY) approach on the results of the heat and moisture transfer simulations of an historic building located in Udine (Italy) and to evaluate if a single year simulation could be representative of the results obtained with the MY. The hygrothermal performance and the moisture related risk are evaluated for a brick wall with and without insulation, with a MY of 25 years and with three single years selected form the MY. The software DELPHIN is used for the simulations and the damage indicators are calculated using simplified methods (number of days with unfavourable conditions). Depending on the damage considered, the years have different effects on the studied wall. The simulations that use the MY weather file allow to obtain more accurate results than using one-year simulations, but the effort and time required for the interpretation of the simulation results could be not acceptable. It is then shown that the choice of a representative weather file is crucial to the results of the risk analysis and that considering more than one weather file is necessary to obtain representative results for different damages mechanisms

    Monitoring of a CO2 commercial refrigeration plant to evaluate the effect of a dedicated mechanical subcooler

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    Since the phase out of high-GWP refrigerants started, it has been necessary to find an environmental-friendly alternative to reduce direct emissions to the atmosphere. At the same time, a high efficiency of refrigeration systems must be ensured, in order to limit also indirect greenhouse gas emissions from the electricity consumption. In commercial refrigeration, CO2 is a refrigerant which can maintain limited the detrimental emissions of a refrigeration plant, and simultaneously can guarantee a high level of safety when used as working fluid. But while the environmental impact of refrigerant leakage and safety risks are easily minimized by the use of CO2, thanks to the fact that it has a GWP of 1, is non-flammable and non-toxic, achieving high energy efficiency of the plants is not trivial. This is mainly due to the fact that the refrigeration cycle becomes transcritical at relatively low heat rejection temperature. Several strategies can be implemented in order to increase the energy efficiency of CO2 refrigeration systems. Among most effective techniques, ejectors [1], overfed evaporators [2] and parallel compression [3] allow to reach an energy performance comparable, or even higher, to that achieved using traditional fluids [4]. In addition, CO2 refrigeration plants can also be profitably integrated with space heating, domestic hot water and air conditioning systems, to the limit case of an all-in-one system which can provide all the thermal loads of a commercial building with a high energy efficiency, as demonstrated by Karampour et al. [5]. Another way which can be used to increase the performance of a CO2 refrigeration plant is the use of a Dedicated Mechanical Subcooler (DMS). It consists of a small refrigeration unit which cools down the refrigerant at the outlet to the condenser/gas cooler of the main plant. As shown, theoretically in D’Agaro et al. [6] and experimentally in Llopis et al. [7], it can be a viable solution to increase energy efficiency of a commercial refrigeration unit. However, there is still a lack of real application monitoring [8]. In this work, the preliminary results of a real commercial CO2 plant are presented, with the aim to confirm through field data that the use of a DMS can achieve a decrease of energy consumption of a real commercial plant

    Control strategies for CO2 heat pump water heater at off design operation

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    CO2 heat pumps for hot water production, using carbon dioxide as a refrigerant, are on the rise due to their potential to reduce greenhouse gas emissions compared to traditional gas boilers and hydrofluorocarbon systems. However, these heat pumps face efficiency challenges, operating in a transcritical mode. Researchers are developing control strategies and solutions like the Internal Heat Exchanger (IHX) to address these issues. Studies in the open literature have focused on CO2 heat pump optimization. Wang et al. [1] identified correlations for optimizing gas cooler pressure based on ambient and water outlet temperatures, while Qi et al. [2] emphasized CO2 temperature at the gas cooler exit as a crucial factor in determining optimal discharge pressure. Efficiency improvement is a central goal for CO2 heat pump designers, with IHX being a promising solution. Kim et al. [3] found that IHX size influences optimal discharge pressure, refrigerant flow rate, and compressor power in water-to-water CO2 heat pumps. Cao et al. [4] explored the impact of IHX on optimal gas cooler pressure, concluding that IHX operation, especially under certain conditions, reduces optimal discharge pressure. They also developed a model accounting for heat exchanger pinch points to assess IHX efficiency's effect on overall system performance. However, it's worth noting that while IHX improves efficiency, it can increase discharge temperatures, particularly with higher return water temperatures at the gas cooler inlet, as observed by Otón-Martinez et al. [5]. In this study, a CO2 water heater heat pump with an IHX is analyzed through a numerical model and validated with experimental data. The research explores three different control strategies with the goal of enhancing performance while managing discharge temperature under off-design conditions
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