Energy Audit of an Industrial Site: A Case Study

Abstract In order to reduce energy consumptions for sustainable and energy-efficient manufacturing, continuous energy audit and process tracking of industrial machines are essential. Compared to other non-residential buildings that have been widely researched, industrial buildings are generally characterized by larger thermal loads, ventilation losses and pollution control requirements. This paper presents the results of a preliminary energy audit carried out on 8 large industrial buildings of a famous car manufacturing holding in Italy. Energy demand for heating varied from 6 to just over 74 kWh/m3year among the buildings of the site. The energy audit enabled to build a specific factory energy model which has been used in order to analyze the impact of various energy saving actions on the primary energy consumptions of the site. It has been demonstrated that in this specific case the improvement of the building envelopes and the optimization of the performances of the existing HVAC systems can determine a reduction of gas consumption up to 15% per year with a predicted annual economic saving of the order of 100000 €; the total simple pay-back time of the proposed thermal retrofitting is evaluated to be less than 6 year

Energy Performance Assessment of the Heating System Refurbishment on a School Building in Modena, Italy

Abstract The aim of this paper is the energy performance assessment of the school building Istituto Comprensivo "G. Marconi", located in Modena, Italy. This work describes the dynamic modeling of the building envelope and its heating system, carried out by means of the simulation software TRNSYS 17. According to the developed model, the school space heating loads, as well as the seasonal energy requirements, are evaluated by considering the actual heating system, which consists of gas-fired condensing boilers coupled to high temperature radiators. Then, the school heating system refurbishment is simulated: the paper evaluates the energy savings obtained by replacing boilers and radiators with an air-to-water multi-compressor heat pump, coupled to low temperature aluminum radiators, and by improving the system control strategy. Finally, the impact of the discussed energy saving measures on building energy performance and students thermal comfort is reported

Climate Influence on Seasonal Performances of Air-to-water Heat Pumps for Heating

Abstract A mathematical model for the evaluation of the seasonal performances of electric air-to-water heat pumps for heating is used to analyze the efficiency of on-off heat pumps, multi-compressor heat pumps and heat pumps with inverter compressor, integrated by electric heaters as back-up system, in the service of several buildings located in different Italian climates. The paper points out the importance of a good dimensioning of the heat pump as a function of the building energy signature and of the climate of the city where the building is placed, in order to enhance the system seasonal efficiency

Influence of the hydronic loop configuration on the energy performance of a CO2 heat pump for domestic hot water production in a multi-family building

In this work, a numerical analysis of the influence of the hydronic loop on the energy performance of a CO2 heat pump dedicated to DHW production for an apartment block located in Bologna (Italy) is presented. The energy model of the whole heating system, implemented in TRNSYS17, has been validated by means of a monitoring campaign performed during the winter season of 2017- 2018. The experimental results highlighted a poor and unexpected energy performance of the heat pump. The comparison between experimental and numerical results showed a significant penalty of the heat pump performance due to an erroneous use of the hot stratified thermal storage system. Outcomes of this paper confirm that CO2 heat pumps are very sensible to the temperature of the fresh water at the inlet of the gas cooler. This value can be strongly reduced thanks to the presence of the stratified tank in the hydronic loop

Modellazione dinamica e valutazione delle prestazioni energetiche stagionali di sistemi basati su pompe di calore aria-acqua

In this Thesis a series of numerical models for the evaluation of the seasonal performance of reversible air-to-water heat pump systems coupled to residential and non-residential buildings are presented. The exploitation of the energy saving potential linked to the adoption of heat pumps is a hard task for designers due to the influence on their energy performance of several factors, like the external climate variability, the heat pump modulation capacity, the system control strategy and the hydronic loop configuration. The aim of this work is to study in detail all these aspects. In the first part of this Thesis a series of models which use a temperature class approach for the prediction of the seasonal performance of reversible air source heat pumps are shown. An innovative methodology for the calculation of the seasonal performance of an air-to-water heat pump has been proposed as an extension of the procedure reported by the European standard EN 14825. This methodology can be applied not only to air-to-water single-stage heat pumps (On-off HPs) but also to multi-stage (MSHPs) and inverter-driven units (IDHPs). In the second part, dynamic simulation has been used with the aim to optimize the control systems of the heat pump and of the HVAC plant. A series of dynamic models, developed by means of TRNSYS, are presented to study the behavior of On-off HPs, MSHPs and IDHPs. The main goal of these dynamic simulations is to show the influence of the heat pump control strategies and of the lay-out of the hydronic loop used to couple the heat pump to the emitters on the seasonal performance of the system. A particular focus is given to the modeling of the energy losses linked to on-off cycling.Questa Tesi presenta una serie di modelli numerici sviluppati per la valutazione delle prestazioni stagionali di sistemi basati su pompe di calore reversibili di tipo aria-acqua accoppiate a edifici residenziali e non residenziali. Lo sfruttamento del potenziale risparmio energetico legato all'adozione di pompe di calore èun compito difficile per i progettisti, in quanto diversi fattori come la variabilità delle condizioni climatiche esterne, la capacità delle pompe di calore di modulare la potenza termica/frigorifera erogata, la logica di controllo del sistema e la configurazione impiantistica utilizzata influiscono sulle prestazioni energetiche ottenibili. Lo scopo di questo lavoro è quello di studiare in dettaglio tutti questi aspetti. Nella prima parte della Tesi viene presentata una serie di modelli basati su un approccio di tipo "temperature class" per la previsione delle prestazioni stagionali di una pompa di calore reversibile aria-acqua. Viene proposta un'innovativa procedura di calcolo per la determinazione dell'efficienza stagionale della pompa di calore costruita come un'estensione della metodologia riportata dalla norma europea EN 14825. Tale procedura può essere applicata non solo per lo studio di pompe di calore mono-compressore (On-off HPs), ma anche di pompe di calore multi-compressore (MSHPs) ed a velocità variabile (IDHPs). Nella seconda parte della Tesi la simulazione dinamica è stata utilizzata allo scopo di ottimizzare il sistema di controllo della pompa di calore e dell’impianto. I modelli dinamici sono stati realizzati utilizzando il software TRNSYS e permettono di simulare il comportamento dinamico di On-off HPs, MSHPs e IDHPs. Lo scopo principale dei modelli dinamici presentati è quello di evidenziare l'influenza dei sistemi di regolazione della pompa di calore e della configurazione del circuito idronico utilizzato per accoppiare la pompa di calore ai terminali sulle prestazioni stagionali dell'impianto. Particolare attenzione è stata rivolta alla modellazione delle perdite energetiche legate ai cicli di on-off della pompa di calore

Summer Performances of Reversible Air-to-water Heat Pumps with Heat Recovery for Domestic Hot Water Production☆

Abstract A numerical model for the seasonal performance evaluation of electric air-to-water reversible heat pumps during summer is presented. The model employs the bin-method, as indicated by the standards EN 14825 and UNI/TS 11300-4, but also considers domestic hot water (DHW) production through condensation heat recovery. The model evaluates the heat pump Seasonal Energy Efficiency Ratio ( SEER ) as function of the heat pump typology (multi-compressor, inverter-driven). The energy saving potential of DHW production integrated with the heat pump cooling function with respect to traditional separate cooling and DHW devices is analyzed as function of the building demand and of the heat pump typology

Annual performances of reversible air source heat pumps for space conditioning

Abstract 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 (SCOP on ), 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

Dynamic Simulation of Outdoor Swimming Pool Solar Heating

Abstract This paper presents a dynamic model of a "passive" solar heating system composed by horizontal solar flat collectors coupled to an outdoor swimming pool. The numerical model has been developed by using the Matlab/Simulink environment and it allows to predict on a hourly basis the thermal energy collected by the solar panels, the inlet/outlet collector working fluid temperature, the pool water temperature and the system efficiency. As a case study, three different pools characterized by different dimensions and three different flat solar collectors (unglazed, glazed and evacuated collectors) have been considered. The Simulink model allows to estimate the warm-up period of the swimming pool as a function of the characteristics of the pool and of the solar collectors. It has been demonstrated that, by using the model, the designer can make the optimal sizing of the solar heating system in order to obtain a water pool temperature ranging within a fixed interval. The results demonstrate that unglazed collectors are appropriate for this kind of use and evacuated collectors can be useful just in case of very big swimming pools in order to reduce the absorbing area of the solar panels

Dynamic modelling of a dual-source heat pump system through a Simulink tool

In this paper, the performance of a reversible Dual-Source Heat Pump (DSHP) system, able to exploit renewable energy from, alternatively, air and ground sources, is evaluated by using Matlab-Simulink. The actual source exploited depends on a simple control strategy on the basis of the current external air temperature. Yearly dynamic simulations have been carried out by coupling the DSHP to a detached residential building located in Bologna, in which heating and cooling loads are strongly unbalanced, and coupled to a borehole heat exchangers (BHEs) field. Different case studies have been analysed in which the length of the borefield has been modified. The obtained results show that an optimal switching temperature can be determined to maximise the Annual Performance Factor (APF) for a fixed BHE field length. Additionally, it has been demonstrated that DSHPs can be very useful in order to reduce the total required length of the borehole heat exchangers and, consequently, the associated costs, and to solve the problems linked to the ground temperature drift, which can be originated by the presence of an undersized borefield and/or by unbalanced building loads. As a consequence, DSHPs can be suggested for the retrofitting of traditional ground-coupled heat pump systems in presence of undersized BHEs

Effect of real temperature data on the seasonal coefficient of performance of air source heat pumps

In this paper, a transient analysis is performed in order to evaluate how effective climate data affect the determination of the seasonal coefficient of performance of ASHPs. Three Italian cities, characterized by different climates, are considered as reference case studies and the influence of real meteorological data, collected from different years, on the heat pump SCOP is performed. The analysis is carried out by employing the dynamic software TRNSYS. Numerical results show small variations in SCOP, while a significant influence on annual thermal energy demand can be observed. The analysis also underlines the absence of a general correlation between annual thermal energy supplied by the heat pump and SCOP and between HDD and SCOP