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

The role of emitters, heat pump size, and building massive envelope elements on the seasonal energy performance of heat pump-based heating systems

The influence of emitters, heat pump size and building envelope thermal inertia was investigated on the energy consumption of a heat pump-based heating system with a numerical study performed with the dynamic software TRNSYS. An algorithm based on a Thermal Inertia Control Logic (TICL), which can exploit the capability of the building envelope to store thermal energy, has been applied. When the proposed algorithm is employed, the indoor air temperature set-point is increased when the outdoor temperature is larger than the bivalent temperature of the building-heat pump system. Different configurations of the heating system were simulated considering either convective (fan-coil) or radiant (radiant floor) emitters coupled to a variable-speed air-to-water heat pump. Simulations have been carried out considering a reference building derived from the IEA SHC Task 44 and evaluating the influence of the proposed control logic on both the heat pump seasonal energy performance and the internal comfort conditions perceived by the building users. The obtained results highlight how the introduced TICL can guarantee the use of downsized heat pumps, coupled to radiant emitters, with a significant enhancement of the seasonal performance factor up to 10% and a slight improvement of comfort conditions. On the other hand, when convective terminal units are considered the proposed logic is not effective and the overall energy consumption of the system increases up to 15%

Experimental measurements of thermal-hydraulic performance of aluminum-foam water-to-air heat exchangers for a HVAC application

In this paper, thermal and hydraulic performance of in-house made prototypes of water-to-air heat exchangers are experimentally investigated and compared to those of a compact heat exchanger, used in a commercial fan coil. The prototypes are built replacing the fins with aluminum foam surfaces characterized by a large porosity, higher than 96%. In order to evaluate the performance of the foam-based heat exchangers in a real-scale application, the geometry of the prototypes was based on that of the reference model and, moreover, experimental tests were performed placing the heat exchangers within the commercial cabinet, under the same fan power. Different bonding techniques were also tested to couple metal foams to copper tubes. Results show that similar hydraulic performance can be obtained with the foam-based heat exchangers, if compared to the commercial device. However, the large foam porosity accounts for a lower value of the surface-to-volume ratio of the aluminum foam media, thus yielding a strong penalty, up to 60%, of the heat transfer rate with respect to that of the conventional finned surface. Moreover, experimental results highlight how the bonding technique and the foam packaging have a strong influence on the contact thermal resistance and, consequently, on the overall heat transfer coefficient. Epoxy bonding allows to increase the thermal performance of the heat exchanger, if compared to press fitting, between 15% and 110%. In conclusion, results presented in this paper suggest that metal foams can be considered as a potential alternative to fins in water-to-air heat exchangers only if the foam tube bonding is obtained by welding or brazing

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

The modelling of reverse defrosting cycles of air-to-water heat pumps with TRNSYS

The most widespread defrosting technique adopted by Air-Source Heat Pumps (ASHPs) during the heating season is Reverse Cycle Defrosting (RCD). In this paper a dynamic model of RCD, based on performance data provided by the heat pump manufacturer, designed for TRNSYS and with a core-structure suitable for commercial units, is presented. A defrost cycle is divided in three phases. First, the unit heating capacity is reduced as a linear function of the ice layer thickness (Pre-Defrost phase). Subsequently, the reverse cycle operating mode is modelled on the basis of the performance data given by the manufacturer (Defrost phase) and, finally, the heat pump performances are altered taking into account the higher surface temperature of the external coil after the reverse mode (Post-Defrost phase). Then, the influence of defrosting energy losses on the heat pump seasonal performance factor in sites characterized by different climatic conditions has been assessed. Results point out that the ASHP seasonal efficiency decreases of about 5% taking into account defrost energy losses; in addition, the influence of defrost cycles on the internal air temperature is studied by assessing under which conditions the indoor thermal comfort can be guaranteed even in presence of frequent defrost cycles

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