1. Introduction
Nowadays, the importance of an energy-saving approach is relevant in all economic sectors such as industrial, civil, and commercial. The geo-political conditions are pushing more than ever for a reduction in energy consumption for many reasons: rising energy prices, restrictions on air pollution, and restrictions on building performances. This case study focuses on the energy consumption of hotels, analyzing a building located in the north-west of Sicily Island. In general, the energy consumption related to the building sector reached 40% of the total energy consumption in the world [
1]. The hotel trade sector has a huge impact on the world economy. The travel and tourism sector moved USD 9.2 trillion in 2019. After the COVID-19 pandemic, the sector lost USD 4.5 trillion [
2]. After such a dark period for all hotel operators and suppliers, many countries have allocated funds to help all affected sectors, including the hotel sector [
3,
4]. In particular, in Italy, a national recovery and resilience plan has been drawn up to help businesses [
5,
6] in relation to the needs envisaged by the European Green Deal and regional energy plans [
7,
8] At the same time, it was necessary to reduce operating costs in order to try to recover some of the lost assets. The ability to reduce the consumption of fossil fuels and take advantage of renewable energy determines a positive impact on building efficiency. This analyzes everything article by means of software that defines the boundary of energy flows to which a hotel is subjected.
The tourism sector is fundamental to the Italian economy, its contribution amounts to about 132 billion US dollars in 2020 [
9]. To ensure high-level accommodation facilities, considering the economic and environmental sustainability, it is necessary to invest in technologies able to reduce costs related to energy consumption, while simultaneously increasing the quality of the services. In hotels today, energy consumption significantly affects the economic balance. A hotel generally guarantees the following services: guest rooms, reception, communal areas, conference rooms, restaurants, swimming pools, and service areas [
10].
Each of these services corresponds to a specific energy consumption which can be divided into the following macro-categories:
Heating
Cooling
Production of domestic hot water
Electrical energy for lighting, refrigeration, household appliances, and electric equipment in the common areas.
These macro-categories of consumption depend a lot on the characteristics of each single structure: geographical area, size and age of the building, type of envelope, exposure, number of rooms, number of days per year open to customers, catering service, type of conditioning system and domestic hot water production [
11].
As seen so far, high consumption not only entails an additional cost for businesses but also represents a significant portion of the production of CO
2, which is released into the atmosphere and generates well-known consequences. The 2030 climate and energy framework, approved by the European Council on 23 and 24 October 2014 [
12,
13], sets three main objectives:
A reduction of at least 40% in greenhouse gas emissions compared to the levels recorded in 1990.
A share of at least 27% of renewable energy.
An improvement in energy efficiency of at least 27%.
To consider the building impact using the European “smart readiness indicator”, the U-CERT digital tool was used. The results confirm that the rating is low because the SRI is 28/100, the rating is F, the energy efficiency is 33%, the energy flexibility and storage is 37%, comfort is 43%, convenience is 30%, and health, wellbeing, and accessibility are 50% [
14]. In the literature, several authors are working on this topic focusing on economic and techno-economic evaluations, smart management, load prediction, and energy-saving measures. In the following lines to mark the importance of this topic, some papers are cited. Haojie Luo et al. examine the use of a wave energy converter and an offshore wind turbine to power a zero-energy coastal building.
The simulations are carried out by TRNSYS 18. They obtained that the optimal choice of an energy mix (including Renewable Energy Sources) is a very important solution to power a building [
15]. Yu Wang et al. analyzed the energy consumption in 15 hotels in Jiangsu Province, China. The results suggested that the (HVAC) system, the monitoring system, the lighting system, the domestic hot water system, and the building envelope are the energy upgrades that generate the most relevant energy savings, with no more than 10 years of payback time [
16].
Adila Eli et al. studied how to optimize the energy consumption of Shanghai hotels. They implemented many machine learning algorithms to predict energy consumption. The results show that an artificial neural network is the best model to predict hotel consumption [
17]. Minglei Shao et al. performed support vector machines to predict the energy consumption of a hotel. They have characterized the loads and carried out a great optimization problem with the machine learning approach [
18]. Petr Scholz et al. proposed a study of a hotel in the Czech Republic, listing what interventions have been carried out in terms of energy saving and social and environmental aspects. They proposed good waste management, saving electricity consumption by using LED lamps, and saving water by implementing intelligent shower systems that recover water [
19]. Yutong Wu et al. focused on the energy consumption of hotels after the COVID-19 pandemic. They list several energy-saving strategies in a hotel located in the south of China. They proposed how to improve the quality of external walls and windows, control the lighting system with automatic dimming devices, and use RES to supply the hotel. All these optimizations can reduce the energy consumption by 16–29% [
20]. D. Wang et al. proposed several old systems replacements to improve the efficiency of the electrical and air conditioning systems of a hotel in China. By replacing the lighting system, the air conditioning system, and the building automation system, high levels of energy savings were achieved. The LED system is the one with the highest electrical savings [
21].
This paper analyses the thermal and electrical loads of a hotel located in Trapani, Sicily, to implement some energy retrofit solutions, focusing the solar cooling technology with the aim of reducing energy consumption. Results obtained from simulations have shown that harnessing solar energy to meet a building’s energy needs is very cost-effective in terms of energy and economic savings. This case study aims to demonstrate that saving energy in nonresidential buildings is possible, especially by using a solar source that is capable of air conditioning in summer. The proposed solutions can be easily replied to in a similar structure, increasing the economic and environmental sustainability of this sector.
3. Conclusions
The energy analysis of the various optimization proposals for the structure under consideration provided clear results regarding the optimal solution to be used, considering not only the economic factor but also the environmental aspect. Solution 1 involves the installation of a water and lithium bromide absorption machine fed by flat-plate solar collectors. These have a significantly lower fluid outlet temperature than the evacuated tube solar collectors analyzed above and a lower cost per square meter installed. From an environmental point of view, they are more impactful due to the higher consumption of gas to reach the set point temperature of the absorption machine; from an economic point of view, on the other hand, they present a return on investment in about two years, less than half of the second hypothesis. The second solution involves the installation of evacuated tube solar collectors coupled to a water and lithium bromide absorption machine. It is necessary to install an auxiliary system that allows the desired water temperature conditions to be reached if the solar collectors do not reach the setpoint temperature of the absorption machine. This second solution is convenient from an environmental point of view because the consumption of electricity and gas is reduced, thus allowing a return on investment in about seven years.
For these reasons, Solution 1 may be considered more advantageous if the objective is purely economic. In contrast, Solution 2 is recommended if the main objective is pollution savings. In any case, the investment would return within an acceptable pay-back time. The simulations performed show the dynamic behavior of a building in terms of energy demand. The case study is a replicable example in all residential and nonresidential structures. A thorough initial audit allows for dynamic simulations capable of characterizing consumption and being able to perform energy retrofit interventions. Improved solutions are not necessarily only those proposed in this paper, but certainly, the possibility of using solar energy to air condition a hotel is a great economic advantage.