The energy consumption of buildings is very important for both economic and environmental reasons. Newly built buildings are characterized by higher insulation and airtightness of the building envelope, and are additionally equipped with technologies that minimize energy consumption in order to meet legal requirements. In existing buildings, the modernization process should be properly planned, taking into account available technologies and implementation possibilities. Hotel buildings are characterized by a large variability of energy demand, both on a daily and a yearly basis. Monitoring systems, therefore, provide the necessary information needed for proper energy management in the building. This article presents an energy analysis of the Turówka hotel located in Wieliczka (southern Poland). The historical hotel facility is being modernized as part of the project to adapt the building to the requirements of a sustainable building. The modernization proposal includes a trigeneration system with a multifunctional reverse regenerator and control module using neural algorithms. The main purpose is to improve the energy efficiency of the building and adapt it to the requirements of low-energy buildings. The implementation of a monitoring system enables energy consumption to be reduced and improves the energy performance of the building, especially through using energy management systems and control modules. The proposed retrofit solution considers the high energy consumption, structure of the energy demand, and limits of retrofit intervention on façades.Energies 2020, 13, 1968 2 of 20 buildings. This negative trend may be halted by using renewable energy sources and new solutions with higher efficiency. The effects achieved in this way are not only beneficial to the environment, but, above all, to the consumer, whose operating costs are significantly reduced. The simplest solution to save energy would be to design a building using materials with low thermal conductivity and high-efficiency heating and/or cooling technology.Both environmental and economic factors have led European Union (EU) regulators to introduce a definition for "nearly Zero-Energy Buildings", hereinafter referred to as "sustainable buildings". Pursuant to the Directive of the European Parliament [4], they are buildings with low demand for heating, cooling, and electricity, which should be covered to a very significant extent by energy from renewable sources. The document [4] does not include the exact values of the coefficients to be met by a building, as these are defined by each Member State. The National Plan for increasing the number of low-energy buildings [5] extends this definition, stating that such a building meets the energy saving and thermal insulation requirements as defined in technical and building regulations.Referring to the Regulation of the Minister of Infrastructure, buildings should correspond to at least the optimum energy performance for new buildings, in force since January 2019 for buildings occupied and owned by pu...