###### Abstract
Alternatively, in cold climates with significant heating loads, the use of Combined Heat and Power (CHP) cogeneration compact units features as a highly attractive option [13]. These plants can exhibit increased economic feasibility in the case of compact steam turbines, operating with locally available biomass fuel [14]. The overall efficiency of such systems, referring to both electricity and heating production, can be in the range of 95% [13]. In common implementations, CHP systems are proposed for commercial and residential buildings for combined heat and electricity production [15,16]. In advanced applications, the combined operation of CHP systems with thermal energy storage have been studied [17] aiming at the minimization of the daily operation cost. Finally, by employing particular technologies, such as chilled ice or absorption chillers, the concept of tri-generation has been introduced, combining the production of heating, cooling and electricity [18, 19, 20]. Thermal energy needs constitute a major energy consumption in stadiums. Most commonly, thermal energy is required in sports facilities for the coverage of hot water needs (e.g., in changing rooms) and heating of any possibly involved swimming pools. The most feasible technology for the coverage of thermal energy needs is the combined operation of solar collectors (selective coating or vacuum tubes for colder climates) with conventional heaters [21, 22, 23]. To maximize the economic feasibility and the energy saving results, biomass heaters can be alternatively introduced [24]. In the most conservative implementations, thermal energy from either the solar collectors' field or the heater is stored in a common thermal storage tank, to be provided for the heating distribution network [24,25]. In more advanced approaches, thermal energy from the solar collectors can be directly provided for the heating distribution network [26]. Additionally, solar combi-systems can be also utilized for combined cooling production, by being co-operated with absorption chillers [27]. Finally, a novel approach is the combined production of thermal energy and electricity with photovoltaic hybrid solar thermal panels, maximizing the overall efficiency of the involved technology and the economic feasibility of the project [28; 29]. The significant lighting needs for both indoor and outdoor space can be covered with the installation of low energy consumption electrical bulbs, i.e., of LED technology, leading to overall annual energy saving percentages higher than 30% [30; 31; 32]. Further energy saving can be achieved with the central management of the lighting system, i.e., with a Building Energy Management System (BEMS). In general, these systems can offer an additional energy saving percentage of 15-20% [33]. Lighting management is most commonly performed with signals received by occupancy detection or luminosity sensors [34], according to which, through advanced operation algorithms [35], the lighting lamps luminosity is regulated and their switching on and off functions are performed. Other energy consumptions related with indoor space conditioning and hot water production (pumps, circulators and fans) should be also controlled by BEMS. The use of cyclo-converters in such inductive loads enables their operation with varied rotational speed, and, hence, reduced power consumption, in case of partial load operation. Traditionally, BEMS are locally introduced in buildings for energy consumption management [36; 37]. In modern applications, BEMS are integrated within the frame of smart grids, to provide advanced demand side management options, providing access to demand management for both sides, namely the customer and the grid's operator [38]. Distributed energy production and storage can be also inspected and regulated by BEMS, realizing the relevant regulation framework (e.g., within electricity wholesale markets) [39; 40].