###### Abstract  
Energy performance upgrade of stadiums constitutes a complex and demanding task because of both the size and the variety of the involved energy loads. The present article aims to summarize the basic results of the implemented study on the energy performance upgrade of the Pancretan Stadium, Crete, Greece. This target was approached with a cluster of passive and active measures: replacement of old openings, a photovoltaic station, an open loop geothermal system, installation of energy-efficient lighting devices, a solar-biomass combi system and a Building Energy Management System (BEMS) for the control of the main energy consumptions. The dimensioning of all the proposed active systems is optimized through the computational simulation of their annual operation. With the applied technologies, the achieved annual energy saving percentage exceeds 83%. The Renewable Energy Sources annual penetration percentage is calculated at 82% versus the annual energy consumption. The Stadium's energy performance is upgraded from rank D to rank A+, according to the European Union's directives. The set-up cost of the under consideration energy performance upgrade systems is approximately calculated at 2,700,000 \(\upxi\), with a payback period of 12 years, calculated versus the achieved monetary savings due to the reduction of the consumed energy resources. s 2019 9 1544 10.3390/app9081544 13 April 2019 13 April 2  
* indoor space heating, cooling and air conditioning,
* hot water for the changing rooms,
* lighting for both the outdoor and the indoor space,
* swimming pools heating,
* power consumed in large size pumps and circulators for the water supply and the hot water distribution networks, and in fans, for the air conditioning network. Although the potentially available energy saving measures do not change with regard to buildings energy performance upgrade applications, the size of the consumptions and the variety of the involved energy loads in large size sports facilities convert their energy performance upgrade into a demanding and challenging task. So far, the relevant research is considerably limited. There is not any article in all of the scientific literature investigating the energy performance upgrade of stadiums. There is only one article dealing with energy performance upgrade of sports facilities, with a case study for a sports centre in Dubai, focusing on the introduction of hydrogen technologies [1]. Additionally, there are two more articles investigating and evaluating alternative passive and active technologies for athletic swimming pools heating [2,3]. However, apart from these articles, there is no other relevant work in the scientific literature approaching the topic of the present article. The optimum mixture of the most feasible available technologies on energy performance upgrade of stadiums depends on several parameters, such as the geographical location, affecting the available Renewable Energy Sources (R.E.S.) potential and the prevailing climate conditions, as well as the size of the stadium and the existing final energy needs. Traditionally, indoor space conditioning constitutes the most important energy consuming process. Geothermal Heat Exchangers (GHE) seem to be the most attractive technology for indoor space conditioning, offering the possibility for both heating and cooling production [4]. Annual electricity consumption saving percentages of 30-40%, with regard to electricity consumption from air-to-air heat pumps, can be achieved with geothermal systems, according to statistical data and simulation results [5,6]. GHE have been widely studied in the relevant scientific literature. Several simulation methods have been developed and proposed for closed loop heat exchangers of horizontal [7,8] and vertical [9,10] layout. Heat transfer analysis have also been executed for open loop geothermal systems [11]. A review of the involved design aspects of GHE can be found in [12].