The medieval village of Montieri (pop 1250) is located in the southern flank of the Larderello Geothermal District, about 15 kms SSE from the city of Larderello in Tuscany. The GEOCOM activities involve the whole community delivering three distinct actions: 1) Building a brand new and highly efficient district heating system to utilize high enthalpy geothermal steam from the Montieri-4 well (courtesy by ENEL) 2) Retrofitting a number of selected public buildings and 3) deploying 8.5 kW solar PV as part of the system integration scheme. The sheer volume and complexity of these investments alone would render the Montieri demonstration site to be the flagship component of the GEOCOM initiative. In addition to this the allocated budget further reinforces its special status among the project demo sites. The total budget of our project is just over 11.5 million Euro of which more than 8 million Euro comes from the Regional Government of Tuscany exclusively to support the activities in Montieri.

Geothermal District Heating System

The project's main objective in Montieri was the construction of a state-of-the-art geothermal district heating system for space heating and domestic hot water production for a total of 425, mostly private users, but including 8 public buildings and institutions, too. The capacity of the heating network and the number of available connection points were sized and calculated to cover the entire demand potential even if new consumers will be connected to the system in the future. Montieri’s unique medieval structure is characterized by a network of narrow alleys, which used to host a very old set of underground utility lines. It was realised early on, in the planning phase that the laying of the pipes for the geothermal district heating system has to be accompanied by the complete overhaul of these auxiliary systems (water, sewer etc) along these cobble stone-covered alleys at the entire project area. One of the several novel elements of the district heating system is that the plant is fully automated and controlled entirely by a special automation and remote control system which also facilitates direct link to the switchboards of the heat metering utilities. The control unit is designed to be able to manage local and remote key system parameters, such as pressure set-points, temperature set-points, operating points of the circle and in addition to that it is capable of intervening on the plant itself in a timely manner via advanced alarm management. It is also connected to ENEL’s network to optimize the synergy between the two systems and promote effective exchange of data. This solution allows a state-of-the-art remote control (via PC or via internet with web-server) optimizing the management phase and allowing the management of the entire district heating system with a single operator.Read more

Basic schematics of the district heating system of Montieri


The heating system chosen to be delivered is technologically highly innovative making in one-of-a-kind among other geothermal district heating systems currently operational in the world. It is supplied primarily by geothermal steam and for a smaller instant by a two-phase fluid both received via separate ducts (one for the steam one for the two-phase fluid) connecting the Montieri-4 well with ENEL’s Travale 3 power plant (20MW) north east of the town. One of the innovative aspects of the project is that the energy content of the available, but previously unused two-phase fluid (flow rate 0,4kg/s, 150°C, 10-12 barA) is also harnessed yielding roughly 10% of the overall output. In addition the two-phase fluid itself can cover for Montieri’s DHW needs during the summer period, but in case of occasional higher demand it can be complemented by steam too. It is evident that the use of this innovative element promotes improved energy efficiency and resource savings. The heating demand was calculated by conducting surveys and comparative evaluations and simulations. The total heated volume was estimated to be in the range of 111.000 m3 which concluded the output of the heating system to be 5700kW. In addition there has been an extra standard 10% safety factor and a specific prerequisite of 0.006kW/m3 for DHW purposes added to this initial value making the final system requirement to be 6164kW. There was special emphasis put on selecting the most ideal locations for the heating stations and planning the best route for the pipeline in order to mitigate any related visual impact and minimize pressure drops, hence energy consumption respectively. The new infrastructure, especially the buildings follow the architectural pattern of the region by using stone revetments, tile-roofing and gutters with wooden beams.

The heating system includes three distinctive and completely separated fluid circles: 1.) steam/two-phase circuit (the condensate derived from the steam is returned directly in the two-phase agent, making a fully closed loop with no emissions); 2) closed loop of heat transport between the primary and secondary heating stations, “A” and “B” respectively by means of circulations of superheated water in DN200 PN25 steel pipes of 2x 2200m, which are insulated by polyurethane foam and enclosed by HDPE liners; 3) the distribution circuit (~5100m) of the heat  by means of hot water starting off from the heating station “B”. The primary heating station (A) uses the steam and two phase fluid received from ENEL to overheat the water circulating in the closed circuit connecting it with the secondary heating station (B), where the heat of the superheated water is transferred via a set of heat exchangers to the water circulating in the closed circuit of the distribution network. The two-phase fluid is primarily used to preheat the returning water from the secondary heating station.

The steam enters to the primary heating station saturated at 207,2°C and 18 barA of pressure. When it leaves the dedicated steam heat exchange modules it is still 150°C and 17 barA and enters the dedicated two-phase heat exchange modules with the same temperature but at a lower pressure of 10-12barA only to exit the same modules at about 100°C and 8-10 barA of pressure. Each heat exchanger is equipped with a self adjusting system to ensure maximum efficiency when making the superheated water to carry the heat to the secondary heating station. At maximum load the plant is capable of generating a 50°C thermal gradient, heating the returning water from 80°C inlet temperature up to 130°C outlet temperature. The superheated water between the two heating stations is circulated by an 11kW rated power pump unit installed at the heating station “A” with a maximum of 115m3/h flow rate at 4 bars of pressure. In addition external inverter was attached to the pump unit to help maintain an economic operation pattern. The device is controlled by the temperature of the returning water from heating station “B” or by the actual heat demand that is required there, which adjust the speed of the pumps, thus no unwanted heat capacities are transferred needlessly. Station “B” accommodates two plate heat exchangers of 4000kW capacity each. One of them is usually on standby, but in case of peak demand both units are operational at 78% of their nominal power, generating 6,26 MW thermal output. The generated hot water of 95°C is pumped to the heating utility network at a maximum flow rate of 180m3/h and 2.5 bars pressure while the returning water has an average temperature of 64°C which concludes the thermal loop. The system is complemented by a number of auxiliary features such as water softening unit, compressor and emergency generator. Figure 4 explains the connection between the various parts of the heating system in detail, demonstrating the combined full use of steam and the two-phase fluid. It is important to point out that system is capable of running with certain modules deactivated both on the steam or the two-phase fluid side in order to match the actual demand the most precisely.

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