The 2 buildings are 50 m distance and are served with the same system for the DHW production. The complex is opened only during the summer season, so it requires only DHW production from the centralized system.
The existing plant was made of a single boiler installed in a dedicated room. This heat generator provided the DHW production with a plate exchanger. The decision of enlarging the accommodations and the consequent increase of DHW need, required the installation of a solar system to integrate the existing plant, with prewarming function. Very important in this evaluation was the necessity of containing the heat generator power and the gas consumption. To grant users’ comfort 2 recycling systems, one for each building, with independent supplying have been employed. In this way, the plant is able to supply DHW in a brief time in any moment of the day.
As said, the increased DHW requirement has led to the installation of a solar system, to integrate the existing 240 kW boiler. To ensure the installation of an adequate number of collectors, avoiding for lack of space of mounting them of the roof, a dedicated structure have been planned on the ground. The collectors have been installed on the flat cover of the parking area in between the 2 buildings. The collectors have been mounted horizontally with in rows of 2 with a multiple connection. The installation is 30° slope with an orientation close to south, values that optimize the summer functioning of the solar plant. The horizontal mounting has reduced the shadows between the collectors and the installation of a bigger number. The structure, besides being an anchor for the panels, is a further benefit for the customers that can use covered parking place. Due to the dimensions of the solar system, it has been cut in 2 parts, to optimize the hydraulic and electrical functioning. The 2 parts have a multiple connection, and, to maximize the efficiency and to help a bigger thermal exchange during spring ad autumn, in the plant with 14 collectors and 2 tanks, the 2 internal exchangers have a serial connection to reach a 14 thermal exchange power of about 105 kW. The management of the solar system flows have been grant by means of 2 circulation groups with multiple connection, in order to win the head losses (localizzate e distribuite) of the solar plant. A precise sizing of the main pipes of 35/32 mm and 28/25 mm and the secondary (interrate) pipes of 22/20 mm, has allowed to contain the head losses and to gain an adequate speed for the correct system working. To have a correct heating fluid flow for the functioning, every solar circulating group have been set to the highest speed in the working range. The solar controller allows the electric management of the circuit, controlling the functioning and with electrical losses reduction, since it makes the fluid circulating only if the collectors are able to exchange a minimum value of solar energy. On the controller have been activated also the protection and cooling functions to protect from temperature peaks, which are very brief due to the DHW requirement. To have an uniform distribution of the head losses related to the project flow of 30 l hour/m2 collector, due to the distance between the collectors and the tanks. If the solar system does not satisfy the primary energy requirement for DHW production, a diverter valve directs the pre-warmed water through the plate exchanger feed by the boiler. The boiler integrates the heat need to get DHW at the desired temperature at any moment. Every recirculating system is supplied with another diverter valve, that directs the water of the recycle circuit through the exchanger or the tanks, depending on the temperature of the return and of the solar tank storage.
The thermal power of the solar system is about 60 kW. During 5 months opening, expected data are:
• Energy from the solar plan for DHW production: 40 MWh
• Energy from the boiler for integration: 18 MWh
• Gas saving: 4500 m3
• CO2 emissions avoided: 12.000 kg
• System efficiency: 50%
Real data, coming from bills of the relevant period, are:
• Opening days: 150/year (5 months)
• Saving in the bill with reference to the old system: 3500 €/year (5 months)
Thanks to the centralized solar plant installation, the structure has had a saving for seasonal energy expenses of about 30% with
reference to the previous year.