POLYCITY Site Torino

The POLYCITY project in the Arquata district of Torino implemented different measures related to energy supply optimization: a district heating network, a communal energy management system called “I_CEMS”, a tri-generation plant, photovoltaic systems and the improvement of building energy efficiency through replacement of windows and using smart heat consumption meters leading to a planned reduction of thermal energy needs by 25%.

A natural gas cogeneration system (CHP) was designed and installed, which now produces warm water and electricity at the ATC high-rise office building. Combined with this co-generator, an absorption chiller provides cooling energy in summer. Additionally, a total of 120 kWpeak photovoltaic systems was installed on the roofs of the residential buildings (Picture 1) and a 50 kWpeak system on the ATC building (Picture 2), altogether providing about 190 MWh of electricity each year.

Within the residential sector a total area of 35,800 m2 (gross floor) of buildings has been refurbished (Picture 3). Main measures have been insulation and replacement of the windows, as most buildings are heritage-protected. Several buildings have been monitored for three years; results can be seen in the “More detailed” section.

Absorption cooling and gas CHP at the ATC Office Building

The headquarters of the “Agenzia Territoriale per la Casa della Provincia di Turin” (Housing Authority
of the Province of Torino ATC) are situated at the northern Arquata district border. The building is a commercial high-rise building of concrete and glass and had been constructed in 1971 with ten stories and two underground floors. It has a total net floor area of 11,350 square meters. Apart from the ATC offices, the building hosts a conference hall, a cafeteria, storages and technical rooms like the server room and the cogeneration plant. During CONCERTO an ambitious retrofit was performed.

Direct solar irradiance strikes almost entirely the southwest and southeast windows during the hottest hours of summer days. The installation of photovoltaic panels on the two facades results in a shading effect for the offices behind them, especially in the middle of the day. The solution from a computer simulation giving the best combined result, also considering architectural aspects and installation constraints, is the one with a tilt angle of 35° and the panels hanging out of the balconies for half their length. The overhangs are thus horizontally extended by 60 cm and consequently the shadowing effect of the windows is amplified. The PV system is constructed of polycrystalline cells, has a peak power of 49 kW and produces around 51 MWh per year.

A gas-fired cogeneration plant (1166 kWtherm, 968 kWel) has been installed in the basement of the ATC building and connected to the district-heating grid (Picture 4). An absorption chiller of 190 kW is connected to the gas CHP and uses its waste heat (90°C hot water) to produce cooling energy. Such capacity is sufficient for the average load of the cold water for the air-conditioning. Diagram 1 shows the measured COP of the unit.

Table 1 lists the calculated and measured energy performance of the building, whereas the heating consumption (kWh/m²) is considering only the areas used as “office” and normalized to five operating days instead of the real six days a week of functioning. Thermal cooling for climatisation balances the heat demand over the year and presents a good way to use excessive district heat during the summer.

Diagram 1 – Measured COP of the absorption chiller during the years 2009 and 2010

Table 1 – Calculated and measured energy figures

Residential Buildings

The demonstration site for POLYCITY covers an area of 87,500 m2 with 30 residential buildings of 622 dwellings. The population involved is between 2,500 and 2,600 persons, of which 2,200-2,300 are inhabitants of the council buildings and 300 are employees of ATC.

The selection of the measures was strongly influenced by the constraints to be applied on the Arquata buildings, especially on the facades, due to their historical and architectural value. Main measures were extra thermal insulation (mainly under the roof) and highly efficient glazing. A very innovative communal energy management has been installed.

Thermal insulation of roofs has been performed
at the 30 residential buildings pertaining to the POLYCITY project. These works were completed
by February 2006. The insulation has been applied to the floor of the garrets using a layer made of sintered expanded polystyrene. The application of the material pans has been more difficult than usual because of the curvilinear shape of the garrets. The insulating material used is a product called “BITUROLL AE 20/G2V”. It is an insulating system in rolls, obtained with the coupling of a waterproof membrane of bitumen-polymer and panelists of sintered expanded polystyrene, with a thickness of 30 mm.

High efficiency glazing has been applied in the ATC owned apartments (on average 2 or 3 windows per dwelling and 20-22 for each building with a total of approximately 500 windows). The conventional glazing has been substituted with low-emission glazing on the windows with large surface and mainly on the northeast and southwest sides, since they give the best ratio between energetic/comfort improvement and financial expenditure. Also the window frames have been substituted. The total window heat transfer coefficient (frame plus glass) decreased from UW = 4 to UW = 1.6 W/m²K.

All buildings were monitored for three years within the project. The consumption data shown in table 1 and diagram 1 have not been degree-day corrected.

Table 1 – Energy figures, heating without degree day adjustment, DHW including losses

Diagram 2 - Heating energy consumption comparison of individual units per heating season