Nearly Zero Energy Building in Lecco Modern technological building compared to an ancient Villa

Nearly Zero Energy Building in Lecco Modern technological building compared to an ancient Villa Matteo BRASCA *, Oscar Luigi PAGANI **, Kanza RAUF*** * partner - AIACE S.r.l. società di ingegneria, contract professor Politecnico di Milano School of Architectural Engineering, Milan, Italy (matteo.brasca@polimi.it) ** partner - AIACE S.r.l. società di ingegneria, contract professor Politecnico di Milano School of Architectural Engineering, Milan, Italy (oscar.pagani@aiace-srl.it) *** student - Politecnico di Milano M.Sc. in Architectural Engineering, Milan, Italy (zk.rauf@gmail.com) Keywords: nearly Zero-energy building, dynamic/static simulation, energy efficiency Field of Interest: Building Design; Topic of Interest: High performance buildings Main paper focus: General Framework; Paper Content Classification: Technical Abstract The building is located in Lecco, Italy, into an industrial area and it hosts offices (600 m 2 ) for a software company. The structure is an extension of an existing building originated as a residential villa. The new headquarter is an example of climate sensitive building, reacting, in an adaptive way, to seasons and different climates. Temperate climate, with cold winter and hot/wet summer has influenced building's shape and different elevations, depending on their orientation. The building is oriented to south, trying to exploit solar gains and balancing them with internal ones. Building's passive envelope minimizes thermal energy dissipation, with strong use of thermal insulation (transmittance from 0.08 to 0.20 W/m 2 K); to the west, a green wall protects offices from solar radiation. Green is watered with raining water, which has been gathered, filtered and stored in underground storage tanks. Photovoltaic panels on the roof (5.5 kwp) and on the south facing facade (6.0 kwp) provide electricity. Building-Envelope technology ensures a quick construction, flexibility, maintainability and possibility to change wall composition, depending on the expected performance. Ventilated rainscreen cladding avoids condensation and overheating; different coatings (fibrecement and copper) cover different volumes. Aluminum frame with thermal break and low-e triple glass give windows an average thermal transmittance U < 1.0 W/m 2 K. Advanced systems have been designed to optimise the contribution of the envelope. A heat pump provides building's heating and cooling through ceiling radiant panels; depending on the external climatic conditions, an efficient air handling unit ensures long free cooling periods. The building has smart thermoregulation and plant s electrical automation. The building uses geothermal and solar energy for heating and cooling. Different energy simulations (performed with different calculation software) show that the building belongs to best Italian energy class (A+ class), with an yearly heating primary energy demand of 2.97 kwh/m 3 y. The result has been obtained through a good integration between building features and installations starting from the design optimization, inspired to nature s efficiency.

1. Introduction The building is located in Lecco, Italy, into an industrial area and it hosts offices (600 m 2 ) for a software company. The structure will be an extension of an existing building originated as a residential villa. The new headquarter will be an example of climate sensitive building reacting, in an adaptive way, to the seasons and different climates. Temperate climate, with cold winter and hot/wet summer has influenced building's shape and different elevations, depending on their orientation. The building is oriented to south, trying to exploit solar gains and balancing them with internal ones. Building's passive envelope minimizes thermal energy dissipation, with strong use of thermal insulation (transmittance from 0.08 to 0.20 W/m 2 K); to the west, a green wall protects offices from solar radiation. Green is watered with raining water, which has been gathered, filtered and stored in underground storage tanks. Photovoltaic panels on the roof (5.5 kwp) and on the south facing facade (6.0 kwp) provide electricity. Building-Envelope technology ensures a quick construction, flexibility, maintainability and possibility to change wall composition depending on the expected performance. Ventilated rainscreen cladding avoids condensation and overheating; different coatings (fibrecement and copper) cover different volumes. Aluminium frames with thermal break and low-e triple glass give windows an average thermal transmittance U < 1.0 W/m 2 K. Advanced systems have been designed to optimise the contribution of the envelope. A heat pump provides building's heating and cooling through ceiling radiant panels; depending on the external climatic conditions, an efficient air handling unit ensures long free cooling periods. The building has smart thermoregulation and plant s electrical automation. The building uses geothermal and solar energy for heating and cooling. The building is an example of a good integration between building features and installations starting from the design optimization, inspired to nature s efficiency [1]: it belongs to best Italian energy class (A+ class), with an yearly heating primary energy demand of 2.97 kwh/m 3 y (CENED software, with the contribution of the photovoltaic system). Figure 1 the new Headquarter of GR informatica company 2. Building Models and Simulation Software Two software were chosen to carry out the energy simulations for the GR Informatica Office building: Cened+ 1 and EnergyPlus 2. EnergyPlus is a simulation engine and it was used coupled with Design Builder 3 software for the setting of the calculation model. Energy Plus and Cened+ offer two complementary types of energy calculations. Cened+ is a software that performs steady state simulation along 24 hours under standard conditions 4. Energy Plus performs dynamic simulation better considering the components of the building heat balance and the issues of the plants and, in particular, in this case, it is able to evaluate the influence of the natural ventilation on the internal comfort conditions. These two complementary approaches were used to

evaluate the different strategies used in the building. Lastly, the use of two software offered a better chance to validate the building models, to verify the accuracy and reliability of the calculation and to have a reference point for future monitoring of the building. 3. Building Models In order to compare the energy requirements of the designed low energy solution with a usual older construction, the existing building, that have approximately the same volume than the new one, was modelled and simulated to calculate the primary energy demand. The location of the new and existing building is shown in Figure 2. Existing Building New Headquarter Figure 2 Plan of the area in Lecco, Italy Models for the two buildings were created using DesignBuilder with the surrounding site plan to take into account the shadows cast by the surrounding buildings (in this case a very critical point because of the shadows that restrict the use of passive solar strategies). The idea was to compare the energy demand of the existing building with the energy efficient solution just next to it. Simulation models are shown in Figure 3. Figure 3 Design Builder Model of the Existing Building (on the left) and New Building (on the right)

Figure 4 Summer (on the Left) and Winter (on the right) Scheme Design 4. Benchmark Models In order to obtain benchmark solutions to compare the results obtained with the dynamic simulations, the software CENED+ was used to create steady state calculation models of the existing building and the new one. At this stage, in order to have comparable results, an EnergyPlus simulation was performed assuming the plant operation for 24 hours a day, both in summer and in winter (without using the natural ventilation) and a fixed comfort temperature. The comparison is shown in Figure 5. Benchmark heating primary energy demand [kwh/m 3 y] Cened Energy Plus 57,00 61,17 Benchmark cooling primary energy demand [kwh/m 3 y] 2,18 2,77 Cened Energy Plus 2,70 2,60 4,84 4,93 New building (without PV system) Existing Building New building (without PV system) Figure 5 Benchmark comparison between Cened+ and EnergyPlus calculation results Existing Building The above graph shows the yearly heating and cooling primary energy demand, calculated (KWh/m 3 y) by Cened+ and EnergyPlus for the existing as well as the new office building (without the contribution of the photovoltaic system). It can be noted that the difference between the results obtained with the two software are almost the same with an error of less than 10%; in the summer season differences obtained are slightly higher. This confirms the reliability of both the models for further analysis. 5. Energy Demand Comparison: Existing and New Office Building The purpose of modelling the existing building was to provide a direct comparison between the primary energy demand of a regular building and a nearly zero-energy building (class A+ CENED). Based on results shown in Figure 5 and Figure 6, we note that the new GR Informatica office building is 10 to 12 lesser energy intensive, compared to the existing building as far as the heating load. The cooling energy demand of the old building, however, is comparable to the new building (Figure 6). The reason is probably that the old building has significant air infiltration and, above all, high-mass walls that

allow to shift the heat wave at night. Another aspect is the presence of the ventilated roof that protects from summer solar radiation the office spaces. Comparison Old and New Buildings Yearly Primary Energy demand (kwh/m 3 y) 70,0 60,0 50,0 40,0 30,0 20,0 10,0 2,77 4,93 2,60 61,17 Cooling Heating 0,0 New building (without PV system) Existing Building Figure 6 Comparing between Existing and New Building primary energy demand 6. Sensitivity Analysis of the New Building Energy Demand After the benchmark models have confirmed the reliability of the building model, the actual use of offices and plant was simulated, in order to estimate the effective primary energy demand of the building. Till now, any analysis were carried out on the basis of continuous operation for 24 hours of the building, the additional simulations assume the actual use of the office, that is from 08:00 to 18:00 with the weekend off. At the same time, various situations were simulated to analyse the impact of each option on the energy demand of the building. Condition 5 window trasmittance U floor = 1.80 W/m 2 K 4,96 86,3% 1,59 69,3% Condition 6 with window shading devices 4,57 71,8% 1,35 43,6% Table 1 Sensitivity analysis of the New Building Primary Energy Demand 6,00 CASES Sensitivity Analysis of the New Building Primary Energy Demand 5,49 Prim.En. Heating demand Difference Prim.En. Cooling demand Difference [kwh/m 3 y] [kwh/m 3 y] Condition 0 final desing with PV panels 2,66 0,0% 0,94 0,0% Condition 1 final desing without PV panels 4,47 68,0% 1,58 68,0% Condition 2 wall trasmittance U wall = 0.27 W/m 2 K 5,49 106,6% 1,57 66,7% Condition 3 roof trasmittance U roof = 0.24 W/m 2 K 4,68 76,1% 1,63 73,1% Condition 4 floor trasmittance U floor = 0.30 W/m 2 K 4,47 68,0% 1,59 69,1% Yearly Primary Energy Demand [kwh/m 3 y] 5,00 4,00 3,00 2,00 1,00 2,66 0,94 4,96 4,68 4,47 4,47 1,58 1,57 1,63 1,59 1,59 4,57 1,35 Heating Cooling 0,00 Condition 0 Condition 1 Condition 2 Condition 3 Condition 4 Condition 5 Condition 6

Figure 7 Sensitivity analysis of the New Building Primary Energy Demand Firstly, the benchmark model of the building was simulated for actual working hours, as mentioned above. The first calculation option (condition 0) has been analysed taking into account the energy production of the photovoltaic panels provided for the building. In this case we used the value of energy production for photovoltaic panels calculated with the software CENED +. The next step was to modify the thermal conductivity (U-Value) of each building component one by one, that is, walls (cond. 2), roofs (cond. 3), floors (cond. 4), and windows (cond. 5), while keeping the other elements unchanged. The components performance assumed, in any case, respect the values of thermal conductivity as required by Law. Results of the parametric study are shown in Table 1 and in Figure 7. Based on the results shown in Figure 7, in the case of heating primary energy, the maximum increase is achieved by increasing the U-value of the walls, up to the minimum requirement of Regulations. This is because a large portion of the building fabric is opaque and walls affect a lot the overall conduction losses through the envelope. This is also the reason why there is a high increase in heating primary energy by reducing the performance of the windows: the percentage of openings is quite low and most of them face south-east or north. From the results, it can be deduced that, by increasing the design transmittance to those required by Regulations, the influence of the roof (from U = 0.19 W/m 2 K to U = 0.24 W/m 2 K, difference +88%) and the floor (from U = 0.16 W/m 2 K to U = 0.30 W/m 2 K, difference +88%) on the heating primary energy are lower than the influence of walls: the reason is mainly due to the articulated shape of the building (high S/V ratio) but also to the better thermal performance which characterizes the vertical envelope (U = 0.10 W/m 2 K compared to U = 0.27 W/m 2 K, difference +170%). The variation of the cooling primary energy demand follows variations of the heating demand too: considerable differences, that can be seen, are the greater influence of the roof (the solar heat load is greater in summer, neglecting the shading effect of photovoltaic panels). 7. Simulating the Performance of the Building Envelope The final step in our analysis was to understand the efficiency of the building without the support of an HVAC system for the thermal treatment of the space inside. Figure 8 and Figure 9 show a comparison of the average monthly inside operative temperature, in comparison with the outside dry-bulb temperatures, with plant and without plant situation. The natural ventilation is kept at 0.8 ach with 0.3 ach as infiltration. Monthly Average Temperatures With Heating and Cooling Plant Temperature ( C) 17,7 17,7 18,0 6,2 19,1 10,9 21,5 15,5 22,8 19,0 24,1 23,9 21,7 20,2 22,7 17,8 19,5 11,6 18,1 17,6 6,3 0,0 2,3 1,7 1 2 3 4 5 6 7 8 9 10 11 12 Months of the Year Operative Temperature C Outside Dry Bulb Temperature C Figure 8 Comparison between outside air temperature and operative temperature with plant contribution

It can be noted here that the average monthly temperature during the heating season is around 18 C. This is because the HVAC system was allowed to set back from 20 C, during the working hours, to 18 C, during the night. Monthly Average Temperatures Without HVAC Plant 27,2 26,6 23,7 23,6 20,9 Temperature ( C) 4,0 5,2 9,4 6,2 15,7 10,9 15,5 19,0 21,7 20,2 17,8 17,9 11,6 11,8 6,3 5,5 2,3 1,7 0,0 1 2 3 4 5 6 7 8 9 10 11 12 Months of the year Operative Temperature C Outside Dry Bulb Temperature C Figure 9 Comparison between outside air temperature and operative temperature without plant contribution In Figure 9, only the natural ventilation is used, and thus results are a direct depiction of the performance of the building envelope elements, in the absence of any HVAC equipment. With the assistance of the plant a temperature gradient of about 15 C is kept but even the envelope alone is able to maintain a constant temperature gradient of 5 C. The two yellow boxes indicate the year period when inside comfort can be attained even without the use of HVAC equipment, for the months of May, June, August and September. This result can be obtained using the adaptive comfort temperature with the following comfort expression proposed by de Dear and Brager [2]: T 0.31 T, 17.8 [1] 35 T comf 20%PPD T comf 10%PPD T daily avrg. 30 25 20 15 10 5 0 5 10 1 Jan 11 Jan 21 Jan 31 Jan 10 Feb 20 Feb 1 Mar T [ C] 11 Mar 21 Mar 31 Mar 10 Apr 20 Apr 30 Apr 10 May 20 May 30 May 9 Jun 19 Jun 29 Jun 9 Jul 19 Jul 29 Jul 8 Aug 18 Aug 28 Aug 7 Sep 17 Sep 27 Sep 7 Oct 17 Oct 27 Oct 6 Nov 16 Nov 26 Nov 6 Dec 16 Dec 26 Dec Figure 10 Outside Temperature Variation During the Year and adaptive comfort temperature Figure 11 Inside Operative Temperature Variation During the Year Figure 10 shows the comfort temperatures for 10% and 20% perception of discomfort conditions by the occupants and it can be used as a reference for assessing comfort feeling in a given month [3]. It can be seen that summer months have a comfort condition at about 25 C.

from Figure 11 too, showing the daily temperature distribution, it can be seen that as the blue line changes quite frequently (showing the dry bulb temperature), the green line showing the operative temperature remains quite constant and this is due to good performance of the envelope. 8. Night Cycle of Natural Ventilation The last step of the natural ventilation analysis was to introduce the concept of night ventilation during three months, namely: April, June and September. Some results are shown in Figure 12. Three analysis were carried out for each of the three months changing the ach (air changes per hour) from 1.0 3.0 1. Temperature Vs. ach for 08-14 July Temperature Vs. ach for 08-14 September 29 26 Operative Temperature 28 27 26 25 24 23 22 21 20 19 Hourly Readings from 08 07 to 14 07 1 ach 2 ach 3 ach Operative Temperature 25,5 25 24,5 24 23,5 23 22,5 22 21,5 Hourly Changes from 08 09 to 14 09 1 ach 2 ach 3 ach Figure 12 Inside Operative Temperature Variation During the Year depending on night ventilation rate Based on of the graphs obtained, it can be concluded that, when ach are increased from 1.0 to 2.0 for a given month, the internal temperatures decrease; however, after further increase of ach from 2.0 to 3.0 no significant change can be seen in operative temperatures. Thus, the most interesting situation is the one with night ventilation introduced into the building with a maximum of 2.0 ach. It is important to note that 2.0 ach is the maximum value of natural ventilation activated only during the night, while a constant value of 0.8 ach is kept during office working hours. Results depicted in Figure 12 are show the effect of night ventilation on operative temperatures of the building. Comparing the operating temperature for 2 ACH cases, it can be noted that, increasing the degree of natural ventilation at night, better indoor temperatures can be attained throughout the day. Thus it can be concluded that better indoor comfort conditions can be attained by natural ventilation if an appropriate amount of night ventilation strategy is put in place. 9. List of References [1] Cursio, V.; Ghilardi, G. Nearly zero energy office building in Lecco, Proceedings of Verso gli edifici ad energia quasi zero : le tecnologie disponibili conference, Milan, October 2011. [2] De Dear, R.J.; Brager, G.S. Thermal comfort in naturally ventilated buildings. Revisions to ASHRAE Standard 55, in Energy and Buildings, Vol. 34 (2002), pp. 549 561. [3] Pagani O.L.; Bonomi M. The Ve.L.E. approach: Energy saving and summer overheating control. Proceedings of ISES Solar World Congress 2005, Orlando, U.S.A, August 2005. 1 From Lombardy Region: http://www.cened.it/software 2 From National Renewable Energy Laboratory: http://apps1.eere.energy.gov/buildings/energyplus/ 3 DesignBuilder Software Ltd: http://www.designbuilder.co.uk/ 4 Comfort temperature constant and continuous running of the plants.