Industrialised, Integrated, Intelligent sustainable Construction - I3con

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SUSTAINABLE CONSTRUCTION HANDBOOK 2 Figure 1. ALLP building before and during retrofit The building has a concrete structure and energy performance was poor due to an old and low-grade internal insulation, single glazed windows and many cold bridges. Existing solar protection was original. There was no mechanical ventilation, thus fresh air came only by infiltration and handopening windows. Adequate air change is necessary to reach good working conditions and cannot be guaranteed in these conditions. A complete diagnostic of the building and the systems was done by an engineering office in 2005 [1]; it showed a heating consumption of about 140kWh/m². The other problem underlined by the building owner was summer overheating and discomfort. For instance a temperature of 34°C was measured in June 2005 in an office on the first floor oriented toward the South. These working conditions were not acceptable for the employees and productivity decreased by almost 20%. This situation accounts for the intent of the ALLP managers to equip the building with an air conditioning system, but the energy audit showed the need to produce a complete refurbishment program. Just before the retrofit operation, we organised a survey led by an independent organism [2]. Questionnaires to the occupants and local measurements confirmed the overall discomfort. This kind of study needs to be more systematic when a refurbishment operation is considered, like the one existing for household, the EPIQR methodology (Energy Performance Indoor Environmental Quality Retrofit) [3], whose goals are: optimisation of energy consumption, improved indoor environmental quality and cost-effectiveness. During the conception phase, ALLP was modelled with the dynamic simulation software TRNSYS and the building was split into eight thermal zones. The ground floor comprises two zones (entry rooms, lobby and workshops); the first and second floors are identically zoned in three parts: one office zone mainly oriented South, one office zone mainly oriented North and a common zone where comfort is not essential (staircase, etc). The two office zones on first and second floors are critical because they comprise most of the people working in the building, inducing a rather high population density and also high internal gains. The dynamic simulation was used to develop sensitivity studies on technical parameters. The building was considered from a macro-scale (envelope) to a micro-scale (regulation of the energy systems) and significant energy savings were identified at each level. The analysis was coupled with an economical approach, keeping in mind that the project had to be a demonstration case and thus reproducible. The main focus for this first case study was energy saving, and the simulation results prove that a reduction by a factor of 2 on primary energy consumption and by a factor of 4 on CO2 emissions can easily be achieved. Thanks to the preliminary studies and with the work of the architect, fluid engineering office, INES and the ALLP managers, the building renovation was planned. First enhancements were passive solutions including improvement of the envelope (low-emissivity double glazing filled with Argon, external insulation), new effective external solar protection (Fig. 2) and night ventilation. However simulations demonstrated that during summer, comfortable conditions would not be reached. The need of a cooling system guided the choice towards a heat pump. The system was chosen reversible even if a highly efficient new gas boiler of 350 kW had been set up in 2004, and so an air-water heat pump of 100kW was installed (Fig. 2). Distribution is done by a fan coil unit in every room. An attempt was also made to improve the efficiency of office lighting (control of artificial lighting in 180
HANDBOOK 2 SUSTAINABLE CONSTRUCTION response to occupancy and amount of daylight). 90 m² of photovoltaic panels were installed on the roof. The 10 kW grid connected system should produce about 11 MWh per year. Figure 2. Details of the renovation: heat pump located on the roof and new solar shading device Monitoring Refurbishment was achieved by mid 2007 and the building was fully equipped with sensors. The monitoring allows the gathering of the necessary feedback on energy consumption and comfort in the offices. The tele-supervision of the building is done by a Building Management System (BMS) that integrates an internet protocol. The remote access permits to automate, control and monitor the building with a lot of freedom in data acquisition. All the results allow feedback at two levels. The first one is focused on the behavior of the building and is based on energy meters and ambient temperature probes, as well as exterior weather sensors. The second one applies to the scale of an office room in which wireless sensors record the temperature, humidity, luminosity, occupancy, opening of window (Fig. 3). The aim of the first level of monitoring is to detect failure, evaluate the performance of the renovation and compare measurements of energy consumption with predicted values. A longer observation period is also necessary to evaluate the software model accuracy. The second level of monitoring illustrates the working conditions in critical office rooms, and thus the occupants’ level of comfort. It also gives an idea of the evaluation of the airflow distribution on comfort. Measurements help to identify potential problems associated with the control of heating, cooling, ventilation and air conditioning (HVAC) regulation. North Nord Presence detector Wireless air temperature sensor Air temperature sensor Magnetic contact switch Integrating sphere Humidity sensor Figure 3. Local monitoring of 4 test offices South Sud 4 test offices The web platform allows access to the data from any internet-connected computer. The interface was made as user-friendly as possible and is under continuous improvement. 181
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