During ENERGYbase project time a comprehensive set of scientific support was done. Herewith, selected actvities and results are presented and following sections reports briefly on ENERGYbase design and system features, e. g. south faced facade, solar-assisted air-conditioning.

1.1 Use of solar energy of the south faced facade

Figure 2 illustrates the solar energy concept and design of the south faced facade. Solar radiation is transformed into electricity by 400 m2 photovoltaics and as well as into useful heat by around 300 m2 flat-plate collectors. Due to the shape of the south faced facade the opaque elements follows two functions. Primary active solar energy systems are faqade integrated and generate power and heat and secondly overheating by solar radiation is prevented because of an optimal shading effect in summer of the opaque faqade elements. According to the passive house concept — which is already applied successfully in residential buildings — the passive use of solar energy in winter time is taken into account and this solar design of the south faced faqade reduces the heating demand of ENERGYbase office building and as well the daylight comfort is improved.

Figure 3 contains a comparison of solar radiation on a vertical south faqade and vertical north faqade. As well figure 3 shows the annual performance of solar radiation on two different surfaces with different declination, e. g. on one hand solar energy which is available on the transparent parts of the south faqade and on the other hand on the active solar components. Two important results are stated by analysing this annual performance of solar energy on different orientated surfaces:

• In summer the south faqade performs like a vertical north faqade

• The special design of the south faced faqade increases the amount of solar radiation in the range of 38% in comparision to vertical south faced faqade, e. g. active solar components generate much more energy.

1.2

Solar-assisted air-conditioning system

The energy systems of ENERGbase office building are designed to use both a water based and an air based energy distribtion system. The basic temperature control of the office areas is realised by the water based heating and cooling system. The air treatment system is only designed in order to control indoor humidity and to supply fresh air to the offices. Consequently the air-conditioning unit is dedicated to treat only supply air, e. g. it controls and covers only latent loads. Herewith the comfort requirements of the air-conditioning unit are much more moderate in terms of energy use. arsenal research proposed to implement a solar-assisted air-conditioning system which is based on the standard configuration of the desiccant evaporative cooling technology and contributes strongly to achieve the energy targets of ENERGYbase (energy efficiency and use of renewables).

The energy efficient air-conditioning technology is using three thermodynamic processes in order to treat supply air: 1) dehumidification of ambient air by means of a rotating sorption wheel 2) pre­cooling by means of adiabatic cooling in return air combined with an energy efficient rotating heat recovery wheel and 3) evaporative cooling of the supply air by means of a humidifier. Figure 4 shows a standard configuration of the desiccant evaporative air-handling unit.

Aiming an energy efficient air treatment by means of solar-assisted DEC technology the system requires high solar fractions for the regeneration of the sorption wheel and for supply air heating in

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winter. arsenal research applied transient system simulation (TRNSYS 16.1) in order to estimate solar fractions and to assess the DEC system performance. Standard TRNSYS types were used and adapted, but the control of the interactive DEC performance is a complete new developement. Figure 5 shows all relevant air treatment components of a DEC system and the control sequence demonstrating when is which component is activ.

Operating mode 1 Heating X X (80%) ^Hx 2 Heat recovery X 3 Free ventilation X (40%) 4 X X (50%) X (40%) 5 X X (60%) X (40%) 6 X X (70%) X (40%) 7 Adiabatic cooling X X (80%) X (40%) 8 (return air) X X (90%) X (40%) 9 X X (95%) X (40%) 10 X X X (95%) X (55%) X 11 X X X (95%) X (70%) X Fig. 5. Control strategy which was developed in order to simulate the annual performance of standard Desiccant Evporative Cooling systems configuration

Transient system simulation were conducted by taking weather data from METEONORM Software (4) for Vienna. The solar system is modelled by flat-plate collectors of around 285 m2 gross area and coupled with two hot water storage each 7.400 l volume. The flat-plate collector type is a SONNENKRAFT SK500N-ECO and is oriented to the south/ 31,5°. Table 1 lists the relevant collector curve coefficients which have been put into the collector modell and used in the transient simulation. The solar system is operated in low flow and the specific mass flow of the flat-plate collector was set to 20 kg/hrs. m2. The TRNSYS simulation time step was defined as a 5 minute interval.

Figure 6 contains transient simulation results of the DEC system performance during one summer week. The ambient air temperature achieve values above Tamb > 30°C and the solar radiation varies day by day. Regarding the simulation results following statements can be stated:

• Considering the selected summer week the DEC system operates mainly in full desiccant evaporative cooling mode, e. g. dehumidification by means of sorption wheel, evaporative cooling by means of return and supply air humidifier and as well heat transfer by means of the heat recovery wheel;

• On sunny days the flat-plate collector system generates sufficient temperature Tcoll < 90°C in order to load the hot water storage;

• On sunny days the hot water storage system provides sufficient temperature around Tstorage < 70°C; an effective temperatures stratification is achieved; on dys without DEC operation hot water storage temperature exceeds Tstorage > 85°C;

• The DEC system is operated solar autonomously, 100% regeneration heat is supplied by the solar system, the DEC system provides supply air temperature in the range of Tsupply air < 23°C also when ambient temperature exceeds Tamb > 30°C;

• According to the cooling concept — where indoor temperature control is done by the water based thermal mass activation and not by air ventilation — it is possible to operate the ENERGYbase DEC system 100% by solar energy;

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The solar DEC system operation will be monitored by arsenal research in 2009 and there will be an assessment and comparison study between transient system simulation results and measured performance data.

2. Conclusion

Passive house standard has long been successfully applied in residential buildings. However, there are comparatively few examples of the passive house standard being applied in larger building complexes across Europe. Three main principles serve as the basis for the passive house concept: insulation against the loss of heat, air-tightedness, and controlled ventilation with heat recovery.

In the design process of the ENERGYbase office building a three step approach was excecuted:

1) building form follows energy — e. g. reducing the energy demand for heating cooling and air­conditioning as much as possible and using daylight as much as possible 2) implementation of energy efficient HVAC systems coupled with low temperature distrubtion systems 3) using renewable energy sources as much as it is possible on-site.

One of the innovative features of ENERGYbase is the exclusive use of renewable energy. The access to local wells water allows to use geothermal energy which completely covers all sensible heating and cooling requirements. Furthermore, 400 m2 photovoltaic panels located on the south facing facade of the building supply around 10% of the total electricity requirements. An innovative ventilation concept enables the integration of solar energy in summertime by means of solar-assisted desiccant evaporative cooling system, as well as the use of greens plants to ensure ecologically-friendly, controlled humidification in winter.

During the planning phase a significant scientific support was provided by using expert tools — like transient building and system simulation and computational fluid dynamics. Whether the energy and comfort targets will be achieved in real operation this is going to be assessed by arsenal research by using comprehensive monitoring equipment which is already implemented.

Taking the results from transient building system simulation and values from practise ENERGYbase is going to require around 57 kWh el/m2 which corresponds to a primary energy demand of 153 kWh/m2 (electricity to primary energy conversion factor of 2.7). This is a significant reduction of primary energy demand in comparision to a standard office building arcross Europe. ENERGYbase will yearly save around 180 tons of CO2 emissions.

ENERG ENERGYbase construction costs are around 14.5 Mio. € which corresponds to specific investment of 1.930 € per square metre useful area. The specific investment for standard Austrian office building is around 1.200 € per square metre useful area. Participants of the ENERGYbase planning team were Vienna Business Agency (developer); POS Architekten ZT KEG (architecture); KWI Engineers GMBH (HVAC planner); RWT plus (building statics); arsenal research (integration of renewables energy systems/ simulation / monitoring); OGUT (project co­ordination Interreg IIIA/ Know-how transfer); IBO — (building physics); Energy Center Bratislava; Institute of Thermal Engineering at the Graz University of Technology (simulation green buffer).

ENERGYbase — designed for a sunny office future — will serve as a reference project highlighting the compatibility of ecological and economic considerations in the construction of state-of-the-art office properties. Since August 2008 ENERGYbase construction phase is finished and the commissioning of each energy related system has been started.

Acknowledgment

ENERGYbase project is funded by European Commission — Programme INTERREG IIIA Austria — Slowakia, by Wiener Wirtschaftsforderungfonds (WWFF/ISTEG), by Programmlinie „Haus der Zukunft“ of the BMVIT, by the City of Vienna — Photovoltaik-Forderungsfonds.

References

[1] www. energybase. at

[2] FLUENT, Fluent Deutschland GmbH, Darmstadt, Version 6.2, 2005

[3] TRNSYS, Transient System Simulation Program, Solar Energy Laboratory, University of Wisconsin Madison, Version 15.09, 2001

[4] METEONORM Version 5.1 Copyright METEOTEST Fabrikstrasse 14, CH-3012 Bern, Switzerland, Swiss Federal Office of Energy, CH-3003 Bern, November 2004