General information

ASHRAE degree days heating/cooling: 1011 / 3102 Kd
Indoor design temperatures/humidities: The mean indoor temperature varies from 21.5 °C during winter to 28.5 °C during the summer period
Design ventilation rates: 30 ach per hour

During the design process the following environmental issues were taken into account wherever possible, in addition to those already discussed:

• The embodied energy of materials and components;
• The reduction of CO2 emissions;
• The avoidance of ozone-layer-depleting substances;
• The use of natural materials;
• The use of wood from managed forests.
• The solar fins operation shows that the control of solar gains and the exploitation of natural lighting can be efficacious.

The solar fins operation shows that the control of solar gains and the exploitation of natural lighting can be efficacious.

The main design concern was the integration of the building into the surrounding built environment and its responsiveness to changes.

Furthermore, the willingness to make the necessary investment is reflected on the entire design procedure, as well as on choice of the materials and methods of construction.

Thus, the constructed building is capable of controlling itself, of keeping its energy consumption low, of preserving the environment from unnecessary pollution, while it is responsive to natural conditions.

• Designed to exploit the natural lighting potential of the area

Shading

• Solar fins (vertical glass silk-screen-printed panels)
• Fixed horizontal metal grills
• External venetian blinds
• Passive/Hybrid cooling techniques
• Night ventilation
• Ceiling fans
• Cold storage system (ice banks)
• Central Building Energy Management System (BEMS)
• HVAC

Good daylight levels are primarily attained through the narrow plan layout of the building and the 'intelligent' nature of the eastern facade. Dimensions of a typical office are 7m wide by 3m deep in order to exploit natural lighting.

The rear facade facing west requires no shading due to its proximity to adjacent buildings (around 3m). The high performance of the daylighting system allows considering the artificial lighting system only as a backup. In order to minimize energy consumption, various design concepts have been adopted. The walls and ceiling are painted in light colours thus increasing the diffusion of the light. The workstations are equipped with task lighting devices under user control, while the general indirect lighting level is low (averagely around 200-250 lux). The most commonly used luminaries are high-efficiency fluorescent lamps. Special automated systems are used to control the level of artificial lighting, in accordance to the natural lighting level. In order to assure the performance of the lighting systems, the users, via infrared remote controls, can manually override the automatic operation of these systems. Installation of presence detectors assures the switching on/off of the general lighting system. Furthermore, a lighting control system is installed in the parking area of the building, which switches on the lighting system only if cars or people are moving. Insulation

The Avax Project adopted wall U-values of 0.8W/m²K. Roof insulation has an U-value of 1.2W/m²K. Whilst heat loss should not be a problem, the potential for unwanted heat gain through the roof from the high summer sun might have required a lower U-value. North and south facades are generally preferred for glazing areas: the north requires no shading and the south can easily be shaded from the high angle of the sun by a simple overhang or horizontal louvre system.

Most of the projects have similar glazing ratios on the north and south facades (although it is zero in the case of the Greek project due to location). This is appropriate for non-domestic buildings, where the benefit of winter solar gains is low due to a relatively small heating load which does not justify extra large areas of south facing glazing. However, this contrasts with domestic buildings where, for the cooler parts of Europe, larger glazing ratios on the south are advantageous.

The solar fins are the dominant daylighting feature, installed on the eastern facade. They are formed by vertical glass silk-screen-printed panels and are able to sufficiently shade the indoor spaces adjacent to the facade. Another important feature is that they are automatically controlled in response to temperature and solar radiation. In order to assure the proper operation of the devices, manual override is provided via infrared remote controls. In addition to these devices a series of fixed white horizontal metal grills provide further shading.

The top and mezzanine floors are shaded by conventional external venetian blinds, also controlled by the central system and with manual override. Windows and skylights (one for each office bay) are manually operable. The window elements have a total height of 1.70 m. They are divided into an upper pane for daylighting (one third of the window height) and a lower pane for vision (two thirds of the window height). The glazing ratio is only 10% on the western elevation of the building, while on the eastern elevation it rises to 45%. All windows are clear, double-glazed units with a U-value of 2.8 W/m²K.

The suspended ceiling is partially or totally absent leading to higher than normal floor to ceiling heights (> 3m). This also facilitates natural ventilation and carries another important advantage of thermally coupling the floor slab mass with the occupied space: this ensures that the beneficial effect of the stabilising effect of the thermal mass is realised.

However, to fully exploit the benefits of thermal mass, the structure must be cooled at night. This is best achieved by increased night-time ventilation rates. Mechanical night-time ventilation carries an energy cost for fan power, but it has been shown that, for well designed systems, this will be well under the equivalent conventional daytime cooling energy. Throughout the majority of the year thermal comfort is achieved by the provided natural ventilation.

To ensure that the natural ventilation design works efficiently, an air flow simulation programme was used, PASSPORT AIR (from the framework of the PASSCOOL Research Programme).

Four different scenarios of the use of windows and doors for natural ventilation were studied:

• open external windows and closed internal doors,
• open external windows and internal doors, but closed rear windows,
• open external windows, internal doors and rear windows,
• open external windows, internal doors of all offices and open rear windows.

The results proved that even in the case of the single sided stack driven ventilation, the air flow rates are sufficient to provide a comfortable environment for the occupants

The HVAC system, formed by the central heat pump, consumes about 34 kWh/m2/year for the heating and the cooling operations. Although resistive heating with electricity is not an acceptable low energy strategy (because of the poor conversion efficiency when electricity is generated), due to the coefficient of performance (COP) of a heat pump being around 2.5 - 3.5, this inefficiency is compensated and heat is generated with an acceptably low CO2 emission.

The storage of heat and coolth (in an ice store) permits the use of off-peak electricity which is economically attractive although it cannot be considered a low energy strategy.

Cooling
The Avax building utilizes ice storage which, even if not an energy saving strategy, surely reduces costs. More importantly, the operation of the building with night ventilation cooling minimises the demand for mechanical cooling. The HVAC system is provided as a back-up system. The raised false floor permits the installation of local air-conditioning units covering the local load demand, fresh air, as well as inlet and extraction fans for natural ventilation. The raised floor acts as an air plenum. The energy design of the building aims at reducing/avoiding the operation of the HVAC system through various passive-cooling techniques. More specifically, the external shading fins are used during the warm days to control the solar gains, while the internal gains due to the operation of the artificial lighting system are minimized and therefore the cooling load of the building is reduced. Furthermore, night ventilation techniques are applied as a 'pre-cooling' strategy by operating a mechanical ventilation system at a rate of 30 Air Changes per Hour (ACH), from 21:30 to 7:00, when the outdoor temperature is lower than the indoor one. Another applied hybrid cooling strategy is the operation of ceiling fans during the summer season, which are manually controlled. This operation permits bringing the comfort zone from 25 °C to 29 °C. Finally, the central cooling system (air/water heat pump) is combined with a cold storage system (ice banks). The installation is controlled and programmed by a central Building Energy Management System (BEMS). The functioning of the BEMS can reduce the cooling through appropriate control of solar shading and night ventilation. On the other hand, occupants are also expected to cooperate in the minimization of the energy consumption (by opening windows and using the ceiling fans or air-conditioning units when required).

The Avax Office Building is expected to consume around 90 kWh/m² of energy per year for heating, ventilation, lighting, cooling and control facilities. This is only half of the consumption of a traditional office building in Greece.

The annual energy consumption per use is also illustrated in the diagram on the left. It is important to underline that the cooling and heating consumption are unbroken, because the same heat pump unit is used for both systems. Therefore the BEMS system records the total energy consumption of this unit. The diagram "performance" shows that the annual low-voltage consumption is close to 80 kWh/m² (consumption of equipment, elevators, and any energy consuming device except the cooling, heating and lighting equipment).

The HVAC system plant, formed by the central heat pump, consumes about 34 kWh/m²/year for heating and cooling. The energy consumption of the artificial lighting system is close to 15 kWh/m², while the fan-coil units and the distribution system consume about 12 kWh/m². The high energy consumption of the low-voltage appliances is due to the ventilation system operating during the night (separated from the HVAC system), the ice banks, the ceiling fans, the operation of the solar fins, etc. The annual energy consumption is close to 140 kWh/m².

Office room, 2nd floor, south facing facade

System: Internal and external shading devices

Sky condition: Sunny day with some clouds and direct sun on the facade

Description: The luminance picture shows a good distribution of luminance on surfaces, also into the depth of the room. As previously presented, the dominant daylighting feature is represented by the solar fins. These shading devices provide a shading coefficient of 70% and are automatically rotated in response to temperature and solar radiation. In order to evaluate the performance of the solar fins, extensive simulations have been performed using the Radiance software tool. The calculated daylight factor for a representative office space is shown in the Figure on the left. According to this figure the daylight factors vary from 2% to 23% with a value close to 10% on top of the workstations.

Rating is excellent for Built Environment and Functionality, while Economy and Responsiveness has also achieved very high credits. Less than 3% of the occupants complain about discomfort and they mostly proved to be able to work efficiently. Moreover, the majority is able to properly operate the terminal devices. The building operators can adjust the systems to optimise performance and energy management is well organized throughout the building. A potential of improvement exists in suitability: more services and facilities could be provided, mainly for disabled persons