The Solar Community Centre was constructed based on the idea of creating a building, which meets and satisfies the objectives for future community buildings for all age groups and social stratums. Furthermore, the goal was to build an optimized building in terms of resource usage and an ecologically sound building both in construction and operation. The finished building is seen in figure 1 to 3.
The Solar Community Centre has a total floor area of 1.050 m². The centre is divided into two sections: The actual community centre to the West, constructed in two stories, and a workshop to the East, for local teenagers. The Solar Community Center is open to the public and contains a café, kitchen facilities, media rooms, workshops, meeting/class-rooms etc.
The following ecological and energetic measures have been incorporated into the Solar Community Centre.
- Building integrated PV-system
- Natural/hybrid ventilation
- Passive cooling
- Passive solar heating
- Solar heating for domestic hot water
- Ecological insulation materials
- Usage of rainwater for flushing
- Visualisation and monitoring program
Each of the measures is described in more detail in the following.Passive design Measures Passive cooling and heating of ventilation air
Preheating and cooling of the ventilation air is done through concrete ground channels. The fresh air is collected on the south side of the building. Collection is either through inlets situated just above the ground outside the building or through inlets placed at the bottom of the space between the two glass panes in the double glass facade. The air is guided through the concrete channels underneath the building to the ventilation basement where the mechanical backup fans are also situated. A heat exchange between the ground and the ventilation air occurs and depending on the season and the control the ventilation air is either heated or cooled. The different control strategies are illustrated in the figures 9 to 11.
There are two concrete channels leading the fresh air into the building.
- To the main building (west). It has a length of 16 m (5m under solid ground and 11m underneath the building) before it enters the ventilation basement.
- To the workshop area (east). It has a total length of 11 m (4 m under solid ground and 7 m underneath the building) before it enters the ventilation basement.
The diameters of both the channels are 800 mm. In the ventilation basement the air is collected and distributed to the different rooms in the building. The supplementary heating of the fresh air is delivered via an air convector.Passive solar heating
Behind the double facade towards the South a light-constructed glass building has been constructed. The space in the glass building is only heated via passive solar heating and functions as a buffer zone for heating of the adjacent rooms. Additionally, the buffer zone reduces the heat loss from the adjacent rooms in the main building. In wintertime the glass building can be used as a protected room against the outdoor climate. In summertime the glass building is partly shaded by the solar cells integrated in the facade. Finally, there are temperature-regulated openings in the glass building and in the facade for ventilation and reduction of the room temperature. In extreme weather situations (very cold or hot days) it is possible to close off the glass building to the rest of the building and thus eliminate cold or warm drafts to the rest of the building. The regular heating system in the building is supplied by a combination of floor heating and radiators.Daylighting
Daylight has been an important issue in the design of the Solar Community Building. The building construction with the glass facade and the high windows in the hallway makes the distribution of daylight very efficient.
The ventilation system is designed using natural ventilation with mechanical backup. The system may therefore also be characterised as a hybrid ventilation system. The system is demand controlled. The BMS logs temperature and CO2 levels in each of the rooms in the building (11 zones) and the ventilation is regulated according to defined set points. The ventilation principle works as displacement ventilation. The inlet ventilation air enters the rooms in the building through inlets integrated in the walls located close to the floor.
In each room the ventilation is guided towards the central hallway running through the building. The exhaust is either ventilated through vents in the roof of the hallway or through motor regulated windows also located high above the hallway. To assist the natural driving forces wind cowls have been attached the exhaust openings on the roof.
46 m2 PV cells have been integrated in the outer glass pane of the South oriented double facade of the Solar Community Centre. The space between the two panes in the double facade is used for preheating of the ventilation air and the PV cells are hereby somewhat cooled, which improves the efficiency. The cells are visible, both from the inside and the outside of the building, ensuring a high demonstration effect. This is illustrated in figure 4.
The PV panels consist of poly-crystalline solar cells with a peak performance of 5,2 kWp. The produced electricity is either used in the building or sold to the utility. The expected yearly electricity yield is 2.700 kWh. The integration of the panels has been designed in such a way that all wiring is hidden from view, but at the same is reachable for future maintenance and inspections. This is illustrated in figure 5 and 6. The aluminium profile system in the facade, in which the PV panels have been inserted, is split up into sections favouring the electrical connections between the PV panels, using whole and half modules. This solution also lowers the production costs of PV cells.
Solar heating for domestic hot water
As a parallel to the glazed sun-space for use of passive solar heating, a solar thermal collector is integrated into the southern facade. The solar thermal collector was primarily installed for demonstration purposes for the users of the community centre but also works as a secondary energy source for domestic hot water. The system is placed vertically and is connected to the hot water tank of the building.
All outer walls are insulated with flax insulation material and heavy concrete back walls. The heavy back wall works as a thermal store for internal- and solar heating. It stores the energy in the daytime and releases it when needed. Furthermore, parts of the walls are insulated with flax wool, (Heraflex), expanded volcanic stone (Perlite), cellulose-wool (Ecofiber) and traditional mineral wool (Rockwool). These sections have been constructed for monitoring purposes in order to evaluate the building materials. Sections of the different types of insulation material are made visible to the users of the Solar Community Centre through small demonstrations “windows” in the inner wall as illustrated in figure 14.
The Solar Community Centre has been prepared to utilise rainwater for toilet flushing, however the system has not yet been connected.Visualisation of system operation
All consumption data, weather conditions, electricity and hot water production from the building integrated PV cells, solar thermal collector, and the indoor climatic conditions are visualised on a big screen in the central meeting room and café. The principal construction of most of the ecological and energetic measures is also displayed on the screen. The visualisation has been made user-friendly, by allowing users to select which displays they want to see.
The indoor climate and energetic measures are evaluated in a monitoring program.The indoor climate
A detailed monitoring programme regulates the indoor climate in the different rooms in the Solar Community Centre. The control strategy consists partly of regulation of the air quality, measured by the levels of CO2 (winter) and partly by measuring the room temperature (summer). The measurements are fed back to the BMS where the control of the hybrid ventilation is regulated. However, measurements of the relative humidity and air velocities at the displacement units have also been carried out in order to fully evaluate the comfort in the building. Temperature and relative humidity is also measured along the ground concrete channel. This information is fed back to the BMS and regulation of opening and closing vents for preheating and cooling of the ventilation air is regulated. All the data is logged in 15 minute intervals. The figure below shows a set of sensors placed in the concrete ground channel.
Both long- and short-term measurements of the PV system performance have been and are being carried out. The long term measurements include the logging of the electricity yield (kW) from the PV system. The short term measurements include:
- UI curves for the panels connected in the connection unit.
- UI curves for partial shading of the panels
- The voltage drop over cabling and connection units
- Inverter efficiency at a selected point
Monitoring of outdoor conditions, including solar radiation (direct- and diffuse-radiation on a horizontal and vertical surface), temperatures and wind speeds are collected in a weather station above the southern facade of the Solar Community Centre. The station logs data in 15 minutes intervals.
In the following section some of the main results from the monitoring program will be presented.The temperature levels
Generally the room temperatures in the Solar Community Centre match expectations. Monitoring results logged in the period March 2002 to May 2003 show the following variations in some of the most critical rooms when the building is in use:
|The workshop||17 °C - 29 °C|
|The three large rooms||18 °C - 30 °C|
|The media-tech room||18 °C - 29 °C|
|The media room||17 °C - 31 °C|
|The large meeting room||19 °C - 30 °C|
Even though the temperature reaches 31 °C, the number of hours where these significant overtemperatures occurs when the building is in use are so little, leading to an acceptable indoor climate in most of the rooms. The media room on the first floor has a significant number of hours with overtemperatures and the users of the room are dissatisfied with the indoor climate. Measures are been taken to overcome this problem. An example of monitored temperatures for the large meeting room is illustrated in figure 18.
As can be seen from figure 18, the very warm periods with temperatures above 27 °C, are only peak values (corresponding to warm outside temperatures and sunny). A closer evaluation of the system shows that night cooling and day ventilation are active when the room temperatures exceed the set point of 24 °C. The inlet air temperature (from the ground channels) varies between 18 and 23 °C (in summer) and therefore offers an opportunity for cooling. There is an unused potential for increased cooling, as the inlet temperature from the ground channels is lower than the room temperatures. Therefore, by changing the set point for starting the ventilation, the overheating can be regulated as the ventilation rate is increased and more cooling is delivered to the critical rooms.The air quality
Generally CO2 concentrations in the Solar Community Centre vary as expected. The monitoring results logged in the period March 2002 to May 2003 show variations from 400 ppm to 1900 ppm. The air quality is regulated at a set point of 1000 ppm and the back up mechanical fans is started at CO2 levels above 1500 ppm. The highest concentrations of CO2 obviously occur when many people are gathered in a single room. Generally, high concentrations only occur as peak values. An example of CO2 concentrations monitored from March 2002 to May 2003 for the large meeting room is shown in figure 19.
Figure 19 shows that the average concentration is about 1000 ppm and there was only one peak concentration of 1900 ppm. The system could be improved by changing the set point for the mechanical backup ventilation fans from 1500 ppm to 1200 ppm.The PV system
The short term monitoring showed that, as a whole, the PV system is operating according to expectations. The conversion losses are small, except for one string where a mismatch loss of 10 % was found. This is however, expected when the distribution on one panel is analysed. To reach a lower mismatch loss sorting of the panels must be improved or a smaller performance tolerance must be defined. In both cases this would increase the panel costs. The wire losses are minimal (under 3 %), which is recommended by the Danish quality check arrangement. This shows that the materials used have been dimensioned correctly. Shadowing tests show that there is a performance drop of 20% when 10% of the panels are in shade. This shows that the electrical configuration is relatively stable in these types of shading situations. The long term monitoring of the PV system showed that the electricity produced from the PV cells is distributed evenly over the year with a performance of 3-4 kW at high solar radiation (the peak value for the cells is 5,2 kWp). The effect is higher in winter (4 kW) than in the summer (3 kW) as the PV panels are placed on a vertical facade and the sun therefore, in winter, when it is low in the sky, has a more direct angle onto the panels. The effect of the cells however corresponds very nicely to the effect of the incoming solar radiation both in summer and in winter. This is illustrated in figure 20, where the effect of the PV cells is plotted in the same graph as the solar radiation measure per m2 for a week in June. Figure 20. The effect of the PV system and the incoming solar radiation.
The 24 hour mean efficiency of the PV system is approximately 8 %. Figure 21 shows the efficiency for a selected period from March to June 2002.
The electricity production for the monitored period February 2002 to May 2003 is illustrated in figure 22
In figure 22 the production of electricity from the PV system is illustrated as both a daily electrical production and an accumulated yield. It shows that the production from March to October is very constant (the slope of the accumulated graph is almost linear). In the winter months, from November to February, the production is smaller. The yearly production was expected to be 2.700 kWh. As can be seen from figure 20 the production from Feb 2002 to Feb 2003 showed an energy yield of about 2.700. The PV system therefore operates as predicted.CONCLUSIONS
Overall the users of the Solar Community Centre are pleased with the facility. The PV system is operating extremely well, and produces 2.700 kWh per year as expected. The indoor climate is, in most of the facility, regulated according to expectations. There have been some problems with overheating in some of the rooms, but the cooling potential in the concrete ground channels has not been fully exploited in the current regulation of the system. Furthermore, external solar shading will be installed during summer 2003, which will be regulated accordingly to the indoor temperature and outdoor solar radiation. The Municipality of Kolding has a reputation of being in the front line when it comes to environmentally sound, energy efficient and ecological issues. The building of the Solar Community Centre has once again proven that the municipality is not afraid to forge ahead, when it comes to state-of-the-art building solutions. The Solar Community Centre has already received the Nordic Environmental label.FUTURE WORK
The Danish Government granted an application for continuation and the establishment of a more compre-hensive monitoring program which will continue until the end of year 2006. Esbensen Consulting Engineers Ltd. will continue its role as the project manager in collaboration with the municipality of Kolding, the Lift of Quarters project, Aalborg University, and the users and workers of the Solar Community Centre in Kolding. The objective of the extended monitoring program is to regulate the system further, hereby reducing or eliminating overheating and draft situations.