Solar House

The Glengariffe Passive Solar House has a South facing Conservatory that supplies 45% of the heating requirement for the house. It was monitored throughout the entire year of 2005, and data of more then 50 sensors was collected at five-minute intervals. The Active Solar House was used to study the effect of a sunspace (or conservatory) on the performance of the entire building.

In order to absorb the maximum quantity of solar radiation, the flooring in the sunspace was covered with dark coloured tiles fixed to a 100mm concrete slab. The 250mm thick wall, separating sunspace from the main structure of the house, has also been painted in a dark colour, making it the main buffer and allowing little radiation to escape from the sunspace due to reflection.

Vents below floor level cover the length of the sunspace, as viewed from west to east.

The solar gains received should be utilised to cover required heating loads or should be stored in the thermal mass of the building

In the experimental design we incorporated two measures to fulfil the above criteria. Ventilation ducts to the inner building can be used on demand and if appropriate to bring warmer sunspace air into the rooms inside. The 100mm concrete slab floor and a 250mm concrete wall inside the sunspace area work as storage buffers

Shading to reduce unwanted solar gains is achieved with retractable insulated blinds controlled by a thermostat. The mobile insulation installation allows us to retain energy when there is no more radiation reaching the sunspace during the night. On the other hand it allows us to provide shading when it is required and to make precise adjustments.

Vents below floor level are opened and closed automatically by the Building Management System when necessary to avoid overheating and overcooling.

Two devices for cooling the sunspace were installed thereby reducing the cooling load of the inner rooms: Ventilation flaps at the top and the bottom of the structure and the retractable shading system. In tandem they form a passive ventilation system.

As shades are lowered from their retracted position, a channel is formed between the glass and the insulation material. The channel, if exposed to sunrays, will heat up and cause convection movement. A ventilation flap at the top end of the channel can be opened to allow this hot air to escape. As it does so, air is drawn into the channel which in turn causes colder air from outside to enter the sunspace through flaps at the bottom of the construction, if these are opened.

The second system consists of a number of ducts that allow warmer air to be ventilated into the inner house. This system is governed by a control system, which monitors the temperature and humidity in the sunspace as well as in the rooms into which the air can be ventilated. If appropriate, flaps will be opened and fans will cause the necessary airflow.

Care was taken in the design of the sunspace so that it will, as far as possible, not obstruct daylight necessary to reach the inner rooms of the house. The shading devices have a highly reflective coating on the bottom side to help to illuminate the inner rooms with diffused day lighting when lowered.

Connecting the main building to the sunspace with air ducts allows the integration of the passive behaviour of the sunspace and responds to solar heating by venting the warm air int

o the heating and air-conditioning system of the house. Its operational integration is achieved by communication between the control system of the sunspace and other control systems for heating in the house by the building management system.

Convector ventilation: The cooling of the Sunspace during warm weather is facilitated through a convection system, facilitated by creating a channel between the insulated aluminum blinds and the glazed roof in combination with opening flaps on the very bottom and very top of the construction.

Hot vent: On sunny, but cold days, the blinds are rolled up and sun light enters the space. Here it heats the air which begins to move upwards. Ducts that connect the inside of the building with the conservatory are opened by the BMS and the warm air travelS through to the inner rooms, being moved by the convection motion. Cold air from in

side the house is brought back to the sunspace at ground floor level, thus creating a circulation of ever warmer air.

Results

Compensating for fluctuations in indoor temperature and using the actual recorded data for the ambient conditions, including the sunspace, the calculations show that, at a permanent indoor temperature of 19°C, the heating load would be 6,560 kWh for the year with a 31.4 % saving over the 9,564 kWh required if the sunspace was not fitted (All figures are gross figures, not taking into account other measures to reduce energy consumption, like active solar and heat pump).

A further 472 kWh was gained from air that was fanned from the sunspace, reducing the heat load to 6,088 kWh and producing a total saving of 36.3%.

It is expected that the figure for fanned air will improve, as software governing the devices has been tuned during the year. Mainly in the first six months of 2005 potential gains were lost, due to inadequate reaction to ambient conditions.

If heating load figures are brought in connection with the size of floor area and three quarters of the sunspace is considered living space (40 m2 / 4 * 3 = 30 m2), then the calculations show an even higher saving potential.

Without Sunspace: Heating load = 9,564 kWh Area = 170 m2 Heating load/m2 = 56.3 kWh/m2

With Sunspace fitted: Heating load = 6,088 kWh Area = 200 m2 Heating load/m2 = 30.44 kWh/m2 Saving on the heating load per m2 = 45.9 %

Conclusion

If constructed with good understanding of the thermodynamics involved, a sunspace can offer a range of benefits. It can be a very comfortable and desirable seasonal living space, whilst making an impressive contribution to the heating of the building and also supplying pre-heated air for internal ventilation. More

over, it can create a buffer zone between living space and outdoor space that can be utilised for plant growth, whilst providing shading for the house in the summer time, and providing cooling in the summer time through controlled ventilation

However, several considerations need to be observed: the orientation of the sunspace, and good design with considerations for thermodynamics. Gains and losses should be calculated carefully before choosing a type of glass to be installed - translucency and insulation properties are often opposing factors with costs rapidly rising when trying for the ideal. The sunspace must not be heated, it must be possible to isolate the sunspace from the rest of the building, efficient controls must be installed, and the use of venting devices and a retractable blind system are absolutely vital.

Sunspaces are suitable for family homes as much as they are for larger and commercial buildings. The biggest obstacle to the introduction of sunspaces is lack of understanding of the subject of thermodynamics. This applies to the house builder or owner as well as to the industry.

Today many houses are built in Ireland with a conservatory. Many of these structures are great heat-losers, as little attention is paid to fundamental heating properties. This can be changed and, as was demonstrated in the experimental design, can be turned into a factor contributing to energy saving on a substantial scale.

So, not only are new technologies to be considered, it appears that there are also great potential gains in refining our methods of building. We may have to start getting used to the idea that long-standing traditional approaches in all aspects of energy consumption are slipping into the past, and try to look forward to the dawning post-fossil-fuel society.