2.3. General

The above study focuses on the analysis of fenestration shading devices and techniques which are developed previously [1], so as to reduce unwanted solar heat gains in the summer, without conflicting with beneficial ones in winter, as solar gains play opposite roles for heating and cooling in the climate of Cyprus. In the study, emphasis is given on occupancy intervention on manually operated shading devices.

For the study, characteristics of windows and shading devices are specified in terms of geometry and physical dimensions profiles, in various simulations. The intention is to describe synthetically how the quality level of the internal environment is affected in response to hypothetical occupant shutter use patterns. These accommodate possibilities of potential conflicts of the double role of solar gains and destructive interference with the effective performance of the “Zero Energy House”.

Tables 1 and 2, sum up the attempt to systematize various possible shading operations by occupants. It illustrates the correlation between solar heat gains or losses resulting from such operations, for the two seasons, and the thermal performance of the “Zero Energy House”. This is done in order to conclude optimum shading design strategies for maintaining comfort conditions in the building considering the operational aspects of shading techniques.

From the results it is evident that the occupants’ interference and misuse of the manually operated window shutters could be counter-effective and might annul the optimized fenestration design. The uncertainties associated with the shading variable and occupant behaviour can be large in occupied buildings. This occurs, where solar gains is a significant part of the design in achieving indoor comfort conditions without the need of mechanical energy, as in the case of the “Zero Energy House”.

2.4. Winter

The results explicitly indicate that the counter — effect of misused south window shutters could be of vital importance for the maintenance of internal thermal comfort level in winter.

Tables land 2 and graphs 1-4, show temperatures of ambient outdoor and indoor air. Table 1, 1.0 portrays optimised design for winter, in which all shutters are open. It illustrates that the ambient outdoor air temperature varies from 6.5 to 14.0 degrees Celsius, the swing in the inside temperature remains within the comfort zone, from 18.6 to 20.6 degrees only.

The other tables and graphs indicate a drop of indoor temperature ranging from 0.1 to 10.5 degrees Celsius, depending on the extent and orientation of window shutters left shut during the winter day. If all window shutters are left shut, the internal temperature drops below outdoor, by 0.1 to 4.0 degrees. The largest drop occurs mainly between 09.00 to 18.00 hours (table 1, 1.4). These results point out the reliance of the “Zero Energy House” on solar gains.

/

T SIMULATION FOR COLD DAY

ALL FENESTRAT ON UNSHADED

D7.00-19.00

T 16

! * Outdoor AIR T

Indoor AIR T

rig.!. Indoor and Outdoor Air temperature in >>inter. All fenestration unshaded

T S MULAT ON FOR COLD DAY

ALL FENESTRATION SHADED

D7 00-19 00

TIME (Hours)

X I. Outdoor AIR T

rig.2. Indoor and Outdoor Air Iemperature in Winter. All fenestration shaded

Furthermore the small extent of deviation of temperature, incurring when shutters are left shut on the house elevations other than south, confirm the validity of the optimisation of fenestration distribution and orientation on the “Zero Energy House.”

2.5. Summer

Table 2, 1.4 and Fig. 4 illustrate the optimised design strategy for summer, with all shading shutters closed, when the outside temperature reaches a maximum of 35.0 degrees Celsius whilst the inside reaches only 25.5 degrees.

Examining the results of the counter-effective human intervention on the manually operated window shutter on the “all-shut” optimised shading profile for summer (Table 2, 1.4), it is noted that this poses no significant conflict on solar control. Comparing the free thermal behaviour of the building under the optimised summer strategy (Table 2, 1.4, Fig.4. “All Fenestration Shaded”), with the less than optimised (Tables 2, 1.3-1.0, Fig.3). The rise 0.4 to 1.0 degrees Celsius of internal temperature indicated for some configurations presents no serious problem. Even when all window shutters remain open during summer day the internal temperature does not deviate from the comfort zone. Over the complete period of investigation the deviation did not exceed 1.00 degree Celsius, indicating at least for the shading variable, the efficient performance of the fixed shading devices of overhangs and vertical extended walls on the southern orientations for the summer season. For both seasons, the results also emphasize the significant role of the optimisation of:

(I) Fenestration distribution and orientation

(II) Permanent shading overhangs and vertical extended walls

On the thermal performance of the “Zero Energy House”. The sun spends very little time during the summer in front of the major fenestration area which faces south; its south passage is at high altitudes, so window design optimization of shading overhangs in conjunction with extended walls, allow effective shielding from direct radiation.

3. Conclusions

The above observations show that although window shutters contribute to limiting thermal gains in the summer, by reducing indoor temperature up to 1.3 degrees Celsius (table2, 1.4 and 1.0), their negative effects of misusing them in winter defeat the optimized performance of the “Zero Energy House” to the extent of dropping indoor temperature below outdoor during winter (Table1, 1.4).

The results also indicate that the combined effect of the optimum design of fenestration orientation and permanent shading devices provide sufficient sun control without the need of the manually operated shutters and its possible counter-effects.

Even so, if design fenestration aspects such as orientation, size, distribution, and sun control devices, differ to those developed for the “Zero Energy House” the application of shutters for shading could be the only solution. For example, the fixed overhangs do not work for window facing east or west, since the sun is low in the sky in the morning and afternoon. In such cases the introduction of automatic controls is imperative in order to eliminate the negative effects of the manually operated shutters misuse presented above.

References

[1] D. k.Serghides, (1994) Zero Energy for the Cyprus House, the Architectural Association, School of Architecture, London.

[2] Centre for Experimental and Numerical Thermoflow and Department of Mechanical Engineering, University of Pretoria, (1991) “Quick-A thermal design tool and load calculation computer programme, Pretoria, Republic of South Africa.

[3] Mathews E. h., Shuttleworth A. G., and Hanna G. H., (1992) Validation of a design tool for Low Energy Architecture” Proceedings 1992 World Renewable Energy Congress. Pergamon

[4] D. k.Serghides (1988), Prototype Solar House for Cyprus, the Architectural Association, School of Architecture, London.

[5] Gunnurshaug J., Windows as Solar Collectors, SINTEF, Norwegian Institute of Technology, University of Trondheim, Norway