Trans RINA, Vol 156, Part C1, Intl J Marine Design, Jan - Dec 2014
and lighting loads as a function of glazing percentage and the lighting control mechanism.
For cabin zones a total reduction in global loads for a 30% glazed façade equates to 4.336% and 4.56% respectively for both north and south facades with and without
light based lighting controls, which is a
culmination of reduced use of artificial lighting and consequently a reduction in the overall annual cooling loads. The relationship is similar with designs that have a greater glazing percentage of 80% with a reduction of global loads of 4.1% in the north and 3.1% in the south between the two lighting control strategies. The greatest increase in global loads however, is noted in the design with the largest glazing percentage which is particularly sensitive to orientation, where by for a given design with 80% glazing loads can be 34.88% higher than the equivalent façade facing north – as is the case when considering cabins which adopt a linear/off daylighting control strategy.
990.89 1000.00
100.00 200.00 300.00 400.00 500.00 600.00 700.00 800.00 900.00
636.92 626.25 609.30 597.66 743.01 961.02 712.50
Overall it is clear that a daylight harvesting scheme could help to reduce operating costs. However, as observed within this case study, with larger glazing percentages, where lighting loads represent less than 17.5% of the total energy consumption of
the cabin, cooling and
heating loads dominate, making elements such as shading, glazing size and characteristics such as solar heat gain coefficients more influential on its overall performance. These results therefore present a paradoxical
challenge for interior designers of these
areas. Due to their lack of daytime occupancy and low lighting requirements, they require the least amount of glazing from an energy perspective but equally require significant glazing for aesthetics, providing a feeling of space and to provide a view of the ocean, which could be argued as what the passenger is actually paying for. The use of a parametric tool with a composite methodology identifies the relative energy cost and compromises that a particular design solution might incur.
0.00 30%
Glazing with
occupancy based
lighting controle
30%
Glazing, with
linear/off lighting control
North Facade 80%
Glazing with
occupancy based
lighting control
80%
Glazing, with
linear off lighting control
South Facade
Figure 24 Comparative analysis of global annual thermal and lighting loads for cabin zones with 1.5m overhang for shading
In any case as diffused light is relatively unaffected by orientation an overall decrease in lighting loads are observed when a linear/off lighting control strategy is adopted. With a 30% glazed cabin this decrease in lighting loads
is between 12.82% and 13.29% with
slighter higher savings of 15.90% observed in cabins with 80% glazing. Facades with greater than 30% glazing tend to exhibit no further gains in lighting as the diffused light supply is sufficient for its quota, as is illustrated by figure 25, where by although a decrease in annual lighting energy is observed, a 30% glazed façade seems to represents the light harvesting saturation point where by any additional natural light may be surplus to the lighting requirements of the zone.
© 2014: The Royal Institution of Naval Architects
A reduction in global loads is also observed in the day and lounge zones represented by figure 26 where by for a south facing cabin with 30% glazing, a decrease of 37.93% is observed in between designs with and without daylight harvesting, similarly a 32.715% reduction is also observed for the same zone with an 80% glazed facade. Overall this represents a much greater reduction in loads compared to cabin areas which is partly responsible due to the lighting requirements being 50% larger than that of cabin zones as well as it have a predominant daytime occupancy. This greater need for lighting is identified in table 10 and 11 where by the idealized glazing percentage
Barcelonan climate. Combining these day/lounge zone can take harvesting, and as it
resides between 30% and 50% for the factors, the
has the greatest
advantage of daylight lighting
requirements for visual comfort the zone has more to save in turns of lighting, which in turn has a profound impact on the cooling loads. This relationship between occupancy and lighting is more adequately expressed
C-111
Figure 25 Percentage energy saving as a function of glazing size in comparison to occupancy based lighting control scheme
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