Trans RINA, Vol 156, Part C1, Intl J Marine Design, Jan –Dec 2014
For this reason a more detailed radiosity method is needed such that interrefelctions and areas susceptible to glare can be considered. Overall the supports the notion that interior surface reflectance has a significant impact on the performance of a daylight harvesting scheme.
3.5 INTEGRATIVE INDICES FOR DAYLIGHT HARVESTING
As the size of the window alone does not adequately describe the
potential context, a metric for passive strategies in this to describe the impacts of both
occupancy and daylight availability has been derived as an integrative metric that can be used by designers to deduce the
viability of daylight harvesting in any
particular space. This has been developed from the daylight availability ratio from the architectural industry. Which is defined as the “fraction of working time in a year during which sufficient daylight is available on the work plane surface” [22]. The new metric developed as part of this study accommodates specific occupancy and lighting requirements. The basic formula below defines the daylight utilization ratio and can be summarised as the fraction of time in which available daylight within the zone is above the specified lighting requirement.
= ℎℎ
The Daylight Utilization Ratio (DUR) is an important compound metric which specifies the influence of many parameters including the glazing percentage, interior surface reflectance, room geometry and occupancy. As an integrative index it serves as a useful design metric to evaluate
the impact of passive strategies on the
utilization of daylight. The DUR values for the first 3 light sensors are considered in all zones for a north facing façade with 30% glazing, in all three locations and is represented in table 9. This indicates that due to higher lighting demands, substantial daytime occupancy and low length to width ratio [51], the day/lounge zone seems to benefit mostly from a daylighting strategy with the mean DUR for the day/lounge zone in Venice being 6.54% larger than the dining zone and 124% larger than the cabin zone, this notion is also apparent in section earlier sections where lighting, heating and cooling loads were compared, revealing that the day/lounge zone continues to benefit the most when considering overall energy performance. It is also evident from this table that an improvement in surface reflectance can help to improve the DUR by an average of 35.9% for cabin zones, 23.3% for day/lounge zones and 5.32% for dining zones, which is also reflected in the reduction in lighting loads explored in the previous section.
The annual daylight utilization factor for equally-distant sensors within a specific case study is shown in Figure 23, where it
is possible to describe the relationship
between glazing percentage and DUR through nonlinear multivariate regression techniques, allowing for the
C-110
Figure 23 Daylight Utilization for day/lounge zones in a southerly orientation with no shading device
DUR values for zones with 30% glazing facing north with wall and ceiling surface reflectance at SLL code, 2009 suggestions
Cabin Zone
Venice 0.2233 Barcelona
0.2421 Cairo 0.3022
Day/Lounge Zone
0.5011 0.5873 0.6473
0.3436 Cairo 0.3864
0.6191 0.7309 0.7891
Dining Zone
0.4703 0.5499 0.5851
DUR values for zones with 30% glazing facing north with wall and ceiling surface reflectance at SLL code, 2012 suggestions Venice 0.3086 Barcelona
0.4986 0.5826 0.6086
Table 9 Comparing DUR values for different zones and locations
3.6 COMPARATIVE ANALYSIS
The use of daylighting is able to reduce the need for artificial lighting. As artificial lighting in itself is an internal heat gain source, its reduction helps to further reduce the cooling load. This relationship is illustrated in figures 24, 26 and 27 whereby for each zone, a comparison is made between the total sensible thermal
©2014: The Royal Institution of Naval Architects prediction of performance based on orientation and
glazing. Furthermore, this data could be used to define the position of photo-sensors for the control of an artificial lighting scheme as well as predicting the performance of other lighting technologies such as LED bulbs,
given occupancy the area, schedules. annual lighting loads and In summary, the degree of
penetration of daylight is limited to the geometry of the glazing system as well as the room. Thus figures 23 offers
harvesting within the interior. Enabling the designer to zone areas
accordance to daylighting potential if the DUR is significant.
useful information on the potential for daylight effectively in
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