Trans RINA, Vol 156, Part C1, Intl J Marine Design, Jan –Dec 2014
system with no user controlled interface and is generated in DesignBuilder for all three of the test case rooms. The system itself uses the operative temperature as a means of controlling thermal systems and in doing so accounts for users in high radiant temperature conditions such as when large glazing ratios are used. Overall heating and cooling energy consumption can be assessed for a particular HVAC
system via its coefficient of
performance (COP). Although not the focus of this research the interaction of HVAC systems and control schemes requires further research as the actual energy consumption will be dependent on its construction, use and control.
2.6 WINDOW MODELLING
EnergyPlus has several methods for modelling windows but often requires more detailed data than standard performance indices such as the U value, SHGC and its visual transmittance properties, in this instance a more detailed layer by layer description is required and is provided by spectral data from WINDOW 7.2. [45] which contains peer-reviewed IGDB spectral data [46]. Spectrally weighted average data is placed within the IDF file over the option of full spectral data as it provides an adequate assessment and comparison of other glazing types without compromising computation time although the use of full spectral data would provide more accurate results especially at higher angles of incidence and presents a potential improvement within the proposed methodology.
Typically a glazing type with a high visual transmittance placed at the highest point upon a façade is preferred as it enables the deeper parts of the room to receive daylight. In addition to its placement, room geometry has a key influence as light penetration depth into the room is twice the distance of the height of the window-top compared to the ground. Suggesting that daylight potential for a given room is limited at a specific room depth [47]. Following these principles and studying typical geometry on a case study, the placement of windows begins at 0.1m from the interior
ceiling. The increased glazing percentage is
achieved by extending total window height from this point downwards.
2.7 GLAZING TRANSMITTANCE CHARACTERISTICS
Typical glazing types often have high visual
transmittance properties of 0.685 and low solar heat gain coefficients of 0.362. The total energy performance is indicative of the spectral properties of the glazing element, which has preference for long wave thermal emissions property in summer and the converse in the winter [48]. The use of a parametric methodology identifies the perfect glazing percentage and the balance between solar transmission and
reflection, it also
accounts for the thermal bias of the vessel at different locations.
Figure 4. Light levels at equidistant reference points of the dining room zone
Figure 5. Example of dining zone occupancy and lighting usage for 21st of December at 12 noon
Figure 4 shows how the light level at specific sensor points deteriorates with depth. The light at this point is influenced by many factors including glazing percentage, room geometry, transmission factors, internal surface reflectance, location and the use of shading devices. This data is handled by the daylight simulation module within the EnergyPlus software bundle to calculate the amount of artificial lighting that is required to maintain adequate illuminance levels within the different interior zones. Simultaneously the thermal contribution to cooling loads from artificial lighting is calculated for every hour of the year allowing for the relative impact on the HVAC system to be determined.
3.8 THE PARAMETRIC METHODOLOGY This
study exploring adopts a parametric methodology for design alternatives and to establish
dependencies between design variables. The use of an open source parametric tool ‘jEPlus’ has made it possible
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©2014: The Royal Institution of Naval Architects
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