Global energy simulation methods

Although whole building simulation programs have daylighting calculation modules, they are mainly focused on the thermal domain. In fact, a survey made on 2008 showed that at that time, even though developers of these tools viewed lighting control as worthy of support, just a few software accepted the full complexity of blinds or translucent facade elements.

The most common energy simulation tools area ESP-r and EnergyPlus.

ESP-r (ESRU, 2013) is an integrated energy modelling tool for the simulation of the thermal, visual and acoustic performance of buildings and the energy use and gaseous emissions associated with associated environmental control systems. By addressing all aspects simultaneously, ESP-r allows the designer to explore the complex relationships between a building’s form, fabric, air flow, plant and control. ESP-r is based on a finite volume, conservation approach in which a problem (specified in terms of geometry, construction, operation, leakage distribution, etc.) is transformed into a set of conservation equations (for energy, mass, momentum, etc.) which are then integrated at successive time-steps in response to climate, occupant and control system influences. ESP-r comprises a central Project Manager around which are arranged support databases, a simulator, various performance assessment tools and a variety of third party applications for CAD, visualisation and report generation.

EnergyPlus (US-DOE: www.energy.gov) has its roots in both the BLAST and DOE–2 programs. BLAST (Building Loads Analysis and System Thermodynamics) and DOE–2 were both developed and released in the late 1970s and early 1980s as energy and load simulation tools (Winkelmann & Selkowitz, 1985). EnergyPlus is an energy analysis and thermal load simulation program. Based on a user’s description of a building from the perspective of the building’s physical make-up, associated mechanical systems, EnergyPlus will calculate the heating and cooling loads necessary to maintain thermal control set points, conditions throughout a secondary HVAC system and coil loads, and the energy consumption of primary plant equipment.

In general, energy-performance-simulation tools are not well prepared for detailed lighting analysis. Limitations are, for example, visual comfort analysis such as the calculation of the Daylight Glare Probability that, for detailed calculations, requires rendering an image (Wienold, 2009; Molina, 2014).

2.5.1 Integrated lighting and thermal simulation methods

One possible option to couple lighting and thermal analysis is to develop a mathematical model for each case to analyze. Tzempelikos and Athienitis (2007) analyzed a perimeter office room using the Radiosity method for the illuminance level calculations and a thermal network approach for the thermal and energy performance calculations. In the study controlled roller shades were considered and modelled as perfectly diffusers.

Since creating a new model for each case can be time consuming and complex, some researchers have worked on combining two single-domain solutions programs. An example is the work proposed by Janak (1997) that did a direct run-time coupling Radiance and ESP-r, which enabled modelling the interactions between electric lighting control and the rest of the building (Molina, 2014).

Another attempt of performing coupled simulations in both domains is proposed by Wienold et al. (2011) where Daysim and ESP-r were indirectly coupled. In this methodology on annual simulation had to be made for window/position of shading combination.

Then, a control algorithm was implemented to choose the shading positions and the electric lighting power required for each time step.

Finally a schedule of electric lighting power and shading positions were passed to ESP-r, used to modify the internal gains and the BSDF description of the CFS on each time step of the simulation. In this approach ESP-r and Daysim are considered to be indirectly coupled because all the control has to be made using lighting sensors (Molina, 2014).

2.5.2 Integrated lighting and thermal simulation software

iDbuild is probably the most standard Thermal-Lighting coupled simulation tool (Petersen & Svendsen, 2010) which implements custom mathematical models for performing integrated analysis. This tool is focused on the early design stage. It’s programmed in Matlab and uses a graphical user interface to accept input and provide results.

It’s essentially the combination of a lighting calculation module called Light Calc (Hviid et al., 2008) and a thermal simulation module called BuildingCalc (Nielsen, 2005). The tool couples both domains by hourly feeding the daylighting calculation results into the thermal calculations.

The main limitation of this software is that it only allows rectangular rooms with one window. BuildingCalc, the thermal module, models the room as a two-node thermal network with one overall thermal transmittance and a lumped effective thermal heat capacity. On the other hand, the solar heat gains are modeled more realistically, being corrected by the incident angle and shading. It calculates hourly values of indoor temperature, heating and cooling demands by solving the thermal network’s differential equation, and allows implementing several systems as shading, heat recovery, variable ventilation, variable insulation, heating and cooling.

LightCalc, on the other hand, uses a simple ray-tracing approach and the luminous existence method (Park & Athienitis, 2003), which is similar to the radiosity method. These calculations have been validated against detailed Radiance calculations, showing that they are accurate enough to be used in early design stages (Molina, 2014).

OpenStudio

Open Studio Software Development Kit (Guglielmetti et al., 2011) is being developed as a way of providing building designers with a full-featured software framework to support rigorous and multidisciplinary building simulations.

It’s, in summary, a cross-platform collection of software tools to support whole building energy modeling using EnergyPlus and advanced daylight analysis using Radiance. It’s an open source project to facilitate community development, extension, and private sector adoption. OpenStudio includes graphical interfaces which include the Trimble SketchUp Plug-in, RunManager, and ResultsViewer. The Trimble SketchUp Plug-in is an extension to Trimble’s popular 3D modeling tool that adds EnergyPlus context to the SketchUp program. The Plug-in allows users to quickly create geometry needed for EnergyPlus using the built-in functionality of Trimble SketchUp including existing drawing tools, integration with Google Earth, Building Maker, and Photo Match. RunManager manages simulations and workflows and gives users access to the output files through a graphical interface. ResultsViewer enables browsing, plotting, and comparing EnergyPlus output data, especially time series. The Radiance capabilities of Open Studio allow implementing the Daylight Coefficient method, the Three-phase method, and calculating simplified Daylight Glare Probability.

CHAPTER 3