This article, by Enda Gilroy a Building Services Engineer with PM Group, appeared in ‘Building Services News’. The article discusses the benefits available to engineers when employing simulation software in their design. With today’s increased complexity in building designs, engineers are turning to simulation models to aid them in producing a comfortable and energy efficient building.
bs news november 2007 page 21 simulation design in building services BUILDING SERVICES designing Enda Gilroy e: [email protected]In this article we will discuss the benefits available to engineers when employing simulation software in their design. With today’s increased complexity in building designs, engineers are turning to simulation models to aid them in producing a comfortable and energy- efficient building. Buildings in the EU use over 40% of Europe’s energy and create over 40% of its carbon dioxide emissions, a proportion which is constantly increasing. In order to better understand our building energy requirements and, more importantly energy usage, we need more complex solutions than the standard steady-state calculation methods. Now, more than ever, designers are turning to simulation software. This is especially true at the early design stage in the case of a new build. Today’s modern designs have led to an increased use of glass with the façade being incorporated as an integral part of the building. The introduction of the Energy Performance of Buildings Directive (EPBD) aims to improve and reduce the energy consumption of buildings through cost-effective measures. To achieve this reduction, designers must look at all aspects of the building, from its orientation through to solar loading, building mass, ventilation options, its HVAC services and its electrical demands. By using simulation software we can use this to better understand how buildings will react to their environment and help predict their environmental impact in terms of energy usage and CO2 output. CIBSE Steady State calculations v Dynamic Thermal Simulations The main difference between the CIBSE steady state heat loss/admittance procedures and dynamic thermal simulation is that dynamic thermal simulation has the ability to take account of variations in weather over the course of an entire year, and to carry forward conditions from previous days. Steady state heat loss is the equivalent of running a 24-hour heated building with no internal heat gains for a long period of time at a constant outside air temperature and no solar income. Remove the internal heat gains from a dynamic thermal simulation model, run the model using a weather file with a constant outside air temperature and no sunshine. At the end of a 30-day period the simulated heating load is exactly the same as the steady state heat loss calculation. The admittance procedure uses a 24-hour harmonic to predict summer design day performance using idealised weather data for the design day. The procedure does not have the ability to carry forward the influence on performance of previous days. In fact, the procedure assumes that the design day has been preceded by an infinite number of identical days. To reproduce this type of analysis with dynamic simulation software an extended period of weather data is used. This weather data contains repeated days of the same idealised weather used in the admittance procedure. At the end of a 30-day simulation on repeated day weather the simulated performance is very close to that predicted by the admittance method. Sustainable Building Design To achieve sustainable building design a new innovative building design is needed. This bs news Nov 2007 TO PRINT 15/11/07 10:43 AM Page 23
In this article we will discuss thebenefits available to engineerswhen employing simulationsoftware in their design. Withtoday’s increased complexity inbuilding designs, engineers areturning to simulation models toaid them in producing acomfortable and energy-efficient building.
Buildings in the EU use over 40%of Europe’s energy and createover 40% of its carbon dioxideemissions, a proportion which isconstantly increasing. In order tobetter understand our buildingenergy requirements and, moreimportantly energy usage, weneed more complex solutionsthan the standard steady-statecalculation methods. Now, morethan ever, designers are turningto simulation software.
This is especially true at the earlydesign stage in the case of anew build. Today’s moderndesigns have led to anincreased use of glass with thefaçade being incorporated asan integral part of the building.The introduction of the EnergyPerformance of BuildingsDirective (EPBD) aims to improveand reduce the energyconsumption of buildingsthrough cost-effective measures.
To achieve this reduction,designers must look at allaspects of the building, from itsorientation through to solarloading, building mass,ventilation options, its HVACservices and its electricaldemands. By using simulationsoftware we can use this tobetter understand how buildingswill react to their environmentand help predict theirenvironmental impact in termsof energy usage and CO2output.
CIBSE Steady State calculationsv Dynamic Thermal SimulationsThe main difference betweenthe CIBSE steady state heatloss/admittance procedures anddynamic thermal simulation isthat dynamic thermal simulationhas the ability to take accountof variations in weather over thecourse of an entire year, and tocarry forward conditions fromprevious days.
Steady state heat loss is theequivalent of running a 24-hourheated building with no internalheat gains for a long period oftime at a constant outside airtemperature and no solarincome. Remove the internalheat gains from a dynamicthermal simulation model, run
the model using a weather filewith a constant outside airtemperature and no sunshine. Atthe end of a 30-day period thesimulated heating load is exactlythe same as the steady stateheat loss calculation.
The admittance procedure usesa 24-hour harmonic to predictsummer design dayperformance using idealisedweather data for the designday. The procedure does nothave the ability to carry forwardthe influence on performanceof previous days. In fact, theprocedure assumes that thedesign day has been precededby an infinite number ofidentical days. To reproduce thistype of analysis with dynamicsimulation software an extendedperiod of weather data is used.This weather data containsrepeated days of the sameidealised weather used in theadmittance procedure. At theend of a 30-day simulation onrepeated day weather thesimulated performance is veryclose to that predicted by theadmittance method.
Sustainable Building DesignTo achieve sustainable buildingdesign a new innovativebuilding design is needed. This
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simulation design in building servicesmethod is based on a 3-Dcomputer model of the buildingand dynamic simulationmethods. The integrated datamodel (IDM) for the computerincludes the building geometry,building constructions,occupancy profiles, etc whichdescribe fully the use andconstruction of the proposedbuilding design.
This IDM is used with thedynamic simulation methods topredict the energy, comfort andvisual aspects of the building.The environmental impact of thebuilding in terms of CO2emissions is also predicted. Thedesign process continues untilthe environmental impact of thebuilding is reduced as much aspossible. Many innovativetechniques such as daylight
design, passive solar design,thermal mass, night cooling,brise soleil, natural ventilation,etc can be evaluated.
By modelling the effect ofnatural ventilation and nightpurging combined with theexposed thermal mass of thebuilding, the peak internaltemperatures can be broughtwithin the recommendedcriteria. Using dynamicmodelling we can predict areasof a building where excessivetemperatures occur, we canthen take remedial action toreduce these temperatures.Simulation software allows thedesigner to model open-ablewindows, roof-vents, andmechanical ventilation; thesecan be brought on individuallyor in tandem with operating
parameters assigned to them.
An example could include high-level windows to open when theinternal temperature rises above22°C, or open when the outsidetemperature is between 15°Cand 20°C. This can be then usedto simulate the effectiveness ofnight purging.
Computational Fluid Dynamics(CFD) The increased use of simulationprograms has enabledengineers to focus on morecomplicated designs. With theincreased use of ComputationalFluid Dynamics (CFD) we cannow use a mathematical modelto predict almost every scenariowithin a space. By using CFD adesigner can see the outcomeof his/her design before itreaches construction. We cannow predict air velocity, airmovement, temperaturegradients and how equipment ina space effects its surroundingenvironment. By using thisinformation we can determine,for example, the best points ofair distribution outlets.
Figure 1 left indicates theeffectiveness of the use of CFD.Here air is supplied at high levelover an operating table. This isused to ensure that theoperating area has adequateair distribution to ensure thepatient’s health and well being.By using CFD the air velocitiesand temperature gradients can
Figure 1 — Computational Fluid Dynamics (CFD) of an operating area(Image courtesy of Integrated Environmental Solutions (IES)
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simulation design in building servicesbe modelled within a space toidentify any stagnant zoneswhere poor air distribution maybe occurring. CFD is also used tomodel air flow around a buildingwhich can be used to see theeffects of exhaust points from abuilding and how these pointswill interact with theirsurrounding environment.
CFD is also being employed intothe effectiveness of doublefacades. Although thesefacades may be aestheticallypleasing, detailed analysis hasshown that the effectiveness ofthese facades is somewhatlimited. Double facades takequite a considerable time todesign correctly and sometimesare not suited to the building
initially anticipated. These resultsmay be conveyed to both thearchitect and client at an earlystage, as they can be costly indesign time and, moreimportantly, are a costly part ofthe building’s construction.Simulation packages are used toshow how these facadesinteract with the building overthe course of a year anddemonstrate their positive andnegative effects to the space.
Daylight AnalysisPeople are more comfortable ifthey can relate to outsideweather conditions and enjoydaylight. The Radianceprogram can simulate theamount of daylight experiencedin the space and allowdesigners a three-dimensional
view of the working conditionsthat occupants will be using.Excessive window area can leadto glare, particularly if peopleare working at computermonitors. The Radiancesimulation program can alsoprovide information on thepossibility of glare.
It can be difficult to determinethe time of day and seasonwhen glare could be a problemon computer screens. This canbe made more difficult if the suncan reach the workstation fromthe perimeter windows or froman atrium. By using theRadiance Simulation (Figure 2),areas of interest or concern canbe identified quickly andremedial action can be taken.
Figure 2 — Radiance Simulationimaging (Image courtesy of IES)
Figure 3 — Simulation to demonstrate what effects glazing will haveinternally within a building (Image courtesy of IES)
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simulation design in building servicesSolar Analysis and SiteConditionsSimulation packages are nowused to determine how abuilding will react within itsproposed environment,parameters such as solarshading, and how surroundingbuildings effect not only shadingbut wind velocities around theproposed model. The orientationof the model can be easilychanged to optimise the bestlocation for the building, wherebefore these aspects werepreviously too complicated ortime-consuming to be analysed.
We can use simulation todemonstrate to a client whateffects glazing will haveinternally within a building(Figure 3, previous page) andproduce detailed studies oflighting effects within a space.This can prove useful indetermining the amount ofnatural light and how lightaffects the visual aspects withinthe building.
Complete Building ServicesDesignSimulation software may also beused in conjunction with HVACsystem sizing software packages.This allows the results ofsimulations to be directlyimported into the sizingprograms of the mechanicaland lighting services within abuilding. This has the addedadvantage during design
development, where changes inthe design can be incorporatedwith the click of a button.
We can also now employ theuse of renewable technologies,wind generation, CHP and solartechnology which can beinputted into the software. Thiscan now be used to offset thebuildings carbon emissions,which in turn may lead to ahigher building energy rating. Anengineer can now check forcompliance with the BuildingRegulations and for theincoming Building Energy Rating(BER). These packages let theengineer explore differentalternatives to reducing thebuilding energy consumptionand carbon dioxide emissions.
ConclusionMore than ever, youngengineers are taking advantageof these simulation packagesand, while they may have thetechnical and academic ability,they may lack in some practical“real world” experience. Withsome basic training anyone canbuild a model and get somebasic results. However, it is theunderstanding of these resultsand how they will affect the sizeand type of services requiredwithin a project that counts. Allresults should be cross-checkedagainst the CIBSE rule of thumbbooks, as these can provide aquick check to see if the resultsobtained from the simulation are
in line with industry norms.
The increased public awarenessof energy usage means thatsimulation packages arebecoming more important whendesigning our buildings. Clientswant a prediction of how theirbuilding will perform before it isconstructed. By modelling abuilding, we can contributemore during the early stages ofdesign and, working with thearchitect, can productivelyinfluence the shape and form ofbuildings to achieve moreefficient designs.
ReferencesCIBSE Briefing 8 Reducingemissions through energyefficiency;
Beattie K. Thesis; An ImprovedDesign Methodology forSustainable Building Design.
Enda Gilroy, Dip. Eng, B. Eng,joined Project ManagementGroup as a Graduate Engineerfrom DIT Bolton St and has beenwith PMG for one and a halfyears. He works in the buildingservices department as a designengineer and is part of theinternal simulation design team.He has a diploma and honoursdegree in building servicesengineering and has previousexperience from the mechanicalcontracting side of the industry.He is also a part-time lecturer inDIT Bolton St.
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