Technicalnote2013/01Internalenvironmentalconditionsforcondensationriskanalysis

1 OverviewThis technicalnotedescribes recent changes to thehandlingof internal environmen-talconditionsforcondensationanalysisinJPA Designer. Itdescribesthetwomainap-proachestointernalconditionsandexplainshowtosavesetsofinternalenvironmentalconditions.

2 InternalconditionsincondensationriskanalysisCondensationriskanalysisrequiresmonthlytemperatureandrelativehumiditydatafortheinternalandexternalclimate. Theexternalclimatedatacomesfromweatherstationdata: JPA DesignerissuppliedwitharangeofdatasetsfortheUK,Ireland, MiddleEast,Asia, AustraliaandNewZealand.Internalclimateconditionsareeither:

derivedfromtheexternalconditionsusingmethodsdescribedinISO 13788:20121.Thismethodissuitablefornaturallyandmechanicallyventilatedbuildingswherethetemperatureiscontrolled, butthereisnocontrolofhumidity.

entereddirectlyintothesoftware. Thismethodissuitableforbuildingswithacon-ditionedinternalclimate.

Both internalandexternalclimateconditionsareset in the Environmentalconditionsdialogue(Figure 1): toopenthedialogueusethebuttononthetoolbaroronthe Editmenuselect EnvironmentalConditions.

1ISO 13788:2012. HygrothermalperformanceofbuildingcomponentsandbuildingelementsInternalsurfacetemperaturetoavoidcriticalsurfacehumidityandinterstitialcondensationmethodsCalculationmethods.

1

Figure 1: The EnvironmentalConditions dialogue

2.1 InternalconditionsderivedfromexternalconditionsInbuildingswhichareheatedand/orcooled, butnotconditioned, theinternalvapourpressureisdependentupontherateofmoisturegenerationwithinthebuildingandtheexternalvapourpressure. ISO 13788hastwomethodsofdeterminingtheinternalrelativehumidityfromtheexternalconditions:

amethodformaritimeclimates, suchasthatintheUK. amethodforcontinentalandtropicalclimates.

2.1.1 Maritimeclimates

FormaritimeclimatesISO 13788denesveinternalhumidityclassesbasedontherateofmoisturegenerationwithinthebuilding. Theyare:

1. Storageareas.2. Ofcesandshops.3. Dwellingswithlowoccupancy.

2

4. Dwellingswith high occupancy, sports halls, kitchens, canteens, and buildingsheatedwithunuedgasheaters.

5. Specialbuildingssuchaslaundries, breweriesandswimmingpools.

Whencarryingoutcondensation riskanalysis it is important toselect theappropriateclimateclass. Ifthereisdoubtastowhichoftwoclassesthebuildingbelongsinalwaysselectthehighest, moreonerousone.Tosettheconditionsforamaritimeclimate:

1. Openthe EnvironmentalConditions dialogue.2. Selectthe Buildinglocation.3. Tick Calculateinternalconditionsbasedonexternalconditions.4. At Climate select Maritime.5. Fromthe Internalhumidityclass listselecttheclasswhichbestmatchesthebuild-

ing.6. Setthe Internaltemperature.7. If thenatureof thebuildingmeans it ismore thanusuallysensitive to interstital

condensationselectanappropriate Risklevel (seeBS 5250:2011fordetails).8. Theprogramnowdisplaysthemonthlyinternalandexternaltemperatureandhu-

miditydata.

2.1.2 Continentalandtropicalclimates

ForcontinentalandtropicalclimatesISO 13788considerstwooccupancyclasses:

normal. high.

Tosettheconditionsforacontinentalclimate:

1. Openthe EnvironmentalConditions dialogue.2. Selectthe Buildinglocation.3. Tick Calculateinternalconditionsbasedonexternalconditions.4. At Climate select Continentalortropical.5. Theprogramnowdisplaysthemonthlyinternalandexternaltemperatureandhu-

miditydata.

3

2.2 DirectlyenteredinternalconditionsForbuildingswheretheinternalconditionsareknown, eitherfromdesignspecicationsorthroughtesting, theenvironmentaldatacanbeentereddirectly. Thesimplestwaytodothisistocreateandsaveaninternaldatasetfollowingtheinstructionsin section 3.Toentertheinternalconditionsdirectly:

1. Tick Usedesigndataforinternalconditions.TheISO databoxesarehidden.

2. Inthelistboxselectoneofthestandardsetsofinternalconditions.Youcanalsoentervaluesdirectlyintothe IntT and IntRH columns, butthosevalueswillonlybeavailableforthatcalculation.

3 Savingsetsofinternalandexternalenvironmentalcondi-tions

Youcanbuildupandsavesetsofinternalandexternalenvironmentalconditionstouseincondensationriskanalysis. Thisisparticularlyusefulwhenexaminingair-conditionedbuildingswhichhavedesignvaluesfortemperatureandhumidity.Userdataisstoredinale Env_user.txt whichiskeptwiththeotheruserdatalesinc:\ProgramData\JPA\JPA Designer (lelocationcorrectforWindows7-seeTechnicalnote2012/01forotherversionsofWindows). Currently, theonlywaytoadddatasetsistoedit Env_user.txt inatexteditor, suchasNotepad(Figure 2). Beforeediting Env_user.txtmakesureJPA Designerisnotrunning.

Figure 2: Editingthe Env_user.txt le

Within Env_user.txt thedataforanexternallocationoraninternaldesignconditionisononeline, witheachlineseparatedbyareturn. Oneachline, thedifferentitemsofdataareseparatedbythepipecharacter, |, withnospacesbeforeorafterthepipe. Thenalcharacteroneverylineisalsoapipe.Thedataitemsare:

4

Item1: whetherthesetisforinternalconditions, 0, orexternalconditions, 1. Item2: whetherthesetissystemdata, 0, oruserdata, 1. Item3: atextdescriptionofthedataset. Thisappearsinthe Buildinglocation or

internalconditions lists, whicharesortedalphabeticallyusingthetextdescription.Thisitemcanstartwiththetildecharacter(), whichdoesnotappearonlists, butcontrolsthewayinwhichitems4--27areinterpreted.

Items427: thesearethemonthlytemperatureandrelativehumiditygures. Tem-peraturesshouldbeenteredindegreescentigradeandrelativehumidityasaper-centage. Theorderofthedatadependsonwhetheritem3startswithatilde().

Ifitem3hasatildethemeanmonthlytemperaturesshouldbeenteredinasequencestartingwithJanuary, followedbytherelativehumiditygures, start-ingwithJanuary(so: Jan temp|Feb temp| |December temp|Jan%rh|Feb %rh| etc.)

If item3hasnotildethetemperatureandrelativehumidityvaluesforeachmonthshouldfolloweachother(thatis: Jan temp|Jan rh|Feb temp|Feb%rh| etc).

Item28: thecountrycode. UK,0. Republicof Ireland, 1. Australia, 2. NewZealand, 3. Asia, 4. MiddleEast, 5.

Item29: appliestoexternalenvironmentalsetsandindicateswhetherinternalcon-ditionsshouldbecalculatedonthebasisofcontinentalconditions, 1, ormaritimeconditions, anyothervalue. Thisitemisusedonlywheninternalconditionsaretobederivedfromtheexternalconditions: itisnotusedifxedinternalconditionsarespecied.

Asanexample:1|1|Newcastle Airport|3.4|92||4.2|89|0|0|

Thisshows:

Externaldata(1). Userdata(1) Location, withnotilde. Pairedmonthlyvaluesfortemperature(3.4and4.2)andrelativehumidity(92and

89). UK (0) Maritimeclimate(0).

5

Oncetheenvironmentalconditionshavebeenenteredandsavedin Env_user.txt andJPADesignerstarted, thenewdatasetswillshowupinthe internalconditions list. Notethattheconditionswillonlyshowiftheirregionmatchestheregionselectedforanalysis.IfthereareseveralusersofJPA Designerwithinthesameorganisationthe Env_user.txtlecanbesetupononePC thencopiedtotheothers, ensuringeveryoneisusingthesamedatasets.

4 FurtherinformationInformationaboutJPA Designermaybefoundonour website2.Technicalsupportenquiriesby emailonly3.JPA TL Ltd2013

2http://www.techlit.co.uk3mailto:support@techlit.co.uk

6

OverviewInternal conditions in condensation risk analysisInternal conditions derived from external conditionsMaritime climatesContinental and tropical climates

Directly entered internal conditions

Saving sets of internal and external environmental conditionsFurther information