Helsinki, August 15 2000

Dear MSG members,

Working on draft 4 and performing the pre-integration modelling in frame
of BS-7 \"HVAC Performance Validation\" project we have reviewed IFC
R2.X model and encountered following problems, which could have general
impact on the IFC-Model, specially in the HVAC Domain:

-   BS-7 project is going to extend already defined property sets
    because of their incompleteness (e.g Pset_AirHandler, Pset_Boiler
    etc.). BS-7\'s draft 4 documents in IAI FTP/Web site contain
    proposed extensions and **we propose that they would be accepted
    already in R2.x**. The same kind of extensions we have made for
    IfcValve, PsetSensor, Pset_ControlDamper and Pset_FluidMover, so
    they **they are proposed to be accepted in a same manner in R2.x.**

-   Additionally, we have defined new property sets for several
    components (e.g Pset_Radiator, Pset_CooledBeam etc.) to include
    these essential types of IfcFlowEquipment object referring to these
    property sets. **We also propose to expand functionality of R2.x to
    include these types.** The same kind of extension we have made for
    IfcActuator, IfcController and IfcDamper so **they are proposed to
    be accepted in a same manner in R2.x.**

-   We think that the property sets definitions are very generic, but
    they do not allow references to object types . Therefore, **we
    propose to consider if all existing property sets describing HVAC
    components would be defined as IFC-classes**. Such a class would
    inherit e.g. from IfcFlowEquipment class and hold component specific
    data such as references to other components (e.g. Pset_AirHandler
    refers using the attribute Fans to IfcFlowEquipment objects
    describing fans). We are convinced that it would improve modelling
    work, because it would simplify adding new components to the
    existing schema. Using inheritance it would not be necessary to
    change any existing class for purposes of defining new subclasses
    (see above).

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-   The property set Pset_HvacSensor, it is a new class released as 2.0,
    defines an attribute Range as IfcReal. Typically, range is expressed
    explicitly by a pair of values (maximum and minimum range). **We
    propose its Data Type would be changed accordingly.**

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-   We have been looking for \"clean\" way how to extend Pset_Coil to
    include electrical coil. The main difference is that an electrical
    coil has also to point to common electrical appliance properties.
    **We propose that such an extension could also be made as a part of
    R2.x.**

-   For sound pressure levels R2.x includes the property set
    Pset_SoundPressureLevels, in which [pressure levels]{.underline} are
    measured in decibels at a reference pressure of 20 microPascals for
    standardised octave band frequencies. There are also applications in
    which sound [power levels]{.underline} are needed in decibels at a
    reference power of 10-12 Watts for the standardised octave band
    frequencies. **To expand its functionality we propose to include the
    corresponding property set Pset_SoundPowerLevels in R2.x**.

Please find attached also an additional Excel document that describes BS
extensions in the context of IFC object hierarchy.

BS-7 project team

  --------------------------------------------------------------------------------------------------------------------------------------------------------
  **Schema**                     **Entity / Type /       **Description**      **Additional description of         **Proposed solution**
                                 Property Set**                               extension**                         
  ------------------------------ ----------------------- -------------------- ----------------------------------- ----------------------------------------
  IfcHvacDomain                  IfcValve                needed extension for                                     IfcInherentCharateristicEnum (Linear,
                                                         inherent                                                 Exponential, IfcPolyline, Other,
                                                         characteristic                                           NotKnown, Unset)

                                 IfcController           extend controller                                        
                                                         type enumeration to                                      
                                                         include heating                                          
                                                         curve. A heating                                         
                                                         curve defines the                                        
                                                         dependency between                                       
                                                         outside temperature                                      
                                                         and inlet                                                
                                                         temperature of a                                         
                                                         radiator heating                                         
                                                         system                                                   

                                 IfcActuator             extend actuator type                                     
                                                         enumeration to                                           
                                                         include the                                              
                                                         thermostatic                                             
                                                         actuator                                                 

                                 IfcDamper               extend damper type                                       
                                                         enumeration to                                           
                                                         include the closing                                      
                                                         damper                                                   

  IfcSharedBldgServiceElements   IfcFlowEquipment        extend flow                                              
                                                         equipment type                                           
                                                         enumeration to                                           
                                                         include following                                        
                                                         components: cooled                                       
                                                         beam, heat recovery                                      
                                                         unit, humidifier,                                        
                                                         ducted silencer,                                         
                                                         radiator                                                 

                                 Pset_Boiler             make this property                                       
                                                         set an IFC class, in                                     
                                                         order to improve                                         
                                                         extensibility of IFC                                     
                                                         model.                                                   

                                                         needed extension for reference to the operating mode of  IfcEnumeratedProperty (Fix, TwoStep,
                                                         operating mode       the boiler                          Modulating, Other, NotKnown, Unset)
                                                         enumeration                                              

                                                         needed extension for thermal output of a boiler related  IfcSimplePropertyWithUnit
                                                         standard thermal     to standard test conditions         (IfcPowerMeasure)
                                                         output                                                   

                                                         needed extension for inlet water temperature related to  IfcSimplePropertyWithUnit
                                                         standard inlet water standard test conditions            (IfcThermodynamicTemperatureMeasure)
                                                         temperature                                              

                                                         needed extension for outlet water temperature related to IfcSimplePropertyWithUnit
                                                         standard outlet      standard test conditions.           (IfcThermodynamicTemperatureMeasure)
                                                         water temperature                                        

                                                         needed extension for maximum energy load rate related to IfcSimplePropertyWithUnit
                                                         standard maximum     standard test conditions            (IfcPowerMeasure)
                                                         load                                                     

                                                         needed extension for minimum energy load rate            IfcSimplePropertyWithUnit
                                                         minimum load                                             (IfcPowerMeasure)

                                                         needed extension for flue gas temperature at maximum     IfcSimplePropertyWithUnit
                                                         maximum flue gas     load                                (IfcThermodynamicTemperatureMeasure)
                                                         temperature                                              

                                                         needed extension for flue gas temperature at part load   IfcSimplePropertyWithUnit
                                                         part load flue gas                                       (IfcThermodynamicTemperatureMeasure)
                                                         temperature                                              

                                                         needed extension for boiler water capacity.              IfcSimplePropertywithUnit
                                                         water capacity                                           (IfcVolumeMeasure)

                                                         needed extension for stoichiometic fuel/air ratio        IfcSimpleProperty (IfcReal)
                                                         lambda                                                   

                                 Pset_AirHandler         make this property                                       
                                                         set an IFC class, in                                     
                                                         order to improve                                         
                                                         extensibility of IFC                                     
                                                         model.                                                   

                                                         needed extension for Bag of zero or more references to   IfcComplexProperty (BAG \[0:?\] OF
                                                         heat recovery units  an IfcFlowEquipment object of type  IfcObjectReference (IfcFlowEquipment))
                                                                              HeatRecoveryUnit that defines the   
                                                                              heat recovery unit(s) that are used 
                                                                              by the AirHandler                   

                                                         needed extension for Bag of zero or more references to   IfcComplexProperty (BAG \[0:?\] OF
                                                         humidifiers          an IfcFlowEquipment object of type  IfcObjectReference (IfcFlowEquipment))
                                                                              Humidifier that defines the         
                                                                              humidifier(s) that are used by the  
                                                                              AirHandler                          

                                                         needed extension for Air leakage of the casing of air    IfcSimplePropertyWithUnit
                                                         air leakage rate     handler subjected to air pressure   (IfcVolumetricFlowrateMeasure)
                                                                              (under a standard test)             

                                                         needed extension for Noise transmitted into the ductwork IfcPropertySet (Pset_SoundPowerLevels)
                                                         transmitted sound    (under a standard test such as ISO  
                                                                              3741, ISO 3744, ISO 9614, ISO       
                                                                              5136). Reference to a property set  
                                                                              Pset_SoundPowerLevels               

                                                         needed extension for Airborne noise emitted by the       IfcPropertySet (Pset_SoundPowerLevels)
                                                         emitted sound        casing of the unit (under a         
                                                                              standard test such as ISO 3741, ISO 
                                                                              3744, ISO 3746, and ISO 9614).      
                                                                              Reference to a property set         
                                                                              Pset_SoundPowerLevels               

                                                         needed extension for Thermal insulation of the casing    IfcPropertySet (Pset_Insulation)
                                                         thermal insulation                                       

                                 Pset_Coil               make this property                                       
                                                         set an IFC class, in                                     
                                                         order to improve                                         
                                                         extensibility of IFC                                     
                                                         model.                                                   

                                                         needed extension for Heat source of coil. If It is an    IfcEnumeratedProperty (Fluid, Electric,
                                                         heat source type     electric coil, reference to a       Steam, Other, NotKnown, Unset)
                                                         enum                 property set Pset_ElectricCoil      

                                                         needed extension for Temperature efficiency (under a     IfcSimpleProperty (IfcReal)
                                                         temperature          standard test)                      
                                                         efficiency                                               

                                                         needed extension for List of air temperatures of         IfcComplexProperty (LIST \[1:2\] OF
                                                         entering air         entering conditions; the list       IfcSimpleProperty
                                                         temperature          consists of dry bulb followed by    (IfcSimplePropertyWithUnit
                                                                              wet bulb                            (IfcThermodynamicTemperatureMeasure)))

                                                         needed extension for List of air temperatures of leaving IfcComplexProperty (LIST \[1:2\] OF
                                                         leaving air          conditions; the list consists of    IfcSimplePropertyWithUnit
                                                         temperature          dry bulb followed by wet bulb       (IfcThermodynamicTemperatureMeasure))

                                                         needed extension for Air flow rate                       IfcSimplePropertyWithUnit
                                                         air flow rate                                            (IfcVolumetricFlowrateMeasure)

                                                         needed extension for Air pressure drop at the related    IfcSimplePropertyWithUnit
                                                         air pressure drop    air flow rate                       (IfcPressureMeasure)

                                                         needed extension for Regenerated sound (under a standard IfcPropertySet (Pset_SoundPowerLevels)
                                                         regenerated sound    test). Reference to a property set  
                                                                              Pset_SoundPowerLevels               

                                                         needed extension for Sound attenuation (under a standard IfcPropertySet (Pset_SoundPowerLevels)
                                                         sound attenuation    test). Reference to a property set  
                                                                              Pset_SoundPowerLevels               

                                 Pset_ControlDamper      make this property                                       
                                                         set an IFC class, in                                     
                                                         order to improve                                         
                                                         extensibility of IFC                                     
                                                         model.                                                   

                                                         needed extension for Inherent characteristic of the      IfcEnumeratedProperty (Linear,
                                                         inherent             control damper                      Exponential, IfcPolyline, Other,
                                                         characteristic enum                                      NotKnown, Unset)

                                                         needed extension for Regenerated sound (under a standard IfcPropertySet (Pset_SoundPowerLevels)
                                                         regenerated sound    test). Reference to a property set  
                                                                              Pset_SoundPowerLevels               

                                                         needed extension for Sound attenuation (under a standard IfcPropertySet (Pset_SoundPowerLevels)
                                                         sound attenuation    test). Reference to a property set  
                                                                              Pset_SoundPowerLevels               

                                                         needed extension for Minimum operating torque (under a   IfcPropertySetWithUnit
                                                         minimum operating    standard test)                      (IfcTorqueMeasure)
                                                         torque                                                   

                                                         needed extension for Maximum allowable torque (under a   IfcPropertySetWithUnit
                                                         maximum allowable    standard test such as EN 1751)      (IfcTorqueMeasure)
                                                         torque                                                   

                                 Pset_FluidMover         make this property                                       
                                                         set an IFC class, in                                     
                                                         order to improve                                         
                                                         extensibility of IFC                                     
                                                         model.                                                   

                                                         needed extension for Fluid flow rate versus pressure     IfcComplexProperty (LIST \[0,?\] OF
                                                         flow vs. pressure    curve (under a standard test)       (x,y)-points (IfcSimplePropertyWithUnit
                                                         curve                                                    (IfcVolumetricFlowrateMeasure),
                                                                                                                  IfcSimplePropertyWithUnit
                                                                                                                  (IfcPressureMeasure)))

                                                         needed extension for Fluid flow rate versus power curve  IfcComplexProperty (LIST \[0,?\] OF
                                                         flow vs. power curve (under a standard test)             (x,y)-points (IfcSimplePropertyWithUnit
                                                                                                                  (IfcVolumetricFlowrateMeasure),
                                                                                                                  IfcSimplePropertyWithUnit
                                                                                                                  (IfcPressureMeasure)))

                                 Pset_HVACSensor         make this property                                       
                                                         set an IFC class, in                                     
                                                         order to improve                                         
                                                         extensibility of IFC                                     
                                                         model.                                                   

                                                         needed extension for The time constant of sensor         IfcSimplePropertyWithUnit
                                                         time constant                                            (IfcTimeMeasure)

                                                         Instead of Ranger                                        
                                                         use pair (a pair of                                      
                                                         values (maximum and                                      
                                                         minimum range).                                          

                                 Pset_ElectricActuator   make this property                                       
                                                         set an IFC class, in                                     
                                                         order to improve                                         
                                                         extensibility of IFC                                     
                                                         model.                                                   

                                                         needed extension for Reference to the \'parent\'         IfcPropertySet
                                                         common electrical    SharedPropertySet                   (Pset_ElectricalApplianceCommon)
                                                         appliance properties (Pset_ElectricalApplianceCommon).   
                                                                              Contains the shared values for this 
                                                                              type \-- properties that are stored 
                                                                              for all types of                    
                                                                              ElectricalAppliances                

                                                         needed extension for Difference between start and stop   IfcSimpleProperty (IfcReal)
                                                         hysteresis           operation                           

                                                         needed extension for Torque                              IfcPropertySetWithUnit
                                                         torque                                                   (IfcTorqueMeasure)

                                                         needed extension for Stroke time                         IfcSimplePropertyWithUnit
                                                         stroke time                                              (IfcTimeMeasure)

                                 Pset_AirFilter          make this property                                       
                                                         set an IFC class, in                                     
                                                         order to improve                                         
                                                         extensibility of IFC                                     
                                                         model.                                                   

                                                         needed extension for Regenerated sound (under a standard IfcPropertySet (Pset_SoundPowerLevels)
                                                         regenerated sound    test). Reference to a property set  
                                                                              Pset_SoundPowerLevels               

                                                         needed extension for Sound attenuation (under a standard IfcPropertySet (Pset_SoundPowerLevels)
                                                         sound attenuation    test). Reference to a property set  
                                                                              Pset_SoundPowerLevels               

                                                         needed extension for The amount of dust by weight        IfcSimplePropertyWithUnit
                                                         dust holding         retained by a filter (under a       (IfcMassMeasure)
                                                         capacity             standard test such as EN779)        
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