ASTM D5157-97(2003)e1
(Guide)Standard Guide for Statistical Evaluation of Indoor Air Quality Models
Standard Guide for Statistical Evaluation of Indoor Air Quality Models
SCOPE
1.1 This guide provides quantitative and qualitative tools for evaluation of indoor air quality (IAQ) models. These tools include methods for assessing overall model performance as well as identifying specific areas of deficiency. Guidance is also provided in choosing data sets for model evaluation and in applying and interpreting the evaluation tools. The focus of the guide is on end results (that is, the accuracy of indoor concentrations predicted by a model), rather than operational details such as the ease of model implementation or the time required for model calculations to be performed.
1.2 Although IAQ models have been used for some time, there is little guidance in the technical literature on the evaluation of such models. Evaluation principles and tools in this guide are drawn from past efforts related to outdoor air quality or meteorological models, which have objectives similar to those for IAQ models and a history of evaluation literature.1 Some limited experience exists in the use of these tools for evaluation of IAQ models.
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Designation:D5157–97 (Reapproved 2003)
Standard Guide for
Statistical Evaluation of Indoor Air Quality Models
This standard is issued under the fixed designation D5157; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
e NOTE—Editorially corrected Equations 2, 3, and 6 in April 2003.
1. Scope 3. Terminology
1.1 Thisguideprovidesquantitativeandqualitativetoolsfor 3.1 Definitions: For definitions of terms used in this stan-
evaluation of indoor air quality (IAQ) models. These tools dard, refer to Terminology D1356.
include methods for assessing overall model performance as 3.2 Definitions of Terms Specific to This Standard:
well as identifying specific areas of deficiency. Guidance is 3.2.1 IAQ model, n—an equation, algorithm, or series of
alsoprovidedinchoosingdatasetsformodelevaluationandin equations/algorithmsusedtocalculateaverageortime-varying
applyingandinterpretingtheevaluationtools.Thefocusofthe pollutant concentrations in one or more indoor chambers for a
guide is on end results (that is, the accuracy of indoor specific situation.
concentrations predicted by a model), rather than operational 3.2.2 model bias, n—asystematicdifferencebetweenmodel
details such as the ease of model implementation or the time predictions and measured indoor concentrations (for example,
required for model calculations to be performed. the model prediction is generally higher than the measured
1.2 Although IAQ models have been used for some time, concentration for a specific situation).
there is little guidance in the technical literature on the 3.2.3 model chamber, n—an indoor airspace of defined
evaluation of such models. Evaluation principles and tools in volume used in model calculations; IAQ models can be
this guide are drawn from past efforts related to outdoor air specified for a single chamber or for multiple, interconnected
quality or meteorological models, which have objectives simi- chambers.
lar to those for IAQ models and a history of evaluation 3.2.4 model evaluation, n—a series of steps through which
literature.(1) Some limited experience exists in the use of a model developer or user assesses a model’s performance for
these tools for evaluation of IAQ models. selected situations.
3.2.5 model parameter, n—a mathematical term in an IAQ
2. Referenced Documents
model that must be estimated by the model developer or user
2.1 ASTM Standards:
before model calculations can be performed.
D1356 Terminology Relating to Sampling andAnalysis of 3.2.6 model residual, n—the difference between an indoor
Atmospheres
concentration predicted by an IAQ model and a representative
measurementofthetrueindoorconcentration;thevalueshould
be stated as positive or negative.
3.2.7 model validation, n—a series of evaluations under-
ThisguideisunderthejurisdictionofASTMCommitteeD22onSamplingand
Analysis of Atmospheres and is the direct responsibility of Subcommittee D22.05
taken by an agency or organization to provide a basis for
on Indoor Air.
endorsing a specific model (or models) for a specific applica-
Current edition approved April 10, 2003. Published June 2003. Originally
tion (or applications).
approved in 1991. Last previous edition approved in 1997 as D5157–97.
3.2.8 pollutant concentration, n—the extent of the occur-
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
this standard.
rence of a pollutant or the parameters describing a pollutant in
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
a defined airspace, expressed in units characteristic to the
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
3 3 3
pollutant(forexample,mg/m ,ppm,Bq/m ,area/m ,orcolony
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. forming units per cubic metre).
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
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D5157–97 (2003)
4. Significance and Use often specified through a differential equation quantifying
factors related to contaminant gain or loss.
4.1 Using the tools described in this guide, an individual
5.1.2.3 Empirical models (3) are generally based on ap-
seekingtoapplyanIAQmodelshouldbeableto(1)assessthe
proaches such as least-squares regression analysis, using mea-
performance of the model for a specific situation or (2)
surements under different conditions across a variety of struc-
recognize or assess its advantages and limitations.
tures, at different times within the same structure, or both.
4.2 Thisguidecanalsobeusedforidentifyingspecificareas
Theoretical models will generally be suitable for a wide range
ofmodeldeficiencythatrequirefurtherdevelopmentorrefine-
of applications, whereas empirical models will generally be
ment.
applicable only within the range of measurements from which
they were developed.
5. Components of Model Evaluation
5.1.2.4 Somecombinationoftheoreticalandempiricalcom-
5.1 The components of model evaluation include the fol-
ponents is also possible. Specific parameters of a theoretical
lowing: (1) stating the purpose(s) or objective(s) of the
model may have relationships with other factors that can be
evaluation, (2) acquiring a basic understanding of the specifi-
more easily quantified than the parameters themselves. For
cation and underlying principles or assumptions, (3) selecting
example, the rate of air infiltration into a structure could
data sets as inputs to the evaluation process, and (4) selecting
dependonoutdoorwindspeedandtheindoor-outdoortempera-
and using appropriate tools for assessing model performance.
ture difference, or the emission rate from a cigarette could
Just as model evaluation has multiple components, model
depend on the combustion rate and the constituents of the
validation consists of one or more evaluations. However,
particular brand smoked. Given sufficient data, such relation-
model validation is beyond the scope of this document.
shipscouldbeestimatedthroughtechniquessuchasregression
5.1.1 Establishing Evaluation Objectives:
analysis.
5.1.1.1 IAQmodelsaregenerallyusedforthefollowing:(1)
5.1.2.5 IAQ models may be specified for a particular pol-
to help explain the temporal and spatial variations in the
lutant or in general terms; this distinction is important, for
occurrences of indoor pollutant concentrations, (2) to improve
example, because particle-phase pollutants behave differently
the understanding of major influencing factors or underlying
from gas-phase pollutants. Particulate matter is subject to
physical/chemical processes, and (3) to predict the temporal/
coagulation, chemical reaction at surfaces, gravitational set-
spatialvariationsinindoorconcentrationsthatcanbeexpected
tling, diffusional deposition, resuspension and interception,
to occur in specific types of situations. However, model
impaction, and diffusional removal by filtration devices;
evaluation relates only to the third type of model use—
whereassomegaseouspollutantsaresubjecttosorptionand,in
prediction of indoor concentrations.
some cases, desorption processes.
5.1.1.2 The most common evaluation objectives are (1)to
5.1.2.6 Dynamic IAQ models predict time-varying indoor
compare the performance of two or more models for a specific
concentrations for time steps that are usually on the order of
situation or set of situations and (2) to assess the performance
seconds, minutes, or hours; whereas integrated models predict
of a specific model for different situations. Secondary objec-
time-averaged indoor concentrations using average values for
tives include identifying specific areas of model deficiency.
each input parameter or averaging these parameters during the
Determination of specific objectives will assist in choosing
course of exercising the model. Models can also differ in the
appropriate data sets and quantitative or qualitative tools for
extent of partitioning of the indoor airspace, with the simplest
model evaluation.
modelstreatingtheentireindoorvolumeasasinglechamberor
5.1.2 Understanding the Model(s) to be Evaluated:
zone assumed to have homogeneous concentrations through-
5.1.2.1 Although a model user will not necessarily know or
out; more complex models can treat the indoor volume as a
understand all details of a particular model, some fundamental
series of interconnected chambers, with a mass balance con-
understanding of the underlying principles and concepts is
ducted without each chamber and consideration given to
important to the evaluation process. Thus, before evaluating a
communicating airflows among chambers.
model, the user should develop some understanding of the
5.1.2.7 Generally speaking, as the model complexity grows
basis for the model and its operation. IAQ models can
in terms of temporal detail, number of chambers, and types of
generally be distinguished by their basis, by the range of
parameters that can be used for calculations, the user’s task of
pollutants they can address, and by the extent of temporal or
supplyingappropriateinputsbecomesincreasinglydemanding.
spatialdetailtheycanaccommodateininputs,calculations,and
Thus users must have a basic understanding of the underlying
outputs.
principles, nature and extent of inputs required, inherent
5.1.2.2 Theoretical models are generally based on physical
limitations, and types of outputs provided so that they can
principles such as mass conservation. (2,3) That is, a mass
choose a level of model complexity providing an appropriate
balance is maintained to keep track of material entering and
balance between input effort and output detail.
leaving a particular airspace. Within this conceptual frame-
work, pollutant concentrations are increased by emissions 5.1.2.8 A number of assumptions are usually made when
within the defined volume and by transport from other air- modeling a complex environment such as the indoor airspace.
spaces, including outdoors. Similarly, concentrations are de- These assumptions, and their potential influence on the mod-
creased by transport exiting the airspace, by removal to eling results, should be identified in the evaluation process.
chemical/physical sinks within the airspace, or for reactive One method of gaining insights is by performing sensitivity
species, by conversion to other forms. Relationships are most analysis.Anexampleofthistechniqueistosystematicallyvary
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D5157–97 (2003)
the values of one input parameter at a time to determine the inverserelationship.Theformulatobeusedfor
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