ASTM D5157-97(2008)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation: D5157 − 97(Reapproved 2008)
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 (´) indicates an editorial change since the last revision or reapproval.
1. Scope 3.2.2 model bias, n—asystematicdifferencebetweenmodel
predictions and measured indoor concentrations (for example,
1.1 Thisguideprovidesquantitativeandqualitativetoolsfor
the model prediction is generally higher than the measured
evaluation of indoor air quality (IAQ) models. These tools
concentration for a specific situation).
include methods for assessing overall model performance as
3.2.3 model chamber, n—an indoor airspace of defined
well as identifying specific areas of deficiency. Guidance is
volume used in model calculations; IAQ models can be
alsoprovidedinchoosingdatasetsformodelevaluationandin
specified for a single chamber or for multiple, interconnected
applyingandinterpretingtheevaluationtools.Thefocusofthe
chambers.
guide is on end results (that is, the accuracy of indoor
concentrations predicted by a model), rather than operational
3.2.4 model evaluation, n—aseriesofstepsthroughwhicha
details such as the ease of model implementation or the time
model developer or user assesses a model’s performance for
required for model calculations to be performed.
selected situations.
1.2 Although IAQ models have been used for some time,
3.2.5 model parameter, n—a mathematical term in an IAQ
there is little guidance in the technical literature on the
model that must be estimated by the model developer or user
evaluation of such models. Evaluation principles and tools in
before model calculations can be performed.
this guide are drawn from past efforts related to outdoor air
3.2.6 model residual, n—the difference between an indoor
quality or meteorological models, which have objectives simi-
concentration predicted by an IAQ model and a representative
lar to those for IAQ models and a history of evaluation
measurementofthetrueindoorconcentration;thevalueshould
literature.(1) Some limited experience exists in the use of
be stated as positive or negative.
these tools for evaluation of IAQ models.
3.2.7 model validation, n—a series of evaluations under-
taken by an agency or organization to provide a basis for
2. Referenced Documents
endorsing a specific model (or models) for a specific applica-
2.1 ASTM Standards:
tion (or applications).
D1356Terminology Relating to Sampling and Analysis of
3.2.8 pollutant concentration, n—the extent of the occur-
Atmospheres
rence of a pollutant or the parameters describing a pollutant in
3. Terminology a defined airspace, expressed in units characteristic to the
3 3 3
pollutant(forexample,mg/m ,ppm,Bq/m ,area/m ,orcolony
3.1 Definitions: For definitions of terms used in this
forming units per cubic metre).
standard, refer to Terminology D1356.
3.2 Definitions of Terms Specific to This Standard:
4. Significance and Use
3.2.1 IAQ model, n—an equation, algorithm, or series of
4.1 Using the tools described in this guide, an individual
equations/algorithmsusedtocalculateaverageortime-varying
seekingtoapplyanIAQmodelshouldbeableto(1)assessthe
pollutant concentrations in one or more indoor chambers for a
performance of the model for a specific situation or (2)
specific situation.
recognize or assess its advantages and limitations.
4.2 Thisguidecanalsobeusedforidentifyingspecificareas
This guide is under the jurisdiction of ASTM Committee D22 on Air
ofmodeldeficiencythatrequirefurtherdevelopmentorrefine-
Qualityand is the direct responsibility of Subcommittee D22.05 on Indoor Air.
Current edition approved April 1, 2008. Published July 2008. Originally
ment.
´1
approved in 1991. Last previous edition approved in 2003 as D5157–97(2003) .
DOI: 10.1520/D5157-97R08.
5. Components of Model Evaluation
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
this standard.
5.1 The components of model evaluation include the fol-
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
lowing: (1) stating the purpose(s) or objective(s) of the
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
evaluation, (2) acquiring a basic understanding of the specifi-
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. cation and underlying principles or assumptions, (3) selecting
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D5157 − 97 (2008)
data sets as inputs to the evaluation process, and (4) selecting example, the rate of air infiltration into a structure could
and using appropriate tools for assessing model performance. dependonoutdoorwindspeedandtheindoor-outdoortempera-
Just as model evaluation has multiple components, model ture difference, or the emission rate from a cigarette could
validation consists of one or more evaluations. However, depend on the combustion rate and the constituents of the
model validation is beyond the scope of this document. particular brand smoked. Given sufficient data, such relation-
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
spatialvariationsinindoorconcentrationsthatcanbeexpected
settling, 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
5.1.2.8 A number of assumptions are usually made when
framework, pollutant concentrations are increased by emis-
modeling a complex environment such as the indoor airspace.
sions within the defined volume and by transport from other
These assumptions, and their potential influence on the mod-
airspaces, including outdoors. Similarly, concentrations are
eling results, should be identified in the evaluation process.
decreased by transport exiting the airspace, by removal to
One method of gaining insights is by performing sensitivity
chemical/physical sinks within the airspace, or for reactive
analysis.Anexampleofthistechniqueistosystematicallyvary
species, by conversion to other forms. Relationships are most
the values of one input parameter at a time to determine the
often specified through a differential equation quantifying
effect of each on the modeling results; each parameter should
factors related to contaminant gain or loss.
be varied over a reasonable range of values likely to be
5.1.2.3 Empirical models (3) are generally based on ap-
encountered for the specific situation(s) of interest.
proaches such as least-squares regression analysis, using mea-
surements under different conditions across a variety of 5.1.3 Choosing Data Sets for Model Evaluation:
structures,atdifferenttimeswithinthesamestructure,orboth.
5.1.3.1 A fundamental requirement for model evaluation is
Theoretical models will generally be suitable for a wide range
that the data used for the evaluation process should be
of applications, whereas empirical models will generally be
independent of the data used to develop the model. This
applicable only within the range of measurements from which
constraint forces a search for available data pertinent to the
they were devel
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