ASTM C1155-95(2007)
(Practice)Standard Practice for Determining Thermal Resistance of Building Envelope Components from the In-Situ Data
Standard Practice for Determining Thermal Resistance of Building Envelope Components from the In-Situ Data
SCOPE
1.1 This practice covers how to obtain and use data from in-situ measurement of temperatures and heat fluxes on building envelopes to compute thermal resistance. Thermal resistance is defined in Terminology C 168 in terms of steady-state conditions only. This practice provides an estimate of that value for the range of temperatures encountered during the measurement of temperatures and heat flux.
1.2 This practice presents two specific techniques, the summation technique and the sum of least squares technique, and permits the use of other techniques that have been properly validated. This practice provides a means for estimating the mean temperature of the building component for estimating the dependence of measured R-value on temperature for the summation technique. The sum of least squares technique produces a calculation of thermal resistance which is a function of mean temperature.
1.3 Each thermal resistance calculation applies to a subsection of the building envelope component that was instrumented. Each calculation applies to temperature conditions similar to those of the measurement. The calculation of thermal resistance from in-situ data represents in-service conditions. However, field measurements of temperature and heat flux may not achieve the accuracy obtainable in laboratory apparatuses.
1.4 This practice permits calculation of thermal resistance on portions of a building envelope that have been properly instrumented with temperature and heat flux sensing instruments. The size of sensors and construction of the building component determine how many sensors shall be used and where they should be placed. Because of the variety of possible construction types, sensor placement and subsequent data analysis require the demonstrated good judgment of the user.
1.5 Each calculation pertains only to a defined subsection of the building envelope. Combining results from different subsections to characterize overall thermal resistance is beyond the scope of this practice.
1.6 This practice sets criteria for the data-collection techniques necessary for the calculation of thermal properties (see Note 1). Any valid technique may provide the data for this practice, but the results of this practice shall not be considered to be from an ASTM standard, unless the instrumentation technique itself is an ASTM standard.
Note 1—Currently only Practice C 1046 can provide the data for this practice. It also offers guidance on how to place sensors in a manner representative of more than just the instrumented portions of the building components.
1.7 This practice pertains to light-through medium-weight construction as defined by example in 5.8. The calculations apply to the range of indoor and outdoor temperatures observed.
1.8 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.
1.9 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
General Information
Relations
Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: C1155 − 95(Reapproved 2007)
Standard Practice for
Determining Thermal Resistance of Building Envelope
Components from the In-Situ Data
This standard is issued under the fixed designation C1155; 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 sectionstocharacterizeoverallthermalresistanceisbeyondthe
scope of this practice.
1.1 This practice covers how to obtain and use data from
in-situ measurement of temperatures and heat fluxes on build-
1.6 This practice sets criteria for the data-collection tech-
ing envelopes to compute thermal resistance. Thermal resis-
niques necessary for the calculation of thermal properties (see
tance is defined in Terminology C168 in terms of steady-state
Note 1). Any valid technique may provide the data for this
conditions only. This practice provides an estimate of that
practice, but the results of this practice shall not be considered
value for the range of temperatures encountered during the
to be from an ASTM standard, unless the instrumentation
measurement of temperatures and heat flux.
technique itself is an ASTM standard.
1.2 This practice presents two specific techniques, the
NOTE 1—Currently only Practice C1046 can provide the data for this
summation technique and the sum of least squares technique,
practice. It also offers guidance on how to place sensors in a manner
representative of more than just the instrumented portions of the building
andpermitstheuseofothertechniquesthathavebeenproperly
components.
validated. This practice provides a means for estimating the
meantemperatureofthebuildingcomponentforestimatingthe
1.7 This practice pertains to light-through medium-weight
dependence of measured R-value on temperature for the
construction as defined by example in 5.8. The calculations
summation technique. The sum of least squares technique
apply to the range of indoor and outdoor temperatures ob-
producesacalculationofthermalresistancewhichisafunction
served.
of mean temperature.
1.8 The values stated in SI units are to be regarded as the
1.3 Each thermal resistance calculation applies to a subsec-
standard. The values given in parentheses are for information
tion of the building envelope component that was instru-
only.
mented. Each calculation applies to temperature conditions
1.9 This standard does not purport to address all of the
similartothoseofthemeasurement.Thecalculationofthermal
safety concerns, if any, associated with its use. It is the
resistance from in-situ data represents in-service conditions.
responsibility of the user of this standard to establish appro-
However,fieldmeasurementsoftemperatureandheatfluxmay
priate safety and health practices and determine the applica-
not achieve the accuracy obtainable in laboratory apparatuses.
bility of regulatory limitations prior to use.
1.4 This practice permits calculation of thermal resistance
on portions of a building envelope that have been properly
2. Referenced Documents
instrumented with temperature and heat flux sensing instru-
2.1 ASTM Standards:
ments. The size of sensors and construction of the building
C168Terminology Relating to Thermal Insulation
component determine how many sensors shall be used and
C1046Practice for In-Situ Measurement of Heat Flux and
wheretheyshouldbeplaced.Becauseofthevarietyofpossible
Temperature on Building Envelope Components
construction types, sensor placement and subsequent data
C1060Practice for Thermographic Inspection of Insulation
analysis require the demonstrated good judgement of the user.
Installations in Envelope Cavities of Frame Buildings
1.5 Eachcalculationpertainsonlytoadefinedsubsectionof
C1130Practice for Calibrating Thin Heat Flux Transducers
the building envelope. Combining results from different sub-
C1153Practice for Location of Wet Insulation in Roofing
Systems Using Infrared Imaging
This practice is under the jurisdiction of ASTM Committee C16 on Thermal
Insulation and is the direct responsibility of Subcommittee C16.30 on Thermal
Measurement. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved May 1, 2007. Published May 2007. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approved in 1990. Last previous edition approved in 2001 as C1155–95(2001). Standards volume information, refer to the standard’s Document Summary page on
DOI: 10.1520/C1155-95R07. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C1155 − 95 (2007)
3. Terminology m =area coverage,
n =test for convergence value.
3.1 Definitions—Fordefinitionsoftermsrelatingtothermal
o =outdoor, and
insulating materials, see Terminology C168.
s =surface,
3.2 Definitions of Terms Specific to This Standard:
3.3.3 Variables for the Sum of Least Squares Technique:
3.2.1 building envelope component—the portion of the
C =material specific heat, J/kg·K (Btu/lb·°F),
ρ
building envelope, such as a wall, roof, floor, window, or door,
Y =measured temperature at indoor node m for time i K
mi
that has consistent construction. — For example, an exterior
(°R, C, °F),
stud wall would be a building envelope component, whereas a
F =measured heat flux at interior node n for time i W/m
ni
layer thereof would not be.
(Btu/h·ft ),
3.2.2 convergence factor for thermal resistance, CR —the
n
λ=apparent thermal conductivity, W/m·K (Btu/h·ft·°F),
differencebetweenR attime,t,andR attime,t−n,dividedby
e e
T =calculated temperature at indoor node m for time i K
mi
R at time, t, where n is a time interval chosen by the user
e
(°R, C, °F),
making the calculation of thermal resistance.
q =calculated heat flux at interior node n for time i W/m
ni
3.2.3 corresponding mean temperature—arithmetic average
(Btu/h·ft ),
of the two boundary temperatures on a building envelope W =weighting factor to normalize temperature contribu-
Tm
component,weightedtoaccountfornon-steady-stateheatflux.
tion to Γ,
W =weighting factor to normalize heat flux contribution
3.2.4 estimate of thermal resistance, R —the working cal- qn
e
to Γ, and
culation of thermal resistance from in-situ data at any one
Γ=weighted sum of squares function.
sensor site. This does not contribute to the thermal resistance
3.3.4 Subscripts for the Sum of Least Squares Technique:
calculated in this practice until criteria for sufficient data and
s=specific heat of value, “s,” J/kg·K (Btu/lb·°F)
for variance of R are met.
e
3.2.5 heat flow sensor—any device that produces a continu-
4. Summary of Practice
ous output which is a function of heat flux or heat flow, for
4.1 This practice presents two mathematical procedures for
example, heat flux transducer (HFT) or portable calorimeter.
calculating the thermal resistance of a building envelope
3.2.6 temperature sensor—any device that produces a con-
subsection from measured in-situ temperature and heat flux
tinuousoutputwhichisafunctionoftemperature,forexample, 3
data.The procedures are the summation technique (1) and the
thermocouple, thermistor, or resistance device.
sumofleastsquarestechnique (2, 3).Propervalidationofother
3.3 Definitions:SymbolsApplied to the Terms Used in This
techniques is required.
Standard:
4.2 The results of each calculation pertain only to a particu-
3.3.1 Variables for the Summation Technique: A =area
larsubsectionthatwasinstrumentedappropriately.Appropriate
associated with a single set of temperature and heat flux
instrumentation implies that heat flow can be substantially
sensors,
accounted for by the placement of sensors within the defined
2 2
C =thermal conductance, W/m ·K (Btu/h·ft ·°R),
subsection. Since data obtained from in-situ measurements are
CR =convergence factor (dimensionless),
unlikely to represent steady-state conditions, a calculation of
2 2
e =error of measurement of heat flux, W/m (Btu/h·ft ),
thermal resistance is possible only when certain criteria are
M =number of values of ∆T and q in the source data,
met. The data also provide an estimate of whether the collec-
N =number of sensor sites,
tion process has run long enough to satisfy an accuracy
n =test for convergence interval, h,
criterion for the calculation of thermal resistance.An estimate
2 2
q =heat flux, W/m (Btu/h·ft ),
of error is also possible.
2 2
R =thermal resistance, m ·K/W (h·ft ·°R/Btu),
4.3 This practice provides a means for estimating the mean
s(x) =standard deviation of x, based on N−1 degrees of
temperature of the building component (see 6.5.1.4) for esti-
freedom,
matingthedependenceofmeasuredR-valueontemperaturefor
T =temperature, K (°R, C, °F),
the summation technique by weighting the recorded tempera-
t =time, h,
turessuchthattheycorrespondtotheobservedheatfluxes.The
V(x) =coefficient of variation of x,
sum of least squares technique has its own means for estimat-
∆T = difference in temperature between indoors and
ing thermal resistance as a function of temperature.
outdoors, K (°R, C, °F),
λ=apparentthermalconductivity,W/m·K(Btu/h·ft·°R),and
5. Significance and Use
x =position coordinate (from 0 to distance L in increments
5.1 Significance of Thermal Resistance Measurements—
of ∆x),
Knowledge of the thermal resistance of new buildings is
3 3
ρ=material density, kg/m (lb/ft ).
important to determine whether the quality of construction
3.3.2 Subscripts for the Summation Technique: a =air,
satisfies criteria set by the designer, by the owner, or by a
e =estimate,
i =indoor,
j =counter for summation of sensor sites, 3
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
k =counter for summation of time-series data, this practice.
C1155 − 95 (2007)
regulatory agency. Differences in quality of materials or 5.6.1 Gather the data over an adequate range of thermal
workmanship may cause building components not to achieve conditions to represent the thermal resistance under the condi-
tions to be characterized.
design performance.
5.1.1 For Existing Buildings—Knowledge of thermal resis-
NOTE 2—The construction of some building components includes
tanceisimportanttotheownersofolderbuildingstodetermine
materialswhosethermalperformanceisdependentonthedirectionofheat
flow, for example, switching modes between convection and stable
whether the buildings should receive insulation or other
stratification in horizontal air spaces.
energy-conserving improvements. Inadequate knowledge of
thethermalpropertiesofmaterialsorheatflowpathswithinthe
5.7 Lateral Heat Flow—Avoid areas with significant lateral
construction or degradation of materials may cause inaccurate
heat flow. Report the location of each source of temperature
assumptions in calculations that use published data.
andheatfluxdata.Identifypossiblesourcesoflateralheatflow,
includingahighlyconductivesurface,thermalbridgesbeneath
5.2 Advantage of In-Situ Data—This practice provides in-
thesurface,convectioncells,etc.,thatmayviolatetheassump-
formation about thermal performance that is based on mea-
tion of heat flow perpendicular to the building envelope
sureddata.Thismaydeterminethequalityofnewconstruction
component.
for acceptance by the owner or occupant or it may provide
justification for an energy conservation investment that could NOTE 3—Appropriate choice of heat flow sensors and placement of
thosesensorscansometimesprovidemeaningfulresultsinthepresenceof
notbemadebasedoncalculationsusingpublisheddesigndata.
lateral heat flow in building components. Metal surfaces and certain
concrete or masonry components may create severe difficulties for
5.3 Heat Flow Paths—This practice assumes that net heat
measurement due to lateral heat flow.
flow is perpendicular to the surface of the building envelope
component within a given subsection. Knowledge of surface
5.8 Light-toMedium-WeightConstruction—Thispracticeis
temperature in the area subject to measurement is required for
limited to light- to medium-weight construction that has an
placing sensors appropriately. Appropriate use of infrared
indoor temperature that varies by less than 3 K (5°F). The
thermography is often used to obtain such information. Ther-
heaviest construction to which this practice applies would
2 2
mography reveals nonuniform surface temperatures caused by weigh 440 kg/m (90 lb/ft ), assuming that the massive
structural members, convection currents, air leakage, and
elements in building construction all have a specific heat of
moisture in insulation. Practices C1060 and C1153 detail the about 0.9 kJ/kg K (0.2 Btu/lb·°F). Examples of the heaviest
2 2
appropriate use of infrared thermography. Note that thermog- construction include: (1) a 390-kg/m (80-lb/ft ) wall with a
raphy as a basis for extrapolating the results obtained at a brick veneer, a layer of insulation, and concrete blocks on the
measurement site to other similar parts of the same building is insidelayeror(2)a76-mm(3-in.)concreteslabwithinsulated
2 2
built-up roofing of 240 kg/m (50 lb/ft ). Insufficient knowl-
beyond the scope of this practice.
edge and experience exists to extend the practice to heavier
5.4 User Knowledge Required—This practice requires that
construction.
the user have knowledge that the data employed represent an
5.9 Heat Flow Modes—The mode of heat flow is a signifi-
adequate sample of locations to describe the thermal perfor-
cant factor determining R-value in construction that contains
mance of the construction. Sources for this knowledge include
air spaces. In horizontal construction, air stratifies or convects,
the referenced literature in Practice C1046 and related works
depending on whether heat flow is downwards or upwards. In
listed in Appendix X2. The accuracy of the calculation is
vertical construction, such as walls with cavities, convection
strongly dependent on the history of the temperature differ-
cells affect determination of R-value significantly. In these
ences across the envelope component. The sensing and data
configurations, apparent R-value is a function of mean
collection apparatuses shall have been used properly. Factors
temperature, temperature difference, and location along the
suchasconvectionandmoisturemigrationaffectinterpretation
height of the convection cell. Measurements on a construction
of the field data.
whose performance is changing with conditions is beyond the
5.5 Indoor-Outdoor Temperature Difference—The speed of
scope of this practice.
convergence of the summation technique described in this
practice improves with the size of the average indoor-outdoor
6. Procedure
temperature difference across the building en
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.