ASTM C1155-95(2021)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: C1155 − 95 (Reapproved 2021)
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
practice. It also offers guidance on how to place sensors in a manner
summation technique and the sum of least squares technique,
representative of more than just the instrumented portions of the building
andpermitstheuseofothertechniquesthathavebeenproperly
components.
validated. This practice provides a means for estimating the
1.7 This practice pertains to light-through medium-weight
meantemperatureofthebuildingcomponentforestimatingthe
construction as defined by example in 5.8. The calculations
dependence of measured R-value on temperature for the
apply to the range of indoor and outdoor temperatures ob-
summation technique. The sum of least squares technique
served.
producesacalculationofthermalresistancewhichisafunction
of mean temperature.
1.8 The values stated in SI units are to be regarded as
standard. No other units of measurement are included in this
1.3 Each thermal resistance calculation applies to a subsec-
standard.
tion of the building envelope component that was instru-
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, health, and environmental practices and deter-
not achieve the accuracy obtainable in laboratory apparatuses.
mine the applicability of regulatory limitations prior to use.
1.10 This international standard was developed in accor-
1.4 This practice permits calculation of thermal resistance
dance with internationally recognized principles on standard-
on portions of a building envelope that have been properly
ization established in the Decision on Principles for the
instrumented with temperature and heat flux sensing instru-
Development of International Standards, Guides and Recom-
ments. The size of sensors and construction of the building
mendations issued by the World Trade Organization Technical
component determine how many sensors shall be used and
Barriers to Trade (TBT) Committee.
wheretheyshouldbeplaced.Becauseofthevarietyofpossible
construction types, sensor placement and subsequent data
2. Referenced Documents
analysis require the demonstrated good judgement of the user.
2.1 ASTM Standards:
1.5 Eachcalculationpertainsonlytoadefinedsubsectionof
C168Terminology Relating to Thermal Insulation
the building envelope. Combining results from different sub-
C1046Practice for In-Situ Measurement of Heat Flux and
Temperature on Building Envelope Components
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 Oct. 1, 2021. Published October 2021. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approved in 1990. Last previous edition approved in 2013 as C1155–95 (2013). Standards volume information, refer to the standard’s Document Summary page on
DOI: 10.1520/C1155-95R21. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C1155 − 95 (2021)
C1060Practice for Thermographic Inspection of Insulation ρ=material density, kg/m .
Installations in Envelope Cavities of Frame Buildings 3.3.2 Subscripts for the Summation Technique: a =air,
C1130Practice for Calibration of Thin Heat Flux Transduc- e=estimate,
ers I=indoor,
C1153Practice for Location of Wet Insulation in Roofing j=counter for summation of sensor sites,
Systems Using Infrared Imaging k=counter for summation of time-series data,
m=area coverage,
3. Terminology
n=test for convergence value.
o=outdoor, and
3.1 Definitions—For definitions of terms relating to thermal
s=surface,
insulating materials, see Terminology C168.
3.3.3 Variables for the Sum of Least Squares Technique:
3.2 Definitions of Terms Specific to This Standard:
C =material specific heat, J/kg·K (Btu/lb·°F),
3.2.1 building envelope component—the portion of the ρ
Y =measured temperature at indoor node m for time IK,
building envelope, such as a wall, roof, floor, window, or door, mi
F =measured heat flux at interior node n for time i W/m ,
that has consistent construction. — For example, an exterior ni
λ=apparent thermal conductivity, W/m·K,
stud wall would be a building envelope component, whereas a
T =calculated temperature at indoor node m for time I K,
layer thereof would not be. mi
q =calculated heat flux at interior node n for time i W/m ,
ni
3.2.2 convergence factor for thermal resistance, CR —the
n
W =weighting factor to normalize temperature contribu-
Tm
differencebetweenR attime,t,andR attime,t−n,dividedby
e e
tion to Γ,
R at time, t, where n is a time interval chosen by the user
e
W =weightingfactortonormalizeheatfluxcontributionto
qn
making the calculation of thermal resistance.
Γ, and
3.2.3 corresponding mean temperature—arithmetic average
Γ=weighted sum of squares function.
of the two boundary temperatures on a building envelope
3.3.4 Subscripts for the Sum of Least Squares Technique:
component,weightedtoaccountfornon-steady-stateheatflux.
s=specific heat of value, “s,” J/kg·K
3.2.4 estimate of thermal resistance, R —the working cal-
e
4. Summary of Practice
culation of thermal resistance from in-situ data at any one
sensor site. This does not contribute to the thermal resistance
4.1 This practice presents two mathematical procedures for
calculated in this practice until criteria for sufficient data and
calculating the thermal resistance of a building envelope
for variance of R are met.
e subsection from measured in-situ temperature and heat flux
3.2.5 heat flow sensor—any device that produces a continu- data.The procedures are the summation technique (1) and the
ous output which is a function of heat flux or heat flow, for sumofleastsquarestechnique (2, 3).Propervalidationofother
example, heat flux transducer (HFT) or portable calorimeter. techniques is required.
3.2.6 temperature sensor—any device that produces a con-
4.2 The results of each calculation pertain only to a particu-
tinuousoutputwhichisafunctionoftemperature,forexample,
larsubsectionthatwasinstrumentedappropriately.Appropriate
thermocouple, thermistor, or resistance device.
instrumentation implies that heat flow can be substantially
accounted for by the placement of sensors within the defined
3.3 Definitions:SymbolsAppliedtotheTermsUsedinThis
subsection. Since data obtained from in-situ measurements are
Standard:
unlikely to represent steady-state conditions, a calculation of
3.3.1 Variables for the Summation Technique: A =area
thermal resistance is possible only when certain criteria are
associated with a single set of temperature and heat flux
met. The data also provide an estimate of whether the collec-
sensors,
tion process has run long enough to satisfy an accuracy
C=thermal conductance, W/m ·K,
criterion for the calculation of thermal resistance.An estimate
CR=convergence factor (dimensionless),
of error is also possible.
e=error of measurement of heat flux, W/m ,
M=number of values of ∆T and q in the source data,
4.3 This practice provides a means for estimating the mean
N=number of sensor sites,
temperature of the building component (see 6.5.1.4) for esti-
n=test for convergence interval, h,
matingthedependenceofmeasuredR-valueontemperaturefor
q=heat flux, W/m ,
the summation technique by weighting the recorded tempera-
R=thermal resistance, m ·K/W,
turessuchthattheycorrespondtotheobservedheatfluxes.The
s(x)=standard deviation of x, based on N−1 degrees of
sum of least squares technique has its own means for estimat-
freedom,
ing thermal resistance as a function of temperature.
T=temperature, K,
t=time, h, 5. Significance and Use
V(x)=coefficient of variation of x,
5.1 Significance of Thermal Resistance Measurements—
∆T = difference in temperature between indoors and
Knowledge of the thermal resistance of new buildings is
outdoors, K,
λ=apparent thermal conductivity, W/m·K, and
x=position coordinate (from 0 to distance L in increments
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
of ∆x), this practice.
C1155 − 95 (2021)
important to determine whether the quality of construction 5.6.1 Gather the data over an adequate range of thermal
satisfies criteria set by the designer, by the owner, or by a conditions to represent the thermal resistance under the condi-
regulatory agency. Differences in quality of materials or tions to be characterized.
workmanship may cause building components not to achieve
NOTE 2—The construction of some building components includes
design performance.
materialswhosethermalperformanceisdependentonthedirectionofheat
5.1.1 For Existing Buildings—Knowledge of thermal resis-
flow, for example, switching modes between convection and stable
stratification in horizontal air spaces.
tanceisimportanttotheownersofolderbuildingstodetermine
whether the buildings should receive insulation or other
5.7 Lateral Heat Flow—Avoid areas with significant lateral
energy-conserving improvements. Inadequate knowledge of
heat flow. Report the location of each source of temperature
thethermalpropertiesofmaterialsorheatflowpathswithinthe
andheatfluxdata.Identifypossiblesourcesoflateralheatflow,
construction or degradation of materials may cause inaccurate
includingahighlyconductivesurface,thermalbridgesbeneath
assumptions in calculations that use published data.
thesurface,convectioncells,etc.,thatmayviolatetheassump-
tion of heat flow perpendicular to the building envelope
5.2 Advantage of In-Situ Data—This practice provides in-
component.
formation about thermal performance that is based on mea-
sureddata.Thismaydeterminethequalityofnewconstruction
NOTE 3—Appropriate choice of heat flow sensors and placement of
for acceptance by the owner or occupant or it may provide thosesensorscansometimesprovidemeaningfulresultsinthepresenceof
lateral heat flow in building components. Metal surfaces and certain
justification for an energy conservation investment that could
concrete or masonry components may create severe difficulties for
notbemadebasedoncalculationsusingpublisheddesigndata.
measurement due to lateral heat flow.
5.3 Heat Flow Paths—This practice assumes that net heat
5.8 Light-toMedium-WeightConstruction—Thispracticeis
flow is perpendicular to the surface of the building envelope
limited to light- to medium-weight construction that has an
component within a given subsection. Knowledge of surface
indoor temperature that varies by less than 3 K. The heaviest
temperature in the area subject to measurement is required for
construction to which this practice applies would weigh 440
placing sensors appropriately. Appropriate use of infrared
kg/m , assuming that the massive elements in building con-
thermography is often used to obtain such information. Ther-
struction all have a specific heat of about 0.9 kJ/kg K.
mography reveals nonuniform surface temperatures caused by
Examplesoftheheaviestconstructioninclude:(1)a390-kg/m
structural members, convection currents, air leakage, and
wall with a brick veneer, a layer of insulation, and concrete
moisture in insulation. Practices C1060 and C1153 detail the
blocks on the inside layer or (2) a 76-mm concrete slab with
appropriate use of infrared thermography. Note that thermog- 2
insulatedbuilt-uproofingof240kg/m .Insufficientknowledge
raphy as a basis for extrapolating the results obtained at a
and experience exists to extend the practice to heavier con-
measurement site to other similar parts of the same building is
struction.
beyond the scope of this practice.
5.9 Heat Flow Modes—The mode of heat flow is a signifi-
5.4 User Knowledge Required—This practice requires that
cant factor determining R-value in construction that contains
the user have knowledge that the data employed represent an
air spaces. In horizontal construction, air stratifies or convects,
adequate sample of locations to describe the thermal perfor-
depending on whether heat flow is downwards or upwards. In
mance of the construction. Sources for this knowledge include
vertical construction, such as walls with cavities, convection
the referenced literature in Practice C1046 and related works
cells affect determination of R-value significantly. In these
listed in Appendix X2. The accuracy of the calculation is
configurations, apparent R-value is a function of mean
strongly dependent on the history of the temperature differ-
temperature, temperature difference, and location along the
ences across the envelope component. The sensing and data
height of the convection cell. Measurements on a construction
collection apparatuses shall have been used properly. Factors
whose performance is changing with conditions is beyond the
suchasconvectionandmoisturemigrationaffectinterpretation
scope of this practice.
of the field data.
5.5 Indoor-Outdoor Temperature Difference—The speed of 6. Procedure
convergence of the summation technique described in this
6.1 Selection of Subsections for Measurement—This prac-
practice improves with the size of the average indoor-outdoor
tice determines thermal resistance within defined regions or
temperature difference across the building envelope. The sum
subsections where perpendicular heat flow has been measured
of least squares technique is insensitive to indoor-outdoor
by placement of heat flux sensors. Choose subsections that
temperature difference, to small and drifting temperature
represent uniform, non-varying thermal resistance and install
differences, and to small accumulated heat fluxes.
theinstrumentationtorepresentthatsubsectionasawhole.The
5.6 Time-Varying Thermal Conditions—The field data rep- defined subsection shall have no significant heat flow that
resent varying thermal conditions. Therefore, obtain time- bypasses the instrumentation in a manner that is uncharacter-
series data at least five times more frequently than the most istic of where the instrumentation was placed. Use thermogra-
frequentcyclicalheatinput,suchasafurnacecycle.Obtainthe phy to identify appropriate subsections. Each subsection is the
dataforalongenoughperiodsuchthattwosetsofdatathatend subject of a separate calculation from in-situ heat flux and
a user-chosen time period apart do not cause the calculation of temperature data from instrumentation that represents that
thermal resistance to be different by more than 10%, as subsection. Demonstration that sensor sites appropriately rep-
discussed in 6.4. resent each subsection is required in the report (7.3).
C1155 − 95 (2021)
NOTE 4—A uniformly insulated region between studs may have an
the building envelope component, as follows, depending on
essentially uniform thermal resistance. Similarly, a framing member may
whether heat flow is perpendicular, or not.
define a consistent region of interest.
6.4.1 Perpendicular Heat Flow—In cases where the as-
6.1.1 Perpendicular Heat Flow—Determine whether the
sumption of heat flow perpendicular to the surface of the
subregions chosen best represent perpendicular or non-
building envelope component is valid, subtract, for each time
perpendicular heat flow by considering evidence of thermal
interval, the outside surface temperature from the indoor
bridges and convection.Assume perpendicular flow in regions
surface temperature to obtain the temperature difference (∆T )
s
where no temperature gradient is detectable at the most
for that surface.
sensitive setting of the thermal imager or other instrumenta-
∆T 5 T 2 T (1)
s is os
tion.
∆T may be obtained directly from the instrumentation, for
6.1.2 Non-Perpendicular Heat Flow—Assume non-
s
example, by connecting indoor and outdoor thermocouples in
perpendicular heat flow for those regions where a temperature
series, if other calculations do not require values for surface
gradient is detectable at the most sensitive setting of the
temperatures.
thermal imager or other instrumentation. Choose the subsec-
6.4.2 Non-Perpendicular Heat Flow—In cases with prob-
tion (6.1) in such a manner that heat flowing between the
able lateral heat flow, for each time interval, average the
indoor and outdoor surfaces is fully accounted for. Averaging
temperatures on each surface and subtract the average outside
temperatures across a subsection satisfies this requirement.
surface temperature from the average indoor surface tempera-
6.1.3 Estimate Thermal Time Constant—Estimate the ther-
ture to obtain the temperature difference (∆T ) for that surface.
mal time constant of the building envelope component. Use s
Practice C1046, Appendix X1 (Estimating Thermal Time
NOTE 6—Eq 1 represents a common case where the sum of heat flux
Constants), or other recognized method. Estimate the thick-
paths from a region on one side of the construction connect to a
corresponding region on the opposite side of the construction. In other
nesses and thermal diffusivities of the constituent layers of the
cases,correspondingregionsonoppositesurfacesmaynotaccountforthe
building component, as required.
totalheatflowthroughthatsegmentoftheconstruction,becauseoflateral
6.2 Sensor Placement—Choose locations for sensors to heat flow. In the general case for Eq 1, surface regions shall be so defined
to represent opposite ends of the heat flow paths of interest.
represent each subsection subject to the measurement. Tem-
perature and heat flux sensors are used at various locations to
6.5 Calculation of Thermal Resistance—This practice pres-
determine the inside and outside surface temperatures of the ents two mathematical procedures for calculating the thermal
subsection and heat flow through the subsection. Refer to the
resistance of a building envelope subsection from measured
appropriate ASTM standards for use of the sensors chosen. If in-situ temperature and heat flux data. The procedures are the
heat flux transducers (HFTs) are employed, then refer to
summation technique and the sum of least squares technique.
Practice C1046, Section 8 (Selection of Sensor Sites), to select Any other technique used shall be shown to calculate thermal
sites for HFTs and temperature sensors on building envelope
resistanceforthepertinentconstruction,basedonamathemati-
components to obtain in-situ data. Refer to Practice C1046,
calderivation(seeNote7).Theprecisionandbiasforanyother
Section 9 (Test Procedures), for applying heat flux transducers
technique shall also be determined.
and temperature sensors to the building. Instrumentation shall
NOTE 7—References (1, 2, and 3) contain examples of such a
be properly calibrated. Refer to Practice C1130 for calibration
derivation applied to the summation and least squares techniques, respec-
ofHFTs.Thefollowingsectionscovertheimportantaspectsof
tively. Other methods (4, 5, 6, 7)
...