ASTM C1155-95(2001)
(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 C168 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 C1046 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 . 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.
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Designation:C1155–95 (Reapproved 2001)
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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope 1.6 This practice sets criteria for the data-collection tech-
niques necessary for the calculation of thermal properties (see
1.1 This practice covers how to obtain and use data from
Note 1). Any valid technique may provide the data for this
in-situ measurement of temperatures and heat fluxes on build-
practice, but the results of this practice shall not be considered
ing envelopes to compute thermal resistance. Thermal resis-
to be from an ASTM standard, unless the instrumentation
tance is defined in Terminology C168 in terms of steady-state
technique itself is an ASTM standard.
conditions only. This practice provides an estimate of that
value for the range of temperatures encountered during the
NOTE 1—Currently only Practice C1046 can provide the data for this
measurement of temperatures and heat flux.
practice. It also offers guidance on how to place sensors in a manner
representative of more than just the instrumented portions of the building
1.2 This practice presents two specific techniques, the
components.
summation technique and the sum of least squares technique,
andpermitstheuseofothertechniquesthathavebeenproperly
1.7 This practice pertains to light-through medium-weight
validated. This practice provides a means for estimating the
construction as defined by example in 5.8. The calculations
meantemperatureofthebuildingcomponentforestimatingthe
apply to the range of indoor and outdoor temperatures ob-
dependence of measured R-value on temperature for the
served.
summation technique. The sum of least squares technique
1.8 The values stated in SI units are to be regarded as the
producesacalculationofthermalresistancewhichisafunction
standard. The values given in parentheses are for information
of mean temperature.
only.
1.3 Each thermal resistance calculation applies to a subsec-
1.9 This standard does not purport to address all of the
tion of the building envelope component that was instru-
safety concerns, if any, associated with its use. It is the
mented. Each calculation applies to temperature conditions
responsibility of the user of this standard to establish appro-
similartothoseofthemeasurement.Thecalculationofthermal
priate safety and health practices and determine the applica-
resistance from in-situ data represents in-service conditions.
bility of regulatory limitations prior to use.
However,fieldmeasurementsoftemperatureandheatfluxmay
2. Referenced Documents
not achieve the accuracy obtainable in laboratory apparatuses.
1.4 This practice permits calculation of thermal resistance
2.1 ASTM Standards:
on portions of a building envelope that have been properly C168 Terminology Relating to Thermal Insulation Materi-
instrumented with temperature and heat flux sensing instru-
als
ments. The size of sensors and construction of the building C1046 Practice for In-Situ Measurement of Heat Flux and
component determine how many sensors shall be used and
Temperature on Building Envelopes
wheretheyshouldbeplaced.Becauseofthevarietyofpossible C1060 PracticeforThermographicInspectionofInsulation
construction types, sensor placement and subsequent data
Installations in Envelope Cavities of Frame Buildings
analysis require the demonstrated good judgement of the user. C1130 Practice for Calibrating Thin Heat Flux Transduc-
1.5 Eachcalculationpertainsonlytoadefinedsubsectionof
ers
the building envelope. Combining results from different sub- C1153 Practice for the Location of Wet Insulation in
sectionstocharacterizeoverallthermalresistanceisbeyondthe
Roofing Systems Using Infrared Imaging
scope of this practice.
3. Terminology
3.1 Definitions—For definitions of terms relating to thermal
This practice is under the jurisdiction of ASTM Committee C16 on Thermal
insulating materials, see Terminology C168.
Insulation and is the direct responsibility of Subcommittee C16.30 on Thermal
Measurement.
Current edition approved Sept. 10, 1995. Published October 1995. Originally
1 2
published as C1155–90. Last previous edition C1155–90e . Annual Book of ASTM Standards, Vol 04.06.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
C1155
3.2 Definitions of Terms Specific to This Standard: C =material specific heat, J/kg·K (Btu/lb·°F),
r
3.2.1 building envelope component—the portion of the Y =measured temperature at indoor node m for time i K
mi
building envelope, such as a wall, roof, floor, window, or door, (°R, C, °F),
that has consistent construction. — For example, an exterior F =measured heat flux at interior node n for time i W/m
ni
stud wall would be a building envelope component, whereas a (Btu/h·ft ),
layer thereof would not be. l=apparent thermal conductivity, W/m·K (Btu/h·ft·°F),
T =calculated temperature at indoor node m for time i K
3.2.2 convergence factor for thermal resistance, CR —the
mi
n
differencebetweenR attime,t,andR attime,t−n,dividedby (°R, C, °F),
e e
q =calculated heat flux at interior node n for time i W/m
R at time, t, where n is a time interval chosen by the user
ni
e
making the calculation of thermal resistance. (Btu/h·ft ),
W =weighting factor to normalize temperature contribu-
3.2.3 corresponding mean temperature—arithmeticaverage
Tm
of the two boundary temperatures on a building envelope tion to G,
W =weightingfactortonormalizeheatfluxcontributionto
component,weightedtoaccountfornon-steady-stateheatflux.
qn
3.2.4 estimate of thermal resistance, R —the working cal- G, and
e
G=weighted sum of squares function.
culation of thermal resistance from in-situ data at any one
3.3.4 Subscripts for the Sum of Least Squares Technique:
sensor site. This does not contribute to the thermal resistance
s=specific heat of value, “s,” J/kg·K (Btu/lb·°F)
calculated in this practice until criteria for sufficient data and
for variance of R are met.
e
4. Summary of Practice
3.2.5 heat flow sensor—anydevicethatproducesacontinu-
ous output which is a function of heat flux or heat flow, for 4.1 This practice presents two mathematical procedures for
calculating the thermal resistance of a building envelope
example, heat flux transducer (HFT) or portable calorimeter.
3.2.6 temperature sensor—any device that produces a con- subsection from measured in-situ temperature and heat flux
data.The procedures are the summation technique (1) and the
tinuousoutputwhichisafunctionoftemperature,forexample,
thermocouple, thermistor, or resistance device. sumofleastsquarestechnique(2,3).Propervalidationofother
techniques is required.
3.3 Symbols Applied to the Terms Used in This Standard:
4.2 The results of each calculation pertain only to a particu-
3.3.1 Variables for the Summation Technique:
larsubsectionthatwasinstrumentedappropriately.Appropriate
A =areaassociatedwithasinglesetoftemperatureandheat
instrumentation implies that heat flow can be substantially
flux sensors,
2 2
accounted for by the placement of sensors within the defined
C =thermal conductance, W/m ·K (Btu/h·ft ·°R),
subsection. Since data obtained from in-situ measurements are
CR =convergence factor (dimensionless),
2 2
unlikely to represent steady-state conditions, a calculation of
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 DT 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,
2 2
criterion for the calculation of thermal resistance.An estimate
q =heat flux, W/m (Btu/h·ft ),
2 2 of error is also possible.
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-
DT =difference in temperature between indoors and out-
ing thermal resistance as a function of temperature.
doors, K (°R, C, °F),
l=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 Dx),
Knowledge of the thermal resistance of new buildings is
3 3
r=material density, kg/m (lb/ft ).
important to determine whether the quality of construction
3.3.2 Subscripts for the Summation Technique:
satisfies criteria set by the designer, by the owner, or by a
a =air,
regulatory agency. Differences in quality of materials or
e =estimate,
workmanship may cause building components not to achieve
i =indoor,
design performance.
j =counter for summation of sensor sites,
5.1.1 For Existing Buildings—Knowledge of thermal resis-
k =counter for summation of time-series data,
tanceisimportanttotheownersofolderbuildingstodetermine
m =area coverage,
whether the buildings should receive insulation or other
n =test for convergence value.
o =outdoor, and
s =surface, 3
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
3.3.3 Variables for the Sum of Least Squares Technique: this practice.
C1155
energy-conserving improvements. Inadequate knowledge of andheatfluxdata.Identifypossiblesourcesoflateralheatflow,
thethermalpropertiesofmaterialsorheatflowpathswithinthe includingahighlyconductivesurface,thermalbridgesbeneath
construction or degradation of materials may cause inaccurate thesurface,convectioncells,etc.,thatmayviolatetheassump-
assumptions in calculations that use published data. tion of heat flow perpendicular to the building envelope
component.
5.2 Advantage of In-Situ Data—This practice provides in-
formation about thermal performance that is based on mea-
NOTE 3—Appropriate choice of heat flow sensors and placement of
sureddata.Thismaydeterminethequalityofnewconstruction
thosesensorscansometimesprovidemeaningfulresultsinthepresenceof
for acceptance by the owner or occupant or it may provide
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- to Medium-Weight Construction—This practice
flow is perpendicular to the surface of the building envelope
is 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 (5°F). The
temperature in the area subject to measurement is required for
heaviest construction to which this practice applies would
placing sensors appropriately. Appropriate use of infrared
2 2
weigh 440 kg/m (90 lb/ft ), assuming that the massive
thermography is often used to obtain such information. Ther-
elements in building construction all have a specific heat of
mography reveals nonuniform surface temperatures caused by
about 0.9 kJ/kg K (0.2 Btu/lb·°F). Examples of the heaviest
structural members, convection currents, air leakage, and
2 2
construction include: (1) a 390-kg/m (80-lb/ft ) wall with a
moisture in insulation. Practices C1060 and C1153 detail the
brick veneer, a layer of insulation, and concrete blocks on the
appropriate use of infrared thermography. Note that thermog-
insidelayeror(2)a76-mm(3-in.)concreteslabwithinsulated
raphy as a basis for extrapolating the results obtained at a 2 2
built-up roofing of 240 kg/m (50 lb/ft ). Insufficient knowl-
measurement site to other similar parts of the same building is
edge and experience exists to extend the practice to heavier
beyond the scope of this practice.
construction.
5.4 User Knowledge Required—This practice requires that
5.9 Heat Flow Modes—The mode of heat flow is a signifi-
the user have knowledge that the data employed represent an
cant factor determining R-value in construction that contains
adequate sample of locations to describe the thermal perfor-
air spaces. In horizontal construction, air stratifies or convects,
mance of the construction. Sources for this knowledge include
depending on whether heat flow is downwards or upwards. In
the referenced literature in Practice C1046 and related works
vertical construction, such as walls with cavities, convection
listed in Appendix X2. The accuracy of the calculation is
cells affect determination of R-value significantly. In these
strongly dependent on the history of the temperature differ-
configurations, apparent R-value is a function of mean tem-
ences across the envelope component. The sensing and data
perature, temperature difference, and location along the height
collection apparatuses shall have been used properly. Factors
of the convection cell. Measurements on a construction whose
suchasconvectionandmoisturemigrationaffectinterpretation
performance is changing with conditions is beyond the scope
of the field data.
of this practice.
5.5 Indoor-Outdoor Temperature Difference—The speed of
convergence of the summation technique described in this
6. Procedure
practice improves with the size of the average indoor-outdoor
6.1 Selection of Subsections for Measurement—This prac-
temperature difference across the building envelope. The sum
tice determines thermal resistance within defined regions or
of least squares technique is insensitive to indoor-outdoor
subsections where perpendicular heat flow has been measured
temperature difference, to small and drifting temperature dif-
by placement of heat flux sensors. Choose subsections that
ferences, and to small accumulated heat fluxes.
represent uniform, non-varying thermal resistance and install
5.6 Time-Varying Thermal Conditions—The field data rep-
theinstrumentationtorepresentthatsubsectionasawhole.The
resent varying thermal conditions. Therefore, obtain time-
defined subsection shall have no significant heat flow that
series data at least five times more frequently than t
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