ASTM C1046-95(2021)
(Practice)Standard Practice for In-Situ Measurement of Heat Flux and Temperature on Building Envelope Components
Standard Practice for In-Situ Measurement of Heat Flux and Temperature on Building Envelope Components
SIGNIFICANCE AND USE
5.1 Traditionally, HFTs have been incorporated into laboratory testing devices, such as the heat flow meter apparatus (Test Method C518), that employ controlled temperatures and heat flow paths to effect a thermal measurement. The application of heat flux transducers and temperature transducers to building components in situ can produce quantitative information about building thermal performance that reflects the existing properties of the building under actual thermal conditions. The literature contains a sample of reports on how these measurements have been used (1-8).3
5.2 The major advantage of this practice is the potential simplicity and ease of application of the sensors. To avoid spurious information, users of HFTs shall: (1) employ an appropriate S, (2) mask the sensors properly, (3) accommodate the time constants of the sensors and the building components, and (4) account for possible distortions of any heat flow paths attributable to the nature of the building construction or the location, size, and thermal resistance of the transducers.
5.3 The user of HFTs and TTs for measurements on buildings shall understand principles of heat flux in building components and have competence to accommodate the following:
5.3.1 Choose sensor sites using building plans, specifications and thermography to determine that the measurement represents the required conditions.
5.3.2 A single HFT site is not representative of a building component. The measurement at an HFT site represents the conditions at the sensing location of the HFT. Use thermography appropriately to identify average and extreme conditions and large surface areas for integration. Use multiple sensor sites to assess overall performance of a building component.
5.3.3 A given HFT calibration is not applicable for all measurements. The HFT disturbs heat flow at the measurement site in a manner unique to the surrounding materials (9, 10); this affects the conversion constant, S, to be used. The us...
SCOPE
1.1 This practice covers a technique for using heat flux transducers (HFTs) and temperature transducers (TTs) in measurements of the in-situ dynamic or steady-state thermal behavior of opaque components of building envelopes. The applications for such data include determination of thermal resistances or of thermal time constants. However, such uses are beyond the scope of this practice (for information on determining thermal resistances, see Practice C1155).
1.2 Use infrared thermography with this technique to locate appropriate sites for HFTs and TTs (hereafter called sensors), unless subsurface conditions are known.
1.3 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.
1.4 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.5 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.
General Information
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Standards Content (Sample)
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: C1046 − 95 (Reapproved 2021)
Standard Practice for
In-Situ Measurement of Heat Flux and Temperature on
Building Envelope Components
This standard is issued under the fixed designation C1046; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 2. Referenced Documents
2.1 ASTM Standards:
1.1 This practice covers a technique for using heat flux
C168 Terminology Relating to Thermal Insulation
transducers (HFTs) and temperature transducers (TTs) in mea-
C518 Test Method for Steady-State Thermal Transmission
surements of the in-situ dynamic or steady-state thermal
Properties by Means of the Heat Flow Meter Apparatus
behavior of opaque components of building envelopes. The
C1060 Practice for Thermographic Inspection of Insulation
applications for such data include determination of thermal
Installations in Envelope Cavities of Frame Buildings
resistances or of thermal time constants. However, such uses
C1130 Practice for Calibration of Thin Heat Flux Transduc-
are beyond the scope of this practice (for information on
ers
determining thermal resistances, see Practice C1155).
C1153 Practice for Location of Wet Insulation in Roofing
Systems Using Infrared Imaging
1.2 Use infrared thermography with this technique to locate
C1155 Practice for Determining Thermal Resistance of
appropriate sites for HFTs and TTs (hereafter called sensors),
Building Envelope Components from the In-Situ Data
unless subsurface conditions are known.
1.3 The values stated in SI units are to be regarded as the
3. Terminology
standard. The values given in parentheses are for information
3.1 Definitions—For definition of terms relating to thermal
only.
insulating materials, see Terminology C168.
1.4 This standard does not purport to address all of the 3.2 Definitions of Terms Specific to This Standard:
3.2.1 building envelope component—a portion of the build-
safety concerns, if any, associated with its use. It is the
ing envelope, such as a wall, roof, floor, window, or door, that
responsibility of the user of this standard to establish appro-
has consistent construction.
priate safety, health, and environmental practices and deter-
3.2.1.1 Discussion—For example, an exterior stud wall
mine the applicability of regulatory limitations prior to use.
would be a building envelope component, whereas a layer
1.5 This international standard was developed in accor-
thereof would not be.
dance with internationally recognized principles on standard-
3.2.2 thermal time constant—the time necessary for a step
ization established in the Decision on Principles for the
change in temperature on one side of an item (for example, an
Development of International Standards, Guides and Recom-
HFT or building component) to cause the corresponding
mendations issued by the World Trade Organization Technical
change in heat flux on the other side to reach 63.2 % of its new
Barriers to Trade (TBT) Committee.
equilibrium value where one-dimensional heat flow occurs. It
is a function of the thickness, placement, and thermal diffusiv-
ity (see Appendix X1) of each constituent layer of the item.
3.2.2.1 Discussion—
t/τ
t 5 τ when q t 5 q 1 q 2 q l 2 e
~ ! ~ !~ !
1 2 1
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 1985. Last previous edition approved in 2013 as C1046 – 95 (2013). Standards volume information, refer to the standard’s Document Summary page on
DOI: 10.1520/C1046-95R21. the ASTM website.
Copyright ©ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA19428-2959. United States
C1046 − 95 (2021)
where: 5.3.2 A single HFT site is not representative of a building
component. The measurement at an HFT site represents the
q = is the previous equilibrium heat flux, and
conditions at the sensing location of the HFT. Use thermogra-
q = is the new heat flux after the step change.
phy appropriately to identify average and extreme conditions
3.3 Symbols Applied to the Terms Used in This Standard:
and large surface areas for integration. Use multiple sensor
sites to assess overall performance of a building component.
E = measured voltage from the HFT, typically in mV,
2 2
q = heat flux, W/m (Btu/h·ft ),
5.3.3 A given HFT calibration is not applicable for all
S = heat-flux transducer conversion factor that relates the
measurements.The HFTdisturbs heat flow at the measurement
output of the HFT, E,to q through the HFT for the
site in a manner unique to the surrounding materials (9, 10);
2 2
conditions of the test, W/m ·V (Btu/h·ft ·mV). This
this affects the conversion constant, S, to be used. The user
may be a function of temperature, heat flux, and other
shall take into account the conditions of measurement as
factors in the environment as discussed in Section 7.
outlined in 7.1.1. In extreme cases, the sensor is the most
This may also be expressed as S(T) to connote a
significant thermal feature at the location where it has been
function of temperature,
placed, for example, on a sheet metal component. In such a
T = temperature, K (°C, °R, or °F),
case, meaningful measurements are difficult to achieve. The
t = time, s (hours, days), and
user shall confirm the conversion factor, S, prior to use of the
τ = thermal time constant, s (hours, days).
HFT to avoid calibration errors. See Section 7.
4. Summary of Practice
5.3.4 The user shall be prepared to accommodate non-
steady-state thermal conditions in employing the measurement
4.1 Heat flux transducers are installed on or within a
technique described in this practice. This requires obtaining
building envelope component in conjunction with temperature
data over long periods, perhaps several days, depending on the
transducers, as required. Heat flux through a surface is influ-
type of building component and on temperature changes.
enced by temperature gradients, thermal conductance, heat
capacity, density and geometry of the test section, and by 5.3.5 Heat flux has a component parallel to the plane of the
convective and radiative coefficients. The resultant heat fluxes HFT. The user shall be able to minimize or accommodate this
aredeterminedbymultiplyingaconversionfactorSoftheHFT factor.
by its electrical output. The S values shall have been obtained
according to Practice C1130.
6. Apparatus
6.1 Essential equipment for measuring heat flux and tem-
5. Significance and Use
perature includes the following:
5.1 Traditionally, HFTs have been incorporated into labora-
6.1.1 Heat Flux Transducer—Arigid or flexible device (see
torytestingdevices,suchastheheatflowmeterapparatus(Test
Appendix X2) in a durable housing, composed of a thermopile
Method C518), that employ controlled temperatures and heat
(or equivalent) for sensing the temperature difference across a
flow paths to effect a thermal measurement. The application of
thin thermal resistive layer, which produces a voltage output
heat flux transducers and temperature transducers to building
that is a function of the corresponding heat flux and the
components in situ can produce quantitative information about
geometry and material properties of the HFT.
building thermal performance that reflects the existing proper-
ties of the building under actual thermal conditions. The
NOTE 1—All calibrations relating output voltage to heat flux shall
literature contains a sample of reports on how these measure-
conform to Practice C1130 and pertain to the measurement at hand.
ments have been used (1-8).
Manufacturers’ calibrations supplied with HFTs often do not conform
with Practice C1130. Obtain the HFT conversion factor as described in
5.2 The major advantage of this practice is the potential
Section 8 of Practice C1130.
simplicity and ease of application of the sensors. To avoid
6.1.2 Temperature Transducer—A thermocouple, resistance
spurious information, users of HFTs shall: (1) employ an
thermal device (RTD), or thermistor for measuring tempera-
appropriate S,(2) mask the sensors properly, (3) accommodate
tures on or within the construction, or for measuring air
the time constants of the sensors and the building components,
temperatures. Some HFTs incorporate thermocouples.
and (4) account for possible distortions of any heat flow paths
attributable to the nature of the building construction or the
6.1.3 Recorder—An instrument that reads sensor output
location, size, and thermal resistance of the transducers.
voltageandrecordseitherthevoltage,heatflux,ortemperature
values calculated from appropriate formulas, with durable
5.3 The user of HFTs and TTs for measurements on build-
output (for example, magnetic tape, magnetic disk, punch tape,
ings shall understand principles of heat flux in building
printer, or plotter).
components and have competence to accommodate the follow-
ing: 6.1.4 Attachment Materials—Pressure-sensitive tape,
adhesive, or other means for holding heat flux and temperature
5.3.1 Choose sensor sites using building plans, specifica-
tions and thermography to determine that the measurement transducers in place on the test surface or within the construc-
tion.
represents the required conditions.
6.1.5 Thermal Contact Materials—Gel toothpaste, heat sink
grease, petroleum jelly, or other means to improve thermal
The boldface numbers in parentheses refer to the list of references at the end of
this practice. contact between an irregular surface and a smooth HFT.
C1046 − 95 (2021)
6.1.6 Absorptance and Emittance Control Supplies— 8.4 Install HFTs either on an indoor surface of the compo-
Coatings or sheet material to match the radiative absorptance nent if the construction is complete or within a building
and emittance of the sensor with that of the surrounding component when the component is being constructed and
surfaces. retrieval is not required. Infrared thermography is required
when the internal configuration of the component is poorly
7. HFT Signal Conversion known. Seek perpendicular flow, and avoid unforeseen thermal
anomalies.
7.1 The conversion factor (S) is a function of the HFT
8.5 Use infrared thermography to determine the character-
design and the thermal environment surrounding the HFT (8,
isticsofcandidatesensorsitesonthebuildingcomponentwhen
9).Adifference between thermal conductivities of the HFTand
the internal configuration of the component is poorly known
its surroundings causes it to act either as a partial blockade or
(see Practices C1060 and C1153).
conduit for heat flux. Radiative heat passes into the HFT at a
different rate than it does into the surrounding surface, depend-
NOTE 3—Close visual inspection of a stud wall can often reveal the
ing on the mismatch between the absorptivities of HFT and
locations of framing members when there are slight imperfections above
surface.The presence of air moving across an HFTcan change nailheads,butthermographycanrevealwhetherornotthereisunexpected
cross blocking, air leakage, or convection owing to missing, incorrectly
the conductance of the air film at the HFT and cause the heat
applied, or shifted insulation.
flux through the HFT to differ from that through the surround-
NOTE4—Thermographicinstrumentsproduceatwo-dimensionalimage
ing surface.
of a surface by measuring thermal radiation emanating from that surface.
7.1.1 Determine S according to the procedure outlined in
Atemperature gradient on the surface is seen as a variation in contrast or
in pseudocolor on a viewer screen. If the radiation gradients are caused by
Practice C1130, as appropriate to the conditions of use, that is,
heat transfer variations in the wall because of thermal anomalies, these
surface-mounted or embedded and surrounded by materials
anomalies and their locations are made visible. Certain thermographic
that will be present.
patterns can be recognized as framing, air leakage, or convection.
7.2 Confirm that the time constant of the HFT is much less
8.6 Determine whether to deploy sensors in a line or in
than the time constant of the building component to be
some other arrangement, based on knowledge of the compo-
measured if the temperatures throughout the HFT and the
nent’s internal configuration. Note that a wall with suspected
construction will not be steady state. If the mass of an HFT of
internal convection requires, at a minimum, sensors at the top,
a certain area is less than one fiftieth of the mass of the same
bottom, and center of the suspected convective area.
area of building component, then its time constant is small
enough. If not, then estimate the thicknesses and thermal
9. Test Procedures
diffusivities of the constituent layers of the HFT and the
9.1 Sensor Site Selection—Select appropriate sensor sites
building component, using Appendix X1 or other recognized
according to Section 8. The HFT shall cover a region of
technique, to determine whether the time constant of the HFT
uniformheatfluxonthechosensite.IftheHFTcoversaregion
is less than one fiftieth of that of the component’s time
with significantly nonuniform heat flux, then demonstrate that
constant.
the HFT correctly averages the input it receives.
8. Selection of Sensor Sites
9.2 Permanent Sensor Installation:
9.2.1 Sensors built into the construction offer more reliable
8.1 The user shall choose a place in the construction for
results than sensors mounted on an exterior surface, because
siting the HFTs where one-dimensional heat flow perpendicu-
they are usually protected from radiant heat sources and
lartotheexteriorsurfacesoccurs,unlesstheuserispreparedto
convection, which may affect the sensor differently than the
deal with multidimensional heat flow in the analysis of the
surrounding building material. The measurement is also likely
data.
to have less variance.
NOTE 2—For example, a sensor site in the center of a fully insulated
9.2.2 Tape or glue the HFTs to a smooth surface within the
stud cavity represents heat flow perpendicular to the wall surface, whereas
construction to ensure good thermal contact.
a location near a stud or blocking does not.Awall incorporating concrete
9.2.3 Position temperature transducers on and within the
maso
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