ASTM C1046-95(2007)
(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
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 C 1155).
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 and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: C1046 − 95(Reapproved 2007)
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 C1153 Practice for Location of Wet Insulation in Roofing
Systems Using Infrared Imaging
1.1 This practice covers a technique for using heat flux
C1155 Practice for Determining Thermal Resistance of
transducers (HFTs) and temperature transducers (TTs) in mea-
Building Envelope Components from the In-Situ Data
surements of the in-situ dynamic or steady-state thermal
behavior of opaque components of building envelopes. The
3. Terminology
applications for such data include determination of thermal
3.1 Definitions—For definition of terms relating to thermal
resistances or of thermal time constants. However, such uses
insulating materials, see Terminology C168.
are beyond the scope of this practice (for information on
3.2 Definitions of Terms Specific to This Standard:
determining thermal resistances, see Practice C1155).
3.2.1 building envelope component—a portion of the build-
1.2 Use infrared thermography with this technique to locate
ing envelope, such as a wall, roof, floor, window, or door, that
appropriate sites for HFTs and TTs (hereafter called sensors),
has consistent construction.
unless subsurface conditions are known.
3.2.1.1 Discussion—For example, an exterior stud wall
1.3 The values stated in SI units are to be regarded as the
would be a building envelope component, whereas a layer
standard. The values given in parentheses are for information
thereof would not be.
only.
3.2.2 thermal time constant—the time necessary for a step
1.4 This standard does not purport to address all of the
change in temperature on one side of an item (for example, an
safety concerns, if any, associated with its use. It is the
HFT or building component) to cause the corresponding
responsibility of the user of this standard to establish appro-
change in heat flux on the other side to reach 63.2 % of its new
priate safety and health practices and determine the applica-
equilibrium value where one-dimensional heat flow occurs. It
bility of regulatory limitations prior to use.
is a function of the thickness, placement, and thermal diffusiv-
ity (see Appendix X1) of each constituent layer of the item.
2. Referenced Documents
3.2.2.1 Discussion—
2.1 ASTM Standards: t/τ
t 5 τ when q~t! 5 q 1~q 2 q !~l 2 e !
1 2 1
C168 Terminology Relating to Thermal Insulation
where:
C518 Test Method for Steady-State Thermal Transmission
q = is the previous equilibrium heat flux, and
Properties by Means of the Heat Flow Meter Apparatus
q = is the new heat flux after the step change.
C1060 Practice for Thermographic Inspection of Insulation 2
Installations in Envelope Cavities of Frame Buildings
3.3 Symbols Applied to the Terms Used in This Standard:
C1130 Practice for Calibrating Thin Heat Flux Transducers
E = measured voltage from the HFT, typically in mV,
2 2
q = heat flux, W/m (Btu/h·ft ),
S = heat-flux transducer conversion factor that relates the
This practice is under the jurisdiction of ASTM Committee C16 on Thermal
output of the HFT, E,to q through the HFT for the
Insulation and is the direct responsibility of Subcommittee C16.30 on Thermal
2 2
Measurement.
conditions of the test, W/m ·V (Btu/h·ft ·mV). This
Current edition approved May 1, 2007. Published May 2007. Originally
may be a function of temperature, heat flux, and other
approved in 1985. Last previous edition approved in 2001 as C1046 – 95 (2001).
factors in the environment as discussed in Section 7.
DOI: 10.1520/C1046-95R07.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or This may also be expressed as S(T) to connote a
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
function of temperature,
Standards volume information, refer to the standard’s Document Summary page on
T = temperature, K (°C, °R, or °F),
the ASTM website.
Copyright ©ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA19428-2959. United States
C1046 − 95 (2007)
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
5.3.5 Heat flux has a component parallel to the plane of the
capacity, density and geometry of the test section, and by
HFT. The user shall be able to minimize or accommodate this
convective and radiative coefficients. The resultant heat fluxes
factor.
aredeterminedbymultiplyingaconversionfactorSoftheHFT
by its electrical output. The S values shall have been obtained
6. Apparatus
according to Practice C1130.
6.1 Essential equipment for measuring heat flux and tem-
perature includes the following:
5. Significance and Use
6.1.1 Heat Flux Transducer—Arigid or flexible device (see
5.1 Traditionally, HFTs have been incorporated into labora-
Appendix X2) in a durable housing, composed of a thermopile
torytestingdevices,suchastheheatflowmeterapparatus(Test
(or equivalent) for sensing the temperature difference across a
Method C518), that employ controlled temperatures and heat
thin thermal resistive layer, which produces a voltage output
flow paths to effect a thermal measurement. The application of
that is a function of the corresponding heat flux and the
heat flux transducers and temperature transducers to building
geometry and material properties of the HFT.
components in situ can produce quantitative information about
NOTE 1—All calibrations relating output voltage to heat flux shall
building thermal performance that reflects the existing proper-
conform to Practice C1130 and pertain to the measurement at hand.
ties of the building under actual thermal conditions. The
Manufacturers’ calibrations supplied with HFTs often do not conform
literature contains a sample of reports on how these measure-
with Practice C1130. Obtain the HFT conversion factor as described in
ments have been used (1-8).
Section 8 of Practice C1130.
5.2 The major advantage of this practice is the potential
6.1.2 Temperature Transducer—A thermocouple, resistance
simplicity and ease of application of the sensors. To avoid thermal device (RTD), or thermistor for measuring tempera-
spurious information, users of HFTs shall: (1) employ an
tures on or within the construction, or for measuring air
appropriate S,(2) mask the sensors properly, (3) accommodate temperatures. Some HFTs incorporate thermocouples.
the time constants of the sensors and the building components,
6.1.3 Recorder—An instrument that reads sensor output
and (4) account for possible distortions of any heat flow paths voltageandrecordseitherthevoltage,heatflux,ortemperature
attributable to the nature of the building construction or the
values calculated from appropriate formulas, with durable
location, size, and thermal resistance of the transducers. output (for example, magnetic tape, magnetic disk, punch tape,
printer, or plotter).
5.3 The user of HFTs and TTs for measurements on build-
6.1.4 Attachment Materials—Pressure-sensitive tape,
ings shall understand principles of heat flux in building
adhesive, or other means for holding heat flux and temperature
components and have competence to accommodate the follow-
transducers in place on the test surface or within the construc-
ing:
tion.
5.3.1 Choose sensor sites using building plans, specifica-
6.1.5 Thermal Contact Materials—Gel toothpaste, heat sink
tions and thermography to determine that the measurement
grease, petroleum jelly, or other means to improve thermal
represents the required conditions.
contact between an irregular surface and a smooth HFT.
5.3.2 A single HFT site is not representative of a building
6.1.6 Absorptance and Emittance Control Supplies—
component. The measurement at an HFT site represents the
Coatings or sheet material to match the radiative absorptance
conditions at the sensing location of the HFT. Use thermogra-
and emittance of the sensor with that of the surrounding
phy appropriately to identify average and extreme conditions
surfaces.
and large surface areas for integration. Use multiple sensor
sites to assess overall performance of a building component.
7. HFT Signal Conversion
5.3.3 A given HFT calibration is not applicable for all
7.1 The conversion factor (S) is a function of the HFT
measurements.The HFTdisturbs heat flow at the measurement
design and the thermal environment surrounding the HFT (8,
site in a manner unique to the surrounding materials (9, 10);
9).Adifference between thermal conductivities of the HFTand
this affects the conversion constant, S, to be used. The user
its surroundings causes it to act either as a partial blockade or
shall take into account the conditions of measurement as
conduit for heat flux. Radiative heat passes into the HFT at a
outlined in 7.1.1. In extreme cases, the sensor is the most
different rate than it does into the surrounding surface, depend-
significant thermal feature at the location where it has been
ing on the mismatch between the absorptivities of HFT and
placed, for example, on a sheet metal component. In such a
surface.The presence of air moving across an HFTcan change
the conductance of the air film at the HFT and cause the heat
flux through the HFT to differ from that through the surround-
The boldface numbers in parentheses refer to the list of references at the end of
this practice. ing surface.
C1046 − 95 (2007)
Atemperature gradient on the surface is seen as a variation in contrast or
7.1.1 Determine S according to the procedure outlined in
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:
8.1 The user shall choose a place in the construction for
9.2.1 Sensors built into the construction offer more reliable
siting the HFTs where one-dimensional heat flow perpendicu-
results than sensors mounted on an exterior surface, because
lartotheexteriorsurfacesoccurs,unlesstheuserispreparedto
they are usually protected from radiant heat sources and
deal with multidimensional heat flow in the analysis of the
convection, which may affect the sensor differently than the
data.
surrounding building material. The measurement is also likely
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
a location near a stud or blocking does not.Awall incorporating concrete
construction to ensure good thermal contact.
masonry units has significant multidimensional heat flow through the
9.2.3 Position temperature transducers on and within the
concrete webs and possible air convection cells in the block cores.
construction, as required, to obtain temperature gradients
(Experience indicates, however, that the face of a concrete masonry unit
across its thickness. Place sensors at the exterior surfaces and
distributes heat flux sufficiently that HFT placement is insensitive to
location on the block.) Similarly, an empty stud cavity has convection as
at interfaces between materials within the construction. Install
a potential lateral heat flow mechanism and a masonry or stone wall has
sensors at the exterior surfaces in one of the following two
vertical heat conduction near the ground level. Air leakage can also be a
ways:
source of multidimensional heat flow.
9.2.3.1 Surface mount temperature transducers with tape or
8.2 Do not place the HFTs where they contribute more than
adhesive. Cover surface-mounted sensors with an opaque
1 % additional resistance to the construction subject to thermal
coating of the same surface absorptance as the surrounding
measurement, unless the thermal properties of the HFTs are
material.
well known and the analysis technique is appropriate.
NOTE 5—Be aware that some visually opaque materials are transparent
8.3 Do not place HFTs on surfaces with high lateral
in the infrared spectrum.
conductance, unless the S has been confirmed for the precise
NOTE 6—Surface mounting results in a slightly lower temperature
condition.
reading in cool ambient conditions an
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