ASTM C1046-95(2001)
(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 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 and health practices and determine the applicability of regulatory limitations prior to use.
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Designation:C1046–95 (Reapproved 2001)
Standard Practice for
In-Situ Measurement of Heat Flux and Temperature on
Building Envelope Components
This standard is issued under the fixed designation C 1046; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope 3. Terminology
1.1 This practice covers a technique for using heat flux 3.1 Definitions—For definition of terms relating to thermal
transducers (HFTs) and temperature transducers (TTs) in mea- insulating materials, see Terminology C 168.
surements of the in-situ dynamic or steady-state thermal 3.2 Definitions of Terms Specific to This Standard:
behavior of opaque components of building envelopes. The 3.2.1 building envelope component—a portion of the build-
applications for such data include determination of thermal ing envelope, such as a wall, roof, floor, window, or door, that
resistances or of thermal time constants. However, such uses has consistent construction.
are beyond the scope of this practice (for information on 3.2.1.1 Discussion—For example, an exterior stud wall
determining thermal resistances, see Practice C 1155). would be a building envelope component, whereas a layer
1.2 Use infrared thermography with this technique to locate thereof would not be.
appropriate sites for HFTs and TTs (hereafter called sensors), 3.2.2 thermal time constant—the time necessary for a step
unless subsurface conditions are known. change in temperature on one side of an item (for example, an
1.3 The values stated in SI units are to be regarded as the HFT or building component) to cause the corresponding
standard. The values given in parentheses are for information change in heat flux on the other side to reach 63.2 % of its new
only. equilibrium value where one-dimensional heat flow occurs. It
1.4 This standard does not purport to address all of the is a function of the thickness, placement, and thermal diffusiv-
safety concerns, if any, associated with its use. It is the ity (see Appendix X1) of each constituent layer of the item.
responsibility of the user of this standard to establish appro- 3.3 Symbols Applied to the Terms Used in This Standard:
priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use.
E = measured voltage from the HFT, typically in mV,
2 2
q = heat flux, W/m (Btu/h·ft ),
2. Referenced Documents
S = heat-flux transducer conversion factor that relates the
2.1 ASTM Standards:
output of the HFT, E,to q through the HFT for the
C 168 Terminology Relating to Thermal Insulating Materi-
2 2
conditions of the test, W/m ·V (Btu/h·ft ·mV). This
als
may be a function of temperature, heat flux, and other
C 518 Test Method for Steady-State Heat Flux Measure-
factors in the environment as discussed in Section 7.
ments and Thermal Transmission Properties by Means of
This may also be expressed as S(T) to connote a
the Heat Flow Meter Apparatus
function of temperature,
C 1060 Practice forThermographic Inspection of Insulation
T = temperature, K (°C, °R, or °F),
Installations in Envelope Cavities of Frame Buildings
t = time, s (hours, days), and
C 1130 Practice for Calibrating Thin Heat Flux Transduc-
t = thermal time constant, s (hours, days).
ers
C 1153 Practice for the Location of Wet Insulation in 4. Summary of Practice
Roofing Systems Using Infrared Imaging
4.1 Heat flux transducers are installed on or within a
C 1155 Practice for Determining Thermal Resistance of
building envelope component in conjunction with temperature
Building Envelope Components from In-Situ Data
transducers, as required. Heat flux through a surface is influ-
enced by temperature gradients, thermal conductance, heat
capacity, density and geometry of the test section, and by
convective and radiative coefficients. The resultant heat fluxes
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.
Current edition approved Sept. 10, 1995. Published October 1995. Originally
published as C 1046 – 85. Last previous edition C 1046 – 91. t = t when q(t)=q +(q −q t/t), where q is the previous equilibrium
1 2 1)(l − e 1
Annual Book of ASTM Standards, Vol 04.06. heat flux, and q is the new heat flux after the step change.
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C1046–95 (2001)
aredeterminedbymultiplyingaconversionfactorSoftheHFT 6. Apparatus
by its electrical output. The S values shall have been obtained
6.1 Essential equipment for measuring heat flux and tem-
according to Practice C 1130.
perature includes the following:
6.1.1 Heat Flux Transducer—Arigid or flexible device (see
5. Significance and Use
Appendix X2) in a durable housing, composed of a thermopile
5.1 Traditionally, HFTs have been incorporated into labora-
(or equivalent) for sensing the temperature difference across a
torytestingdevices,suchastheheatflowmeterapparatus(Test
thin thermal resistive layer, which produces a voltage output
Method C 518), that employ controlled temperatures and heat
that is a function of the corresponding heat flux and the
flow paths to effect a thermal measurement. The application of
geometry and material properties of the HFT.
heat flux transducers and temperature transducers to building
NOTE 1—All calibrations relating output voltage to heat flux shall
components in situ can produce quantitative information about
conform to Practice C 1130 and pertain to the measurement at hand.
building thermal performance that reflects the existing proper-
Manufacturers’ calibrations supplied with HFTs often do not conform
ties of the building under actual thermal conditions. The
with Practice C 1130. Obtain the HFT conversion factor as described in
literature contains a sample of reports on how these measure-
Section 8 of Practice C 1130.
ments have been used (1-8).
6.1.2 Temperature Transducer—Athermocouple, resistance
5.2 The major advantage of this practice is the potential
thermal device (RTD), or thermistor for measuring tempera-
simplicity and ease of application of the sensors. To avoid
tures on or within the construction, or for measuring air
spurious information, users of HFTs shall: (1) employ an
temperatures. Some HFTs incorporate thermocouples.
appropriate S,(2) mask the sensors properly, (3) accommodate
6.1.3 Recorder—An instrument that reads sensor output
the time constants of the sensors and the building components,
voltageandrecordseitherthevoltage,heatflux,ortemperature
and (4) account for possible distortions of any heat flow paths
values calculated from appropriate formulas, with durable
attributable to the nature of the building construction or the
output (for example, magnetic tape, magnetic disk, punch tape,
location, size, and thermal resistance of the transducers.
printer, or plotter).
5.3 The user of HFTs and TTs for measurements on build-
6.1.4 Attachment Materials—Pressure-sensitive tape, adhe-
ings shall understand principles of heat flux in building
sive, 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 ThermalContactMaterials—Geltoothpaste,heatsink
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 HFT can change
case, meaningful measurements are difficult to achieve. The
the conductance of the air film at the HFT and cause the heat
user shall confirm the conversion factor, S, prior to use of the
flux through the HFT to differ from that through the surround-
HFT to avoid calibration errors. See Section 7.
ing surface.
5.3.4 The user shall be prepared to accommodate non-
7.1.1 Determine S according to the procedure outlined in
steady-state thermal conditions in employing the measurement
Practice C 1130, as appropriate to the conditions of use, that is,
technique described in this practice. This requires obtaining
surface-mounted or embedded and surrounded by materials
data over long periods, perhaps several days, depending on the
that will be present.
type of building component and on temperature changes.
7.2 Confirm that the time constant of the HFT is much less
5.3.5 Heat flux has a component parallel to the plane of the
than the time constant of the building component to be
HFT. The user shall be able to minimize or accommodate this
measured if the temperatures throughout the HFT and the
factor.
construction will not be steady state. If the mass of an HFT of
a certain area is less than one fiftieth of the mass of the same
area of building component, then its time constant is small
The boldface numbers in parentheses refer to the list of references at the end of
this practice. enough. If not, then estimate the thicknesses and thermal
C1046–95 (2001)
diffusivities of the constituent layers of the HFT and the internal convection requires, at a minimum, sensors at the top,
building component, using Appendix X1 or other recognized bottom, and center of the suspected convective area.
technique, to determine whether the time constant of the HFT
9. Test Procedures
is less than one fiftieth of that of the component’s time
constant. 9.1 Sensor Site Selection—Select appropriate sensor sites
according to Section 8. The HFT shall cover a region of
8. Selection of Sensor Sites uniformheatfluxonthechosensite.IftheHFTcoversaregion
with significantly nonuniform heat flux, then demonstrate that
8.1 The user shall choose a place in the construction for
the HFT correctly averages the input it receives.
siting the HFTs where one-dimensional heat flow perpendicu-
9.2 Permanent Sensor Installation:
lartotheexteriorsurfacesoccurs,unlesstheuserispreparedto
9.2.1 Sensors built into the construction offer more reliable
deal with multidimensional heat flow in the analysis of the
results than sensors mounted on an exterior surface, because
data.
they are usually protected from radiant heat sources and
NOTE 2—For example, a sensor site in the center of a fully insulated
convection, which may affect the sensor differently than the
stud cavity represents heat flow perpendicular to the wall surface, whereas
surrounding building material. The measurement is also likely
a location near a stud or blocking does not.Awall incorporating concrete
to have less variance.
masonry units has significant multidimensional heat flow through the
9.2.2 Tape or glue the HFTs to a smooth surface within the
concrete webs and possible air convection cells in the block cores.
Similarly, an empty stud cavity has convection as a potential lateral heat construction to ensure good thermal contact.
flow mechanism and a masonry or stone wall has vertical heat conduction
9.2.3 Position temperature transducers on and within the
near the ground level. Air leakage can also be a source of multidimen-
construction, as required, to obtain temperature gradients
sional heat flow.
across its thickness. Place sensors at the exterior surfaces and
8.2 Do not place the HFTs where they contribute more than
at interfaces between materials within the construction. Install
1 % additional resistance to the construction subject to thermal
sensors at the exterior surfaces in one of the following two
measurement, unless the thermal properties of the HFTs are
ways:
well known and the analysis technique is appropriate.
9.2.3.1 Surface mount temperature transducers with tape or
8.3 Do not place HFTs on surfaces with high lateral con-
adhesive. Cover surface-mounted sensors with an opaque
ductance, unless the S has been confirmed for the precise
coating of the same surface absorptance as the surrounding
condition.
material.
8.4 Install HFTs either on an indoor surface of the compo-
NOTE 5—Be aware that some visually opaque materials are transparent
nent if the construction is complete or within a building
in the infrared spectrum.
component when the component is being constructed and
NOTE 6—Surface mounting results in a slightly lower temperature
retrieval is not required. Infrared thermography is required
reading in cool ambient conditions and a slightly higher reading in warm
when the internal configuration of the component is poorly ambient conditions than the surface temperature, since the protruding
sensor is more affected by air film temperature.
known. Seek perpendicular flow, and avoid unforeseen thermal
anomalies.
9.2.3.2 Flush mount temperature transducers by burying
8.5 Use infrared thermography to determine the character-
them at the same depth that the sensor is thick. Use the same
isticsofcandidatesensorsitesonthebuildingcomponentwhen
paint, or in the case of a natural finish, such as brick or wood,
the internal configuration of the component is poorly known
a powder of that finish material m
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