ASTM C1155-95
(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 judgement 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.
General Information
Relations
Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
Designation: C 1155 – 95
Standard Practice for
Determining Thermal Resistance of Building Envelope
Components from the In-Situ Data
This standard is issued under the fixed designation C 1155; 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 Note 1). Any valid technique may provide the data for this
practice, but the results of this practice shall not be considered
1.1 This practice covers how to obtain and use data from
to be from an ASTM standard, unless the instrumentation
in-situ measurement of temperatures and heat fluxes on build-
technique itself is an ASTM standard.
ing envelopes to compute thermal resistance. Thermal resis-
tance is defined in Terminology C 168 in terms of steady-state
NOTE 1—Currently only Practice C 1046 can provide the data for this
conditions only. This practice provides an estimate of that practice. It also offers guidance on how to place sensors in a manner
representative of more than just the instrumented portions of the building
value for the range of temperatures encountered during the
components.
measurement of temperatures and heat flux.
1.2 This practice presents two specific techniques, the
1.7 This practice pertains to light-through medium-weight
summation technique and the sum of least squares technique,
construction as defined by example in 5.8. The calculations
and permits the use of other techniques that have been properly
apply to the range of indoor and outdoor temperatures ob-
validated. This practice provides a means for estimating the
served.
mean temperature of the building component for estimating the
1.8 The values stated in SI units are to be regarded as the
dependence of measured R-value on temperature for the
standard. The values given in parentheses are for information
summation technique. The sum of least squares technique
only.
produces a calculation of thermal resistance which is a function
1.9 This standard does not purport to address all of the
of mean temperature.
safety concerns, if any, associated with its use. It is the
1.3 Each thermal resistance calculation applies to a subsec-
responsibility of the user of this standard to establish appro-
tion of the building envelope component that was instru-
priate safety and health practices and determine the applica-
mented. Each calculation applies to temperature conditions
bility of regulatory limitations prior to use.
similar to those of the measurement. The calculation of thermal
2. Referenced Documents
resistance from in-situ data represents in-service conditions.
However, field measurements of temperature and heat flux may 2.1 ASTM Standards:
not achieve the accuracy obtainable in laboratory apparatuses.
C 168 Terminology Relating to Thermal Insulating Materi-
1.4 This practice permits calculation of thermal resistance als
on portions of a building envelope that have been properly
C 1046 Practice for In-Situ Measurement of Heat Flux and
instrumented with temperature and heat flux sensing instru- Temperature on Building Envelopes
ments. The size of sensors and construction of the building
C 1060 Practice for Thermographic Inspection of Insulation
component determine how many sensors shall be used and
Installations in Envelope Cavities of Frame Buildings
where they should be placed. Because of the variety of possible C 1130 Practice for Calibrating Thin Heat Flux Transduc-
construction types, sensor placement and subsequent data
ers
analysis require the demonstrated good judgement of the user. C 1153 Practice for the Location of Wet Insulation in
1.5 Each calculation pertains only to a defined subsection of
Roofing Systems Using Infrared Imaging
the building envelope. Combining results from different sub-
3. Terminology
sections to characterize overall thermal resistance is beyond the
scope of this practice. 3.1 Definitions—For definitions of terms relating to thermal
1.6 This practice sets criteria for the data-collection tech- insulating materials, see Terminology C 168.
niques necessary for the calculation of thermal properties (see 3.2 Definitions of Terms Specific to This Standard:
3.2.1 building envelope component—the portion of the
building envelope, such as a wall, roof, floor, window, or door,
that has consistent construction. — For example, an exterior
This practice is under the jurisdiction of ASTM Committee C-16 on Thermal
Insulation and is the direct responsibility of Subcommittee C16.30 on Thermal
stud wall would be a building envelope component, whereas a
Measurement.
Current edition approved Sept. 10, 1995. Published October 1995. Originally
1 2
published as C 1155 – 90. Last previous edition C 1155 – 90e . Annual Book of ASTM Standards, Vol 04.06.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
C 1155
layer thereof would not be. F 5 measured heat flux at interior node n for time i W/m
ni
3.2.2 convergence factor for thermal resistance, CR —the (Btu/h·ft ),
n
l5 apparent thermal conductivity, W/m·K (Btu/h·ft·°F),
difference between R at time, t, and R at time, t−n, divided by
e e
R at time, t, where n is a time interval chosen by the user T 5 calculated temperature at indoor node m for time i K
mi
e
(°R, C, °F),
making the calculation of thermal resistance.
q 5 calculated heat flux at interior node n for time i W/m
3.2.3 corresponding mean temperature—arithmetic average
ni
(Btu/h·ft ),
of the two boundary temperatures on a building envelope
W 5 weighting factor to normalize temperature contribu-
component, weighted to account for non-steady-state heat flux.
Tm
tion to G,
3.2.4 estimate of thermal resistance, R —the working cal-
e
W 5 weighting factor to normalize heat flux contribution
culation of thermal resistance from in-situ data at any one
qn
to G, and
sensor site. This does not contribute to the thermal resistance
G5 weighted sum of squares function.
calculated in this practice until criteria for sufficient data and
3.3.4 Subscripts for the Sum of Least Squares Technique:
for variance of R are met.
e
s 5 specific heat of value, “s,” J/kg·K (Btu/lb·°F)
3.2.5 heat flow sensor—any device that produces a continu-
ous output which is a function of heat flux or heat flow, for
4. Summary of Practice
example, heat flux transducer (HFT) or portable calorimeter.
4.1 This practice presents two mathematical procedures for
3.2.6 temperature sensor—any device that produces a con-
calculating the thermal resistance of a building envelope
tinuous output which is a function of temperature, for example,
subsection from measured in-situ temperature and heat flux
thermocouple, thermistor, or resistance device.
data. The procedures are the summation technique (1) and the
3.3 Symbols Applied to the Terms Used in This Standard:
sum of least squares technique (2, 3). Proper validation of other
3.3.1 Variables for the Summation Technique:
techniques is required.
A 5 area associated with a single set of temperature and
4.2 The results of each calculation pertain only to a particu-
heat flux sensors,
lar subsection that was instrumented appropriately. Appropriate
2 2
C 5 thermal conductance, W/m ·K (Btu/h·ft ·°R),
instrumentation implies that heat flow can be substantially
CR 5 convergence factor (dimensionless),
accounted for by the placement of sensors within the defined
2 2
e 5 error of measurement of heat flux, W/m (Btu/h·ft ),
subsection. Since data obtained from in-situ measurements are
M 5 number of values of DT and q in the source data,
unlikely to represent steady-state conditions, a calculation of
N 5 number of sensor sites,
thermal resistance is possible only when certain criteria are
n 5 test for convergence interval, h,
met. The data also provide an estimate of whether the collec-
2 2
q 5 heat flux, W/m (Btu/h·ft ),
tion process has run long enough to satisfy an accuracy
2 2
R 5 thermal resistance, m ·K/W (h·ft ·°R/Btu),
criterion for the calculation of thermal resistance. An estimate
s(x) 5 standard deviation of x, based on N−1 degrees of
of error is also possible.
freedom, 4.3 This practice provides a means for estimating the mean
T 5 temperature, K (°R, C, °F), temperature of the building component (see 6.5.1.4) for esti-
mating the dependence of measured R-value on temperature for
t 5 time, h,
the summation technique by weighting the recorded tempera-
V(x) 5 coefficient of variation of x,
tures such that they correspond to the observed heat fluxes. The
DT 5 difference in temperature between indoors and out-
sum of least squares technique has its own means for estimat-
doors, K (°R, C, °F),
ing thermal resistance as a function of temperature.
l5 apparent thermal conductivity, W/m·K (Btu/h·ft·°R),
and
5. Significance and Use
x 5 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
r5 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 5 air,
regulatory agency. Differences in quality of materials or
e 5 estimate,
workmanship may cause building components not to achieve
i 5 indoor,
design performance.
j 5 counter for summation of sensor sites,
5.1.1 For Existing Buildings—Knowledge of thermal resis-
k 5 counter for summation of time-series data,
tance is important to the owners of older buildings to determine
m 5 area coverage,
whether the buildings should receive insulation or other
n 5 test for convergence value.
energy-conserving improvements. Inadequate knowledge of
o 5 outdoor, and
the thermal properties of materials or heat flow paths within the
construction or degradation of materials may cause inaccurate
s 5 surface,
assumptions in calculations that use published data.
3.3.3 Variables for the Sum of Least Squares Technique:
C 5 material specific heat, J/kg·K (Btu/lb·°F),
r
Y 5 measured temperature at indoor node m for time i K
mi The boldface numbers in parentheses refer to the list of references at the end of
(°R, C, °F), this practice.
C 1155
5.2 Advantage of In-Situ Data—This practice provides in- tion of heat flow perpendicular to the building envelope
formation about thermal performance that is based on mea- component.
sured data. This may determine the quality of new construction
NOTE 3—Appropriate choice of heat flow sensors and placement of
for acceptance by the owner or occupant or it may provide
those sensors can sometimes provide meaningful results in the presence of
justification for an energy conservation investment that could
lateral heat flow in building components. Metal surfaces and certain
not be made based on calculations using published design data.
concrete or masonry components may create severe difficulties for
measurement due to lateral heat flow.
5.3 Heat Flow Paths—This practice assumes that net heat
flow is perpendicular to the surface of the building envelope
5.8 Light- to Medium-Weight Construction—This practice
component within a given subsection. Knowledge of surface
is limited to light- to medium-weight construction that has an
temperature in the area subject to measurement is required for
indoor temperature that varies by less than 3 K (5°F). The
placing sensors appropriately. Appropriate use of infrared
heaviest construction to which this practice applies would
2 2
thermography is often used to obtain such information. Ther-
weigh 440 kg/m (90 lb/ft ), assuming that the massive
mography reveals nonuniform surface temperatures caused by
elements in building construction all have a specific heat of
structural members, convection currents, air leakage, and
about 0.9 kJ/kg K (0.2 Btu/lb·°F). Examples of the heaviest
2 2
moisture in insulation. Practices C 1060 and C 1153 detail the
construction include: (1) a 390-kg/m (80-lb/ft ) wall with a
appropriate use of infrared thermography. Note that thermog-
brick veneer, a layer of insulation, and concrete blocks on the
raphy as a basis for extrapolating the results obtained at a
inside layer or (2) a 76-mm (3-in.) concrete slab with insulated
2 2
measurement site to other similar parts of the same building is
built-up roofing of 240 kg/m (50 lb/ft ). Insufficient knowl-
beyond the scope of this practice.
edge and experience exists to extend the practice to heavier
5.4 User Knowledge Required—This practice requires that construction.
the user have knowledge that the data employed represent an
5.9 Heat Flow Modes—The mode of heat flow is a signifi-
adequate sample of locations to describe the thermal perfor-
cant factor determining R-value in construction that contains
mance of the construction. Sources for this knowledge include
air spaces. In horizontal construction, air stratifies or convects,
the referenced literature in Practice C 1046 and related works
depending on whether heat flow is downwards or upwards. In
listed in Appendix X2. The accuracy of the calculation is
vertical construction, such as walls with cavities, convection
strongly dependent on the history of the temperature differ-
cells affect determination of R-value significantly. In these
ences across the envelope component. The sensing and data
configurations, apparent R-value is a function of mean tem-
collection apparatuses shall have been used properly. Factors
perature, temperature difference, and location along the height
such as convection and moisture migration affect interpretation of the convection cell. Measurements on a construction whose
of the field data. performance is changing with conditions is beyond the scope
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
temperature difference across the building envelope. The sum
6.1 Selection of Subsections for Measurement—This prac-
of least squares technique is insensitive to indoor-outdoor
tice determines thermal resistance within defined regions or
temperature difference, to small and drifting temperature dif-
subsections where perpendicular heat flow has been measured
ferences, and to small accumulated heat fluxes.
by placement of heat flux sensors. Choose subsections that
5.6 Time-Varying Thermal Conditions—The field data rep-
represent uniform, non-varying thermal resistance and install
resent varying thermal conditions. Therefore, obtain time-
the instrumentation to represent that subsection as a whole. The
ser
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.