Hukseflux HFP01 User manual

Copyright by Hukseflux | manual v1620 | www.hukseflux.com | [e-mail]
USER MANUAL
HFP01 &HFP03
Heat flux plate / heat flux sensor
Hukseflux
Thermal Sensors

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Warning statements
Putting more than 12 Volt across the sensor wiring
can lead to permanent damage to the sensor.
Do not use “open circuit detection” when measuring
the sensor output.

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Contents
Warning statements 2
Contents 3
List of symbols 4
Introduction 5
1Ordering and checking at delivery 8
1.1 Ordering HFP01 8
1.2 Included items 8
1.3 Quick instrument check 8
2Instrument principle and theory 9
3Specifications of HFP01 11
3.2 Dimensions of HFP01 14
4Standards and recommended practices for use 15
4.1 Heat flux measurement in building physics 15
4.2 Heat flux measurement in meteorology 19
5Installation of HFP01 22
5.1 Site selection and installation in building physics 22
5.2 Site selection and installation in meteorology / the soil 25
5.3 Electrical connection 26
5.4 Requirements for data acquisition / amplification 28
6Making a dependable measurement 29
6.1 Uncertainty evaluation 29
6.2 Typical measurement uncertainty budget 30
6.3 Contributions to the uncertainty budget 30
7Maintenance and trouble shooting 34
7.1 Recommended maintenance and quality assurance 34
7.2 Trouble shooting 35
7.3 Calibration and checks in the field 36
8HFP03 37
8.1 Introduction HFP03 37
9Appendices 40
9.1 Appendix on cable extension / replacement 40
9.2 Appendix on standards for calibration 41
9.3 Appendix on calibration hierarchy 41
9.4 EU declaration of conformity 42

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List of symbols
Quantities Symbol Unit
Heat flux ΦW/m²
Voltage output U V
Sensitivity S V/(W/m2)
Temperature T °C
Temperature difference ΔT °C, K
Time constant τs
Thermal resistance per unit area Rthermal,A K/(W/m²)
Λ-Value, thermal conductance ΛW/(m²·K)
Thermal resistance per unit area,
including ambient air boundary layer resistances Rthermal,A,BK/(W/m²)
U-Value, thermal transmittance U W/(m²·K)
Time t s
Thermal conductivity λW/(m∙K)
Thermal resistivity r m∙K/W
Ambient air / wind speed V m/s
Volumic heat capacity cvolumic J/(m³∙K)
Resistance R Ω
Heat transfer coefficient h W/(m2·K)
Convection heat transfer coefficient hcW/(m2·K)
Radiation heat transfer coefficient hrW/(m2·K)
Storage term S W/m²
Thermal conductivity dependence Dλ%/(W/(m∙K))
Depth of installation x m
Water content (on mass basis) Q kg/kg
Subscripts
property of thermopile sensor sensor
property of ambient air ambient
calibration reference condition reference
property of the object on which HFP01 is mounted object
property at the (wall or soil) surface surface
property at indoor location indoor
property at outdoor location outdoor
property of the surrounding environment environment

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Introduction
HFP01 is the world’s most popular sensor for heat flux measurement in the soil as well as
through walls and building envelopes. The total thermal resistance is kept small by using
a ceramics-plastic composite body. The sensor is very robust and stable. It is suitable for
long term use on one location as well as repeated installation when a measuring system
is used at multiple locations.
HFP03 is the high-sensitivity version of HFP01. It differs in sensor technology and has a
larger size. The sensor working principle and considerations for use are the same. This
manual is written for model HFP01, but most content is applicable to HFP03 as
well. HFP03 has a dedicated chapter in this manual focusing on the differences
between HFP03 and HFP01.
HFP01 measures heat flux through the object in which it is incorporated or on which it is
mounted, in W/m2. The sensor in HFP01 is a thermopile. This thermopile measures the
temperature difference across the ceramics-plastic composite body of HFP01. A
thermopile is a passive sensor; it does not require power.
Using HFP01 is easy. It can be connected directly to commonly used data logging
systems. The heat flux, Φ, in W/m2, is calculated by dividing the HFP01 output, a small
voltage U, by the sensitivity S.
The measurement function of HFP01 is:
Φ = U/S (Formula 0.1)
The sensitivity is provided with HFP01 on its product certificate.
Figure 0.1 HFP01 heat flux plate / sensor. The opposite side has a blue coloured cover.

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A typical measurement location is equipped with 2 heat flux sensors for good spatial
averaging. If the sensitivity of a single sensor is too low, two or more sensors can
electrically be put in series, creating an amplified single output signal.
HFP01 can be used for on-site measurement of building envelope thermal resistance per
unit area (R-value) and thermal transmittance (U-value) according to the standardised
practices of ISO 9869, ASTM C1046 and ASTM 1155.
Equipped with heavy duty cabling, protective covers at both sides and potted so that
moisture does not penetrate the sensor, HFP01 has proven to be very robust and stable.
It survives long-term installation in soils, as well as repeated installation when a
measuring system such as TRSYS01 is used at multiple locations.
Suggested use of HFP01:
•building heat flux
•U-value and R-value measurements
•soil heat flux
Figure 0.2 HFP01. The opposite side has a red coloured cover. Standard cable length is 5 m.
The uncertainty of a measurement with HFP01 is a function of:
•calibration uncertainty
•differences between reference conditions during calibration and measurement
conditions, for example uncertainty caused by temperature dependence of the
sensitivity
•the duration of sensor employment (involving the non-stability)
•application errors: the measurement conditions and environment in relation to the
sensor properties, the influence of the sensor on the measurand, the
representativeness of the measurement location
The user should make his own uncertainty evaluation. Detailed suggestions for
experimental design and uncertainty evaluation can be found in the following chapters.

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HFP01 calibration is traceable to international standards. The factory calibration method
follows the recommended practice of ASTM C1130. The recommended calibration interval
of heat flux sensors is 2 years.
See also:
•if measuring in soil, in case a high level quality assurance and accuracy of the
measurement is needed, consider use of model HFP01SC.
•model HFP03 for increased sensitivity; an alternative is putting two or more HFP01’s
electrically in series. HFP03 specifications can be found in a dedicated chapter of this
manual.
•view our complete product range of heat flux sensors.
•view the TRSYS01 building thermal resistance measuring system which includes
2 x HFP01 and 4 x matched thermocouples type K.

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1Ordering and checking at delivery
1.1 Ordering HFP01
The standard configuration of HFP01 is with 5 metres cable.
Common options are:
•longer cable in multiples of 5 m, cable lengths above 20 m in multiples of 10 m.
specify total cable length.
1.2 Included items
Arriving at the customer, the delivery should include:
•heat flux sensor HFP01
•cable of the length as ordered
•product certificate matching the instrument serial number
1.3 Quick instrument check
A quick test of the instrument can be done by connecting it to a multimeter.
1 Check the electrical resistance of the sensor between the green [-] and white [+]
wires. Use a multimeter at the 100 Ω range. Measure the sensor resistance first with one
polarity, then reverse the polarity. Take the average value. The typical resistance of the
wiring is 0.1 Ω/m. Typical resistance should be the nominal sensor resistance of 2 Ω for
plus 1.5 Ω for the total resistance of two wires (back and forth) of each 5 m. Infinite
resistance indicates a broken circuit; zero or a lower than 1 Ωresistance indicates a short
circuit.
2. Check if the sensor reacts to heat: put the multimeter at its most sensitive range of
DC voltage measurement, typically the 100 x 10-3 VDC range or lower. Expose the sensor
heat, for instance touching it with your hand. The signal should read > 2 x 10-3 V now.
Touching or exposing the red side should generate a positive signal, doing the same at
the opposite side the sign of the output voltage reverses.
3. Inspect the instrument for any damage.
4. Check the sensor serial number and sensitivity on the 2 x cable labels (one at sensor
end, one at cable end) against the certificate provided with the sensor.

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2Instrument principle and theory
HFP01’s scientific name is heat flux sensor. A heat flux sensor measures the heat flux
density through the sensor itself. This quantity, expressed in W/m2, is usually called
“heat flux”.
HFP01 users typically assume that the measured heat flux is representative of the
undisturbed heat flux at the location of the sensor. Users may also apply corrections
based on scientific judgement.
The sensor in HFP01 is a thermopile. This thermopile measures the temperature
difference across the ceramics-plastic composite body of HFP01. Working completely
passive, the thermopile generates a small voltage that is a linear function of this
temperature difference. The heat flux is proportional to the same temperature difference
divided by the effective thermal conductivity of the heat flux sensor body.
Using HFP01 is easy. For readout the user only needs an accurate voltmeter that works
in the millivolt range. To convert the measured voltage, U, to a heat flux Φ, the voltage
must be divided by the sensitivity S, a constant that is supplied with each individual
sensor.
Figure 2.1 The general working principle of a heat flux sensor. The sensor inside HFP01
is a thermopile. A thermopile consists of a number of thermocouples, each consisting of
two metal alloys marked 1 and 2, electrically connected in series. A single thermocouple
will generate an output voltage that is proportional to the temperature difference
between its hot- and cold joints. Putting thermocouples in series amplifies the signal. In
a heat flux sensor, the hot- and cold joints are located at the opposite sensor surfaces 4
and 5. In steady state, the heat flux 6 is a linear function of the temperature difference
across the sensor and the average thermal conductivity of the sensor body, 3. The
thermopile generates a voltage output proportional to the heat flux through the sensor.
The exact sensitivity of the sensor is determined at the manufacturer by calibration, and
is found on the calibration certificate that is supplied with each sensor.
5
4
321
6

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Heat flux sensors such as HFP01, for use in the soil and on building envelopes, are
typically calibrated under the following reference conditions:
•conductive heat flux (as opposed to radiative or convective heat flux)
•homogeneous heat flux across the sensor and guard surface
•room temperature
•heat flux in the order of 350 W/m2
Unique features of HFP01 are:
•low thermal resistance (essential for use on walls and windows)
•large guard area (required by the ISO 9869 standard)
•low electrical resistance (low pickup of electrical noise)
•high sensitivity (good signal to noise ratio in low-flux enviroments such as
buildings)
•robustness, including a strong cable
•IP protection class: IP67 (essential for outdoor application)
Measuring with heat flux sensors, errors may be caused by differences between
calibration reference conditions and the conditions during use. The user should analyse
his own experiment and make his own uncertainty evaluation. Comments on the most
common error sources can be found in the chapter about uncertainty evaluation.