Heat loss test for thermal insulation structure and evaluation methods for thermal insulation efficiency of district heating pipes
1 Scope
This document specifies the test method, test classification and requirements, test procedure, data processing, test error, thermal insulation efficiency evaluation and test report of heat loss test and thermal insulation efficiency evaluation of district heating pipes.
This document is applicable to the heat loss test and insulation efficiency evaluation of thermal insulation structure at district heating pipes, pipe accessories and pipe interfaces.
2 Normative references
The following documents contain provisions which, through reference in this text, constitute provisions of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
GB/T 4132 Definitions of terms relating to thermal insulating materials
GB/T 8174 Method of measuring and evaluating thermal insulation effects for equipments and pipes
GB/T 10295 Thermal insulation-Determination of steady-state thermal resistance and related properties - Heat flow meter apparatus
GB/T 10296 Thermal insulation - Determination of steady-state thermal transmission properties - pipe insulation apparatus
GB/T 27418 Guide to the evaluation and expression of uncertainty in measurement
GB/T 29046 Detection methods of technical specification for pre-insulated district heating pipes
3 Terms and definitions
For the purposes of this document, the terms and definitions specified in GB/T 4132 and GB/T 8174 and the following apply.
3.1 integrated thermal resistance of pipe insulation structure
the ratio of the temperature difference between the inner and outer surfaces of the pipe insulation structure and the linear heat flux per unit length of the pipes in the steady state of heat transfer
3.2 laboratory simulation test
the heat dissipation loss test of pipe insulation structure carried out by simulating the environmental conditions and operating conditions of heating pipes in the laboratory
3.3 apparent thermal conductivity of pipe insulation structure
the thermal conductivity of thermal insulation structure calculated from the heat flux measured on the pipes and the temperature of the inner and outer surfaces of the thermal insulation structure of pipes in laboratory simulation test
3.4 pseudo steady state
the heat transfer state when the average reading of the heat flow sensor does not differ by more than 2% during two consecutive 5-minute cycles
4 Test methods
4.1 Heat flow meter method
4.1.1 The heat flow meter method is applicable to the test of the following heating pipes:
a) Site and laboratory;
b) Above-ground, pipe trench, pipe gallery, tunnel and directly buried laying mode.
4.1.2 The heat flux of thermal insulation structure of heating pipes is directly measured by heat flux meter. When the heat flux flows vertically through the heat flux sensor, the heat flux of heat loss is calculated by using Equation (1).
q=KcE (1)
where,
q——the heat flux of heat loss, W/m2;
Kc——the coefficient of probe, W/(m2·mV);
E——the output potential of heat flow sensor, mV.
4.1.3 The coefficient of probe shall be given after calibration by the method given in GB/T 10295. The calibration curve between the probe coefficient and the measured surface temperature (the temperature regarded as the heat flux sensor) may be drawn, and the curve shall indicate the applicable range of working temperature and heat flux.
4.1.4 The attachment of heat flow sensor includes the following requirements.
a) Before attachment, the dust on the attachment surface shall be removed, and a proper amount of thermal contact materials to reduce contact thermal resistance shall be coated on the attachment surface. After attachment, pressure-sensitive adhesive tape or elastic ring should be used for compaction. Thermal contact materials may be butter, silicone grease, thermal conductive grease, thermal conductive epoxy resin, etc.
b) The thermal contact surface of the heat flux sensor shall be perpendicular to the heat flux direction, and the surface of the heat flux sensor should be in an isothermal surface.
c) The heat flux sensor should be embedded in the inner surface of the outer protective pipe of the thermal insulation structure in advance, and may be attached to the outer surface of the outer protective pipe of the thermal insulation structure when the inner setting conditions are not available.
d) When attached to the outer surface of the thermal insulation structure, the contact between the heat flux sensor and the measured surface shall be good. The attached surface shall be smooth and free of gaps and bubbles.
e) The thermal emissivity (surface blackness) of the heat flux sensor surface shall be consistent with that of the measured pipe surface when attaching to the outer surface of the heat thermal insulation structure of the heating pipes laid on the ground, in pipe trenches, pipe corridors and tunnels. In case of inconsistency, the surface of the heat flux sensor may be coated with a coating similar to the thermal emissivity of the measured pipeline surface or attached with a film similar to the thermal emissivity, or the heat flux value of heat dissipation may be corrected according to Annex A.
f) Waterproof measures shall be taken for the heat flux sensor and its wiring, and no water shall penetrate between the thermal contact surfaces.
4.1.5 The temperature of the attached position of the heat flux sensor shall be within the calibrated temperature range of the heat flux sensor, or the heat flux value displayed by the heat flux meter shall be corrected using Equation (2) according to the temperature correction coefficient given by the verification certificate of the heat flux sensor.
Foreword i
1 Scope
2 Normative references
3 Terms and definitions
4 Test methods
5 Test grading and requirements
6 Test procedure
7 Data processing
8 Test error
9 Evaluation of thermal insulation efficiency
10 Test report
Annex A (Normative) Correction of heat flux value of heat loss
Annex B (Normative) Calculation of general heat release coefficient of outer surface of thermal insulation structure
Annex C (Informative) Investigation table for heating pipe and meteorological data
Annex D (Normative) Test data processing by heat balance method
Annex E (Informative) Data record table on test for heat loss of thermal insulation structure of heating pipe
Annex F (Normative) Maximum allowable value for heat loss of thermal insulation structure of heating pipe
