Heat Flow Meter Research Articles

Building energy performance analysis: A case study

International standards, in particular the Italian one, evaluate buildings energy performance assuming steady-state working conditions: currently, the study of the energy performance of buildings is based on a simplified calculation that estimates the energy demand using monthly or seasonal average outdoor temperatures. For this reason we have conducted a comparative analysis of the energy performances of an old building using a semi-stationary software and a dynamic one. The studied building is placed in the peripheral part of an historical city located in the center of Italy. We have performed three simulations considering transparent elements characterized by progressively improved properties of thermal transmittance and solar gain factor. A comparison between the outputs of the two codes, in order to highlight the different ways of evaluating the energy contributions to annual energy demand, has been performed. Finally, the models were validated by means of an in-situ measurement campaign using a heat flow meter – in order to measure the thermal transmittance of the opaque walls – and a thermographic camera. This modus operandi allowed us to appreciate how the use of a dynamic software is essential to deal with the inertial properties of the structure and to calculate in an accurate way the annual energy demand.

Factors affecting the in situ measurement accuracy of the wall heat transfer coefficient using the heat flow meter method

This paper aims at determining the combined influence of the location of thermocouples and heat flow meters, the size, shape and pasting angle of the heat flow meters on the measurement accuracy of the wall heat transfer coefficient (U-value) using the heat flow meter method. A three-dimensional wall heat transfer model is established, including the thermal bridge effects of mortar joints, and validated by thermoelectricity analogy theory. The results show that the measurement error can be up to 6% when the thermocouples are improperly pasted, and up to 26% when the heat flow meters are improperly pasted. It clearly demonstrates that correct layouts obviously improve the measurement accuracy. For a symmetrical structural wall, a higher accuracy can be obtained when the heat flow meter is located on the inner surface, while for an asymmetrical structural wall, the measurement accuracy can be much higher when the heat flow meter is located on the side with greater thermal resistance. The positive error is a maximum when the meter location is at the mortar joint intersection, while the negative error is a maximum when the meter location is exactly at the center of a block. The best distance is 20–32mm away from the mortar joint edge. Moreover, the size, shape and pasting angle of the heat flow meters have influence on the measurement accuracy with different degrees.

Development of Innovative Aerogel Based Plasters: Preliminary Thermal and Acoustic Performance Evaluation

The thermal and acoustic properties of innovative insulating systems used as building coatings were investigated: Granular silica aerogel was mixed with natural plaster in different percentages. This coating solution is transpiring and insulating, thanks to the use of a natural lime coat and aerogel, a highly porous light material with very low thermal conductivity. The thermal conductivity of the proposed solution was evaluated by means of a Heat Flow meter apparatus (EN ISO 12667), considering different percentages of aerogel. The natural plaster without aerogel has a thermal conductivity of about 0.50 W/m K; considering a percentage of granular aerogel of about 90% in volume, the thermal conductivity of the insulating natural coating falls to 0.050 W/m K. Increasing the percentage of granular aerogel, a value of about 0.018–0.020 W/m K can be reached. The acoustic properties were also evaluated in terms of the acoustic absorption coefficient, measured by means of a Kundt’s Tube (ISO 10534-2). Two samples composed by a plasterboard support, an insulation plaster with aerogel (thicknesses 10 mm and 30 mm respectively) and a final coat were assembled. The results showed that the absorption coefficient strongly depends on the final coat, so the aerogel-based plaster layer moderately influences the final value. The application of this innovative solution can be a useful tool for new buildings, but also for the refurbishment of existing ones. This material is in development: until now, the best value of the thermal conductivity obtained from manufacturers is about 0.015 W/m K.

Laser Flash Analysis | Guarded Heat Flow Meter | Heat Flow Meter | Guarded Hot Plate

Laser Flash Analysis | Guarded Heat Flow Meter | Heat Flow Meter | Guarded Hot Plate

Estimation of the thermal properties of hardened cement paste on the basis of guarded heat flow meter measurements

In the present study, a new analysis method is proposed to measure thermal conductivity, thermal diffusivity, volumetric specific heat capacity, and specific heat capacity of cement-based materials based on the guarded heat flow meter apparatus. We tested hydrated cement paste specimens with 0.4 water-to-cement ratio and applied both steady and non-steady state data to compute thermal properties of the hydrated cement paste. Thermal conductivity and thermal contact resistance were determined as 1.28 W m−1 K−1 and 0.038 m−2 K W−1 using steady state data. Furthermore, using a computerized system of heat flow meters and non-linear regression, we used non-steady state data to measure thermal diffusivity, volumetric specific heat capacity and specific heat capacity of the hydrated cement paste as 4.77 × 10−7 m2 s−1, 2685.4 kJ m−3 K−1, and 1.28 kJ kg−1 K−1. The relative uncertainties of these properties fell within 2–7% range and the residual distributions were validated to follow a normal distribution based on quantile–quantile tests.

Experimental validation of a numerical code by thin film heat flux sensors for the resolution of thermal bridges in dynamic conditions

Thermal bridges are areas of risk of the building envelope, inducing uncontrolled increments of heat transfer, mainly in winter. This notwithstanding, thermal bridges are often neglected in energy audits, since many numerical codes for building energy simulations adopt heat transfer models based on one-dimensional heat flux: this can cause lack of reliability.This paper validates a numerical model, written in MatLab™, which solves thermal bridges – under bi-dimensional heat transfer conditions – in transient regime. More in detail, the model – developed by the same authors – allows estimation of thermal bridge effects under dynamic conditions (hourly and sub-hourly). The model is validated through a comparison with experimental data, measured by means of a proper apparatus, consisting in a set of heat flow meters, thin flux sensors, temperature probes, infrared thermographic camera. A typical L-shaped thermal bridge has been investigated and the numerical methodology – compared to the experimental study – reveals very satisfactory results in reliability and accuracy. The percentage gap between calculated and measured heat fluxes varies between −12% and +6%, with an average value close to zero. A satisfactory agreement has been evaluated also with reference to the thermal power through the investigated envelope element.

Comparison of the Thermal Properties of Different Insulating Materials

Currently thermal insulating of the buildings is sorely needed from the point of view of energy as well as money savings. It is important to highlight that the most commonly used insulation materials in the building sector are the expanded polystyrene (EPS), the extruded polystyrene (XPS) and the fibrous (mineral, rock) ones. In this communication we confront 6 different insulating materials slabs (EPS 30, 100, 150, 200, a yellow XPS and a mineral wool by their thermal properties. Therefore two types of hypothetic building structures were created and they were insulated with the above presented materials from 0.01 m to 0.3 m thicknesses. For the calculations the thermal conductivity of each sample was determined using a Holometrix 2000 (HLS) heat flow meter. As a result their heat transfer coefficients, delaying abilities, energy storing capabilities and thermal diffusion coefficients were confronted. Besides a material constant had been defined and was paired with the measured thermal conductivity.

Durability of vacuum insulation panels in the cavity of an insulating glass unit

The durability of vacuum insulating panels included in the cavity of insulating glass panels has been studied using a heat flow meter to monitor the thermal conductivity evolution upon accelerated aging. The study highlighted that, thanks to the high degree of protection of the inner cavity against moisture, the vacuum insulation panel maintains its thermal insulation performances even after 25 weeks of cycling from −20°C to 80°C and from 10% to 90% relative humidity. In comparison, unprotected vacuum insulation panels show a steady increase of thermal conductivity, which is setting them close to the end of their theoretical service lifetime. Comparing the slopes of the thermal conductivity evolution over time, the calculated degree of protection provided by such an assembly is superior to 10 in comparison to unprotected panels. This mode of protection could be useful to extend the lifetime of vacuum insulation panels in various building applications.

Determination of Thermoelectric Module Efficiency: A Survey

The development of thermoelectrics (TE) for energy conversion is in the transition phase from laboratory research to device development. There is an increasing demand to accurately determine the module efficiency, especially for the power generation mode. For many TE, the figure of merit, ZT, of the material sometimes cannot be fully realized at the device level. Reliable efficiency testing of thermoelectric modules is important to assess the device ZT and provide end-users with realistic values for how much power can be generated under specific conditions. We conducted a general survey of efficiency testing devices and their performance. The results indicated a lack of industry standards and test procedures. This study included a commercial test system and several laboratory systems. Most systems are based on the heat flow meter method, and some are based on the Harman method. They are usually reproducible in evaluating thermoelectric modules. However, different systems often showed large differences that are likely caused by uncertain heat loss and thermal resistance. Efficiency testing is an important capability for the thermoelectric community to improve. A follow-up international standardization effort is planned.

Measurement and Estimation of High-Vacuum Effective Thermal Conductivity of Polyimide Foam in the Temperature Range from 160 K to 370 K for Outer Space Applications

Polyimide foam (PF) is a low-thermal conductivity and lightweight material with high resistances against heat, protons, and UV irradiation. A new thermal insulation composed of PFs and multiple aluminized films (PF–MLI) has potential to be used in outer space as an alternative to conventional multilayer insulation (MLI). As fundamental numerical data, the effective thermal conductivity of PF in wide ranges of density and temperature need to be determined. In the present study, thermal-conductivity measurements were performed by both the periodic heating method and the guarded hot-plate method in the temperature range from 160 K to 370 K and the density range from 6.67 \(\mathrm{kg} \cdot \mathrm{m}^{-3}\) to 242.63 \(\mathrm{kg}\cdot \mathrm{m}^{-3}\). The experiments were carried out in a vacuum and under atmospheric pressure. For confirmation of the validity of the present guarded hot-plate apparatus under atmospheric pressure, the effective thermal conductivity of the lowest-density PF was measured with the aid of the heat flow meter apparatus calibrated by the standard reference material (NIST SRM 1450c) in the temperature range from 303 K to 323 K. In order to cross-check the present experimental results, the temperature and density dependences of the effective thermal conductivity of PF were estimated by means of the lattice Boltzmann method based on a dodecahedron inner microscopic complex structure model which reflects a real 3D X-ray CT image of PF.

Calculation and Experimental Evaluation of the Thermal Resistance of a Structure with Reflective Insulation

As reason of increasing requirements of thermal insulation properties of the exposed envelope, reflective insulation are among kind of modern thermal insulation materials ones, which can significantly increased thermal insulation performance if their application is correct. Thermal insulation performance is caused by reduction of the heat transfer by radiation. Conjunction of low-emissivity surface of the reflective insulation and air layer is important to account. This article is focused on the determination of thermal properties of reflective insulation and the results of measured values thermal resistance of determination by hot box method using heat flow meter are presented here. As part of determination of thermal properties of reflective insulation by experimental methods, the test element used to measure the thermal resistance of an insulated air cavity had to be created for concordance with the normative requirements. The part of this article is determination of the thermal resistance by the calculation of derived physical relations and comparison with values of the laboratory measurement.

An Integrated Approach for an Historical Buildings Energy Analysis in a Smart Cities Perspective

Currently, the study of the energy performance of buildings is based on a simplified calculation that estimates the thermal loads using monthly or seasonal average outdoor temperatures. In addition, the employed software require technical data such as the specific heat capacity of materials, but at the same time they are not able to properly consider the thermal inertia of buildings. The more precise evaluation allows to assess the correct interventions for energy requalification under a smart cities perspective. This study was performed considering a stationary software (Aermec MC11300) and a dynamic software (TRNSYS). Three simulations considering transparent elements characterized by progressively improved properties of thermal transmittance and solar gain factor have been performed. It has been performed a comparison between the outputs of the two software in order to highlight the different ways of evaluating the energy contributions on thermal loads. Finally, the models were validated by means of an in-situ measurement campaign using a heat flow meter - in order to measure the thermal transmittance of the opaque walls - and a thermographic camera. This modus operandi allowed to appreciate how the use of a dynamic software is more appropriate to deal with the inertial properties of the structure to calculate in a more detailed way the annual thermal loads and to obtain more information on individual heating zones.

Tests of thermal resistance of simulated walls with the reflective insulation

The paper presents the thermal resistance characteristics of walls with multilayer reflective insulation. The tests have been performed using a heat flow meter to determine the resistivity of the layers simulating partition walls in buildings. A modification of the structure has also been proposed and analysed with a view to increase the thermal resistance and, consequently, reduce the heat flux transferred through the walls. Consequently, walls produced with layers that ensure higher thermal insulation lead to better thermal performance properties of the whole buildings, which reduce heating/cooling costs throughout the year.

The Effect of Different Materials Joint in Vacuum Insulation Panels

During recent years the use of Vacuum Insulation Panels in buildings applications has been improved, because of their both higher performances and lower thickness compared to traditional insulation materials.These performances are due to the interior vacuum degree, which represent also the main problem connected with the applications of this technological solution in buildings constructions: to maintain the vacuum condition the panels are enclosed in an envelope layer, characterized by an higher thermal conductivity. Moreover they have to be assembled to each other or to additional different joint materials in practical building application, generating a thermal bridging effect.The aim of present work is to analyse the critical aspects related to this insulation technology for building application.An experimental campaign through heat flow meter apparatus was carried out with the purpose of assessing the decrease of performance due to the thermal bridges effects considering different joint materials in VIPs assemblies.

Thermal conductivity measurements with different methods: a procedure for the estimation of the retardation time

As it is known that nowadays, reduction of the heating energy loss of buildings is achieved mainly by thermal insulation. This is one of the most important objectives of buildings constructions and retrofitting of buildings. Therefore research, calculation and simulation on the energy efficiency of buildings are of great importance. In this paper we give an expansive presentation about the measurements of the thermal conductivity, heat flux and thermal resistance of individual insulation materials as well as in-built wall constructions executed in our laboratory. Thermal diffusion coefficients and wall delaying ability of the systems will be given resulting from the measurements. First of all, thermal conductivity measurement results of individual insulation materials achieved by a Holometrix type Heat flow Meter will be presented. Afterwards, two different steady-state methods for measuring thermal resistance of wall structures (Calibration hot box method and Heat Flux measurements by Hukseflux apparatus) will be introduced. These measurements were accomplished through either an inbuilt plaster/brick/plaster wall construction insulated internally at the first time and later externally with different materials. The main target of this paper is the presented theoretical procedure for the estimation of the retardation time of wall structures. Furthermore in this publication the determination of thermal performance of Expanded Polystyrene Insulation applied to walls in building constructions can also be found. Moreover numerical predictions for thermal resistance are presented. Besides, infrared thermographs were used to visualise the insulation ability of the layer structures.

Experimental Study on Thermal Conductivity of Concrete for Building Reinforced Concrete Composite Wall

In order to determine the thermal conductivity of the concrete for building reinforced concrete composite wall, the fine-aggregate concrete for the thermal insulation layer and the composite concrete for the reinforced concrete wall were made from the ordinary concrete by in-situ wet-sieving techniques. The compositions of these three kinds of fresh concrete were determined, which expressed by the volume fraction of crushed stone and the volume ratio of crushed stone to mortar. The thermal conductivity of concrete was measured by the one-dimensional steady heat flow meter. Based on the tests, the changes of thermal conductivity of concrete affected by the volume fraction of crushed stone and the volume ratio of crushed stone to mortar were analyzed. The correlation analysis shows that the correlation of the thermal conductivity is better with the volume ratio of crushed stone to mortar. The formula for forecasting the thermal conductivity of concrete is proposed.

Study on Thermal Conductivity of Reinforced Concrete Plate

By the heat flow meter method, the thermal conductivity of reinforced concrete was experimental studied for the energy conservation design of reinforced concrete composite wall as building envelop. The steel bars were arranged as horizontal one-way, horizontal two-way and vertical in the reinforced concrete plates with different reinforcement volume ratio. Based on the test results, the effects of arrangement of steel bar and reinforcement volume ratio on thermal conductivity of reinforced concrete were analyzed. It can be concluded that the thermal conductivity of reinforced concrete was higher than that of concrete and increased with the reinforcement volume fraction, the steel bars in horizontal two-way arrangement brought the reinforced concrete with greater thermal conductivity than that in one-way arrangement, the vertical steel bar made the reinforced concrete with significantly higher thermal conductivity. The series-parallel model and parallel-series model are proposed for predicating the thermal conductivity of reinforced concrete with horizontal steel bars.

Application of Double-Sided Heat Flow Meter in Testing of Overall Heat Transfer Coefficient of Building Envelope

It is essential to find out the thermal property of building envelope in order to design economical and reasonable scheme of energy-saving reconstruction. Field testing is a method of receiving the thermal property of envelope when existing buildings are reconstructed. In this paper, we focus on the need for obtaining the thermal transfer coefficient. A methoddouble-sided heat flow meter was introduced and used to test the thermal property of wall. The testing results show that it provides a feasible method for colleting basal data of energy-saving reconstruction of existing buildings.

Thermal conductivity of flat-pressed wood plastic composites at different temperatures and filler content

AbstractThe thermal conductivity of wood flour (WF) filled high-density polyethylene composites (wood plastic composite, WPC) is investigated experimentally as a function of filler content and temperature. Samples are prepared by compression molding process of previously blended and extruded WPC pellets, up to 50% weight content of WF. The thermal conductivity is measured by the heat flow meter technique in a temperature range from -15°C to 80°C. Experimental results show that the WPC thermal conductivity decreases with temperature and WF content, with the last effect due to the increase in porosity with the filler content, as confirmed by density measurements. Using the thermal conductivity of bare WF, the thermal conductivity of the wood material in WPC is estimated. This value successfully predicts the upper and lower bounds of the WPC thermal conductivity by means of the parallel and series conduction model of a multiphase composite material.

Assessment of the thermal emissivity value of building materials using an infrared thermovision technique emissometer

Following international standards concerning energy performance of buildings, in absence of reliable data on the envelope characteristics, thermal transmittance of building elements should be measured in situ. The method commonly used, based on ISO recommendations, is the heat flow meter measurement method. An alternative approach is based on the infrared thermovision technique (ITT). In this case, actual thermal emissivity value of the surface finishing material is paramount to obtain the true value of the surface temperature. Several methods and instrumentations are available for laboratory measurement of emissivity of materials, whose values can be even retrieved in databases. In this study a novel method for a direct evaluation of the emissivity of common building finishing materials by means of ITT is presented, using a portable instrument affording a comparatively fast but still quite accurate procedure. The laboratory experimental results, referring to six different building materials, provide promising indications on the possibility of applying the methodology to on site tests, so taking into account real material conditions, like environmental pollution, aging, laying mode.