This paper compares the equivalent thermal transmittances of different façades built using commercial clay bricks with three different thicknesses and façades made using the same method but with ceramic bricks with optimized rhomboidal interior geometry.
Equivalent thermal transmittances of 0.300 W/m2·K were recorded for the rhomboidal brick with a thickness of 0.290 m and a façade with thermo-acoustic insulation and a large format brick on the interior, but the final thickness of the façade was 0.445 m.
For ventilated façades made of the proposed rhomboidal brick with thicknesses of 0.290 and 0.240 m an 8–9% improvement was found, with values of 0.312 W/m2·K and 0.339 W/m2·K, respectively.
It can be concluded that in view of the small difference in thermal terms, the best option is to use a brick 0.240 m thick, as the overall thickness of the façade will not then exceed 0.300 m.
Se ha obtenido una transmitancia térmica equivalente de 0,300 W/m2·K para el ladrillo con geometría romboidal de 0,290 m de espesor y pared con aislamiento termoacústico y gran formato en el interior, con un espesor total de fachada de 0,445 m.
Para fachadas ventiladas con el ladrillo romboidal propuesto con espesores de 0,290 y 0,240 m, se obtiene una mejora de un 8%–9%, con valores de 0,312 W/m2·K y 0,339 W/m2·K, respectivamente.
Podemos concluir que, dada la pequeña diferencia en términos térmicos, la mejor opción es el uso de ladrillos de 0,240 m de espesor, siempre y cuando el espesor total de fachada no exceda los 0,300 m.
Improving the energy efficiency of machinery and premises is one of the most important ways of achieving global energy sustainability. Energy that is not used is the cheapest energy of all.
Many buildings are ecologically unsustainable: they are not environmentally friendly, and may even be causing pollution by consuming large quantities of energy, with the substantial harmful atmospheric emissions that this entails (
Buildings are large consumers of thermal energy. In fact, the residential and services sectors account for around 27% of the total energy consumed in the EU-28, i.e. 275 MTEP (Million-Ton Equivalent of Petroleum) (
One construction solution for outer envelopes that is now being implemented to improve the thermal efficiency of buildings and reduce energy losses is to use low-density, “lightweight” clay bricks.
Recent studies have considered the impact of the cladding materials used on building walls on CO2 emissions, and their influence on energy consumption (
Numerous studies have been conducted on the materials used in building envelopes. These studies have individually characterized the influence of the type of internal void in large format bricks (
Other studies have looked at reducing the thermal conductivity of clay by using additives, and have shown how those additives reduce thermal conductivity due to gas micropores generated in the volume of baked clay (
The research reported here studies the possibility of improving the equivalent thermal transmittance of building façades by using bricks available on the market with thicknesses of 0.290 m, 0.240 m and 0.190 m, and optimized internal geometry with rhomboidal internal voids (
Equivalent thermal transmittance,
As its reference product, the study took commercially available TermoarcillaTM bricks with a herringbone internal geometry and three different thicknesses (with “thickness” taken to mean the dimension in the direction of which heat flows through the wall): 0.290 m, 0.240 m and 0.190 m, as shown in
Commercial TermoarcillaTM brick (
The bricks proposed in this research had a rhomboidal internal geometry and a tongue and groove configuration with internal voids extending into them, referred to as a “continuous tongue and groove system” (
Proposed bricks with rhomboidal internal voids.
The study considered the same clays used by the commercial manufacturers, with paper pulp as an additive. Clay conductivity was 0.500 W/m·K, measured by the hot plate method as specified in (
Each different type of façade involves the use of bonding mortars as horizontal joint, plaster renderings and other cladding materials. The conductivity for each material was standardized as per regulations or standard market specifications.
Following the standard (
This study examines the following types of façade:
Single-leaf façades provide suitable levels of thermal insulation, offset and shock absorbance, together with excellent thermal inertia. This ensures that they perform well in both summer and winter.
Ventilated façades are a high-performance design for building envelopes whose main feature is to separate the role of waterproofing from the role of thermal insulation. They comply with all requirements in terms of thermal protection, energy saving and environmental protection.
With the ETICS located on the outer face of the envelope, it contributes 90% of the envelope's mass to the building's thermal inertia. This outer insulation resolves any issues of thermal bridges, as the entire thickness of the insulating element is flush against the building envelope.
Single-leaf façade with blocks 0.290 m thick and discontinuous joint 0.030 m air, view from inside.
Ventilated façade with blocks 0.290 m thick and discontinuous joint 0.030 m air, view from outside.
Façade with blocks 0.290 m thick and discontinuous joint 0.030 m air, and external thermal insulation composite system, view from outside.
Façade with blocks 0.290 m thick and discontinuous joint 0.030 m air, and internal thermal acoustic insulation composite system, view from inside.
Thermal calculations were performed according to Spanish standards (
The brick cross-section featured vertical perforations referred to as voids. The equivalent conductivity of the air in these voids can only be calculated if they are rectangular, so for non-rectangular voids an equivalent rectangular void was created in accordance with the standard (
The thermal conductivity of the uncoated clay bricks thus obtained was then used to calculate the equivalent thermal transmittances of the four different types of façade proposed.
The target model for analysis by numerical methods was the part of the wall represented by the assembly of two bricks as shown in
Part of the wall representing the assembly of two blocks and the heights of each characteristic cross-section.
Using the finite element method, the first two characteristic cross-sections of each wall (the “clay/air cross-section” and the “clay/mortar cross-section”) were obtained with the boundary conditions specified by the aforementioned standards, as shown in
Boundary conditions for obtaining the heat flow,
Once the heat flow,
For the horizontal joint, (the “tendel cross-section”), the data on the conductivity of the bonding mortar and the size of the air joint served immediately to calculate the resistance to the passage of heat: For a joint with standard mortar and a 0.030 m air gap resistance is given by equation [ Whereas for a thin joint resistance is given by equation [
Where λm is the conductivity of the bonding mortar, λair is the conductivity of the air, and
Based on the resistance value for each specific section,
The data on the conductivity of the component material enabled the resistance to the passage of heat of all the other layers that made up the façade to be calculated immediately via equation [
Finally, the equivalent thermal transmittance of the envelope cladding was obtained for each of the four types of façade using equation [
Where
For the sake of clarity, a schematic of the thermal network is shown in
Thermal network.
To compare the results for the new bricks proposed, we sought to characterize the four types of wall assemblies with commercial bricks with herringbone voids, referred to as type 29, 24 and 19 TermoarcillaTM bricks.
As mentioned above, several manufacturers that market these bricks certify a thermal transmittance of around 0.500 W/m·K (
Properties of TermoarcillaTM bricks
Name | THICKNESS (m) | THERMAL CONDUCTIVITY (W/m·k) | THERMAL RESISTANCE UNCOATED (m2·K/W) |
---|---|---|---|
TermoarcillaTM 29 | 0.290 | 0.240 | 1.208 |
TermoarcillaTM 24 | 0.240 | 0.240 | 1.000 |
TermoarcillaTM 19 | 0.190 | 0.280 | 0.679 |
It should be noted that the walls with 0.290 m and 0.240 m bricks considered were made with a discontinuous joint with a 0.030 m air space, in compliance with the relevant standards (
The data for the thermal resistance of each brick enabled the equivalent thermal transmittance for each type of façade under study to be obtained.
Values of each layer in the different types of façades made from a main brick of TermoarcillaTM 29, and equivalent thermal transmittance obtained
LAYER No. | NAME | THICKNESS (m) | CONDUCTIVITY (W/m·K) | RESISTANCE (m2·K/W) |
---|---|---|---|---|
|
||||
INTERIOR | SURFACE CHANGE | 0.130 | ||
1 | PLASTER RENDER | 0.015 | 0.570 | 0.026 |
2 | TermoarcillaTM 29 | 0.290 | 0.240 | 1.208 |
3 | THERMOCAL | 0.025 | 0.068 | 0.368 |
EXTERIOR | SURFACE CHANGE | 0.040 | ||
WALL THICKNESS | 0.330 | RESISTANCE = | 1.772 | |
|
0.564 | |||
|
||||
|
||||
INTERIOR | SURFACE CHANGE | 0.130 | ||
1 | PLASTER RENDER | 0.015 | 0.570 | 0.026 |
2 | TermoarcillaTM 29 | 0.290 | 0.240 | 1.208 |
3 | POLYURETHANE INSUL | 0.040 | 0.028 | 1.429 |
4 | WELL VENTILATED CHAMBER. | |||
5 | OUTER SKIN | |||
EXTERIOR | SURFACE CHANGE | 0.130 | ||
WALL THICKNESS | 0.345 | RESISTANCE = | 2.923 | |
|
0.342 | |||
|
||||
|
||||
INTERIOR | SURFACE CHANGE | 0.130 | ||
1 | PLASTER RENDER | 0.015 | 0.570 | 0.026 |
2 | TermoarcillaTM 29 | 0.290 | 0.240 | 1.208 |
3 | SATEN PROPAM AISTERM | 0.040 | 0.037 | 1.081 |
4 | CLADDING | 0.020 | ||
EXTERIOR | SURFACE CHANGE | 0.040 | ||
WALL THICKNESS | 0.345 | RESISTANCE = | 2.506 | |
|
|
|||
|
||||
|
||||
INTERIOR | SURFACE CHANGE | 0,130 | ||
1 | PLASTER RENDER | 0.015 | 0.570 | 0.026 |
2 | TGF-7 | 0.070 | 0.290 | 0.241 |
3 | GLASS WOOL | 0.050 | 0.036 | 1.389 |
4 | PNEUM. APPL. MORTAR | 0.005 | 0.650 | 0.008 |
5 | TermoarcillaTM 29 | 0.290 | 0.240 | 1.208 |
6 | SINGLE-LAYER MORTAR | 0.015 | 1.300 | 0.012 |
EXTERIOR | SURFACE CHANGE | 0.040 | ||
WALL THICKNESS | 0.445 | RESISTANCE = | 3.054 | |
|
0.327 |
Once the reference assembly had been characterized for each type of façade, the next step was to compare the thermal results for the façades made with the different thicknesses of commercial bricks proposed for the study.
Equivalent thermal transmittance of the envelope for each type of façade with commercial bricks and thicknesses affecting the useful surface area of the housing unit
THICKNESSES (m) | Ueq (W/m2·K) | |||||
---|---|---|---|---|---|---|
TA-29 | TA-24 | TA-19 | TA-29 | TA-24 | TA-19 | |
SINGLE-LEAF FAÇADE | 0.330 | 0.280 | 0.230 | 0.564 | 0.639 | 0.805 |
VENTILATED FAÇADE | 0.345 | 0.295 | 0.245 | 0.342 | 0.368 | 0.418 |
FAÇADE + ETICS | 0.345 | 0.295 | 0.245 | 0.399 | 0.435 | 0.506 |
FAÇADE + ITAICS + LFB | 0.445 | 0.395 | 0.345 | 0.327 | 0.370 | 0.396 |
As can be seen, a single-leaf façade made of TermoarcillaTM 29 brick was found to comply with the strict standard that specifies 0.570 W/m2·K as the most restrictive value in the most climatically adverse regions (
The best solution found here was clearly the ventilated façade with a type 24 or 29 brick, with an equivalent thermal transmittance of around 0.350 W/m2·K and a reduction of less than 0.350 m in the useful area of the housing unit. This thickness may however be considered excessive for housing units. Depending on the thermal requirements in each building, the façade + ITAICS+ LFB with a TermoarcillaTM 19 brick could be considered as acceptable.
This study involved a proposed brick with the same dimensions as the commercial TermoarcillaTM bricks with rhomboidal voids to optimize its internal geometry (
Cross-section of the proposed bricks under study.
An analysis of the specific cross-sections of each type of wall showed that the 0.290 m and 0.240 m thick bricks had a discontinuous horizontal joint with an air space 0.030 m wide, while the 0.190 m brick had a continuous joint. Finite element software (
Heat flow of the specific clay/air cross-section for the proposed brick with a thickness of 0.240 m.
Equivalent thermal transmittance of the envelope for each type of façade with the proposed TermoarcillaTM bricks with rhomboidal internal voids and thicknesses affecting the useful surface area of the housing unit
THICKNESSES (m) | Ueq (W/m2·K) | |||||
---|---|---|---|---|---|---|
TA-29 | TA-24 | TA-19 | TA-29 | TA-24 | TA-19 | |
SINGLE-LEAF FAÇADE | 0.330 | 0.280 | 0.230 | 0.486 | 0.556 | 0.767 |
VENTILATED FAÇADE | 0.345 | 0.295 | 0.245 | 0.312 | 0.339 | 0.407 |
FAÇADE + ETICS | 0.345 | 0.295 | 0.245 | 0.358 | 0.395 | 0.491 |
FAÇADE + ITAICS + LFB | 0.445 | 0.395 | 0.345 | 0.299 | 0.325 | 0.387 |
The results provided by the bricks proposed revealed that for single-leaf façades, 0.290 m and 0.240 m thick bricks met the standards applicable in the most restrictive Spanish regions, where an equivalent thermal transmittance of less than 0.570 W/m2·K is required.
Equivalent thermal transmittances below 0.300 W/m2·K were also observed: such figures were not obtained with any of the wall types using the commercial herringbone bricks.
A joint analysis of the figures in
Comparison in % of improvement in types of façade between the bricks proposed and commercial bricks
Ueq (W/m2·K) | % IMPROVEMENT | ||||||||
---|---|---|---|---|---|---|---|---|---|
HERRINGBONE | RHOMBOIDAL | RHOMB/HERRINGBONE | |||||||
TA-29 | TA-24 | TA-19 | TA-29 | TA-24 | TA-19 | TA-29 | TA-24 | TA-19 | |
SINGLE-LEAF FAÇADE | 0.564 | 0.639 | 0.805 | 0.486 | 0.556 | 0.767 | −14% | −13% | −5% |
VENTILATED FAÇADE | 0.342 | 0.368 | 0.418 | 0.312 | 0.339 | 0.407 | −9% | −8% | −2% |
FAÇADE + ETICS | 0.399 | 0.435 | 0.506 | 0.358 | 0.395 | 0.491 | −10% | −9% | −3% |
FAÇADE + ITAICS + LFB | 0.327 | 0.370 | 0.396 | 0.299 | 0.325 | 0.387 | −9% | −12% | −2% |
The 0.290 m and 0.240 m bricks showed improvements of more than 13% for single-leaf façades, which we consider to be a very important result. For 0.190 m bricks the improvement in such walls was not so great.
In general the 0.190 m brick showed no significant differences for almost any type of façade, which means that it is not worth changing the internal geometry of bricks of that specific thickness.
By contrast, the thermal improvements for the 0.290 m and 0.240 m bricks were significant for all the types of façade proposed here, ranging between 8% and 14%. These improvements can be considered important in terms of the thermal insulation of façades.
As shown in
The 0.240 m rhomboidal brick proposed here showed an improvement of between 8% and 13%, and can therefore be considered as recommendable.
The best value recorded for equivalent thermal transmittance was 0.299 W/m2·K, for the rhomboidal brick on the façade + ITAICS + LFB, where there was a 9% improvement on the performance of the commercial herringbone brick for the same type of wall. However this type of façade is 0.445 m thick, which may be considered somewhat high as it reduces the useful surface area of the housing unit. Its use would therefore depend on the thermal requirements of each building.
The use of clay bricks in façades provides building envelopes with good thermal performance levels. This paper reports a study comparing the equivalent thermal transmittances of façades for two kinds of brick: one that is commercially available and another proposed by the authors, using three different brick thicknesses and four types of façade: single-leaf façades, ventilated façades, façades with an exterior thermal insulation system and façades with internal thermo-acoustic insulation and a large format brick on the inside.
Commercial TermoarcillaTM bricks with herringbone internal voids were used as a baseline reference, but the study focused on bricks with rhomboidal internal voids. All the bricks used had the same outside face measurements. Thicknesses of 0.290 m, 0.240 m and 0.190 m were studied.
It can be concluded that the 0.190 m thick rhomboidal brick proposed offers little improvement on the 0.190 m brick already commercially available: the improvement is less than 5% in the best of cases. This type of brick has a continuous horizontal joint, while the other two types have discontinuous joints with a 0.030 m air space. By contrast, the thermal performances of the 0.290 m and 0.240 m rhomboidal bricks proposed were between 8% and 14% better than those of the commercially available bricks for all the types of wall studied.
For single-leaf façades the thermal performances recorded for the 0.290 m and 0.240 m bricks proposed were better by a highly significant 13%–14%, with a thermal transmittance of 0.486 W/m2·K for the 0.290 m brick.
If façades must not exceed 0.350 m in thickness, only 0.190 m thick bricks can feasibly be used on multilayer façades with thermo-acoustic insulation and a large format brick on the inside. In this case, the equivalent thermal transmittance would be close to 0.400 W/m2·K. For either of the other two bricks the façade thickness would exceed 0.400 m.
Equivalent thermal transmittances of 0.300 W/m2·K were recorded for the 0.290 m thick rhomboidal brick on façades with thermo-acoustic insulation and a large format brick on the inside, but the final thickness of the wall was 0.445 m.
For ventilated façades the 0.290 m and 0.240 m thick rhomboidal bricks proposed gave 8%–9% improvements, with values of 0.312 W/m2·K and 0.339 W/m2·K, respectively. In view of the small difference in thermal terms, the best option would therefore be to use 0.240 m bricks, as the overall thickness of the façade would not then exceed 0.300 m.