Prof. Dipl.-Ing. Dr.nat.techn. Oliver Englhardt
Institute of Building Construction Graz University of Technology
Copyright © with the authors. All rights reserved.
Experimental assessment of the energy
performance of an advanced ventilated clay bricks
façade
Stefano Fantucci, PhD fellow
Department of Energy, Politecnico di Torino, Italy, [email protected]
Valentina Serra, Associate Professor
Department of Energy, Politecnico di Torino, Italy, [email protected]
Marco Perino, Full Professor
Department of Energy, Politecnico di Torino, Italy, [email protected]
Summary
Advanced façade integrating ventilation, such as dynamic insulated and naturally or mechanically
ventilated façade are currently under investigation and new solutions are being made available in
the market. This paper presents the results of an extensive experimental campaign on a ventilated
opaque double skin façade based on hollow clay bricks. Summer and winter thermal performance
has been investigated on three different façade configurations both through an in-field monitoring
campaign and through a series of laboratory tests in a double climatic chamber apparatus. For both
tests, temperatures and heat fluxes were continuously monitored. Results are encouraging and
underline the great potential of this technology, which can lead to a noticeable energy demand
reduction along the whole year.
Keywords: Ventilated façade, dynamic insulation, climatic chamber, energy performance.
1 Introduction
In Italy the use of clay bricks is largely diffused in the building sector, due to the high thermal mass
and good thermal resistance provided, particularly suitable in temperate climates [1]. Unfortunately
according to the latest energy legislation, that is focused mainly on the reduction of the U-value, theirs
thermal performance results to be not sufficient to fulfill the energy requirements unless the clay brick
system is coupled with high thickness insulation layers. In order to allow an extensive use of this
construction system both in new buildings and retrofit interventions, maintaining standard wall
thicknesses, new concepts have to be developed.
In recent years advanced façade such as dynamic insulated façade (DIF) and naturally or mechanically
ventilated façade (MVF-NVF) have thus been developed focusing on the reduction of energy need for
heating and cooling respectively [2]. In this direction the integration of ventilation strategies in the
clay brick systems seems to offer an interesting opportunity to be investigated.
Considering the high potential and the lack of knowledge on these technologies a Research Project
aimed at developing a new clay bricks system was carried out. A ventilated façade working under
different operating conditions was specifically developed in Politecnico di Torino and an extensive
experimental campaign was carried out in order to assess its energy performance. The purpose of the
research was to explore the possibility to combine different ventilation strategies, generating an
Advanced Building Skins
adaptive ventilated double skin façade for both new buildings and energy retrofit of existing buildings,
improving the performance along the whole year.
In particular an extensive in-field monitoring campaign was carried out during the summer period in
Turin (Lat 45.67N, Lon 7.65E), on a NVF installed on an existing building , with the aim of assessing
the potentials of the naturally ventilated clay brick façade on lowering the entering heat fluxes.
Moreover a further experimental campaign in a double climatic chamber was carried out on the same
ventilated façade but working under different ventilation strategy in order to estimate the heat loss
reduction in representative winter conditions.
The climatic chamber test was carried out on two different DIF configurations where the façade was
highly integrated with a mechanical ventilation system:
the Exhaust air façade (EAF) using the façade as an indoor exhaust air heat recovery;
the Supply air façade (SAF) using the façade as a supply air pre-heater.
1.1 The opaque ventilated façades OVF
In Advanced Integrated Façade (AIF), the most common classification considers the ventilation
strategy, the flow path and the system configuration as major items [2].
In particular, three different strategies can be considered: natural ventilation (NV), mechanical
ventilation (MV) and hybrid ventilation (HV) that utilizes both natural and mechanical ventilation as
driving forces.
The possible façade arrangements are schematically represented and classified according to the air
flow path and the ventilation typology, as shown in figure 1, where: (EA) is the exhaust air
configuration, (SA) is the supply air configuration, (OAC) and (IAC) represent the outdoor air curtain
and indoor air curtain configurations respectively.
Figure 1: Façade classification scheme.
SA and EA configurations, which are commonly considered as dynamic insulation systems [2], are
still not widely adopted, despite their great potential, mainly because there is a lack of case studies and
experimental results about their actual performance in building applications.
Nevertheless, in recent years some researchers tried to fill the gap, focusing their attention on the
performance of this kind of technology. The most studied DIF configurations proposed in literature
were principally divided in permeodynamic breathing wall, analyzed in [3] and [4], and
parietodynamic walls, studied in [5].
For what concern OAC façades investigated broader range of investigations were carried out. In
particular, [6] presented the results of a long term experimental campaign and [7] focused on the
analysis of a ventilated wall with an external clay cladding. Some other authors suggested analytical
model to assess the thermal performance of a ventilated façade [8] while in [9] and [10] numerical
models were experimentally validated.
The most known IAC façade commonly identified as “Trombe-wall” is a well-known technology and
has not been investigated in this paper.
2 Wall systems configuration
The different façade configurations used for the experimental tests that presented here, are reported in
figure 2 and also summarized in table 1.
Experimental assessment of the energy performance of an advanced ventilated clay bricks façade
Figure 2: Tested façades, (a) Exhaust air façade EAF, (b) Supply air façade SAF, (c) Reference unventilated
façade RUF, (d) Outdoor air curtain OAC
Table 1: Overview of the tested façade configurations.
Test
Sample
Ventilation
Type
Air Flow
Path
Experimental
Condition
Performance
Investigated
Air Flow
Origin
Air Flow
Destination
a MV EA laboratory winter interior exterior
b MV SA laboratory winter exterior interior
c unventilated - in field/laboratory summer/winter - -
d NV OAC in field summer exterior exterior
2.1 The mechanically ventilated EA-SA façade
Tests specimens (a) and (b) (figure 3) consisted of brick ventilated façades (height 230 cm and width
76 cm). The wall assembly is summarized in table 2.
Samples (a) and (b) are mainly divided in two parts:
the ventilated façade (layer 1,2,3,4,5);
the structural wall (layer 6).
The reference structural brick wall was constituted only by the layer 6 and it was realized with the aim
of comparing the thermal performance of the dynamic insulated façade and assess the performance
improvement of the dynamic insulated façade (a) and (b).
Sample (a) consisted of an exhaust air façade configuration (EA) while sample (b) is a supply air (SA)
façade configuration, as represented in figure 2. The two façades differs for the direction of the air
flow and also for the air flow origin and destination.
Table 2: Sample assembly from inside to outside
number name Thickness
[mm]
Thermal
Conductivity
[W/mK]
Thermal
Resistance
[m2K/W]
1 EPS 20 0.035 0.571
2 MDF 12 0.103 0.117
3 External brick layer 10 0.401 0.025
4 Ventilated air cavity 50 - -
5 Internal brick layer 10 0.401 0.025
6 Structural brick 250 - 1.05
Advanced Building Skins
Figure 3: Samples schemes, (b-left), (a-right).
2.2 The naturally ventilated OAC façade
The external air curtain façade (OAC) was built on a South-West façade of a laboratory building
(LATEC) in Politecnico di Torino.
The ventilated brick façade was build adherent to the existing lightweight insulated precast façade. At
the same time a reference non ventilated façade (made of the same materials) was built in order to
compare and quantify the ventilation effect on reducing the heat load in summer conditions.
The wall assembly is represented in figure 4 and summarized in table 3.
Figure 4: Specimen (d) stratigraphy.
Table 3: Assembly from inside to outside
number name Thickness
[mm]
Thermal Conductivity
[W/mK]
Thermal Resistance
[m2K/W]
1 Hollow brick cladding 10 0.401 0.025
2 Ventilated air cavity 50 - -
3 Hollow brick cladding 10 0.401 0.025
4 Existing wall (mineral wool) 100 - 2.700
Experimental assessment of the energy performance of an advanced ventilated clay bricks façade
3 Methodology
The façades thermal performance was assessed through an experimental campaign, both through in-
field and in laboratory measurement and different synthetic parameters were defined with the aim of
quantifying in a simple way the performance of the façades under different operating conditions.
3.1 In field measurements
The in-field tests were carried out on sample (c) and (d), during summer 2014.
For the continuous monitoring of the façades summer performance, a series of sensors and devices
were adopted. Air and surfaces temperatures were measured using thermocouples type-T, the heat flux
crossing the walls was measured using heat flux meter plates HFP01, while a hot wire anemometer
was used for a spot measuring of air velocity inside the external air channels; finally, in order to
measure the solar irradiance on the same vertical plane of the façade, a pyranometer was used.
The in-field test was carried out for different façade configurations (figure 5), varying the air channel
height, the ventilation grills opening and the joint typology. In this paper, for the sake of brevity, only
the results of the configuration described in section 2.2 were reported.
Figure 5: (OAC) samples installed on the south-west façade of the laboratory.
3.2 Laboratory measurements
For the steady state experimental characterization (samples a and b) a climatic chamber (Building
Envelope Test Cell “BET cell”) was adopted (figure 6). Moreover for the experimental evaluation of
the thermal resistance of the materials that constitute the wall samples, a guarded heat flux meter
LASERCOMP FOX600 was used, according to the international standard EN ISO 12667:2002 [13].
Figure 6: BET cell schematic representation.
Advanced Building Skins
The climatic chamber called “BET cell” has been specifically implemented to test advanced building
envelope component and consists of a double room with a separation frame that can host the sample
walls.
The test-cell rooms dimensions for both the sub-module “A” (outdoor condition) and sub-module “B”
(indoor condition) are 240 cm height and 275 cm width, while the depth is respectively 300 cm (A)
and 165 cm (B).
The external environment is recreated in the sub module “A”, which is equipped with an HVAC
systems that allows to simulate both steady state and transient dynamic boundary conditions. The sub-
module can be continuously maintained at the desired set point temperature, with an accuracy of
±0.5 °C, by means of an all air system working on temperature range of 12/40°C.
The internal boundary condition was recreated in the sub module “B” equipped with a radiant heating
system. The sub module can be continuously maintained at the desired set point temperature, with an
accuracy of ±0.3 °C, the maximum and minimum temperature range depends on the temperature
difference between the two modules and the thermal transmittance of the samples.
The testing apparatus is equipped with a monitoring system for the measurement of thermal resistance
and thermal transmittance, according to EN ISO 9869:2014 [14], consisting into 4 heat flux meters
(HFP01) and 36 (TT) thermocouples, connected to a datataker.
3.3 Performance Metrics
In order to assess the thermal performance of the tested façades under different operating conditions
specific metrics have been used. In particular the following configurations were analysed:
external ventilated façade configuration, outdoor air curtain (OAC) - summer thermal
performance;
supply air façade configuration (SAF) - winter thermal performance;
exhaust air façade configuration (EAF) - winter thermal performance.
The summer thermal performance of the external naturally ventilated façade, outdoor air curtain
(OAC) configuration was investigated through a heat flux metering campaign.
The façade systems were constituted by a ventilated cavity brick (d) and a reference unventilated
configuration unventilated (c), as presented in figure 4.
Equation (1) and (2) were used for the summer thermal performance evaluation. The TL parameter
introduced in [6] represents the daily thermal load energy reduction obtained by using a fixed
unventilated façade configuration (sample - c) compared to the ventilated façade configuration
(sample - d).
'
)(
'
)(2
)(
)(
)]()([
)]()([
11
dTTtC
dTTtC
E
ETL
dsise
csis
d
c (1)
and hence:
'
)(
'
)(2
)]()([
)]()([
1
dTT
dTT
TL
dsise
csis
(2)
where:
Ts2 is the temperature of the inside cavity surface (interface 2-3, figure 4);
E(c) represents the daily thermal energy crossing the unventilated façade (c);
E(d) represents the daily thermal energy crossing the ventilated façade (d);
Tsi is the internal surface temperature;
Tse is the external surface temperature;
Experimental assessment of the energy performance of an advanced ventilated clay bricks façade
The integer interval is between the hour of day in which the temperature difference becomes >0,
indicated with , and the hour of day in which the temperature difference becomes <0 indicated with ’.
The winter thermal performance of the supply air façade (SAF) configuration was investigated with a
heat flux metering experimental campaign using the double climatic chamber facility described in
section 3.2.
The experimental samples consist of two different wall assemblies. First of all the thermal resistance
of a simple brick wall (reference wall) without the adoption of any ventilation strategies was assessed
through heat flux meter measurements, according to EN ISO 9869:2014 [14]. After that the
experiments with ventilated walls were performed using different electrical fans and the air flow rate
for the entire wall cavity was measured through the tracer gas method.
The thermal performance of the supply air configuration, as shown in figure 9, was evaluated through
the pre-heating efficiency pre-heat parameter[11], calculated using equation (3):
)(
)(
outin
outinletheatpre
TT
TT
(3)
Where:
Tinlet is the supply air temperature measured at the top of the façade air cavity;
Tout is the outside air temperature, maintained at 39°C (cold side A);
Tin is the inside air temperature, maintained at 14°C (hot side B).
The experimental performance evaluation of the exhaust air façade (EAF) configuration was carried
out comparing the heat fluxes crossing respectively the tested façade and the reference wall (without
the ventilated layer).
The heat loss reduction q due to the exhaust air façade was calculated using eq. (4)
)(
)(1
ref
b
q
qq (4)
Where:
q(b) is the average heat flux measured in the sample wall (b);
q(ref) is the heat flux measured in the center of the reference wall (ref).
4 Results
Results concerning the different configurations and based on the metrics described in section 3.3, are
here presented.
4.1 OAC summer thermal performance
The daily trends of temperatures registered in the reference unventilated façade RUF and in the OAC
configuration for a typical sunny day are presented in figure 7, while the results of the whole
monitoring period are reported in figure 8. The TL value was varied in the range between 34% and
80% (triangle points) depending on the daily average outdoor temperature, represented by circle points.
Moreover a 42.4% reduction of the average thermal energy (TLavg) were calculated for the whole
monitoring period, and reported in dash-dotted line in figure 8.
Advanced Building Skins
Figure 7: Surface temperatures daily profile for reference unventilated façade RUF (c) and outdoor air curtain
configuration OAC (d).
Figure 8: Average daily temperature Text,avg and TL for each monitoring day.
4.2 SAF winter thermal performance
The results of the air cavity temperature Tcav and the pre-heating efficiencypre-heat at different façade
heights (between 0 cm - Tinlet and 205 cm - Toutlet ) are reported in figure 9. In this height ranges the
results present a linear behavior increasing by around 2°C for each meter height. At 205 cm height the
air results pre-heated from 14.2 °C to 19.2 °C, corresponding to a 20% of pre-heating efficiency.
Experimental assessment of the energy performance of an advanced ventilated clay bricks façade
Figure 9: Air cavity temperature Tcav and pre-heat at different façade heights.
4.3 EAF winter thermal performance
For what concern the EAF, the heat flux reduction Δq, increases with increasing the air flow rate Q
(between 46% and 68%), as presented in figure 10.
The graph shows an asymptotic behavior for air flow rates higher than 35 m3/h for a 76 cm façade
width, which means that any additional increase of the air flow rate have a low impact on the façade
thermal performance.
Figure 10: Heat flux reduction for different air flow rates Q and air velocity v.
5 Conclusions
An extensive experimental campaign was carried out on different ventilated façade configurations.
Main results can be synthetized as:
for OAC, a daily thermal energy reduction around 42% can be obtained considering the whole
monitoring period;
for SAF, the air pre-heating efficiency can reach 20% for a 205 cm height façade;
for EAF, the heat loss can be reduced by 46% ÷ 68% relating to the air flow rate.
Results obtained for the OAC façade are in good agreement with the few results reported in literature
[6], [7] and [8].
EAF configuration showed important improvements of the performance (more than 46%) for air flow
rate higher than 9 m3/h for a 76 cm width façade.
Advanced Building Skins
SAF façade did not present noticeable thermal advantages, but it should be noticed that the steady
state experimental campaign did not take into account the influence of the dynamic external boundary
conditions and in particular neglected the effect of the solar radiation, that could play a key role in pre-
heating the supply air.
It is important to underline that the experimental results presented in this paper are related to the single
season performance of each façade configuration. Nevertheless in order to optimize the façade thermal
efficiency and the adaptive behavior in every season, the three different façade configurations should
be combined and integrated with the HVAC systems.
In particular the coupling of SAF and HVAC systems could significantly increase the coefficient of
performance COP due to the minimization of the temperature difference [12].
This work represents a first step of a wider research activity on these kinds of façades. Results are
encouraging and underline the great potential of this technology, demonstrating how the alternative
use of the three configurations EAF, SAF and OAC integrated with adaptive and dynamic controls,
can lead to a noticeable energy demand reduction along the whole year.
6 Acknowledgements
The research was developed in the framework of the POLIGHT project “BLOCK-PLASTER –funded
by Regione Piemonte. The project was developed in cooperation with DAD_Politecnico di Torino,
VIMARK s.r.l., VINCENZO PILONE s.p.a. and NovaRes s.r.l.
7 References
[1] Federazione delle costruzioni FEDERCOSTRUZIONI - Il Sistema delle costruzioni in Italia – Rapporto
2013; <http://www.confindustriasi.it/files/FC%2020.11.13_Low%20Res%202_VERS_ONLINE.pdf>;
[accessed 06.03.2015].
[2] Perino, M., – Annex 44-State of the art review. Vol. 2A. Responsive building elements, Oyvind Aschehoug:
Norwegian of science and technology (NTNU), Trondheim, Norway, Marco Perino, Politecnico di Torino,
Dipartimento di Energia (Torino), 2010.
[3] Taylor, B.J., Imbabi, M.S., The application of dynamic insulation in buildings, Renewable Energy 15
(1998) 377-382.
[4] Taylor, B. J., Webster, R., Imbabi, M. S., The building envelope as an air filter, Building and Environment
34 (1999) 353-361.
[5] Imbabi, M.S., A passive-active dynamic insulation system for all climates; International journal of
sustainable built environment 1 (2012) 247-258.
[6] Marinosci, C., Semprini, G., Morini, G.L., Experimental analysis of the summer thermal performances of a
naturally ventilated rainscreen façade building, Energy Build. 72 (2014) 280-287.
[7] Stazi, F., Tomassoni, F., Vegliò, A., Di Perna, C., Experimental evaluation of ventilated walls with an
external clay cladding, Renewable Energy 36 (2011) 3373-3385.
[8] Balocco, C., A simple model to study ventilated façades energy performance, Energy Build. 34 (2002)
469–475.
[9] Marinosci, C., Strachan, P.A., Semprini, G., Morini, G.L., Empirical validation and modelling of a
naturally ventilated rainscreen façade buildings, Energy Build. 43(2011) 853–863.
[10] Seferis, P., Strachan, P., Dimoudi, A., Androutsopoulos, A., Investigation of the performance of a
ventilated wall, Energy Build. 43 (2011) 2167–2178
[11] Serra, V., Zanghirella, F., Perino, M., Experimental evaluation of a climate facade: energy efficiency and
thermal comfort performance; Energy and buildings 42; 2010; pp. 50-62.
[12] Cianfrini, C., Corcione, M., Habib, E., Quintino, A., Energy performance of a lightweight opaque
ventilated façade integrated with the HVAC system using saturated exhaust indoor air, Energy and
Buildings 50 (2012) 26–34.
[13] EN ISO 12667:2002 Thermal performance of building materials and products - Determination of thermal
resistance by means of guarded hot plate and heat flow meter methods - Products of high and medium
thermal resistance.
[14] EN ISO 9869:2014 Thermal insulation - Building elements - In-situ measurement of thermal resistance and
thermal transmittance.
