REHVA Journal – January 2013

Jordi Pascual
Oscar Cámara
Senior energyconsultant
Damien Tavan
Junior energyconsultant
Maria Casanova
Senior energy consultant
All authors are from AIGUASOL, Barcelona, Spain



The major consequences of infiltration are the thermal losses derived from it, which account, in some instances, for high percentages of the total building’s thermal demands [1] and therefore, in energy intensive buildings, cause important economic losses. However, air leakage careful analysis and management is usually the exception rather than the norm.

Four office buildings in Madrid have been analysed at two different levels: air leakage tests and mathematical modelling. In this way real ELA, and the instantaneous and mean infiltration values have been determined, as well as its effects on the heating and cooling demands. This process highlighted different recurring building pathologies, which, although only tested in this small simple, lead to belief this could be a clear picture of the current situation.

This analysis is a part of a bigger project on the multidisciplinary study of the energy behaviour of commercial buildings in Madrid, under the umbrella of the major commercial district development “DesarrolloUrbanístico de Chamartín (DUCH)”.


The methodology used is structured in two separate steps: firstly, the air leakage tests to determine the main parameters of the case study buildings. Secondly, modelling of infiltration allowing the characterisation of the transient model and the resulting data analysis.

Air leakage test

The different air leakage test standards consist in pressurizing and de-pressurizing the study zone using ventilators (usually placing a BlowerDoor [2]) and determining the necessary airflow to achieve a set pressure. In the present case the tests were carried out in the four buildings at store level.

This technique yields the Effective Leakage Area (ELA). Assuming the total building’s air leakage through the different cracks can be represented as the infiltration through a mouthpiece of equivalent area, the cracks’ dimensions can be represented as a single effective area [3], or ELA. Thus, the ELA is usually used, at a set reference pressure, to represent the leakage through the envelope.

However, as some previous studies have shown [4], and for a couple of the current analysed buildings, substantial infiltration occurs between the study zones and some adjacent ones, some of which are unconditioned, consequence of a deficient building process. Thus, it becomes necessary to differentiate between external and internal air leakage. To achieve this, the Zone Pressure Diagnostic (ZPD) was used, which indicates what the corresponding ELA is for the analysis zone with regards to the adjacent and non-external surfaces, and so the ELA for the external ones [5].

Infiltration modelling

Infiltration can be broken down into a climate independent component (ELA), and another dependent on climate conditions, in a non-lineal effect. The climate independent component can be partially quantified by the field tests, whilst the climate interaction requires of a model to calculate its effect. The ASHRAE’s [6] recommended Lawrence Berkeley Laboratory (LBL) have been used for this purpose. This model establishes that air infiltrations are a function of permeability of the building and the pressure differences through its envelope. These pressure differences are induced by air temperature differences (Stack effect) and the wind’s pressure.

The above-described methodology has been implemented in TRNSYS, considering weather and monitored data, with the aim of achieving transitory infiltration values, and the determination of the effect of air leakage in the buildings’ thermal behaviour.

Results and discussion

The exposed methodology has only been implemented in three of the four buildings originally selected. In the remaining one, although the air leakage test was tried, the required pressure differential values (50 Pa) were not achieved due to the construction pathologies. Both the influence of the pathologies in the building envelope and the ones in the internal partitions adjacent to unconditioned spaces posed too high an obstacle for the consecution of reliable results.

The characterisation of the three analysed buildings is determined through the parameters on Table 1.

Table  1. Characterisation of the analysed buildings.




Building A

Building B

Building C



Year of building






Number of storeys





Type of construction






Percentage of window






5 398

10 632

7 448



25 147

93 600

36 689








Out of the field test undertaken for the three buildings, Table 2 shows their characteristic values.


Table 2. Summary results of the air leakage tests.


Building A

Building B

Building C

ELAtest (cm²)




ELAZPD (cm²)




ELA (cm²)




ELA (cm²/m² facade)




Roof and slab infiltration ratio over the total (R)




It can be observed that the infiltration levels between floors are only relevant in Building A, and that the ELA of building B is greater than for the other two buildings. These parameters are the ones used in the equations of the LBL methodology implemented.

The shown results, although being one of the objectives of the analysis, are not very intuitive. In order to make them clearer, they are applied to the different conditions and TRNSYS [7] models for the buildings, so that the air renovations due to infiltration and their effect on the buildings’ thermal demands can be obtained. As an example, the infiltration instantaneous values for the same week in April are shown for the three buildings (Figure 1).

Figure 1. Instantaneous values of infiltration in the three buildings, for a week in April.

The results were synthesized into a weighted average value for infiltration (average infiltration values for the considered time interval, based on wind speed ratios for each orientation), a variation in demands and power on the Spanish regulatory reference (variation of thermal demands with calculated instantaneous infiltration vs. infiltration derived from the interpretation of the Spanish regulation [4-8]), and variation in demands and power supposing no infiltration (variation of thermal demands with calculated instantaneous infiltration vs. no infiltration). Table 3 shows values obtained using monitored climate data from February to September.

Where the variations on demands are obtained by comparing the excess (positive) or the default (negative) of the integrated temporal values of the reference case over the entire period, versus the integrated temporal values of the real case over the entire period. By following the same procedure, positive values for Power means that reference case have a bigger value, while negative one’s means the opposite. The variables whose values are 100, indicate that in the reference case, the values of demand or power are zero.

In the data can be observed the proportion of the weighted infiltrations and, most importantly, the great variation in demands and powers between the models based on real data and those based on regulations. Also the weight of the infiltration on energy demands and powers can be noticed through the comparisons with no infiltration scenarios. The major influence on heating demands vs. cooling ones could be due to a combination of the high internal loads of these buildings, and because of minor infiltrations in summer season when, at the same time, non-occupancy periods exists.

It is worth mentioning, based on the established values and the singularities observed during the field tests, that, mainly in the A and B buildings, the result is a reflection of a poor quality in the construction process, rather than not meeting the current regulatory standards. Equally, comparing the results obtained with other references for office buildings in the US [1] or Australia [9], the magnitude order is very similar.

However, it is very complicate to compare the results for the three different buildings, as those have very different characteristic parameters. That is why the results were normalised based on the buildings’ height (parameter affecting the wind speed directly), the ELA (air tightness level for the façade), and the form factor for the building (ratio envelope surface/volume). Normalizing each of these parameters for Building A the following are obtained:


Table 3.Summary of transitory results of the infiltration models.




Building A

Building B

Building C








Cooling demand variation percentage on Spanish regulation reference






Heating demand variation percentage on Spanish regulation reference






Cooling power variation percentage on Spanish regulation reference






Heating power variation percentage on Spanish regulation reference






Cooling demand variation percentage on no infiltration






Heatingdemandvariationpercentage on no infiltration






Cooling power variation percentage on no infiltration






Heating power variation percentage on no infiltration





Table 4.Infiltrations for the comparative analysis between buildings and on key parameters.



Building A

Building B

Building C






















Figure 2 is a graphic representation, hourly based and for a week in April, of the values in Table 4.

It is seen that the ELA is the main factor in the models. The second one is the height which conditions the wind on the façades. The form factor appears as a second order derivative influenced for the other two parameters.


Figure 2. Infiltrations, for a week in April, of the three buildings considering B and C normalised to A-building’s height (top), ELA (centre), and form factor (bottom).


The main conclusions refer to the feasibility, necessity and interest in undertaking this type of test, both in new construction and in existing buildings. It is also necessary to integrate detailed models in the design tools, verification and buildings’ intelligent energy management, as well as in certification tools. Implementing such analysis in the building process would detect building pathologies, enabling the improvement of the construction processes by establishing priorities depending on the constructive solutions adopted. It would also allow the design process to be informed under cost-efficiency parameters, closer to reality certifications, as well as a more accurate intelligent building management. Equally, and taking into account other similar projects undertaken in different latitudes [10], a more deep analysis and from a stronger architectural point of view could relate constructive pathologies and architectural solutions, with different values for the present latitudes.

For the analysed buildings, their infiltration values are considerably high, with the consequent effect on the thermal demands and high-energy bills. This is mainly due to a poor construction process and practice, although having small form factors, or being low buildings, helps minimizing such effect. Equally, the order of magnitude in the variation of demands with respect to the normative case would justify, in terms of running costs, undertaking the necessary reforms to fix these problems. The strongest evidence lies in the building where the test could not be successfully completed due to the elevated air leakage both with the outside and the adjacent spaces. One should question if this is just an exception or the norm in old enough buildings (1992) in this geographical location.


[1]               Impact of Infiltration on Heating and Cooling Loads in U.S. Office Buildings. S. J. Emmerich, et Al. US. Department of Energy, Office of Building Technologies. Agreement No. DE-AI01-01EE27615.


[3]               M.H. Sherman, “Estimation of Infiltration from Leakage and Climate Indicators”, Lawrence Berkeley Laboratory, University of California, Berkeley (1980).

[4]               Gong, X., Claridge, D.E., Archer, D.H. 2010. Infiltration Investigation of a Radiantly Heated and Cooled Office. ASHRAE Transactions, Vol 116, Part 1.

[5]               “Zone Pressure Diagnostics (ZPD) Calculation Utility, Software User’s Guide”. The Energy Conservatory, Minneapolis (2004).

[6]               “Handbook of Fundamentals, Chapter 25: Ventilation and Infiltration”, ASHRAE (1997).

[7]               TRNSYS, Transient System Simulation Tool. © University of Wisconsin 2012.

[8]               Código Técnico de la Edificación (CTE) HE 2.3, y Condiciones de aceptación de procedimientos alternativos. Instituto para la Diversificación y Ahorro Energético (IDAE), Ministerio de Indústria, Turismo y Comercio 2007.

[9]               Air tightness of australian offices buildings: reality versus typical assumptions used in energy performance simulation. A. M. Egan. Australian National University. Proceedings of Building Simulation 2011, P_1133.

[10]             Methods and techniques for airtight buildings. F.R. Carrié, R. Jobert, V. Leprince. AIVC - Document -CR14. © CETE de Lyon

Jordi Pascual, Oscar Cámara, Aleksandar Ivancic, Damien Tavan and Maria CasanovaPages 36 - 40

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