Download A0 - Commissioning

IEA Annex 40
Final Subtask B2
Development of Functional Performance Testing procedures
Building Tightness and Air Renewal
Date: 13/01/2005
Authors:
Gabrielle MASY
HEPL Rennequin Sualem
LIEGE
Cleide APARECIDA SILVA
Jules HANNAY
Jean LEBRUN
University of Liège
Laboratory of Thermodynamics
Christophe ADAM
Philippe ANDRE
Patrick LACÔTE
University of Liège
Department of Environmental Sciences and Management
ARLON
1. Introduction
1.1. Operating principles
A building is intended to give its occupants an optimised comfort. This comfort should be
reached with a minimum of energy consumption in order to encounter cost and environment
concerns.
Human comfort requires air renewal flow rates reaching at least 10-3 m3/s per square meter of
floor area.
Residential buildings can be are provided with natural and/or mechanical ventilation system(s).
Both are intended to reach ventilation airflow requirements.
The determinant building parameters affecting its energy consumption are the transmission heat
transfer coefficient and the rate of air renewal. Building tightness and air renewal can be
quantified by blowing door pressurisation and by a tracer gas experiment, respectively.
The infiltration air flow can be compared to performance design goals.
A common benchmark is 0,3 h-1 in residential buildings.
Infiltration can also be characterised by a specific air leakage area, expressed in cm2 per square
meter of heated floor area (common benchmark: 5 cm2/ m2).
1.2. Manufacturers data
Ventilation grid manufacturers publish performances data such as air flow curves as function of
the pressure drop through the gird. Ventilation air flows through girds are sometimes given as
unique values corresponding to a fixed pressure drop (for example 2 Pa).
1.3. Problems to be considered
Problems encountered in buildings result from the lack of ventilation: increasing condensation
risks and affecting human heath, or from the excess of infiltration affecting comfort.
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2. Pressurisation test
2.1. Summary
2.1.1. Objectives and test sequence
The objective of a blowing door pressurisation test is the determination of the total air leakage
area of a building (A0) and of the repartition of this leakage area between the floor, the walls and
the ceiling. The parameter A0 may be introduced in a calculation model in order to evaluate the
building infiltration rate for any weather conditions. Thus, the heat losses due to air infiltration
may be calculated. The determination of those losses is important as they may represent 20 to 40
% of the total building heat losses (even 50 % in very well insulated buildings).
2.1.2. Experimental conditions
The experiment requires a variable speed fan (2000 W power) involved in a box, a flexible pipe
(300 mm diameter, 3 m lenght) , two pressure captors and one thermometer . A smoke pen is also
required in order to assess the reparition of the air leakage area between floor, roof and walls.
The experiment can be performed by two techniciens working half a day per dwelling.
2.2. Preparation phase
A preliminary calibration of the fan is necessary in order to define the relation existing between
the ventilation air flow (V) and the pressure différence (∆pF) measured at the ventilation aperture
of the fan
V= cV . ∆ pF 0.5.ρ - 0.5
ρ [kg/m3 ] : specific air mass depending on the indoor air temperature (depressurisation) or on the
outdoor air temperature (pressurisation). Those two temperatures have to be measured.
The calibration process, allowing the determination of the cV coefficient, is realised in a
laboratory. The fan outlet is connected to a "Venturi pipe" and the ventilation air flow ( VÝ) is
evaluated from the pressure drop measured in the Venturi.
2.3. Test method
2.3.1. Summary of the test method
The pressurisation test consists in submitting a building to a pressure higher than the outdoor
pressure (pressurisation) and then to a pressure lower than the outdoor pressure
(depressurization). The pressurisation and de-pressurisation tests are usually realized with the
help of a variable speed fan (figure 4.5). The box involving the fan can be connected to a window
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or to an external door by a flexible pipe. Only the heated volume of the building is submitted to
the pressurisation test. All the interna1 doors of this volume are opened during the test.
2.3.2. Experimental method
The building is submitted to different (positive and negative) values of indoor-outdoor pressure
difference (∆pB ) by modifying the fan rotation speed (Figure 1). The pressure difference (∆pB ) is
usually stabilised within no more than one minute after the starting phase of the fan. The pressure
difference (∆pB ) is then measured in different rooms and averaged in order to get one value of
for the whole building.
Manometer
Flow meter
Fan
Thermometer
Regulator
Figure 1: Air-tightness measurement of residential building
While the pressure difference (∆pB ) is easy to measure, the ventilation air flow is not. directly
accessible by measurement. It is deducted from the pressure difference measured at the
ventilation aperture of the fan (∆pF ). That's why a preliminary calibration of the fan is necessary
in order to define the relation existing between the ventilation air flow (V) and the pressure
difference (∆pF ).
The data to be collected during the experiment are the two pressure differences ∆pB and ∆pF.
The data post-processing includes first an estimation of the building air leakage area, performed
by curve fitting, and then an estimation of the infiltration air flow.
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- Determination of the building air leakage area: A0 [cm2].
The building is submitted to different pressure differences ∆pB and the corresponding air flows V
are collected in order to compute the parameters a and b of the following law, by curve fitting
(Figure 2):
b
V&= a.(∆pB )
V&
∆pB
with 0,5 (turbulent) < b < 1 (laminar).
m3/s
Pa
air flow
pressure difference between indoor and outdoor
Figure 2 Pressurisation and depressurisation curve of a house
A typical "natural" yearly mean value of ∆pB is 4 Pa ; the corresponding air flow is calculated
and introduced in the following formula in order to get the total leakage area of the building (A0)
⎛ 2.∆pB ⎞
A0 = V&.⎜⎜
⎟⎟
⎝ ρ ⎠
A0
−1 / 2
m2
equivalent building air leakage area
During the pressurisation test, a qualitative examination of the building is performed with a
smoke-pen in order to evaluate the distribution of the total leakage area
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- Determination of the building infiltration air flow VÝtot [m3.s-1]
A calculation model has been developed to combine the influences of the stack affect ( VÝs ) and of
the wind effect ( VÝw ) on the total infiltration air flow ( VÝtot ).
The following assumptions are made:
• the infiltration air flow through building apertures is turbulent, thus proportional to the
square root of the pressure difference at the aperture;
• the superposition of the stack effect and of the wind effect is obtained by addition of the
corresponding pressure effects.
The repartition of the total air leakage area A0 between vertical walls Awl , roof Acl and floor Afl is
characterised by the parameters R and X :
R = (Acl + Afl ) A0
A0 = Awl + Acl + A fl
X = (Acl − Afl ) A0
Two parameters ( fw and fs ) are then identified. They represent the contributions from the
different walls to the wind effect (w index) and to the stack effect (s index) :
3/ 2
⎛ 2 + R⎞ ⎛ ⎛ X ⎞ 2 ⎞
g.H
fs = ⎜
⎟ ⎜⎜1 − ⎜
⎟ ⎟⎟
⎝ 6 ⎠ ⎝ ⎝ 2 − R⎠ ⎠
T
f w = C' .(1 − R)
1/ 3
g
H
T
m/s2
m
K
gravity acceleration
building height
indoor temperature
C' is a dimensionless shielding coefficient quantifying the level of wind protection related to the
building site. It ranges from 0,05 for a highly protected site, to 0,4 for an unprotected site.
The total infiltration air flow, resulting from the wind and stack effects, is then expressed as
function of the climatic data:
2
&2 &2
V&
tot = Vw + Vs
V&
tot
&
V
w
V&s
A0
v
∆T
V&
w = A0 . f w .v
V&
s = A0 . f s . ∆T
total infiltration air flow
m3/s
wind infiltration air flow
m3/s
stack infiltration air flow
air leakage area
wind speed at 10 m from the ground level
indoor- outdoor temperature difference
m3/s
m2
m/s
K
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2.3.3. Additional possibilities
The pressurisation test, as described here above may be applied to any building type but the size
of the building is limited. Anyway, the test may also be applied to large buildings if they are
provided with an air handling system. In this case, the fans of the air handling system are used to
pressurize the building.
2. Tracer gas experiment
2.1. Summary
2.1.1. Objective and test sequence
The objective of the tracer gas method is an experimental measurement of the infiltration rate of a
building. The value of the infiltration rate obtained by this method depends on the outside
weather conditions prevailing during the period of the experiment. Thus, the result of the tracer
gas method is different from that of the pressurisation test: the pressurisation test provides an air
leakage area from which it is possible to evaluate the ventilation rate corresponding to any
weather conditions.
The knowledge of the ventilation rate is desirable in commissioning in order to evaluate the
importance of the infiltration losses in the energy balance of the building.
2.1.2. Experimental conditions
SF6 is a very common tracer gas.
Tight bags can be used for air sampling, if the samples of air are analysed in a laboratory. The
analysis requires a chromatograph equipped with a special detection device (source nickel 63)
and with a gas injection device (gas valve). The bags are in plastic and aluminium, they must be
tight and their inner surface is not allowed to absorb the tracer gas. The experiment also requires
a thermometer, an anemometer and at least one mixing fan. The time required for the experiment
is half a day.
2.2. Preparation phase
A preliminary calibration of the chromatograph is necessary in the range of concentration to be
measured (very low levels of concentration).
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2.3. Test method
2.3.1. Summary of the test method
The tracer gas method consists in injecting a tracer gas in the building heated volume, all the
internal doors of this volume being opened. The decontamination curve of the tracer gas is
observed by detecting the time evolution of the tracer gas concentration.
2.3.2. Experimental method
One advantage of using sulfurhexafluoride (SF6) as tracer gas is that this gas is naturally not
present in atmosphere; it is not toxic and it is detectable at low concentrations (PPB) with a
chromatograph. A volume of a few 2 cm3 of SF6 can be injected in the building volume with a
syringe. A fan is used to mix the indoor air in order to get the same initial concentration of tracer
gas in all the rooms. The tracer gas must be well mixed to the air at the beginning of the
experiment, otherwise it might fall down as it is 10 times heavier than the air.
The evolution of the concentration is observed during at least one or two hours. Samples are
taken in air bags at regular intervals, for example every 15 minutes since the moment of the gas
injection. Each sample involves a mixture of air coming from the different rooms. The mixture of
collected air should be done in proportion to the respective volumes of the different rooms. This
can approximately realised, for example, by counting the number of pumping realised in each
room to fill up the bag with air. A chromatographic analysis allows the determination of the
tracer gas concentration of each sample.
The evolution of the tracer gas concentration ( Ct ) during the decontamination is described by a
decreasing exponential law (Figure 3):
Ct = C0 .e
Ct
C0
n
− n.t
: tracer gas concentration at time t (PPB)
: initial tracer gas concentration (PPB)
: rate of air renewal (h-1)
A least square adjustment allows the determination of the rate of air renewal (n).
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12
10
C = 8,97.e
-0,000183.t
n0,75 = 0,66 ± 0,10 vol/h
8
6
4
2
0
0
3500
Temps en s
7000
Figure3: Tracer gas decontamination curve
The tracer gas can also be CO2, as in the examples presented in Figures 4 and 5.
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7
6
y = -0.0498x + 7.1695
V = 149 m³/h
ln(X-Xinf)
5
4
y = -0.0696x + 6.6896
V = 209 m³/h
3
2
1
0
0
10
20
30
40
50
60
70
80
Time [min]
CO2_B3708
CO2_B3508
Figure 4 Airflow rate supplied to two offices (20.03.2002 13:20)
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8
7
y = -0.1619x + 7.2717
V = 485 m³/h
6
ln(X-Xinf)
5
y = -0.1485x + 7.0393
V = 445 m³/h
4
3
2
1
0
0
5
10
15
20
25
30
35
40
Time [min]
CO2_B3708
CO2_B3508
Figure 5 Airflow rate supplied to the two same offices as in Figure 4, but at another time
(21.03.2002 15:20)
2.3.3. Additional possibilities
The building size is limited. The test may be applied to large buildings if they are provided with
an air handling system. The tracer gas is then injected in the air handling system.
3. References
[1]
M. W. LIDDAMENT
"A Guide to Energy Efficient Ventilation"
Energy Conservation in Buildings & Community Systems Programme
IEA Annex V : Air Infiltration and Ventilation Centre
March, 1996.
[2]
A. BOYENS, P. NINANE
"Concours Habitat Thermique : test de pressurisation - dépressurisation"
Laboratoire de Physique du bâtiment, Université de Liège
[3]
P. NINANE
"Infiltration naturelle : test au gaz traceur"
Rapport d'avancement pour le concours CHT
PN 830410-01
10
[4]
G. MASY
"Review and evaluation of specific audit procedures"
IEA Annex XI
Réf.: GM 831015-01
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