Sharp JX-9400 Informations techniques Page 25
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- Table des matières
- MARQUE LIVRES
Noté. / 5. Basé sur avis des utilisateurs
Constant concentration
Using an electronic mass flow controller monitored by the tracer gas analyser,
the concentration of tracer gas can be maintained constant by varying the
injection rate in an appropriate way. In this case, the time derivative of the
concentration is zero and Equation 1.4 becomes very simple:
I þ Q
io
ðC
i
C
o
Þ¼0 ð1:15Þ
hence:
Q
io
¼
I
ðC
i
C
o
Þ
¼
I
C
ð1:16Þ
This method provides an unbiased estimate of the airflow rate, even when it
varies with time.
Pulse injection
The method can also be used with the tracer injected as a short pulse at time t
0
.
The injected mass M will result in a tracer gas concentration at sampling loca-
tion that varies with time, starting from background concentration C
0
, growing
and then decaying back to background concentration. Let C(t) be the tracer
concentration above background.The total mass of tracer gas passing at the
sampling location is then:
M ¼
ð
1
t
0
CðtÞ QðtÞdt ð1:17Þ
An app roximation to infinite time can be good enough when the experiment
(and the integral) is stopped at time t
f
, when the concentration is close
enough to background.
Since both functions C(t) and Q(t) are positive and continuously derivable,
we can apply the integral mean value theorem (Axley and Persily, 1988), that is:
M ¼ QðÞ
ð
t
f
t
0
Cð tÞdt with t
0
<<t
f
ð1:18Þ
This means that there exists a time during the experiment, when the airflow
rate Q has a value satisfying the above equation. The knowledge of the injected
mass M and measurements of the integral of the concentration down wind can
then provide a value of Q.
The integral of the concentration can be calculated from the mass of
tracer m sampled downwind from the injection port by pumping the air at
known rate Q
s;i
through a tube. The sa mpled mass is related to concentration
by:
m ¼
ð
1
0
CðtÞQ
s
ðtÞdt ð1:19Þ
4 Ventilation and Airflow in Buildings
- Claude-Alain Roulet 4
- Contents 6
- List of Figures and Tables 8
- List of Figures and Tables ix 10
- List of Figures and Tables xi 12
- Preamble 13
- Introduction 14
- Outdoor airflow rate 15
- Recirculation rates 16
- Exfiltration 17
- Ventilation efficiency 18
- Airtightness 20
- Energy efficiency 20
- Common techniques 21
- Airflow Rates in Buildings 22
- Tracer decay, no injection 24
- Constant injection rate 24
- Constant concentration 25
- Pulse injection 25
- Airflow Rates in Buildings 5 26
- Airflow Rates in Buildings 7 28
- Global system of equations 29
- Airflow Rates in Buildings 9 30
- Properties of the flow matrix 31
- Airflow Rates in Buildings 11 32
- Note: y Under condition 34
- Source: Sherman, 1990 34
- Airflow Rates in Buildings 13 34
- Airflow Rates 36
- Source: Roulet et al., 2000a 37
- Velocity traverse 38
- Test procedure 39
- Tracer gas dilution 39
- Source: Awbi, 2007 40
- Inflatable bag 41
- Flowmeter 41
- Compensated flowmeter 41
- Tracer gas injection ports 41
- Source: Roulet et al., 1999 42
- Node by node method 44
- Least square solution 48
- Eliminating some equations 48
- Simplest way 49
- Less than four tracer gases 53
- Planning tool 54
- Simple measurement using CO 55
- Age of Air and 60
- Ventilation Efficiency 60
- Nominal time constant 61
- Air exchange efficiency 61
- Source: Roulet, 2004 62
- Measurement method 63
- Concentration [ppm] 65
- Source: Roulet et al., 1998 69
- The model matrix M 73
- Condition of the model matrix 74
- Factorial designs 75
- 3-D designs 76
- Measurement methods 80
- Reductive sealing 82
- Density corrections 84
- Two measurement points 85
- Airtightness 65 86
- Airtightness of buildings 88
- External fan 89
- Internal fan 90
- Leakage visualization 90
- The stack effect method 91
- Airtightness 71 92
- Neutral height method 93
- Airtightness 73 94
- Pressurization method 95
- Flow rate difference method 96
- Conditioned space 97
- SealSeal 97
- Measurements and Measures 98
- Related to Energy Efficiency 98
- Energy in air handling units 100
- Heat exchangers 104
- Types of heat exchangers 105
- Rotating heat exchangers 106
- Glycol heat exchanger 107
- Heat pump 107
- Heat exchange efficiency 107
- Ventilated 110
- Global heat recovery efficiency 111
- Source: Roulet et al., 2001 114
- Examples of application 115
- Energy for ventilation 118
- Measurement of airflow rate 120
- Measurement of electric power 121
- Simulation results 126
- Recirculation 126
- Humidification 127
- Heat recovery 127
- Ductwork 128
- Contaminants in 129
- Air Handling Units 129
- Source: Bjo 130
- Humidifiers 131
- Source: Roulet et al., 2000 133
- Measurement protocols 134
- Selecting the panel 135
- Source: Bluyssen, 1990 136
- Training procedure 137
- Experimental day 138
- Principle of the method 138
- Injection technique 139
- Hot air blower (200 °C) 140
- Stainless steel 140
- Ø 6 mm copper tube 140
- Example of application 141
- Evidence for adsorption 144
- HVAC systems 146
- Common Methods 153
- Properties of tracer gases 155
- Source: Dietz et al., 1983 157
- Mixing tracer gases 158
- Tracer density problem 159
- Sampling methods 160
- Grab sampling 160
- Passive sampling 160
- Networks, pumps and pipes 161
- Tracer gas analysers 163
- Objective of the analysis 163
- Photo-acoustic detector 165
- Mass spectrometry 165
- Gas chromatography 167
- Chemical indicator tubes 167
- Identification methods 168
- Confidence in the coefficients 170
- Regression of the second kind 171
- Orthogonal regression 171
- Bayesian identification 172
- Error analysis 174
- Definitions 175
- A few statistics 175
- Covariance 177
- Statistical distributions 177
- What is the problem? 180
- Most simple error analysis 180
- Estimate of the variance 181
- Linear equations systems 181
- Upper bound of the errors 183
- References 187
- Unit Conversion Tables 192
- Pressure 194
- Volume flow rate 194
- Mass flow rate 194
- Glossary 195
- Glossary 175 196
- Glossary 177 198
- Glossary 179 200
- Glossary 181 202
- Glossary 183 204
- Glossary 185 206
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