Sharp JX-9400 Technické informace Strana 109
- Strana / 211
- Tabulka s obsahem
- KNIHY
Hodnocené. / 5. Na základě hodnocení zákazníků
Leakage through heat exchangers
Some heat exchangers let some air leak between both air channels. This is in
most cases not expected, since there are very few air handling units equipped
with both recirculation and a heat exchanger. In addition, some air is entrained
by the rotation of the wheel in rotating heat exchangers. The amount of air
transferred this way can be measured with tracer gases (see Chapter 2, ‘Airflow
measurements at ventilation grilles’), and the leakage flow rate is one of the
results of the measurement of airflow rates in the air handling unit.
As mentioned in Chapter 2, the glob al recirculation rate can easily be
checked by measur ing the concentration of a tracer injected in the ventilated
space, such as the carbon dioxide exhaled by occupants. Assuming that there
is no inverse recirculation and no leaks in the air handling unit, the global
recirculation rate is:
R ¼
C
supply
C
outdoor
C
exhaust
C
outdoor
ð5:14Þ
If no recirculation is expected, but a significant recirculation rate is observed, it
may be the result of leakage through the heat exchanger. If more information is
required, in particular to check whether it is the exchanger or another part of
the air handling unit that leaks, additional measurements could be performed,
as described in Chapter 2, ‘Airflow rate measurements in air handing units’.
Pressure differential measurements are useful to explain leakage. In addi-
tion, these are easier to perform than leakage measurements and can readily
bring information for a diagnosis. Pressure differentials should be measured
between the following locations (see Figure 5.7):
.
Between one and six on one hand, and three and four on the other hand.
These pressure differentials drive the leakage direction. They should be
zero or slightly posi tive, so that a possible leakage flow goes from supply
to exhaust, and not the contrary.
.
Between one and three on one hand, and four and six on the other hand.
These pressure differentials increase with clogging. Compare them with
the nominal pressure differential gi ven by the factory for the actual airflow
4
Exhaust air
Outdoor air
Supply air
Extract air
- +
31
6
Figure 5.7 Schematics of an air handling unit, showing locatio n of
pressure taps for pressure differential measurements
88 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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