1 introduction -basic principles - users.fs.cvut.czzmrhavla/vent/01_ven_introduction.pdf · 1 1...
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Ventilation
1 Introduction - Basic principles
Vladimír Zmrhal (room no. 814)
http://users.fs.cvut.cz/~zmrhavla/index.htm Dpt. Of
Environmental
Engineering
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Principle of ventilation
Ventilation
� is intentional supply of outdoor air into the buildings (cars,
trains …)
� to dilute and remove indoor air contaminants
� affect the indoor air quality
� healthy buildings
Good indoor air quality (IAQ) is necessary for maintaining
health and high productivity !!!
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Principle of ventilation
Natural ventilation
� is driven by pressure differences across the building envelope,
caused by wind and air density differences because of
temperature differences between indoor and outdoor air
� the flow of air through open windows, doors, grilles and
other planned building envelope penetrations
Mechanical (forced) ventilation
� intentional movement of air into and out of building using
mechanical force
� is driven by fans
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Terminology
Nominal air exchange rate (ventilation rate)
[1/h]
Space air exchange rate
[1/h]
[m3/h]
sS
r
VI
V
⋅
=
.
e
r
VI
V=
s e cV V V⋅ ⋅ ⋅
= +
Ve … outdoor air volume air flow
rate [m3/h]
Vc … recirculation air flow rate
[m3/h]
Vr…interior volume of space [m3]
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Terminology
Outside air fraction
[-]
Percent outside air
[%]
Xoa = 100 % …means no recirculation of return air
. .
e eoa
s e c
V VX
V V V⋅ ⋅ ⋅= =
+
.
100eoa
e c
VX
V V⋅ ⋅= ⋅+
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Terminology
Airflows
1 Outside air
2 Supply air
3 Return air
4 Exhaustt air
5 Recirculated air
6 Indoor air
7 Transfer air
8 Mixed air
9 By-pass air
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Terminology
Air-Handling Unit
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Heat and Pollutants
Sources of heat and pollutants
� internal
- persons
- electronic appliances, lighting, technology, electric motors
- animals, biological processes in agriculture, …
� external
- outdoor air
- external climatic conditions
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Indoor Contaminants
� CO2
� water vapour
� combustion products
� tobacco smoke
� VOC
� aldehydes
� pesticides
� asbestos
� radon
� …
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Ventilation Requirements
� hygienic – for the people
� technological – for technology processes
� biological – agricultural processes
� micro-biological
� safety
� fire
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Parameters of the pollutants
Concentration of pollutants
� mass [mg/m3]
� volumetric [cm3/m3]
� ppm (parts per million) 1 ppm = 10-4 %
� number of particles in m3 – clean rooms
Dimension of the particles
� a = 0 – 100 µm
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Parameters of the pollutants
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Conversion X [mg/m3] ���� Y [ppm]
M …molecular weight of the gass [g/mol]
Note:
1000 ppm = 0,1 % vol.
= 324,44[ppm] [mg/m ]Y X
M
Parameters of the pollutants
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Mass Balance of the Ventilated Room
�� � �
τ τ τ⋅ ⋅ ⋅
+ = +s r
source exhaustsupply storage
Gd V c d V c d V dc
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� τ → ∞; steady state
� solution
τ⋅
G d τ⋅
+ sV c d τ⋅
=V c d + rV dc
τ
τ
τ
⋅ ⋅⋅
⋅ ⋅ ⋅
⋅
⋅
⋅
= =− −
+ − =
=
+ −∫ ∫
0 0
s s
s r
c
c r
s
G GV
c c PEL c
G V c V c d V dc
dc Vd
VGc c
V
Mass Balance of the Ventilated Room
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τ τ+ − + −
= ⇒ =+ − + −
0 0
ln lns s
r
rs s
G Gc c c c
V VV VG GV Vc c c cV V
τ τ− − = + + − 0 1r r
V V
V V
s
Gc c e c e
V
( ) ( )τ τ τ
= − + + − − − −
2
0 0 02 2r r rG V G V G V
Vc c c c c c
Mass Balance of the Ventilated Room
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Concentration of the pollutant
Time ττττ [h]
Concentration c [g/m
3]
V →→→→ 0 m3/h
V1
V2 = 2V1
V
G = const.
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� s i r
source exhaust storagesupply
Q d V c t d V c t d V c dtτ ρ τ ρ τ ρ⋅ ⋅ ⋅⋅ + ⋅ ⋅ ⋅ ⋅ = ⋅ ⋅ ⋅ ⋅ + ⋅ ⋅ ⋅
����������� ��������������������
Thermal Balance of the Ventilated Room
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c …specific heat of the air = 1010 [kJ/kgK]
ρ …density of the air = 1.2 [kg/m3]
� t → ∞; steady state
Q dτ⋅
sV ct dρ τ⋅
+ iV ct dρ τ⋅
= rV cdtρ+
( )i s
QV
c t tρ
⋅⋅
=−
Thermal Balance of the Ventilated Room
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Limit Concentrations
Maximum permission concentration (MPC)
… in any time !!
for τ → ∞ and steady state
≤maxc MPC
⋅
⋅= +max s
Gc c
V
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Permission exposure limit PEL
� for τ → ∞ and steady state
WHY ?
⋅⋅
=− p
GV
PEL c
Návrh větrání
?!=c PEL
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Limit Concentrations
Permission exposure limit PEL
…where τ = 8 hours
0
1avgc c d
τ
τ ττ
= ∫
( )τ
τ
⋅ ⋅
− ⋅⋅ ⋅
= − − − + + ⋅
0
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avg s s
G Gc c c e c
I V V
≤,8avgc PEL
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Average concentration for periodical pollutant generation
( )τ ττ
⋅ ⋅
−⋅ ⋅
=
= − − − + +
∑ 0,1
1 11 i i
nIi i
avg i s s iitot i
i i
G Gc c c e c
I V V
1
8 hoursn
tot ii
τ τ=
= =∑
Limit Concentrations
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Limit Concentrations
<≤
max
prům
c MPC
c PEL
!
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Example 1
Permanent pollutant generation Ventilation strategy:
1) cmax,1 > MPC
cavg,1> PEL
!!! Ve ↑↑↑↑
2) cmax,2 < MPC
cavg,2 < PEL
OK
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Example 2
Variable pollutant generation Ventilation strategy:
1) cmax,1 < MPC
cavg,1> PEL
!!! Ve ↑↑↑↑, ττττ ↓↓↓↓
2) cmax,2 > MPC
cavg,2 < PEL
!!! Ve ↑↑↑↑ , ττττ ↓↓↓↓
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Example 3
Periodical pollutant generation Ventilation strategy:
cmax < MPC …OK
cavg> PEL …!!!
!!! Ve ↑↑↑↑, ττττ ↓↓↓↓
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Hygienic aspects
Adition of the pollutants
� for two and more chemical substance
+ + + ≤1 2 1
1 2
... 1n
n
c c c
PEL PEL PEL
+ + + ≤1 2
1 2
... 1n
n
c c c
MPC MPC MPC
= + + +1 2
1 2
; ... n
n
G G GV
PEL PEL PEL
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The pollutants with independent effect
= = =1 2,1 ,2 ,
1 2
; ; ... ne e e n
n
G G GV V V
PEL PEL PEL
( ),1 ,2 ,max ; ; ...e e e e nV V V V=
Hygienic aspects
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Mauna Loa
(Havaj)
> 380 ppm
Carbon dioxide CO2
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Example1
Example 1: Pettenkoffer‘s criterion
1 people exhale 0.42 m3/h of air
Concentration of CO2 in exhaled air is 4 % vol.
Concentration of CO2 in outdoor air CCO2 = 0.035 % vol. = 350 ppm
Max. concentration of CO2 in the room Cmax = 0.1 % vol. = 1000 ppm
Calculate volume air flow rate of outdoor air Ve = ? [m3/h]
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Pettenkofer‘s criterion
Max von Pettenkofer (1818 - 1901)
� main metabolite: CO2 a water vapour
� CO2 production depends on activity level - 16 dm3/h CO2 for
unsleeping person (10 dm3/h when sleeping)
� CO2 concentration in indoor environments
informs about quality of ventilation
� CL = 0.1 vol. % = 1000 ppm
→ Pettenkofer criterion
� 25 m3/h per person
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• 360 - 400 ppm: concentration in outdoor air
• 800 - 1 000 ppm: recomended indoor air concentration
• 1 200 až 1 500 ppm: maximum (real) indoor air concentration
• > 1 500 ppm: tideness, sleepiness, lethargy, headache…
• < 5 000 ppm: maximum safety concentration without health risk
• > 5 000 ppm: sickness, higher pulsation (sick building syndromme -
SBS)
• > 10 000 ppm: health hazards
• > 40 000 ppm: dangerous to live
1 000 ppm = 0,1 % obj.
Carbon dioxide CO2
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Ventilation Requirements
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Ventilation Requirements
Space Occupancy
[m2/person]
Required air flow rate
[m2/h.person]
Office spaces 10 36
Land-scape office 15 36
Classroom 2 29
Kidergarten 2 30
Conference room 2 36
Department store 7 23
EN 15251 - Indoor environmental input parameters for design and
assessment of energy performance of buildings- addressing indoor
air quality, thermal environment, lighting and acoustics
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Ventilation Requirements
ASHRAE
10 cfm = 17 m3/h
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Health Risk
Group 1 Group 2 Group 3
Risk of death or
sickness
Risk of respiratory
sickness
Risk of less important
sickness or discomfort
Radon Fungi Temperature
Carcinogenic VOC Allergens Noise
Asbestos Dust particles Lighting
Passive smoking (ETS) NOx Non-carcinogenic VOC
CO (high concentrations) Ozone CO (low concentrations)
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Example 2
Example 2: Calculation of volume air flow rate
Mass flow of pollutant G = 0.2 kg/h of FexOy
Permission exposure limit PEL = 0,015 g/m3
Concentration in outdor air cs = 0
Calculate volume air flow rate V = ?
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Example 3
Example 3: Calculate time ττττ of ventilation after accident of NH3 in machine room.
Volume of the machine room Vr = 500 m3
Amount of escaped NH3 m = 1.2 kg
Max. permission concentration MPC = 0.036 g/m3
Ventilation rate I = 5 h-1
How long it takes achieving of MPC …
ττττ = ?
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Thank you for your
attention