Hoval RoofVent CON-9, Design Handbook

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164
4 Design example
Design data
■ necessary fresh air flow rate or air change rate
1)
■ Hall geometry (length, width, height)
■ Design fresh air temperature
■ Desired room temperature (in the occupied area)
■ Extract air conditions
2)
■ Fabric heat losses (portion to be covered by the
RoofVent
®
units)
■ Internal heat gains (machines, lighting, etc.)
1)
Check if local regulations and project-specific requirements allow the
reduction of the fresh air flow rate when outside temperatures are low. If
so, use mixed air operation (50% fresh air, 50 % recirculation) for your
design calculation.
2)
The extract air temperature is generally higher than the temperature in the
occupied area. This is the result of unavoidable temperature stratifica-
tion in high spaces, but is reduced to a minimum with the Air-Injector. A
temperature gradient of only 0.2 K per metre hall height can therefore be
assumed.
Example
Fresh air flow rate ......................................44'000 m³/h
Hall geometry (L x W x H) ...................... 72 x 50 x 9 m
Design fresh air temp. ......................................... -5 °C
Desired room temperature...................................18 °C
Extract air conditions ............................... 20 °C / 40 %
Fabric heat losses ........................................... 250 kW
Internal heat gains ............................................. 28 kW
Room temperature:..............................................18 °C
Temperature gradient: .................................... 9 · 0.2 K
Extract air temperature: ....................................≈ 20 °C
Required number of units n
req
Based on the air flow rate per unit (see Table G4), calculate
the required number of units.
n
req
= V
req
/ V
U
V
req
= required fresh air flow rate in m³/h
V
U
= air flow rate for the selected unit size in m³/h
n
req
= 44'000 / 8'000
n
req
= 5.5
Select 6 CON-9s.
Actual fresh air flow rate V (in m³/h)
V = n · V
U
n = Selected number of units
V = 6 · 8'000
V = 48'000 m³/h
Effective fabric heat losses Q
Teff
(in kW)
Q
Teff
= Q
L
– Q
M
Q
L
= fabric heat losses in kW
Q
M
= internal heat gains in kW
Use the following criteria for calculation of internal heat
gains (connected loads of machines and lighting): Operating
times, diversity, direct heat output through convection, indi-
rect heat output through radiation, etc.
Q
Teff
= 250 – 28
Q
Teff
= 222 kW
Necessary output to cover fabric heat losses per unit
Q
TG
(in kW)
Q
TG
= Q
Teff
/ n
Q
TG
= 222 / 6
Q
TG
= 37 kW
RoofVent
®
condens
Design example