TFA, AHU, HRV

These data and calculations are copied from the System Air Catalogue

Treated Fresh Air Units: Only Fresh air is Supplied to the required Rooms. 

Heat Recovery Ventilation HRV: The air is also exhausted, not only supplied. The cold air inside which is stale while exhausting transfers its hotness or coldness to the fresh air supplied to the rooms. 

AHU-Air Handling Units: Similar to ductable units but with Filters, Humidifiers, and Dehumidifiers. It supplies the fresh air as well as returned air by filtering, humidifying or dehumidifying. 



 Centrifugal fan

There are three types of fans that cover all needs: the
forward and aerofoil models for low pressures and the
backward for medium and high pressures.
Horizontal air handling unit, composed of the following
sections:
• Air mixture.
• Extended surface filters.
• Cooling unit based on chilled water.
• Hot-water heating unit.
• Low-pressure fan section.
Technical data:
• Air flow rate: 19,200 m3/h;
• External static pressure: 45 mm w.g.;
• Cooling power: 107 kw;
• Chilled water temperature: 7ºC;
• Temp. difference of chilled water: 5ºC;
• Conditions of inlet air: 26.4ºC BS, 48.4% RH;
• Conditions of outlet air: 14ºC BS, 86.2% RH;
• Temperature rise of motor: approx. 1ºC;
• Heating power: 196 kw;
• Hot water temperature: 85ºC;
• Temp. difference of heated water: 15ºC;
• Conditions of inlet air: 18.0ºC BS;
• Conditions of outlet air: 26.4ºC BS.
BA Air Handling Unit Selection
Using the quick selection table, the appropriate model for
a flow rate of air of 19,200 m3/h and an air velocity of
2.7 m/s is the
BA-20 with a cross sectional area (afo) of 2.22 m2.
Step 1:
To determine the air velocity through the unit:
First, divide the flow rate of air expressed in m3/h by
3600 seconds to obtain the flow rate of air in m3/s:
19.200 / 3.600 = 5,33 m3/s
Divide this flow rate, in m3/s, by the afo for the BA-20 air
handling unit, in m2, to obtain the air velocity in m/s:
Air velocity through heating/cooling unit= 5,33/2,22 =
2,4 m/s
STEP 2:
To determine the number of rows and depth of each
cooling and heating unit, with an air velocity of 2.4 m/s:
Cooling, water at 7-12ºC, 99100 -kcal/h = 4R
Heating, water 85/70ºC, 69120 kcal/h = 1R



Step 3:
Determine the static pressure of the air handling unit by
adding the various pressure drops for the unit for an air
velocity of 2.4 m/s:
• Air mixing section (M) 30 pa
• Extended surface filter section (F) 72 pa
• Heating unit (BC) 2R 35 pa
• Cooling unit (BF) 4R 85 pa
______________
Total sum for the air handling unit
• Available static pressure 		24 mm w.g.
45 mm w.g.
______________
69 mm w.g.
Total static pressure
Step 4:
Determine the operating conditions of the fan, in this
case for low speed, 560 model, on the respective curves:
The pressures indicated on the curves are “total
pressures”. Therefore, the dynamic pressure (Pd) for
19,200 m3/h of air flow must be added to the static
pressure obtained earlier:
Total pressure (Pd + Pe) = 6.6 mm + 69 rnm =76.28mmw.g.
Total pressure (Pt)76.28 mm w.g. = 76.28 x 9,80665 = 740 Pa
The following values are obtained from the intersection
of the air flowrate and total pressure:
Revolutions:
Input power:
Sound power:
Efficiency: 		776 r.p.m.
6.2 kw
87 dB
64 %
Air outlet velocity: 10.4 m/s



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