Post on 15-Dec-2015
VAV SYSTEM FEATURES( One Of Many Types )
• Electric or Pneumaticor Digital Controls
• “In Duct” &/or “At Diffuser”Locations
• Pressure, Temperature And/Or Flow Sensors
------------------------------------------- VAV The Current State
Of TechnologyIn HVAC !
• Good site to visit & seeanimations of various VAV systems types!
• How different systems work and why !
POSSIBLEMAIN DUCT
VAV
Fan
Sp
eed
>
Current Basic Commercial HVAC Systems
VAVs partial open Typically
Fan
17
HVACGeneral Rules of Installation
Distance from InDuct to Air Outlets.
Do not exceed 20 meters
It’s more of an art than a science.
Even the Prosdon’t always agree !
GENERAL COMMERCIAL “Duct Cell” PLACEMENT. You Have Two Options !
1] You can place ALL duct cell units in the “plenum”.
OR IF there are reasons that this approach might not work;
2] Then review the duct blueprint and split the duct system into sections that
have approximately the “ =< ft2 coverage” of the duct cell you have
selected . Then place a cell at any suitable upstream “insertion point”
for that section. REMEMBER: Sq Ft coverage ( 8’ ceilings) ~= CFM
Sum-total cfm = 3000
400cfm
400cfm
500cfm
500cfm
600cfm
600cfm
500cfm
500cfm
1000cfm
1000cfm
300 ft duct Plus anIn-line
VAV valve
Sum-totalcfm=3000
6000cfm
54” x 8”~3500 cfm
1750 sum cfmRadiusBends
50 ft
41” x 8”duct
EXAMPLE # 3
Bahrain- Multi Story Bldg - ½ of floor• Total of 5,118 sq ft per floor- 3 floors • 8 ft drop ceilings – 10 ft total• 4 air handlers = 2 mains & 2 overload• 1 cell guideline 2000 sq ft - very bad air
InsideWalls
2140 sum cfm
Possible cell locations
VCD boxReturn air registers
32”x 8”900cfm
Loading Issues • A/C only runs at night• Return air is Via dead space• Occupancy can spike to 150