Fan Speed Up

If any one can help me that would be tops.

I have a VAV system and over the years extras boxes have been added on to the system with out taking into account the effects on the static pressure, flow rates etc. Which means now i am struggling to condition tenancies at the end of the duct run. I have the following fan info and am wondering how to work out the maximum speed i can drive the fan for maximum efficiency before getting cavitation etc.
Is there a program data can be input to show direct changes on motor load etc when adjusting pulley sizes?



Make : Howden
Size : 270DW Duplex
S/N : HFC 3523

Fan Motor Name plate amps : 29.5 amps
Fan motor RPM : 1460 RPM
Fan motor running current @ 50hz : 20.0 amps

Fan Motor Pulley Size : 170mm
Fan motor Shaft Size : 42mm

Fan Pulley Size : 236mm
Fan Shaft Size : 50mm

Belts : 2 x SPB-1500

Hi Koopy
Welcome to the forum. You will need to measure the r/m with a taco (buy one from jaycar), static pressures and volume flow rate. Then check this data with the manufacuters fan curve for that fan. Or you could pay an air ballancing company to do it for you. Another way is to increase your cooling by dropping the coil temp (not very efficient) - you may need to do both. Another issue is has it been balanced? are there some vavs at a much lower % open?, have the dampers been stroked/commissioned properly. One other consideration is fresh air or economy cycle.
Firstly check to see if the load on this AHU can be reduced with efficiency measures like shading, lighting, insulation and sealing up leaky ducts.
Let us know how you go on this one.

Hello Koopy

In addition to Teslas' advice you should figure in a rebalance (even if you are running cv boxes) and an evaluation of any heating/ cooling plant and all associated equipment.
Its not very often you get to increase your plants duty without something suffering.

Hi Koopy and welcome.

Basic Fan Laws here for you to play with. ;)

http://www.gorhamschaffler.com/fan_laws.htm

Note: For motor amperage read BHP

would it be accurate to say that the HP of a motor is is the max current x voltage and bhp is the run amps x voltage ofcourse converted to hp from kw's by divinding by 754.5?

So by knowing this i can work out my motors max capacity before needing to upgrade.
I am in the middle of having the static pressure and duct measurements taken, also i have found out that the maximum fan rpm is 1200rpm.

All in all its not looking to good for me.

Maybe a spot on air balance of the whole system and leave the fan as is will be the best option.

Hi Koopy
HP to kW is yes, bhp not sure.
In your first post you said the fan was 1460 RPM? That sounds like the motor r/m, as I sugested buy a taco for about $60, put the sticker on the shaft and measure it. The motor can handle a fair bit more by the Amps - it depends on the fan curve and max fan speed.
As for the air balance, that's where I think you should start (aside from reducing the load). But buyer be aware there are some dodgy air balancing companies and technicians out there.
Best bet is to try hard to find the as-built or original drawings which should have the air figures on them.