Variable frequency drive for Belt driven fans 2

[genieconseil]

I have a dossier where I have an unballanced ventilation syst. Where the évacuation is twice the amount of cfm than is supplied for air compensation. This is in a 7 story condo project, dating from 2006. the central evac fans for the dryers and toilets and kitchen hoods are seperate as per code (montreal, Canada)and are belt driven and on the roof. I need to know if it is possible to install a variable speed drive on the belt driven evac fans so as to reduce the speed to 30% of the capacity of each fan for it's continuous opperation and install a pressure differential sensor at 2/3 of the duct length so to activate the fan to bring the speed of the fan to full capacity for the time of demand and then return to the minimum of 30% of its capacity. This will solve my problem.

Also I need to know if it correct to assume that the flow for a STD domestic cloth dryer is 180 cfm ( the year of design is 2006) I think it is reasonable especially considering that there is a 4'' duct connection outlet on the machine" The manufacturers recommend an evac speed of 1200 fpm to make sure the exess lint and condensation is taken care of.

Thanks for your help

Genieconseil

 

[EnergyProfessional]

VFD on belt drive is no problem. in fact, the softstart of a VFD will save many belts.

 

[DomSh]

Hi,

1. According to the ASHRAE code, the minimum exhaust rates for a toilet (private) is 25CFM/unit. With a shower, it is a good pratice to add 50CFM, for a total of 75CFM. If the exhaust ventilation for the bathroom is above 75CFM, I suggest you to change the gear ratio on the fan to help your negative pressure case.

2. Is it possible to decrease the return ventilation ? What is the actual system ? You could decrease the return ventilation when the toilet/kitchen/dryer is activate (with a differential sensor).

3. For the belt driven evac fan, a rep from Cook or EHPrice (greenheck distributor) will have the answer, no doubt.

4. In your case, 180CFM in 4'' is 2000fpm. You can decrease the exhaust fan to 110CFM for 1200fpm (according to your manufacturers).

For a whirlpool dryer, the exhaust system requirement is 230 CFM in 4''.

https://www.whirlpool.com/digitalassets/WED99HEDW/Ventilation Specification_EN.pdf

Hope this help! Let me know if you find other idea!

 

[rogzog]

Belt driven is not a problem but you need to check the motors to see if they are compatible with VFD. Not all motors will last with VFD drive.

 

[QualityTime]

VFD's need filters and line reactors to prevent harmonics backfeed onto the line side