Varialbe Frequency Drives

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Power Saver™ Program
Variable Frequency Drives

We provide Variable Frequency Drives (VFD) rebates to Austin Energy customers as part of our Commercial offerings. If you would like to apply for this commercial rebate, please review our rebate information below and email commercialrebates@austinenergy.com.

Rebate Package
Description	Offering
Guidelines and Rebate Application	Variable Frequency Drives Qualifications, Guidelines & Rebate Application (pdf)
Guidelines	Commercial Energy Management

Rebate Summary
The following formulas are applied to all VFD retrofits when used with HVAC equipment. The formulas apply to variable air volume air handling units, cooling tower fans, and variable flow primary and secondary chilled water pumps. These formulas only apply to the installation of variable (not constant) torque VFDs. The rebate is calculated at $250 per Direct kW.

Air Handling Units
	If you had Inlet Guide Vane Air Volume Controls: Direct kW = 0.08 kW/hp x Motor hp
	If you had Outlet Damper Air Volume Controls: Direct kW = 0.19 kW/hp x Motor hp
	If you had a Constant Volume System with no Air Volume Controls: Direct kW = 0.13 kW/hp x Motor hp

Cooling Tower Fans

DFex and OFex are the diversity and oversize factors of existing cooling towers. The table below shows the default diversity factors and the formula below shows the oversize factor calculation.


Diversity Factor
	Number of Cooling Tower Fan Motors	DFex
	1 or 2	1.0
	2 to 4	0.9
	Over 4	0.8
Oversize Factor [at design conditions, (@97°F DB and 75°F WB)]	OFex = Cooling Tower Rated Capacity / [Building Peak Load Tons] Direct kW = 0.62 kW/hp x No. or Fan Motors x Fan Motor hp x [(1/OFex) – (1/OFex)³] x DFex

HVAC Water Pumps

DFex and OFex are the diversity and oversize factors of the existing secondary chilled water pumping system. The table below shows the default diversity factors and the formula below shows the oversize factor calculation.


Diversity Factor
	Number of Secondary Chilled Water Pumps	DFex
	1 or 2	1.0
	2 to 4	0.9
	Over 4	0.8
Oversize Factor [at design condition, (@97°F DB and 75°F WB)]	OFex = Design Water Flow Rate (GPM) / Required Water Flow Rate at Peak Conditions (GPM) Direct kW = 0.62 kW/hp x Pump Motor hp x [1-(1/OFex)³ x DFex

Funding
Funding is limited and is available only to Austin Energy customers on a first-come, first-served basis. The offering is subject to change without notice.

Power Saver™ Program — Saving Energy Together

Links

Qualifications,Guidelines & Rebate Application (pdf)