As a HVAC what is the logic of VFD speed ram up and ram down ,and why the using of DPT At HVAC Field?

Dear Mr. Ikram,

The Answer is the use of VFD is using where?

1. with AHU Motor, 2. With Pump Motor, 3. with Chiller compressor 

Use of VFD with AHU is for Capacity Modulation and the input of VFD is from Temperature Controler & DDC

Use of VFD with Pump will be use to control the Water Demand and water demand will be from AHU if Two way Valve of AHU will close the Pressure inside Supply line will be measure by DPT and signal will go tho VDF for Speed Modlualtion or the BMS will give the signal to VFD and take input from DDC.

Use of VFD inside Chiller is to modulate the Compressor Speed & to Control the Chiller Capacity and input of VFD/ Invverter will be from Chiler Mircroprocessor and Plant Manager.