Voltage drop for Chiller

[binwork91]

Hi, I am using software to do the voltage drop.
In the riser, there is chiller. I know the original engineer use MCA to calculate the load for chiller.
The question come to me is: is chiller a motor?
I have transformer at the line side upstream of chiller.
let us assume chiller MCA is 90A
If I treat chiller load as a normal load, then I show load as 90*460*1.732=71704.8VA.
compare with i treat chiller as a motor about 72HP.
They pull similar amp on feeder, however, motor cause bigger voltage drop on upstream transformer.
chiller as regular load, transformer voltage drop is : 0.5%
chiller as motor, transformer voltage drop is 1.2%

Now question is : is chiller a motor? it contains motors, but is it a motor?

 

[ptonsparky]

Hi, I am using software to do the voltage drop.
In the riser, there is chiller. I know the original engineer use MCA to calculate the load for chiller.
The question come to me is: is chiller a motor?
I have transformer at the line side upstream of chiller.
let us assume chiller MCA is 90A
If I treat chiller load as a normal load, then I show load as 90*460*1.732=71704.8VA.
compare with i treat chiller as a motor about 72HP.
They pull similar amp on feeder, however, motor cause bigger voltage drop on upstream transformer.
chiller as regular load, transformer voltage drop is : 0.5%
chiller as motor, transformer voltage drop is 1.2%

Now question is : is chiller a motor? it contains motors, but is it a motor?

Multiple motors. Same as an AC condensing unit.

 

[infinity]

let us assume chiller MCA is 90A
If I treat chiller load as a normal load, then I show load as 90*460*1.732=71704.8VA.
compare with i treat chiller as a motor about 72HP.

Is using the MCA an accurate way to calculate this?

 

[wwhitney]

They pull similar amp on feeder, however, motor cause bigger voltage drop on upstream transformer.

What is the basis for that statement?

Are you using some software that asks if the load is a motor, and then calculates voltage drop due to the peak current of motor startup? That may be a useful number to know, although I've not seen guidelines on what results are reasonable to allow for such a calculation (surely it would be more than the typical 3% or 5% voltage drop allowance). But it's not something that's comparable to a steady state voltage drop.

Cheers, Wayne

 

[winnie]

To add to @wwhitney 's question: are you using software which is considering load power factor and transformer impedance? If so what values of power factor is used for 'regular load' and 'motor load', and what is the transformer impedance and X/R.

A transformer feeding an inductive load will give greater voltage drop than one feeding a resistive load. The software may be trying to accommodate this.

A chiller contains one or more motors, possibly fed by VFDs, possibly with power factor correction. If your software is actually considering transformer voltage drop, then you need the details of the load to give the software accurate inputs.

 

[binwork91]

Is using the MCA an accurate way to calculate this?

To be honest, I am not sure. Base on the cut sheet submittal provide by contractor, electrical data shows cooling input power 30.2kw, input current 52A, heating input power 38.9kw, input current 59A.
However, MCA show 90A. MOP 110A.
I did not do the design. But base on the load provide on the riser, the design engineer show 71.71KW. I believe he/she use 90A MCA to do the calculation.
However, supply house tell us we can use 59A to do the voltage drop calculation.
I don't have any motor data, all I know it motor is not more than 15HP.

 

[binwork91]

What is the basis for that statement?

Are you using some software that asks if the load is a motor, and then calculates voltage drop due to the peak current of motor startup? That may be a useful number to know, although I've not seen guidelines on what results are reasonable to allow for such a calculation (surely it would be more than the typical 3% or 5% voltage drop allowance). But it's not something that's comparable to a steady state voltage drop.

Cheers, Wayne

Yes, I use easypower to run the voltage drop.
I don't know how to show chiller correctly. Since chiller has motor, but it is not a motor. And i don't have motor information in chiller.
In the software, I can show load in "KVA with PF" or "kva & kvr" or "amp with PF". or I can show as a motor provide HP, with default PF 0.82 EFF 0.91 and other default setting.
And it also find out if i add AFD to the motor, it voltage drop will be better.

 

[binwork91]

To add to @wwhitney 's question: are you using software which is considering load power factor and transformer impedance? If so what values of power factor is used for 'regular load' and 'motor load', and what is the transformer impedance and X/R.

A transformer feeding an inductive load will give greater voltage drop than one feeding a resistive load. The software may be trying to accommodate this.

A chiller contains one or more motors, possibly fed by VFDs, possibly with power factor correction. If your software is actually considering transformer voltage drop, then you need the details of the load to give the software accurate inputs.

Yes, the software will required to input KVA and impedance of transformer. It will calculate X/R. The Z% is 7%, X/R: 5.84147. Z0%: 5.95. The software will calculate X/R and Z0% by itself.

 

[binwork91]

What is the basis for that statement?

I check the power flow for each scenario, and compare the voltage drop and load in Amp.

 

[tortuga]

Yes, I use easypower to run the voltage drop.
I don't know how to show chiller correctly. Since chiller has motor, but it is not a motor. And i don't have motor information in chiller.

I'd just use the larger heating kva 38.9kva and the system voltage is 480V not 460 see NEC 220.5

 

[binwork91]

I'd just use the larger heating kva 38.9kva and the system voltage is 480V not 460 see NEC 220.5

Yes, system is 480V.
Motor is 460V. chiller submittal show 460V. Is it because chiller has motor?
Why do you use 38.9kva instead of using input current 59A to do the calculation?

 

[tortuga]

Why do you use 38.9kva instead of using input current 59A to do the calculation?

So I can use the 480V as the voltage for the VD calculation, like in Example D3(a)

 

[jim dungar]

Why not show it as two devices in your software, a heater and a motor?

Voltage drop calculations should use the maximum current expected. Motor starting voltage drop is all steady state currents plus any additional motor starting current.

 

[binwork91]

Why not show it as two devices in your software, a heater and a motor?

That is a good idea.