UPS Sizing for Workstation Outlets

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jojo

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Electrical Engineer
Hello, good day! I just want to ask if the demand factor for receptacles applies in sizing UPS (i.e. 1st 10kVA at 100% demand factor plus remaining at 50%). Thank you.
 
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jojo

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Location
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Electrical Engineer
Hi gadfly56 and JoeStillman, thank you. Yes, our electrical code in the country (PEC - Philippine Electrical Code) acknowledges the adoption of NEC/NFPA70 as the basis for the PEC.

The reason I asked about the sizing is, I'm checking the actual workstation loads against the minimum requirement per Code, and based on the CPU&monitor input watts.

For the sake of discussion, let's say there's a 90 workstations plus 10 future workstations = 100 workstations; 1 quad receptacle outlet (360VA) per workstation. Total demand load per Code will be = [(36,000 VA - 10,000 VA)(0.5)] + 10,000VA = 23,000 VA. Assuming 20%spares plus 25% load growth, we may multiply it by 1.5 (i.e. 1.2 x 1.25 = 1.5). The total demand plus growth will be 34,500VA. A minimum 40kVA/32kW UPS may be used.

Using the actual load based on the cutsheet: the typical power for monitor is 36W (HP Z24n) while the CPU power input (HP Z240 Tower) is 400W. If there are two (2) monitors and CPU, the total load watts will be 472 W or 590 VA (at 80% PF). Again, if we calculate the demand per Code, the total demand load for the 100 workstations will be = [(59,000VA - 10,000VA)(0.5)] + 10,000 VA = 34,500VA. With 20% spares plus 25% load growth, the demand load will be 51,750VA. A 60kVA/48kW UPS will be used.

I am aware that in case of conflict with the code minimum criteria and the actual loads, the higher load density applies. In this case, I might go for a 60kVA/48kW UPS.

My concern is, since this is a workstation, the demand is high. If we neglect the spares and growth, the demand for the workstations per Code (using the actual load scenario) is 34,500VA/ 59,000VA = 0.58 or 58%. What I'm planning is to use 100% demand plus 20%growth which is 70,800VA and use 80kVA/64kW UPS. Not sure if this is too much. Please advise. Thanks again. :)
 
gadfly56

gadfly56

Senior Member
Location
New Jersey
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Professional Engineer, Fire & Life Safety
jojo said:
Hi gadfly56 and JoeStillman, thank you. Yes, our electrical code in the country (PEC - Philippine Electrical Code) acknowledges the adoption of NEC/NFPA70 as the basis for the PEC.

The reason I asked about the sizing is, I'm checking the actual workstation loads against the minimum requirement per Code, and based on the CPU&monitor input watts.

For the sake of discussion, let's say there's a 90 workstations plus 10 future workstations = 100 workstations; 1 quad receptacle outlet (360VA) per workstation. Total demand load per Code will be = [(36,000 VA - 10,000 VA)(0.5)] + 10,000VA = 23,000 VA. Assuming 20%spares plus 25% load growth, we may multiply it by 1.5 (i.e. 1.2 x 1.25 = 1.5). The total demand plus growth will be 34,500VA. A minimum 40kVA/32kW UPS may be used.

Using the actual load based on the cutsheet: the typical power for monitor is 36W (HP Z24n) while the CPU power input (HP Z240 Tower) is 400W. If there are two (2) monitors and CPU, the total load watts will be 472 W or 590 VA (at 80% PF). Again, if we calculate the demand per Code, the total demand load for the 100 workstations will be = [(59,000VA - 10,000VA)(0.5)] + 10,000 VA = 34,500VA. With 20% spares plus 25% load growth, the demand load will be 51,750VA. A 60kVA/48kW UPS will be used.

I am aware that in case of conflict with the code minimum criteria and the actual loads, the higher load density applies. In this case, I might go for a 60kVA/48kW UPS.

My concern is, since this is a workstation, the demand is high. If we neglect the spares and growth, the demand for the workstations per Code (using the actual load scenario) is 34,500VA/ 59,000VA = 0.58 or 58%. What I'm planning is to use 100% demand plus 20%growth which is 70,800VA and use 80kVA/64kW UPS. Not sure if this is too much. Please advise. Thanks again. :)
Click to expand...

Since anticipated demand and growth looks to exceed the code minimums you should really have a sit-down with the end-user and discuss it with them. Since all these devices are cord-connected, in the US designers would likely use only the code minimums, barring specifications to the contrary. Once the installation is built, you have no control regarding what gets plugged in. If these were permanently connected loads with known demand then the code would drive you more in the direction you are thinking, but even so it would not demand that you plan for any specific future loads. Really, the client has to drive this bus.
 
J

jojo

Member
Location
Philippines
Occupation
Electrical Engineer
gadfly56 said:
Since anticipated demand and growth looks to exceed the code minimums you should really have a sit-down with the end-user and discuss it with them. Since all these devices are cord-connected, in the US designers would likely use only the code minimums, barring specifications to the contrary. Once the installation is built, you have no control regarding what gets plugged in. If these were permanently connected loads with known demand then the code would drive you more in the direction you are thinking, but even so it would not demand that you plan for any specific future loads. Really, the client has to drive this bus.
Click to expand...

Thank you for your quick response gadlfy56. I really appreciate it. I will consider your advise as one of the options. Even if I use the actual loads, I might also think of using the demand calculation per Code and go for a 60kVA UPS.

I spent years on "work sharing" with a US company before and I know that the plug load demands there is already reducing the 5VA/SF (connected). As the actual demand based on studies/research is more or less than 1.0 VA/SF.

Thanks again gadfly56.
 
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