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szwasta
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Join Date: Feb 2008
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Total System Equipment Power Consumption/Load Calculations

05/22/2012 1:28 PM

Can estimating system power consumption when sizing sources or distribution panels be reasonable or less subjective? In my experience, the estimate consistently far exceeds the actual fielded load.

For starters, there is the list of equipment manufacturer name plate power consumption ratings. The assumption here is that the manufacturer must(?) conform to some industry standards in arriving at the name plate rating. Granted, the average consumption will be less. However, the rating (at max temperature, max capacity) cannot be ignored.

To satisfy design review critiques, one must be able to demonstrate your support system will supply enough power over the life of the system in the extreme environments.

On the other hand, there are the "let's use measured power only" theorist's that tend to overlook that this data is in a controlled (lab) environment; that it only provides a snapshot of total power consumption where equipment may not be at peak load capacities.

Generally speaking, not all equipment consumes max power all the time.

One approach I often use is 70% to 80% of the total of name plate ratings (the old 80/20 rule); see 80% of max ratings 20% of the time.

What are your methods of arriving at efficient total power load consumption analysis for systems of many equipment items?

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lyn
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#1

Re: Total System Equipment Power Consumption/Load Calculations

05/22/2012 2:08 PM

FLA nameplate amperage for all equipment, if you're conforming to NEC.
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WJMFIRE
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#2

Re: Total System Equipment Power Consumption/Load Calculations

05/22/2012 3:05 PM

Lyn is right. Anything less and somebody goes to jail (or worse) if there's a problem.

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nobodysomebody47
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#3

Re: Total System Equipment Power Consumption/Load Calculations

05/22/2012 5:16 PM

This may help you

Energy Usage Estimation

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lyn
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#4
In reply to #3

Re: Total System Equipment Power Consumption/Load Calculations

05/22/2012 5:23 PM

No it will not help.

You miss the point entirely, hopefully the OP sees this.

We aren't talking reducing the amout of power a fan or a water heater uses.

The National Electrical Code specifies what is required for electrical installations in the USA.

You don't get to make estimates or assumptioons. You are required to provide provision for the total amount of power the equipment COULD consume under maximum load. Period.
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Tornado
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Technical Fields - Technical Writing - New Member Engineering Fields - Piping Design Engineering - New Member

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#5

Re: Total System Equipment Power Consumption/Load Calculations

05/22/2012 11:56 PM

The NEC allows for load diversity in some conditions, and one can also document nonconcurrent loads from among the total connected load. However, I think that the loads that remain to be counted must be done so at FLA.

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lyn
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#6
In reply to #5

Re: Total System Equipment Power Consumption/Load Calculations

05/23/2012 12:26 AM

.
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debata07
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#7

Re: Total System Equipment Power Consumption/Load Calculations

05/23/2012 2:38 AM

For estimation purpose the maximum demand is calculated as follows:

Maximum demand = (total connected load x demand factor)/ diversity factor

Maintenance equipment like hoists/ cranes, power socket outlets etc. need not be considered under total connected load as these are seldom used and mostly are in operation when the plant is under shutdown

Demand factor is generally considered as 0.8 keeping in view the safety margin provided over the calculated brake horse power as well as the increase in KW while selecting a motor of standard frame size.

Diversity factor is considered as 1.05 to 1.2 depending on the process and the standby equipment envisaged. Also plant ligting is not needed 24 hours a day.

If you would like to estmate the energy consumption, it can be calculated as follows:

Total energy consumption in kWh = average demand x number of working hours

= maximum demand x load factor x hours

Load factor is to be assessed on the basis of the equipment selected for the plant. Typically it is 0.7 to 0.8.
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amnakhan1245
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#8

Re: Total System Equipment Power Consumption/Load Calculations

06/07/2012 1:26 PM

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