1. Electric Load Estimating 2011 SWEDE Conference

2. Customer’s Connected Load & Electric Utility’s Demand Load
Customers provide the utility company with connected load based on the National Electric Code requirements.
This means everything is turned on and running at instantaneous peak loading. The code may even require them to add safety factors that increase the load over 100%.
The electric utility company will determine the diversified demand load based on the customer’s total connected load information. The utility company does not have to use the NEC requirements for sizing its facilities.
The customer, electrician and engineer will try to get you to match their connected load for sizing transformers and services, but don’t let them. Demand load will typically range from 25% to 75% of their total connected load.
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3. Electric Load Estimating
One of the most important responsibilities of the Utility Project Manager is to accurately prepare a commercial or industrial load estimate for service to the customer. This load estimate influences the design & installation cost of the electric utility facilities. It becomes a factor in determining the cost to the customer for electric service.
Accurate load estimating is one of your most important responsibilities because it effects the project cost and the customer’s cost

4. Demand Meters
For all commercial and industrial customers the demand is metered to be the highest average demand in any 15 minute period during each billing cycle month.
Average is the key word here. It is not the maximum KW during the 15 minute period!
The meters reset the demand to zero every 15 minutes, keeping only the highest.
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5. Demand Factor
How does the load data from the customer get estimated into metered demand? This is done by using a term called demand factor.
Demand factor is the ratio of the peak demand kW of a system or load to the total connected kW of a system or load. It can be written as follows:
Demand Factor [D.F.] = peak demand kW [metered]
total connected kW
If you are calculating the peak metered demand, the equation may be rewritten as follows:
Peak demand kW [metered] = total connected kW X D.F.
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6. OBTAINING LOAD INFORMATION
To calculate the peak meter demand of a load you must know the total connected kW and the demand factor.
It is the responsibility of the customer to provide you with proper connected electrical load data, not the main disconnect size, panel size, or service amps.
The customer should provide connected kW information for each piece of equipment as well as phase and voltage.
This information can be obtained by having the customer complete your Customer Load Requirements Form or by obtaining a copy of the electrical and mechanical plans of the project.
Now lets talk about getting good load information from the customer.
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7. Motor Loads
Motor horsepower [hp] - For motor loads, hp is the common way for the customer to indicate connected load. For large motors requiring a motor start calculation you also need to secure the starting code of the motor. To convert this information into the desired kW, the following equation is used.
connected kW = connected hp X .75
This is derived from the fact that there are 746 watts/hp. So, there is .746kW/hp and it is simply rounded off to .75
Since this is just for estimating purposes, motor efficiency is not taken into consideration.
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How do you determine if a motor is large and needs a motor start calculation?
Ask someone in audience – What horsepower size do you consider to be large?
A 25 hp motor may be considered large and a 100 hp may not!
It depends on where it is located on our distribution system!

8. Motor Load Example
The typical Demand Factor for an elevator motor is 20%.
This is because the elevator is often starting, stopping and idle during a 15 minute period.
A 30 hp motor would only have a 4.5 kW demand.
30 hp x .75 (kW/hp) x .20 (D.F.) = 4.5 kW
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I hope it doesn’t take 15 minutes for the elevator to take you from the 1st floor to the 21st floor!
Also – the 30 hp was sized to pull 1600 pounds of people up the to the top of the building.
Is it using 30 hp of load to pull only 2 people?
Not unless they each weigh 800 pounds!

9. Air Conditioning Load
Air conditioning - to properly determine air conditioning connected kW the Energy Efficiency Rating [EER] of the air conditioning unit and the rated tonnage of the unit must be known.
Equation connected kW = tons X 12
EER
This equation is derived from the fact that:
EER is in units of BTUH/watt
kW = watts
1000
1 ton=12,000 BTUH
This equation calculates connected load. Then, a demand factor is utilized to reduce it to the demand load.
Rule of Thumb:
1 Ton = 1 kW of Connected Load (if the EER is 12)
1 Ton times 12 divided by EER Rating of 12 = 1 KW
Ask – What if this was a very old A/C unit and the EER was 8?
If the EER was Ton x 12 divided by 8 = 1.5 kW
You can see the difference efficiency makes in A/C Load!!
EER = Energy Efficiency Rating (3 phase units)
SEER = Seasonal Energy Efficiency Rating (single phase units)

10. Demand and Diversity Factors
Once you have secured proper load information from the customer you can determine the connected kW for each load.
After the connected kW is determined, the peak metered demand may be calculated if the demand factor is known.
To determine the appropriate demand factor for a connected load the Demand Interval Factor and the Diversity Factor need to be determined.
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11. Demand Interval Factor
The demand interval factor is the percentage of operational run time of the load during a 15 minute demand interval.
For example a motor cycles 10 minutes on and 5 minutes off during a 15 minute demand interval. Therefore the demand interval factor would be:
Demand Interval Factor = 10 minute run time / 15 minutes = .67
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10 divided by 15 = .67 or 67% demand factor

12. Diversity Factor
The diversity factor is defined as the probability that a load will be operating during the period when the demand meter records the high peak demand.
Typically we use a diversity factor of 100% if the load is expected to operate during the peak period and 0% if the load is expected to operate only outside the peak period (Off-Peak Load).
For two or more loads of the same type, the diversity factor will reflect the probability that these same types of loads will all operate during the peak period. The range of diversity factors for these same type of loads could be anywhere from 0% to 100%.
For example the probability that all the receptacle outlets in a building will all be used during the peak period is fairly low and is typically given a diversity factor of 10%.
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13. Example 1:
Tom's Machine Shop is a building that has 5 kW of fluorescent fixtures, 15 receptacle outlets at 1500w each, 1-10 hp lathe, 1-20 hp air compressor and 1-15 hp fire pump.
After questioning the customer about the various loads, the information is further deciphered as follows:
The shop lights are on only during the hours of 8 a.m. to 5 p.m.
The receptacle outlets are in the office only, and will have computers and other small loads plugged into them.
The lathe is fully loaded for 5 minutes periods. The rest of the time is setup time. This procedure repeats every 15 minutes.
The air compressor supplies air to air tools and cycles off and on about half the time.
The fire pump only runs for 30 minutes when tested which is once a month after hours.
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14. Example 1 – Summary
Lighting Demand Factor = Demand Interval Factor x Diversity Factor
= (15 minute run time/ 15 minutes) x 1.0
= 1.0
Lighting Demand Load = 5 kW x 1.0 = 5 kW
Receptacle Outlet Demand Factor = Demand Interval Factor x Diversity Factor
= (15 minute run time / 15 minutes) x 0.1
= 0.1
Receptacle Outlet Demand Load = 15 x 1500 watts x 0.1 = 2.25 kW
Lathe Demand Factor = Demand Interval Factor x Diversity Factor
= (5 minute run time / 15 minutes) x 1.0
= .33
Lathe Demand Load = 10 hp x .746 x .33 = 2.46 kW
Air Compressor Demand Factor = Demand Interval Factor x Diversity Factor
= (7.5 minute run time / 15 minutes) x 1.0
= .5
Air Compressor Demand Load = 20 hp x .746 x .5 = 7.46 kW
Fire Pump Demand Factor = Demand Interval Factor x Diversity Factor
= (15 minute run time/ 15 minutes) x 0.0
= 0.0
Fire Pump Demand Load = 15 hp x .746 x 0.0 = 0.0 kW
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15. Example 1 – Chart Summary of Demand Loads
Equipment HP kW D.F. Demand KW
Lighting
Receptacle Outlets
Lathe
Air Compressor
Fire Pump
TOTAL kW kW
This chart shows that kW of connected load is only kW of demand load (28% of connected load)
This makes a significant difference in the sizing of our facilities!
Typically your diversified demand load will be between 25% and 75% of the customers connected load.

16. Connected KW Vs Demand KW
Customer's Connected KW Vs Actual Demand KW
Project Name
Customer Connected KW
Actual Metered Demand KW
Demand Factor
Sam's Club
1,477
773 52
HEB Grocery
2,135
1,060 50
HEB Gas & Car Wash Site
116 27 23
IKEA Store
3,409
1259 37
Stone Oak Elementary School
1,557
554 36
Holiday Inn
539
118 22
Sundance Office Building
1952
1115 57
Texas A&M Health Science Bldg
2272
930 41
This slide compares the customer’s connected load to the actual demand load on a few projects in Round Rock.

17. Typical Demand Factors
The following factors can be used as a guideline to check the calculated demand factor. Good judgment must be used. Do not use this information as correct in all situations because it is not. The demand factor and diversity factor determination must be answered to ensure correct demand factor assignment.
Air Conditioning 1 unit %
several small units %
bldg. core cooling in winter %
Chiller systems (A/C) entire %
Heating 1 unit %
several small units %
aux. heat for heat pumps %
Interior lighting under 100 fixtures %
over 100 fixtures %
w/large storage & conference areas, etc %
External lighting (off day, on evening)
summer %
winter, closed at night %
winter, open at night %
Sign lighting sign on during day %
summer %
winter, closed at night %
winter, open at night %
Water heating %
Water circulation pumps %
Process equipment continuous %
non-continuous %
Air Compressor %
Computers main frame %
Welders %
CAT or X-RAY %
Laundry & Dry Cleaning Equipment commercial %
Refrigeration %
Miscellaneous Motors gas pump %
pneumatic tubes %
elevators %
Commercial cooking fast foods %
other applications %
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18. Watts Per Square Foot
Sometimes a situation exists in which obtaining accurate load data is not possible.
An example of this situation is a strip shopping center where the developer does not know what type of tenants will lease the spaces.
Table 1 lists the watts/sq. ft. estimates for situations where the load is not available such as speculative lease spaces.
This table can also be used as a comparison tool to validate your calculated demand load.
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19. Watts Per Square Foot TABLE 1 (This Information is 20 Years Old!)
LOAD INFORMATION – WATTS per SQ. FT. ESTIMATES
These may be used when actual load data is not available.
Watts Per Square Foot
Air Conditioning comfort cooling 4 watts/sq ft.
computer rooms 5 watts/sq. ft.
Heating 6 watts/sq. ft.
Office Lighting 3 watts/sq. ft.
Warehouse Lighting 1 watt/sq. ft.
Office miscellaneous 1 watt/sq. ft.
Warehouse miscellaneous 1/2 watt/sq. ft.
Air Conditioning – By Tons
A/C (at 8.0 SEER) 1.5 kW/ton
Chiller units (including auxiliary equip.) kW/ton
Fluorescent Lighting
2' x 4' lay-in 2 lamp (4') 100 watts/fixture
2' x 4' lay-in 4 lamp (4') 200 watts/fixture
2' x 8' lay-in 2 lamp (8') 200 watts/fixture
Other Guidelines
1 phase or 3 phase motor 750 watts/ horsepower
Swimming pool pumps (inefficient) 1.2 kW/horsepower
Refrigeration compressors 1.4 kW/ton
The information in this table is over 20 years old and some of the numbers need to be revised!
I would probably use 3 watts for A/C instead of 4
and 2 watts for office lighting instead of 3
New Fluorescent Lighting is more efficient than shown in table.
You can see this table uses 8.0 SEER for A/C and you cannot buy a new ac unit that has a SEER less than 12?

20. Watts Per Square Foot Example Typical Office Building
TABLE 1
LOAD INFORMATION – WATTS per SQ. FT. ESTIMATES
These may be used when actual load data is not available.
Watts Per Square Foot
Air Conditioning
comfort cooling watts/sq ft.
computer rooms 5 watts/sq. ft.
[summer & winter]
Heating watts/sq. ft.
Office Lighting 3 watts/sq. ft.
Warehouse Lighting 1 watt/sq. ft.
Office miscellaneous 1 watt/sq. ft.
Warehouse miscellaneous 1/2 watt/sq. ft.
TOTAL= 8 watts/sq. ft.
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8 watts per sq ft may be too high! This table has not been updated in over 20 years and with higher efficiency a/c and lighting -- 6 watts may more accurate.

21. Do You Know Jack?
Another way to check your Demand KW estimate is by comparing it to an existing facility on your distribution system.
You are probably not serving the first “Jack in the Box” restaurant on your electric distribution system.
If you are serving a customer that has other existing facilities located on the distribution system – check your meter information system for the Demand KW of the existing locations.
Give example stories: Stone Oak Elementary School, HEB Gas Station & Car Wash, Red, Hot & Blue Restaurant.