Difference between Demand Factor & Diversity Factor
There are two terms that seem to confuse electrical designers. These terms are “diversity factor” and “demand factor“.
The diversity factor is the ratio between the sum of the maximum individual demands of the different subdivisions of a system (or parts of a system) and the maximum demand of the whole system (or part of the system) under consideration.
Diversity factor = sum individual maximum demands / maximum demand of the entire system.
The demand factor is the ratio between the sum of the maximum demand of a system (or part of a system) and the total load connected to the system (or part of the system) under consideration.
Demand factor = maximum demand / total installed load.
Important considerations of the diversity factor:
The diversity factor is always> = 1.
The diversity factor is always> 1 because the sum of the individual maximum loads> Max. A demand of the system.
70% diversity means that the device operates at its nominal or maximum charge level 70% of the time it is connected and ON.
The diversity factor is an extended version of the demand factor. It is the maximum demand of different units / maximum demand of the whole system.
The greater the diversity factor, the lower the energy consumption.
The diversity factor for all other facilities will be applied at different times. Supposing that it is 1.0 in some occasions, it results in a supply feeder and classification of much larger equipment that guarantees the operation of the electrical system, and an overinvestment in cable and equipment to handle the nominal load current. It is better to evaluate the pattern of use of the loads and calculate an acceptable factor of diversity for each particular case.
Application examples of the diversity factor:
Diversity factors have been developed for the main feeders that supply a series of loads, and typically, are from 1.10 to 1.50 for lighting loads and from 1.50 to 2.00 for mixed loads of power and lighting.
The diversity factor can be determined as follows:
Diversity factor = Sum of the total maximum demands ÷ Maximum demand in the feeder = 420 ÷ 250 = 1.68 × 100 = 168%
Example of feeder calculation with demand and diversity factors:
Calculate the size of the main feeder that from the breaker of the substation supplies power to five feeders with loads of 400, 350, 300, 250 and 200 kilovolt-amperes (kVA)
Calculate the demand of each feeder:
- 400 kVA × 95% = 380 kVA
- 350 kVA × 90% = 315 kVA
- 300 kVA × 85% = 255 kVA
- 250 kVA × 80% = 200 kVA
- 200 kVA × 75% = 150 kVA
The individual demands are equal to 1,300 kVA
The transformer that supplies the power to the main feeder and the wiring can be dimensioned from this classification of kilovolt-amperes.
The main feeder has two secondary feeders (Sub Feeder A and Sub Feeder B). The demand for sub-feeder A has 35 KW and the secondary feeder B has a demand of 42 KW.
- Total individual maximum demand = 35 + 42 = 77 KW.
- Maximum demand of the whole system = 70 KW
- The diversity factor must be above 1 or equal to 1.
Important considerations about the demand factor:
- The demand factor is always <= 1.
- if you know the demand factor of a given supply at different time intervals and seasons.
- The lower the demand factor, the lower the system capacity required to handle the connected load.
Example of calculation of demand factor:
(1)Here the total load connected or installed is 10 × 400 W. The maximum demand of the consumer is 9 × 40 = 360 W.
(2) A consumer has 10 outlets at 60 kW each in the kitchen, the load is 60 kW x 10 = 600 KW.
The estimated load = 600 kW X 0.5 = 300 kW.