Categorically, Demand It on Your Schedule: You Con-Du-It in Autodesk® Revit® MEP Martin Schmid, P.E. Industry Success Manager, Autodesk

Load Categories Typically, Demand Factors are assigned on a per category basis. I.e., a demand factor ‘rule’ is associated with Elevators, and a separate rule applies to Receptacles. Thus, each load is assigned a Load Category. Each Load Category is assigned a Demand Factor (rule). Multiple Load Categories can use the same Demand Factor rule. For example, you may associate the Lighting category and the Electric Heat category with a single Continuous Demand Factor rule… or, you can create separate Demand Factor rules for each. You can only associate one Demand Factor rule with a load Category, but the Demand Factor rules are flexible and let you associate multiple factors with the rule.

Demand Factors Demand factors are adjustments to the Connected Load to account for physical phenomenon, and affect the Calculated (or Demand) Load on Equipment. Why kind of physical phenomenon? greater Inrush Current – when a motor starts up, it draws more current (to overcome inertia) to get the motor running. Once the motor is running, the ‘nameplate rating current’ is drawn. Thus, the Demand is greater than the Connected. greater Heat – as current is drawn through a conductor, over time, heat accumulates. Thus for continuous loads, the Demand is greater than the Connected to provide a ‘buffer’. less Usage – things like receptacles, elevators, commercial kitchen equipment, etc, are not all likely to be used at the same time. Thus, factors are prescribed that allows the Demand to be less than the Connected load.

Electrical Connectors – Load Classification

Constant

Example: Lighting – 125% C: Connected D: Demand P1A C: 10kVA D: 12.5kVA P1B C: 6kVA D: 7.5kVA P2A C: 12kVA D: 15kVA P2B C: 8kVA D: 10kVA P1 C: 16kVA D: 20kVA P2 C: 20kVA D: 25kVA DP C: 36kVA D: 45kVA

By Quantity / Total

Example: Elevators C: Connected D: Demand Factor P1 C: 3 elev D: 0.90 P2 C: 4 elev D: 0.85 DP C: 7 elev D: 0.77 Qty of Elevators Demand Factor

By Quantity / Total Limitation NEC : “In no case shall the feeder or service calculated load be less than the sum of the largest two kitchen equipment loads.” In most cases not an issue. I.e., other loads will bring up the calculated load. Load Qty23 Load Load Load Sum Factor100%90% Result

By Quantity / Incrementally

Example: Farm Load C: Connected D: Demand Factor P1 C: 60kVA D: 51.5kVA P2 C: 30kVA D: 27.5kVA DP C: 90kVA D: 68kVA QuantityDemand Factor kVA 100%100% 20kVA 75%65% 10kVA 65%50% 20kVA 100%75% 10kVA 75%50% Italics Italics indicate what the ‘parent’ panel sees. P1 CDFD P2 CDFD DP CDFD

By Load / Total

Greater ThanLess Than or Equal % Demand Factor 0kVA10kVA100 10kVA20kVA90 20kVAunlimited80 P1A C: 6kVA D: 6kVA (100%) P1B C: 12kVA D: 10.8kVA (90%) P2A C: 9.5kVA D: 9.5kVA (100%) P2B C: 10.5kVA D: 9.45kVA (90%) P1 C: 18kVA D: 16.2kVA (90%) P2 C: 20kVA D: 18kVA (90%) DP C: 38kVA D: 30.4kVA (80%) C: Connected D: Demand No real-world example to my knowledge By Load Total

By Load / Incrementally

Greater ThanLess Than or Equal % Demand Factor 0kVA10kVA100 10kVAunlimited50 P1A C: 6kVA D: 6kVA (100%) P1B C: 12kVA D: 11kVA (91.7%) P2A C: 9.5kVA D: 9.5kVA (100%) P2B C: 10.5kVA D: 10.25kVA (97.6%) P1 C: 18kVA D: 14kVA (77.7%) P2 C: 20kVA D: 15kVA (75%) DP C: 38kVA D: 24kVA (63.2%) C: Connected D: Demand Receptacles

Motor Loads Any load can be a motor load (i.e., Elevator) See subclassification-motor-parameter.html#tp for how to map the parameter (this must be mapped for the functionality to work.). subclassification-motor-parameter.html#tp If the load is the largest motor load, it is deducted from its Load Category total, and associated with the Motor category. Note: In some cases, this may result in a conservative calculation. I.e., for Elevators, this would mean there is one less elevator, thus a greater factor being applied. The Demand Factor rule associated with the Motor category will then be applied accordingly.

Motor Loads The largest motor connected to each component in the distribution system is increased per the Motor load category (which, by default, is associated with the Motor Demand Factor).

Limitations Non-Coincident Loads : Five pumps, two as backup, for example. Non-Coincident Load Types : Heating vs. Cooling where building is in only one ‘mode’ or the other. Not designed for residential applications (i.e., where loads are based on a per-area basis) Demand is ALWAYS computed at the Panel (not on the circuit). Sample from “The Electricity Wiring Regulations 2007”, published by the Regulation and Supervision Bureau for the Water, Wastewater and Electricity Sector in the Emirate of Abu Dhabi. The basis of this document is the IEE Wiring Regulations (BS 7671)

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