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Elevator Control and Motor Drive Renewal

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  rev. 2008-11-25        

Existing Conditions

Assuming existing elevators are old vintage from original building construction.  Cab cosmetic upgrades often cover old mechanical, electrical, and control systems.

The building is equipped with xxx elevators, which are the age of the facility.  The existing system operates using DC generators to drive DC hoist motors.  The control system is based on simple relay logic.

Retrofit Conditions

The existing elevator hoist motors can be replaced with variable frequency AC drives and inverter duty motors {or SCR drives on the existing DC motors}.  A variable frequency AC drive system is regenerative, returning braking energy to the building electrical system.

A VFD system will use about 50% of the electrical consumption of the existing DC generator system.

An SCR drive system will use about 59% of the electrical consumption of the existing DC generator system.

As the drive system is upgraded, the control system should also be replaced.  A modern dispatch control system uses a sophisticated neural network “auction” system to determine which car will respond to a call from a floor button.  This kind of algorithm reduces the total number of starts and stops by quickly ranking each car for each call, assigning the most suitable one, and then continuously refining the choices as new information arrives (new floor calls, full car, jammed doors…).  This means the shortest waiting times and also minimizes energy consumption.

Budget costing: $100,000 per car for mechanical and control upgrade, $10,000 per car for cab cosmetic upgrade.

Research in apartment buildings found that an old DC drive system uses between 30kWh and 100kWh per day per cab, depending upon height of building, occupant density and other factors.  After VFD installation, use went down to 13kWh to 60kWh per day.  Savings in three buildings averaged 8kWh, 30kWh, and 42kWh per day per cab.

Further Benefits




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