Today we
will explain the following:
 How to size the lift motor KW/HP,
 How to calculate the Lift Energy Consumption.
First: How To Size The Lift Motor KW/HP

There are many methods
for sizing the lift motor KW/HP like:

1 Professional Formulas Method
This method has two checks to be made:
1.1 Power Check
The
formula for sizing the motor for a lift is as follows:
Where:
Note:
Example#1:
In
a lift system which has an MG set supplying its DC hoist, calculate the size
of the AC prime mover for a 49 passenger lift, running at 1.6 m/s, if the
efficiency of the installation (including the MG set, the DC hoist motor and
the shaft efficiency) is 70%, and the counterweight ratio is 40%.
Solution:
Applying
the formula above gives:
M
= (P x 75 x 9.81 x s x (1CF)) / η = 49 x 75 x 9.81 x 1.6 x (10.4) / 0.7 = 49.44
KW
So,
50 kW (or 55 kW) motor can be selected.
Example#2:
An
8 passenger hydraulic lift, runs at a speed of 1 m/s, and has an overall
efficiency of 80%. If the mass of the car is equal to the rated load in the
car, then calculate the required minimum size of the motor for the pump unit.
Solution:
As
the mass of the car and associated equipment is equal to the rated load, then
CF can be taken as Thus, applying the formula gives a motor size of:
M
= (P x 75 x 9.81 x s x (1CF)) / η = 8 x 75 x 9.81 x 1 x (1(1)) / 0.8= 14.7
KW
Thus
a motor sized at 16 kW could be used.
Example#3:
A
two speed lift has a rated speed of 1.2 m/s, and a car load of 13 passengers.
If the overall system efficiency is 75%, and the counterweight ratio of 50%
is used, calculate the size of the motor.
Solution:
Applying
the above formula, gives:
M
= (P x 75 x 9.81 x s x (1CF)) / η = 13 x 75 x 9.81 x 1.2 x (10.5) / 0.75 =
7.65 KW
Thus,
an 8.4 kW motor can be selected.
Example#4:
A
VVAC driven lift has a rated speed of 1.0 m/s, and a car load of 78
passengers. If the overall system efficiency is 68%, and the counterweight
ratio of 45%, calculate the size of the motor.
Solution:
Applying
the above formula, gives:
M
= (P x 75 x 9.81 x s x (1CF)) / η = 78 x 75 x 9.81 x 1 x (10.45) / 0.68 =
46.4 KW
Thus,
a 50 kW motor can be selected.
1.2 Acceleration Check
Acceleration Check is used to ensure that the torque rating of the
motor is sufficient to accelerate the motor in the necessary time.
The maximum value of linear acceleration supplied by
the motor can be calculated from the following formula:
Where:
The values of accepted acceleration is 0.81.0 m/s2 And If the
acceleration is less than 0.6 m/s2, then the motor is not adequate, and a
larger size motor with a higher torque needs to be selected, or the masses
have to be reduced.
Notes:
1
If the value of acceleration is more than 1.0 m/s2, this is still acceptable
if the drive is a variable speed drive because they drive the exact required
voltage to achieve the required acceleration. Variable speed drives are like:
2
If the drive is a two speed drive, then a flywheel might be needed to reduce
the value of acceleration.
Example#5:
A
lift system is designed to run at 1.75 m/s, with a car capacity of 28
passengers. The car mass is 1000 kg, and the counterweight ratio is 50%.
Select a motor which will run at a speed of 920 rpm from the table below.
Solution:
First:
Applying the power check, gives a required power of:
M
= (P x 75 x 9.81 x s x (1CF)) / η = 28 x 75 x 9.81 x 1.75 x (10.5) / 0.75 =
24 KW
The nearest motor is motor D.
Second: Applying acceleration Check:
Thus, the motor will also be capable of accelerating
the system at the required acceleration.
Example#6:
Taking
the installation in Example#4 again, find out the maximum value of linear
acceleration it is capable of assuming the following additional parameters:
Trated=
729 Nm
Tmax
= 2.34 Trated
Jmot
= 2.1 kg m2
Jcoupling
= 0.25 kg m2
n
= 610 rpm
C
= 8700 kg
C/W
= 11365 kg
Applying
acceleration Check for calculating the linear acceleration
gives:
Thus, the motor will also be capable of accelerating
the system at the required acceleration.

2 Baldor Formula Method
For a
given Elevator, the required motor HP may be calculated using the following
formula:
Where:
Also, for
a given Elevator, the required motor KW may be calculated using the following
formula:
Where:
Table1:
Elevator Mechanical Efficiency

3 Equivalent Weight Method
The following steps can be used to size the motor HP by using
Equivalent Weight Method:
First: calculate the total weight W in
KGs as follows:
Second: calculate Equivalent weight in KGs
= 0.5 Total weight W in KGs
Third: calculate Motor HP = Equivalent
weight in KGs X 1.5/75
Example#7:
Calculate
the size of the AC prime mover for 80 passenger lift while The car mass is
1000 kg By using Equivalent Weight Method.
Solution:
First: calculate the total weight W in
KGs as follows:
The car weight in KGs = 1000 kg
Total Passengers weight in KGs = 75 x total numbers of Passengers
= 75 x 80 = 6000 kg
Total weight W in KGs = car weight in KGs + total Passengers
weight in KGs = 1000 + 6000 = 7000 kg
Second: calculate Equivalent weight in KGs
Equivalent weight in KGs = 0.5 Total weight W in KGs = 0.5 x
1600 = 800 kg
Third: calculate Motor HP
Motor HP = Equivalent weight in KGs X 1.5/75 = 800 x 1.5 / 75 =
16 HP

4 Buildings Energy Code (BEC)’S Tables
Method
Buildings Energy Code (BEC)’S Tables are applied only for the following
lift and escalator installations:
Buildings Energy Code (BEC)’S Tables are not applied for
the following lift and escalator installations:
4.1 Buildings Energy Code (BEC)’S Tables for Traction
Drive Lift
The running
active electrical power of the motor drive of a traction drive lift carrying
a rated load at its rated speed in an upward direction should not exceed the
corresponding maximum allowable value given in Table 2 and Table3.
Table
2
Table
3
The requirement
in Tables2&3 should not be applicable to:
4.2
Buildings Energy Code (BEC)’S Tables for Hydraulic
Lift
The running
active electrical power of the hydraulic oil pump motor of a hydraulic lift
carrying a rated load at its rated speed in an upward direction should not
exceed the corresponding maximum allowable value given in Table4.
Table4
4.3 Buildings Energy Code (BEC)’S Tables for Escalator
The running
active electrical power of the steps driving motor of an escalator with
nominal width W and rise R when operating under noload condition at rated
speed Vr should not exceed the corresponding maximum allowable value given in
Table5.
Table5
4.4 Buildings Energy Code (BEC)’S Tables for Passenger
Conveyor
The running
active electrical power of the steps driving motor of a passenger conveyor
with length L and nominal width W at an inclination up to 60 from horizontal
when operating under noload condition at rated speed Vr should not exceed
the corresponding maximum allowable value given in Table6.
Table6

5 Baldor Tables Method
Baldor Tables7&8 can be used to determine the elevator motor HP/KW
to use for your application by making the following steps:
Table7: Motor HP Sizes for Geared Elevators
Table8: Motor KW Sizes for Geared Elevators
Note:

6 Curves Method
From Curve1, you can find the motor power in KW as follows:
Curve1
Table9:
Demand Factor for Group of Lifts
Example#8:
Calculate
the motor KW for each lift from group of 4 numbers Gearless lifts with speed
3 m/s each noting that the total weight of each lift is 1500 kg.
Solution:
Step#1: Find the value of
lift speed on the lift speed axis = 3 m/s
Step#2: Draw a
perpendicular line to the “lift Speed” axis at the point determined in step#1
to intersect the curve represent the total weight of the lift,
Step#3: Draw a horizontal
line from the point of intersection assigned in step#2 to intersect with the
motor power axis,
Step#4: Read the intersection
point to give the motor power in KW for gearless or geared machines = 30 KW
Step#5: Apply the demand
factor as per the required number of lifts to the reading fromstep#4 to
calculate the required actual KW of the motor.
Demand factor for 4 nos. lifts = 0.72
x 30 KW = 21.6 KW for each lift

Second: How to calculate the Lift Energy
Consumption

We have two methods for
calculating the energy consumption of lift drives as follows:

1
Schroeder Calculation Method
Schroeder carried out a
large number of measurements, and developed a general formula for calculating
the daily energy consumption of a lift installation as follows:
The
daily energy consumed E_{d} = R
x ST x TP / 3600
Where:
Note:
Schroeder
defined the trip time factor according to the type of lift drive as in below Table10:
Table10
The Ed value found is then used
to calculate the yearly energy consumed per unit floor area (kWh/m2), as
follows:
W= (E_{d} x number of days per
year x 0.85) / (Population x floor area per person)
Where W is the yearly
energy consumed per unit floor area (kWh/m2).
And
The Annual
energy cost = nos. of working days per year x Ed x cost per
KWH
Example#9:
A building has six
intensive duty lifts (with gearless thyristor drive), each running at 4 m/s
with 23 passengers. The motor size is 45 kW. The space allocation for the
occupants is 20 m2/person and the building population is 2000 persons.
Calculate:
Solution:
From Table10, TP is 4 s
(the mean value).
The number of starts per day
can be estimated by assuming two peaks of two hours each, during which the
maximum value of 240 starts per hour is achieved, and an eight hour period of
offpeak activity, during which there are 40 starts per hour. (This assumes a
12hour day, 7:0019:00). This gives the total number of starts per day as
follows:
ST = (2 x 240) + (2 x
240) + (8 x 40) = 1280 starts per day
Then the total daily
consumption per lift is:
E_{d}
= R x ST x TP /
3600
= 45 x 1280 x 4 / 3600 = 64 kWh/day per lift
Hence, for all six lifts
in the group:
Ed = 6 x 64 = 384 kWh/day
Hence, for 260 working
days per year, total annual energy consumption per m2 of floor area:
W= (E_{d} x number of days per year
x 0.85) / (Population x floor area per person) = 384 x 260 x 0.85 / 2000 x 20
= 2.12 kWh/m2
Annual energy cost = nos.
of working days per year x Ed x cost per KWH = 260 x 384 x 0.065 = £6490

2
ISO Standard Calculation Method
Energy used (E)
by a lift per year (kWh) can be calculated by ISO standard from the following
formula:
Where:
With the
following Assumptions:
And the
following Guidance values can be used:
Note:

In the next article, we will explain the
Lift Traffic design calculations by using Software Programs.
Please, keep following.
The previous and related articles
are listed in below table:
Subject Of Previous
Article

Article

Applicable Standards and Codes
Used In This Course,
The Need for Lifts,
The Efficient Elevator Design Solution
Parts of Elevator System Design Process
Overview of Elevator Design and
Supply Chain Process.


The
Concept of Traffic Planning,
The (4) Methods
of Traffic Design Calculations,
Principles of
Interior Building Circulation:
A Efficiency of Interior
Circulation


B Human Factors


C Circulation and Handling Capacity
Factors:
Corridor handling capacity,
Portal handling capacity,
Stairway handling capacity,
Escalator handling capacity,


Passenger Conveyors (Moving Walkways and Ramps) handling
capacity,
Lifts Handling Capacity.
D Location And Arrangement Of Transportation Facilities


Traffic design calculations:
1 Calculation of the Number of Round Trips for a Single Car,
2 Estimation of Population,
3 Calculation of the Average Number of Passengers per Trip (P),
4 Calculation of the Uppeak Handling Capacity (UPPHC),
5 Calculation of the Waiting Interval (Passenger Waiting Time),
6 Calculation of The percentage population served (%POP),


7 Estimation of Arrival Rate,
8 Calculation of the Round Trip Time RTT,


9 Calculation of the quality of service (Grade of
Service)


Methods for Lift Traffic Design Calculations:
First Method: The Conventional Design Method


Second Method: The Iterative Balance Method

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