Page 22 - Industrial Process Plant Construction Estimating and Man Hour Analysis

Introduction xxxvii

Comparison of graphic analysis of data (Fig. 3)

Comparison of estimated direct craft man-hours Man-hours
MH β ¼equipment quantities are decreased; estimated man-hours are 1712
decreased
MHc¼know unit man-hour based on historical data 1930
MH ə ¼equipment quantity is increase; estimated man-hours are increased 2100

2500
2000
Man-hours 1500 Series1
1000
y = 194.19x + 1525.7
500
2
R = 0.995 Linear (Series1)
0 Linear (Series1)
0 1 2 3 4
Tables 5–7
FIG. 3 Comparison of direct craft man-hours.
MHc is based on historical data from field erection of over fire duct work in
a coal-fired power plant, and the scope and quantity differences can be identi-
fied and the impacts estimate; therefore,

MH β <¼ MHc <¼ MH ə
The proposed unit is based on the estimator’s quantity takeoff, and erection
quantities are either ( ) 10%.
Direct proportion (straight-line graph): comparison method quantities are
directly proportional to estimate MHs.
MHc is directly proportional to MH β and MH ə .
Whenever one variable increases or decreases, the other increases or
decreases and vice versa.
Equation of straight line:
y is directly proportional to quantity x if y¼kx for some k>0.
Therefore, quantities are directly proportional to estimate MHs.

Unit quantity method
Many estimating methods are qualitative and depend on few facts. The unit
method uses historical and quantitative evidence that leads to a cost driver eas-
ily understood. This method is important for detailed estimating for assemblies.
The method starts with the quantity takeoff arranged in the erection sequence
required to assemble and install the equipment. The estimator selects the task
description by defining the work scope for the task to be installed. Each task
is related to and performed by direct craft and divided into one or more subsys-
tems that are further divided into assemblies made up of construction line items.