Estimate conceptual

Page, J., Conceptual Estimating Manual for Process Plant Design and Construction, Gulf Publishing Co., Houston, Texas, 1984. 

The 40% cost difference should be of concern to the project sponsor but is still within the range of accuracy of conceptual estimating. 

A Conceptual Design is the starting point for a basic process design (Phase 0) and can be used to prepare both order-of-magnitude and conceptual estimates to support initial business planning decisions. 

Project Execution Plan/Master Project Schedule Table 9,1 Conceptual estimate summary. 

Fortunately, with the tools provided in Chapter 19, the Project Manager was able to prepare quickly, before completion of Phase 1, a conceptual estimate that revealed the potential delay early enough to take meaningful corrective action. 

In the meantime, the breakdown of the construction hours by disciplines provided with the conceptual estimate enables the Project Manager to refine, with the aid of the scheduling guidelines in Fig. 9.1, the staffing requirements and prepare a firm plan for contracting the construction work. 

This can be done easily by first laying out the duration of the various construction activities over the estimated 10-month construction duration period in the sequence indicated in Fig. 9.1. The estimated hours for each activity are then distributed over their corresponding durations and totaled, as illustrated in Fig. 9.2, to draw the projected construction staffing and progress curves. The staffing curve peak is 115 versus the 135 estimated with the rules of thumb in the conceptual estimate. 

Please note that the schedule delay feared at the conceptual estimate did not materialize and the construction duration has been reduced to 8 months. 

Conceptual estimates are typically prepared during the advanced R D and early process design stages. They are normally used to build the preliminary project economics, prepare preliminary execution plans, and develop cost estimates for the preparation of a complete process design (Phase 1) and a definitive cost estimate. The Phase 0 design package, described in Chapter 6, contains all the information required for conceptual estimates. See Table 9.1 for an example of a conceptual estimate. 

In general, the factored method is recommended only for conceptual estimates or those cases when reliable information is available on the actual cost of similar projects. 

Come up with quick conceptual estimates to evaluate the cost impact of proposed alternatives. 

General Order of Magnitude and Conceptual Estimates Semi-Detailed Estimate... 

Develop order-of-magnitude and conceptual estimates from minimal information. 

When the equipment list with brief description is also available (annotated equipment list), a conceptual estimate broken down by construction disciplines can be developed in a couple of days for a plant with 50 to 100 equipment items. 

A conceptual estimate can be developed in a few minutes from the preliminary equipment list as follows ... 

The shortcut techniques included here are very useful for quickly checking estimates as well as developing conceptual estimates. Most have been derived from the analysis of several organic chemical plants, built or estimated others come from personal observations. Table 19.34 reflects the analysis of nine actual chemical projects and five estimates of the following common characteristics ... 

This information provides tools for the instant checking of the reasonableness of estimates as well the preparation of order of magnitude, or even conceptual, estimates with minimal information. 

Prepare conceptual estimates of the process options being considered to assess their cost impact. 

Five or six weeks later, when the process configuration was finalized and an annotated equipment list was available (Phase 0), the Project Manager prepared a quick conceptual estimate using the procedures in Chapter 19 in order to validate the assumptions of the Initial Plan of Action (see Table 9.1). 

For a Conceptual Estimate where P ID s and Arrangement Drawings are not available, heat tracing must be estimated as an allowance based on the available process and site information. 

As mentioned in section 19.11 the total field cost factor (TFCF) can be modified and adapted to facilities that differ from those in the original study. The modified factor is developed by adjusting each of its cost components (see Table 19.36) to meet the requirements of specific cases. This approach can be very useful for conceptual estimating as well as for the quick checking of estimates prepared by others. 

Section 19.15 on quick conceptual estimates has been expanded to cover a wider range of projects including retrofits. 

The preliminary design phase is also where sufficient design work is done to assure operability of the project without additional scope. The first step is to evaluate what work must be done to assure that the required scope is comprehensive for the project what work must be done, to what detail, to achieve the required accuracy of the estimate (Fig. 3). If a conceptual estimate has been made, a quick study of it shows which are its largest accoimts and then focus can be on the improvement of their accuracy. A second review that is painfully forgotten is the evaluation of the project for overall completeness of the scope. Questions to ask at this point are ... 

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