Industrial Utility Efficiency    

Detailed Design — An Ounce of Design is Worth a Pound of Project

Insufficient focus at the design phase will kill a project. In one aerospace project, insufficient detail was paid to the physical size of the air compressor. The compressor didn’t fit in the allocated space—requiring the extension of the building, and costing tens of thousands of unbudgeted dollars. That had a significant, negative impact on the project return. 

In another job, the client had hired an air compressor company to perform an audit from which a good project emerged. The client then asked the compressor company to do the detailed design work. That company didn’t have the capability to do the work in house, so they went back to the auditor, whom they had sub-contracted out to do the design work. This auditor was very experienced at audits and specifying equipment. However, he had come from the compressor side of the business and consequently didn’t have much plant engineering experience. The result was that he put together an excellent equipment specification but fell far short on the mechanical and electrical portion. When the client got the documentation, they refused to pay.  While the client could go out to bid on the equipment side, there was too much risk associated with the installation, because the specification for the scope of work for the trades was so threadbare.

Figure 1 shows the four steps in a compressed air system improvement project. The analysis, or audit, provides a big picture plan on what needs to be done to achieve the economic objectives of the project. The implementation or project phase is where that plan is physically executed. 



Figure 1: The four steps of a compressed air system improvement


What lies in between analysis and implementation is an often overlooked or inadequately addressed step—design. “Detailed Design” or “Detailed Engineering” is nothing more than the conversion of action items in an audit report to scopes of work for the various trades, as well as specifications for the equipment. There can also be a basis-of-design document describing the objectives of the project and the underlying assumptions. 

Detailed design provides rich detail on the mechanical and electrical side. An example of the written portion of an actual project detailed the following information (generalized for publication purposes):

Communication Wiring Between the Pack House PLC, the 75-hp Pack House, and D Air Compressors: Run a new 1-inch galvanized rigid conduit from the Pack House PLC to the 75-hp Brand Y air compressor located outside of the Pack House. The approximate run is 50 feet. Run Device Net cable in the 1-inch conduit from the Pack House PLC to the 75-hp Pack House air compressor control panel. Mount the Device Net I/O (provided by the compressor automation vendor). Termination of the Device Net cable to the I/O block will be completed by the compressor automation vendor.

Run a 1-inch rigid galvanized conduit from the 75-hp Brand Z compressor to the closest low voltage cable tray located by the Load Out area. The approximate conduit run is 54 feet. At Compressor D, run a 1-inch conduit from the existing overhead cable tray to the control panel located on the West side of Air Compressor D. The approximate conduit is 45 feet. A Device Net cable can now be run between the 75-hp Pack House air compressor and Air Compressor A. The approximate run is 250 feet. Install a Device Net I/O block in Compressor D, provided by others.

Additionally, Figure 2, which was also supplied during the design phase, showed the overall strategy of how the equipment would communicate with each other and the control room. 


Proposed PLC

Figure 2: Supplied during the design phase, this schematic illustrates how communication between the equipment would be achieved.
Click here to enlarge


The winning electrical contractor said: “The reason my price was as low as it was is that I knew exactly what I needed to do and had to put minimal fudge factor into it.” The contractor did a fantastic job and finished the job on time with zero cost overruns. 


The Four Main Values of Detailed Design

Audits by design are there to deliver a big picture. Knowing that the devil is in the details, performing the detailed engineering can be the step that makes or breaks the project. There are four main values of detailed design:

1. Detailed Design Reduces Installation and Performance Risk: The design phase allows the plant to get into the nitty-gritty to increase the certainty that the project will meet projections. It is highly probable that modifications to the original audit plan will occur. In most cases, they are minor. However, if something major should come along, such as insufficient electrical capacity at the bucket, the detailed design allows the plant to make a business decision on what to do next, rather than just implement a project that won’t meet return.

The detailed design work can confirm the cost of the project prior to the company committing its capital dollars to the project. By doing the design in detail rather than on the fly, there will be fewer change orders. Detailed design also confirms the original projected savings and cost, which then increases the certainty that the project will perform as anticipated. This reduces the performance risk. 

2. Project Costs Are Driven Down Through Detailed Design: The more precise the instructions are for the contractors, the smaller the safety factors they have to put in their bids. As the quality of the scope of equipment and works increase, it becomes easier to invite more bidders, as there are fewer questions and less hand-holding required. A greater number of vendors increases the pressure on price, which ultimately improves the ROI portion of the equation.

It should be noted that many air compressor companies have installation crews. However, what is often not known is that the installation crews often cost the same as a service tech—not a tradesperson. The difference in cost per hour can be double. By writing up the scope of work for the trades, rather than just handing it over to a compressor company, pricing pressure is maintained. While it may be convenient to have compressor companies install the equipment, it can cause havoc for the project ROI. 

3. Detailed Design Allows Outsourcing of the Project Management: In this day and age, quite a few companies lack the resources immediately available to do a project in a timely fashion. Often, the project will sit on a shelf for a year or two until resources are allocated. Consider a project that saves $240,000 per year. Every month the plant doesn’t implement costs, the company loses $20,000.

In addition, without detailed design work, someone within the company has to oversee the contractor, and keep a very watchful eye on everything that happens during the installation.  With the detailed design work, the plant can often afford to outsource the project management or the entire project. And speaking from experience, when skilled subcontractors are chosen and good communication is maintained, the project manager may have to spend only 50 percent of this time on site—further keeping costs down and driving project ROI up.

4. The Value of Detailed Design Increases with the Size and Complexity of the Project: The value of detailed design is a function of the size and complexity of a project. If a plant is installing a 100-scfm refrigerated air dryer, the design portion can be done on the back of a napkin. However, if the plant is installing a 3000 scfm heat-of-compression dryer, the cost of a miss is commensurately larger. 


Examining Other Examples

While the biggest potential headaches are on the supply side, detailed design can be done on the demand and distribution side of a compressed air system as well. Consider the general description and picture (Figure 3) for an improvement to a sparging system. 




Install oil-free, positive displacement blower to feed air to the CSM sparge. Back up with high-pressure system. Investigate DCS to take signal from pressure transducer and control feed valve.






Figure 3: This schematic shows a proposed improvement to a sparging system.


The odds are high that implementing the aforementioned action item without further engineering would result in a cost overrun, delay in the project, or underwhelming performance of the process or the savings. Contrast this with a simpler application in which the detailed engineering is provided for installing a spring-loaded valve to a viewport on a kiln cooler, as shown in the following chart. 





Install a 0.75-inch precision regulator and 0.75-inch spring return valve on the main feed line to the viewport lens.


Install a parallel 0.25-inch line with a brass needle valve in parallel to the main feed line. Set the needle valve to maintain a positive pressure of 10 inches of water column to the viewport.


While the second is a far simpler installation, the scope of work should be crystal clear to both the mechanical contractor and the project manager, leaving no ambiguity of the task at hand. 

An example from the mechanical portion of detailed design work could look something like the following:


Item 33.

Install new cross tie piping and valve labeled (1M) between the existing 1-inch header from the Mill Compressor System to the existing 3-inch dry loop header for the Pack House. Downtime required.



Item 34.

Remove existing abandoned 3-inch piping (Old Pack House Loop), and reuse the existing 3-inch hangers. Install new 3-inch butterfly valves labled (14M and 15M), and install new 3-inch sch. 40 piping to complete and re-commission the Pack House loop system. Downtime required for valve installation only.



Item 35.

Remove existing 2-inch gate valve (13M) in the conveyor house between the Mill Compressor System and the Pack House Compressor System. Install a 4-inch by 3-inch concentric reducer and any piping required to tie the system together. Downtime required. 




Detailed Design for Better Projects

An ounce of design is worth a pound of project. Detailed design can cost as much as the audit—but skipping the step will decrease the overall project return for projects of medium or high complexity. That would be due to a potential increase in capital costs, a decrease in the savings, or some significant miss during the installation process. 


For more information, contact Paul Edwards, tel: (704) 376-2600, email:, or visit

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