Avoid Problems with Facility Fuel Systems

You mean well, of course you do!  You dedicate your education and experience to create practical and reliable designs for your clients.  But, when it comes to specialty areas such as fuel system design, researching new codes and technologies can be a big challenge, especially while trying to meet fast-approaching project deadlines.

So, is it inevitable that some design flaws will find their way to the final construction documents?  Well, don’t give up just yet!

While reviewing specifications related to “facility fuel systems”, I often find that most problems originate from a rather small number of root causes. Take a quick review of your last project and see if you can identify any of the problems outlined below. If they seem familiar, take steps to correct them and you’ll be on your way to a more productive situation.

About those master specifications…

To achieve uniform designs, some engineering firms create master specifications templates, which are distributed among the various engineering departments to be used as the starting point for a given project. Including best-practices and preferred methodologies, master specifications will have been cultivated and updated over time, with technical committees in charge of their upkeep. Other firms may choose a slightly different route, opting for master specifications furnished by a commercial third-party. These “master specs” are then tailored from project to project as required. When executed properly, either of these methods can be efficient and productive, but quite often, I see problems that can lead to substantial errors in design:

  1. Lack of Editing – master specifications, especially those obtained from third parties, should be reviewed to insure that they are indeed valid for the intended application (healthcare, telecommunications, water works, etc.). By intending to cover a broad base of potential applications, it is unlikely that a generic specification will be perfect for your project right out of the box. Careful editing of a master specification for a given project is a critical process that often gets overlooked.
  2. Lack of Regular Maintenance – after developing or adopting a “master specifications” document, the engineering firm fails to create a mechanism that allows the staff to report technical errors found in the specifications. The end result is that any deficiencies carry forward and get applied from project to project, over and over. Beyond having a clear “specification maintenance” process for the staff to follow, be sure that someone is responsible for implementing the proposed modifications.
Other pitfalls to avoid…

Besides ensuring that your specifications are technically correct, try to avoid these other problems:

  1. Division 23 or Division 26? – projects that involve emergency generators will likely include some form of engine fuel day tank (whether freestanding or generator base-mounted). Fuel day tanks are one point where mechanical and electrical specifications come together, and a lack of coordination between these disciplines can lead to serious issues. Example: Day tanks are traditionally furnished with the generator set package, which is specified under Division 26. As such, the electrical engineer will include day tank specifications in his/her scope of work. Separately, a mechanical engineer might be designing the main fuel storage and fuel distribution system (Division 23). Since the mechanical engineer will want to coordinate fuel demand signals (boiler, day tanks, etc) with the fuel delivery system, he may design and specify the fuel system right up to, and including, the day tanks. The disconnect occurs when these two engineers fail to coordinate their work. If the conflict is not caught before procurement, mechanical contractors might see a day tank specified in the mechanical drawings, while electrical contractors see a day tank in the electrical specifications. In practice, this situation often leads to both mechanical and electrical contractors carrying costs associated with the day tank. Or worse, they each may assume that the other is covering the requirement, and neither includes the day tank in their scope of work. Solution: ask for progress drawings from potentially-related disciplines to see how they may be impacting your own work. Reciprocate with your own specifications and drawings, and make adjustments to incorporate each other’s design.
  2. Getting fuel there – fuel delivery systems for generators consist of either a day tank-mounted fuel transfer pump, or a remote (skid-mounted) fuel transfer pump. Which to specify is dependent on the location of the equipment (where is the bulk fuel tank in relation to the day tank?). This is one of the most common problem areas in fuel system design for emergency generators. Positive-displacement pumps (typically used for fuel delivery to generator day tanks) are great at pushing fuel. Although also very good at self-priming , they are limited in their suction capacity. P-D pumps have a vertical lift limit of ~18 feet, and their suction capacity must account for pressure losses in the piping run from the source tank to the pump’s inlet. In general terms, the vacuum on a P-D pump’s suction side should not exceed 15″Hg. For this reason, in applications where the day tank is at a much higher elevation than the source tank, the fuel transfer pump will be specified to be away from the day tank, and closer to the source tank. Drawing fuel from a close-by source tank, and pushing a relatively long distance to the day tank is the correct design method. If the pump were to be installed at the day tank, it would not have sufficient suction capacity to draw fuel from the far-away source tank, and the pump would be more prone to premature failure due to cavitation. You have probably gathered by now that it is imperative that the electrical and mechanical designers understand the physical relationship between the emergency generator and the bulk fuel source. Systems with multiple source tanks and multiple day tanks, as well as those requiring auxiliary hand pumps (which are also limited in their suction capacity), will require special design features to conform to national and local code requirements. Solution: as before, be sure to communicate with your colleagues in related disciplines to ensure that both mechanical and electrical elements of the design will tie well together. For complex applications, contact a trusted vendor that can guide you towards a satisfactory solution.
  3. Basis of design – from time to time, I see instances were a piece of equipment has been designed from scratch by the design engineer. Without a basis of design, contractors are often left guessing where to find such equipment. Presented with a specification for a “custom design”, most vendors will propose their standard product and take exception to the custom requirements appearing in the specifications. If you are tasked with reviewing the product submittals, you may be inclined to reject them and ask for a resubmittal. But what if the specifications can’t be met, whether technically or because no vendor is willing or able to redesign their product for the sale of one unit? Solution: whenever possible, contact vendors in advance to see what they might offer that is already similar to your needs. Coordinating your design with pre-engineered equipment does not mean that you will compromise on quality. With substantial prior sales, pre-engineered equipment will have been tested and (hopefully) perfected. You may also see the benefits of lower equipment cost, reduced fabrication lead time and existing certification by a third-party agency (UL, CSA, FM, etc.).
  4. Don’t leave the equipment’s design up to others – do your specifications include statements such as “day tank as recommended by the generator manufacturer” or “fuel transfer pump as selected by the generator manufacturer“? It may surprise you to know that in most cases, the generator vendor has not reviewed the mechanical plans, and has little knowledge of the fuel system as a whole. Not having a detailed specification leaves the door wide open to less than ideal proposals from second or third-tier vendors. Sure, at the end of the day, the vendor can be forced to comply with local code requirements, but after how many RFI’s, submittal delays and uncomfortable communications with your client? And, even if met, are minimum code requirements all that is required for your client’s facility? Solution: if you are not comfortable with specifying a particular piece of equipment, contact a reputable vendor and ask for guidance. Ask for support in developing a specification tailored to your project, and be sure to coordinate any written specifications to what is indicated on the project plans.

Whatever the reason, problems with technical specifications ultimately lead to time-consuming RFI’s, expensive change orders and project delays, all with negative consequences to your relationship with your client. Keeping a specific project clear of these hazards is a step in the right direction, but I would encourage you to dig deeper and look to address any deficiencies at the source – in your master specifications. Depending on the size of your firm, this might seem like a daunting task, but don’t hesitate to ask for help. This effort may require a formal initiative, created by the department’s head. Or, for smaller firms, an outside consultant might be a good source of assistance.

Whether your firm is large or small, improving your specifications will be time well spent. With clear and detailed specifications, you will have a better foundation to undertake new projects and a better understanding of each completed design. All the while, you will be reducing the questions and potential issues associated with the scope of your work, which can only make your client that much more satisfied with you.

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