Understanding Auto-Header

Tuesday, March 7, 2017

In LoopLink PRO we spent a lot of time on header design. We spent so much time on it in fact, most users will never need to spend more than a few seconds on the page. But the speed with which the auto-header function does its job, belies the complexity and importance of what it is doing.

This article describes generally how the LoopLink PRO auto-header system works so it feels less magical and becomes more useful.

Fixed Assumptions

In order to automate the design of your loopfield headers, the LoopLink PRO auto-header tool was built using three fundamental assumptions.

  • Headers are broken into evenly-sized groups of bores we call circuits.
  • Circuits are designed using step-down, step-up reverse-return principles (SDSU-RR).
  • Regardless of u-bend material being used, the header pipe is constructed using HDPE.

We arrived at these assumptions through our own experience and by reviewing hundreds of header designs from other engineers and system designers. From our research, we have found that this method of piping design is the most common and least error prone.

Basic Logic

With those assumptions set, the auto-header function follows a pretty simple set of rules based on IGSHPA's Design & Installation Standards and supplemented by best practices. The scope of the problem is bounded first by the pipe sizes you select to include. After that, we simply analyze the theoretical velocity and pressure drop through a section of pipe and make a choice as to which pipe diameter makes the most sense to minimize head loss while maintaining the minimum velocity required for the flushing process.

You Choose the Available Pipes

The smallest pipe size available is always the diameter and dimension ratio of your U-Bend selection. When your header is initially designed, LoopLink PRO will by default use the same dimension ratio as your U-Bend selection for all sizes of pipe. After that, you can select the nominal diameter and dimension ratio pipe you would like to include in your design.

So, if for example you wanted to design headers to skip 1.25” pipe, all you would do is turn off 1.25”. If you want everything larger than 2” to be DR 13.5… turn those pipes on.

LoopLink PRO will only design your headers using the pipe sizes you specify.

When to Step

LoopLink PRO is designed to first minimize head loss then maintain minimum flushing flow velocities. The minimum flushing flow velocity is defaulted to 2ft/s based on IGSHPA's Design & Installation Standards. That said, you can easily override this value if specified by local code or as a matter of professional preference.

LoopLink PRO will first determine the smallest available pipe size that will result in a head loss value that is less than 3 ft. H2O per 100 ft. of pipe length but is still capable of maintaining the minimum flushing velocity specified in that section.

At every intersection where the header will ‘feed’ a loop, the loop’s design flow is subtracted from the total flow required to provide design flow to the last bore in a circuit. The auto-header then decides if the next section of pipe should be the same size as the last or if a diameter change is needed to minimize head loss and maintain flushing velocity.

The process is exactly what you would do if you were solving the header on paper… just faster and with a lot less eraser debris on your desk.

You Can Step In

LoopLink PRO does its best to behave like we do during header design but it isn’t always practical or reasonable to program common sense choices that fall outside of design standards. Sometimes an engineer needs to step in and apply their experience. Which is why we included manual edit mode.

This allows you to start with an excellent base header configuration and quickly apply changes to make the design your own. The system will even warn you if you fall outside of the standards and provide you with feedback that will help you choose if the decision is appropriate.

The auto-header isn’t meant to take the designer out of the equation. It is meant to take the tedium out of your design process so that you can iterate and optimize quickly to find the best solution for your application.