2022-02-21 – Authors Note:
I have done a lot of work on the model used for this exercise over the years and finally have created a new, improved version of the exercise that includes video self-study modules and self-guided exercises. You can access them by visiting this blog post.
This post provides an answer for the exercise in the previous post where I provided you with screen shots and a SketchUp model of a chiller plant and proposed that you develop a chilled water system diagram for it.
In the video clip below, I illustrate how I would go about developing the diagram and then use the diagram to illustrate how a variable flow primary-secondary chilled water system works. The example also reveals how a very small difference in the way a system is physically piped can make a huge difference in how the system functions.
Bear in mind that while the example uses a chilled water system to illustrate the concept, the principles that are used apply to virtually any type of piping system and service, including condenser water systems, heating water systems, steam and condensate systems, and domestic water systems.
Additional Resources
If you would like to know more about variable flow systems and central plants, you might find the following resources to be of interest.
- Click here for a set of PowerPoint slides that illustrate the operation of variable flow primary-secondary and variable flow primary only systems under different load conditions along with some of the things that can go wrong, like over-flow or low delta t syndrome.
- Click here for a narrative description of how a variable flow primary-secondary chilled water system operates.
- Click here for links to CoolTools and other design resources with a energy efficient design perspective. CoolTools is a design resource targeted at central chilled water plants. In addition to a design guide, the resource includes spreadsheet tools to help you design piping and purchase chillers using a life cycle cost perspective.
David Sellers
Senior Engineer – Facility Dynamics Engineering
A Field Perspective on Engineering 