#804 Discussion of Fan Updates for Terminal Units and AHUs

Cory Mosiman Thu 16 Apr

This post is a follow on to a conversation started in 797. It has a few parts:

  1. Moving the airVolumeAdjustability to be a property on a {fan motor equip}
  2. Adding stepped as a choice of the above
  3. Adding the concept of Fan Placement as a property of an airHandlingEquip and/or airTerminalUnit. Choices for this are proposed as:
    • blowThrough - airHandlingEquip
    • drawThrough - airHandlingEquip
    • parallel - airTerminalUnit
    • series - airTerminalUnit

Adjustability and Stepped

For stepped, I believe we should also have a required accompanying tag, something like numSteps:N where N is an integer value, so as to know the exact number of fan steps (although typically 2). This would help with templating out expected points.

I didn't find a great definition for stepped, but ASHRAE 90.1-2016 utilizes the concept in Section and in Table 11.5.2-1. So how about this as a first pass: "A stepped motor utilizes discrete control speeds, represented as integer values beginning at 1, 2, etc. This is in contrast to near-continuous speeds of motor control, as is the case of an electronically commutated motor or variable speed drive."

  • Do we want to represent a two-stage fan differently than two fans which are staged? If so, how to tackle? Thoughts appreciated.

References: Trane

Fan Placement

Regarding blowThrough and drawThrough:

  • I propose this on the airHandlingEquip as it is typically used to describe the configuration of fans in relation to other things, i.e. heating / cooling elements or filters
  • Generally thought of as upstream (blowThrough) vs. downstream (drawThrough) of filters or heating / cooling elements. Can somebody with mechanical engineering expertise chime in thoughts.

Reference: Engineering360

Regarding definitions for series and parallel:

  • These can either be used on terminal units or for AHUs.
  • When applied to terminal units, it is describing the fan in relation to the upstream air being delivered by an AHU and also denotes something about the expected operation of the terminal unit.
  • Should this also be applicable to AHUs?, Based on the ACHR article, fans in series can happen? Do fans in parallel also happen?

References: ACHR, Trane

Additional Questions

  • In an AHU application, how should we describe:
    • Multiple fans in series?
    • Multiple fans in parallel (what is generally referred to as a fan wall)?

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