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Appendix G Pumps Input Power

asked 2015-01-25 19:36:59 -0500

dannyllim gravatar image

updated 2015-07-10 21:33:26 -0500

I am modeling a high rise 48 story building consisting of retail spaces for the first 6 levels and office spaces on top. The retail spaces are cooled by 3 chillers and 3 cooling towers located on the 6th level.

The office spaces are cooled separately by 5 water cooled chillers with primary-secondary distribution configuration. These chillers are located on the 7th level which houses other mechanical equipment while the 5 cooling towers are located on the roof deck of 48th floor. Chilled water distribution is constant primary-variable secondary configuration. The office floor levels (4m floor to floor height) are divided into low zone, mid zone, and high zone with each zone served by secondary chilled water pumps sized accordingly to meet the head required. The project is registered for LEED certification.

My question is regarding the Appendix G pump input power of 22 W/gpm and 19 W/gpm for the chilled water pumps and condenser water pumps, respectively. The designed capacities of the pumps for the office cooling system are double these limits and therefore negatively affecting the energy performance of the project. Has anyone encountered this situation? Is there any allowed adjustment to the Appendix G limits to account for the high head of the cooling system? Any suggestion is highly appreciated. Thank you in advance.

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answered 2015-02-05 13:57:00 -0500

jfirrantello gravatar image

updated 2015-02-05 14:49:34 -0500

It's been a few years since I last worked on an Appendix G calculation for LEED, but I don't recall any sort of credit. After skimming through the latest edition of 90.1, it still doesn't appear that there is one. I've got a few other thoughts, forgive me if you're familiar with the concepts already or if I'm talking too simply.

  • Make sure that you're using what you think your system's actual maximum operating condition will be, which may differ from what's scheduled. That is, the older PMs where I worked would throw a lot of slop (a technical term, obviously) on pump head sizing calculations to keep from getting burned down the road. However, in my model's design head I'd consider the pump head calculations without the liability-insurance-safety-factor on it. So, think about what you think the head will be operationally. (Analogous to the difference between load and energy calculations, I'd say) edit: to clarify, talking about a variable speed pump in this situation
  • I'd take full credit for what I knew about "my" system versus the App G system to squeeze what I could out of it...
  • The situations where the App G pump would ride the pump curve rather than have variable speed
  • The VFD curve packaged in the energy simulation software versus the actual curves from the specified manufacturer
  • Make sure the pump minimum turndown on your system isn't too high, check your chiller/tower GPMs vs time to see if they make sense, etc.

I'll admit that a good portion of the work I did was big ground-coupled heat pump systems, so the pumping energy tended to kill us regardless.

Not sure if any of this helps, but good luck!

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Asked: 2015-01-25 19:36:59 -0500

Seen: 644 times

Last updated: Feb 05 '15