[Trace-users] Reheat Loads

Eurek, John S NWO via Trace-users trace-users at lists.onebuilding.org
Tue May 17 12:19:29 PDT 2016

I'm addressing this to the Trane engineer who helped me select the equipment and the energy modeling list serve:

I am adding 2 air handling unit to serve 1/2 of the basement for a 3 story building.  All the other systems won't be touched. The building has an existing boiler and chiller which will not be changed.

My concern is that if the unit cools the air down to 55F and then the VAV boxes (re)heat the air back up, which is how the these systems commonly operate, this reheating load will add to the cooling coil which will add to the load of the chiller.  My concern increases since it is a basement level that will likely have a low cooling load, so the reheat coils will have to heat up the 55F to 70F to provide neutral air.  Then the return air will have to be cooled back down....  The heating and cooling coils will be fighting each other, but it will give the benefit of controlling humidity.

Question 1 - How can I tell how much extra heating and cooling is required due to the fact the air is cooled to 55F then reheated?  (I know this dependent on the minimum settings and if the VAV boxes are allowed to throttle back to 0% open, this reheat value would be zero.)

....  I think I may have answered my question while trying to figure out how to formulate the question, but I think I'll sent it out anyways.

Question 2 - Is there a place on the System Checksum or some other report that would show the about of reheat if reheat is happening?

Thank you,

John Eurek PE, LEED AP
Mechanical Engineer,
US Army Corps of Engineers
Omaha District CENWO-ED-DA
1616 Capitol Avenue
Omaha, NE 68102
Phone: (402) 995-2134
email: john.s.eurek at usace.army.mil

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