RE: [EnergyPlus_Support] Heat recovery warning

If you are autosizing the flow rate, then compare the autosize result (in the eio file) to the flows you are getting on those nodes.

There is a trick if you are brave; if your curve is “flat” then the warnings can be ignored. This is less necessary now that the field is autosizable but we used to do it all the time. The model can vary effectiveness linearly as flows depart from the nominal. But if you enter in the same effectiveness at all the flow rates, then the curve is “flat” and the linear changes won’t go out of range and cause numerical problems. (e.g. negative effectiveness at low flows) Use decent averaged values for effectiveness rather than too high of a number. The warnings still get produced but you can ignore them.

From: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] On Behalf Of johnnyklemke
Sent: Friday, September 25, 2009 9:17 AM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: [EnergyPlus_Support] Heat recovery warning

Hi all,

I've been running a model with ASHRAE system 8 (VAV with heat recovery) and could not solve a warning with the heat recovery component:

HeatExchanger:AirToAir:SensibleAndLatent "AHU HEAT RECOVERY"
** ~~~ ** Average air volume flow rate is <50% or >130% of the nominal HX supply air volume flow rate.
** ~~~ ** Air volume flow rate ratio = 7.454E-002. Occurrence info=SAO_PAULO/CONGONHAS - BRA TMY3-837800 WMO#=837800, 01/02 06:00 - 06:10

===== Recurring Error Summary =====
************* The following recurring error messages occurred.
*************
************* ** Warning ** HeatExchanger:AirToAir:SensibleAndLatent "AHU HEAT RECOVERY": Average air volume flow rate is <50% or >130% warning continues. Air flow rate ratio statistics follow.
************* ** ~~~ ** This error occurred 999249 times.
************* ** ~~~ ** Max=0.499985 Min=7.383128E-002

Can anyone help me on this? How can I solve this issue? I don't know how to measure this 50/130% of average air volume flow rate.

Thanks,
John

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