Re: [EnergyPlus_Support] DOE Reference Building, Elementary School, Chicago problem with NoEconomizer uni

Homero

On Wed, May 16, 2012 at 1:01 PM, Jim Dirkes <jim@xxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:

·         Minimum outdoor air flow will not reduce to prevent freezing. You must define the minimum flow using the Controller: OutdoorAir or other outdoor air object (e.g., DesignSpecification:OutdoorAir)

·         If there is no economizer, the only means of cooling will be the DX coil.

·         If you have allowed the coil to be available in the cold weather and there is a cooling demand (in a core area, for example), the DX coil will ?operate?

·         E+ provides a warning to alert you, not to say that it is impossible or wrong, since certain DX systems are designed to operate during very cold weather.

·         In your case, it looks unusual for the coil outlet temperature to be -4C. Perhaps there is a fairly large minimum outdoor air flow which causes the mixed air / coil entering temperature to be very low?

·         If operation of the DX coil is supposed to occur, you may ignore those warnings, but may want to adjust the part load curves to reflect performance during cold weather.

The Building Performance Team
James V. Dirkes II, P.E., BEMP , LEED AP
1631 Acacia Drive NW
Grand Rapids, MI 49504
616 450 8653

From: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] On Behalf Of hnoboam
Sent: Wednesday, May 16, 2012 12:17 PM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: [EnergyPlus_Support] DOE Reference Building, Elementary School, Chicago problem with NoEconomizer uni

I am running the Elementary School, Chicago model from the DOE Reference buildings (after converting to E+7). When I run it, E+ reports 12K warnings, mostly repeats of these two:
** Warning ** Coil:Cooling:DX:SingleSpeed "PSZ-AC_2:5_COOLC DXCOIL" - Air-cooled condenser inlet dry-bulb temperature below 0 C. Outdoor dry-bulb temperature = -10.00
** ~~~ ** ... Occurrence info = Chicago Ohare Intl Ap IL USA TMY3 WMO#=725300, 01/01 07:52 - 07:54

** Warning ** Coil:Cooling:DX:SingleSpeed "PSZ-AC_2:5_COOLC DXCOIL" - Full load outlet air dry-bulb temperature < 2C. This indicates the possibility of coil frost/freeze. Outlet temperature = -3.99 C.
** ~~~ ** ...Occurrence info = Chicago Ohare Intl Ap IL USA TMY3 WMO#=725300, 01/01 07:52 - 07:54

The economizer type is "NoEconomizer".

Why the Controller does not limit the OA flow to prevent the coil from freezing?

What is the model missing?

I posted the file, in the file section of our group as: ES_Chicago.idf .
Thanks for any help

Homero Noboa, Ph. D.