[bldg-sim] Package VAV w/reheat Versus CHW VAV w/reheat

Mark Nieman MARKN at McKinstry.com
Tue Jan 30 07:54:20 PST 2007


John, you might run hourly reports on the compressor power inputs to see
if their unloading curves are reasonable.

Here's a step through for those not familiar with the hourly reports:
1. Under the "Mode" menu, switch to "Detailed Data Edit".
2. Select the "Project & Site" button.
3. Right-click on the Project name and select, "Create Hourly Report
Block..."
4. Name your block and "Create from scratch".
5. Under Variable Type, select one of your chillers (something like
Chiller1a if using the default name).
6. Under the Variable List, pick your variables, like "Assigned load
(already selected", "Operating capacity at current conditions" and
"Electrical power consumed".
7. Then, under the Hourly Results Selection dialog, pick "New Report" at
the bottom of the dialog.
8. Name your report, create from scratch.
9. For Report Schedule, select "Hourly Report Schedule". For First
Report Block, select your newly created Report Block.
10. Create any other required Report Blocks and then highlight your new
Report and select all the applicable Report Blocks.
11. Select Done and run your model.
12. With the current version of eQUEST on the doe2.com website, you can
now return to the Input Building Description and select "File" on the
menu and "Export Hourly Results...". Select the appropriate run and
click Export. It will create a .csv file and asks you to select the
report and select Open.
13. You'll likely see the default reports in the first 30 columns, but
your new custom reports will be to the right of that default output
data.
14. You can then do a little post production work on the numbers to see
if the part loading is reasonable. I did a simple test building with
chilled water and got between 0.3 kW/ton and 3.4 kW/ton for the chiller
operation. You can then compare this kind of info with your chiller
manufacturer data to see if it makes sense. Often, water cooled chillers
can only unload to 30% (lower with VFD's), depending on the type. Also,
don't forget that there is also cooling tower energy in addition to the
pumps. You may want to create hourly reports for those too. You might
find some surprises (depending on your inputs, of course) with the way
the CT and pumps are operating. Reports can also be made for the CHW and
CW temperatures to verify reset.


Mark Nieman, PE, CEM
Sr. Energy Engineer
McKinstry Essention
Direct: (206) 832-8152
Cell: (206) 510-4760
FAX: (206) 832-8552
http://www.mckinstry.com
"For The Life Of Your Building"

-----Original Message-----
From: bldg-sim at gard.com [mailto:bldg-sim at gard.com] On Behalf Of Aulbach,
John
Sent: Monday, January 29, 2007 1:37 PM
To: bldg-sim at gard.com
Subject: [bldg-sim] Package VAV w/reheat Versus CHW VAV w/reheat

 
Hi all:

I swear this continued comparison will send me to an early grave.

ASHRAE 90.1 requires a building less than 5 stories and between 75K -
150K floor area to have a package VAV/reheat as its system. There are
those designers that like the CHW VAV system better. There is a penalty
of having a running CHW pump in that case.

However, I just did an eQuest comparison between the two systems, all
things equal (I hope). The CHW system space cooling used 60% MORE energy
than the package system. In the dead of summer, the CHW beats the
package. But in the winter, there seems to be a false load the chiller
is seeing, as the package cooling is almost nil, but the CHW system is
still has 2/3 of the summer usage.

I THINK I have CHW reset correctly programmed for the CHW system.

ANY IDEAS ???

John R. Aulbach, PE, CEM
Project Manager
Nexant, Inc.
100 North Barranca, Suite 820
West Covina, CA 91791 USA
Phone: 626-430-9054
Fax: 626-430-9060
email: jaulbach at nexant.com
 

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