Problem with Fan Power in the Baseline Model System 6

3 posts / 0 new
Last post

Dear Experts,

* *I am straggling to input Fan Power in the baseline model (System 6 -
Packaged VAV with PFP Boxes) and have the following issues:

1- In Table 1.4.6 - General HVAC, there is a note for this type of system
that requires

?All Baseline fans in parallel VAV fan-powered boxes sized for 50% of peak
primary airflow and modeled with 0.35 W/cfm fan power and a minimum flow
setpoint of 30% of peak (or minimum ventilation rate) per G3.1.3.14?.

Supply and return air of the system are equal, 49,202 cfm for each. Based
on this cfm, supply fan power and return fan power is 17.22 KW (49,202 *
0.35). This number is different with the figure from ASHRAE 90.1-2007
Baseline Fan Power Calculator (The spreadsheet from 7group). In addition,
when I input the supply and return cfm and 17.22 KW for both fans in ?Table
1.4.7A - Baseline Air-Side HVAC System Schedule?, it indicates ?Allowed Fan
Power? to be 55.4 KW and it will be red out with any other numbers input as
system fan power.

2- In eQUEST?s ?Fan Power and Control? screen, the input boxes for supply
and return design KW/cfm are grayed out (n/) and I cannot input any data
for the fan powers.

As always, I would truly appreciate your comments,

Morteza

Morteza Kasmai's picture
Offline
Joined: 2011-09-30
Reputation: 0

Hi Morteza!

1. Recognize there are separate rules/requirements to determine power for system supply/return fans (Pfan), and for terminal unit fans. The rules you cited regarding minimum flow fraction and 0.35 W/CFM are specific to the fans in the terminal units. Power for the associated supply fan delivering pre-reheat air to those terminal units is determined through the "Pfan" procedures. I advise reviewing the associated passages in 90.1 appendix G to ensure you understand what others' spreadsheets are replicating before proceeding. This will help you to utilize such tools correctly and effectively.

2. There are two means of specifying fan power in eQuest - you may use one or the other. Coming out of the wizards, by default eQuest will start with the ESP/fan+motor efficiency inputs. To instead utilize the kW/CFM inputs, navigate to the system fan tab, then right click the inputs for ESP/efficiency on the same screen and press 'r' or click "restore default" in the context menu. This will switch the input method back to kW/CFM and an option to manually define the temperature rise across the fan.

Regards,

~Nick
[cid:489575314 at 22072009-0ABB]

NICK CATON, P.E.

Nick-Caton's picture
Offline
Joined: 2011-09-30
Reputation: 605

Nick,

Thank you so much. You solved my problem. I am always learning from your
comments.

Regards,

Morteza

Morteza Kasmai's picture
Offline
Joined: 2011-09-30
Reputation: 0