[Bldg-sim] Fan Power calculations in ASHRAE User Manual

Maria Karpman maria.karpman at karpmanconsulting.net
Mon Mar 14 07:57:24 PDT 2011


I don't see contradictions in fan-related baseline system requirements in App G. Procedure for determining baseline system parameters involves two steps:

Step 1: Determine COOLING-EIR of baseline system following the equation in the attached document, which is based on physical meaning and definition of rated EER. EER for the calculation must be taken from Table 6.8.1A based on the size and type of baseline system. Result of the calculation is entered as cooling EIR on Unitary Power tab in detailed mode. This step is independent of baseline fan power requirements in Appendix G, and captures inherent efficiency of the system at ARI conditions. 
Step 2: Determine fan power of the baseline system based on G3.1.2.9. Examples G-J and G-K in 90.1 User Manual is a good reference for that. Result is then entered on Fan Power and Control tab in Detailed Mode as Design kW/cfm.   

For the proposed system, equipment efficiency and fan power may be calculated based on Example G-G in the User Manual. 

Does anyone have different perspective on that?  



-----Original Message-----
From: bldg-sim-bounces at lists.onebuilding.org [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Nick Caton
Sent: Sunday, March 13, 2011 11:25 AM
To: Ashraf Khan; bldg-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] Fan Power calculations in ASHRAE User Manual

Hi Ashraf,

I'm not sure about 2004, but the 2007 users manual includes an example showing how to "back out" fan energy from a fan-inclusive efficiency rating.

I will be sharing a guide of sorts in the near future touching on this topic, with eQuest/DOE2 procedures defined explicitly.  Keep your eyes open for that! 

For now, let me offer an extra caution to your assertion regarding "fan power should be broken out at ARI conditions:" in the case of proposed systems, I'd agree that fan power entered may be entered as calculated (or ideally, documented) at ARI testing conditions.  In the case of baseline systems however, 90.1 is very explicit in setting a procedure independent of the prescribed efficiency to determine fan power for the system.  I'm pretty sure that calculated quantity (Pfan) takes precedence.

~ Nick

Ashraf Khan <ashraf at mecsd.com> wrote:

Recently Fan power calculations topic have discussed. I have a question
regarding the breaking power in to components.


According to Section G3.1.2.1 requires that “where efficiency ratings, such
as EER and COP, include fan energy, the descriptor shall be broken down into
its components so that supply fan energy can be modeled separately.”

Since the efficiency ratings are calculated at ARI‐rated conditions, the
fans should also be broken out at ARI‐rated conditions.


Kindly guide me where can I find calculations in ASHRAE 90.1-2004 User’s
Manual showing that the calculation has been performed at ARI rated
conditions or any other reference.




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