[Equest-users] Ashrae 90.1 query: Design air flow rates - return fans

[Nick Caton]

Hi Katherine,

 

Your quote looks incomplete - be sure you're reading the whole section
to avoid unnecessary confusion ;)

1)      Baseline fans are auto-sized.  Return fans (when required) must
be specified with a  CFM capacity equal to either 0.90 x (the auto-sized
CFM of the SA fan), or (the auto-sized CFM of the SA fan) minus the OA
for the same system, whichever is greater.  This is relatively simple if
you let excel do the legwork.

2)      No.  Whether you model return fans in addition to your SA fans
in your baseline model systems is stipulated, not a choice.  Re-read
that section.

3)      No and Yes.  "90% of SA" = 0.90xSA = SA - (0.10xSA)

4)      Baseline RA fan power is calculated following the same equations
as SA fans.  See following section G3.1.2.9.

 

~Nick

 

 

 

NICK CATON, E.I.T.

PROJECT ENGINEER

25501 west valley parkway

olathe ks 66061

direct 913 344.0036

fax 913 345.0617

Check out our new web-site @ www.smithboucher.com 

 

From: equest-users-bounces at lists.onebuilding.org
[mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of
Katherine Roberts
Sent: Tuesday, November 16, 2010 10:04 AM
To: equest-users at lists.onebuilding.org
Subject: Ashrae 90.1 query: Design air flow rates - return fans

 

Dear all,

 

We are submitting a LEED project and have a query regarding ASHRAE 90.1
(2004) section G.3.1.2.8 - Design Air flow rates. It states that the
baseline building should be modelled with fans serving the 'same
functions and sized for the baseline system supply fan air quantity less
the minimum outdoor air, or 90% of the supply fan air quantity,
whichever is larger.'

 

We figure there are 3 different ways to interpret this sentence:

1)      Model the baseline building with supply fans as normal, plus
return fans with either 90% supply or supply minus outside air.

2)      Only model supply fans but change the supply flow rate to 90% or
supply minus outside air.

3)      Does 90% mean supply minus 90% or supply minus 10%? 

 

If someone could provide an example that would be very useful.

 

How do we incorporate the return fan power when reporting total fan
power allowances, i.e. do we subtract return fans from the total?

 

Thanks in advance

 

Kat

 

 

Katherine Roberts

Engineer  |  Enviromental Physics

 

Arup

13 Fitzroy Street  London W1T 4BQ  United Kingdom

t +44 20 7636 1531  d +44 20 7755 5454  

www.arup.com

 

 

 

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