[Bldg-sim] eQUEST - Fan Staging for High-Plume Dilution Fans

[Paul Erickson]

Greetings All,

I've run up against an issue for which I'd appreciate some advice.  I'm trying to model the staging of dilution fans which run at 100% even if the building exhaust flow is varying.  At times when the building exhaust flow is reduced sufficiently, we will turn one or more of the fans off.  This is essentially the same as stepped dimming for daylight applications.

I've attempted to create a part-load curve using data points, but the cubic formula that is generated does not even come close to reflecting the "curve" or steps that I actually need.  I've also played around a bit with writing a user expression, but to no avail.  I was attempting to "get" the hourly return fan CFM and use IF/THEN statements to establish a new kW/CFM.  But, I don't that the kW/CFM is used after design and for determining the starting point on the part-load curve.  It does seem like I can get the hourly value for return CFM.  

Has anyone had any success with staging constant speed fans?  If you have suggestions for creating a curve, or on how to use multiple linear curves (a expression for curve selection), I would be grateful.  Or, if you have ideas on syntax for writing the appropriate user expression, I'd be thankful as well.

Obliged,

Paul

Paul Erickson
Sustainable Systems Engineer
Affiliated Engineers, Inc.
www.aeieng.com 
608.236.1112



>>> Alex Lekov <ABLekov at lbl.gov> 1/8/2008 12:11 PM >>>
Andrew,

It is probably incorrect to baseline the instantaneous water heater 
using the current minimum efficiency standard for the residential size 
gas instantaneous water heaters (EF=0.62). According to GAMA's 
Consumer's Directory of Certified Efficiency Ratings for Heating and 
Water Heating Equipment's directory, very few gas instantaneous water 
heater models have EF below 0.80.

Alex Lekov, Ph.D., P.E.
office 925-486-6849


Andrew McNamara wrote:

> Hello all,
>
> I am modeling a building with eQUEST that has a tankless, a.k.a. 
> instantaneous, gas-fired hot water heater.  I am uncertain of how to 
> baseline the system according to ASHRAE 90.1-2004 Appendix G. The 
> standard states that for a 180,000 BTU/h system the EF (Energy Factor) 
> = 0.62-0.0019V.  So, I set V equal to zero for the 
> tankless/instantaneous gas water heater and get an EF =0.62. 
>
> The question I have for everyone is: How do I translate this baseline 
> EF to HIR (Heat-input-ratio) for eQUEST?  Is there an accepted method 
> for doing so?  I saw in a previous post from David Eldridge on 3/21/07 
> that calculating HIR = 1/EF leads to unreasonably high values for HIR 
> (In my example, 1/0.62 = 1.61), but I'm having trouble seeing how else 
> to come up with a baseline.
>
> Thanks in advance for your help.
>
> Best,
> Andy
>
> -- 
> Andrew McNamara, LEED AP
> tel: 212.803.5868
> fax: 866.379.8026
> cell: 917.974.4499
>
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