[Bldg-sim] Cooling Tower Approach

[Julien MARREC via Bldg-sim]

Judy,

You didn't specify which software you're using, but in general (and for e+ Specifically) you should pay attention to the difference between design input values and the operation conditions.
In e+ that's the different between what you input in the Cooling tower and the plantloop and sizing objects, versus the setpointManager (setpointmanager:followoutdoorairtemperature set to wetbulb control in particular) you use on the plant outlet to determine the operating conditions at each hour.

(Excuse any typos or misnamed objects above, going off memory here).

In reality and as was said by others, if you design a cooling tower for a smaller approach but with the same fan power you end up with an oversized hear exchanger thus allowing lower fan energy across the full year.

Best,
Julien

Envoyé de mon iPhone

> Le 19 juin 2017 à 18:26, "Peters, Judith M via Bldg-sim" <bldg-sim at lists.onebuilding.org> a écrit :
> 
> Dan and Danielle,
>  
> Thank you for your excellent comments.  The results make more sense to me now.
>  
> Thanks again,
> Judy
>  
>  
> Judy Peters, PE LEED-AP BEMP
> Energy Modeling Engineer
> Daikin Applied
> 763.553.5155
> judith.peters at daikinapplied.com | www.DaikinApplied.com
>  
>  
> From: Danielle Bond [mailto:danielle at ecapnet.com] 
> Sent: Monday, June 19, 2017 11:07 AM
> To: Dan Nall
> Cc: Peters, Judith M; bldg-sim at lists.onebuilding.org
> Subject: Re: [Bldg-sim] Cooling Tower Approach
>  
> In general, a smaller approach means the cooling tower is more efficiently rejecting heat, i.e. better performance. This overview is pretty good: http://spxcooling.com/pdf/TR-016.pdf
>  
> Best,
> Danielle
>  
> -- 
> Danielle Bond, Ph.D.
> Energy Engineer, eCap Network
> http://www.ecapnet.com/
>  
>  
> On Mon, Jun 19, 2017 at 11:50 AM, Dan Nall via Bldg-sim <bldg-sim at lists.onebuilding.org> wrote:
> If you input a tower with a lower approach but with the same fan power, you would wind up with less annual fan energy consumption, because your fan with the lower approach temperature would hit the minimum condenser water temperature at a higher wet-bulb temperature, allowing the fan to back off more hours of the year. 
> 
> -----Original Message----- 
> From: "Peters, Judith M via Bldg-sim" 
> Sent: Jun 19, 2017 11:13 AM 
> To: "bldg-sim at lists.onebuilding.org" 
> Subject: [Bldg-sim] Cooling Tower Approach
> 
> I am looking for tips on how to properly compare tower approach temps.  Currently, I am comparing a 7 F approach with a 5 F approach.  The tower has 4 cells with 44 kW fan energy for each cell and a 10 F range. 
>  
> Regardless of control parameters, the program shows less tower energy for a smaller approach and I was expecting the opposite.
>  
> Can anyone shed some light on this issue?
>  
> Thank you!
>  
>  
>  
> Judy Peters, PE LEED-AP BEMP
> Energy Modeling Engineer
> Daikin Applied
> 763.553.5155
> judith.peters at daikinapplied.com | www.DaikinApplied.com
>  
>  
> 
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