[Bldg-sim] Cooling Tower Approach

Mon Jun 19 13:27:27 PDT 2017

It’s a little unclear from this thread if the original post is asking about decreasing the tower DESIGN approach (i.e. evaluating a different tower design), or decreasing the approach of some given tower DURING OPERATION via the control settings of the condenser water temperature.

In eQUEST, and I think in the tower design world, the “approach” is a design parameter, not just a control parameter.

The post says “the tower” has a 44 kW fan in both cases. But typically for the same heat rejection, to achieve a closer approach requires either the same physical tower with a “bigger fan” (more air through the tower, often just by higher rpm) and higher fan rated fan kW, or a bigger physical tower with that higher airflow, but lower velocities and dP, to achieve the same RATED fan kW.

One can separately set the condenser water loop temperature setpoint (in eQ, that’s the tower leaving temperature, aka chiller entering condenser water temperature) or setpoint strategies so any given tower attempts to achieve less than the design approach during some or most hours. That will increase tower fan energy, but will decrease compressor energy in attached systems.

Fred
Fred Porter, BEMP, LEED© AP
Principal Engineer
Sustainability Services
NORESCO

From: Bldg-sim [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Peters, Judith M via Bldg-sim
Sent: Monday, June 19, 2017 10:26 AM
To: Danielle Bond; Dan Nall
Cc: bldg-sim at lists.onebuilding.org
Subject: [External] Re: [Bldg-sim] Cooling Tower Approach

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<mailto:judith.peters at daikinapplied.com> | www.DaikinApplied.com<https://urldefense.proofpoint.com/v2/url?u=http-3A__www.daikinapplied.com_&d=DwMGaQ&c=ilBQI1lupc9Y65XwNblLtw&r=3xdcdPfNRiIRbdcNOFLTvgBFEa2F6BAz_UMLqgqXn6k&m=wTrSz7jpELLIQueGCv4m5qWPPYVpheqlLap10Y7IxFI&s=RqZ_dsCG6N2XAQg73o0GaqqM1jQyKJ_Qv1Hddny9rz4&e=>

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<mailto: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<https://urldefense.proofpoint.com/v2/url?u=http-3A__spxcooling.com_pdf_TR-2D016.pdf&d=DwMGaQ&c=ilBQI1lupc9Y65XwNblLtw&r=3xdcdPfNRiIRbdcNOFLTvgBFEa2F6BAz_UMLqgqXn6k&m=wTrSz7jpELLIQueGCv4m5qWPPYVpheqlLap10Y7IxFI&s=EOHIMO4Z2p9zDaAx0ZYENGgubrMSmdHJWFO-YrhG5cA&e=>

Best,
Danielle

--
Danielle Bond, Ph.D.
Energy Engineer, eCap Network
http://www.ecapnet.com/<https://urldefense.proofpoint.com/v2/url?u=http-3A__www.ecapnet.com_&d=DwMGaQ&c=ilBQI1lupc9Y65XwNblLtw&r=3xdcdPfNRiIRbdcNOFLTvgBFEa2F6BAz_UMLqgqXn6k&m=wTrSz7jpELLIQueGCv4m5qWPPYVpheqlLap10Y7IxFI&s=syhTrCg01_YaMQf7Uo9XhfZ4YGadvTsY5FRO-tQK1oA&e=>

On Mon, Jun 19, 2017 at 11:50 AM, Dan Nall via Bldg-sim <bldg-sim at lists.onebuilding.org<mailto: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<mailto: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<tel:(763)%20553-5155>
judith.peters at daikinapplied.com<mailto:judith.peters at daikinapplied.com> | www.DaikinApplied.com<https://urldefense.proofpoint.com/v2/url?u=http-3A__www.daikinapplied.com_&d=DwMGaQ&c=ilBQI1lupc9Y65XwNblLtw&r=3xdcdPfNRiIRbdcNOFLTvgBFEa2F6BAz_UMLqgqXn6k&m=wTrSz7jpELLIQueGCv4m5qWPPYVpheqlLap10Y7IxFI&s=RqZ_dsCG6N2XAQg73o0GaqqM1jQyKJ_Qv1Hddny9rz4&e=>

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