[Equest-users] VFD Pumping

[Aaron Powers]

Michael,

One other item to consider once you solve your flow capacity issues is the
system head aspect.  eQuest doesn't apply the head input at the pump to the
system, but rather the system head at design conditions is set to the sum
of the  largest chiller evaporator head, pipe head, and the largest coil
head.  The defaults (at design conditions) for a centrifugal chiller and a
cooling coil are 20 ft. and 15 ft. respectively, which are more or less
universally good assumptions if you don't have any other data.  However,
the piping head can vary greatly project to project, and most people don't
bother to change the default of 21.6 ft.  So, in your case, the total head
at a design flow of 4650 gpm is 20 + 15 + 21.6 = 56.6 ft.  Since your pumps
are rated for 200 ft head, I would guess that 56 ft. is way too low.  A
good practice is to enter a User Expression for the loop Pipe Head field
like the following:

0.9*200 - 20 - 15

Where the 200 is the head you entered for the pump, 20 is the head loss
across the chiller, and 15 is the head loss across one coil.  This will set
the total system head to 90% of the rated pump head at design conditions
(accounts for the safety factor that engineers apply to pump selections).
If you keep the piping head as default, your savings will be greatly
exaggerated once you fix your flow capacity issues.  You can check the
design values for loop flow and head in the PV-A report.

Aaron

---------- Forwarded message ----------
From: Julien Marrec <julien.marrec at gmail.com>
To: Joe Fleming <joe at thespinnakergroupinc.com>
Cc: "equest-users at lists.onebuilding.org" <equest-users at lists.onebuilding.org
>
Date: Fri, 19 Jun 2015 10:22:28 +0200
Subject: Re: [Equest-users] VFD Pumping
All,

I looked briefly at Mike's input file.

*Paul,*

It's two-way, so that's ok. For those who may be wondering why you need
two-way valves, that is in order to have a pressure change (as they close)
going back to the VFD for modulation. That's true in real life too.

*Joe,*

Bingo on your 1) point. (see extract of warnings below).

*Mike,*

I suggest you also investigate your tons of warning about insufficient
heating capability, because you do have 1851 hours below heating throttling
range...

-------------------------------------------------------------------------------------------


Here are an extract of the warnings

 **WARNING**********************************************************************
             Pump: Chlr1 (ElCentHerm) Pump          has a total
user-specified flow
             of      1300. gpm, but the loop flow is      2325. gpm.

 **WARNING**********************************************************************
             Pump: Chlr2 (ElCentHerm) Pump          has a total
user-specified flow
             of      1300. gpm, but the loop flow is      2325. gpm.

 **WARNING**********************************************************************
             Pump: CW Loop Pump                     has a total
user-specified flow
             of      1500. gpm, but the loop flow is      5649. gpm.

 **WARNING**********************************************************************
             Pump: CW Loop Pump                     cannot match the system
             flow at the minimum required head.
             Required system flow = 2824.3 gpm at head =  47.2
             Pump balance point = 2665.2 gpm at head of  43.5
             If the pump was sized by default, most likely this
             is caused by a primary equipment unit operating at
             greater than its design flow, and causing a pressure
             drop greater than design.  Try increasing the pump
             head or head ratio to compensate.
             First occurrence is on  1/ 1, hour  9

 **WARNING**********************************************************************
             Pump: Chlr1 (ElCentHerm) Pump          cannot match the system
             flow at the minimum required head.
             Required system flow = 2325.4 gpm at head =  42.6
             Pump balance point = 2314.3 gpm at head of  42.3
             If the pump was sized by default, most likely this
             is caused by a primary equipment unit operating at
             greater than its design flow, and causing a pressure
             drop greater than design.  Try increasing the pump
             head or head ratio to compensate.
             First occurrence is on  4/27, hour 15

 **WARNING**********************************************************************
             Pump: Chlr2 (ElCentHerm) Pump          cannot match the system
             flow at the minimum required head.
             Required system flow = 2325.4 gpm at head =  48.6
             Pump balance point = 2289.5 gpm at head of  47.3
             If the pump was sized by default, most likely this
             is caused by a primary equipment unit operating at
             greater than its design flow, and causing a pressure
             drop greater than design.  Try increasing the pump
             head or head ratio to compensate.
             First occurrence is on  4/29, hour 10

--
Julien Marrec, EBCP, BPI MFBA
Energy&Sustainability Engineer
T: +33 6 95 14 42 13

LinkedIn (en) : www.linkedin.com/in/julienmarrec
LinkedIn (fr) : www.linkedin.com/in/julienmarrec/fr
<http://www.linkedin.com/in/julienmarrec>

2015-06-18 21:28 GMT+02:00 Joe Fleming <joe at thespinnakergroupinc.com>:

> Hi Michael,
>
>
>
> To add to what Paul mentioned about 2-way valves;
>
>
>
> What are your building loads looking like in the eQuest output reports?
> There are 2 potential scenarios that may lead to limited savings from a
> properly modeled VFD installation;
>
> 1.       If the pump is under sized for the loads input
>
> 2.       If the loads are constant and mostly internal
>
>
>
> Kind Regards
>
>
>
>
>
> *Joe Fleming *|*  PE, *LEED AP BD+C, BEMP
>
> *Commissioning Agent & Energy Consultant *| *The Spinnaker Group*
>
> *joe at thespinnakergroupinc.com <joe at thespinnakergroupinc.com>*
>
> *Cell*  561-602-3132  |  *Office*  754-800-3100
>
>
>
> *From:* Equest-users [mailto:equest-users-bounces at lists.onebuilding.org] *On
> Behalf Of *Mike Schaefer
> *Sent:* Thursday, June 18, 2015 2:49 PM
> *To:* equest-users at lists.onebuilding.org
> *Subject:* [Equest-users] VFD Pumping
>
>
>
> I’ve performing an energy model to compare VFD Chiller pumping and
> Constant Volume Chiller pumping for a multi-story office building using
> eQUEST v 3.65. Although I expect to save pump energy utilizing VFD pumping
> I’m not seeing a savings and I believe this is due to my “Pump Properties
> Inputs”.
>
>
>
> For both the VFD and constant volume pump scenarios I’ve input the
> scheduled pump flow (1,300 gpm) and head (200 ft) and the other pump inputs
> are default values. The energy difference between the two pumping scenarios
> is negligible, however, if I set the pump gpm to a default, which inputs a
> 1.00 Flow Ratio, the energy savings is significant in the VFD pumping model.
>
>
>
> Am I over defining the pumps by inputting the scheduled pump gpm? Should
> the pump gpm always be set to default?
>
>
>
> Thanks,
>
>
>
> *Michael*
>
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