VFD Pumping

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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

Mike Schaefer's picture
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Joined: 2011-09-30
Reputation: 0

Michael. can you send your .pd2 and .inp for us to check youtvinputd, please?

John R. Aulbach ,PE

Sent from Yahoo Mail on Android

From:"Mike Schaefer"
Date:Thu, Jun 18, 2015 at 11:49 AM
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
?

John Aulbach's picture
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Joined: 2011-09-30
Reputation: 1

Confirm whether you have two-way or three-way CHW valves.

Paul Riemer, PE, LEED AP BD+C
DUNHAM

Paul Riemer's picture
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Joined: 2011-09-30
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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

Cell 561-602-3132 | Office 754-800-3100

Joe Fleming's picture
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Joined: 2011-09-30
Reputation: 0

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

2015-06-18 21:28 GMT+02:00 Joe Fleming :

jmarrec's picture
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Joined: 2013-01-09
Reputation: 0

Hi Michael,

Kindly find my responses in blue.

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,

[SK] As i think that over defining the inputs may be not perfect, as there
is default flow based head and power defining curve which are also in
eQUEST. So may be over defining the inputs may over-ride or lessen the
effect of these curves.

.............................................................................................................
If there is no input in the pumps then the default value of the pumps will
be as per the design flow of the loop.

These design loop flow may be calculated as per loop design delta T, which
is normally 10-12 degrees Fahrenheit.
So as per me the default values may also be right if the specification
value are not perfectly calculated.
.............................................................................................................
Sometime in past i have felt that by inputting all the technical
specification values, may cause simulation error, if they mismatch with the
default pump properties.

So the eQUEST pump values calculation stream is like this, Delta T in
circulation loop< Loop design flow head and power of the pump.

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?

[SK] The default pump curves and input values may be conflicting so i get
dependent on the default properties of pumps as per my experience.
eQUEST can guide you by default values.
Hope this is helpful. Other related posts are also helpful.

Thanks,

*Michael*

Thanks,
Sharad.Kumar

Sharad Kumar2's picture
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Joined: 2015-05-21
Reputation: 0

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
To: Joe Fleming
Cc: "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

2015-06-18 21:28 GMT+02:00 Joe Fleming :

Aaron Powers2's picture
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Joined: 2011-09-30
Reputation: 0