eQUEST - serios trouble with LEED review

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Hi Everyone,

I got a review comment that got me in big trouble and I can't find the
solution yet.

May be there is no solution for this in eQUEST....!

I rate this forum as the very best address for difficulties with eQUEST and
LEED EAc1 simulation.

So please give me some guidance and feel free to test the model attached.

Here are the two comments of the reviewer.

"It appears as if the pumps and circulation loops were not modeled correctly
for the Baseline Case. It appears based on the PS-C reports that there is
only one primary chilled water pump and one condenser water pump for the
Baseline Case. However, ASHRAE 90.1 Section G3.1.11 requires that each
chiller be modeled with separate condenser water and chilled water pumps
interlocked to operate with each associated chiller. Please model two
primary chilled water pumps and two primary condenser water pumps in
accordance with Section G3.1.11. Also update the chilled water valves to
two-way valves so that the secondary chilled water loop operates as a
variable flow loop with pumps riding the curve. Provide updated PS-C reports
confirming that the changes have been made."

"It is unclear why the pump flow for the secondary chilled water loop is so
much larger than that of the primary chilled water loop when the temperature
differential for both loops is expected to be the same. It also appears
based on the outputs in PS-C that the secondary chilled water loop is
operated at the same load for every hour that it is on even though it is a
variable speed pump. Please update the secondary chilled water loop flow to
be consistent with the primary chilled water loop flow, and confirm that the
secondary chilled water loop is operating as a variable flow loop."

I have to say:

I didn't see any equest-model modeled with separate condenser water and
chilled water pumps interlocked to operate with each associated chiller.

I manually resized the boilers and chillers with reference to SS-D report,
because auto sizing of eQUEST generated capacities that were double the size
of SS-D report. Resizing of the volume flow of secondary loop of chillers
according to primary loop of chillers generated warning messages but changed
nothing.

Heinrich

heinrich's picture
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With respect to your first point, you can have either a single loop
pump, a chiller pump or both. (this can be set up in the wizard or
detailed interface -- obviously you are well into the detailed interface
on this project.)

For each chiller in eQUEST, one of the tabs is "loop attachments" where
you can specify a chiller chilled water pump and a chiller condenser
water pump which will then operate with the chiller. Once you have
defined the pumps there, you can delete the main loop pump.

Note that I have found it helpful to save and then reopen and eQUEST
file once water side changes have been made -- especially when you are
reconfiguring loops and pumps. Sometimes saving and reopening clears
.bdl errors that would otherwise crop up.

With regard to your 2nd query, I have not had time to open your file.
You can change the loop "sizing option" from secondary (where it adds up
all connected coil capacities) to primary (where it looks at capacity of
primary equipment on the loop). Perhaps this may resolve the issue.
Apologies if I missed the point on this one.

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Heinrich,

The chiller pumps requirement your reviewer is referring to is in
Section G3.1.3.11 (not G3.1.11). The model you sent currently has one
primary CHW pump attached to each of your two chillers, a separate
primary CHW pump on the primary loop, one secondary CHW pump and one
condenser water pump. You labeled your primary chiller pumps "Secondary
Pump CHW 1" and "Secondary Pump CHW 2", which is probably why the
reviewer thinks you only have one primary pump (the one on the primary
CHW loop labeled "Primary CHW Pump"). I suggest making the following
changes:
* Delete the separate pump attached to the primary CHW loop
* Relabel the chiller pumps to indicate they are primary loop
pumps
* Add condenser water pumps for each chiller through the "Loop
Attachments" tab of the chillers; delete the other CW pump.
* Change both the primary loop and secondary loop sizing option to
"secondary" to allow eQUEST to size based on coil loads.
* Change the chiller capacity ratio for each chiller to 0.50. (Or
use 0.575 if you want to oversize by 15% per G3.1.2.2 - I don't know if
this is supposed to apply to chillers.) Each chiller will be sized for
half the total load.
* Allow the chiller capacity to default (remove the 0.9 MBtu/h).
* Make sure you include both/all pages of the PS-C report - your
reviewer will then see that the secondary CHW pump is variable flow.
(Your zones have two-way valves already.)
* The PV-A report will show that the total primary CHW pump flow
will nearly match the secondary CHW pump flow.

Regards,
Bill

William Bishop, PE, BEMP, LEED(r) AP

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Dear Bill,

I hope I understood your email properly.

Please find attached 3 printscreens of my Baseline input.

* For the "Chiller Loop Attachments.jpg", is the "Flow Ctrl"
correct? i.e., Constant flor for the Chiller Water Pump and Variable
Flow for the Condenser Water Pump

* For the "Water Side.jpg", is the number of pumps correct on the
left tab? i.e., 2 for each chiller and none under the Chilled Water Loop

* I assume that I do not have to do the same for the Hot Water
Loop, right? Should I create 1 pump under each boiler?

* For the "Chilled Water Loop.jpg", is the Loop Subtype (Primary)
and the Sizing Option (Secondary) the correct inputs?

I set my CHW Valves to 2-way valves as per your email..

Many thanks!

Omar Katanani

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Bill,

thank you for your advice.
I followed your instructions to change the model.
So I resolved the indicated reviewer comments.
Now there is no difference between secondary and primary chilled water loop.

But now I have the dilemma that chillers and boilers of Baseline are heavily
oversized and are not sized to 115% and 125% respectively according to
demands of ASHRAE-90.1 App. G.
For checkup you can look at the Screenshots of the PS-C report, PV-A report
and the SS-D report that I have attached.
The part load of the chillers is about 40%-50% meaning a size 200%-250% (see
pump secondary CHW in PS-C report).
The part load of the boilers is about 50%-60% meaning a size of 167%-200%
(see pump HW in PS-C report).

So I still have a serious problem. Any help would heavily appreciated.
Can we solve this problem in eQUEST?

Heinrich

_____

Von: Bishop, Bill [mailto:wbishop at pathfinder-ea.com]
Gesendet: Montag, 24. Januar 2011 19:49
An: Heinrich.ib-bauklima.de; equest-users at lists.onebuilding.org
Betreff: RE: [Equest-users] eQUEST - serios trouble with LEED review

Heinrich,

The chiller pumps requirement your reviewer is referring to is in Section
G3.1.3.11 (not G3.1.11). The model you sent currently has one primary CHW
pump attached to each of your two chillers, a separate primary CHW pump on
the primary loop, one secondary CHW pump and one condenser water pump. You
labeled your primary chiller pumps "Secondary Pump CHW 1" and "Secondary
Pump CHW 2", which is probably why the reviewer thinks you only have one
primary pump (the one on the primary CHW loop labeled "Primary CHW Pump"). I
suggest making the following changes:
* Delete the separate pump attached to the primary CHW loop

* Relabel the chiller pumps to indicate they are primary loop pumps

* Add condenser water pumps for each chiller through the "Loop
Attachments" tab of the chillers; delete the other CW pump.

* Change both the primary loop and secondary loop sizing option to
"secondary" to allow eQUEST to size based on coil loads.

* Change the chiller capacity ratio for each chiller to 0.50. (Or use
0.575 if you want to oversize by 15% per G3.1.2.2 - I don't know if this is
supposed to apply to chillers.) Each chiller will be sized for half the
total load.

* Allow the chiller capacity to default (remove the 0.9 MBtu/h).

* Make sure you include both/all pages of the PS-C report - your
reviewer will then see that the secondary CHW pump is variable flow. (Your
zones have two-way valves already.)

* The PV-A report will show that the total primary CHW pump flow will
nearly match the secondary CHW pump flow.

Regards,
Bill

William Bishop, PE, BEMP, LEEDR AP

heinrich's picture
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Heinrich,

As Ravi Srinivasan suggested yesterday, don't oversize the chillers and
boilers. Use 0.50 for their capacity ratios. I believe the consensus in
the modeling community is to do the oversizing only at the system level,
adjusting the cool sizing ratio and heat sizing ratio (not the system
sizing ratio). It would not be surprising for the chillers and boilers
to spend a majority of the time at low part load, since they are
autosized based on total design loads and flowrates of all attached
equipment and processes. This is not a "problem" for the baseline.

Bill**

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Bill,

I didn't oversize the chillers and boilers. I used 0.5 for the capacity
ratios of the chillers and boilers as you told me, more precisely 0.575 for
the 2 chillers and 0.625 for the 2 boilers.
You can see it in the eQUEST model.
eQUEST calculates this big capacities that create this poor part loads.
Don't you think part loads < 50% are a problem for the model review?

Heinrich

_____

Von: Bishop, Bill 
Gesendet: Dienstag, 25. Januar 2011 18:20
An: Heinrich.ib-bauklima.de; equest-users at lists.onebuilding.org
Betreff: RE: Again: eQUEST - serious trouble with LEED review

Heinrich,

As Ravi Srinivasan suggested yesterday, don't oversize the chillers and
boilers. Use 0.50 for their capacity ratios. I believe the consensus in the
modeling community is to do the oversizing only at the system level,
adjusting the cool sizing ratio and heat sizing ratio (not the system sizing
ratio). It would not be surprising for the chillers and boilers to spend a
majority of the time at low part load, since they are autosized based on
total design loads and flowrates of all attached equipment and processes.
This is not a "problem" for the baseline.

Bill**

heinrich's picture
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Hello Omar,

I assume you are doing a LEED model using ASHRAE 90.1-2007, Appendix G.
(2004 is not much different.) My comments below apply to modeling the
baseline.

* Correct, CHW pumps attached to chillers should be constant flow.
Appendix G does not specify if condenser water pumps should be variable
or not. I would argue for constant flow since G3.1.3.11 specifies
two-speed fans for tower capacity control.
* Correct, two pumps per chiller and none for the primary CHW
loop. However, you need to create a secondary CHW loop and pump and
control it per G3.1.3.10.
* Correct, use a single HW pump on the HW loop and none for the
boiler(s).
* Correct, subtype for a primary CHW loop should be "primary". The
secondary CHW loop that you need to create will be "secondary". For the
baseline, "secondary" sizing is correct, since you are not specifying
chiller capacity manually.
* CHW valves at the system/zone coils should be 2-way if the
secondary CHW loop pump is variable speed, and 3-way if the pump rides
the curve. G3.1.3.10 tells you which way to model the secondary CHW
pump.

Regards,
Bill

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Dear Bill,

Many thanks for your feedback. I am really grateful!

Attached are updated screenshots as per your email. Please find my
questions/comments below:

* For "Secondary CHW Pump.JPG", there appears to be a conflict in
the "Capacity Control" input box with your previous email:

If you check the help function of "Capacity Control", you get the
following:

CAP-CTRL

Accepts a code-word that defines how the pump modulates as the flow
varies. When you specify NUMBER to be more than one, then the pumps
will first stage according to the load and then modulate capacity
according to the CAP-CTRL mode:

ONE-SPEED-PUMP The pump rides its curve as the flow varies (2-way
valves in at least one system are necessary for this to happen).

TWO-SPEED-PUMP The pump can operate at two speeds. The low-speed
is determined by MIN-SPEED. You should choose MIN-SPEED to match the
actual low speed ratio of the pump, typically 0.67 or 0.5.

VAR-SPEED-PUMP The pump has a variable frequency drive. The
minimum pump speed is specified by MIN-SPEED. Note that a pump's speed
is not usually proportional to flow; speed is a function of both the
pump flow as well as the pump head requirement. If the pump head
requirement does not fall off as the square of flow (for example, when
the pump has a fixed head setpoint), then the pump will operate at a
speed higher than it would otherwise.

As per Appendix G, my conditioned area is less than 11,148 m2, therefore
the secondary pump must ride the curve. According to the DOE help above
(underlined), 2-way valves must be selected in order for the pump to
ride its curve. You said in your email that 3-way valves are required if
the pump rides the curve.

* Shall I input 3-way or 2-way valves for the "Valve Type" of the
secondary chilled water loop ("Secondary CHW Loop.JPG")?

In total, there are 3 inputs which I need to make sure of and hereby
request your kind comments:

1. Air-Side HVAC System Properties > Cooling > CHW Valve Type
2. Secondary Chiller Water Loop > Basic Specifications > Valve Type
3. Secondary Chiller Water Pump > Basic Specifications > Capacity
Control

Thanks again!

Omar Katanani

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Oh and 1 more thing,

I am getting an error once I do perform a run. It says:

"Secondary Chilled Water Loop has zero design flow. Check
input for consistency, or specify design loads."

Any idea of what may be the reason?

Thanks!

Omar Katanani

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Omar,
You have to assign your systems/coils to the new secondary loop. They
are currently all assigned to the primary loop.
Bill

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To model variable loop flow with a single-speed pump, at least one 2-way
valve is needed in a loop. How are people approaching the requirement
for "riding the pump curve" in HW and CHW loops per G3.1.3.5 and
G3.1.3.10? Set all system/zone valves to 2-way and use the default
loop-mimimum-flow ratio of 0.05?

Thanks,
Bill

William Bishop, PE, BEMP, LEED(r) AP

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Thanks Bill & Ravi,

Assigning to the secondary loop fixed the problem.

I have a couple of extra questions:

1. The Loop Design DT for the Primary CHW loop is 10F, as per the
Mechanical specifications. I was wondering if I need to put the same
number for the Secondary CHW loop. Shall I put the Secondary CHW loop
design DT to be 10F, or should it be zero ( in order not to consider the
delta 10deg twice) ?
2. I have more than 1 secondary CHW pump in my design. However, it
seems that I can only specify 1 secondary CHW pump. Any suggestions? (I
currently have 1 pump with the capacity kW and flow (gpm) equal to the
sum of the proposed secondary pumps.

Many thanks for your continuous help,

Omar Katanani

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