Ncbc 2010 Chilled Water Commissioning Villani

8/8/2019 Ncbc 2010 Chilled Water Commissioning Villani

1/40

Chilled Water System Commissioning:Variable Primary Flow

John D. Villani, P.E.Associate

Grumman/Butkus

Associates


2/40

Learning Objectives

1. History of chilled water system configurations2. Variable Primary Flow (VPF) chilled water systemconfiguration3. Design and Controls Considerations for properoperation of VPF chilled water systems4. Things to look for when commissioning VPF chilledwater systems

AIA Quality Assurance


3/40

Chilled Water System History

Constant Primary Flow1

Constant Primary Flow was used before

primary/secondary Advent of low delta T problem

1000 ton1000 ton

2 gpm/ton

1000 gpm 1000 gpm

12dT 10dT

Loss of capacityand capital

investment916 tons


4/40


Primary/Secondary (Balanced) 1

Constant Primary Flow / Variable Secondary

Flow has been the industry standard fordecades.2

1000 ton 1000 ton

2 gpm/ton

1000 gpm

12dT 10dT

998 gpm

2000 gpm

1998 gpm53 Deg F

2

gpm4

2DegF

53 Deg F

42 Deg F

54 Deg F Design

916 tons

VF

D


5/40


Primary/Secondary (Imbalanced) 1

Problems propagate when secondary load

and flow exceed primary

1000 ton 1000 ton

2 gpm/ton

1000 gpm

12dT 10dT

1200 gpm

2000 gpm

53DegF20

0gpm

ADDED

54 Deg F Design

42 Deg F

VF

DRampsup

2200 gpm53 Deg F53 Deg F 1008 tons

SCHWS Temp increases

Flow throughchiller remains

constant

47 Deg F


6/40


Primary/Secondary1

Constant Primary Flow / Variable Secondary

Flow with check valve, one of many options

1000 ton 1000 ton

2 gpm/ton

1000 gpm

12dT 10dT

1200 gpm

Check valveprevents

secondaryflow fromexceeding

primary flow

VF

D


7/40


Variable Primary1

Variable Primary Flow with Low Flow Bypass

Variable Flow

VF D


8/40


Why is Variable Primary Flow (VPF) New?

(According to survey of chiller manufacturers1

) Always technicallyfeasible

Practical application limited by on-board

controls in use prior to mid-1990sCapacity modulation

Freeze protection

Flow detection Improvements in all areas have increasedmanufacturer support for variable primary flow


9/40

VPF Design Considerations

Design Issues

Pumps are controlled by load differential pressure(dP), not staged with chillers

Low Flow Bypass is critical to maintain minimumchilled water flow through the chillers

Flow Rate Range Limits

Typical 3

12 ft/s tube velocity range

maximum turn down to ~25%

Rate of change of flow

Do not exceed rate of change greater than 30% ofdesign flow per minute3

Older constant speed chillers, do not exceed 10%3


10/40

VPF Controls Considerations

Controls Complications with VPF

Differential Pressure (dP) pumping control

Low Flow Bypass controls

Chiller staging effect on flow through chillers

Chiller modulating flow control valves tobalance flow through multiple chillers inoperation


11/40


Differential Pressure (dP) pumpingcontrol

Common chilled water systems feed multipleloads, air handlers and buildings System configurations typically have multiplerisers and/or buildings

Resulting in varying dP requirements

throughout the system

VPF pumps need to satisfy the hydraulicallymost critical zone, which is the zone furthestbelow set point


12/40



Need a sequence to stage pumps

Pumps can be staged to keep several pumps

running at a lower speed Dont let pump speed go below 40% or24Hz, pump will not flow water, look at the

pump curve Stage up/down at 80%, 60%, 53% Put in a dP dead band so pumps dont hunt!!


13/40



LOADdP STPT

16 psi

LOADdP STPT

12 psi

VF D


14/40

(dP) pumpingcontrol2 zones

Evaluates

one zone vs.other zones

If both zones areunder setpoint,

determine which

has a greater %under set point

Calculate %under

setpoint


15/40



Valve type and actuator must be fast acting

Bypass control proportional, integral,derivative (PID) loop must be fast acting Bypass control loop must be able to handlechanges in system operation such as a

failure of a load (air handler) which suddenly

shuts the CHW control valve


16/40

Case Study Results

Case Study - Low Flow Bypass

(3) electric centrifugal 400 ton chillers

2 gpm chilled water design flow rate per ton 800 gpm per chiller Minimum Flow Rate = 210 gpm Chilled water header = 10

Low Flow Bypass Line Size = 6

Lesson Learned: size the bypass lineappropriately and select a fast actingmodulating actuator; controllability of thebypass can be extremely difficult


17/40

Case Study Results

Case Study - Low Flow Bypass

6ChilledWater

BypassfromCHWS

Header

10 ChilledWaterBypassControlValve

BrayButterfly

Valve


18/40


Chiller Staging

Pumps are controlled by system dPs

Chillers are staged based on leaving chilledwater supply water temperatureAND

Chiller chilled water flow rates or differentialpressure across evaporator


19/40


Chiller Staging Problems

Due to decoupled pumps and chillers

Load can increase demanding more pumping

Chillers may be able to still meet the leaving

CHW setpoint Flow through chiller may exceed the systemallowable

pressure drop and cause loss of

pressure in the field


20/40

Excess Flow causes increased PD

DESIGN


21/40



1 Chiller operating near full load

CHWS temperature setpoint may be low 42 F

VF D

1000 gpm 1200 gpm

2000 gpm(design)

2200 gpm(actual)

MM OPENCLOSED


22/40



Staging on the second chillers

Valves must be modulating and slow acting

VF D

1000 gpm 1200 gpm

2000 gpm(design)

1100 gpm(actual)

MM OPENOPEN

2000 gpm(design)

1100 gpm(actual)


23/40



24/40



Rate of change limit 30%, 2000 gpm = 600 gpm

Flow drops 1100 gpm, need to take 2 minutes toopen second chillers control valve

VF D

1000 gpm 1200 gpm

2000 gpm(design)

1100 gpm(actual)

MM OPENOPEN

2000 gpm(design)

1100 gpm(actual)


25/40

Chiller Staging Suggestions

Chiller Staging Sequence Suggestions

Before staging on next chiller, raise the

operating chillers setpoint This should be done a few minutes beforeopening the second chillers evaporator flow

control valve

This will back off how hard the first chiller is

working and help prepare it for the suddendrop in chilled water flow


26/40

Chiller Staging Suggestions

Chiller Staging Sequence Suggestions

After the second chiller is staged on for a

period of several minutes, start resetting theCHWS temp setpoint back down

LOCK THE PUMPS at their current speed

while staging chillers on and off

You dont want to pump control sequence to

start speeding up pumps due to a drop insystem pressure as the second chiller stageson, this will cause faster flow through the

chiller


27/40

Staging & Hydraulically Most Remote Chiller


Plants consist of both variable speed chillers and

constant speed chillers of different capacities

Need to assess pressure drop across chillers & piping

VF D

1050 ton3 pass

1500 gpm28.6 ft wg

MM OPEN Modulate

750 ton3 pass

1124 gpm25.1 ft wg


28/40


Which chiller is hydraulically the most remote?

Take piping into account when determining this

How do you select which chiller valves areopen and which modulate?

Chiller# 1 2 3 4ratedtonnage 1050 1050 750 1190#ofEvapPasses 3 3 3 2

Evapgpm 1500 1500 1124 1783EvapPDftwg 28.6 28.6 25.1 20.5

ChillerPerformanceCharacteristics


29/40


DESIGN

FLOW ANDPRESSUREDROP TOMATCHOTHER

CHILLERS


30/40

Chiller Staging and Pressure Drop Problems


31/40

Chiller Staging and Pressure Drop Problems


32/40

VPF Cx Considerations and Realities


Review bypass valve size and actuator stroke

time

Hard to Cx without load on the building.Without load the system will operate withbypass open and no load on chillers

Maximum turn down to 25% is optimistic.

Too little water through the evaporator tokeep the system stable

Expect some surging at low flow conditions

and Low Evaporator Temperaturealarm trips


33/40


Sequence of Operations

Request from the design team the chiller

plant and pumping staging sequence

Request a matrix on which chillers ANDpiping make the hydraulically most remotechillers and how to modulate the CHW flowcontrol valves


34/40


Chiller Performance Submittal

Review chiller minimum and maximum flow

rates

Review chiller rated pressure drop Review chiller pressure drop curve This many not be provided in a standardchiller submittal and must be requested If all this information is not provided, there willbe guess work in the field

C C


35/40


Controls

Limit the speed at which the chilled water

pump VFDs can speed up and down

Limit the time span the chilled water flowcontrol valve actuators can stroke from min tomax

Review the system dPs and how the pumps

track to maintain the lowest from setpoint Put in a dead band so the pumps are notalways hunting due to system size and

complexity

VPFC S i M Effi i


36/40

VPF Cx Squeezing More Efficiency

Controls

TREND air handler control valves and bypass

valve

RESET chilled water supply temperaturesetpoint based something, valve position This will provide chiller electrical savings atthe expense of increased pumping Condenser water reset still works great!

VPF C t k thi t ff !!


37/40

VPF Cx you cant make this stuff up!!

Controls

Johnson Controls buys York, Aug 2005

May 2010, York startup tech says chilledwater reset is not a good idea and disallowsJCI from doing chilled water reset

After a Cx discussion, the next days . . .

York allows JCI access to do CHW reset

Only to find out that now you have tocontrol the chillers demand limiting functionas well?? Limit to 80% for the first 30 min.

4

R f


38/40

References

References1.

William P. Bahnfleth, Eric B. Peyer, 2003, Variable Primary Flow: PotentialBenefits and Application Issues

2.

ASHRAE Handbook HVAC Systems and Equipment, 1996

2.

McQuiston, F., J. Parker and J. Spitler, 2000 Heating, ventilating and airconditioning

analysis and design, 5th

edition

3.

Carrier Corporation

(Project and Chiller Specific, refer to your particular

chiller manufacturers details)4.

Johnson Controls Inc./York International Corporation

(Project and Chiller

Specific, refer to your particular chiller manufacturers details)

AIA Q lit A


39/40

AIA Quality Assurance

Portland Energy Conservation, Inc is a registered provider with TheAmerican Institute of Architects Continuing Education Systems. Creditearned on completion of this program will be reported to CES Recordsfor AIA members. Certificates of Completion for non-AIA members are

available on request.

This program is registered with the AIA/CES for continuingprofessional education. As such, it does not include content that maybe deemed or construed to be an approval or endorsement by the AIAof any material of construction or any method or manner of handling,using, distributing, or dealing in any material or product. Questions

related to specific materials, methods, and services will be addressedat the conclusion of this presentation.


40/40

Questions AND thank you

John D. Villani, P.E., LEED AP, C.E.M., QCxPGrumman/Butkus Associates

[email protected]

(847) 328-3555
mailto:[email protected]:[email protected]

Ncbc 2010 Chilled Water Commissioning Villani

Documents

Transcript of Ncbc 2010 Chilled Water Commissioning Villani