variable primary flow.ppt

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Presentation Title

Presenters:Andrew Clancy, Business Development Sr Manager - NavyScott Schmittel, Account ExecutiveJason Richwine , Application Engineer

Proprietary & Confidential

Consulting Engineer’s Office

3


The Project

University Classroom Building

Central Chilled Water Plant

This building cannot be connected

Cooling tower will not work

Variable Primary Flow

4


Discovery

5

Scott Branch Account Manager - Buddy


Discovery

Low Delta T Syndrome

300Tons – Cooling

Two 150 Ton Chillers

Scroll

Screw

6


Johnson Controls Capabilities

7

Dave Jason Richwine


Primary/Secondary System

Constant Speed Primary Pumps

Variable Speed Secondary Pumps

Common Pipe

Typical load with two way valves


Primary/Secondary System at Design

54.0 °F

54.0 °F

54.0 °F

44.0 °F

44.0 °F

44.0 °F

Primary Pumps

360 GPM Each

1080 GPM @ 54.0 °F

Secondary Pumps

1080 GPM @ 44.0 °F

Typical Coil

No flow

44.0 °F

54.0 °F

150 ton chillers360 GPM Each54.0-44.0°F

1080 GPM @ 54.0 °F


Primary/Secondary System at Part Load

51.5 °F

51.5 °F

51.5 °F

44.0 °F

44.0 °F

44.0 °F

Primary Pumps

360 GPM Each

1080 GPM @ 51.5 °F

Secondary Pumps

810 GPM @ 44.0 °F

Typical Coil

44.0 °F

54.0 °F

270 GPM @ 44.0 °F

810 GPM @ 54.0 °F

75% System Load



54.0 °F

54.0 °F

44.0 °F

44.0 °F

Primary Pumps

360 GPM Each

720 GPM @ 54.0 °F

Secondary Pumps

720 GPM @ 44.0 °F

Typical Coil

44.0 °F

54.0 °F

No Flow

720 GPM @ 54.0 °F

OFF 67% System LoadClean Coils



54.0 °F

54.0 °F

44.0 °F

44.0 °F

Primary Pumps

360 GPM Each

720 GPM @ 54.0 °F

Secondary Pumps

792 GPM @ 44.0 °F

Typical Coil

44.0 °F

53.0 °F

72 GPM @ 53.0 °F

792 GPM @ 53.0 °F

OFF 67% System LoadDirty Coils



53.0 °F

53.0 °F

44.0 °F

44.0 °F

Primary Pumps

360 GPM Each

720 GPM @ 53.0 °F

Secondary Pumps

792 GPM @ 44.8 °F

Typical Coil

44.8 °F

53.0 °F

72 GPM @ 53.0 °F

792 GPM @ 53.0 °F




51.9 °F

51.9 °F

44.0 °F

44.0 °F

Primary Pumps

360 GPM Each

720 GPM @ 51.9 °F

Secondary Pumps

900 GPM @ 44.8 °F

Typical Coil

44.8 °F

51.9 °F

180 GPM @ 51.9 °F

900 GPM @ 51.9 °F




Variable Primary System

Secondary Pumps

Primary Pumps

Primary Pumps

Flow Meter

BypassValve

Automatic Isolation Valve

Typical load with 2 way valve

Typical load with 2 way valve


Variable Primary System at Design

54.0 °F

54.0 °F

54.0 °F

44.0 °F

44.0 °F

44.0 °F

Primary Pumps

360 GPM Each

1080 GPM @ 56.0 °F

1080 GPM @ 44.0 °F


Bypass Closed




Variable Primary System – Part Load

54.0 °F

54.0 °F

54.0 °F

44.0 °F

44.0 °F

44.0 °F

Primary Pumps

270 GPM Each

810 GPM @ 54.0 °F

810 GPM @ 44.0 °F


Bypass Closed

Typical load with two way valve

75% System Load

810 GPM @ 54.0 °F


Variable Primary System – Part Load

54.0 °F

54.0 °F

44.0 °F

44.0 °F

Primary Pumps

180 GPM Each

540 GPM @ 54.0 °F

540 GPM @ 44.0 °F


Bypass Closed


50% System LoadChiller off

540 GPM @ 54.0 °F


Variable Primary System – Min Flow (120 gpm each)

51.5 °F

44.0 °F

Primary Pumps

120 GPM (one operating)

120 GPM @ 51.5 °F

90 GPM @ 44.0 °F


Bypass Open


System flow below chiller minimum flow

Chiller off

Chiller off

Closed

Closed

30 GPM @ 44.0

90 GPM @ 54.0 °FFlow meter

Pumps off


Designing a VPF Bypass

Size for minimum flow through one chiller

Bypass valve shall be the normally open type

Valve head ratings must be higher than pump dead head

Linear characteristic - valve position % equals flow %

Fast actuator

Valve control range 100:1

Flow meter controls bypass to maintain chiller minimum flow


Variable Primary System – Min Flow (120 gpm each)

51.5 °F

44.0 °F

Primary Pumps

120 GPM (one operating)

120 GPM @ 51.5 °F

90 GPM @ 44.0 °F


Bypass Open


Pumps maintain system pressure

Bypass maintains minimum flow

Chiller off

Chiller off

Closed

Closed

30 GPM @ 44.0

90 GPM @ 54.0 °FFlow meter

Pumps off


Selecting a VPF Flow Meter for Small Tonnage Systems

Best accuracy job can afford

Minimum +/- 5% at evaporator minimum flow

Set bypass to open when flow equals minimum plus 2 times flow meter accuracy rating

Example: 120 gpm minimum, flow meter +/- 5%, set minimum flow at 120 + 120*10% = 132 gpm

Calibrate flow meter at least as often as manufacturer recommends

Buy the best


Selecting VPF AHU Control Valves

All valve pressure ratings greater than pump dead head

Sized by pressure

% valve position equals % coil capacity

Control range 200:1


Selecting VPF Chiller Isolation Valves

All valve pressure ratings greater than pump dead head

Linear characteristic - valve position % equals flow %

Modulating valve with slow actuator


VPF Design Considerations

Flow rate changes – Staging on additional chillers


Variable Primary System (1 chiller running)

54.0 °F

44.0 °F

Primary Pumps

120 GPM Each

360 GPM @ 546.0 °F

360 GPM @ 44.0 °F


Bypass Closed

Typical load with two way valve360 GPM


Variable Primary System (Staging on second chiller)

54.0 °F

45.0 °F

Primary Pumps

132 GPM Each

396 GPM @ 55.0 °F

396 GPM @ 45.0 °F


Bypass Closed


Need to add chiller


Variable Primary System (Open isolation valve)

55.0 °F

35.0 °F

Primary Pumps

132 GPM Each

396 GPM @ 55.0 °F

396 GPM @ 45.0 °F


Bypass Closed


198 GPM55.0 °F

55.0 °F



55.0 °F

35.0 °F

Primary Pumps

132 GPM Each

396 GPM @ 55.0 °F

396 GPM @ 45.0 °F


Bypass Closed


198 GPM55.0 °F

55.0 °F

LCHWT approaches 35F

LWT Cutout at 40F

Off goes chiller 1



55.0 °F

40.0 °F

Primary Pumps

132 GPM Each

396 GPM @ 55.0 °F

396 GPM @ 45.0 °F


Bypass Closed


132 GPM55.0 °F

55.0 °F

Open slowly

Chiller 2 comes on when flow exceeds minimum

Chiller 1 unloads to maintain set point



54.0 °F

44.0 °F

Primary Pumps

132 GPM Each

396 GPM @ 54.0 °F

396 GPM @ 44.0 °F


Bypass Closed


198 GPM44.0 °F

54.0 °F

Both valves fully open

Flow equalizes

Chillers modulate to maintain chilled water set point



55.0 °F

42.0 °F

Primary Pumps

132 GPM Each

396 GPM @ 55.0 °F

396 GPM @ 45.9 °F


Bypass Closed


120 GPM55.0 °F

55.0 °F

Open to change flow 36gpm/min

Chiller 2 comes on when flow is 120gpm – in 3 min 20 sec

Chiller 1 is still producing 100% capacity



54.0 °F

44.0 °F

Primary Pumps

132 GPM Each

396 GPM @ 54.0 °F

396 GPM @ 44.0 °F


Bypass Closed


198 GPM44.0 °F

54.0 °F

Both valves fully open

Flow equalizes

Chillers modulate to maintain chilled water set point


Staging on Chiller 2 in VPF Systems

Maintain minimum flow through the operating chiller

Avoid sudden changes in flow anywhere in the system

Prefer schemes that work when bringing on any chiller


Setting Flow Rate of Change

Start with 10% of design flow per minute

YORK small tonnage chillers can handle faster changes

If the project requires rapid flow changes, contact application engineering

If problems occur during operation, adjust the rate


Variable Primary System – Handling Rapidly Decreasing Loads

54.0 °F

54.0 °F

54.0 °F

44.0 °F

44.0 °F

44.0 °F

Primary Pumps

360 GPM Each

1080 GPM @ 56.0 °F

1080 GPM @ 44.0 °F


Bypass Closed





54.0 °F

54.0 °F

54.0 °F

44.0 °F

44.0 °F

44.0 °F

Primary Pumps

360 GPM Each

1080 GPM @ 44.0 °F

0 GPM @ 44.0 °F


Bypass Open





54.0 °F

54.0 °F

54.0 °F

44.0 °F

44.0 °F

44.0 °F

Primary Pumps

324 GPM Each

972 GPM @ 44.0 °F

972 GPM @ 44.0 °F


Bypass Closed


Close the closest valve first



54.0 °F

54.0 °F

54.0 °F

44.0 °F

44.0 °F

44.0 °F

Primary Pumps

288 GPM Each

864 GPM @ 44.0 °F

864 GPM @ 44.0 °F


Bypass Closed


Close the next closest valve



54.0 °F

54.0 °F

54.0 °F

44.0 °F

44.0 °F

44.0 °F

Primary Pumps

252 GPM Each

756 GPM @ 44.0 °F

756 GPM @ 44.0 °F


Bypass Closed


Close the next closest valve


Selecting a Small Tonnage Chiller for VPF

Look at all applicable selections

Evaluate based on full load performance

Evaluate based on part load performance

Evaluate based on evaporator minimum flow

Evaluate based on required temperature control accuracy


Selecting a Small Tonnage Chiller for VPF


Optimizing Air-cooled Chiller Operation

Optimize Chiller Efficiency

Optimize Pump Efficiency

Define loading and unloading sequences

Model annual energy use



Chiller is more efficient at 80% than at 40% for the given ambient temperature.


288 GPM


9 Ft. Head

288 GPM144 GPM each 2.5 Ft. Head



Chiller is more efficient at 40% than at 80% for the given ambient temperature.


STC Special Case – How would you design this system?

The Setup 20 ton VPF cooling system

One chiller, one AHU

44F chilled water with 54F return

Chiller has two scroll compressors (0%, 50%, or 100% capacity)

The Problem Load remains constant at around 55% or 60% for several hours

Chiller can’t meet demand with one compressor on

Chiller severely over-cools with both compressors on

System is unstable

The Hint Start by thinking about how increasing system water volume can add stability


Summary

How VPF systems work

How to select control components for system stability

How to sequence chillers on and off

How to control the chillers, pumps, and valves

How to size the bypass

56

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variable primary flow.ppt

Documents

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f72 gpm

f792 gpm

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0f1080 gpm

f900 gpm

f270 gpm