PRIMARY VFD AND CHILLER SYSTEM

Phone Topics

Applying 19XRV Chillers in Variable Primary Systems

Ron Beliveau

Carrier Commercial Sales

Middletown, CT

Phone Topics

Outline

19XRV chillers in VPF systems.

19XRV Chillers in Variable Primary Systems

1. Review conventional Primary Secondary System.

2. Review Variable Primary Flow System.

3. Review the Benefits of “Max Cap” in both P/S and VPF systems.

4. Review the Benefits of VFD driven chillers in both P/S and VPF systems.

5. Review chiller selection guidelines for VPF applications.

.

WARNING:

55 slides in 45 minutes –

We will be moving very quickly!

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Why VPF?

Why all the interest in VPF?19XRV Chillers in Variable Primary Systems

1. Unlike many items –this isn’t a “sell up” concept – it is actually a lower installed cost.

- VPF Reduces pumping and piping complexities and lowers installation costs.

- Less real estate in mechanical and electrical rooms.

2. Unlike many cost reductions, VPF can offer lower operational costs.

- VPF reduces low T, increasing eff.

- Fewer, but larger pumps have better efficiency.

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Primary Secondary Systems.

Primary Secondary Systems use constant speed pumps to supply water to the chillers.

OFF = 0 gpm

ON = 1200 gpm

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The chiller controls to a leaving chilled water set point.

OFF = 0 gpm

ON = 1200 gpm

44 F

Chiller cools 1200 gpm of water to 44F.

How much work is the chiller doing?

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The amount of work the chiller does is related to the return water temperature.

GPM is fixed.

LCHWT is fixed.

Only variable is return temp.

OFF = 0 gpm

ON = 1200 gpm

Tons = GPM x T 24

500 = 1200 x (54-44) / 24

400 = 1200 x (52-44) / 24

300 = 1200 x (50-44) / 24

44 F??

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Chiller (primary) pumps are constant speed (flow).

Secondary pumps are variable speed.

Secondary pump speed (gpm) controlled by DP switch at most hydraulically remote coil.


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If primary gpm equals secondary gpm, there is no flow through the hydraulic decoupler line.


0 gpm 3600 gpm3600 gpm

1200 gpm

1200 gpm

1200 gpm

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If primary gpm is greater than secondary gpm, chilled water flows through the decoupler line, bypassing the coils.

This cold water mixes with the return water, lowering the return temperature to the chillers.


600 gpm 3000 gpm3600 gpm

1200 gpm

1200 gpm

1200 gpm

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If primary gpm is less than secondary gpm, return water flows through decoupler line.

This warm water mixes with the chilled water, raising the entering chilled water temperature to the coils.

If return temp is too high, another chiller / pump set is started.


600 gpm 3000 gpm2400 gpm

0 gpm

1200 gpm

1200 gpm

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Start up.

Coils call for load.

One chiller / pump started and a secondary pump started.

Secondary pump only needs 240 gpm to satisfy coil load.

0 gpm

0 gpm

1200 gpm

240 gpm

0 tons

0 tons

100 tons

960 gpm 240 gpm1200 gpm

46 F 44 F

EX: 100 ton building load


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At 500 tons of building load the secondary pumps require 1200 gpm.

Primary gpm equals secondary gpm and there is no flow through decoupler line.

0 gpm

0 gpm

1200 gpm

1200 gpm

0 tons

0 tons

500 tons


54 F 44 F



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At 550 tons of building load the secondary pumps require 1320 gpm.

For a brief time, primary gpm is less than secondary gpm warm water flows back through decoupler line.

0 gpm

0 gpm

1200 gpm

1320 gpm

0 tons

0 tons

500 tons

120 gpm 1320 gpm1200 gpm

54 F 44 F



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To meet coil load, temp sensor turns on chiller and pump set.

Now primary gpm > secondary gpm and chilled water flows through decoupler line bypassing the load.

0 gpm

1200 gpm

1200 gpm

1320 gpm

0 tons

275 tons

275 tons

1080 gpm 1320 gpm2400 gpm

49. 5 F 44 F



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When the building reaches 1000 tons, in theory, the chillers are fully utilized and there is no flow through the decoupler line.

0 gpm

0 gpm

1200 gpm

1200 gpm

2400 gpm

2400 gpm

0 tons

500 tons

500 tons

2400 gpm

54 F 44 F



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When building is at full load, there is 1500 tons required by coils and 1500 tons provided by chillers.

System is balanced and there is no flow through decoupler

1200 gpm

1200 gpm

1200 gpm

3600 gpm

500 tons

500 tons

500 tons


54 F 44 F



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As we unload, the system can shut off the 3rd chiller only if the delta T is at design.

0 gpm

0 gpm

1200 gpm

1200 gpm

2400 gpm

2400 gpm

0 tons

500 tons

500 tons

2400 gpm

54 F 44 F



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If not controlled properly, 1000 ton load could look like this.

3 chillers running at 67% load!


1200 gpm

1200 gpm

1200 gpm

1200 gpm

2400 gpm

2400 gpm

334 tons

333 tons

333 tons

3600 gpm

50.7 F 44 F


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1029 gpm

1200 gpm

1200 gpm

1200 gpm

2571 gpm

2571 gpm3600 gpm

49 F 44 F

EX: 750 ton building load with Low Delta T syndromePrimary

Secondary Systems.

T across dirty coil = 7

Load is 750 Tons, GPM=?

44 F51 F

TONS = GPM x DT / 24

TONS = 1200 X 7 / 24

TONS = 350 ???

TONS = GPM x DT / 24

TONS = 1200 X 5 / 24

TONS = 250

Tons = GPM x T 24

GPM = Tons x 24 TIn perfect world (2)

chillers operate @ 375 tons each.

2@ .479 IKW/Ton

With low delta T (3) chillers operate @ 250 tons each.

3 @ .518 IKW/Ton

Extra pump power is also consumed. T across dirty coil = 7

Load is 750 Tons,

750 x 24 /7 = 2571 gpm

250 tons

250 tons

250 tons

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Outline








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Variable Primary Systems use variable speed pumps to supply water to the chillers.

OFF = 0 gpm

ON = ??? gpm

(within min / max flow)

Variable Primary Systems

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The chiller controls to a leaving chilled water set point. 44 F

Chiller cools 54F water to 44F.

How much work is the chiller doing?


OFF = 0 gpm

ON = ??? gpm

54

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The amount of work the chiller does is related to the flow through the cooler.

ECHWT is fixed.

LCHWT is fixed.

Only variable is cooler gpm.

OFF = 0 gpm

ON = 1200 gpm

Tons = GPM x T 24

500 = 1200 x (54-44) / 24

400 = 960 x (54-44) / 24

300 = 720 x (54-44) / 24

44 F54


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Tons = GPM x T

24


Primary Secondary

GPM = Constant, T changes as load changes

Variable Primary

T constant, GPM changes as load changes.

Pump only the chilled water necessary to serve the load.

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Only one set of pumps.

No decoupler line

All pumps are Variable speed.

Flow (gpm) is regulated to

maintain T.

Tons = GPM x T

24

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Start up.

Coils call for load.

One chiller / pump started.

Min. flow rate of chiller is 500 gpm.

Therefore, 260 gpm must bypass around coils

240 gpm

500 gpm

0 gpm

500 gpm

500 gpm

100 tons

0 tons

0 tons

48.8 F

44 F

260 gpm bypass

500 gpm

0 gpm

0 gpm


44 F54 F

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At 208 tons, the design T (of 10F)

is achieved.

Flow is no longer required to bypass coils.

208 = 500 x 10 24

500 gpm

500 gpm

0 gpm

500 gpm

500 gpm

208 tons

0 tons

0 tons

54 F 44 F

500 gpm

0 gpm

0 gpm

0 gpm


44 F54 F

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is achieved with 1200 gpm of flow.

(1) chiller is now fully loaded.

500 = 1200 x 10 24

1200 gpm

1200 gpm

0 gpm

1200 gpm

1200 gpm

500 tons

0 tons

0 tons

54 F44 F

1200 gpm

0 gpm

0 gpm

0 gpm


44 F54 F

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(2) Chillers are now part loaded.

Flow split equally.

550 = 1320 x 10 24

1320 gpm

1320 gpm

0 gpm

1320 gpm

1320 gpm

275 tons

275 tons

0 tons

54 F44 F

660 gpm

0 gpm

660 gpm

0 gpm


44 F54 F

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The 2nd pump is turned on.

Flow split equally.

750 = 1800 x 10 24

1800 gpm

900 gpm

900 gpm

1800 gpm

1800 gpm

375 tons

375 tons

0 tons

54 F44 F

900 gpm

0 gpm

900 gpm

0 gpm


44 F54 F

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(2) Chillers are now fully loaded.

Flow split equally.

1000 = 2400 x 10 24

2400 gpm

1200 gpm

1200 gpm

2400 gpm

2400 gpm

500 tons

500 tons

0 tons

54 F44 F

1200 gpm

0 gpm

1200 gpm

0 gpm


44 F54 F

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(3) Chillers are now part loaded.

Flow split equally.

1100 = 2640 x 10 24

2640 gpm

1320 gpm

1320 gpm

2640 gpm

2640 gpm

367 tons

367 tons

366 tons

54 F 44 F

880 gpm

0 gpm

880 gpm

880 gpm


44 F54 F

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Flow split equally.

1500 = 3600 x 10 24

3600 gpm

1800 gpm

1800 gpm

3600 gpm

3600 gpm

500 tons

500 tons

500 tons

54 F44 F

1200 gpm

0 gpm

1200 gpm

1200 gpm


44 F54 F

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Primary Secondary Pumping System Constant Speed

Variable Speed

Building Load GPM

Qty of Chillers

Chiller % Load ECWT

Chiller IKW/Ton

Chiller IKW/Ton

100 1200 1 20% 65 0.954 0.551208 1200 1 42% 65 0.619 0.36500 1200 1 100% 65 0.446 0.384550 2400 2 55% 65 0.537 0.332750 2400 2 75% 65 0.479 0.33

1000 2400 2 100.0% 71.8 0.485 0.4361100 3600 3 73.4% 74.2 0.527 0.4441500 3600 3 100% 85 0.59 0.589

Variable Primary Pumping SystemConstant Speed

Variable Speed

Building Load GPM

Qty of Chillers

Chiller % Load ECWT

Chiller IKW/Ton

Chiller IKW/Ton

100 500 1 20% 65 0.954 0.548208 500 1 42% 65 0.619 0.358500 1200 1 100% 65 0.446 0.384550 1320 2 55% 65 0.537 0.332750 1800 2 75% 65 0.479 0.328

1000 2400 2 100% 71.8 0.485 0.4361100 2640 3 73.4% 74.2 0.527 0.4421500 3600 3 100% 85 0.59 0.589

When comparing the two systems we find that chiller efficiency is basically equal


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Compressor HP ~

Mass Flow X Lift

Load

Chiller

CoolingTower

Compressor/Cycle Efficiency


Why is chiller performance identical for both systems?

KW = Tons x Lift

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Lift is equivalent in both Primary / Secondary and VPF

systems.

Lift is SCT – SST.

SST – based on LCHWT

SCT – based on Tower Performance

Tons – Building load identical in VPF and P/S systems – just adjust flow and T .


All of this is exactly the same regardless of chilled water system type!

The Efficiency Advantage of VFD Chillers is just as powerful on VPF systems!

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Variable Speed

Building Load GPM

Qty of Chillers

Chiller % Load ECWT

Chiller IKW/Ton

Chiller IKW/Ton

100 1200 1 20% 65 0.954 0.551208 1200 1 42% 65 0.619 0.36500 1200 1 100% 65 0.446 0.384550 2400 2 55% 65 0.537 0.332750 3600 2 75% 65 0.479 0.33

1000 3600 2 100.0% 71.8 0.485 0.4361100 3600 3 73.4% 74.2 0.527 0.4441500 3600 3 100% 85 0.59 0.589


Variable Speed

Building Load GPM

Qty of Chillers

Chiller % Load ECWT

Chiller IKW/Ton

Chiller IKW/Ton

100 500 1 20% 65 0.954 0.548208 500 1 42% 65 0.619 0.358500 1200 1 100% 65 0.446 0.384550 1320 2 55% 65 0.537 0.332750 1800 2 75% 65 0.479 0.328

1000 2400 2 100% 71.8 0.485 0.4361100 2640 3 73.4% 74.2 0.527 0.4421500 3600 3 100% 85 0.59 0.589

750 3600 3 50% 65 0.562 0.3391000 3600 3 66.7% 71.8 0.533 0.414

When comparing the two systems we find that chiller efficiency is basically equal


750 1800 2 75% 65 0.479 0.3281000 2400 2 100% 71.8 0.485 0.436

Except when the VPF chiller is able to operate fewer chillers than the Primary / Secondary system.

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Outline








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Positive Pressure chillers typically can produce above rated tons as entering condenser water drops.

The “Max Cap” Advantage Applied in VPF Systems?


570570

600600

630630

643643

630 630

Tons

8585ooFF 7575ooFF 7070ooFF <65<65ooFF8080ooFF

550550

Carrier

Others

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With MAX CAP feature,



(1) Chiller is fully loaded.

550 = 1320 x 10 24

1320 gpm

1320 gpm

0 gpm

1320 gpm

1320 gpm

550 tons

0 tons

0 tons

54 F44 F

1320 gpm

0 gpm

0 gpm

0 gpm


44 F54 F

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With MAX CAP feature.




1100 = 2640 x 10 24

2640 gpm

1320 gpm

1320 gpm

2640 gpm

2640 gpm

550 tons

550 tons

0 tons

54 F

44 F

1320 gpm

0 gpm

1320 gpm

0 gpm


44 F54 F

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With MAX CAP feature.

At 1100 tons, the T can be increased from 10F to 11F by

lowering the LCHWT.

(2) Chillers are fully loaded.

1100 = 2400 x 11 24

2400 gpm

1200 gpm

1200 gpm

2400 gpm

2400 gpm

550 tons

550 tons

0 tons

54 F43 F

1200 gpm

0 gpm

1200 gpm

0 gpm


43 F54 F

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Max Cap advantage – increasing evaporator flow.

Good idea on constant speed, not the way to control VFD chillers.



Variable Speed

Building Load GPM

Qty of Chillers

Chiller % Load ECWT

Chiller IKW/Ton

Chiller IKW/Ton

100 1200 65208 1200 77500 1200 65550 2400 2 55% 65 0.537 0.332750 3600 65900 3600 69

1000 3600 71.81100 3600 3 73.4% 74.2 0.527 0.4441500 3600 85

MAX CAP ADVANTAGE - MORE EVAPORATOR FLOW.


Variable Speed

Building Load GPM

Qty of Chillers

Chiller % Load ECWT

Chiller IKW/Ton

Chiller IKW/Ton

100 500 65208 500 77500 1200 65550 1320 1 110% 65 0.453 0.433750 1800 65900 2160 69

1000 2400 71.81100 2640 2 110.0% 74.2 0.507 0.4971500 3600 85

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Max Cap advantage holding evaporator flow constant and lowering LCHWT.

Increased lift on chiller – less efficient than increasing flow.



Variable Speed

Building Load GPM

Qty of Chillers

Chiller % Load ECWT

Chiller IKW/Ton

Chiller IKW/Ton

100 1200 65208 1200 77500 1200 65550 2400 2 55% 65 0.537 0.332750 3600 65900 3600 69

1000 3600 71.81100 3600 3 73.4% 74.2 0.527 0.4441500 3600 85

MAX CAP ADVANTAGE - CONSTANT EVAP FLOW, LOWER LCHWT.


Variable Speed

Building Load GPM

Qty of Chillers

Chiller % Load ECWT

Chiller IKW/Ton

Chiller IKW/Ton

100 500 65208 500 77500 1200 65550 1320 1 110% 65 0.458 0.443750 1800 65900 2160 69

1000 2400 71.81100 2640 2 110.0% 74.2 0.517 0.5091500 3600 85

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Same reasons you would supply 19XRV on Primary Secondary Systems.

Why Provide Variable Speed Chillers in VPF?


VFD driven chillers take advantage of reduced lift and/or reduced load hours offering annual power costs unmatched by any constant speed chiller.

.

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Flow ~ V, ATo increase flow, increase flow area or rotor speed

Lift ~ V2

To increase lift, increase diameter or rotor speed

Power ~ Flow x Lift ~ V2

With constant flow and reduced lift, reduce speed to reduce power

Affinity laws for centrifugal fans, pumps and compressors.

V

Diameter

FlowArea

How 19XRV Chillers save kW in P/S & VPF Systems

Ideal Fan Laws Dictate the relationship between speed, flow and lift


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Methods to Improve Efficiency - Lift Reduction

- Aerodynamics

- Motor efficiency

- Transmission efficiency

- Metering devices

- Refrigerant

- Cycle enhancements

Compressor HP ~

Mass Flow X Lift

Load

Chiller

CoolingTower

Compressor/Cycle Efficiency


How 19XRV Chillers save kW in P/S & VPF Systems

LiftECWT

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Efficiency improves dramatically as ECWT drops.


Reduced Lift at 100% tons(500 Tons)

0.30.35

0.40.45

0.50.55

0.6

85 80 75 70 65 60

Entering Condenser Water Temperature

IKW

/ Ton 19XRV

19XR

All points shown are 100% load (500 tons)

19XRV “unlifts” much better then constant speed machine.

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Variable Speed

Building Load GPM

Qty of Chillers

Chiller % Load ECWT

Chiller IKW/Ton

Chiller IKW/Ton

100 1200 1 20% 65 0.954 0.551208 1200 1 42% 65 0.619 0.36500 1200 1 100% 65 0.446 0.384550 2400 2 55% 65 0.537 0.332750 2400 2 75% 65 0.479 0.33

1000 2400 2 100.0% 71.8 0.485 0.4361100 3600 3 73.4% 74.2 0.527 0.4441500 3600 3 100% 85 0.59 0.589


Variable Speed

Building Load GPM

Qty of Chillers

Chiller % Load ECWT

Chiller IKW/Ton

Chiller IKW/Ton

100 500 1 20% 65 0.954 0.548208 500 1 42% 65 0.619 0.358500 1200 1 100% 65 0.446 0.384550 1320 2 55% 65 0.537 0.332750 1800 2 75% 65 0.479 0.328

1000 2400 2 100% 71.8 0.485 0.4361100 2640 3 73.4% 74.2 0.527 0.4421500 3600 3 100% 85 0.59 0.589

VFD column better than constant speed column at every point!

* VFD was selected for same FL IKW/Ton – therefore a bit larger and $$$.


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Outline








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Minimum flow rate is 1.5 feet / second (intermittent) and 3.0 feet / second (extended)

Maximum flow rate is 12 feet / second.

Rate of change of flow can be up to 30% per minute.

Evaporator should be selected such that design flow rate is at least double the minimum flow rate (if equally sized chillers).

Evaporator flow rate and pressure drops must be carefully coordinated if unequally sized chillers.

VFD chiller selection guidelines for VPF applications.

VPF systems save pump energy – don’t forget to save on chiller energy too.

Remember – you can have both!


Documents

PRIMARY VFD AND CHILLER SYSTEM