development of centrifugal chiller and heat pump using...

© 2017 MITSUBISHI HEAVY INDUSTRIES THERMAL SYSTEMS, LTD. All Rights Reserved.

2017.5.17

Development of centrifugal chiller and heat pump using low GWP refrigerant

Ryosuke Suemitsu1*, Naoya Miyoshi1, Yasushi Hasegawa1,

Kazuki Wajima1, Yoshinori Shirakata1, Kenji Ueda1

1Mitsubushi Heavy Industries Thermal Systems, Ltd.

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Today’s Presentation

1. Introduction

2. Development of centrifugal chiller using low GWP refrigerant

3. Development of centrifugal heat pump using low GWP refrigerant

4. Conclusions

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1. Introduction

Paris Agreement (in December 2015, COP21)

Every country shall update and submit the own country’s reduction goal every 5 years.

Montreal Protocol “Kigali Revision” (in October 2016)

Mandatory of the HFC production and the step-by-step reduction

There is a need to transfer

to low GWP refrigerants.

1 5,000 100 1,000 (USRT)

Capacity(kW)

Centrifugal Chiller

Co

oli

ng

s

ou

rce

He

ati

ng

so

urc

e

Centrifugal heat pump

Shopping center/mall Clean room

Tall building Building

Capacity and temperature needs

1990s 2000s 2010s

ＨＦＣs （Ex. R-134a） GWP:100～4,000

Paris Agreement

Montreal Protocol (2016)

The next-generation

alternative refrigerant GWP: low

Transition of refrigerant

We use R-134a as the refrigerant of centrifugal chillers and heat pumps.

3.5 350 3,500

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1. Introduction

We need to take into consideration the following requirements to select alternative refrigerants;

Environmental conditions: GWP ≦ 150, ODP ≦ 0.001, allowable concentration ≧ 800 ppm.

Low toxicity and low flammability Physical properties: The design pressure must not be excessively high, because of the price of machines.

Cycle efficiency is equivalent to that of R-134a.

Cost

Refrigerant HFC Olefins

134a 1234yf 1234ze(E) 1233zd(E)

Global Warming Potential (GWP) ＊5thIPCC 1300 <1 <1 1

Ozone Depletion Potential (ODP) 0 0 0 0

Allowable concentration [ppm] 1000 500 800 800

Toxicity low low low low

Flammability non low low non

Safety class ＊ASHRAE34 A1 A2L A2L A1

Saturated pressure (@38℃)[kPaG] 861.9 866.4 624.3 100.8

Theoretical COP ＊@ET=5,CT=38,η＝0.9 6.58 6.31 6.56 6.93

Price / R-1233zd(E) rated value - 2.5 1.5 1

Comparison of R-134a and olefins

R-1234ze(E) and R-1233zd(E) meet our requirements.

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1. Introduction

We selected R-1234ze(E) and R-1233zd(E) for centrifugal chillers.

A R-1234ze(E) type has been developed

for the capacity from 300 to 5000 USRt.

A R-1233zd(E) type has been developed

for the capacity from 150 to 700 USRt.

There are still some candidate refrigerants for centrifugal heat pumps.

1234ze(E) 1233zd(E)

1 5,000 100 1,000 Capacity (USRT)

(kW)

Centrifugal Chiller

Co

oli

ng

s

ou

rce

H

ea

tin

g s

ou

rce

Centrifugal heat pump

Shopping center/mall Clean room

Tall building Building

Capacity and temperature needs

3.5 350 3,500

some candidate refrigerants

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R-1233zd(E)’s cycle efficiency is better than R-134a,

and the cost is better than R-1234ze(E).

However,

the specific gas volume

is about five times larger than R-134a.

Advanced and compact design is made

to replace with centrifugal chillers using R-1233zd(E).


134a 1234ze(E) 1233zd(E)

Standard boiling point [℃] −26.1 −19.0 18.3

Saturated pressure (@6℃)[kPaG] 260.7 167.3 −39.1

Saturated pressure (@38℃)[kPaG] 861.9 624.3 100.8

Saturated vapor specific volume (@6℃)[m3/kg] 0.056 0.069 0.277

Theoretical COP ＊@ET=5,CT=38,η＝0.9 6.58 6.56 6.93

Price / R-1233zd(E) rated value - 1.5 1

2. Development of centrifugal chiller

Refrigerant

Comparison of R-134a and olefins for chiller

R-1234ze(E)’s physical properties

are similar to R-134a.

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Compressor

Improvement of aerodynamic design

CFD analysis was performed to optimize the impeller, the inlet guide vane, and the path form of refrigerant gas.

Compared with R-134a,

the volume of compressor reduces to 140%.

the adiabatic efficiency is improved by 3% for the same capacity.

Refrigerant 134a 1233zd(E)

Saturated vapor specific volume (@6℃)[m3/kg] 0.056 0.277

About five times larger

Impeller

Inlet guide vane

Path of refrigerant gas

Outline drawing

of centrifugal compressor

Ref. inlet

Ref. outlet

Reduce

to 140%

compared

with R-134a


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Compressor

Direct-connected motor

For R-1233zd(E), the impeller is

directly mounted on the motor shaft,

For R-134a, the impeller is rotated

by the motor via a step-up gear.

as the lower vapor sound speed can be achieved

even if the capacity is same.

A compact compressor unit with a motor

Improved performance by reducing the losses as the result of eliminating the step-up gear and minimizing the number of compressor bearings


Refrigerant 134a 1233zd(E)

Saturated vapor sound speed (@6℃)[m/s] 146.7 135.8

Lower

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Evaporator and condenser

The shell & tube type heat exchanger, and flooded type evaporator Since the specific gas volume is larger, and the differential pressure between the condenser and evaporator is smaller than R-134a, pressure drop should be carefully considered.

We analyzed the actual chiller and measured the verification test

Evaporator Condenser


Inlet

Chilled water

Ref. outlet

Ref. inlet

Outlet

Inlet

Cooling water

Ref. outlet

Ref. inlet

Outlet

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Evaporator and condenser

Compared with R-134a,

The volume of the evaporator and condenser reduce to 120%.

The outside heat-transfer coefficient of evaporator registers no more than 10% decrease, and the coefficient of condenser registers no more than 20% decrease at the rated condition.

Test results of evaporator Test result of condenser


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Model Existing Developed

Rated capacity 200 USRt (703 kW)

Refrigerant R-134a R-1233zd(E)

Chilled water temp. 12.0°C → 7.0°C

Chilled water flow rate 120.7 m3/h

Cooling water temp. 32.0°C → 37.0°C

Cooling water flow rate 141.5 m3/h 139.6 m3/h

Power consumption 115.0 kW 111.3 kW

COP 6.1 6.3

Dimensions L×W×H 3.7×1.5×1.8 m 3.8×1.6×1.7 m

Installation area 5.55 m2 5.83 m2

Shipping weight 3.9 ton 4.3 ton

The COP is improved by 3% compared with an existing type that had the same capacity, under the rated capacity conditions.

The installation area reduces about 105% that of the existing type for the capacity from 150 to 700 USRt.

Model machine verification

＊machine rated value = 200 USRt

Test machine appearance


Comparison of specification

Performance Result

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3. Development of centrifugal heat pump

Industrial customers have required us heat pumps to use high temperature heat.

We have been developing a high temperature heat pump

heating pressurized water to the temperature from 160°C to 200°C

The target COP is 3.5 with the aim of boiler replacement.

Refrigerant

The operational temperature must be considered. This requires the following;

Stability at high temperature: Prevention of isomerization and decomposition.

Standard boiling point: The size of compressor should not be too small for the adiabatic efficiency. The design pressure should not be too high for the manufacturing.

Critical point: The critical temperature should be higher than the operating temperature to improve the efficiency of the cycle.

Lubricant oil

The lubricant oil must maintain the stability at high temperature, requiring the temperature-dependent viscosity and solubility in the refrigerant.

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134a 1234ze(E) 1233zd(E)

Standard boiling point [°C] -26.1 -19.0 18.3

Critical temperature [°C] 101.1 109.4 166.5

Saturated pressure (@90°C)[MPaA] 3.244 2.476 0.833

Saturated vapor specific volume (@30°C)[m3/kg]

0.0266 0.0328 0.1175

Theoretical COP ＊@ET=25,CT=91,η＝0.9 2.00 2.04 2.46


Test condition Result

R-1233zd(E)

: Mineral oil

Temperature [°C]

Duration [h]

Air/moisture [ppm]

Acid Value [kOH/g]

50:50 150 168 100/100 <0.01

50:50 150 168 500/100 <0.01

50:50 150 168 1000/1000 0.03

50:50 200 168 500/1000 0.02

50:50 200 336 500/1000 0.01

R-1233zd(E) meets our requirements

Stability: at up to 150°C

but, poor at 200°C…

We still have

some candidate refrigerants.

Mineral oil was selected

Stability of R-1233zd(E): Thermal stability for 90°C applications

Enough solubility and viscosity: Kinetic viscosity and solubility are 125% and 112%, compared with requirements for the bearings of up to 160°C applications.

Refrigerant and lubricant oil First step; We investigated the replacement with a low GWP refrigerant in a 90°C application.

Accelerated thermal stability testing for 90°C applications

Comparison of R-134a and olefins for 90°C applications

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Aerodynamic shape of compressor The compressor was designed for a high head and large volume flow rate

to reduce the number and the capacity.

The compression ratio is larger by 40%, compared with a chiller.

The flow rate is larger by 39%, and

the adiabatic efficiency is improved by 3.5%, compared with an existing type.


Equipment design Heat pump cycle

We adopted the compression bleeding cycle for the temperature from 160°C applications.

The bleeding cycle is highly efficient

by using some of the refrigerant gas

to discharge from the low stage compressor

for intermediate heating.

The compressors have two-stages compression. Two-stage compression bleeding cycle

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Future work

The heat pumps operating at high temperature using low GWP refrigerants are going to be developed through the stages, 90°C, 160°C, 200°C.

The development of refrigerants and lubricant oil are being conducted in parallel with that of the heat pump.

We focus to introduce a model to heat pressurized water to 200°C in practical applications by 2023.

Application

Heat pumps heating water to the temperature from 160°C to 200°C are suitable for industrial applications, for example, chemical reaction and dried processes.

We have been investigating the details to propose a heat system for industrial processes. ex) heat and energy balance operating time temporal axis of thermal demand and heat source

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4. Conclusions and Acknowledgements

A centrifugal chiller using low GWP refrigerant have been developed.

A R-1234ze(E) type have been developed for the capacity from 300 to 5000 USRt.

A R-1233zd(E) type have been developed for the capacity from 150 to 700 USRt.

A centrifugal heat pump using a low GWP refrigerant is being developed.

In the experiments, R-1233zd(E) was selected for a heat pump heating water to 90°C. The design have been completed and we are preparing for drop-in testing.

The developments of heat pumps heating water to 90°C, and higher temperatures are going to be carried out, with a final goal of operation at 200°C.

This work is supported by New Energy and Industrial Technology Development

Organization(NEDO).

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