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Daniel Giguère, ASHRAE, Ste-Foy, February 2, 2009

Refrigeration

Technologies under development

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Themes

BackgroundFundamental principlesSecondary fluids Carbon dioxide refrigerantEjectors

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BackgroundFor the past 20 years, the refrigeration industry has been hit hard by the environmental impacts of synthetic refrigerants.

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Schedule for the Gradual Phase-Out of HCFCs

HCFC Production100.0%

65.0%

35.0%

10.0%0.5% 0.0%

0%

20%

40%

60%

80%

100%

1989 2004 2010 2015 2020 2030

In 2010, demand for HCFCs in the USA will exceed supply by 12.5 million kilograms in the refrigeration sector.

(U.S. Environmental Protection Agency)

No new R22 equipment

2,000,000 kg

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PRESERVATION OF THE OZONE LAYER AND THE EARTH’S CLIMATE SYSTEMQuestions about hydrofluorocarbons and perfluorocarbonsIPCC/TEAP, 2005 http://www.ipcc.ch/ipccreports/special-reports.htm

Refrigerant leaks projected using a bottom-up approach suggest an annual global emission rate of 30% of the stored load.

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GWP (PRG) of HFC Refrigerants

R404a = R125/143a/134aR410a = R32/125R507a = R125/143a

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Fundamental PrinciplesRefrigeration cycle

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Refrigeration Cycle

Pre

ssur

e

Enthalpy

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Definition of COP

Qf + W = 4 kW

Qf = 3 kW

W= 1 kW

Pre

ssur

e

Enthalpy

COP = Qf = 3W

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Secondary Fluids Indirect Refrigeration Systems

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Secondary Fluid

-25oF-20oF

-20oF

HFCs

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Secondary Fluid

-20oF

Secondary fluid

Secondary fluid

Refrigerant limited to the mechanical room

Mechanical room

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Advantages of Indirect Systems

1. Much less synthetic refrigerant

2. Better functioning

3. Much less complex

4. Lower maintenance costs

5. Increase in the quality and longevity of food products (for systems in supermarkets)

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Significant Reduction in Refrigerant

75 to 90% less synthetic refrigerant;

At about $10/lb, could correspond to over $25,000 for an average supermarket;

Dramatic reduction in the potential for refrigerant leaks.

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Better Operation

Less overheating of the compressor and therefore improved efficiency

Better possibility of installing sub-cooling; again, improved efficiency

More stable condensation pressure

Better controllability

No oil return problems

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Less Complex

Only one evaporator with two expansion valves, located in the mechanical room rather than 50 evaporators with as many expansion valves several dozens of metres away from itNo pressure regulators to adjust or control. Secondary fluid balancing valves adjusted at start-upLow-pressure piping (often pre-isolated in synthetic material)

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Less Expensive to Maintain

Refrigerant leaks are limited to the mechanical room and therefore easier to detect and less expensive

Overall maintenance costs can be reduced by almost 50% compared to a conventional direct expansion (DX) system (FMI Energy)

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Product Quality

Less product loss

A more stable product temperature (1oF rather than 2.5oF for DX)

Shorter defrost cycle

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The Disadvantages of Indirect Systems

Change

Expected loss of efficiency

Cost

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Change

Not common practiceNew design and assessment criteria to learn and applyMaking these changes must be planned far in advance (who is doing what?)Tenders from contractors do not reflect the anticipated benefitsThis job is added to the many tasks and responsibilities for all stakeholders in the construction project

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Expected Loss of Efficiency

Evaporation and condensation temperatures for secondary fluid systems are equal if not better than those for direct expansion (DX) systemsOverheating of compressors during suction is reduced to a minimumSub-cooling is very easy to integrate and it increases the refrigeration system’s efficiency by 10 to 25%The thermal inertia of the secondary fluid contributes to stabilizing the operation of the systemHeat recovery is more effective and can meet the heating load of a building

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Cost

There are several hundred installations in North AmericaThe design criteria and choice of materials are increasingly being masteredThe cost is still higher than that of a DX system, but the difference is decreasing with time and will soon become a standard in the refrigeration industryOperating costs are less than or equal to those of DX systems

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DX vs. Secondary Fluid

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Types of Secondary Fluids

Without phase changeEthylene glycol (heat rejection in the condenser)Propylene glycol (10 to 32oF)Potassium formate (-30 to 0oF)Other antifreezes

With phase changeCarbon dioxide (CO2) (-50 to +20oF)Slurry (water, methanol, glycol, etc.) (0 to 32oF)

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CO2: the Ideal Secondary FluidLiquid CO2 cools a fluid by evaporating in a

heat exchanger. A simple liquid pump is used to circulate the CO2

No corrosion Negligible pumping powerNo oil management problemsMinimal pipe diameterExceptional heat transfer features

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CO2: Breadboard Model-30°C, CO2 Test chamber

Air coil

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Slurries: the Secondary Fluid that Stores Energy

Slurry?Fine ice crystals (

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CO2: The Indispensable Refrigerant

http://www.r744.com/articles/2009-01-29-ashrae-winter-conference-r744-seminar.php

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Carbon Dioxide

Is present in the atmosphere in a proportion of 375 ppmv (parts per million in volume) The concentration is increasing rapidly, by about 2 ppmv/yearR744 is a natural refrigerant, like water, air, ammonia and hydrocarbons

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1850 199319601920 ----------1930

Golden age of CO2

Reinvention of CO2 in refrigeration

(G. Lorentzen) of NorwayInitial concept of CO2as a refrigerant (Alexander Twining, British patent)

Danfoss, Niels P Vestergaard Niels P Vestergaard Ver 2004-04-SI+US

First CO2 refrigeration system: Carle Linde

J&E Hall: first two-stage CO2 refrigeration system

CO2 transcritical cycle

CFCs invented, 1928

History of CO2

Montreal protocol

1Jan. 1, 1989

CO2 compressor

Around 1900

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88°F

1070

145

400

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0.33.42.1Saturated ΔT / ΔP = 1 psi at -40 [oF]2262436BTU/cubic foot at -40 [oF]16144137Boiling point at 400 psig [oF]

NOhighNOToxicity

1-3260Global Warming Potential GWP

1067/881640/270541/162Critical condition [psi/ oF]-69-28-51 Boiling point at 15 psig [oF]

NO(slightly)NOFlammability

000Ozone Depletion Potential ODPYESYESNONatural refrigerantCO2NH3R404ARefrigerant

Properties

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+86oF

Enthalpy

717- CO2 Cascade System

CO2

-4oF

+5oF

Pres

sure

Enthalpy

Pres

sure

CO2

R717

-40oF

-40oF (135 psi)

+5oF (333 psi)

+86oF (171 psi)

-4oF (28 psi)

-40oF

Danfoss, Niels P Vestergaard Niels P Vestergaard Ver 2004-04-SI+US

R717

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HFC - CO2 Cascade Systems

CO2

-4oF

+5oF

-40oF

-40oF

HFCs

-20oF

10oF20oF

20oF

HFCs

CO2

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CO2 as a Secondary Fluid

-25oF-20oF

-20oF

HFCs

NO OIL

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Transcritical CycleP

ress

ure

Enthalpy

The Eco-Cute hot water HP produces hot water at 180oF with a COP of 4 to 8!

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IndustrialCommercialStrong arguments

Why CO2?

EnvironmentGradual elimination of substances that have an impact on the environment (HCFCs, HFCs):(ODP (Ozone Depletion Potential), GWP (Global Warming Potential) )

SafetyToxicity and flammability for systems using large quantities of ammonia

Costs• Lower operating costs• More efficient systems • Lower refrigerant costs• Lower component volume

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ConclusionsIn the last 10 years, products available for applications using CO2 have become increasingly abundant. These applications cover all sectors.

Low-temperature refrigeration and heat pumps are especially appealing.

Operating pressures can be high, but the equipment is more compact and often more efficient.

It is a natural refrigerant that is safe and inexpensive.

Every refrigeration equipment manufacturer around the world is interested in CO2 as a refrigerant.

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Ejectors

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What is an Ejector?

Primary nozzle Secondary nozzle

Actuating or primary fluid

Entrained,or secondary fluid

Diffuser

No moving parts

Mixing zone

Ejectors convert kinetic energy into pressure and quantity of movement. It is a thermocompressor.

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Why Ejectors?

They are simple

They have no moving parts

They use no oil

There is a large variety of materials for building one

They can use any gas or refrigerant

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Weaknesses

Operation is not a very flexible

Low apparent efficiency

Not well known; used primarily for recompressing vapour

Complex design (supersonic flow)

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Applications

Using effluent as a source of energy for cooling

Or to recover heat through heat pumping

Trigeneration

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Trithermal Combined Cycle

TC

Generator

Evaporator

Condenser

Qevap

Free Qgen !

W

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Ejector Cycle Output

TC

wtwc

Qevap

Free Qgen !

W

Qgen

TC

Generator

Evaporator

Condenser

Qevap

W

ηeject = Qevap ≈ 0.5Qgen

Pre

ssur

e

Enthalpy

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Applications

Integration into the refrigeration cycle to recover the expansion energy and increase the COP

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Ejector Regulator

20oF

0oF

COP 26% higher

Pre

ssur

e

Enthalpy

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Applications

Integration into the refrigeration cycle to recover the condensation energy to increase the thermal discharge temperature, thereby making it useful for heat recovery or increasing the COP of the refrigeration system.

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Ejector Condenser

0oF

COP 20% higher

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5151

Thank you