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INTRODUCTION

Two technologies used in climate chambers for heating/cooling will be discussed today:

PELTIER TECHNOLOGY COMPRESSOR TECHNOLOGY

1. Difference between the two technologies2. Advantages and disadvantages3. Ideal cooling unit for laboratory applications

PHYSICAL PRINCIPLES | THERMOELECTRIC EFFECTS

Energy converters such as thermoelectric elements are used to generate electricity and thermoelectric cooler (TEC – called Peltíer elements) are used for heating and cooling.

This is based off the “Seebeck effect” from Thomas Johann Seebeck (German Physicist) observed 200 years ago.

PHYSICAL PRINCIPLES | THERMOELECTRIC EFFECTS

End point made of two different materials of a conductor heatedElectrons diffuse to the cold side through thermodiffusionTemperature gradient creates thermoelectric voltageElectrical current flows when circuit is closed

PELTIER PRINCIPLES | PELTIER ELEMENT

In 1834 Jean Peltier (French physicist) discovered the Peltier effect based on the Seebeck effect.

Working principle: In an electrical circuit, a temperature difference is created at the contact points of two differently conducting materials – one side becomes cold, the other side warm.

Commercially successful applications only emerged with the development of the semiconductors. Their resistance decreases with increasing temperature and conductivity increases. In modern thermocouples, predominantly differently doped semiconductors are used.

PHYSICAL PRINCIPLES | FUNCTIONAL PRINCIPLE OFA PELTIER ELEMENT

Peltier element works like a heat pumpEnergy is pumped from the cold to the hot sideWaste heat expelled on the hot side is the result of the electrical energy supplied and the cooling capacityBy reversing the polarity of the current, the hot and cold sides can be reversedWhen direct current flows through the Peltier element, a temperature difference builds upThe cold side of the Peltier element extracts from the environment and releases it to the opposite side

PHYSICAL PRINCIPLES | COOLING CAPACITY OFA PELTIER ELEMENT

The actual cooling capacity is reduced1. due to the lost heat (increases quadratically with

the current intensity).2. due to the heat reflux to the cold side

(proportional to the thermal conductivity of the material and the temperature difference).

Peltier units are integrated into cooling units.The waste heat must be removed as efficiently as possible.This is done with demand-controlled internal/ external fans and a sufficiently dimensioned cooling element.

Objectives achieved:• avoid overheating of the Peltier elements• optimize efficiency• enable greatest possible temperature difference

between the cold and hot sides

PHYSICAL PRINCIPLES | STRUCTURE OF A PELTIER ELEMENT

PHYSICAL PRINCIPLES | FUNCTIONAL PRINCIPLE OFA REFRIGERATION MACHINE

• Thermal energy required during transition from the liquid to the gaseous aggregate state

• Refrigerant circulates through the machine piping system• Refrigerant absorbs heat from introduced sampled or food

in the evaporator• Compressor compresses the refrigerant under high

pressure• Condenser on the exterior of the unit releases heat to the

environment• Refrigerant cools down and changes into liquid state• Pressure is reduced again in the throttle valve• Boiling point drops & process starts again

PELTIER TECHNOLOGY FOR LABORATORY APPLICATIONS

• Peltier for heating and cooling in cooled incubator and climate chamber• No air exchange between the chamber and the environment• Condensation during the cooling process occurs on the heat sink – not

somewhere in the chamber• Fans integrated in the Peltier elements (inside and outside of the

chamber) ensure rapid transport of energy and optimal temperature distribution

• HPPeco and IPPeco appliances launched beginning of 2021 expand energy-efficient operation across the entire temperature range

PELTIER TECHNOLOGY FOR LABORATORY APPLICATIONS

Comparison of energy consumption of Memmert constant climate chambers HPPeco with Advanced Peltier Technology (introduced in 2021) with comparable appliances on the market

ADVANTAGES OF PELTIER TECHNOLOGY

More compact since no additional installation space needed for refrigeration machineAlmost vibration-free and very low-noiseLack of refrigerant is much more climate friendlyNo more need for a dedicated heat sourceTemperature cycles can be run with the same heating-cooling unitReacts immediately and without cooling medium as everything is electrically operated with extreme high accuracy

COMPRESSOR TECHNOLOGY FOR LABORATORY APPLICATIONS

• Memmert cooled incubator ICP and climate chamber ICH have a closed system

• Arrangement of the cooling unit and heating in a circulating air jacket prevents the occurrence of „hot and cold spots“ as well as dehumidification of the working space

• Defrosting cycles counteract the icing up of the evaporator

• Targeted and controlled dehumidification takes place in the climate chamber via Peltier humidity traps on the rear wall Air jacket temperature control system in the Memmert

cooled incubator ICP and climate chamber ICH

AIR JACKET TEMPERATURE CONTROL SYSTEM | HEATING

Closed air jacketLarge-area all-round heatingVery good temperature distributionPrevention of hot/ cold spotsNo contact between the medium and the heating chamberAdjustable recirculation fan

Identical conditions for all samples in the entire interior

AIR JACKET TEMPERATURE CONTROL SYSTEM | COOLING

Closed air jacketLarge-area all-round coolingVery good temperature distributionPrevention of hot/ cold spotsNo contact between the medium and the heating chamberAdjustable recirculation fan

Identical conditions for all samples in the entire interior

ADVANTAGES OF COMPRESSOR TECHNOLOGY

Higher heat compensation (specially while frequently opening the door, additional heat emission from load) unlike the Peltier-cooled unitEspecially designed for applications introducing heat into the working space, i.e. electronic assemblies or halogen lamps

DECIDING FACTORS

Temperature homogeneity and consistencyHeating and recovery timeLow sound pollution and noise levelAmbient temperature and temperature rangeRefrigerant and global warming considerationService and maintenance

DECIDING FACTORS | TEMPERATURE HOMOGENEITY AND CONSISTENCY

Temperature consistency (temperature variation in time):Deflection of the measuring point with the largest temperature variation in time

Temperature homogeneity (temperature uniformity):Difference between the temperature variation in time averages of the two measuring points with the most different results

Measuring setup with 27 measuring points for appliances with more than 50 litres working volume according to DIN 12880:2007

DECIDING FACTORS | HEATING AND RECOVERY TIME

Rapid heating, cooling and recovery times are important when cooled incubators are opened several times in daily practice, causing the temperature in the interior to rise.

According to DIN 12880:2007, measurements are taken until 100 % minus mentioned tolerance according to DIN 12880:2007 of the set temperature is reached; the actual temperature is not allowed to exceed defined limit deviations from this point.

Determination of the heating up time of a heating oven as an example for 180 °C according to DIN 12880:2007

DECIDING FACTORS | LOW SOUND POLLUTION AND NOISE LEVEL

• Sound pressure level expressed in dB (A) determined according to DIN EN ISO 3743-1:2010

• Peltier-cooled appliances have advantages in terms of both noise and vibrations

• Vibrations in a compressor-cooled incubator are primarily due to the compressor, the noise is from solenoid valves and condenser fans

DECIDING FACTORS | AMBIENT TEMPERATURE ANDTEMPERATURE RANGE

• In Peltier units, the waste heat is expelled by the external installed fan• Peltier units still function reliably up to a temperature difference of

approximately 25 K above ambient (at an ambient temperature of 25 °C for sure 0 °C inside the chamber will be reached)

• Compressor appliances can safely reach temperatures below freezing – with the limitation of the permissible ambient temperature

DECIDING FACTORS | REFRIGERANT AND GLOBALWARMING CONSIDERATION

• Ability to cool without refrigerant is one of the greatest advantages of the Peltier technology

• Compressor appliances use different refrigerants which contribute to global warming to greater or lesser extend when released

• GWP value (Global Warming Potential) serves as a guide – it relates refrigerant to climate-neutral CO2

Example: The CO2 equivalent of R134a refrigerant is 1430 over a 100-year period. One kilogram of the refrigerant R134a contributes 1,430 as much to the greenhouse effect within the first 100 years of its release as one kilogram CO2.

DECIDING FACTORS | SERVICE AND MAINTENANCE

Peltier devices are• simple in design• not required the handle the refrigerants• less complicated to maintaincompared to their compressor-cooled counterparts.

APPLICATIONS FOR CLIMATE CHAMBER | ICH GUIDELINES Q1A (R2) and Q1B

Q1A (R2)• This guideline describes the controlled storage conditions (temperature and humidity) and the storage period for

stability tests of active substances (API) and finished pharmaceutical products for long term stability tests and packing of same for transport/storage in different climate zones on earth.

• The chemical-physical stability after the end of the tests enables statements to be made about the shelf life and the storage conditions.

Q1B• With a lighting unit combining daylight lamps and UV light, additional testing can be conducted under ICH

Guidelines Q1B, Option 2 (Photostability).• A climate chamber with controllable temperature, humidity and separately controllable illumination for daylight

and UV light, the possibility can be kept open to also test photostability for defined humidities.• The high flexibility in testing and the low heat input from the illumination units compared with the xenon lamps

under Option 1 speaks in favor of these appliances.

APPLICATIONS FOR CLIMATE CHAMBER |STABILITY AND CLIMATE TESTS

Main advantages of the compressor climate chamber: High level of flexibility with a wide range of requirements: • temperature ranges from minus to plus• photostability tests in combination with many temperature-humidity

combinations• alternating tests• heat compensation at Q1B

Main advantages of the Peltier climate chamber:• at constant storage climate high energy efficiency• lower likelihood of failure of the Peltier elements• quiet operation

APPLICATIONS FOR CLIMATE CHAMBER |PROTEIN CRYSTALLOGRAPHY

Main advantages of the Peltier-cooled incubator:• Almost vibration-free and low-noise operation• High-precision control

APPLICATIONS FOR COOLED INCUBATOR |MODEL ORGANISMS

Main advantages of the Peltier-cooled incubator in cultivating zebrafish:• Almost vibration-free and low-noise operation

Main advantages of the compressor-cooled incubator in cultivating Drosophila:• Reliable temperature ramps

APPLICATIONS FOR COOLED INCUBATOR |SWING TESTS

Main advantages of the compressor-cooled incubator:• Rapid heating up and cooling down times• Rapid and precise alternating from heating up to cooling down phases• More economical energy consumption• Suitable for high temperature differences

APPLICATIONS FOR COOLED INCUBATOR |CULTIVATION, MICROBIOLOGICAL TESTS, GERM COUNT DETERMINATION

Main advantages of the Peltier-cooled incubator:• Compact design• Low-noise operation• More economical energy consumption

Main advantages of the compressor-cooled incubator:• Rapid heating up and cooling down times• Fast recovery times

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