understanding air -to-air energy recovery technologies · 3. identify different types of...

A Nortek Company

Understanding Air-to-Air Energy Recovery Technologies 22nd Annual Technical Conference: Shaping the Next… Lisa Gerspacher, A. Sc. T. Sales and Applications Engineering, Venmar CES

Presenter Biography

Lisa Gerspacher is in Sales and Applications Engineering at Venmar CES, Inc., an innovative manufacturer of cost-effective, energy efficient energy recovery solutions for the commercial ventilation market. She has spent nearly 10 years with the company starting her career in the Engineering and Design departments moving over to Sales 3 years ago. She works with the Sales Representative network on a daily basis assisting them with matching specifications and creating custom solutions for their application.

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Learning Objectives

1. Understand the fundamentals of heat and moisture transfer as they relate to different types air-to-air energy recovery devices.

2. Describe the key metrics used to evaluate different technologies and recognize the different psychometric processes associated with these technologies.

3. Identify different types of commercially available air-to-air energy recovery technologies that are commonly used in commercial applications (optionally understand the frost control strategies that are applicable) and where and when to apply them.

4. Recognize the maintenance implications of employing air-to-air energy recovery devices to ensure that equipment operates at peak performance and for long life.

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Ventilation Air

• The process of introducing outside air into occupied spaces for dilution of indoor pollutants

• Reduces occupant discomfort and complaints

• A well designed and ventilated area will result in high levels of human productivity and health

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Energy Recovery Ventilation

• The march towards net zero energy buildings and sustainability

• Economic pressures, escalating fuel costs and global financial crisis

• Increasingly stringent standards and guidelines

ERV provides the most cost-effective way to recycle waste energy and create quiet and comfortable indoor environments.

High Performance Buildings and the Green Economy

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ANSI/ASHRAE Standard 62.1-2013 Ventilation for Acceptable Indoor Air Quality

§5.16.1 Classification. Air (return, transfer, or exhaust) leaving each space or location shall be designated at an expected air quality classification not less than shown in Tables 5.16.1, 6.2.2.1, or 6.5. or as approved by the authority having jurisdiction.

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ANSI/ASHRAE Standard 62.1-2013 Ventilation for Acceptable Indoor Air Quality

§5.16.2 Redesignation

Excluding the provisions outlined in §5.16.2.1 Air Cleaning and §5.16.2.3 Ancillary Spaces a mixture of air is classified with the highest classification among the air classes mixed per §5.16.2.2 Transfer.

However, a certain amount of mixing is allowed without having to redesignate when air-to-air energy recovery is used under §5.16.3 Recirculation Limitations.

Exception: When using any energy recovery device, recirculation from leakage, carryover, or transfer from the exhaust side of the energy recovery device is permitted, provided that: Class 2 air shall not exceed 10% of the outdoor air intake flow and Class 3 air shall not exceed 5% of the outdoor air intake flow.

Class 4 air shall NOT be re-circulated or transferred to any space. 7

ANSI/ASHRAE/IESNA Standard 90.1-2013

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§ 6.5.6.1 Exhaust Air Energy Recovery Each fan system shall have an energy recovery system when the system’s supply airflow rate exceeds the value listed in Table 6.5.6.1-1 and Table 6.5.6.1-2, based on the climate zone and percentage of outdoor airflow rate at design conditions. Table 6.5.6.1-1 shall be used of all ventilation systems that operate less than 8,000 hours per year, and Table 6.5.6.1-2 shall be used for all ventilation systems that operate 8,000 or more hours per year.

ASHRAE Standard 90.1 DOE Climate Map

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Continuous and Non-continuous Ventilation

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ASHRAE Standard 84-2008 Method of Test for Air-to-Air Heat/Energy Exchangers

SPC 84-2008 – Revision project committee authorized 2/01/1995 with revised TPS. Revised TPS approved June 23, 2007 (Long Beach).

Purpose: • To establish a uniform method of test

• Specify the test conditions, data required, uncertainty analysis to be performed, calculations to be used and reporting procedures

• Specify the types of test equipment for performing such tests

• Is NOT a Ratings Program

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AHRI Standard 1060-2005 Performance Rating of Air-to-Air Heat Exchangers for ERV

Purpose: To establish definitions, test requirements, rating requirements, minimum data requirements for Published Ratings, marking and nameplate data and conformance conditions for Air-to-Air Heat Exchangers intended for use in Air-to-Air Energy Recovery Ventilation Equipment.

ARI Certification Program started in Q1 2001

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Old New

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Standard Rating Conditions

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AHRI Standard 1060-2005

Exhaust Air Transfer Ratio (EATR): Ratio of the tracer gas concentration difference between the Leaving Supply Airflow and the Entering Supply Airflow and the difference between the Entering Exhaust Airflow and the Entering Supply Airflow (expressed as percentage)

Outdoor Air Correction Factor (OACF): The Entering Supply Airflow divided by the measured Leaving Supply Airflow

Performance Rating of Air-to-Air Heat Exchangers for ERV

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Factors Affecting EATR and OACF Fan Placement and the Effect on EATR and OACF

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MIN-imizes OACF Provides reasonable EATR

Factors Affecting EATR and OACF Fan Placement and the Effect on EATR and OACF

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MAX-imizes OACF MIN-imizes EATR

Effectiveness Formulae 90.1 Effectiveness, Traditional Effectiveness and Net Effectiveness

90.1 Effectiveness Traditional Effectiveness Net Effectiveness

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X1 Supply Air (Entering)

X2 Supply Air (Leaving)

X4 Exhaust Air (Leaving)

X3 Exhaust Air (Entering)

Outdoor Air Correction Factor (OACF) Educate Yourself on the Impact

Outdoor Air Correction Factor: The Entering Supply Airflow divided by the measured (gross) Leaving Supply Airflow

Some Manufacturers can go as high as 1.70!

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Estimated Annual Increase in Fan Operating Cost

OACF = 1.02 OACF = 1.08 OACF = 1.15

San Francisco, CA ($0.13 kWh) $210 $839 $1,573

Miami, FL ($0.11/kWh) $177 $710 $1,331

Burlington, VT ($0.12/kWh) $194 $775 $1,452

Seattle, WA ($0.06/kWh) $97 $387 $726

Specification Verbiage

AHRI Certified Manufacturer

Energy transfer ratings shall be AHRI Certified to Standard 1060 and bear the AHRI certification seal for AHRI Air-to-Air Energy Recovery Ventilation Equipment Program based on AHRI 1060. Ratings “in accordance with 1060” without certification shall be deemed unacceptable.

Non-AHRI Certified Manufacturer

The Manufacturer shall provide certified performance data in accordance with ASHRAE Standard 84 and AHRI 1060. Independent performance test results shall be used to rate the product in accordance with the AHRI Air-to-Air Energy Recovery Ventilation Equipment Program.

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AHRI Certified Components http://www.ahridirectory.org

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Ideal Air-to-Air Energy Exchange

• Allows temperature-driven heat transfer between airstreams • Allows partial-pressure-driven moisture transfer between airstreams • Minimizes the additional amount of outside air required (OACF), while

maintaining an acceptable amount of exhaust air transfer (EATR) based on application requirements

• Optimizes energy recovery performance to minimize pressure drop, while providing reasonable cost, dimensions and weight

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Passive vs. Active Energy Recovery

Passive Systems:

No external energy source is required for heat transfer to take place.

Active Systems:

Continuous external energy input is required for heat transfer to take place.

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Passive vs. Active Energy Recovery

Passive Systems:

• Heat pipe • Fixed plate

Active Systems:

• Rotary wheel • Run-around loop • Twin towers

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Heat Pipe Heat Exchanger

Advantages: • No moving parts, low maintenance

• Size flexibility, ideal for retrofit

• A variety of performance enhancement strategies: tilt packages, pre-cooler re-heater, indirect and direct evaporative cooling

Considerations: • AHRI 1060 Certification

• Medium sensible effectiveness (45% to 65%)

• Installation sensitivity

• Medium cost

Theory of Operation: • Closed loop evaporation /

condensation cycle between the evaporator and condenser sections

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Heat Pipe Theory of Operation

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Performance Summary Heat Pipe Heat Exchanger

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Summer Comfort

Zone

RA (T3) EA (T4)

SA (T2) OA (T1) X1 Supply Air (Entering)




Performance Summary: • 57,355 Btu/h (4.78 tons)

• 51.5% Sensible Effectiveness

• 19.8% Total Effectiveness

• 33.03 RER Sensible

• 31.94 RER Total

at 5,000 cfm and ARI design conditions

Fixed Plate Heat Exchanger

Advantages:

• High sensible effectiveness (50% to 80%)

• Durable construction, high differential pressures

• No moving parts, low maintenance

• A variety of performance enhancement strategies are available: pre-cooler re-heater, indirect and direct evaporative cooling

Considerations:

• AHRI 1060 Certification

• High pressure drop and cost associated with counter-flow heat exchangers

• Large size at large volumetric flow rates

• NFPA 90A rating for polypropylene plates

Theory of Operation:

• Heat transfer occurs through a combination of conduction and convection within the channels

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Membrane Plates

Advantages:

• No moving parts, low maintenance

• Sensible and latent energy transfer

• Medium total effectiveness (50% to 73%)

• Low pressure drop and air leakage

Considerations:

• Fewer suppliers, although improving

• Enthalpy cores have lower latent effectiveness than equivalent wheel technology

• Should be used for applications where low EATR is desired and no moving parts are favored

• Depending on the volumetric flow rate, cores may become cost prohibitive

• Proper upstream filtration

• AHRI 1060 Certified performance and NFPA 90A


• Plates are manufactured with water-vapor-permeable materials, such as treated paper and microporous polymeric membranes

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Summer Comfort

Zone

RA (T3) EA (T4)

SA (T2) OA (T1)

Psychrometrics and Theory of Operation Aluminum Fixed Plate Heat Exchanger

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Performance Summary Aluminum Fixed Plate Heat Exchanger

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Summer Comfort

Zone

RA (T3) EA (T4)

SA (T2) OA (T1) X1 Supply Air (Entering)








• 35.75 RER Total


Performance Summary Heat and Moisture Membrane Plate Heat Exchanger

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Summer Comfort

Zone

RA (T3) EA (T4)

SA (T2) OA (T1)

EA (T4)

SA (T2)

X1 Supply Air (Entering)








• 37.58 RER Total

at 5,000 cfm and ARI design conditions and 4,000 fpm

Rotary Heat Exchanger

Advantages:

• High total effectiveness (up to 85%)

• Self-cleaning effect for counter-flow exchanger

• Available as sensible or enthalpy device

• Compact at large volumetric flow rates

• Low pressure drop

• Available in almost all ventilation systems

Considerations:

• AHRI 1060 Certification

• Possibility of carry over for critical applications


• Sensible heat is transferred through the substrate while latent energy is transferred as the medium adsorbs water vapor from the higher humidity airstream and desorbs moisture into the lower humidity airstream

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Anatomy of an Enthalpy Wheel

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The Need for Wheel Purge

• Purge significantly increases OACF, increasing energy costs

• Majority of applications – Dilution ventilation, Class I

EATR is not critical

– Class 2 air ≤10% EATR

– Class 3 air ≤ 5% EATR

• Source Control – Class 5 – Mechanical seals minimize

leakage; wear over time?

– For wheel, consider blow through draw through, but watch OACF

– Plates and heat pipes, peace of mind

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Psychrometrics and Theory of Operation Heat Wheel Heat Exchanger

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Summer Comfort

Zone

RA (T3)

EA (T4) SA (T2)

OA (T1)

Performance Summary Heat Wheel Heat Exchanger

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Summer Comfort

Zone

RA (T3)

EA (T4) SA (T2)

OA (T1) Performance Summary: • 207,560 Btu/h (17.30 tons)




• 119.10 RER Total


Typical Ranges for OACF and EATR

• OACF: 0.99 to 1.01 • EATR: 0 to 1%

Sensible Plates • OACF: 0.97 to 1.06 • EATR: 0 to 5% Membrane Plates • OACF: 0.97 to 1.06 • EATR: 0 to 5%

• OACF: 0.99 to 1.10 • EATR: 0.5 to 10% Highly dependent on differential pressures

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Standard Operation and Maintenance

• Filters • Dampers • Actuators • Fans • Motors • Water coils • Electric heaters

• Gas burners • Dx coils • Compressors • Water source heat pumps • Air source heat pumps • etc.

Typical Components in an AHU or RTU Requiring Maintenance

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Heat Pipe Heat Exchanger

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General:

• No moving parts, very robust

• Maintain proper upstream filtration

Cleaning:

• Once every 12 months or once every 6 months for dirty environments

• Use of hot water (less than 120°F) and mild detergents under pressure or compressed air

• If other cleaning solutions are used, must check for reactivity against aluminum

Considerations:

• Always check with the Manufacturer if you have questions about operations and maintenance

• Ensure full-length drain pans and access sections are present to allow usage of high pressure systems within the unit

• Dampers, performance enhancement strategies may require additional maintenance

Fixed Plated Heat Exchanger

General:

• No moving parts


• Check core tracks and seals for proper operation

Cleaning:


• Use of hot water and mild detergents, steam chemicals or compressed air

• Always verify for reactivity against aluminum

• HX can soak for 3 hours in warm water and mild detergent, and then rinse heavily under warm water

Considerations:


• Ensure full-length drain pans and access sections are present to allow usage of high pressure systems within the unit


Aluminum Plates

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General:

• No moving parts



Cleaning:


• Use of hot water and mild detergents or compressed air

• Steam chemicals are NOT recommended for cleaning the polypropylene flat plate heat exchanger

• Always verify for reactivity against polypropylene

Considerations:


• Ensure full length drain pans and access sections are present to allow usage of high pressure systems within the unit


Polypropylene Plates

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General:

• No moving parts



Cleaning:


• Use a vacuum cleaner or low pressure air to remove any buildup of debris

• Do not use solvents or detergents as these may damage the media or structure of the heat exchanger

Considerations:



Membrane Plates

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Energy Recovery Wheels

General:

• Self-cleaning effect for counter-flow exchange


• Wheel bearings, gearbox, set screws, motor, seals and belts

Cleaning:


• Use a vacuum cleaner or low pressure air to remove any buildup of debris

• Do not use solvents or detergents as these may damage the media or structure of the heat exchanger, although low pressure water or steam may be used with some Manufacturers

Considerations:



Hygroscopic Wheels

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Proper Care and Feeding

• Address potential issues in your specifications • Select the proper technology for your application • Have a good understanding of basic controls • Filtration, filtration, filtration • Allow for proper drainage and access • Always consult your Manufacturer if you have questions

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Frost Control Strategies

• Face and bypass defrost • Traversing defrost • Recirculation defrost • Exhaust only defrost • Pre-heat frost prevention • Variable speed defrost • Tilting base control

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Technology Specific Strategies

• Recirculation • Exhaust only • Pre-heat • Face and bypass • Tilt control

• Recirculation • Exhaust only • Pre-heat • Face and bypass • Traversing

• Recirculation • Exhaust only • Pre-heat • Face and bypass • Variable speed

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Face and Bypass

• Defrost is done by covering the face of the energy recovery technology and bypassing air

• If you have post-heating, make sure you upsize based on the OA temperature

• Gives you free cooling in summer applications

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Traversing Face and Bypass

• Similar to face and bypass, but is done with several banks of dampers

• Allows some energy recovery to be done

• So the heating does not have to be upsized to the OA conditions

• Allows free cooling option in the summer time

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VSD Defrost

• Defrost is done by decreasing the rotational speed of the rotor.

• If you have post-heating, make sure you upsize based on the OA temperature

• Gives you free cooling in summer applications

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Recirculation

• Cost-effective way to defrost • Turn off EA fan and open

recirculation damper • Does not do continuous

ventilation so you have to add about 25% more OA to compensate for the defrost times

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Exhaust Only

• Most cost-effective form of defrost

• Turns off the supply fan and shuts OA damper

• Puts a slight negative pressure on the building

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Pre-heat

• Usually done with electric, steam or hot water

• Allows for continuous ventilation, but uses a lot of energy

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Questions?

Meeting and exceeding high performance standards, codes and guidelines with air-to-air energy recovery systems and equipment. Any questions?

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In Conclusion

AHRI: http://ahrinet.org/

AHRI Certification: http://www.ahridirectory.org

TC 5.5 Air-to-Air Energy Recovery: http://tc55.ashraetcs.org/

ASHRAE Advanced Energy Design Guides: www.ashrae.org/freeaedg

AHRI Publications: http://www.ahrinet.org/ahri+publications.aspx

Useful References

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AHRI Standard 1060-2005: Performance Rating of Air-to-Air Heat Exchangers for ERV

AHRI Guideline V: Calculating the Efficiency of Energy Recovery Ventilation and Its Effect on Efficiency and Sizing of Building HVAC Systems

AHRI Guideline W: Selecting, Sizing and Specifying Packaged Air-to-Air Energy Recovery Ventilation Equipment (2005)

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