Energy recovery ventilation

Short description: Uses the energy in air exhausted from a building to treat the incoming air

counter-flow cross-plate energy recovery heat exchanger

Energy recovery ventilation (ERV) is the energy recovery process in residential and commercial HVAC systems that exchanges the energy contained in normally exhausted air of a building or conditioned space, using it to treat (precondition) the incoming outdoor ventilation air. The specific equipment involved may be called an Energy Recovery Ventilator, also commonly referred to simply as an ERV.[1]

During the warmer seasons, an ERV system pre-cools and de-humidifies the intake air; during cooler seasons the system humidifies and pre-heats the incoming air.[2] The exchange of humidity across the intake and exhaust airflows is the main differentiating factor in how an ERV operates as compared to a standard residential heat recovery ventilator (HRV), which does not allow the transfer of humidity between the airstreams.[3]

An ERV system helps HVAC systems design meet ventilation and energy standards (e.g., ASHRAE), improves indoor air quality, and reduces total HVAC equipment loads, thereby reducing energy consumption.

ERV systems enable an HVAC system to maintain a 40-50% indoor relative humidity, essentially in all conditions. ERV's must use power for a blower to overcome the pressure drop in the system, hence incurring a slight energy demand.[2]

## Contents

* 1 Importance
* 2 Methods of transfer
* 3 Efficiency
* 4 Types of energy recovery devices
* 5 Rotary air-to-air enthalpy wheel
* 6 Plate heat exchanger
* 7 References
* 8 External links

## Importance

Nearly half of global energy is used in buildings,[4] and half of heating/cooling cost is caused by ventilation when it is done by the "open window" method [definition needed] according to the regulations[citation needed]. Secondly, energy generation and grid is made to meet the peak demand of power. To use proper ventilation; recovery is a cost-efficient, sustainable and quick way to reduce global energy consumption and give better indoor air quality (IAQ) and protect buildings, and environment.

## Methods of transfer

An ERV is a type of air-to-air heat exchanger that transfers sensible heat as well as latent heat. Because both temperature and moisture are transferred, ERVs are described as total enthalpic devices. In contrast, a heat recovery ventilator (HRV) can only transfer sensible heat. HRVs can be considered sensible only devices because they only exchange sensible heat. In other words, all ERVs are HRVs, but not all HRVs are ERVs. It is incorrect to use the terms HRV, AAHX (air-to-air heat exchanger), and ERV interchangeably.[5]

During the cooling season, the system works to cool and dehumidify the incoming, outside air. To do this, the system takes the rejected heat and sends it into the exhaust airstream. Subsequently, this air cools the condenser coil at a lower temperature than if the rejected heat had not entered the exhaust airstream. During the heating seasons, the system works in reverse. Instead of discharging the heat into the exhaust airstream, the system draws heat from the exhaust airstream in order to pre-heat the incoming air. At this stage, the air passes through a primary unit and then into the space being conditioned. With this type of system, it is normal during the cooling seasons for the exhaust air to be cooler than the ventilation air and, during the heating seasons, warmer than the ventilation air. It is for this reason the system works efficiently and effectively. The coefficient of performance (COP) will increase as the conditions become more extreme (i.e., more hot and humid for cooling and colder for heating).[6]

## Efficiency

The efficiency of an ERV system is the ratio of energy transferred between the two air streams compared with the total energy transported through the heat exchanger.[7][8]

With the variety of products on the market, efficiency will vary as well. Some of these systems have been known to have heat exchange efficiencies as high as 70-80% while others have as low as 50%. Even though this lower figure is preferable to the basic HVAC system, it is not up to par with the rest of its class. Studies are being done to increase the heat transfer efficiency to 90%.[7]

The use of modern low-cost gas-phase heat exchanger technology will allow for significant improvements in efficiency. The use of high conductivity porous material is believed to produce an exchange effectiveness in excess of 90%, producing a five times improvement in energy recovery.[7]

The Home Ventilating Institute (HVI) has developed a standard test for any and all units manufactured within the United States. Regardless, not all have been tested. It is imperative to investigate efficiency claims, comparing data produced by HVI as well as that produced by the manufacturer. (Note: all units sold in Canada are placed through the R-2000 program, a standard test equivalent to the HVI test).[8]

## Types of energy recovery devices

Energy recovery device  | Type of transfer

|

Rotary enthalpy wheel | Total & sensible
Fixed plate | Total** & sensible
Heat pipe | Sensible
Run around coil  | Sensible
Thermosiphon | Sensible
Twin towers[9] | Sensible

**Total energy exchange only available on hygroscopic units and condensate return units

## Rotary air-to-air enthalpy wheel

Main article: Engineering:Thermal wheel

The rotating wheel heat exchanger is a rotating cylinder filled with an air permeable material, typically polymer, aluminum, or synthetic fiber, providing the large surface area required for the sensible enthalpy transfer. (Enthalpy is a measure of heat.) As the wheel rotates between the supply and exhaust air streams it picks up heat energy and releases it into the colder air stream. The driving force behind the exchange is the difference in temperatures between the opposing air streams (the thermal gradient).

The enthalpy exchange is accomplished through the use of desiccants. Desiccants transfer moisture through the process of adsorption which is predominately driven by the difference in the partial pressure of vapor within the opposing air-streams. Typical desiccants consist of silica gel, and molecular sieves.

Enthalpy wheels are the most effective devices to transfer both latent and sensible heat energy. Choice of construction materials for the rotor, most commonly polymer, aluminum, or fiberglass, determines durability.

When using rotary energy recovery devices the two air streams must be adjacent to one another to allow for the local transfer of energy. Also, there should be special considerations paid in colder climates to avoid wheel frosting. Systems can avoid frosting by modulating wheel speed, preheating the air, or stop/jogging the system.

## Plate heat exchanger

Main article: Physics:Recuperator

Fixed plate heat exchangers have no moving parts, and consist of alternating layers of plates that are separated and sealed. Typical flow is cross current and since the majority of plates are solid and non permeable, sensible only transfer is the result.

The tempering of incoming fresh air is done by a heat or energy recovery core. In this case, the core is made of aluminum or plastic plates. Humidity levels are adjusted through the transferring of water vapor. This is done with a rotating wheel either containing a desiccant material or permeable plates.[10]

Enthalpy plates were introduced in 2006 by Paul, a special company for ventilation systems for passive houses. A crosscurrent countercurrent air-to-air heat exchanger built with a humidity permeable material. Polymer fixed-plate countercurrent energy recovery ventilators were introduced in 1998 by Building Performance Equipment (BPE), a residential, commercial, and industrial air-to-air energy recovery manufacturer. These heat exchangers can be both introduced as a retrofit for increased energy savings and fresh air as well as an alternative to new construction. In new construction situations, energy recovery will effectively reduce the required heating/cooling capacity of the system. The percentage of the total energy saved will depend on the efficiency of the device (up to 90% sensible) and the latitude of the building.

Due to the need to use multiple sections, fixed plate energy exchangers are often associated with high pressure drop and larger footprints. Due to their inability to offer a high amount of latent energy transfer these systems also have a high chance for frosting in colder climates.

The technology patented by Finnish company RecyclingEnergy Int. Corp.[11] is based on a regenerative plate heat exchanger taking advantage of humidity of air by cyclical condensation and evaporation, e.g. latent heat, enabling not only high annual thermal efficiency but also microbe-free plates due to self-cleaning/washing method. Therefore the unit is called an enthalpy recovery ventilator rather than heat or energy recovery ventilator. Company´s patented LatentHeatPump is based on its enthalpy recovery ventilator having COP of 33 in the summer and 15 in the winter.

## References

1. ↑ "All About Residential Air Exchangers - Your #1 Guide to Air Exchangers" (in en). https://bphsales.ca/blogs/indoor-air-quality/air-exchangers.
2. ↑ 2.0 2.1 Dieckmann, John. "Improving Humidity Control with Energy Recovery Ventilation." ASHRAE Journal. 50, no. 8, (2008)
3. ↑ "All About Residential Air Exchangers - Your #1 Guide to Air Exchangers" (in en). https://bphsales.ca/blogs/indoor-air-quality/air-exchangers.
4. ↑ "2.3 The buildings sector - InterAcademy Council". http://www.interacademycouncil.net/CMS/Reports/11840/11914/11920.aspx.
5. ↑ The Healthy House Institute. Staff. "ERV". Understanding Ventilation: How to Design, Select, and Install Residential Ventilation Systems. June 4, 2009. December 9, 2009.
6. ↑ Braun, James E, Kevin B Mercer. "Symposium Papers - OR-05-11 - Energy Recovery Ventilation: Energy, Humidity, and Economic Implications - Evaluation of a Ventilation Heat Pump for Small Commercial Buildings." ASHRAE Transactions. 111, no. 1, (2005)
7. ↑ 7.0 7.1 7.2 Pulsifer, J. E., A. R. Raffray, and M. S. Tillack. "Improved Performance of Energy Recovery Ventilators Using Advanced Porous Heat Transfer Media." UCSD-ENG-089. December 2001.
8. ↑ 8.0 8.1 Christensen, Bill. “Sustainable Building Sourcebook.” City of Austin’s Green Building Program. Guidelines 3.0. 1994.
9. ↑ "Chapter 44: Air-Air Energy Recovery". ASHRAE Systems and Equipment Handbook. American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE). July 2000. p. 44.17. ISBN 978-1883413804. http://reverseflow.com/wp-content/uploads/2013/05/ASHRAE-Chapter-44.pdf.
10. ↑ Huelman, Pat, Wanda Olson. Common Questions about Heating and Energy Recovery Ventilators University of Minnesota Extension. 1999. 2010.
11. ↑ Recycling Energy

## External links

* Delta's PM2.5 Energy Recovery Ventilator (ERV)
* http://www.engineeringtoolbox.com/heat-recovery-efficiency-d_201.html
* Designing Dedicated Outdoor Air Systems, Stanley A. Mumma
* http://www.lowkwh.com \- energy recovery methods and publications
* http://www.UltimateAir.com
* Energy and Heat Recovery Ventilators (ERV/HRV)
* Heat Recovery Ventilation TANGRA

* v
* t
* e

Heating, ventilation, and air conditioning

Fundamental concepts|

* Air changes per hour
* Bake-out
* Building envelope
* Convection
* Dilution
* Domestic energy consumption
* Enthalpy
* Fluid dynamics
* Gas compressor
* Heat pump and refrigeration cycle
* Heat transfer
* Humidity
* Infiltration
* Latent heat
* Noise control
* Outgassing
* Particulates
* Psychrometrics
* Sensible heat
* Stack effect
* Thermal comfort
* Thermal destratification
* Thermal mass
* Thermodynamics
* Vapour pressure of water

Technology|

* Absorption refrigerator
* Air barrier
* Air conditioning
* Antifreeze
* Automobile air conditioning
* Autonomous building
* Building insulation materials
* Central heating
* Central solar heating
* Chilled beam
* Chilled water
* Constant air volume (CAV)
* Coolant
* Dedicated outdoor air system (DOAS)
* Deep water source cooling
* Demand-controlled ventilation (DCV)
* Displacement ventilation
* District cooling
* District heating
* Electric heating
* Energy recovery ventilation (ERV)
* Firestop
* Forced-air
* Forced-air gas
* Free cooling
* Heat recovery ventilation (HRV)
* Hybrid heat
* Hydronics
* HVAC
* Ice storage air conditioning
* Kitchen ventilation
* Mixed-mode ventilation
* Microgeneration
* Natural ventilation
* Passive cooling
* Passive house
* Radiant heating and cooling system
* Radiant cooling
* Radiant heating
* Radon mitigation
* Refrigeration
* Renewable heat
* Room air distribution
* Solar air heat
* Solar combisystem
* Solar cooling
* Solar heating
* Thermal insulation
* Underfloor air distribution
* Underfloor heating
* Vapor barrier
* Vapor-compression refrigeration (VCRS)
* Variable air volume (VAV)
* Variable refrigerant flow (VRF)
* Ventilation

Components|

* Air conditioner inverter
* Air door
* Air filter
* Air handler
* Air ionizer
* Air-mixing plenum
* Air purifier
* Air source heat pumps
* Automatic balancing valve
* Back boiler
* Barrier pipe
* Blast damper
* Boiler
* Centrifugal fan
* Ceramic heater
* Chiller
* Condensate pump
* Condenser
* Condensing boiler
* Convection heater
* Compressor
* Cooling tower
* Damper
* Dehumidifier
* Duct
* Economizer
* Electrostatic precipitator
* Evaporative cooler
* Evaporator
* Exhaust hood
* Expansion tank
* Fan coil unit
* Fan filter unit
* Fan heater
* Fire damper
* Fireplace
* Fireplace insert
* Freeze stat
* Flue
* Freon
* Fume hood
* Furnace
* Furnace room
* Gas compressor
* Gas heater
* Gasoline heater
* Geothermal heat pump
* Grease duct
* Grille
* Ground-coupled heat exchanger
* Heat exchanger
* Heat pipe
* Heat pump
* Heating film
* Heating system
* High efficiency glandless circulating pump
* High-efficiency particulate air (HEPA)
* High pressure cut off switch
* Humidifier
* Infrared heater
* Inverter compressor
* Kerosene heater
* Louver
* Mechanical fan
* Mechanical room
* Oil heater
* Packaged terminal air conditioner
* Plenum space
* Pressurisation ductwork
* Process duct work
* Radiator
* Radiator reflector
* Recuperator
* Refrigerant
* Register
* Reversing valve
* Run-around coil
* Scroll compressor
* Solar chimney
* Solar-assisted heat pump
* Space heater
* Smoke exhaust ductwork
* Thermal expansion valve
* Thermal wheel
* Thermosiphon
* Thermostatic radiator valve
* Trickle vent
* Trombe wall
* Turning vanes
* Ultra-low particulate air (ULPA)
* Whole-house fan
* Windcatcher
* Wood-burning stove

Measurement
and control|

* Air flow meter
* Aquastat
* BACnet
* Blower door
* Building automation
* Carbon dioxide sensor
* Clean Air Delivery Rate (CADR)
* Gas sensor
* Home energy monitor
* Humidistat
* HVAC control system
* Intelligent buildings
* LonWorks
* Minimum efficiency reporting value (MERV)
* OpenTherm
* Programmable communicating thermostat
* Programmable thermostat
* Psychrometrics
* Room temperature
* Smart thermostat
* Thermostat
* Thermostatic radiator valve

Professions, trades,
and services|

* Architectural acoustics
* Architectural engineering
* Architectural technologist
* Building services engineering
* Building information modeling (BIM)
* Deep energy retrofit
* Duct leakage testing
* Environmental engineering
* Hydronic balancing
* Kitchen exhaust cleaning
* Mechanical engineering
* Mechanical, electrical, and plumbing
* Mold growth, assessment, and remediation
* Refrigerant reclamation
* Testing, adjusting, balancing

Industry organizations|

* ACCA
* AHRI
* AMCA
* ASHRAE
* ASTM International
* BRE
* BSRIA
* CIBSE
* Institute of Refrigeration
* IIR
* LEED
* SMACNA

Health and safety|

* Indoor air quality (IAQ)
* Passive smoking
* Sick building syndrome (SBS)
* Volatile organic compound (VOC)

See also|

* ASHRAE Handbook
* Building science
* Fireproofing
* Glossary of HVAC terms
* World Refrigeration Day

* Template:Home automation
* Template:Solar energy

pl:Rekuperator

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