Editing Heat recovery ventilation (section)

==Types==
=== Thermal wheel ===
{{Excerpt|Thermal wheel}}

=== Fixed plate heat exchanger ===
{{main|Recuperator}}

[[File:Heat exchanger.svg|thumb|280x280px|Types of [[heat exchanger]]s.{{citation needed|date=April 2022|reason=Source needed for efficiencies.}}|alt=]]

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.<ref>Huelman, Pat, Wanda Olson. [http://www.extension.umn.edu/distribution/housingandclothing/dk7284.html Common Questions about Heating and Energy Recovery Ventilators] {{webarchive|url=https://web.archive.org/web/20101230120234/http://www.extension.umn.edu/distribution/housingandclothing/DK7284.html |date=2010-12-30 }} University of Minnesota Extension. 1999. 2010.</ref>

Enthalpy plates were introduced in 2006 by Paul, a special company for ventilation systems for [[passive house]]s. 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 of frosting in colder climates.

The technology patented by Finnish company RecyclingEnergy Int. Corp.<ref>[http://www.recyclingenergy.com Recycling Energy]</ref> 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.

Fixed plate [[heat exchangers]] are the most commonly used type of heat exchanger and have been developed for 40 years. Thin metal plates are stacked with a small spacing between plates. Two different air streams pass through these spaces, adjacent to each other. Heat transfer occurs as the temperature transfers through the plate from one air stream to the other. The efficiency of these devices has reached 90% sensible heat efficiency in transferring sensible heat from one air stream to another.<ref>{{Cite journal|last1=Nielsen|first1=Toke Rammer|last2=Rose|first2=Jørgen|last3=Kragh|first3=Jesper|date=February 2009|title=Dynamic model of counter flow air to air heat exchanger for comfort ventilation with condensation and frost formation|journal=Applied Thermal Engineering|volume=29|issue=2–3|pages=462–468|doi=10.1016/j.applthermaleng.2008.03.006|bibcode=2009AppTE..29..462N |issn=1359-4311}}</ref> The high levels of efficiency are attributed to the high heat transfer coefficients of the materials used, operational pressure and temperature range.<ref name=":1"/>

=== Heat pipes ===
[[Heat pipe]]s are a heat recovery device that uses a multi-phase process to transfer heat from one air stream to another.<ref name=":1" /> Heat is transferred using an evaporator and condenser within a wicked, sealed pipe containing a fluid which undergoes a constant phase change to transfer heat. The fluid within the pipes changes from a fluid to a gas in the evaporator section, absorbing the thermal energy from the warm air stream. The gas condenses back to a fluid in the condenser section where the thermal energy is dissipated into the cooler air stream raising the temperature. The fluid/gas is transported from one side of the heat pipe to the other through pressure, wick forces or gravity, depending on the arrangement of the heat pipe.

=== Run-around ===
Run-around systems are hybrid heat recovery system that incorporates characteristics from other heat recovery technology to form a single device, capable of recovering heat from one air stream and delivering to another a significant distance away. The general case of run-around heat recovery, two fixed plate heat exchangers are located in two separate air streams and are linked by a closed loop containing a fluid that is continually pumped between the two heat exchangers. The fluid is heated and cooled constantly as it flows around the loop, providing heat recovery. The constant flow of the fluid through the loop requires pumps to move between the two heat exchangers. Though this is an additional energy demand, using pumps to circulate fluid is less energy intensive than fans to circulate air.<ref>{{Cite journal|last1=Vali|first1=Alireza|last2=Simonson|first2=Carey J.|last3=Besant|first3=Robert W.|last4=Mahmood|first4=Gazi|date=December 2009|title=Numerical model and effectiveness correlations for a run-around heat recovery system with combined counter and cross flow exchangers|journal=International Journal of Heat and Mass Transfer|volume=52|issue=25–26|pages=5827–5840|doi=10.1016/j.ijheatmasstransfer.2009.07.020|issn=0017-9310}}</ref>

=== Phase change materials ===
[[Phase-change material|Phase change materials]], or PCMs, are a technology that is used to store sensible and latent heat within a building structure at a higher storage capacity than standard building materials. PCMs have been studied extensively due to their ability to store heat and transfer heating and cooling demands from conventional peak times to off-peak times.

The concept of the thermal mass of a building for heat storage, that the physical structure of the building absorbs heat to help cool the air, has long been understood and investigated. A study of PCMs in comparison to traditional building materials has shown that the thermal storage capacity of PCMs is twelve times higher than standard building materials over the same temperature range.<ref>{{Cite journal|last1=Feldman|first1=D.|last2=Banu|first2=D.|last3=Hawes|first3=D.W.|date=February 1995|title=Development and application of organic phase change mixtures in thermal storage gypsum wallboard|journal=Solar Energy Materials and Solar Cells|volume=36|issue=2|pages=147–157|doi=10.1016/0927-0248(94)00168-r|issn=0927-0248}}</ref> The pressure drop across PCMs has not been investigated to be able to comment on the effect that the material may have on air streams. However, as the PCM can be incorporated directly into the building structure, this would not affect the flow in the same way other heat exchanger technologies do, it can be suggested that there is no pressure loss created by the inclusion of PCMs in the building fabric.<ref name=":2">{{Cite journal|last1=O’Connor|first1=Dominic|last2=Calautit|first2=John Kaiser S.|last3=Hughes|first3=Ben Richard|date=February 2016|title=A review of heat recovery technology for passive ventilation applications|journal=Renewable and Sustainable Energy Reviews|volume=54|pages=1481–1493|doi=10.1016/j.rser.2015.10.039|issn=1364-0321|url=http://eprints.whiterose.ac.uk/104584/1/Manuscript%20-%20Revised%20Final.pdf}}</ref>