Editing Heat recovery ventilation (section)

== Applications ==
[[File:Passivhaus section en.jpg|thumb|274x274px|Heat recovery ventilation with an earth-to-air heat exchanger, which is essential to achieve German [[Passivhaus]] standards.|alt=]]

=== Fixed plate heat exchangers ===
[[File:Płytowy GPWC wewnątrz obrysu fundamentowego.JPG|thumb|277x277px|Plate ground heat exchanger inside the foundation walls]]Mardiana et al.<ref>{{Cite book|title=Mardiana A, Riffat SB, Worall M. Integrated heat recovery system with windcatcher for building applications: towards energy-efficient technologies. In: Mendez-Vilas A, editor. Materials and processes for energy: communicating current research and technological developments. Badajoz: Formatex Research Center; 2013.}}</ref> integrated a fixed plate heat exchanger into a commercial wind tower, highlighting the advantages of this type of system as a means of zero energy ventilation which can be simply modified. Full scale laboratory testing was undertaken in order to determine the effects and efficiency of the combined system. A wind tower was integrated with a fixed plate heat exchanger and was mounted centrally in a sealed test room.

The results from this study indicate that the combination of a wind tower passive ventilation system and a fixed plate heat recovery device could provide an effective combined technology to recover waste heat from exhaust air and cool incoming warm air with zero energy demand. Though no quantitative data for the ventilation rates within the test room was provided, it can be assumed that due to the high-pressure loss across the heat exchanger that these were significantly reduced from the standard operation of a wind tower. Further investigation of this combined technology is essential in understanding the air flow characteristics of the system.<ref name=":2" />

=== Heat pipes ===
Due to the low-pressure loss of heat pipe systems, more research has been conducted into the integration of this technology into [[passive ventilation]] than other heat recovery systems. Commercial wind towers were again used as the passive ventilation system for integrating this heat recovery technology. This further enhances the suggestion that commercial wind towers provide a worthwhile alternative to mechanical ventilation, capable of supplying and exhausting air at the same time.<ref name=":2" />

=== Run-around systems ===
Flaga-Maryanczyk et al.<ref>{{Cite journal|last1=Flaga-Maryanczyk|first1=Agnieszka|last2=Schnotale|first2=Jacek|last3=Radon|first3=Jan|last4=Was|first4=Krzysztof|date=January 2014|title=Experimental measurements and CFD simulation of a ground source heat exchanger operating at a cold climate for a passive house ventilation system|journal=Energy and Buildings|volume=68|pages=562–570|doi=10.1016/j.enbuild.2013.09.008|bibcode=2014EneBu..68..562F |issn=0378-7788}}</ref> conducted a study in Sweden which examined a passive ventilation system which integrated a run-around system using a ground source heat pump as the heat source to warm incoming air. Experimental measurements and weather data were taken from the passive house used in the study. A CFD model of the passive house was created with the measurements taken from the sensors and weather station used as input data. The model was run to calculate the effectiveness of the run-around system and the capabilities of the ground source heat pump.

Ground source heat pumps provide a reliable source of consistent thermal energy when buried 10–20 m below the ground surface. The ground temperature is warmer than the ambient air in winter and cooler than the ambient air in summer, providing both a heat source and a heat sink. It was found that in February, the coldest month in the climate, the ground source heat pump was capable of delivering almost 25% of the heating needs of the house and occupants.<ref name=":2" />

=== Phase change materials ===
The majority of research interest in PCMs is the application of phase change material integration into traditional porous building materials such as concrete and wall boards. Kosny et al.<ref>{{Cite book|title=Kosny J, Yarbrough D, Miller W, Petrie T, Childs P, Syed AM, Leuthold D. Thermal performance of PCM-enhanced building envelope systems. In: Proceedings of the ASHRAE/DOE/BTECC conference on the thermal performance of the exterior envelopes of whole buildings X. Clear Water Beach, FL; 2–7 December 2007. p. 1–8.}}</ref> analyzed the thermal performance of buildings that have PCM-enhanced construction materials within the structure. Analysis showed that the addition of PCMs is beneficial in terms of improving thermal performance.

A significant drawback of PCM used in a passive ventilation system for heat recovery is the lack of instantaneous heat transfer across different airstreams. Phase change materials are a heat storage technology, whereby the heat is stored within the PCM until the air temperature has fallen to a significant level where it can be released back into the air stream. No research has been conducted into the use of PCMs between two airstreams of different temperatures where continuous, instantaneous heat transfer can occur. An investigation into this area would be beneficial for passive ventilation heat recovery research.<ref name=":2" />