Problems with heat recovery There are issues that can affect the effi ciency of heat recovery systems: ● Uncontrolled air leakage reduces potential heat recovery. Even in quite airtight buildings, air leakage provides a signifi cant part of our ventilation needs. If a building is moderately leaky, there is no point in a heat recovery unit. Designers also have to bear in mind that buildings become less tight over time.
● Mechanical ventilation systems use electricity and typically become 1% less effi cient every year, delivering less energy effi ciency than expected. A survey of thousands of units in Sweden7
provide a real shock:
average heat recovery is less than 30%. And in a warming climate with lower heating needs, potential heat recovery decreases.
● Precision on site is required for passive builds – we are often not realistic about what the construction industry can deliver on site. ● The embodied energy of the
References 1
Butters, C. and Leland, B., 2012: Fra passivhus til sunne hus (From passive building to healthy building), GAIA agenda, Oslo, Norway.
2 Liddell, H. 2008, GAIA Edinburgh: Ecominimalism: The Antidote to Eco-Bling. RIBA Publishing, London.
3 Berge, B., 2009: The Ecology of Building Materials. Second edition, Architectural Press, Oxford.
4 Simonson, C.J et al., 2004: Moderating indoor air conditions with hygroscopic building materials and outdoor ventilation. ASHRAE Transactions 110(2), Atlanta, USA.
Monitoring in Acharacle classrooms
ventilation equipment and the technical ventilation spaces should be accounted for when considering CO2
. 8
● Airtightness is near impossible in many old buildings, hence heat recovery effi ciency in retrofi tted properties will be compromised.
● There are non-technical risks such as noise, dry air, electromagnetic radiation, and change of building use.
● Serious damage to the building can occur if the unit fails while occupants are away.
5 Butters, C,. 2012: A Holistic Tool for Evaluating Sustainability in: Haas, T. (ed.), Sustainable Urbanism and Beyond, Rizzoli, New York, USA.
Research suggest that dogmas
surrounding heat recovery are starting to look shaky
6 Brunklaus, Birgit, Thormark, Catarina, Baumann, Henrikke, 2010: Illustrating limitations of energy studies of buildings with LCA and actor analysis. Building research and information 38:3, 265-279, Sweden
7 Ringstrom, Lisa, 2009: Liten nyta med FTX (Little effect from ventilation heat recovery – report from 11,000 Swedish units), see:
http://www.byggvarlden.se/nyheter/energi_ miljo/
article88331.ece , Sweden
8 Nordby, A.S. 2011: Etterlysning: Miljøregnskap for Ventilasjonsanlegg. Arkitektur N 03/2011, Oslo
● CHRIS BUTTERS, Chris Butters architect and consultant, Gaia Architects
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11/03/2013 16:14 April 2013 CIBSE Journal 19
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