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Energy and defrosting contributions of preheating cold supply air in buildings with balanced ventilation
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Fluid and Climate Technology.
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Fluid and Climate Technology. Uponor AB, Hackstavägen 1, S-72132 Västerås, Sweden..ORCID iD: 0000-0001-6266-8485
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Fluid and Climate Technology. Bravida Holding AB, Mikrofonvägen 28, S-12637 Hägersten, Sweden..ORCID iD: 0000-0001-5902-2886
2019 (English)In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 146, p. 180-189Article in journal (Refereed) Published
Abstract [en]

Residential wastewater is a constant and available source for saving energy. This paper mainly investigated the possibility of utilizing wastewater heat to reduce ventilation heat load. Swedish residential buildings are to a significant extent served by mechanical ventilation with heat recovery (MVHR) systems. MVHR in airtight buildings has greatly reduced ventilation heat loads, especially in cold climate countries such as Sweden. However, cold outdoor air might lead to frost formation in heat recovery exchangers which increases the energy use. Therefore, this study focused on reducing the defrosting need by preheating the incoming cold outdoor air to MVHR during the coldest days. The effects of preheating the incoming air to MVHR on ventilation heat load and annual ventilation heating demand were also studied. It was found that the heat recovery efficiency of MVHR is the most decisive factor in rating the performance of the combined system with an air preheater. Contributions of the studied air preheater to annual energy savings were negligible. On the other hand, the reduction of the initial defrosting need was significant. The obtained results showed that the defrosting need in a building located in central Sweden in two cases of an MVHR system equipped with a rotary heat exchanger/plate heat exchanger was eliminated/reduced to one-third. The defrosting need was reduced by 50% in northern Sweden for both cases.

Place, publisher, year, edition, pages
PERGAMON-ELSEVIER SCIENCE LTD , 2019. Vol. 146, p. 180-189
Keywords [en]
Balanced ventilation, Heat recovery efficiency, Defrosting reduction, Wastewater heat recovery, Multi-family buildings, Energy saving
National Category
Architectural Engineering
Identifiers
URN: urn:nbn:se:kth:diva-241185DOI: 10.1016/j.applthermaleng.2018.09.118ISI: 000454465900017Scopus ID: 2-s2.0-85054338548OAI: oai:DiVA.org:kth-241185DiVA, id: diva2:1281111
Note

QC 20190121

Available from: 2019-01-21 Created: 2019-01-21 Last updated: 2019-08-30Bibliographically approved
In thesis
1. Sustainable building ventilation solutions with heat recovery from waste heat
Open this publication in new window or tab >>Sustainable building ventilation solutions with heat recovery from waste heat
2019 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The energy used by building sector accounts for approximately 40% of the total energy usage. In residential buildings, 30-60% of this energy is used for space heating which is mainly wasted by transmission heat losses. A share of 20-30% is lost by the discarded residential wastewater and the rest is devoted to ventilation heat loss.

 

The main objective of this work was to evaluate the thermal potential of residential wastewater for improving the performance of mechanical ventilation with heat recovery (MVHR) systems during the coldest periods of year. The recovered heat from wastewater was used to preheat the incoming cold outdoor air to the MVHR in order to avoid frost formation on the heat exchanger surface.

 

Dynamic simulations using TRNSYS were used to evaluate the performance of the suggested air preheating systems as well as the impact of air preheating on the entire system. Temperature control systems were suggested based on the identified frost thresholds in order to optimally use the limited thermal capacity of wastewater and maintain high temperature efficiency of MVHR. Two configurations of air preheating systems with temperature stratified and unstratified tanks were designed and compared. A life cycle cost analysis further investigated the cost effectiveness of the studied systems.

 

The results obtained by this research work indicated that residential wastewater had the sufficient thermal potential to reduce the defrosting need of MVHR systems (equipped with a plate heat exchanger) in central Swedish cities to 25%. For colder regions in northern Sweden, the defrosting time was decreased by 50%. The temperature control systems could assure MVHR temperature efficiencies of more than 80% for most of the heating season while frosting period was minimized. LCC analysis revealed that wastewater air preheating systems equipped with temperature stratified and unstratified storage tanks could pay off their costs in 17 and 8 years, respectively.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2019
Series
TRITA-ABE-DLT ; 1928
Keywords
wastewater heat recovery, balanced mechanical ventilation, defrosting reduction, heat recovery efficiency, thermal load shifting, renewables
National Category
Building Technologies
Research subject
Civil and Architectural Engineering
Identifiers
urn:nbn:se:kth:diva-256567 (URN)978-91-7873-297-5 (ISBN)
Presentation
2019-09-20, M108, Stora konferensrummet, Brinellvägen 23, Stockholm, 09:00 (English)
Opponent
Supervisors
Funder
Svenska Byggbranschens Utvecklingsfond (SBUF), D6563
Note

QC 20190830

Available from: 2019-08-30 Created: 2019-08-28 Last updated: 2019-08-30Bibliographically approved

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