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Sustainable building ventilation solutions with heat recovery from waste heat
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Sustainable Buildings.ORCID iD: 0000-0002-5938-4614
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 [en]
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: urn:nbn:se:kth:diva-256567ISBN: 978-91-7873-297-5 (print)OAI: oai:DiVA.org:kth-256567DiVA, id: diva2:1346703
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
List of papers
1. Maximizing thermal performance of building ventilation using geothermal and wastewater heat
Open this publication in new window or tab >>Maximizing thermal performance of building ventilation using geothermal and wastewater heat
2019 (English)In: Resources, Conservation and Recycling, ISSN 0921-3449, E-ISSN 1879-0658, Vol. 143, p. 90-98Article in journal (Refereed) Published
Abstract [en]

An efficient use of waste heat recovery and geothermal heat can play an important role in lowering the overall energy use of buildings. This study evaluated the potential of geothermal energy and heat recovery from residential wastewater to reduce the energy need of building-ventilation in cold climates. The performance of the mechanical ventilation with heat recovery (MVHR) system in a multi-family building located in central Sweden was studied. The focus of the investigation was on reduction of frosting in the air handling unit during the coldest months. Three configurations of one air preheating system fed by two renewable heat sources, wastewater and geothermal energy, were studied. It was found that compared to building without an air preheating system, the suggested air preheating systems reduced the defrosting time to 25%. By controlling and maintaining the preheated air temperature to slightly above the defrosting start, air heat recovery efficiency of MVHR above 80% was achieved for 90% of the studied time during heating season when frosting occurs. The energy need for the circulation pumps in the suggested air preheating systems was 5% of the recovered thermal energy from wastewater. The simulation results suggested that the air preheating system using wastewater heat recovery with a temperature-stratified storage tank was the most efficient one among the studied systems.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE BV, 2019
Keywords
Renewables, Wastewater heat recovery, Geothermal heating, Balanced mechanical ventilation, Sustainability, Energy saving
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-245125 (URN)10.1016/j.resconrec.2018.12.025 (DOI)000458222600010 ()2-s2.0-85058947734 (Scopus ID)
Note

QC 20190315

Available from: 2019-03-15 Created: 2019-03-15 Last updated: 2019-08-30Bibliographically approved
2. Energy and defrosting contributions of preheating cold supply air in buildings with balanced ventilation
Open this publication in new window or tab >>Energy and defrosting contributions of preheating cold supply air in buildings with balanced ventilation
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
Keywords
Balanced ventilation, Heat recovery efficiency, Defrosting reduction, Wastewater heat recovery, Multi-family buildings, Energy saving
National Category
Architectural Engineering
Identifiers
urn:nbn:se:kth:diva-241185 (URN)10.1016/j.applthermaleng.2018.09.118 (DOI)000454465900017 ()2-s2.0-85054338548 (Scopus ID)
Note

QC 20190121

Available from: 2019-01-21 Created: 2019-01-21 Last updated: 2019-08-30Bibliographically approved
3. Identifying frost threshold in a balanced mechanical ventilation system by inlet and exhaust air temperature control
Open this publication in new window or tab >>Identifying frost threshold in a balanced mechanical ventilation system by inlet and exhaust air temperature control
2019 (English)Conference paper, Published paper (Refereed)
Abstract [en]

Frosting is a common issue in air-to-air heat recovery exchangers installed in buildings in cold climate countries. Further to the developed defrosting methods, frost prevention by preheating the outdoor air can reduce the energy usage in buildings. In this study, residential wastewater as a renewable heat source is used to preheat the outdoor air. Due to limited wastewater hourly flowrate and the impact of preheated air temperature on the efficiency of heat exchanger, controlling the preheating temperature is of utmost importance. In this investigation, preheated and exhaust air temperatures are monitored to generate an operational signal to the wastewater circulation pump. The cold surface at the heat exchanger and the dew point of the return air are analyzed to comprehend the condensation and frosting temperatures. The results show that in case of 30% relative humidity in the return air, the frosting threshold is at preheated and exhaust air temperatures below -2.2°C and 2.1°C, respectively. Using these temperatures as controlling parameters, the frosting period has decreased by 23%.

Keywords
Balanced mechanical ventilation; Frosting; Frosting threshold; Wastewater heat recovery; Energy saving
National Category
Building Technologies
Identifiers
urn:nbn:se:kth:diva-255622 (URN)
Conference
The 11th International Symposium on Heating, Ventilation and Air Conditioning (ISHVAC2019)
Note

QC 20190926

Available from: 2019-08-02 Created: 2019-08-02 Last updated: 2019-09-26Bibliographically approved
4. Preheating Cold Supply Air to Mechanical Balanced Ventilation using Wastewater or Passive Geothermal Energy
Open this publication in new window or tab >>Preheating Cold Supply Air to Mechanical Balanced Ventilation using Wastewater or Passive Geothermal Energy
2019 (English)Conference paper, Published paper (Refereed)
Abstract [en]

This study investigated the thermal potential of two renewable heat sources, residential wastewater and geothermal energy, for preheating the incoming air to the air-handling unit (AHU) in a multi-family building. The main purpose of preheating the inlet air was to avoid the frost formation inside AHU due to low outdoor temperatures during winter. Wastewater extraction flowrate and temperature, as two design parameters, were studied in detail by employing two types of wastewater storage tanks.The suggested outdoor air preheating systems equally reduced the defrosting period to 26% compared to the mechanical ventilation with heat recovery system (MVHR) without air preheating. The system that utilized a temperature stratified wastewater storage tank provided a higher ratio of heat output to electricity input. The other outdoor air preheating system, which was equipped with an unstratified wastewater storage tank, provided a lower ratio of heat output to pumping power. However, this ratio was not disturbed by variations in outdoor air temperature.

National Category
Building Technologies
Research subject
Civil and Architectural Engineering
Identifiers
urn:nbn:se:kth:diva-257493 (URN)
Conference
The 16th International Building Performance Simulation Association (IBPSA), 2-4 September 2019, Rome, Italy
Note

QC 20190926

Available from: 2019-08-30 Created: 2019-08-30 Last updated: 2019-10-10Bibliographically approved
5. Frost reduction in mechanical balanced ventilation by efficient means of preheating cold supply air
Open this publication in new window or tab >>Frost reduction in mechanical balanced ventilation by efficient means of preheating cold supply air
2019 (English)Conference paper, Published paper (Refereed)
Abstract [en]

This study has focused on evaluating the financial potential of wastewater and geothermal heat recovery systems in a multi-family building. The recovered heat was used to improve the performance of mechanical ventilation with heat recovery (MVHR) system during the coldest days in central Sweden. The main issue, which was targeted with these solutions, was to reduce frost formation in the system and hence increase its thermal efficiency. By looking at the life cycle cost over a lifespan of 20 years, the observed systems were being evaluated economically. Furthermore, statistical analyses were carried-out to counter the uncertainty that comes with the calculation. It was found that the studied wastewater systems have a high possibility of generating savings in this period, while the one fed by geothermal energy is less likely to compensate for its high initial cost. All designed systems however, managed to reduce operational cost by 35-45% due to lower energy usage.

National Category
Building Technologies
Research subject
Civil and Architectural Engineering
Identifiers
urn:nbn:se:kth:diva-257495 (URN)
Conference
The 10th International Conference on Indoor Air Quality, Ventilation and Energy Conservation in Buildings (IAQVEC), 5-7 September 2019, Bari, Italy
Available from: 2019-08-30 Created: 2019-08-30 Last updated: 2019-09-03Bibliographically approved

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