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Design strategies for residential ventilation systems

Jelle Laverge (UGent)
(2013)
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(UGent)
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Abstract
In the literature on ventilation, residential ventilation systems have traditionally received less attention due to their relatively low capacity and complexity. Nevertheless, the large energy saving potential of the residential building sector has made it one of the key targets of climate change mitigation strategies in the European Union. With the rather successful penetration of insulation measures and weatherization, ventilation heat loss now dominates the total heating demand in newly built dwellings, opening a renewed debate on ventilation rates and sizing. Meanwhile, demand control and heat recovery technologies claim to provide substantially better performance than traditional systems. Both have acquired an important but highly competitive share in the market. This dissertation addresses the performance trade-off between heat loss and indoor air quality inherent to ventilation and focusses on the effectiveness of design strategies, demand control and heat recovery for residential systems with respect to this trade-off. After sketching a context and defining a set of design objectives for residential ventilation in the first chapter, it explores the performance level achieved by the ‘state of the art’, represented by the design strategies included in a series of contemporary residential ventilation standards in the second chapter. The performance of systems sized in accordance with the different standards proves to be substantially different, with an occurrence of poor perceived air quality in 5% or less of the occupation time for the Belgian, Dutch and French standard, and about 15% for the British and ASHRAE standard. Mechanical supply and exhaust ventilation is shown to be more robust than natural or mechanical exhaust ventilation across all standards and a clear interaction between the performance of mechanical exhaust ventilation and envelope leakage is found. Considering average exposure to carbon dioxide, optimized mechanical supply and exhaust ventilation concept performs only slightly better compared to mechanical exhaust ventilation, while the latter in turn achieves slightly better performance than natural ventilation. The spread in optimal performance increases when exposure to peak concentrations is considered instead of average exposure. Nevertheless, the differences remained moderate. A more substantial spread in optimal performance of natural ventilation cases with optimal mechanical exhaust and mechanical supply and exhaust ventilation cases is found with respect to exposure to humidity and odours, due to the more frequent occurrence of backdraft from the service spaces to living spaces. All system concepts show superior optimal performance in airtight than in leaky conditions. Additionally, dedicated ventilation systems achieve 30-40% lower exposure at equal ventilation heat loss than leakage as a means of ventilation. Subsequently, the effectiveness of the different ventilation strategies is assessed in the third chapter by relating their performance to the Pareto optimal performance, revealing that, can power reductions found reached up to 85%, but in a case without frequency controlled fan, this reduction was only 20%. Exhaust flow rate reductions were between 55 and 70%. Taking estimations for adventitious ventilation and infiltration from the simulations into account, however, the estimated heat loss reductions for ventilation were only 15 to 40%. It strongly depends on the type of conversion coefficient between electrical energy and fuel combustion for heating that is used. With primary energy, carbon dioxide emission, price and exergy, 4 broadly accepted frameworks for the comparison of these types of energy are used to calculate the profitability of heat recovery ventilation. The results demonstrate that, unless low specific fan power is achieved, for the moderate climate region of middle Europe, natural ventilation, mechanical exhaust ventilation and heat recovery ventilation have no clear advantage over each other as far as operating energy and associated ecologic (CO2) and economic (Household consumer price) effects are concerned. The choice between the different systems should be made based on building specific characteristics, investment and maintenance cost. In the Mediterranean basin, heat recovery ventilation can only be operated profitably in low pressure drop and low fan power systems, while it is advantageous under virtually all tested conditions in the Scandinavian region. In contrast to low fan power, high thermal building performance tends to create unfavorable conditions for heat recovery ventilation. Overall, heat recovery ventilation can be made profitable all over Europe with regard to primary energy, carbon dioxide emissions and household consumer operating energy cost by achieving realistic best practice low specific fan power. In the first section of the chapter, carbon dioxide measurements in the living room and bedroom of 81 cases confirm the observations made in simulations that the probability of exposure to carbon dioxide concentrations generally accepted to be an indication of undesirable indoor air quality is up to 10 times higher in the bedrooms than it is in the living room. Although the results from the first section are cause for some alarm, the occupants are asleep most of the time spent in the bedroom. The second part of the chapter presents Using these results as a reference, the energy saving potential of demand controlled ventilation is investigated in the fourth chapter. Again starting from the ‘state of the art’ based on a performance assessment of systems available on the Belgian market, a substantial energy saving potential for demand controlled residential ventilation systems is found. This potential is then confirmed in practise in a series of case studies. In the latter, f The analysis then expands to the impact of the local context created by ventilation standards or climate and demonstrates that the proposed definition for an energy reduction coefficient renders a relatively robust estimate for the energy saving potential of a specific demand control approach. Finally, further analysis demonstrates that the performance of optimized demand controlled ventilation is up to 50% better than that of continuous flow systems. The performance of the main competitive technology, heat recovery ventilation, is studied under different boundary conditions in the fifth chapter. The sixth chapter of the dissertation revisits the design objectives for residential ventilation by highlighting the dominance of the exposure in the bedrooms in the assessment of residential indoor air quality as well as the poor validity of available performance indicators and assessment methods in this environment. The results from an intervention study using carbon dioxide measurements and sleep-actigraphy, from which one could conclude that, although indoor air quality conditions in the bedroom are less than optimal considering traditional assessment parameters based on perceived air quality and bio-effluents, there seem to be little to no obvious acute repercussions on sleep quality associated with these exposure levels. An experimental assessment of the impact of typical sleep micro-environments on the exposure to near field sources of gaseous pollutants presented in the third part of the chapter found that these are generally higher than the estimates based on well mixed conditions used in exposure risk assessments for consumer products. This, combined with the fact that the concentrations measured in the first section exceeded the level considered a threshold for health effects in just under 25 % of the occupancy time in the bedrooms, warrants great caution in lowering design flow rates in response to the results of sleep intervention study. Combined, the conclusions from the different chapters summed up in the seventh and last chapter, clearly demonstrate that current practise in residential ventilation is suboptimal, while a substantial improvement in performance can be achieved with demand control and heat recovery technology. The questionable validity of the common design objectives for exposure in bedrooms, the most intensively used space of a dwelling, however stresses the need for further research in this area to achieve a comprehensive assessment methodology for residential ventilation systems.
Keywords
Residential, Sizing, Standards, Ventilation, Design

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Citation

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Chicago
Laverge, Jelle. 2013. “Design Strategies for Residential Ventilation Systems”. Ghent, Belgium: Ghent University. Faculty of Engineering and Architecture.
APA
Laverge, J. (2013). Design strategies for residential ventilation systems. Ghent University. Faculty of Engineering and Architecture, Ghent, Belgium.
Vancouver
1.
Laverge J. Design strategies for residential ventilation systems. [Ghent, Belgium]: Ghent University. Faculty of Engineering and Architecture; 2013.
MLA
Laverge, Jelle. “Design Strategies for Residential Ventilation Systems.” 2013 : n. pag. Print.
@phdthesis{4095357,
  abstract     = {In the literature on ventilation, residential ventilation systems have traditionally received less attention due to their relatively low capacity and complexity. Nevertheless, the large energy saving potential of the residential building sector has made it one of the key targets of climate change mitigation strategies in the European Union. With the rather successful penetration of insulation measures and weatherization, ventilation heat loss now dominates the total heating demand in newly built dwellings, opening a renewed debate on ventilation rates and sizing. Meanwhile, demand control and heat recovery technologies claim to provide substantially better performance than traditional systems. Both have acquired an important but highly competitive share in the market.
This dissertation addresses the performance trade-off between heat loss and indoor air quality inherent to ventilation and focusses on the effectiveness of design strategies, demand control and heat recovery for residential systems with respect to this trade-off. After sketching a context and defining a set of design objectives for residential ventilation in the first chapter, it explores the performance level achieved by the ‘state of the art’, represented by the design strategies included in a series of contemporary residential ventilation standards in the second chapter.
The performance of systems sized in accordance with the different standards proves to be substantially different, with an occurrence of poor perceived air quality in 5% or less of the occupation time for the Belgian, Dutch and French standard, and about 15% for the British and ASHRAE standard. Mechanical supply and exhaust ventilation is shown to be more robust than natural or mechanical exhaust ventilation across all standards and a clear interaction between the performance of mechanical exhaust ventilation and envelope leakage is found.
Considering average exposure to carbon dioxide, optimized mechanical supply and exhaust ventilation concept performs only slightly better compared to mechanical exhaust ventilation, while the latter in turn achieves slightly better performance than natural ventilation. The spread in optimal performance increases when exposure to peak concentrations is considered instead of average exposure. Nevertheless, the differences remained moderate. A more substantial spread in optimal performance of natural ventilation cases with optimal mechanical exhaust and mechanical supply and exhaust ventilation cases is found with respect to exposure to humidity and odours, due to the more frequent occurrence of backdraft from the service spaces to living spaces. All system concepts show superior optimal performance in airtight than in leaky conditions. Additionally, dedicated ventilation systems achieve 30-40% lower exposure at equal ventilation heat loss than leakage as a means of ventilation.
Subsequently, the effectiveness of the different ventilation strategies is assessed in the third chapter by relating their performance to the Pareto optimal performance, revealing that, can power reductions found reached up to 85%, but in a case without frequency controlled fan, this reduction was only 20%. Exhaust flow rate reductions were between 55 and 70%. Taking estimations for adventitious ventilation and infiltration from the simulations into account, however, the estimated heat loss reductions for ventilation were only 15 to 40%.
It strongly depends on the type of conversion coefficient between electrical energy and fuel combustion for heating that is used. With primary energy, carbon dioxide emission, price and exergy, 4 broadly accepted frameworks for the comparison of these types of energy are used to calculate the profitability of heat recovery ventilation. The results demonstrate that, unless low specific fan power is achieved, for the moderate climate region of middle Europe, natural ventilation, mechanical exhaust ventilation and heat recovery ventilation have no clear advantage over each other as far as operating energy and associated ecologic (CO2) and economic (Household consumer price) effects are concerned. The choice between the different systems should be made based on building specific characteristics, investment and maintenance cost. In the Mediterranean basin, heat recovery ventilation can only be operated profitably in low pressure drop and low fan power systems, while it is advantageous under virtually all tested conditions in the Scandinavian region. In contrast to low fan power, high thermal building performance tends to create unfavorable conditions for heat recovery ventilation. Overall, heat recovery ventilation can be made profitable all over Europe with regard to primary energy, carbon dioxide emissions and household consumer operating energy cost by achieving realistic best practice low specific fan power.
In the first section of the chapter, carbon dioxide measurements in the living room and bedroom of 81 cases confirm the observations made in simulations that the probability of exposure to carbon dioxide concentrations generally accepted to be an indication of undesirable indoor air quality is up to 10 times higher in the bedrooms than it is in the living room. Although the results from the first section are cause for some alarm, the occupants are asleep most of the time spent in the bedroom. The second part of the chapter presents Using these results as a reference, the energy saving potential of demand controlled ventilation is investigated in the fourth chapter. Again starting from the ‘state of the art’ based on a performance assessment of systems available on the Belgian market, a substantial energy saving potential for demand controlled residential ventilation systems is found. This potential is then confirmed in practise in a series of case studies. In the latter, f The analysis then expands to the impact of the local context created by ventilation standards or climate and demonstrates that the proposed definition for an energy reduction coefficient renders a relatively robust estimate for the energy saving potential of a specific demand control approach. Finally, further analysis demonstrates that the performance of optimized demand controlled ventilation is up to 50% better than that of continuous flow systems.
The performance of the main competitive technology, heat recovery ventilation, is studied under different boundary conditions in the fifth chapter.
The sixth chapter of the dissertation revisits the design objectives for residential ventilation by highlighting the dominance of the exposure in the bedrooms in the assessment of residential indoor air quality as well as the poor validity of available performance indicators and assessment methods in this environment. The results from an intervention study using carbon dioxide measurements and sleep-actigraphy, from which one could conclude that, although indoor air quality conditions in the bedroom are less than optimal considering traditional assessment parameters based on perceived air quality and bio-effluents, there seem to be little to no obvious acute repercussions on sleep quality associated with these exposure levels. An experimental assessment of the impact of typical sleep micro-environments on the exposure to near field sources of gaseous pollutants presented in the third part of the chapter found that these are generally higher than the estimates based on well mixed conditions used in exposure risk assessments for consumer products. This, combined with the fact that the concentrations measured in the first section exceeded the level considered a threshold for health effects in just under 25 % of the occupancy time in the bedrooms, warrants great caution in lowering design flow rates in response to the results of sleep intervention study.
Combined, the conclusions from the different chapters summed up in the seventh and last chapter, clearly demonstrate that current practise in residential ventilation is suboptimal, while a substantial improvement in performance can be achieved with demand control and heat recovery technology. The questionable validity of the common design objectives for exposure in bedrooms, the most intensively used space of a dwelling, however stresses the need for further research in this area to achieve a comprehensive assessment methodology for residential ventilation systems.},
  author       = {Laverge, Jelle},
  isbn         = {9789085786085},
  keywords     = {Residential,Sizing,Standards,Ventilation,Design},
  language     = {eng},
  pages        = {XXI, 221},
  publisher    = {Ghent University. Faculty of Engineering and Architecture},
  school       = {Ghent University},
  title        = {Design strategies for residential ventilation systems},
  year         = {2013},
}