Comfort and perceived air quality in refurbished social houses with mechanical ventialtion system: The impact of occupants behaviour

Abstract The ever-growing demand for a better indoor air quality in residential buildings is increasing the number of whole-house ventilation system installations in new constructions and renovation. In Italy, for residential sector, the national code does not prescribe the use of mechanical ventilation (MV) systems, so their installation is left to the choice of house owners. Two three-storey social housing apartment blocks in Northern Italy were studied. To reduce energy consumption, building envelopes as well as heating systems were refurbished. The thermal insulation was increased and the existing gas heater units were replaced with more efficient radiant ceiling systems. The refurbishment measures were the same for both constructions beside the MV system, which was installed in only one building. Indoor temperature and relative humidity were monitored for several apartments during the heating season. The occupants were surveyed to investigate their thermal comfort and perceived air quality. The occupants were interviewed to better understand their responses, and to know how they operate the heating system and the mechanical ventilation system (when present). Survey results show that there are no differences in terms of thermal comfort and perceived air quality between the occupants of the buildings with and without MV systems. The findings may be related to occupants' behaviour

Comfort and perceived air quality in refurbished social houses with mechanical ventilation system: The impact of occupants behaviour

The ever-growing demand for a better indoor air quality in residential buildings is increasing the number of whole-house ventilation system installations in new constructions and renovation. In Italy, for residential sector, the national code does not prescribe the use of mechanical ventilation (MV) systems, so their installation is left to the choice of house owners. Two three-storey social housing apartment blocks in Northern Italy were studied. To reduce energy consumption, building envelopes as well as heating systems were refurbished. The thermal insulation was increased and the existing gas heater units were replaced with more efficient radiant ceiling systems. The refurbishment measures were the same for both constructions beside the MV system, which was installed in only one building. Indoor temperature and relative humidity were monitored for several apartments during the heating season. The occupants were surveyed to investigate their thermal comfort and perceived air quality. The occupants were interviewed to better understand their responses, and to know how they operate the heating system and the mechanical ventilation system (when present). Survey results show that there are no differences in terms of thermal comfort and perceived air quality between the occupants of the buildings with and without MV systems. The findings may be related to occupants' behaviour. © 2015 The Authors

Indirect Effects of High-Performance Buildings at Household and Community Level: A Systematic Literature Review

Towards a carbon-neutral society, the building sector has a pivotal role with still a great potential for improvement. A new generation of buildings is rising but, to set a more ambitious shift in the paradigm and to fully justify the additional efforts (technological and economic) needed to fill the gap between net zero and plus energy performances, it is essential to consider not only the direct effects, but also all the indirect impacts. However, research conducted in the last decade solely focuses on the direct effects, mainly energy savings, while the indirect impacts neither have a clear identity nor terminology and a defined list of the impacts and methodologies for their quantification is still missing. With these premises, a systematic literature review on the current state of the art was performed in this work, with the aim of (i) investigating the heterogeneous terminology used for such indirect effects, (ii) identifying a final potential list of impacts both at the household and at the community level and (iii) their macro-categorizations, and (iv) exploring the current implemented methodologies and indicators for an economic quantification. As a final result of the analysis, the authors propose a unique terminology for addressing the indirect effects of high-performance buildings. This paper sets the needed basis and common ground for future research in this field, meant to economically quantify the indirect effects in the building sector

Sensation of draft at uncovered ankles for women exposed to displacement ventilation and underfloor air distribution systems

Draft is defined as unwanted local convective cooling. Existing draft risk models, developed in the 1970s, focus on air movement at the neck. The purpose of the present study is to experimentally evaluate ankle draft risk for women with uncovered ankles because of current widespread use of displacement ventilation and underfloor air distribution systems and changes in dress customs. Thirty female university students participated in nine double-blind randomized tests. The subjects wore sandals with lower legs, ankles and feet uncovered. Exposures occurred in an environmental chamber resembling an office environment. The operative temperature at 1.1 m above the floor was maintained at 24.1 °C. The measured air speeds at the ankle varied between 0.16 and 0.59 m/s and the air temperature at the ankle varied between 18.0 and 21.7 °C. Subjective responses were obtained to assess these parameters: thermal acceptability, comfort, preference and sensation, air movement acceptability and preference, local thermal sensation and comfort, and perceived air quality. Subjects were more sensitive to ankle draft than expected. For all the tested conditions, between 20 and 37% of the subjects found the overall thermal environment not acceptable, while between 23 and 57% of the subjects found air movement at the ankle unacceptable. These dissatisfaction percentages are higher than those of international, American and European standards, indicating the need to develop a draft risk model for displacement ventilation and underfloor air distribution systems

Using ductwork to improve supply plenum temperature distribution in underfloor air distribution (UFAD) system

Cool supply air flowing through the underfloor plenum is exposed to heat gain from both the concrete slab (conducted from the warm return air on the adjacent floor below the slab) and the raised floor panels (conducted from the warmer room above). The magnitude of this heat gain can be quite high, resulting in undesirable loss of control of the supply air temperature from the plenum into the occupied space (sometimes referred to as thermal decay). These warmer supply air temperatures can make it more difficult to maintain comfort in the occupied space (without increasing airflow rates), particularly in perimeter zones where cooling loads reach their highest levels. How to predict plenum thermal performance is one of the key design issues facing practicing engineers – evidence from completed projects indicates that excessive thermal decay can be a problem. Current research at the Center for the Built Environment (CBE) at the University of California, Berkeley indicates that unless slab insulation or other means is used to reduce plenum heat gain, one of the strategies that should be considered consists in providing the coolest supply air into the perimeter plenum zones, allowing warmer plenum temperature in interior plenums. The three approaches that have been used to accomplish this include: • Use plenum inlets with higher inlet velocities directed at critical perimeter locations. • Use ductwork (or DuctSox) to deliver cool air to/towards the perimeter. This is the subject of this research work. • Instead of the typical interior plenum inlet locations, consider designing the plenum with perimeter inlets (shafts), if possible. As described above, one of the recommended strategies for addressing thermal decay problems in UFAD systems is the use of ductwork (flexible or rigid) within the underfloor plenum to deliver cool air preferentially to perimeter zones or other critical areas of high cooling demand. Several tests, in an underfloor plenum facility, were done to investigate the use of ductwork to improve supply plenum temperature distribution. Experimental tests have shown that using ductwork, especially vented duct with solid end cap, can cause significant pressure rising in the HVAC system. The test results were used to calibrate and validate a CFD model. This model was compared with a previous CFD model developed and validated at the Center for the Built Environment, used by the researcher to investigate the temperature distributions in an underfloor plenum for different ways (number of inlets and inlet momentum) of supplying air into the plenum. The two models are representative of the first two strategies proposed before to reduce perimeter air temperatures in the underfloor plenum. Analyzing the simulation results comparing the models under the same operative conditions it is possible to conclude that: • Delivering air into the plenum with a high momentum to reach the perimeter loses its capability to reduce perimeter air temperature under partial load conditions. More than this, under part load conditions (25%) there is a reversed result, i.e., the perimeter air is warmer than interior air.; • Under the same load condition, using ductwork produces always lower perimeter temperatures; • Delivering fresh air into the perimeter plenum with high momentum could reduce the perimeter temperatures but not the heat flux, while using a well designed ductwork reduces the heat flux and, as a consequence, the perimeter temperatures.I sistemi per la distribuzione dell’aria sottopavimento (UFAD), utilizzati nella climatizzazione degli ambienti, espongono l’aria fresca che circola nel plenum allo scambio termico con il solaio (riscaldato dall’aria di ritorno nell’ambiente sottostante) e con il pavimento rialzato ( riscaldato dall’ambiente sovrastante). L’entità di questo scambio termico può essere rilevante, poiché ne consegue una di controllo sulla temperatura dell’aria di mandata (denominato Thermal Decay). L’aumento non desiderato della temperatura di mandata può creare difficoltà nel mantenimento del comfort termico nell’ambiente, in particolare nelle zone perimetrali dove i carichi termici raggiungono il loro picco. Un lavoro condotto presso il Center for the Built Environment (CBE) ha evidenziato che, in assenza di un adeguato isolamento del solaio, dovrebbero essere prese in considerazione strategie per la riduzione della temperatura nelle zone perimetrali del plenum, anche a discapito di un aumento della stessa nelle parti interne. Le tre principali strategie utilizzate a questo scopo sono: • immissione di aria nel plenum ad alta velocità, al fine di raggiungere le zone perimetrali dell’underfloor; • utilizzo di condutture aerauliche(sia in metallo che in tessuto) per portare l’aria direttamente nelle zone critiche del plenum; • considerare la possibilità di immettere l’aria nelle zone perimetrali del plenum anziché nella parte centrale. Lo sviluppo e l’analisi del secondo punto qui esposto è l’oggetto di questo lavoro. Utilizzando il modello di UFAD in scala 1:1, presso l’Università di Berkeley, in California, si sono potuti investigare i profili di temperatura in pavimenti rialzati dotati di tale sistema. I test hanno evidenziato fin da subito il problema dell’aumento di pressione nel sistema HVAC legato alle perdite di carico nei condotti. Il problema è ancora più marcato quando viene utilizzata una particolare tipologia di condotto che possiamo definire ventilato. Tale elemento, in tessuto nella versione analizzata, presenta lungo due lati opposti delle file di fori che permettono di distribuire l’aria in modo più efficiente. I risultati sperimentali sono stati utilizzati per validare un modello CFD che simuli la soluzione impiantistica oggetto di analisi. Utilizzando il modello CFD appena descritto ed un secondo, testato e validato presso il CBE, che simula la prima delle strategie illustrate in precedenza, è stato possibile confrontare le due soluzioni in situazioni reali di funzionamento. Per rendere le simulazioni il quanto più possibile coerenti con un caso reale, le condizioni al contorno sono state ottenute con il programma di simulazione energetica Energy Plus. La simulazione energetica è stata eseguita per il giorno di progetto estivo, per un pavimento rialzato situato al secondo di tre piani di uno stabile uso ufficio. Come zona climatica è stata scelta la località di Sacramento, California. Si è giunti così alle seguenti conclusioni: • mandare l’aria nel plenum ad alta velocità non garantisce la riduzione di temperatura nelle zone perimetrali in condizioni di carico parziale. La distribuzione di temperatura nel plenum, inoltre varia notevolmente al variare del carico di raffrescamento richiesto, rendendo così difficile predire le performance termiche dell’underfloor; • dal confronto delle due tipologie di distribuzione dell’aria sotto il pavimento emerge che nel caso si utilizzino condutture aerauliche le temperature perimetrali sono, per ogni condizioni di carico, inferiori a quelle registrate nel caso di mandate ad alta velocità; • la distribuzione delle temperature in plenum che utilizzano i condotti d’aria rimane pressoché invariata per ogni condizione di carico, facilitando così il controllo delle temperature e del comfort termico nell’ambiente condizionato; • l’utilizzo di condutture, unito ad un’attenta analisi delle strategie di distribuzione dell’aria attraverso le stesse, consente una riduzione del flusso termico tra plenum e ambienti circostanti fino al 15% del totale

Using ductwork to improve supply plenum temperature distribution in underfloor air distribution (UFAD) system

Cool supply air flowing through the underfloor plenum is exposed to heat gain from both the concrete slab (conducted from the warm return air on the adjacent floor below the slab) and the raised floor panels (conducted from the warmer room above). The magnitude of this heat gain can be quite high, resulting in undesirable loss of control of the supply air temperature from the plenum into the occupied space (sometimes referred to as thermal decay). These warmer supply air temperatures can make it more difficult to maintain comfort in the occupied space (without increasing airflow rates), particularly in perimeter zones where cooling loads reach their highest levels. How to predict plenum thermal performance is one of the key design issues facing practicing engineers – evidence from completed projects indicates that excessive thermal decay can be a problem. Current research at the Center for the Built Environment (CBE) at the University of California, Berkeley indicates that unless slab insulation or other means is used to reduce plenum heat gain, one of the strategies that should be considered consists in providing the coolest supply air into the perimeter plenum zones, allowing warmer plenum temperature in interior plenums. The three approaches that have been used to accomplish this include: • Use plenum inlets with higher inlet velocities directed at critical perimeter locations. • Use ductwork (or DuctSox) to deliver cool air to/towards the perimeter. This is the subject of this research work. • Instead of the typical interior plenum inlet locations, consider designing the plenum with perimeter inlets (shafts), if possible. As described above, one of the recommended strategies for addressing thermal decay problems in UFAD systems is the use of ductwork (flexible or rigid) within the underfloor plenum to deliver cool air preferentially to perimeter zones or other critical areas of high cooling demand. Several tests, in an underfloor plenum facility, were done to investigate the use of ductwork to improve supply plenum temperature distribution. Experimental tests have shown that using ductwork, especially vented duct with solid end cap, can cause significant pressure rising in the HVAC system. The test results were used to calibrate and validate a CFD model. This model was compared with a previous CFD model developed and validated at the Center for the Built Environment, used by the researcher to investigate the temperature distributions in an underfloor plenum for different ways (number of inlets and inlet momentum) of supplying air into the plenum. The two models are representative of the first two strategies proposed before to reduce perimeter air temperatures in the underfloor plenum. Analyzing the simulation results comparing the models under the same operative conditions it is possible to conclude that: • Delivering air into the plenum with a high momentum to reach the perimeter loses its capability to reduce perimeter air temperature under partial load conditions. More than this, under part load conditions (25%) there is a reversed result, i.e., the perimeter air is warmer than interior air.; • Under the same load condition, using ductwork produces always lower perimeter temperatures; • Delivering fresh air into the perimeter plenum with high momentum could reduce the perimeter temperatures but not the heat flux, while using a well designed ductwork reduces the heat flux and, as a consequence, the perimeter temperatures.I sistemi per la distribuzione dell’aria sottopavimento (UFAD), utilizzati nella climatizzazione degli ambienti, espongono l’aria fresca che circola nel plenum allo scambio termico con il solaio (riscaldato dall’aria di ritorno nell’ambiente sottostante) e con il pavimento rialzato ( riscaldato dall’ambiente sovrastante). L’entità di questo scambio termico può essere rilevante, poiché ne consegue una di controllo sulla temperatura dell’aria di mandata (denominato Thermal Decay). L’aumento non desiderato della temperatura di mandata può creare difficoltà nel mantenimento del comfort termico nell’ambiente, in particolare nelle zone perimetrali dove i carichi termici raggiungono il loro picco. Un lavoro condotto presso il Center for the Built Environment (CBE) ha evidenziato che, in assenza di un adeguato isolamento del solaio, dovrebbero essere prese in considerazione strategie per la riduzione della temperatura nelle zone perimetrali del plenum, anche a discapito di un aumento della stessa nelle parti interne. Le tre principali strategie utilizzate a questo scopo sono: • immissione di aria nel plenum ad alta velocità, al fine di raggiungere le zone perimetrali dell’underfloor; • utilizzo di condutture aerauliche(sia in metallo che in tessuto) per portare l’aria direttamente nelle zone critiche del plenum; • considerare la possibilità di immettere l’aria nelle zone perimetrali del plenum anziché nella parte centrale. Lo sviluppo e l’analisi del secondo punto qui esposto è l’oggetto di questo lavoro. Utilizzando il modello di UFAD in scala 1:1, presso l’Università di Berkeley, in California, si sono potuti investigare i profili di temperatura in pavimenti rialzati dotati di tale sistema. I test hanno evidenziato fin da subito il problema dell’aumento di pressione nel sistema HVAC legato alle perdite di carico nei condotti. Il problema è ancora più marcato quando viene utilizzata una particolare tipologia di condotto che possiamo definire ventilato. Tale elemento, in tessuto nella versione analizzata, presenta lungo due lati opposti delle file di fori che permettono di distribuire l’aria in modo più efficiente. I risultati sperimentali sono stati utilizzati per validare un modello CFD che simuli la soluzione impiantistica oggetto di analisi. Utilizzando il modello CFD appena descritto ed un secondo, testato e validato presso il CBE, che simula la prima delle strategie illustrate in precedenza, è stato possibile confrontare le due soluzioni in situazioni reali di funzionamento. Per rendere le simulazioni il quanto più possibile coerenti con un caso reale, le condizioni al contorno sono state ottenute con il programma di simulazione energetica Energy Plus. La simulazione energetica è stata eseguita per il giorno di progetto estivo, per un pavimento rialzato situato al secondo di tre piani di uno stabile uso ufficio. Come zona climatica è stata scelta la località di Sacramento, California. Si è giunti così alle seguenti conclusioni: • mandare l’aria nel plenum ad alta velocità non garantisce la riduzione di temperatura nelle zone perimetrali in condizioni di carico parziale. La distribuzione di temperatura nel plenum, inoltre varia notevolmente al variare del carico di raffrescamento richiesto, rendendo così difficile predire le performance termiche dell’underfloor; • dal confronto delle due tipologie di distribuzione dell’aria sotto il pavimento emerge che nel caso si utilizzino condutture aerauliche le temperature perimetrali sono, per ogni condizioni di carico, inferiori a quelle registrate nel caso di mandate ad alta velocità; • la distribuzione delle temperature in plenum che utilizzano i condotti d’aria rimane pressoché invariata per ogni condizione di carico, facilitando così il controllo delle temperature e del comfort termico nell’ambiente condizionato; • l’utilizzo di condutture, unito ad un’attenta analisi delle strategie di distribuzione dell’aria attraverso le stesse, consente una riduzione del flusso termico tra plenum e ambienti circostanti fino al 15% del totale