Night-time Ventilation Research Articles

Parameter study on performance of building cooling by night-time ventilation

Especially for commercial buildings in moderate climates, night-time ventilation seems to be a simple and energy-efficient approach to improve thermal comfort in summer. However, due to uncertainties in the prediction of thermal comfort in buildings with night-time ventilation, architects and engineers are still hesitant to apply this technique. In order to reduce the uncertainties, the most important parameters affecting night ventilation performance need to be identified. A typical office room was therefore modelled using a building energy simulation programme (HELIOS), and the effect of different parameters such as building construction, heat gains, air change rates, heat transfer coefficients and climatic conditions including annual variations on the number of overheating degree hours (operative room temperature >26 °C) was evaluated. Climatic conditions and air flow rate during night-time ventilation were found to have the largest effect. But thermal mass and internal heat gains also have a significant effect on cooling performance and the achievable level of thermal comfort. Using this modelling approach, significant sensitivity to heat transfer was found only for total heat transfer coefficients below about 4 W/m 2 K.

Impact of climate warming on passive night cooling potential

Night-time ventilation is often seen as a promising passive cooling concept. However, as it requires a sufficiently high temperature difference between ambient air and the building structure, this technique is highly sensitive to changes in climatic conditions. In order to quantify the impact of climate warming on the night-time ventilative cooling potential in Europe, eight representative locations across a latitudinal transect were considered. Based on a degree-hours method, site-specific regression models were developed to predict the climatic cooling potential (CCP) from minimum daily air temperature (T min). CCP was computed for present conditions (1961–90) using measured T min data from the European Climate Assessment (ECA) database. Possible time-dependent changes in CCP were assessed for 1990–2100, with particular emphasis on the Intergovernmental Panel on Climate Change (IPCC) ‘A2’ and ‘B2’ scenarios for future emissions of greenhouse gases and aerosols. Time-dependent, site-specific T min scenarios were constructed from 30 Regional Climate Model (RCM) simulated data sets, as obtained from the European PRUDENCE project. Under both emissions scenarios and across all locations and seasons, CCP was found to decrease substantially by the end of the 21st century. For the six Central and Northern European locations (>47°N) CCP was found to decrease in summer (June–August) by 20–50%. For the two Southern European locations (Madrid and Athens), future CCP was found to become negligible during the summer and to decrease by 20–55% during the spring and the autumn. The study clearly shows that night-time cooling potential will cease to be sufficient to ensure thermal comfort in many Southern and Central European buildings. In Central and Northern Europe, a significant passive cooling potential is likely to remain, at least for the next few decades. Upper and lower bound estimates for future CCP were found to diverge strongly in the course of the 21st century, suggesting the need for flexible building design and for risk assessments that account for a wide range of emissions scenarios and uncertainty in climate model results. La ventilation nocturne est souvent considérée comme un concept de refroidissement passif prometteur. Toutefois, cette technique nécessitant une différence de température suffisamment élevée entre l'air ambiant et la structure du bâtiment, elle est très sensible aux changements des conditions climatiques. Pour quantifier l'impact du réchauffement climatique sur les possibilités de refroidissement par ventilation nocturne, on a considéré huit emplacements représentatifs sur une transversale latitudinale en Europe. Sur la base d'une méthode ‘degrés-heures’, on a développé des modèles de régression spécifiques à des sites pour prévoir le potentiel de refroidissement climatique (CCP) à partir de la température quotidienne minimale de l'air (T min). On a calculé le CCP pour les conditions présentes pendant la période 1961–90 en utilisant les données T min de la base de données ECA (Evaluation du climat européen). On a évalué de possibles changements du CCP liés à la durée pour la période 1990–2100, en mettant l'accent sur les scénarios A2 et B2 du GIEC (Groupe d'experts intergouvernemental sur l'évolution du climat) relatifs aux futures émissions de gaz à effet de serre et aux aérosols. Des scénarios liés à la durée, avec T min spécifiques aux sites ont été élaborés à partir de 30 ensembles de données de modèles de climats régionaux simulés obtenus dans le cadre du projet européen PRUDENCE. Pour les deux scénarios d'émission et pour tous les emplacements et saisons, on a constaté que le CCP diminuait de façon substantielle dès la fin du XXIe siècle. Pour les six emplacements en Europe centrale et en Europe du Nord (>47° nord), on a constaté que le CCP diminuait de 20–50% (juin–août). Pour les deux emplacements en Europe du Sud (Madrid et Athènes), on a constaté que le futur CCP devenait négligeable pendant l'été et diminuait de 20–55% pendant le printemps et l'automne. Cette étude montre clairement que le potentiel de refroidissement nocturne cessera d'être suffisant pour assurer le confort thermique dans de nombreux bâtiments construits en Europe du Sud et en Europe centrale. En Europe centrale et en Europe du Nord, un potentiel significatif de refroidissement passif va vraisemblablement durer pendant au moins les prochaines décennies. Il s'est avéré que les estimations supérieures et inférieures du futur CCP divergeaient nettement dans le courant du XXIe siècle, ce qui suggère la nécessité de concevoir les bâtiments avec souplesse et d'évaluer le risque en tenant compte d'une large gamme de scénarios d'émission et de l'incertitude des résultats des modèles climatiques. Mots clés: changements climatiques, scénarios climatiques, potentiel de refroidissement climatique, ventilation nocturne, refroidissement passif, Europe

Climatic potential for passive cooling of buildings by night-time ventilation in Europe

Due to an overall trend towards less heating and more cooling demands in buildings in many European countries over the last few decades, passive cooling by night-time ventilation is seen as a promising technique, particularly for commercial buildings in the moderate or cold climates of Central, Eastern and Northern Europe. The basic concept involves cooling the building structure overnight in order to provide a heat sink that is available during the occupancy period. In this study, the potential for passive cooling of buildings by night-time ventilation was evaluated by analysing climatic data, without considering any building-specific parameters. An approach for calculating degree–hours based on a variable building temperature – within a standardized range of thermal comfort – is presented and applied to climatic data of 259 stations all over Europe. The results show a high potential for night-time ventilative cooling over the whole of Northern Europe and still significant potential in Central, Eastern and even some regions of Southern Europe. However, due to the inherent stochastic properties of weather patterns, a series of warmer nights can occur at some locations, where passive cooling by night-time ventilation alone might not be sufficient to guarantee thermal comfort.

Thermal simulation of buildings with double-skin façades

Highly glazed commercial buildings with double-skin façades may overheat during summertime due to a coincidence of high outside temperatures, solar gains and internal heat gains. To optimize thermal comfort and minimize cooling loads, the thermal behaviour of this type of building, therefore, requires careful investigation at the design stage. However, complex physical phenomena—notably optical, thermodynamic and fluid dynamic processes—are involved and as yet, no single simulation tool is able to handle all these processes while remaining an efficient design tool. This paper presents a method based on the coupling of three different types of simulation models that is economical in terms of computing time, and thereby, suitable for design purposes. These models are: spectral optical model, computational fluid dynamics model and building energy simulation model. Various tools are available at each modelling level. The method is demonstrated on a commercial building with double-skin façades and additionally, night-time ventilation.

The French Congenital Central Hypoventilation Syndrome Registry

To analyze the main clinical features, genetic mutations, and outcomes of patients of the French Congenital Central Hypoventilation Syndrome (CCHS) Registry. A country-wide cohort established throughout a long-term multicenter effort. Seventy French patients with CCHS (29 male patients and 41 female patients). The following items were analyzed: the most important moments of the disease course; the main clinical characteristics; associated pathologic conditions; management; clinical outcome; and genetic mutations. An average of four new cases of CCHS per year was observed in the last 5 years. Thus, the incidence may be estimated to be 1 per 200,000 live births in France. The median age at diagnosis was 3.5 months (range, 0.5 to 15 months) before 1995 and < 2 weeks in the last 5 years (p = 0.01). CCHS occurred in isolation in 58 of 70 patients. In the remainder, it was associated with Hirschsprung disease (HSCR) [nine patients], Hirschsprung and neural crest tumor (two patients), and growth hormone deficiency (one patient). Among the 50 patients who lived beyond 1 year of age, all but one received nighttime ventilation, with 10 of them (20%) receiving it noninvasively. Three patients (6%) required daytime ventilatory support in addition to nighttime ventilation. The overall mortality rate was 38% (95% confidence interval [CI], 27 to 49%). The median age at death was 3 months (range, 0.4 months to 21 years). The 2-year mortality rate was greater in male patients than in female patients (p = 0.02; relative risk [RR], 2.71; 95% CI, 1.14 to 6.47) but was not affected by HSCR (p = 0.93; RR, 0.95; 95% CI, 0.28 to 3.2). The 43 patients who are currently alive (11 men; sex ratio, 0.4) have a mean age of 9 years (range, 2 months to 27 years). Among the 34 patients tested thus far, heterozygous mutations of the paired-like homeobox gene 2B (PHOX2B) gene were found in 31 patients (91%). Our four major findings are the extreme rarity of CCHS, the improved recognition over time, the lack of effect of HSCR on the mortality rate, and the high frequency of PHOX2B mutations.

PCM-facade-panel for daylighting and room heating

Double glazings combined with phase change materials (PCM) result in daylighting elements with promising properties. Light transmittances in the range of 0.4 can be achieved with such facade panels. Compared to a double glazing without PCM, a facade panel with PCM shows about 30% less heat losses in south oriented facades. Solar heat gains are also reduced by about 50%. This results in calculated U eff-values of −0.3 to −0.5 W m −2 K −1, depending on PCM used. For an optimised panel, we calculated an U eff-value of −0.6 W m −2 K −1. Although the U eff-value of a double glazing is −0.8 W m −2 K −1, the PCM-systems may prove advantageous in lightweight constructed buildings due to their equalised energy balance during the course of day. Facade panels with PCM improve thermal comfort considerably in winter, especially during evenings. In summer, such systems show low heat gains, which reduces peak cooling loads during the day. Additional heat gains in the evening can be drawn off by night-time ventilation. If a PCM with a low melting temperature of up to 30 °C is used, thermal comfort in summer will also improve during the day, compared to a double glazing without or with inner sun protection. A homogeneous appearance of the PCM-systems is achievable by use of a concealment, like a screen-print glazing.

Home mechanical ventilation in Sweden, with reference to Danish experiences

The Swedish Society of Chest Medicine has started a national register of patients on home mechanical ventilation, to establish reliable national prevalence data and to accurately document patient and treatment characteristics to enable a scientific evaluation of this treatment.In this first collection of retrospective register data, covering patients on home mechanical ventilation at the register start on 1 January 1996, we found 541 patients, corresponding to 6·1/100 000 inhabitants, using home mechanical ventilation. Non-invasive ventilation, night-time ventilation and volume controlled ventilation dominated.We found four diagnosis categories of approximately equal size, namely post-polio, chest wall deformities, neuromuscular diseases and ‘other diseases’. The age distribution was bimodal, with one small peak in the 20–29 year group and a large peak in the 60–69 year group. A survey of Danish patients on home mechanical ventilation showed that they were considerably younger and that almost half of them suffered from neuromuscular diseases. Further work will be done to follow the situation in Sweden and in Denmark to elucidate the obvious differences in the selection of patients for home mechanical ventilation.

Improving night ventilation into low-rise buildings in hot-arid climates exploring a combined wall–roof solar chimney

A theoretical investigation of a combined wall–roof solar chimney to improve night time ventilation in buildings is presented. A spreadsheet computer program is used for the parametric study to find out the optimum configuration of the wall–roof chimney. It has been reported that a roof solar chimney alone can induce an air flow rate of 0.81 m 3/s when the average incident solar radiation is 850 W/m 2. The maximum air velocity induced is 1.1 m/s when the 25° inclined chimney plates are 0.25 m apart. The aim of the paper is to predict the induced air flow rate as a result of the combined effect and to find the best height. The wall chimney height is varied from 1.95 to 3.45 m to determine the optimum length in relation to the chimney inlet. The results show that the air flow rate is three times more than that of the roof solar chimney alone (0.81 to 2.3 m 3/s). The maximum air flow rate of 2.3 m 3/s occurs at 3.45 m wall height. ACTION Psychrometrics Software (Sunshine Technology, USA, 1995) is used to predict the mean cooling load corresponding to the induced ACH. An air change per hour up to 26 could be achieved for a flat volume (321 m 3). Such ACH could be utilized to improve night ventilation to reduce indoor air temperature and cool low-rise heavy buildings with large diurnal outdoor temperature variations.

Mechanisms underlying effects of nocturnal ventilation on daytime blood gases in neuromuscular diseases.

The hypothesis that, in neuromuscular and chest wall diseases, improvement in central respiratory drive explains the effects of night-time ventilation on diurnal gas exchanges was tested. The effects at 6 months, 1, 2 and 3 yrs of intermittent positive pressure ventilation (IPPV) on arterial blood gas tension, pulmonary function, muscle strength, sleep parameters, respiratory parameters during sleep and ventilatory response to CO2 were evaluated in 16 consecutive patients with neuromuscular or chest wall disorders. As compared with baseline, after IPPV daytime arterial oxygen tension (Pa,O2) increased (+2.3 kPa at peak effect) and arterial carbon dioxide tension (Pa,CO2) and total bicarbonate decreased (-1.8 kPa and -5 mmol x L(-1), respectively) significantly; vital capacity, total lung capacity, maximal inspiratory and expiratory pressures and alveolar-arterial oxygen gradient did not change; the apnoea-hypo-opnoea index and the time spent with an arterial oxygen saturation (Sa,O2) value <90% decreased (-24 and -101 min, respectively), sleep efficiency and mean Sa,O2 increased (+16% and +5%, respectively); and ventilatory response to CO2 increased (+4.56 L x min(-1) x kPa(-1)) significantly. The reduction in Pa,CO2 observed after IPPV correlated solely with the increase in the slope of ventilatory response to the CO2 curve (r=-0.68, p=0.008). In neuromuscular or chest wall diseases, improvement of daytime hypoventilation with nocturnal intermittent positive pressure ventilation may represent an adaptation of the central chemoreceptors to the reduction of profound hypercapnia during sleep or reflect change in the quality of sleep.

Incorporation of thermal inertia in the aim of installing a natural nighttime ventilation system in buildings

The objective of this study is to propose a simplified characterization of thermal inertia, as part of the installation of a system of summer refreshment by means of nighttime cooling ventilation. On the basis of a previous study, conducted by relying upon a modal analysis, the interactions between the thermal inertia of a building and the variation of the air exchange rate have been explained. It can then be shown that the notion of useful thermal mass has herein been altered in order to take the thermal inertia of the building into account; it would then be suitable to substitute this notion for an approximated calculation of the building's main time constant. Moreover, the necessity of adding a parameter that characterizes the rapid dynamics of a particular zone's air temperature can be justified. Lastly, a characterization of the thermal inertia based upon the three-criteria calculation is proposed. An approximated value of the time constant both during the period of nighttime cooling and beyond this period, as well as an approximated value of the height of the line associated with the rapid dynamics, can be computed.

高断熱高気密住宅における熱環境特性と居住者の健康に関する調査

The indoor thermal environment, air quality and occupant behavior in well-insulated and airtight houses in and around Tohoku district are investigated through questionnaire and field measurement. This report describes the results from the questionnaire survey conducted in summer of 1993 and winter of 1994, and thermal environment of 16 well-insulated and airtight houses in Morioka and Sendai by the field measurement in winter and summer of 1994. The number of houses investigated by the questionnaire survey is about 350. The well-insulated and airtight houses investigated have mechanical ventilation system and space heating system for a whole house. The main findings are as follows: 1. Indoor environment during the heating season of almost houses is thermally comfortable, compared with that of existing house in Japan. 2. The houses provide a comfortable indoor environment and also have a good influence on occupant' health. However, there are some problems related to dry feeling, which should be investigated in future. 3. During the summer, the room temperatures are stable compared with the change of the outdoor temperature in the day, but it doesn't decrease at night even if the outdoor temperature drops. It is possible to improve the indoor environment by cross ventilation with opening windows or night time ventilation.

An early onset muscular dystrophy with diaphragmatic involvement, early respiratory failure and secondary α2 laminin deficiency unlinked to the LAMA2 locus on 6q22

We present four subjects from one family and one subject (with an affected sibling who had died) from a second, unrelated family, with early onset, Duchenne-like, muscular dystrophy who presented with proximal girdle weakness, calf and generalized muscle hypertrophy, selective wasting of the sternomastoid muscles, rigidity of the spine and contractures of the tendo Achilles. Intellect was normal. Serum creatine kinase was grossly elevated and the muscle biopsies showed a dystrophic picture. All five subjects have developed early respiratory failure due to severe diaphragmatic involvement; two have already died aged 4 and 7 years of age and the remaining three are dependent on night time ventilation. There has been very little deterioration over time in the skeletal muscle function, and the survivors remain ambulant, the oldest being 11 years. Immunocytochemical studies of the muscle biopsy showed a normal pattern for dystrophin and the dystrophin-associated glycoproteins, but a reduction of the laminin alpha2 chain of merosin. Magnetic resonance imaging of the brain was normal. The disease did not link to the LAMA2 locus for laminin alpha2 on chromosome 6q, so that these families seem to represent a new form of autosomal recessive muscular dystrophy with a secondary merosin deficiency. The primary protein deficiency has not yet been identified.

Chest wall motion before and during mechanical ventilation in children with neuromuscular disease

Patients with neuromuscular disease can display paradoxic motion of the rib cage (RC) and abdomen (AB), which increases the work of breathing and predisposes to respiratory muscle fatigue. Long-term mechanical ventilation can reverse chronic hypercapnea and decrease the work of breathing in these patients. Changes in chest wall motion (CWM) that occur during mechanical ventilation have not been studied. We have assessed CWM using a calibrated respiratory inductive plethysmograph before and during mechanical ventilation in 5 children and young adults with neuromuscular disease and paradoxic breathing at rest. Asynchrony of CWM was quantitated by measuring the phase shift, theta, between RC and AB motion (0 degree = synchronous motion, 180 degrees = paradoxic motion). The volume contribution of the paradoxing compartment to tidal volume (PC/VT) was calculated. Before mechanical ventilation, mean +/- SEM VT was 122 +/- 17 mL, theta was 131 +/- 15 degrees C, and PC/VT was -27 +/- 6%. During mechanical ventilation, VT increased to 274 +/- 47 mL (P < 0.05), theta decreased to 41 +/- 14 degrees (P < 0.05), and PC/VT increased to +39 +/- 9% (P < 0.02). We conclude that mechanical ventilation improves RC/AB asynchrony and reverses the negative contribution to tidal volume of the paradoxing compartment in children and young adults with neuromuscular disease. This implies that mechanical ventilation assumes most or all the role of the respiratory pump in these patients, which provides a rationale for the use of chronic or nighttime ventilation in the treatment of respiratory muscle fatigue. Assessment of CWM may be useful in the determination of optimal ventilator settings in this population.

The Swedish modification of the tracheostomy tube to permit speech.

Over the last 20 years the Respiratory Unit at Danderyd Hospital, Sweden has treated and rehabilitated more than 90 patients on domiciliary ventilation, the majority of whom require night-time ventilation. Sixteen patients (11 men and 5 women) with high spinal cord lesions have been treated. Of these 16 patients, 9 are using diaphragmatic pacing. Every patient has a customised tube. If the patient can use diaphragmatic pacing the tube, as a rule, is single fenestrated. In patients using the ventilator full time, the tube is made to fit snugly in the trachea. When such a tube fits 'as a bullet in its tube' there is no need for a cuff. The patient has adequate ventilation and the small leak around the tube also permits good speech function. Sometimes a PEEP-valve is used to get a better voice.

Long-term ventilatory support in spinal muscular atrophy

Before ethical issues regarding prolonging life in patients with degenerative disease can be considered, the quality of life with medical intervention must be delineated. We have followed 15 patients with spinal muscular atrophy who have been treated with mechanical ventilation. They have received assisted ventilation for an average of 8 years 10 months (range 5 months to 23 years 10 months). Three of the patients required full-time ventilator assistance at the time of initiation of ventilation; the remaining 12 used nighttime ventilation for an average of 8 years 7 months. Nine patients continue to receive nighttime ventilation only. Two patients died after 5 years and 14 years of assisted ventilation, respectively. Of the 10 patients more than 18 years of age, three graduated from college, two are in college, three graduated from high school, and two completed eleventh grade. One patient is a mother of a healthy child. Two patients are employed, and two others have found fulfilling volunteer work. Ventilator support has not significantly interfered with these patients' plans and expectations.

Long-term management of diaphragmatic paralysis complicating prosthetic valve replacement.

The exact incidence of diaphragmatic paralysis complicating secondary heart procedures is not known. The postoperative period can be complicated by difficulty in weaning from mechanical ventilation and misinterpretation of the clinical signs of respiratory muscle fatigue for congestive heart failure and acute bronchospasm. We present 3 patients, all of whom had right diaphragmatic paralysis and recurrent respiratory failure after a second mitral valve replacement. Long-term management with night-time ventilation in 2 patients resulted in no further episodes of respiratory failure and physical rehabilitation with exercise tolerance significantly greater than the preoperative state.