Interactions with ventilation systems Simulating window opening

40% of participants in a postal questionnaire study by Lindén et al. (2006) reported that they were engaging in daily airing using windows (sample of 600 Swedish homes). This result supports many of the findings presented in the previous section which were based on research carried out during the 1980s. There seems to be general agreement within the literature that windows are being opened at times when it would be more efficient (in terms of energy) for them to be closed. Consequently, much of the more recent research around window opening is concerned with improving building simulation models to account for this; however, the work tends to rely on reported information (from buildings users) and measured environmental variables (e.g. Jian et al., 2011, Park and Kim, 2012). Use of window sensors is relatively rare, although some studies have incorporated sensor data into their investigations, albeit with much

71 Other findings from the same study are published in Phaff and van Dongen (1985) and Phaff (1986), and were discussed earlier in this section on p63.

smaller samples (e.g. Rijal et al., 2012, Andersen et al., 2013).⁷² Also, research reported in Schweiker et al. (2011), measured the angle of window opening using a potentiometer.

A recent review of the literature on window opening behaviour in dwellings and offices, by Fabi et al. (2012), identified physiological, psychological, social, physical and contextual drivers behind ‘energy-related’ window opening (Table 12). With such a wide range of contributing factors the task of accurately simulating window-opening behaviour in a model is challenging, with inevitable simplifications and assumptions limiting the validity of results (e.g. Conan, 1982, Eftekhari and Marjanovic, 2003, Koinakis, 2005). Measured window opening data appear to be rarely used to develop simulation tools. However, even if opening data are collected they do not reliably predict the impact on ventilation rate or energy use.

Table 12: Factors influencing residential, energy-related window opening⁷³

Physiological Psychological Social Physical

Recently, a more sophisticated probabilistic approach has been adopted in several projects which attempt to simulate window opening in schools and offices (e.g. Nicol, 2001, Rijal et al., 2007, Haldi and Robinson, 2008, Yun et al., 2009, Dutton and Shao, 2010). Work by Sorensen (2011) used measured data to develop and test a probabilistic model of window opening behaviour in dwellings. The model considered environmental and climatic variables such as temperature and relative humidity (RH%), alongside building envelope parameters such as level of insulation and thermal mass to see if different designs were more or less robust to occupant interactions. A probabilistic model of domestic window opening behaviour is also proposed in Fabi et al. (2013).

Curtains and blinds

Opening and closing curtains and blinds can aid the prevention of excessive solar gains during summer and reduce draughts and heat losses during winter. Windows can also be covered and uncovered for other reasons, such as to admit natural light, to provide a view out or to maintain privacy. A small number of studies have considered whether, and to what extent, windows in

72 The first of these references was based on a study of 30 homes and the second on a sample of 15 homes.

73 From Fabi et al. (2012). Other physical environment factors could include temperature difference between indoors and outdoors and noise.

homes are covered at night time. For example, Lindén et al. (2006) note the ‘reluctance among most households to cover windows by night with curtains or blinds’ (p.1924). Similar findings are reported in Carlsson‐Kanyama et al. (2005), where the average questionnaire score was 2.1 (1

= never close at night, 5 = aways close at night) (based on further analysis of the same dataset). Interestingly, higher scores were reported by respondents living in apartments as well as those with low incomes. What is not clear, however, is why respondents drew curtains or blinds and whether energy saving, or, for example, matters of privacy, were involved.

A case study of two dwellings conducted by Ridley et al. (2014) revealed that occupants ‘did not fully understand how to use the external blinds, or tilt the louvres’, which had been provided for the purpose of summer shading. Consequently, the slatted components were not being utilised and the residents found that closing the blinds blocked the view and daylight. The study also mentioned the reluctance of residents to ventilate bedrooms using windows in summer, owing to spiders. Both of these factors can increase the risk of summertime overheating. These findings were based on a combination of in depth methods which included technical monitoring, an occupant questionnaire and walkthrough interviews with the residents.

Interaction with mechanical ventilation components

Several studies have found that people are not using mechanical fans as often as is recommended. For example, a large scale questionnaire study of over 5000 homes, by Price and Sherman (2006), found Californian homes to be under-ventilated; 30% of households

‘rarely or never’ switched on the bathroom fan and a third of respondents experienced dusty, stagnant, humid or dry air. Furthermore, energy saving was one of the top two reasons people cited for closing, or keeping closed, windows. Park and Kim (2012) focused their investigation on 139 mechanically ventilated apartments in Seoul (supply and extract, unbalanced, no heat recovery). Almost 70% of respondents reported never used the ventilation during the heating season, citing concern over increased heating costs as the main reason for not doing so. In a questionnaire study of 7000 Dutch homes with MEV and mechanical ventilation with heat recovery (MVHR), 51% of residents responded that the ventilation system was turned on for less than three hours a day (Guerra-Santin and Itard, 2010). Instead, over 50% of people claimed to leave bedroom and living room vents open all the time and the majority of occupants use windows for several hours every day, even during winter.

A study by Soldaat and Itard (2007) conducted 18 interviews in Dutch homes with MVHR, alongside a theoretical modelling exercise, to try to quantify the energy impact of occupant ventilation. The interviews revealed that residents were largely unaware of the potential energy benefits of MVHR, or of the energy implications of wintertime window opening. During the summer the bypass mode was not being utilised, as most occupants were not aware of its existence. The authors quote a Dutch study which found that MVHR units are not being cleaned regularly enough in half of homes with the system. Similar findings are reported in Balvers et al.

(2012). The findings of the modelling by Soldaat and Itard indicate that occupant interactions can negate the energy saving potential of MVHR, so that in some cases NV may be more

energy efficient. A similar conclusion was also reached by Macintosh and Steemers (2005).

47% of the occupants surveyed across a new development of 59 homes kept the MVHR on the same setting all year, 40% on ‘normal’ mode, 5% (2 users) on ‘boost’ and one household had it disabled altogether. The study proposes that the main problem was lack of understanding of the MVHR system’s intended operation. Misconceptions included the belief that windows should be opened to provide fresh air and the idea that using windows and MVHR together would increase the effectiveness. Misunderstanding of intended operation was also raised in Banfill et al. (2012) and Stevenson and Rijal (2008).

Lemaire and Trotignon (2000) report that over 25% of people in dwellings with MV regularly turn off the ventilation and that just over 13% of households admitted to blocking off aeration vents.

More positively, over 60% of respondents claimed to clean the ventilation system once a year or more. The same study concluded that although ventilation type has little effect on satisfaction levels, the ability to switch off the ventilation returned increased satisfaction levels, especially among those people who seldom made use of this option.

Meyringer and Trepte (1986), report a German study which found ‘a high probability of inhabitants rejecting or counteracting ventilation systems which do not comply with user expectations’ (Meyringer et al., 1987).⁷⁴ They identified the following six requirements for a ventilation system to meet user expectations:

 Avoidance of draught effects

 Tolerance of ill-attendance

 Minimal maintenance requirement

 Low noise level

 Freedom to interfere

 Familiarisation with a system

The aforementioned study also found that occupants perceived overheated inlet air as ‘stale’

and ‘not fresh’. A weakness of this piece of work is that it fails to acknowledge any theoretical research in the areas of user acceptance and innovation which was being carried out at that time (e.g. Pinch and Bijker, 1984); this limits the scope of its contribution.

The results of a questionnaire conducted in Austria by Rohracher (2001) show that people in blocks of flats are significantly less satisfied with their ventilation systems than those in single family houses (Figure 21, Figure 22, based on 50 semi-structured interviews with residents and 144 completed questionnaires). The author interprets this by observing that ‘owners connote this product with ecology, health and comfort, tenants rather stress ventilation systems being a

74 This reference is for a book published in German, which is currently out of print and not held in a UK library. The abstract is available at

http://www.baufachinformation.de/literatur.jsp?bu=1987089040472.

modern technology’, adding that ‘the view of architects and planners best corresponded with the connotations of house owners’ (p.299).

Figure 21: General satisfaction with ventilation systems⁷⁵

Figure 22: Benefits of living with MVHR⁷⁶

Some of the reported problems included noise (40%), poor controls, and dislike of the

‘(supposed) requirement to keep windows shut’ during winter (p.298), especially at night. Some people were found to be using supplementary heating devices and there were even those who sabotaged the system by blocking the air vents.

75 Reproduced from Rohracher (2001), p.297.

76 Reproduced from Rohracher (2001), p.299.

More recently, Brown and Gorgolewski (2014) conducted a POE study of four high rise apartment blocks in Canada using the Building Use Studies (BUS) Methodology questionnaire (ARUP, 2015) and semi-structured interviews. The study found that less than half of respondents were using their heat recovery ventilation (HRV) systems. The main reason for the under-use was acoustic discomfort and difficulty changing filters. Those people who had read the training manual were over seven times more likely to use the HRV, suggesting that a lack of knowledge may also contribute to the under-use. Furthermore, 76% of respondents from three of the blocks stated that balcony doors and openable windows were the primary source of ventilation during winter, compared to only 15% stating that it was HRV. This statistic corroborates the findings reported in section 3.2.2 that people frequently open windows during the heating season.

Introducing social dimensions to quantitative studies of ventilation

Certain studies have introduced socio-demographic dimensions into research about window opening. Dale and Smith (1985) concluded that concerns about health lie behind their finding that 13% of people in the UK sleep with the window open regardless of the weather.⁷⁷ The authors argue that 19^th Century writings about hygiene and good housekeeping, such as those of Florence Nightingale and Mrs Beeton, have filtered down into the common conscious and shape contemporary beliefs, despite the fact the ‘Miasma’ or ‘bad air’ theories have been disproven and modern plumbing has replaced the practice of keeping a chamber pot under the bed (Baldwin, 2003, Johnson, 2006). A recent campaign by Age UK sought to encourage older people to close bedroom windows at night to reduce excess winter morbidity (Age UK, 2012), following research by Gascoigne et al. (2010) which found evidence of deeply held beliefs about the importance and benefits of leaving windows open at night.

A study by Fleury and Nicolas (1992) concluded that whether or not the wife stays at home and the presence and age of children are the main sociological factors affecting ventilation behaviour in the kitchen, bathroom and children’s bedroom, while in the living room the orientation with respect to the sun is the main factor. The study also found that people tend to underestimate how long they open windows for, especially in the living room and master bedroom (Figure 23).

77 The study also reported that 71% of respondents stated ‘sometimes’ and 17% ‘never’ in this questionnaire.

Figure 23: Percentage (%) of occupants over and underestimating window opening duration⁷⁸

A follow up to the Twin Rivers project, this time with a focus on ventilation and occupant behaviour, is reported in Harrje and Kempton (1986). The paper considers the behaviour change potential of encouraging occupants to use the windows to provide cooling, rather than relying on air conditioning, during the summer. A blue light was used to indicate that the external temperature was below 20°C and that the air conditioning should be switched off and a window opened instead. The study was conducted in 40 homes in New Jersey over the hottest summer month (August). 10 homes received energy consumption feedback alongside the blue light warning, 10 received feedback only and 10 just the blue light, alongside a control group of 10 further dwellings. Results indicated that, at the end of the month long study, the homes with the blue light indicator (with or without feedback) used 15.7% less electricity than the control group, with the feedback alone having a slightly reduced positive impact; however, it is unclear whether this change was sustained over time. Encouraging passive cooling is increasingly relevant as parts of the UK feel the effects of climate change, and mechanical cooling becomes more prevalent in housing, as it has done in commercial buildings.

Another study reported in Harrje and Kempton (1986) used 12 open ended ethnographic interviews to investigate why people were opening windows during the heating season in an airtight apartment block (0.3 ACH) of 57 apartments. A follow up questionnaire was used to interview residents at 53 of the dwellings, with results indicating that 84% of tenants were using windows to reduce the effects of persistent overheating, compared to only 35% turning down the radiator valve. Windows were also being opened to provide ‘fresh air’ and to reduce stuffiness. The questionnaire-interviews also revealed that tenants opened windows a small amount (10-15cm) to provide fresh air, and much wider to reduce temperature. The study demonstrated the need for understanding ventilation practices in the context of thermal comfort and heating provision, as they are clearly interconnected. Most of the residents felt that fresh air was healthy, something which the author’s attribute to the fact that many of them were older people and would have grown up in homes heated by wood and coal, when opening windows would have been advisable to maintain a healthy IAQ. However, there were no younger participants in the sample to compare with the older people. A further interesting finding was that one of the reasons residents were using the windows instead of calling maintenance to ask

78 Reproduced from Fleury and Nicolas (1992).

for help (29%), was that they did not want to be labelled ‘complainers’ and risk losing their home; thus, opening windows became a more attractive solution, especially for lower-income residents. Finally, the study calls for increased research about the relationship between the building management and the housing authority, to understand why these inefficiencies were being allowed to proliferate.

A mixed method case study approach was also adopted in two further studies of residential ventilation behaviour (Diamond et al., 1986, Hainard et al., 1986). Diamond et al. used a combination of technical measurements of environmental parameters alongside an occupant survey of attitudes and behaviour towards comfort, IAQ, ventilation and energy consumption.

Similar explanations for opening and closing windows were reported in Dubrul (1988), with the addition of painted or sealed windows inhibiting window opening, as well as health and the ability to ‘maintain contact with the street’ being cited as reasons for opening windows. In contrast to other studies, windows were very rarely opened during winter. Possible explanations include the observation that many residents believed the building was cold and draughty, as well as the fact that the study was conducted in Chicago, where the winter design temperature is -22°C.

Hainard et al. (1986) carried out the first study of residential ventilation behaviour with explicit reference to the social sciences, at a case study site in Switzerland. Technical measurements were combined with occupant interviews in 15 apartments, to investigate ‘psychosocial and cultural dimensions of the ventilation of an urban rented habitat’ (p.12.3). The paper suggests that by understanding the ‘underlying motivations’ of people’s behaviour ‘we should then be able to create suitable technically innovative improvements’ (p12.3). The quantitative data identified different patterns of behaviour in relation to external temperature, as well as according to storey and orientation of the flat. Attempts to triangulate these results with the survey data proved problematic. More interesting are the explanatory implications of the qualitative investigation; the study concludes that comfort expectations play a significant role in shaping window opening practices, but acknowledges the important contribution of other ‘interactions’

and ‘motivations’ related to window opening, as outlined in Table 13.

Table 13: ‘Interactions’ and 'motivations' for opening windows⁷⁹

79 Table compiled using information from Hainard et al. (1986).

Ecological motivations

and shaped by the ‘existing infrastructure’ which is outside of a person’s control, as well as the personal preferences of occupants (p.12.7). Some interesting observations are made, such as the use of windows for communication (e.g. to supervise children) and of the ‘instinctive’ and

‘compulsive’ nature of window opening (p.12.12). However, the study lacks a theoretical underpinning which ultimately limits the usefulness and credibility of its findings. Theories are useful in social science as they can help locate a piece of research in the context of what has been studied before. Theories can also provide a vocabulary of concepts, categories and processes with which to investigate data and, in certain cases, with which to generalize findings beyond the specific study (Swanson and Chermack, 2013).