How Often Do People Adjust Manually-Operated Window Coverings?

Pretty much anything that can be researched has been researched, and the usage of manually operated window coverings is no exception.

This topic first took off after the 1973 energy crisis, and was initially aimed at investigating factors that affect the energy consumed in lighting and heating of office and (to a lesser extent) residential buildings. The research is still relevant for that purpose, but today it’s also relevant to the requirements for—and potential benefits of—automated window shading technologies.

The research addresses two primary aspects of window covering usage:

• the frequency with which manually operated window coverings are adjusted, and
• the distribution of actual settings (i.e. degree of openness or closure) of manually operated window coverings.

This post addresses only the frequency of adjustment; a separate post describes research showing that most window coverings are typically left in a mostly-closed position.

Window-Covering Adjustment Frequency in Office Buildings

Most of the research on window covering usage has focused on office buildings, for two reasons. First, window coverings have a greater impact on energy consumption in office buildings than in any other building type because office buildings have a greater ratio of window to wall area than other building types. Second, photographic observation of a single office building can yield data for a relatively large number of window coverings.

The bulk of the data on window covering usage in office buildings has been for horizontal venetian blinds, because they’re the most widely used (and arguably the most versatile) window coverings in both office and residential buildings.

While blinds are physically the easiest type of window covering to operate (via the slat-tilt function), the pertinent studies have repeatedly shown that office building occupants buildings rarely adjust them:

• Monitoring of 700 manually operated blinds across 6 buildings and two façade orientations (north and south) revealed that only 50 blinds were adjusted during a one-week period (Rubin et al. 1978, page 29).
• Observation of three facades of a 16-story office building showed that occupants made little or no attempt to change blind settings over the course of a day (Rea 1984, page 7).
• A total of 228 adjustments of manually operated blinds were observed in seven offices over a 58-day period, yielding an average adjustment rate of 0.7 per day. But in eight different offices equipped with motorized, remotely controlled blinds, 832 adjustments were observed over a 50-day period, for an average of 2.1 adjustments per day (Sutter et al. 2006, paragraph 3.2.1).
• A survey of 113 office occupants found that 64.6% of the respondents adjusted their blinds less than once per day, 17.7% adjusted their blinds once per day, and only 17.7% adjusted their blinds more than once per day (Inkarojrit 2005, page 117, Figure 4.11).

The data consistently indicates an adjustment frequency of less than one per day for manually-operated blinds. The data from Sutter et al is unique in that it also includes some data for motorized blinds, which were adjusted three times more frequently than the manually operated blinds in the same study.

Window-Covering Adjustment Frequency in Residential Buildings

Perhaps the most comprehensive source of information on window covering usage in U.S. residential buildings is a 2013 report prepared by D&R International for the Department of Energy. The report provides window covering usage data collected from 2,100 U.S. households via an online survey conducted in 2012. In addition to the impressively large sample size, the survey also addressed factors such as type of window covering, window orientation, type of room (e.g. living room, bedroom, etc.), and climate zone (northern, mid-tier, and southern).

One of the key findings was that—as noted above for office buildings—manually operated window coverings in residential buildings are typically adjusted less than once per day. In fact, the data suggests that not only are most window coverings kept in the same position over the course of a day, the majority of households keep all of their window coverings in the same position over the course of a day:

Further, a substantial fraction of surveyed households left their window coverings in the same position over the course of a whole week, and—for a surprisingly large number of households—even over the course of a whole year:

Implications

There are at least three significant implications of the adjustment frequency data summarized above; two are clear-cut while the third is debatable.

Manual Shading Isn’t Responsive to Daily Changes in Irradiance

An obvious implication is that, with an average adjustment frequency of less than one per day, people don’t adjust manually operated window coverings according to daily movements of the sun and clouds.

It might be expected that people would prefer too much shading to too little shading (e.g. to avoid occasional glare and maintain privacy), and that most shades would therefore be left in a mostly closed position—and that indeed turns out to be true.

This means that the average level of glare-free daylight in buildings is much lower than it could be if the shading were responsive to changes in the incident solar irradiance.

Manual Shading Isn’t Responsive to Seasonal Changes in Temperature

Another implication is that most people don’t adjust manually operated window coverings according changes in season, so there seems to be little attempt to use window coverings to minimize HVAC energy consumption.

Specifically, since a majority of windows coverings are left mostly closed (see separate post cited above), the potential of window coverings to maximize daytime heat gain during the heating season—or maximize nighttime radiational cooling during the cooling season—isn’t being utilized.

Elimination of Physical Effort Might Not be the Most Compelling Benefit of Automated Shading

Before getting to the third (less clear-cut) implication summarized in the heading above, it’s worth noting that automation of a manually operated device can provide two types of benefit: it can eliminate the physical effort to operate the device, and it can also potentially enable the device to do things that wouldn’t be practical if it were still manually operated.

For example, before the introduction of the bimetallic thermostat in the late 19th century, gas-fired heating systems were available which eliminated the physical effort previously needed to operate coal-fired and wood-fired stoves. But without the thermostat, those gas-fired systems couldn’t provide accurate regulation of the temperature, especially unattended. So, the thermostat-equipped heating system didn’t just eliminate physical effort; it also provided a capability that wasn’t practical with manually operated heating systems.

Automated shading obviously eliminates the physical effort associated with manually operated window coverings. However, as with the thermostat in a heating system, automated shading can potentially also regulate the shading in a way that simply wouldn’t be practical with manually operated window coverings. Specifically (and as alluded to above), automated shading could potentially respond to (1) daily movements of the sun and clouds, and (2) daily and seasonal changes in temperature (on this site we refer to the former as responsive daylight control, and to the latter as responsive thermal control). Of course, automated shading could also provide any other shading protocol preferred by the user, assuming that it’s programmed to do so.

This brings us to the third implication of these studies for automated shading. Since they show that little effort is currently being expended to adjust manually operated window coverings, automation won’t address an existing pain point for users. That’s in contrast to (for example) automotive power windows and door locks, which were necessarily operated frequently even in manual form.

The implication is that advanced capabilities—beyond just remote-controlled motorized operation—are probably going to be necessary to give automated shading a compelling value proposition to mainstream buyers.

References

Bickel, Stephen; Phan-Gruber; Emily; and Christie, Shannon. “Residential Window Coverings: A Detailed View of the Installed Base and User Behavior”. Report prepared by D&R International, Ltd., Silver Spring, MD, for the Building Technologies Office, Office of Energy Efficiency and Renewable Energy, U.S. Department of Energy. 2013. https://basc.pnnl.gov/library/residential-windows-and-window-coverings-detailed-view-installed-base-and-user-behavior

Bulow-Hube, Helena. “Office Worker Preferences of Exterior Shading Devices: a Pilot Study.” Article IV in Doctoral Dissertation, “Energy-Efficient Window Systems. Effects on Energy Use and Daylight in Buildings.” Department of Construction and Architecture, Lund University, Division of Energy and Building Design, Lund, Sweeden. 2001. Report No TABK-01/1022.

Foster, Michelle and Oreszczyn, Tadj. “Occupant control of passive systems: the use of Venetian blinds.” Building and Environment 36 (2001) 149-155. Accepted 10 October 1999.

Haldi, Frederic and Robinson, Darren. “A Comprehensive Stochastic Model of Blind Usage: Theory and Validation.” Proceedings of the Eleventh Annual International Building Performance Simulation Association (IBPSA) Conference, Glasgow, Scotland, 2009. https://publications.ibpsa.org/proceedings/bs/2009/papers/bs2009_0529_536.pdf‎

Inkarojrit, Vorapat. “Balancing Comfort: Occupants’ Control of Window Blinds in Private Offices.” Diss. University of California, Berkeley, 2005.

Inoue, T, T. Kawase, T. Ibamoto, S. Takakusa, Y. Matsuo. “The Development of an Optimal Control System for Window Shading Devices Based on Investigations in Office Buildings.” ASHRAE Transactions 94[2], 1988, 1034-1049.

Lambeva, Lyudmila and Mahdavi, Lyudmila. “User Control of Indoor-Environmental Conditions in Buildings: an Empirical Case Study.” Proceedings Building Simulation 2007.

Rea M. S. “Window Blind Occlusion: a Pilot Study.” Building and Environment 19[2], 1984, 133-137.

Rubin et al. “Window Blinds as Potential Energy Saver—a Case Study.” NSB Science Series 112, 1978, National Bureau of Standards, Washington DC.

Sutter, Yannick, Dominique Dumortier, Marc Fontoynont. “The Use of Shading Systems in VDU Task Offices: A Pilot Study”. Energy and Buildings, 38[7], 2006, 780-789.