Some Like It Hot: Exploring Thermal Comfort in the Office
Despite some hints that spring is around the corner here in San Francisco, many areas of the country are still experiencing the throes of winter weather. And with outdoor temperatures still dropping below freezing, indoor temperatures can soar to almost tropical levels, or feel like an icebox. Whether you’re bundled up in your parka or stripping off extra layers, managing your thermal comfort at work can drain your energy and make you less productive. To get a sense of the data behind our comfort challenges, we turned to our in-house sensor network to answer some questions at Aclima’s San Francisco office.
Thermal comfort doesn’t only matter to employees. It’s also a common cause for occupant complaints to a building’s facilities manager and property owners, affecting occupant wellbeing and the monthly utility bill. For many, thermal comfort can be achieved by simply adjusting a thermostat. However, experienced owners and facility managers know that maintaining comfortable conditions and avoiding complaints requires understanding a myriad of factors, including space size, occupancy, solar radiation, and HVAC system capabilities. Moreover, thermal comfort is not entirely determined by building design and operation. Human metabolism and personal preferences play a major role in determining whether or not spaces feel warm or cold.
With so many factors in play, how can we objectively understand and improve individual comfort levels in the office? Hyper-local, real-time environmental data collected from distributed sensor networks can provide a foundation of facts to manage these challenges. This allows facility managers to identify problem areas and take corrective action before receiving occupants complaints.
Let’s consider our small office room on the south side of the building, which often feels stuffy in the afternoon. We know that when occupants report that a room feels “stuffy” it can be attributed to different combinations of environmental factors. For instance, occupants could be experiencing a buildup of carbon dioxide in the enclosed space. Alternatively, a HVAC vent may be blocked, or a south-facing window may be causing the room to feel too warm in the afternoon. To address this, we turn to data from Aclima’s Environmental Intelligence platform™ for a pulse on what’s going on.
Our Data
Over several days, we looked at carbon dioxide (CO2) and temperature data to assess how the office room responded to a series of controlled changes. CO2 levels usually reflect how well a space is ventilated when occupied, while a number of factors, including ventilation, can affect room temperature. For comparison, we used a significantly larger adjoining main office space where the temperature is more comfortable and consistent.
During our experiment, we maintained consistent occupant levels as we created a series of experimental conditions:
- Door open: We kept the door to the enclosed office room open to the main office space.
- Door closed: We kept the enclosed office door closed and relied on the HVAC system.
- Windows open: We kept the door closed and opened outside windows.
In testing these typical room conditions, we found that CO2 concentrations were comparable between the two spaces, as shown in Figure 1, indicating that poor ventilation was not the cause of the stuffiness. Our data confirmed that the south-facing, exposed window drove the heat up most afternoons and gave occupants the feeling of the room being “stuffy”.
As you can see, Figure 2 highlights the significant differences in temperature between the two rooms. When we calculated the “ΔT”, or the temperature difference (delta), between the enclosed room versus the main room for each day, the Friday temperature in the small office was more than double the temperature difference compared to Thursday. From consulting historical weather data, we see that Friday was the sunniest day during our experiment.
To make sure what we were seeing wasn’t an anomaly, we compared the enclosed office room to an office that has similar square footage, ventilation, and occupancy but is located on the north-facing, shady-side of the building. In looking at the same time period and date range, the shady office maintained a lower temperature throughout the day and had no problems with CO2 levels. This again confirmed for us that the thermal issues in the enclosed office room stem from solar radiation as opposed to inadequate ventilation.
Finding Solutions
Unwanted solar heat gain is one of the most common comfort issues facing commercial building designers and managers. The most common solution is increasing air flow either manually or automatically through an HVAC system, or using a small fan, all of which require additional energy costs without addressing the root cause of the problem or ensuring comfort.
In our case, our solution was to install reflective, adjustable shades to cover the window when the sun is shining directly on the glass, while still allowing for natural light when the sun isn’t so bright. We could also take this a step further and replace the window with smart glass that does not allow as much heat gain, but this is a more expensive option. While the best option for maintaining a comfortable temperature in our space included keeping the outside window open, we decided to keep the window closed because of street noise and potentially more exposure to outside pollutants.
Ultimately, the ideal solution for our second story office would be to plant a tall, leafy tree outside of our office window. We’d reap added benefits like improved local air quality, reduced storm runoff, and reduce the heat island effect. Planting more trees in urban regions has been shown to decrease temperatures while providing the additional benefit of soaking up pollution.
Bottom Line
Continuous distributed environmental sensing can help building owners and managers identify thermal comfort issues before occupants complain. Data from sensing networks can help managers diagnose and address the root causes of discomfort. This allows building managers to make data-based decisions and, critically, provide objective data on the results of their interventions. We can literally “see” improvements in real time. Much like energy efficiency has improved how we operate buildings while reducing our carbon footprint, environmental data adds a personal layer of insight informing our physical comfort and productivity. This new building pulse is the next step to inform and support worker wellness and wellbeing.
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