By Ramtin Motahar
It’s a universal truth: The temperature at the office is never quite right. Whether it’s too hot or too cold, discomfort keeps office tenants in a game of thermal tug-of-war—leaving facility managers frustrated and owners footing the bill for inefficient energy usage.
The causes of temperature fluctuations at the office are complicated. From climate change to clothing preferences to architectural design, there are a slew of factors contributing to office workers’ thermal discomfort.
At the heart of this issue lies temperature setpoint guidelines. In the U.S., the temperature setpoint for office buildings is recommended by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) and is suggested to fall between 65 to 80 degrees Fahrenheit depending upon occupancy and other factors (time of day, season, etc.). Though updated throughout the years, these standards were established by ASHRAE in 1966 based on the average office user’s clothing and metabolic rate. You can imagine how gender played a role—men, usually sporting wool suits at the office, made up approximately 80% of the workforce in 1970. Men also have a higher metabolic rate than women.
Setpoints and building controls are only a few considerations. Technical causes of temperature fluctuations at the office could include problems with the building envelope or faulty equipment, or simply come down to the location of a temperature sensor.
One of the most overlooked causes, particularly in aging buildings, is a phenomenon often referred to as “sensor creep.” Identifying and solving this underdiagnosed problem can save building owners hundreds of thousands of dollars annually in energy costs, in addition to keeping office users comfortable.
Understanding Sensor Creep
All temperature sensors have a sensor tolerance, or a margin of error—essentially a level of inaccuracy with respect to the nominal specification deemed acceptable by the manufacturer. Typically, the more expensive products are more precise. But this means your temperature sensor is never going to be flawlessly accurate, even when it’s brand new.
However, sensor creep occurs when the reading on a temperature sensor is outside of standard accuracy requirements. A common standard for this would be more than two degrees Fahrenheit. In other words, if your setpoint is 72 degrees Fahrenheit, and the sensor believes it is 72 degrees Fahrenheit, the actual temperature of the room could be warmer or cooler than this by several degrees. Worse, sensor creep can convince the temperature sensor that the space is not at setpoint, at which point it will call for heating or cooling even if neither is necessary. Unchecked sensor creep can render setpoints useless.
Sensor creep becomes more prevalent with age, depending on the quality of the sensor purchased. The process of diagnosing sensor creep is surprisingly simple. Any trusted temperature sensing device can be employed to check the accuracy of the temperature sensors. For instance, personnel can use a reliable thermal gun to measure the actual temperature of a room and compare this value to the one displayed on a nearby temperature sensor.
To address this issue, one option is recalibration. Devices experiencing this sensor creep can be serviced by the manufacturer or a trained control technician. While this can be the cheaper of the two options, it will not always be possible. In many cases, repairing an inaccurate temperature sensor will be more costly than replacing the sensor.
The cost of replacement varies by building and sensor type. In a 500,000-square-foot building, there may be approximately 550 temperature sensors. With a price tag of about $12 to $16 each, replacing all the temperature sensors in a building of this size will cost between approximately $6,600 to $8,800, excluding labor which can vary based on use case.
A Worthwhile Investment: Case Study
The savings available from correcting this issue far outweigh the costs.
For example, a 13-floor, 500,000-square-foot building in Midtown Atlanta was determined to be overcooling and overheating by two degrees Fahrenheit due to sensor creep. At 20 years old, it’s likely the sensors deteriorated over time. It was discovered that the sensor creep was creating large areas where heating and cooling equipment were being forced to compete. This is a phenomenon known as simultaneous heating and cooling. This drives heating, cooling and ventilation equipment loads far higher than necessary. The combination of sensor creep and suboptimal HVAC design generated an excess of $146,000 in wasted electricity or 16% of their total consumption. This translates to 1.1 million kWh in savings and 3.6 tons of carbon equivalent savings in GHG emissions.
Why It Matters
Solving the over-conditioning problems in office buildings will provide financial, energy and environmental savings.
Dissatisfaction with temperature consistently ranks among office tenants’ top complaints about their work environments. Research has shown that improvement of thermal comfort issues results in higher office tenant satisfaction scores, which leads to better retention rates.
Overall, approximately 33% of the budget spent on energy usage in office buildings is wasted due to inefficiencies. Further, over-conditioning of commercial buildings is estimated to cost upwards of $10 billion in wasted electricity annually, or about 7.5% of the total commercial building electricity cost. It is the fastest-growing source of energy use in buildings, tripling between 1990 and 2016.
Over-conditioning also presents a significant barrier to curbing greenhouse gas (GHG) emissions in commercial buildings. In the U.S., GHG emissions from the built environment account for disproportionately higher total emissions than not only the entire passenger car market, but also the entire transportation market. Operational emissions reached an all-time high in 2020. We must accelerate our decarbonization efforts in the building sector.
Warmer temperatures bring with them an increase in over-conditioning complaints at office buildings. Before summer arrives, make a plan for thoroughly inspecting your building’s HVAC system. From building envelope anomalies and suboptimal controls to underdiagnosed problems like sensor creep, a swath of issues could be causing your office building to over-condition. Repairs will pay for themselves by capturing energy savings and lessening your environmental impact.
