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May 2017
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Investing in Occupant Comfort

How thermal comfort enhances productivity, and how to achieve it without sending your energy bill through the roof.
Brenna Buckwalter
Brenna Buckwalter,
Marketing Manager
BuildPulse

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Six variables drive an occupant’s thermal comfort: air temperature, surface temperature, humidity, clothing level, activity level, and air velocity, but these factors don’t tell the full story behind the maintenance involved in optimizing temperature in office buildings, commercial buildings, K-12 schools, and on university campuses. Thermal comfort depends on other factors as well, like climate and occupant preferences – for example, occupants in Colorado may be more susceptible to humidity and heat than occupants in Hawaii.

The biggest challenges for Commissioning Agents and Facility Managers lie in finding a temperature which is satisfactory for the majority of their occupants, all who may have slightly different preferences, and doing so without sending the energy bill through the roof.

OCCUPANT-CONTROLLED TEMPERATURES

Giving occupants control over their own thermostats can be a double-edged sword: occupant complaints will likely go down, but energy bills typically rise. Occupants often have a ‘not my bill, not my problem’ mentality, leading occupants to leave lights on or excessively raise and lower temperature carelessly.

A good rule of thumb to combat this is to utilize thermostats in individual offices, accompanied by an occupancy sensor in order to avoid excessive heating or cooling when the room is vacant. In an open office or classroom, refer to ASHRAE guidelines and keep the setpoint temperature at 69°F for heating and 73°F for cooling. If complaints are low, a verbal response may be all that is necessary to solve the issue, as thermal comfort is so subjective that it is impossible to keep everyone happy. If complaints are high, however, Peter Turek, a commissioning agent at DLR Group, suggests that a survey is conducted. Ask occupants if they are receiving enough airflow and ventilation and if they feel their space is stuffy or humid to get a pulse on the issue.

USING DATA TO MANAGE ENERGY AND TEMPERATURE

Besides simply lowering temperature, Facility Managers and Commissioning Agents can lower energy costs by installing occupancy sensors, using insulation to stop the heated or cooled air from leaking out, and taking advantage of their existing Building Automation System.

TAKE ADVANTAGE OF THE BUILDING AUTOMATION SYSTEM

Collect Temperature and Humidity trend data – it’s available in your existing systems, and you cannot change what you don’t measure.

CALCULATE TIME INSIDE AND OUTSIDE OF THE SETPOINT DEADBAND
Rank the zones by time inside or outside of the setpoint and if they are in the “Hot” or “Cold” zones. In winter, if spaces are consistently “Hot” verify that the heating valve that serves the zone is not leaking or that the occupant has not bought a space heater to work; if a space is consistently cold, check air flow to make sure that too much air is not being delivered, and confirm that the temperature of the air entering the space is no more than 30 degrees above the ambient air temperature for proper mixing in the space, (See High-Performance VAV Systems – ASHRAE ). In summer, if spaces are Hot verify that blinds or natural shading are still effective and that proper airflow is being delivered to the space; if spaces are cold, they are most likely over-cooled. Confirm the pitots have not kinked or become loose and the box is getting a good measurement of the air flow to the space. Calibrate as needed.

Bar Graph

COMPARE THE ROOM TEMPERATURE TO THE OUTDOOR AIR TEMPERATURE
If the room temperature follows the same arc as the outdoor air temperature, check that the space is getting an appropriate amount of airflow: too little impacts the spaces ability to heat and too much can over cool the space and force simultaneous heating and cooling at the zone level.

Line Graph

LOOK FOR RAPID CHANGES IN TEMPERATURE
Cycling of equipment is detrimental to the equipment lifetime and negatively impacts occupant comfort. If working with a VAV’s system, this is a sign of over ventilation for both heating and cooling; it can also be caused by too low of a discharge air temperature setpoint at the parent AHU. If working with a HeatPump System, and the change in temperature is rapid in one direction, increase the minimum run time of the unit, so that float time is increased, versus cycling the fan and compressor every 5 or 15 minutes. In either case, this will prolong the lifetime of the equipment and improve comfort as the occupant is not being blasted with Cold and or Hot air, four or five times an hour.

Rapid Temperature Changes

CHECK SENSORS
Location, location, location. If a sensor has not changed by more than one or two degrees Fahrenheit over the course of a day, it has external influences that were not part of the design intent. For example, a bookshelf may have been placed in front of the sensor. If it does not change at all, then the sensor has been disabled, and the value should not be trusted. Replace or calibrate the sensor as required.

OPENING CONVERSATIONS ACROSS DEPARTMENTS

Even energy efficient buildings have their challenges. One issue that Turek noted is that “a lot of times, the good design intent is overridden by operators so that they don’t have to deal with occupant complaints.” Ideally, during the training period, the design engineer should explain the intent and answer questions for the operations staff to eliminate or reduce the practice of overriding or disabling set points. In the case that this doesn’t occur, the key to solving this problem is to get organization’s management on the same page as Facility Managers by making occupants aware of the consequences of energy waste on their organization. Though occupants may not directly pay the energy bill, it is important that they know that the cost does affect them in the long run, because “that investment in energy savings is returned back into higher salaries or other benefits for employees.”

Control Solutions, Inc INVESTING IN OCCUPANTS

With up to 90% of our time being spent indoors (especially during the winter months, when our energy bills tend to reach their peak in most parts of the US), it’s important that occupants are comfortable and happy in their office and school environments, despite the cost.

The cost of neglecting occupant comfort is actually higher, however: one study from the University of Helsinki and Lawrence Berkeley National Laboratory found that “a typical office could save $330 per employee per year by maintaining office temperatures within” an optimum range. Another study, conducted by PLOS One, found that in schools, “subjects exposed to a difference of 1°C (1.8°F) in indoor T differed by 13 points” on test scores. Small changes can truly produce big results.
________________________________________

Managing a space full of occupants with different temperature preferences can certainly be a challenge for Facility Managers and Commissioning Agents who are under pressure to lower, or even maintain energy costs. Focusing on keeping a majority satisfied and at their most productive level is the best way to approach setting temperature in communal spaces.

For more information on thermal comfort, view these resources from ASHRAE, Rocky Mountain Institute, PLOS One, and the Lawrence Berkeley National Laboratory.


About the Author
 
Brenna Buckwalter, Marketing Manager at BuildPulse
Brenna has a business degree from the University of New Hampshire. Before joining the team at BuildPulse, she gained experience in marketing working with startups across the industry and international borders.

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