Key Objectives
- Temperature control – maintain heating and cooling set points
- Reduced utility expense – unoccupied / occupied modes
- Accessibility and usability
As with most technologies, there are numerous varieties, makes, and models of thermostats. The point of this article is to identify their purpose, and effective strategies in a general sense. While commercial buildings typically have a wall sensor that accept a few user inputs and contain the “smarts” on a controller elsewhere, the occupant’s interaction with residential and commercial thermostats are often similar.
Temperature control through maintaining set points is a primary focus of thermostats.
The heating, ventilation, and air conditioning (HVAC) unit operates to maintain defined heating and cooling set point based on the information it receives from the thermostat. Desired set points lie outside the scope of this narrative, but it is worth noting that the topic has received a great deal of discussion throughout homes, facilities, and engineering design groups the world over. ASHRAE Standard 55: Thermal Environmental Conditions for Human Occupancy was developed by the American Society of Heating, Refrigeration and Air-Conditioning Engineers (ASHRAE) and addresses this topic, among others.
Typically, a heating set point, as well as a cooling set point, is defined within the stated standards of ASHRAE Standard 55. While these set points are aimed at satisfying most users, an adjustment range is typically included for some slight modifications. In other words, while these standards meet most of the population demands, an individual user may raise or lower the set point slightly to meet their preferences. Depending on the system type, the unit will likely switch between heating/cooling modes depending on indoor or outdoor conditions. Otherwise, the user selects the mode seasonally.
When the room temperature is outside the set point range, the unit reacts by heating or cooling the space. To avoid constant cycling of the unit on/off, the temperature is driven slightly past the set point before shutting down and allowed to drift slightly past it again before returning to heating/cooling.
Reducing utility expenses through unoccupied / occupied modes is another benefit of modern thermostats.
Reduced equipment wear/tear and energy consumption are also worth noting. As mentioned above, maintaining occupant comfortable is an important focus. Therefore, when the space is occupied, a tighter tolerance of set points is needed. Whereas when the space is unoccupied, it can be allowed to operate under a wider range of temperature conditions. Inanimate objects are largely unconcerned with the temperature (not withstanding exceptions of museums, specialized equipment storage, etc.). This approach reduces the stress and runtime on equipment substantially and is made possible through setting a schedule either online or at the thermostat itself.
Setting an “occupied” schedule is great, but what happens when a room inevitably becomes occupied without being scheduled? A local override on the thermostat allows the user to temporarily override the schedule for a timed duration. This allows the occupants to utilize the desired set points and then the system returns to unoccupied schedule thereafter.
Accessibility is key to achieving your heating, cooling, and ventilation goals.
The ability to conveniently set operating parameters around schedules and set points quickly and conveniently is critical. The feature to easily put the system into occupancy mode temporarily thermostat avoids the over/under scheduling. Without the override, occupants will be frustrated, or the space will run occupied while vacant more frequently. Offering a limited adjustment of set points at the thermostat provides greater occupant satisfaction without sacrificing equipment runtime and energy. Having the ability to view current conditions and make changes remotely is highly advantageous. Lastly, simplicity leads to greater results.
In summary, there are four main attributes of thermostats to be considered beyond accuracy, dependability, and functional needs of the equipment.
- Indicator of occupied / unoccupied mode
- Ability to temporarily override occupancy mode
- Ability to adjust the set points up/down within a defined range
- Web access
About the author – Zack Flageolle is Navitas’ Director of Optimization Services. His experience in planning, design, and construction has allowed him to gain a greater understanding of what makes a successful project. He provides leadership of our Optimization Services activities for our clients and is instrumental in ensuring the program is successful. He can be reached at zflageolle@navitas.us.com.