Save energy by integrating lighting controls, HVAC systems
Traditionally, hospitals, nursing homes, dormitories, correctional facilities, and other buildings that have 24-hour-a-day or varied occupancy patterns have been poor candidates for nighttime and unoccupied setback. However, with the decreasing cost of occupancy sensing hardware and the increasing requirements of energy codes to prefer automation of control systems, the use of occupancy sensing devices in HVAC controls has grown.
In health care and similar institutional occupancies, an added energy driver over that of business occupancy is the minimum required airflows stipulated by state health care codes and other guidelines such as ANSI/ASHRAE/ASHE Standard 170-2008: Ventilation of Health Care Facilities. This standard explains minimum air change rate, pressurization relationship requirement, humidity, and temperature conditions. These requirements are intended to assist in infection control. The minimum air change rates prescribed by the various health care codes vary by the use of the space. Patient rooms, for instance, have a lower airflow requirement than that of critical care or operating rooms. Figures 2 and 3 demonstrate the various air change rates stipulated in FGI Guidelines 2010. In many cases and in many climates, the required rates are above the airflow rates necessary to meet the thermal conditions.
The interface selected for the HVAC system must take into consideration both the preferences of the hospital staff and the needs of the visitors and patients. While staff may be trained and capable of understanding more complex systems, the interface in a patient room needs to be intuitive and easily explained to the ever-changing patient and visitor population.
Each department in the hospital has varying needs based on its use and the patient population. While a time of day setback strategy with minimum manual interface and occupancy sensors may suffice in an outpatient clinic area, operating suites and nursing floors may require more intricate systems to meet the department’s needs.
The American Society for Healthcare Engineering (ASHE) has published several white papers on the topic of setback strategies in the health care environment that can be used as a guide to best practice. In its guide Operating Rooms HVAC Setback Strategies, ASHE offers the following advice on interface selection:
“…Some users prefer a simple system interface such as a series of pushbuttons, while others are more comfortable interacting with the system directly, perhaps using a control panel that shows the temperature, pressure, and humidity settings. To respond to these differences, the control options installed may vary between operating rooms (ORs) in the same facility. For instance, one OR may be kept in “ready” mode (i.e., in occupied mode), even though there is no code requirement to do so. It is important to work with both clinical and facility staff to establish an interface control solution that best achieves the joint goals of meeting user needs and saving energy. Described below are a few common interface options.
3.6.1 Time Schedule Program
A time schedule program can be an effective means of controlling the HVAC settings in ORs that are used regularly throughout a typical day or week. The schedule shows when each OR is scheduled for occupied or unoccupied mode. A time schedule program is easy to understand and modify and does not require interaction from users as it is usually part of the building automation system. Time schedule controls are well-suited for use in ambulatory surgery centers, where surgical teams keep finite hours and no emergency cases are anticipated.
3.6.2 Occupancy Sensors
Occupancy sensors (which can combine audio, infrared, and motion detection) are used to switch an OR between unoccupied and occupied modes. These sensors provide an automatic mode of control that does not require user interaction. The sensor controls often embed a delay in the change to unoccupied mode so the system ramps down slowly enough to maintain positive pressure in the HVAC system. The sensors may also embed a delay in the switchover from unoccupied to occupied mode to correct for brief entries into the room (e.g., users borrowing equipment or passing through).
3.6.4 Manual Switchover
An OR can be fitted with controls (typically using an OR interface panel) that are manually activated when the room is to be occupied. The time it takes the HVAC system to reach occupied mode settings is typically much shorter than the time it takes the surgery team to prepare for surgery. When this control method is chosen, though, staff must be trained to press the button that reactivates the HVAC system when it anticipates the OR will be needed.
3.6.5 Combined Control Methods
Any of the control methods described above can be combined to provide flexibility as operational patterns change over time. For example, one comprehensive approach may be to operate on a time schedule, but to install occupancy sensors and a manual override button for use during unscheduled events. When the time schedule is in unoccupied mode (e.g., overnight) but the occupancy sensors indicate the room is occupied, the system will switch to occupied mode after a defined delay (e.g., 30 minutes). This will account for temporary, non-surgery-related occupancies such as cleaning. The override button allows the surgery team to override the delay immediately if the room is needed for an unscheduled surgery. After a manual switchover, the OR can be set to remain in occupied mode until the next unoccupied cycle in the time schedule (usually the next day). Any of the user interface methods can also be paired with visible indicators such as a green light in the OR when the OR is in full occupied mode and a red light when it is in unoccupied mode.”
When considering airflow reduction strategies based on occupancy in health care environments, it is important to conduct thorough code research for each project. While some jurisdictions rely on ASHRAE and FGI guidelines, many have enacted their own state or local codes that may differ from these standards organizations. In some cases, the state codes may have prohibitions on setback strategies or give minimum requirements for air changes in both occupied and unoccupied modes.
As more municipalities continue to adopt the latest versions of ASHRAE 90.1 and owners continue to look to the design community for innovative strategies to reduce building energy usage, the use of occupancy controls and integration of these controls with both lighting and HVAC systems will continue to grow. It is important for all parties in the design and construction process to understand the wide variety of strategies available and their constraints and challenges.
Douglas Lacy is a senior associate and project manager with ccrd partners. He serves as a lead electrical engineer, is group production coordinator, and manages variety of projects including hospitals, corporate headquarters, and data centers. Shaun Grimm is an associate principal and project manager with ccrd partners. He is the lead electrical engineer, and leads the electrical design of different projects including hospitals, institutional facilities, and office buildings.