March 26, 2018
Operating rooms (ORs) are one of the most critical aspects of Hospital Operations. They must be available at all times to support critical operations and procedures. As a result, most hospital ORs operate HVAC systems 24 hours per day.
ORs are incredibly profitable when they are active, but healthcare facilities lose money when they are unused. Operating costs for ORs are susceptible to a variety of factors that affect profit such as disposable medical supplies, drug prescription waste, schedule delays, etc. But one money-saving factor is often overlooked: HVAC systems setbacks.
ORs within healthcare facilities require a significant amount of supply air by code for infection prevention. This airflow is typically 4-5 times more than what is required to meet the temperature and humidity requirements for the space. These ORs are unused for a significant portion of a typical day for a lot of facilities. One St. Louis area hospital was recently assessed and found to only be utilizing its ORs 40% of the hours in a year. There are 8,760 hours in a year. You can do the math, but that is a lot of energy wasted. The good news is that this kind of waste can be prevented. Healthcare facilities can experience significant energy savings by reducing airflows when their ORs are unoccupied.
Reduce Airflow Using ASHRAE Standards & Local Code
ASHRAE 170 – Ventilation of Health Care Facilities is the most commonly used standard for hospital HVAC systems. This standard establishes criteria for the minimum amount of supply and ventilation air, temperature, and humidity requirements to be provided in healthcare facilities. ASHRAE 170-2017 requires ORs to be supplied with 20 Air Changes per Hour (ACH) of supply air and 4 ACH of ventilation air when occupied. These air change requirements have been reduced over time, but many hospitals are still operating at air change rates well over this requirement. In some cases, as high as 30 air changes per hour.
Airflow rates can typically be reduced by as much as 75% when the space is not occupied depending on local codes. Reducing these airflow rates will allow these facilities to achieve energy savings in
- fan energy (reduced airflow)
- heating energy (reheat)
- cooling energy (air handling unit cooling coil, especially for a 100% outdoor air system)
- pump energy (reduced water flow)
The opportunity to reduce airflow rates and achieve energy savings potential will vary depending on the local code requirements and the frequency that the OR rooms are used in each facility.
Airflow Setback Strategy in Action
The St. Louis area hospital mentioned above implemented an airflow reduction and setback strategy for its ORs resulting in an annual savings of $55,000 per year. This facility utilized an occupancy schedule to keep ORs fully active during normal business hours and push button for un-occupied period overrides. In addition to energy savings, the hospital received the added benefit of reduced maintenance and increased system life by reducing the overall demand on the HVAC systems. Local utility incentives were utilized to help fund the project and the overall project paid for itself in less than 4 years.
There are many things to consider when choosing to implement an OR airflow reduction and setback strategy.
1. Systems must have the right components to allow setbacks
The existing system must have the ability to adjust airflow rates while maintaining pressurization requirements. Air-Handling units must have variable speed supply fans; exhaust fans and return fans; and pressure independent control of supply and return air to spaces typically using variable air volume (VAV) terminals and DDC controls.
2. Occupancy Control Options Vary, Hospital Staff must buy-in
There are multiple ways to determine if a space is un-occupied, some options include the use of occupancy sensors, local push button controls, or both. Occupancy sensors should default to occupied mode during a sensor failure. Push button controls can be used to activate an OR for surgery or used as a local override at the nurse station. Pilot lights can be added to push buttons to provide visual notification that the OR is ready for occupancy. Proving a way for human intervention or override can provide a sense of much needed control for the staff and flexibility during unique circumstances. Staff should be trained so there is confidence in the system.
3. Space pressure control must be maintained
ORs must remain a positive pressure to surrounding spaces, even when unoccupied, and space pressure relationships within surrounding spaces must not be compromised by reduced airflow rates. Maintaining space pressure is not that difficult in a static (constant volume) system. It becomes more complicated in a variable volume system and space pressure balancing should be carefully thought out and reviewed.
4. Space temperature and humidity should be maintained during setbacks
When an OR is switched to Occupied mode, the air change rate can be increased in a matter of seconds with little or no perceivable change in environmental conditions to the operating team. Temperature and humidity setpoints could take minutes or hours to recover from a setback condition. For most facilities this is unacceptable. Instead space temperature and humidity requirements should be maintained at all times to avoid disruptions to operations.
Are Setbacks Right In Your Operating Room?
Airflow reductions and setback strategies for ORs can provide significant energy savings in healthcare facilities, especially where existing ORs operate with constant airflow, temperature and humidity setpoints. The potential savings will vary depending on the existing system configuration and local code requirements. Hospital staff must have complete buy-in to the new system operation and receive proper training. This strategy is just one of the many ways to reduce operating costs in your operating room suite.
Learn more about how HVAC system setbacks can help your healthcare facility by contacting our team of professionals.
About the Authors
Brian Bieker, PE, LEED AP. Brian has over 20 years of experience as a mechanical engineer with a strong focus on healthcare design. Designing buildings and building systems has always been a passion for Brian and he takes pride in watching new living, breathing buildings come to life.
Ryan Walsh, PE, CEM, LEED AP BD+C. Ryan is the Director of Energy Services for Ross & Baruzzini. He has spent the last 20 years helping his customers find innovative and sustainable solutions for their most challenging and complex engineering projects including healthcare facilities.