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Efficient Control of Operating and
& Angela Lewis
July Issue - BAS Column
are few areas in a Hospital that have more critical control needs than
those where surgical procedures occur. These areas have exacting
requirements for temperature, humidity, pressurization, and
ventilation. The drivers for these conditions are literally “life
and death” and are critical for both infection control as well as for
the condition of the patient and the effectiveness of the operating
By necessity these critical areas are energy intensive, in fact they are arguably the most energy intense spaces in a healthcare facility. But that doesn’t mean that they can’t readily be controlled in a method that is safe, productive and efficient.
Let's start by looking at the basic parameters of control for a surgical or procedure area:
Temperature: In general the temperature for operating rooms is the same as for other areas of a hospital – in the range of 68o – 75o F. But it is not unusual to find surgical teams that like to have the ability to have a colder operating room. Maintaining lower temperatures, and still holding humidity levels is a challenge that generally requires specialized system and control design.
Humidity: While control of temperature is primarily a comfort issue, control of high humidity is important for infection control. Historically the recommended levels were in the range of 30% - 60% although this has recently been revised to allow usage down to as low as 20%. Reducing the lower level of humidity control can provide savings, but it is recommended that it be carefully evaluated.
Air Movement: There are varying requirements for air movement ranging from 15 – 25 (or higher) air changes per hour. The ventilation level needs to be carefully considered when setting up the airflow distribution and will often require the use of systems with reheat.
Fresh Air: Most standards require about 20% outdoor air for operating rooms, but some hospitals prefer to have 100% OA.
Space Pressurization: For infection control operating rooms need to be kept at a net positive pressure in relation to adjacent spaces. This helps assure that the operating room is not contaminated. Note that the space pressure (unlike temperature, humidity, or airflow) generally must be maintained at all times, even when the room is not in active use.
So how do you do all of this efficiently? We recommend a few different approaches. The first is to make sure you have the right requirements. Can humidity drift down to 20%? Can you keep the operating rooms closer to 70o than 65o F? Do air changes need to be at 30 ACH or is 20 ACH OK? Finally we have found the greatest savings through improved control of space pressurization. Using positive pressure controls that measure and control based on actual pressure differential between the OR and adjacent sterile corridor are both more efficient and also help assure that you are maintaining and recording that pressure relationship. Finally consider adding in an unoccupied cycle. We find that most OR’s operate around 50 hours per week, but are often fully conditioned 24x7. Adding an unoccupied cycle that allows temperatures to drift, reduces airflow, but continues to maintain positive pressure when unoccupied, provides incredible energy savings. Generally in a medical center one OR can be kept fully ready for emergency and the rest can readily come up to operating conditions within a few minutes if needed.
About the Authors
Paul and Ira first worked together on a series of ASHRAE projects including the BACnet committee and Guideline 13 – Specifying DDC Controls. The formation of Building Intelligence Group provided them the ability to work together professionally providing assistance to owners with the planning, design and development of Intelligent Building Systems. Building Intelligence Group provides services for clients worldwide including leading Universities, Corporations, and Developers. More information can be found at www.buildingintelligencegroup.com We also invite you to contact us directly at Paul@buildingintelligencegroup.com or email@example.com
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