ROOM DESIGN
8.3 OPERATING ROOMS
8.3.3 Laminar Array Systems
system forms a single assembly in the ceiling with all openings gas-keted. Thus, gasketed ceiling systems designed for ORs are acceptable.
An air curtain system (Figure 8-8) is another method for ventilating an operating room. It consists of a laminar array above the operating table with a four-sided linear slot diffuser outside the perimeter of the surgical area. Between 67% and 75% of the total supply air is provided by the air curtain, with the balance supplied through the laminars. The laminar diffusers are sized for 25 to 35 cfm/ft2 [127 to 178 L/s per m2] of diffuser face area and the air curtain is sized to provide 25 to 45 cfm/linear foot [38.8 to 69.8 L/s per m] of slot. At a minimum, the inside dimension of the linear air curtain is approximately 3 ft [0.9 m]
beyond each side of the surgical table; allowing sufficient room around the table for the surgical staff and its equipment without the staff being inside the jet of the air curtain. This system may be best suited for very large ORs where large volumes of air are required to achieve 20 ach.
The use of imaging systems is both growing and changing rapidly because of advances in technology and increasing applications. As with most computer-based equipment, imaging systems have a life of about five years. Therefore, it is crucial to design for the flexibility to frequently replace imaging equipment. Another challenge for the designer is that medical staff work hard to find new uses for existing imaging systems. For example, a room designed for diagnostics may become a treatment room, thus increasing the air change requirements from 6 ach to 12 or 15 ach. The room may even become a hybrid OR, 8.4 IMAGING ROOMS
Figure 8-8 Air Curtain Concept
thus requiring 20 ach. Providing for future flexibility generally requires oversizing equipment for immediate use, which usually results in increased first cost. The judicious HVAC engineer will bring this to the attention of the owner early in the process and obtain the owner’s guidance, preferably in writing.
Imaging systems generally consist of an assemblage of electronic devices that perform diagnostic imaging and/or patient treatment.
They can generally be grouped as four types of devices: X-ray, ultrasound, magnetic, and radioactive. As shown in Figure 8-9, many of the systems, including fluoroscopy and CT, are based on X-ray
Imaging Type Applications
Computerized tomography (CT) Orthopedic, emergency, neurology
Fluoroscopy Vascular, cardiac catherization, cystoscopy, electrophoresis (EP)
Gamma knife Oncology
Linear accelerator Oncology
Magnetic resonance imaging (MRI) Orthopedic, neurology, vascular
Nuclear camera Cardiology
Positron emission tomography (PET) Neurology
Ultrasound Prenatal, oncology
X-ray Mammography, orthopedic, emergency, pulmonary
Source: Koenigshofer (2009).
Table 8-5 Typical Applications of Imaging Modalities Figure 8-9 Basic Imaging Modalities
Source: Koenigshofer (2009).
technology. With this technology, X-rays generated in an X-ray tube pass through the patient and are then collected for imaging. Fluoroscopy is essentially a real-time X-ray, analogous to a video as compared to a photograph. CT falls in the middle of these technologies by taking multiple X-rays (slices) in an extremely short period of time. All of these technologies use an X-ray generator and image intensifier as detailed in Figure 8-10.
Table 8-5 shows various imaging modalities and their typical applications. As indicated, there is a great deal of overlap in the application of the differing technologies.
Figure 8-10 shows the components of typical imaging systems and the locations of energy input and heat output. As indicated, many systems have remote cooling units to remove heat from the imaging equipment. These remote coolers may be air-cooled exterior units, remote water coolers located inside the building, and/or remote chiller plants. Depending upon the manufacturer, the various devices shown may involve separate or combined components. Figure 8-11 shows one version of a chilled-water cooling system using house chilled water and interconnected process chillers.
A typical CT system installation consists of three rooms. The following three functions/rooms are typical for virtually all imaging systems that involve multiple components:
Figure 8-10 Imaging System Energy Flows Source: Koenigshofer (2009).
• Control Room: monitors and computers for staff operation of the system
• Procedure Room: imaging equipment for patient diagnostics and treatment
• Equipment Room: housing data and electrical equipment
Typically, the main panel, computer, power distribution, UPS, and power generator are located in the equipment room. The actual imaging device is located in the Procedure Room along with some monitors, motorized patient table, exam lights, and injector. The data output items (e.g., computers, monitors, and printers) are located in the Control Room.
Manufacturers use different terminology for the overall system and for the individual components. Occasionally, the data systems are located in the Procedure Room; this location uses valuable space, can create a significant cooling load, and should be avoided. Because the loads for each of the three rooms are so different, each room should be provided with a separate thermostatic zone (reheat box).
Table 8-6 gives heat gain values (energy consumption) as reported by the manufacturer for a typical CT system. As indicated, there are twelve devices that consume energy and produce heat.
Control Rooms are generally small, crowded, and busy, containing computers, monitors, and printers that produce heat while the staff is usually wearing heavy clothing and head and face protection. Therefore, this area must usually be maintained at 68°F to 70°F [20.0°C to 21.1°C]
and airflow of over 20 ach is common.
Figure 8-11 Imaging System Cooling-Water Piping Schematic Source: Koenigshofer (2009).
Item
system – 1700 [498] – – – On customer’s counter
5 Image evaluation
keyboard (option) – – – – – On customer’s counter
6
system (option) 220 [100] 1708 [500] – – – On floor/in container
8 Ethernet switch
workplace computer 55 [25] – 18.8
[478]
13 Gantry 4410 [2000] 4708 [1380 57
[1449]
14 Patient table 1103 [500] 512 [150] 26.5
[637]
Cabinet 1213 [550] 4085 [1197] 35.5
[902]
cabinet (water/water) 441 [200] 1706 [500] 35.5 [902]
system 285 [129] 4777 [1400] 12.6
[320]
27.8 [706]
80.6 [2047]
18 Monitor 131 [59.4] 238 [70] – – – Ceiling mounted
19 Surge suppressor 51 [23] 205 [60] 24
[610]
8.9 [226]
24
[610] Wall mounted Table 8-6 Typical CT Equipment Heat Gain Data
In the Procedure Room, the required supply airflow is dictated by either the cooling load or the airflow recommended by ANSI/ASHRAE/
ASHE Standard 170-2008, whichever is greater. In most cases, the required room air change is greater than the required air for cooling a Procedure Room, where the required airflow is 12 to 15 ach. However, if all electrical equipment is located in the Procedure Room, airflow may be load driven. Sometimes, the control equipment is located in an area of the Procedure Room separated by only a partition; thus, the load from the control equipment is in the Procedure Room.
If there is a separate Equipment Room, the airflow required for that space is determined by the sensible heat gain from the devices in the room. These rooms often look like data centers, with raised floors and computer room air-conditioning systems. The computers for several imaging systems may be in one room. Air changes may be 50 to 100 ach.
Table 8-7 compares the reported heat loads for actual Catherization Lab systems (fluoroscopy) that have been designed by the authors.
System features and performance may not be comparable. Each system consists of 13–20 energy-consuming components. The sum of the indicated loads ranges from 25,000 to 46,000 Btuh [7.3 to 13.4 kW].
There is no indication in the literature if these are the maximum or average loads. Typically, however, manufacturers state that these are maximum, undiversified loads.
As indicated in Table 8-8, under idle and high-use modes, heat gains to the water cooling system for this MRI are nearly identical. This is substantiated by the graph of electrical demand shown in Figure 8-12.
Manufacturer Procedure
Btu/h [kW]
Equipment Btu/h [kW]
Control Btu/h [kW]
Total Btu/h [kW]
GE 4323 [1.26] 31,386 [9.14] 4592 [1.34] 40,301 [11.74]
Siemens (biplane) 3585 [1.04] 35,838 [10.44] 6385 [1.86] 45,808 [13.34]
Philips 5024 [1.46] 16,929 [4.93] 2994 [0.97] 24,947 [7.27]
Toshiba (biplane) 1092 [0.32] 34,769 [10.13] 1445 [0.42] 37,306 [10.87]
Table 8-7 Comparison of Reported Heat Gain for Cardiac Cath Systems
Source: Koenigshofer (2009).
Device Manufacturer Model Idle High
Btu/h [kW] Btu/h [kW]
MRI Siemens Vision 30,285 [8.82] 31,882 [9.29]
Table 8-8 Field-Test Results for Heat Gain to Water for Imaging Systems
Source: Koenigshofer (2009).
Note: 9:00 a.m. to 4:00 p.m.
The base (sleep) mode’s demand is about 15% below the 1 h time-weighted average (TWA). As discussed earlier, MRIs often have a stand-alone process chiller. Good design practice will also tie the MRI into the house chilled-water system.
Table 8-9 summarizes the results of testing to determine heat gain from imaging systems (Koenigshofer 2009). As indicated, in some of the modalities, there is very little difference between the idle energy use and the 60 min maximum time-weighted average (TWA). Note that field-measured results can vary considerably from values reported by a manufacturer in their installation drawings. It is expected that Phase II of this research project will result in a much more extensive database for heat gains to air and water for imaging systems.
The most common imaging modalities in operating rooms at this time are fluoroscope and CT. As discussed previously, the 20 ach for ORs must be applied, which will likely exceed the internal cooling load, even with imaging equipment. However, internal loads should be double checked in cases where there is a relatively high supply air temperature (52°F to 56°F [11.1°C to 13.3°C]). Often, a hybrid OR will contain a number of devices (including large flat-screen monitors) that generate considerable cooling loads. The control area may be inside or outside of the OR.
Imaging equipment and articulating booms require significant structure above the ceiling, which makes routing ductwork very diffi-cult. The HVAC designer should insist on obtaining manufacturer’s installation drawings as early as possible.
Figure 8-12 Electrical Power Use by MRI Source: Koenigshofer (2009).
Several features of MRI systems create unique challenges for the HVAC designer: an intense magnetic field, cooling, and emergency procedures for power outages. Because of the intense magnetic field produced by an MRI, all materials in the room must be nonferrous. Air distribution components are usually aluminum or a very-high-grade stainless steel. Wave guides must be installed to mitigate transmission of electromagnetic waves in and out of the MRI room. Rotating equip-ment (e.g., motors, fans, etc.) within the 1 gauss [100 microtesla] field can cause loss of image quality. The 1 gauss magnetic field usually extends outside the Procedure Room. Thus, the MRI may affect, or be affected by, metal objects outside the room. The manufacturer will supply this type of information. The walls of the MRI room will be lined with a nonmagnetic material such as copper, which will affect all penetrations. The ceiling/roof will frequently be a “knock out” arrange-ment to allow installation and replacearrange-ment of the MRI from above.
There may not be shielding in the ceiling/roof.
MRIs are supercooled magnets. The cooling is accomplished using liquid helium. The overall system is usually cooled with chilled
System Manufacturer Max. 60 min TWA,
Btu/h [kW] Calculated Idle Btu/h [kW]
Manufacturer- Recommended
Btu/h [kW]
MRI Vision* Siemens 83,331 [24.27] 75,873 [22.10] Not available
MRI Sonata* Siemens 80,475 [23.44] 65,323 [19.03] Not available
X-ray Philips 4,258 [1.24] 3,692 [1.08] 4,604 [1.34]
Fluoroscopy Philips 41,384 [12.06] 31,322 [9.12] 24,946 [7.27]
Fluoroscopy Siemens 17,100 [4.98] 15,105 [4.40] 20,123 [5.86]
CT Philips 24,085 [7.02] 22,437 [6.54] 65,450 [19.07]
PET/CT* Siemens 43,008 [12.53] 33,438 [9.74] N/A
Nuclear camera Siemens 3,790 [1.10] 3,620 [1.06] N/A
Linear accelerator* Siemens 111,238 [32.40] 67,807 [19.75] 31,249 [9.10]
Ultrasound Acuson/Siemens 2,927 [0.85] 1,692 [0.49] Not available
Cyberknife
(robotic surgery) Accuray 45,720 [13.32] 35,440 [10.32] Not available
Table 8-9 Field-Test Results of Heat Gain to Air for Imaging Systems
Source: Koenigshofer (2009).
* Load to room air; unit is water-cooled with house chilled water or exterior condenser.