Critical Environments Engineering Guide

SECTION E Photo Courtesy of Bruce T. Martin© 2 011 Engineering Guide Critical Environments Please refer to the Price Engineer’s HVAC Handbook for more information on Critical Environments. Critical Environments Engineering Guide Introduction to Patient Care Areas Each different room type in the hospital environment requires a unique and strategic approach to air distribution and temperature control. Past and ongoing industry research continues to impact the thinking of HVAC engineers involved in the design of health care facilities or the development of governing standards. This section will help explain some of the key North American codes and standards for health care facility design as they relate to each space type, as well as the logic behind these design Neutral Pressure Space guidelines. Following these design standards, air distribution strategies are presented for PATIENT ROOM patient care areas, waiting rooms, operating rooms, and hospital pharmacies and labs. Corridor The many design examples included in this Negative chapter should serve to further clarify the key Pressure Space points presented in each section. The health care facility includes a number of different spaces, all with unique HVAC requirements. Well designed hospital HVAC Figure 1: Typical patient room systems should support asepsis control The variability in occupancy levels, solar/ with the discharge pattern of horizontal throw while also taking advantage of energy saving conduction loads through exterior walls, and diffusers. Lift rails or curtains may redirect technologies and strategies. Understanding equipment loads will generally facilitate the high velocity supply air directly at the the needs and goals of each space as well as need for reheat, VAV control, supplemental patient if positioned too close to the diffuser. the regulations that govern their design are room heating or cooling, exterior shading, Exhaust outlets can be located at a low level, important first steps toward building a high or any combination of these features. If but eggcrate style ceiling returns are more performing facility. insulating liners are used for supply terminal common and preferred. The following chapter will discuss a number boxes, no fibers should be exposed to the Isolation Rooms CRITICAL ENVIRONMENTS of key areas in the hospital and provide air stream, with closed-cell foam liners the recommendation on available HVAC preferred option. Venturi valves are becoming Isolation rooms can be separated into two technology and how it can be applied. more popular for return/exhaust applications main categories: Airborne Infection Isolation Examples throughout the chapter give more in patient rooms as they can provide accurate (AII) and Protective Environment (PE) clarity on practical application of the concepts flow control without the need for cross-flow rooms. As the names would suggest, these and standards presented. sensors. Frequent linen changes in patient rooms have different functions. AII rooms are designed for patients with serious and Patient care areas in a health care facility rooms can result in high levels of airborne lint which may interfere with the function contagious conditions (e.g. Tuberculosis), are carefully controlled environments while PE rooms exist to protect patients designed to provide contaminant control of the cross-flow sensors typical to most ENGINEERING GUIDE - with weakened immune systems or some without sacrificing the comfort of patients terminal boxes. Another common design practice is to locate a radiant panel above the form of impairment to their natural defense or other occupants. Various hospital rooms system. AII rooms are designed with the fall into the ‘Patient Care’ category, including window on an exterior wall.The radiant panel serves to moderate the temperature around primary purpose of protecting hospital standard patient rooms, isolation rooms, and occupants (other than the patient) from burn center intensive care units.These spaces the exterior wall as to prevent unfavorable influence over the room air pattern. airborne infection, while PE rooms should are similar in that they are all used for patient protect the more vulnerable patients (e.g. treatment and/or recovery, however, each has ASHRAE suggests the use of either bone marrow transplant patients) from unique design characteristics which clearly group A (horizontal throw) or group E airborne contaminants present in the distinguish one type from another. With a (vertical throw) diffusers in standard patient hospital environment. different purpose for each room type, the rooms, however, the former is far more standards and general HVAC considerations common for these applications. Use of Airborne Infection Isolation that dictate the design of the local air displacement ventilation products in patient (AII) Rooms distribution systems are also different. rooms is also gaining traction as research The general layout and some design Standard Patient Rooms surrounding the contaminant control conditions of an AII room will be similar to that benefits of ‘single-pass’ DV air flow continues of a standard patient room. The possibility The majority of patient care areas in a hospital to justify support for the technology. of exterior walls and windows, an attached are standard patient rooms. As such, the Supply and exhaust diffusers should be toilet room, and similar equipment loads design of the air distribution systems in these are a few commonalities between these rooms can greatly affect the performance and selected and located in such a way as to promote the movement of air from spaces. Yet the AII room serves a different cost of operating the overall HVAC system. purpose and consequently has a number of Standard patient rooms can be either single clean to less clean areas and also prevent uncomfortable drafts. Mixing type, group key differences with respect to standards and or multiple patient spaces and are typically air distribution equipment. dedicated to the care of individuals without A diffusers will typically be located directly serious health risk. These rooms will often above the patient bed with exhaust outlets The minimum total air-change rate for an AII have an exterior wall and window which can located near the door to the corridor or toilet room is typically 12 ach, but this may vary have a significant impact on room air patterns room. Attention should be given to ceiling- depending on the applicable code. in certain climatic regions. mounted obstructions that may interfere All Metric dimensions ( ) are soft conversion. © Copyright Price Industries Limited 2011. E-2 Imperial dimensions are converted to metric and rounded to the nearest millimeter. Critical Environments Engineering Guide Introduction to Patient Care Areas An Airborne Infection Isolation (AII) room must maintain a negative pressure VV differential relative to the hospital corridor.To achieve an acceptable pressure differential it Exhaust is usually necessary to supply approximately TU 20% less air to the room than is exhausted. The actual air flow offset will need to be Supply determined at the time of commissioning. Furthermore, all air exhausted from the Anteroom AII room, or associated toilet room and TU anteroom, should be exhausted directly Supply outdoors without mixing with the exhaust Exhaust air from any other spaces. TU HEPA filtration of the AII exhaust air is required in cases where the air is not discharged clear of building openings or CV mixes with exhaust air from non-AII spaces Exhaust prior to being discharged outside. Supply Duct Most standards do not require anterooms for Exhaust Duct AII rooms, however, most modern medical facilities utilize them. An AII anteroom should have a negative pressure differential Figure 2: Airborne infection isolation (AII) venturi valve setup relative to the corridor, and a positive pressure differential relative to the AII room. The minimum relative pressure differential between these spaces will depend on the Exhaust jurisdiction and applicable standards. 1 way RFD This pressurization scheme supports the movement of air and contaminants from clean (the corridor) to less clean (AII room) 1 way RFD Anteroom spaces, reducing the potential for further CRITICAL ENVIRONMENTS spread of infection. AII rooms also require a permanently installed device to monitor Exhaust the differential pressure between the room and adjacent areas (ASHRAE Standard 170- 2008; CSA Z317.2-10). Most modern health care facilities achieve this level of monitoring by using a room pressure monitor with a Corridor Exhaust built-in pressure sensor. Typically, the room pressure monitor is only used to detect and ENGINEERING GUIDE - display differential pressure between the room and corridor, however, some models also include an integral controller for supply and exhaust valve control. Audible alarms Figure 3: Airborne infection isolation (AII) supply and exhaust outlets are often used in conjunction with the visual signal displayed on the screen of the room A typical VAV configuration for an AII room Cleaning staff may inadvertently move pressure monitor. is shown in Figure 2. Venturi valve exhaust pattern controllers, compromising the safety units are sometimes preferred in areas of healthy room occupants. The relatively high air-change rate where airborne lint might be a concern. requirements for AII rooms typically mean The position of the radial flow diffuser is additional supply air is not necessary to The current ASHRAE Standard 170 suggests equally as important

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