CHAPTER 1
OVERVIEW OF HEALTHCARE HVAC SYSTEMS
1.1 INTRODUCTION
HVAC systems in health care
facilities provide a broad range of services in support of populations who are
uniquely vulnerable to an elevated risk of health, fire, and safety hazard.
These heavily regulated, high-stakes facilities undergo continuous maintenance,
verification, inspection, and recertification; typically operate 24 hours/day,
7 days/ week; and are owner-occupied for long life cycles. Health care HVACsystems must be installed, operated, and maintained in spatial and functional
conjunction with a host of other essential building services, including
emergency and normal power, plumbing and medical-gas systems, automatic
transport, fire protection, and myriad IT systems, all within a constrained
building envelope. Health care facilities and services are characterized by
high rates of modification because of the continuously evolving science and
economics of health care, and consume large quantities of energy and potable
water. The often unique environmental conditions associated with these
facilities, and the critical performance, reliability, and maintainability of
the HVAC systems necessary to their success, demand a specialized set of
engineering practices and design criteria established by model codes and
standards and enforced by authorities having jurisdiction.
1.2 BASIC
CLASSIFICATION OF HEALTH CARE FACILITIES
Health care facilities vary
widely in the nature and complexity of services they provide and the relative
degree of illness or injury of the patients treated—from a neighborhood general
practitioner’s office to large regional or university medical centers and
specialty hospitals. Facilities in the health care category can include, in
addition to the practitioner’s office, neighborhood clinics, mental wellness
centers, birthing centers, imaging facilities, hospice care, and long-term
nursing care, among others. As a rule, environmental control requirements and
the role of the HVAC system in life safety and infection control become more
important with increasing complexity of the medical services provided and the
acuity of illness of the patient population. This manual is primarily intended
to address HVAC systems for inpatient hospitals, except where otherwise
indicated.
1.3 HEALTH
CARE HVAC SYSTEM FUNCTIONS
In support of the health care process,
HVAC systems are called upon to perform several vital functions that affect
environmental conditions, infection and hazard control, and building life
safety. Staff and patient comfort, and the provision of therapeutic space
conditions, facilitate optimum patient treatment outcomes. Environmental
conditioning for electronic data storage, supporting IT systems, and special
imaging and other medical equipment is critical to the operation of these
essential services. Through containment, dilution, and removal of pathogens and
toxins, the HVAC system is a key component of facility safety and infection
control. In inpatient and many ambulatory treatment facilities, the inability
(or reduced ability) of patients to respond properly to fire emergencies
requires the HVAC system to support vital smoke exhaust and building
compartmentation features of the life safety system. Finally, the HVAC system
should interact with the architectural building envelope to control the entry
of unconditioned air, together with outdoor contaminants and moisture.
1.3.1 Comfort
Conditioning
Across the range of health care
facilities, health care practices often expose patients and staff to conditions
that dictate unique environmental requirements. As in any facility, the comfort
of building occupants is fundamental to overall well-being and productivity. In
the health care facility, a comfortable environment has a significant role in
facilitating healing and recovery. A sick or injured patient in an
uncomfortable environment is subject to thermal stress that may hinder the
body’s ability to properly regulate body heat, interfere with rest, and be
psychologically harmful. At the same time, a health care provider stressed by
an uncomfortable environment may not function at peak performance levels.
Patients clothed in a simple gown in an examination room, for example, or
orthopedic surgical staff heavily garbed in scrub suits during an hours-long,
complex, and stressful procedure, require special room temperature and humidity
levels and controls. Similarly, room airflow patterns and air change rates
influence thermal comfort. For these reasons, health care codes and criteria
establish specific requirements for space temperature, relative humidity, and
total air change rates.
1.3.2 Therapeutic Conditioning
Certain medical functions,
treatments, or healing processes demand controlled environmental temperature
and/or relative humidity conditions that deviate from the requirements for
personal comfort. Operating rooms and nursery units, for example, often require
a range of room temperatures spanning several degrees, regardless of the
season, to best facilitate a given procedure or patient condition. Burn-patient
treatment rooms and bedrooms may require elevated temperature and relative
humidity (RH) conditions (up to 100°F [37.7°C] and 35% to 40% rh, according to
DOD [2011]). Some clinicians desire the ability to reset emergency department
room temperatures to as high as 90°F [32.2°C] for treatment of hypothermia
cases. Criteria call for long-term in-patient spaces to be humidified to
minimum levels to avoid the dry skin and mucous membranes associated with very
low RH levels that add to discomfort and possibly impede respiratory immune
function. As of the date of this publication, however, there is no scientific
evidence to firmly establish that extended exposure to very low humidity
contributes to poorer patient outcomes.
1.3.3
Infection Control
With few exceptions (such as
free-standing behavioral health, sports medicine, or maternity care centers),
medical facilities are places where relatively high levels of pathogenic
(disease-causing) microorganisms are generated and concentrated by an infected
patient population or by procedures that handle or manipulate infected human
tissues and bodily fluids. These pathogens are spread by a number of contact
and, to a lesser extent, noncontact (airborne) causes, which are dealt with in
detail in Chapter 2. To some degree, the entire building population is at
elevated risk of exposure to these pathogens. Sick and injured patients, having
suppressed or compromised immune function, are highly susceptible to new
infections. Visitors often accompany sick or injured friends or loved ones to
high-exposure areas such as clinical waiting rooms and emergency departments.
By the nature of their profession, health care staff work in proximity to
infectious agents on a daily basis. Health care facilities therefore require
stringent operational practices and engineering controls to safeguard the
building population. The HVAC system is one of several tools and processes used
in the control of infection.
1.3.4
Ventilation and Environmental Control for Special Functions
Many medical facilities include
functions or processes in which chemical fumes, aerosols, or harmful gases are
stored and generated, posing health or safety hazards. Examples include
laboratories where aerosolizing chemicals are used to fix slide specimens,
preserve tissues, or perform other processes; orthopedic appliance and
artificial limb shops involving adhesives and other aerosolizing agents; and
anesthetizing locations, in which long-term exposure to even trace
concentrations of anesthetizing gases can have harmful consequences. In such
applications, HVAC equipment operates in conjunction with primary containment
equipment, such as fume hoods, radioisotope hoods, laminar flow benches, and
waste anesthesia evacuation systems, to contain and exhaust these contaminants
or dilute them to safe levels.
In other health care
applications, the HVAC system is called upon to assist in the maintenance of a
sterile environment for products or procedures that must be protected from
environmental contamination. Laboratory culturing procedures, and certain
pharmaceutical handling and compounding procedures, are examples where the HVAC
system functions in conjunction with containment equipment to protect the
product.
1.3.5 Life Safety
In facilities classified as
Health Care or Ambulatory Health Care by NFPA 101: Life Safety Code®
(NFPA 2012) from the National Fire
Protection Association or Type I-2 by the International Building Code®
(IBC®) (ICC 2012), HVAC
systems are required to support special building compartmentation, opening
protection, smoke control, and detection systems providing for the “defend in
place” concept of life safety. Containment is facilitated by the application of
smoke and fire dampers and, in some cases, by restricting HVAC system
cross-over between smoke zones. HVAC systems contribute to the detection and
containment of fire and smoke and may be called upon to evacuate or exclude
smoke from atria or exit enclosures. Engineered smoke control systems may be
required to provide complex zoned pressurization control. More detailed
information on HVAC applications and building life safety is provided in
Chapter 5.
1.3.6 Role of
the Building Envelope
The integrity of the building
envelope is essential to minimize the introduction of unconditioned, unfiltered
air into a building, as well as to effectively exclude moisture. Condensation
of humid outdoor air within building envelope assemblies is conducive to mold
colonization, which, in addition to causing expensive material damage, poses a
risk of deadly infection from Aspergillus and other so-called
opportunistic mold genera. No envelope is perfect, and abundant evidence shows
that even well-designed and constructed envelopes allow some degree of
infiltration from building pressurization differentials caused by wind, stack
effect, and operation of the HVAC system. Generally, with the exception of very
cold climates where neutral pressurization may be called for, it is desirable
to positively pressurize the building interior to minimize infiltration. Some
HVAC designs approach controlled, continuous, positive pressurization by
maintaining a controlled offset between outdoor ventilation air and exhaust.
These systems are simple and reliable. More complex pressure-control approaches
are now being suggested by some design engineers. HVAC designers should be
aware, and make the building architect aware, that the deliberate
depressurization of spaces on the building perimeter, including disease
isolation rooms and patient toilets, and the depressurization of plenums and exterior
wall cavities by plenum return systems, poorly balanced ducted return systems,
and central exhaust systems can exacerbate the passage of moisture and
unconditioned, unfiltered air across the building envelope in those locations.
1.3.7 Patient
Privacy
The need to prevent room-to-room
transmission of private patient conversations is addressed by codes and
standards and by the Health Care Information Portability and Accountability Act
(HIPAA). Codes and standards provide minimum sound transmission class (STC), or
other acoustical performance criteria, for the architectural enclosure elements
of critical spaces such as provider office and exam rooms, and may address
recommendations for background noise, and for minimizing sound transmission
through connecting ductwork. Transfer air ductwork and common plenum returns
for such spaces require special consideration and treatment, such as built-in
attenuating features, to minimize “crosstalk.” Even with fully ducted returns,
consideration must be given to the attenuating qualities (chiefly the extent
and configuration of layout and fittings) of interconnecting ductwork. Although
a great deal of attention is normally focused on minimizing HVAC backgroundnoise, some degree of “white noise” from HVAC systems helps to minimize
conversation intelligibility
1.4 CRITERIA
AND ACCREDITATION
1.4.1 Design
Criteria
One of the HVAC designer’s first
tasks is to establish the project design criteria. Most state and federal
government agencies, and many local governments, establish criteria for the
design of health care facilities within their jurisdictions. A jurisdiction may
utilize its own criteria and codes or cite model, national, or international
building codes or design standards. Some private health care institutions and
corporations also establish their own design criteria that go beyond
jurisdictional requirements. Frequently adopted or cited codes, standards, and
design guidelines relating to health care facility HVAC systems include the
following:
Guidelines for Design and
Construction of Hospital and Health Care Facilities (known as the “FGI Guidelines”), 2010, The Facility
Guidelines Institute (FGI)
ANSI/ASHRAE/ASHE Standard
170-2008, Ventilation of Health Care Facilities
ANSI/ASHRAE/IES Standard
90.1-2010, Energy Standard for Buildings Except Low-Rise Residential
Buildings
(Proposed) ASHRAE Standard
189.3P, Design, Construction and Operation of Sustainable High Performance
Health Care Facilities (under development as of date of this publication)
HVAC Design Manual for New,
Replacement, Addition, and Renovation of Existing VA Facilities, 2011, U.S. Department of Veteran Affairs
The Joint Commission,
Environment of Care standards
National Fire Protection
Association (NFPA) standards
Industrial Ventilation, 2004, American Conference of Governmental Industrial
Hygienists (ACGIH)
Centers for Disease Control and
Prevention (CDC) guidelines and recommended practices
Model building and mechanical
codes, including the International Building Code (IBC), International
Energy Code, and International Mechanical Code
Leadership in Energy and
Environmental Design (LEED®) for HealthcareTM
Unified Facilities Criteria
(UFC) Manual 4-510-01, U.S. Department of Defense
CAN/CSA Z317.2-10, Special
Requirements for Heating, Ventilation, and Air Conditioning (HVAC) Systems in
Health Care Facilities
United States Pharmacopoeia
Chapter 797
Typical criteria for HVAC design
include indoor and outdoor environmental design conditions; outdoor air and
total air change requirements; economic considerations for equipment selection;
requirements for redundancy or backup
equipment capacity, room pressure relationships, required filtration, and other
benchmarks for systems and equipment selection and sizing. Other criteria that
influence the HVAC design may involve envelope configuration and thermal
performance, environmental requirements for special equipment and processes,
operation and maintenance considerations, and clearance and conditioning
requirements for electrical and electronic equipment. Every jurisdiction can be
expected to have its own design criteria, more or less supplemented by that of
the building owner, which must be understood by the designer at project
initiation. These criteria normally include much of the information in the
previously listed sources, but may include only certain elements of these
documents, or involve modifications of the published requirements. With rare
exceptions, a designer can never safely assume appropriate criteria.
Authorities having jurisdiction and building owners must be consulted.
Authorities and owners should also be consulted as to design preferences, which
often dictate specific system and equipment types, configurations,
redundancies, and operating and maintenance considerations; such
project-specific preferences may also involve building and space design
conditions that deviate from standard criteria. In addition to fundamental
design criteria, the designer is responsible for becoming acquainted with
applicable government environmental regulations and should establish in the
project’s scope of work who has responsibility for permits required by the
jurisdiction.
1.4.2 Role of
Accrediting Organizations
For a health care organization
to participate in and receive payment from the U.S. Medicare or Medicaid
programs, it must meet conditions and standards established under federal
regulations by the Centers for Medicare & Medicaid Services (CMS).
Eligibility requires a certification of compliance with the CMS conditions of
participation, which is typically provided by a national accrediting
organization providing and enforcing standards recognized by CMS as meeting or
exceeding its own. Such organizations are considered by CMS to have “deeming
authority,” and the primary such deeming authority for health care facilities
in the United States is The Joint Commission, formerly known as The Joint
Commission for the Accreditation of Healthcare Organizations. The CMS conducts
random validation surveys of health care facilities certified by deeming
authorities.
The Joint Commission in an
independent, not-for-profit organization governed by a board of commissioners
that includes clinicians, facility administrators, health plan leaders,
educators, and a variety of other professionals experienced in health care
practice, administration, and public policy. The Joint Commission publishes a
variety of educational materials and standards including its Environment of
Care (EOC) standards, which establish both administrative and physical
requirements for creating and maintaining an optimally safe and healing health
care environment.
The Environment of Care
standards extend to the facility’s physical plant. Of greatest interest to the
HVAC engineer, the EOC standards require compliance with the FGI Guidelines and
ANSI/ASHRAE/ ASHE Standard 170, or with equivalent state or federal agency
codes establishing design criteria for health care facilities. EOC standards
(utility section) also establish facility administrative, documentation, and
operational requirements relating to HVAC systems and the built environment,
some of which include
documentation of the intervals
for inspecting, testing, and maintaining “all operating components of the
utility system;”
a process to minimize Legionella
colonization of cooling towers and heating water systems;
maintenance of drawings of
utility distribution systems;
proper ventilation systems to
maintain required airflow rates, pressurization, and filtration levels for
spaces or areas with airborne contaminant control requirements;
control of noise levels and
maintenance of speech privacy; and
maintenance of building
documentation, including distribution plans for building mechanical,
electrical, and plumbing (MEP) services, utility system maintenance records,
and building life safety plan.
The Joint Commission has a
survey staff of approximately 1000 inspectors who conduct the random facility
surveys required for a facility to maintain its accreditation status.
1.5 SUSTAINABLE DESIGN
Sustainable design embraces the
conservation of energy, water, and other natural resources to minimize a
building’s impact on the earth’s environment, while promoting evidence-based
design elements that enhance the health, comfort, and efficiency of the
building occupants. Considering that health care facilities in general are
serious energy and water consumers, and their user populations are
physiologically and psychologically sensitive, sustainable design approaches
can uniquely impact the efficiency and effectiveness of health care delivery.
Environmental design guidelines published by the U. S. Green Building Council
(USGBC) and ASHRAE establish target design outcomes that encourage building
owners and designers to minimize utility costs, improve building flexibility
and maintainability, and maximize the application of building features that
improve the comfort and sense of well being of the building occupants.
USGBC has published several
rating systems with potential application to health care, including LEED for
New Construction and Major RenovationsTM, LEED for Commercial InteriorsTM, and
LEED
1.5.1
Sustainable Sites
for HealthcareTM, the latter
being developed specifically for inpatient and outpatient medical treatment
facilities. Each rating system establishes minimum rating point values
necessary to achieve a range of certification levels. In addition to providing
a green rating tool, the LEED certifications and publications provide valuable
insight into the advantages of green/sustainable design features and encourage
a project team to exceed code-minimum requirements. Some owners may not choose
to pursue LEED or other certifications; when pursued, however, the HVAC
designer should consider payback, performance, and reliability in determining
which features and strategies to implement. Three important categories of
design considerations addressed in LEED are discussed in the following
sections.
The main thrust of this category
is to encourage selection of a building site that will have minimal impact on
the natural environment. Two credits within this category (in LEED for
Healthcare), however, directly affect the well being of patients, staff, and
visitors: connection to the natural world via places of respite, and/or direct
exterior access for patients. These credits address the advantages of human
contact with nature in reducing stress and depression, through the provision of
interior places of respite, healing gardens, exposure to daylight, views to the
outdoors, ready accessibility to the outdoors, and walking paths, among other
approaches.
1.5.2 Water
Conservation
Hospitals are among the largest
consumers of domestic water among all building types because of a variety of
requirements that may include HVAC systems (chiefly via makeup for cooling
tower and steam generation systems), sanitation, sterilization, humidification,
food preparation, laundry, dialysis and other water treatment systems, and
equipment cooling for vacuum and other process equipment. Sustainable design
guidelines are a valuable tool for education and encouragement regarding water
conservation practices that can substantially reduce water consumption and the
considerable costs associated with metered water and sewage utilities.
1.5.3 Energy
and Atmosphere
The objective of this category
is a reduction in energy use and associated pollution. The U.S. Department of
Energy (DOE) reports that hospitals have more than 2.5 times the energy
intensity of commercial office buildings, with these energy costs representing
1% to 3% of a typical hospital’s budget or an estimated 15% of profits (DOE
2009). The average energy use index (EUI) for hospitals in the northwestern
United States is 270 kBtu/ft2·yr [851 kWh/m2·yr] (BetterBricks 2010). To
qualify for the U.S. Environmental Protection Agency’s (EPA) ENERGY STAR® certification,
hospitals must meet EUI criteria that are based on size and location. For
example, a 500-bed hospital in central North Carolina would require an EUI of
170 kBtu/ft2·yr [536 kWh/ m2·yr] to qualify for ENERGY STAR. At that EUI, the
hospital is in the top 25% of similar hospitals in the country. For more
information, refer to the ENERGY STAR website.
Baseline energy modeling data
from Advanced Energy Design Guide for Large Hospitals (ASHRAE 2012)
suggest that, on average across the continental United States, HVAC energy
consumption in conventional large hospitals (i.e., those not utilizing the best
currently available approaches) amounts to more than 80% of these facilities’
total energy consumption. Given these statistics, the cost savings potential in
HVAC energy and the corresponding environmental benefits of reducing the carbon
footprint of a facility give building owners a powerful incentive to pursue
energy-conserving features and equipment.
1.6 EQUIPMENT
SIZING FOR HEATING AND COOLING LOADS
1.6.1 Design
Capacity
Design criteria for health care
facilities that affect equipment capacity and cooling/heating loads include
temperature, relative humidity, and ventilation requirements. In some cases, it
may be necessary to establish and maintain a range of room conditions, with
different setpoints for summer or winter operation or for differing patient
requirements. The HVAC design must provide for the required room conditions
under the most stringent operational or weather conditions defined by applicable
design criteria.
1.6.2 Exterior
Design Conditions
ASHRAE has several design
weather publications and products to aid the designer, including the Weather
Data Viewer CD, WYEC2 data, and ASHRAE Extremes (see www.ashrae.org
for further information). Many design criteria call for use of the ASHRAE 0.4%
dry-bulb (DB) and mean coincident wet-bulb (MWB) temperatures for cooling
applications and the 99.6% dry-bulb temperature for heating—typically for
inpatient and some outpatient (normally surgical) facilities where
environmental conditions are relatively critical to patient well-being. Typical
criteria for outpatient clinics call for using the ASHRAE 1% and 99% design
temperatures for cooling and heating loads, respectively. Maximum cooling load
can occur at peak WB conditions when outdoor air demands are high; for this
reason, and for sizing evaporative and dehumidification equipment, designers
should consider peak total load (latent plus sensible) climatic conditions for
each project. The designer should also consider that many parts of the world
are experiencing temperatures higher than the 0.4% design conditions. If the
HVAC system is designed so that it cannot accommodate more extreme design
conditions (when outdoor conditions exceed the 0.4% or 99.6% values) interior
design requirements may not be met. Most hospital owners would deem this
situation unacceptable.
1.6.3
Equipment Redundancy and Service Continuity
The fundamental importance of
maintaining reasonable interior conditions in critical patient applications
often dictates that some degree of backup heating capacity and, in many cases,
cooling and/or ventilation capability, be available in the event of major HVAC
equipment failure. Additionally, health care facilities are typically the go-to
place in the case of natural or human-caused disasters, and may represent the
single source of critical utility service availability (e.g., water,
electricity, sanitary, shelter, etc.) within a stricken region.
Applicable codes or criteria may
require inpatient facilities (and many outpatient surgical facilities) to have
up to 100% backup capability for equipment essential to system operation. Even
in cases when loss of a major HVAC service does not jeopardize life or health,
it may lead to inability to continue medical functions and unacceptable
economic impact to the building owner. Designers should also recognize that
routine maintenance requirements will, at least on an annual or seasonal basis,
require major plant equipment to be taken off-line for extended periods. Even
where 100% redundancy is not required, it is often prudent to size and
configure plant equipment for “off season” operation to enable extended
maintenance of individual units.
Emergency power systems (EPS)
are mandated by several codes and standards for HVAC equipment consideredessential for safety and health. Facility heating, particularly for critical
and patient room spaces, must normally be connected to the EPS, as is the
cooling system, in some jurisdictions. Federal government regulations and/or
guidelines require that ventilation equipment serving disease isolation and
protective isolation rooms be connected to the EPS. The AHJ and/ or owner may
require that cooling sources, pumps, air-handling units, and other equipment
necessary to provide cooling for critical inpatient or sensitive equipment
areas be supplied by an EPS.
1.7 VENTILATION AND OUTDOOR AIR QUALITY
Ventilation rates for typical
health care spaces are addressed by ANSI/ASHRAE/ASHE Standard 170, Ventilation
of Health Care Facilities. Such facilities require large amounts of fresh,
clean, outdoor air for occupants and for control of contaminants and odors
through dilution ventilation and exhaust makeup. In addition to outdoor air
change rates, minimum total air change rates are provided in order to
supplement ventilation “air cleaning,” or to establish adequate distribution
and circulation of air within a space. Filters with a minimum efficiency
reporting value (MERV) 14 or higher (MERVs established by procedures specified
in ANSI/ASHRAE Standard 52.2-2007) are very effective at removing
microorganisms and similarly sized particulates. In certain locations, the
quality of outdoor air may be compromised by combustion exhaust fumes or other
objectionable or harmful odors or gases, such as ozone, which require the
provision of activated carbon or other adsorption filtration of outdoor air.
1.7.1 Location of Outdoor Air Intakes
Outdoor air intakes must be
located an adequate distance away from potential contamination sources to avoid
intake of contaminants. Typical minimum separation requirements are 25 ft [7.6
m], established by the FGI Guidelines, and 30 ft [9.1 m], according to the ASHRAE
Handbook—HVAC Applications. These distances should be considered only as
preliminary guides: greater separation may be required, depending upon the
nature of the contaminant, direction of prevailing winds, and relative
locations of the intake and contaminant sources. The ASHRAE
Handbook—Fundamentals provides further design guidance and calculation
methods to help predict airflow
characteristics around
buildings, stack/exhaust outlet performance, and suitable locations for
intakes. See Chapter 3 of this manual for more details.
1.7.2
Air-Mixing and Ventilation Effectiveness
In most health care
applications, it is desirable to introduce supply air into a space in such a
manner as to maximize distribution throughout the space and minimize
stratification. Doing so maximizes the effectiveness of ventilation and
contributes to overall comfort. Good air mixing is enhanced by meeting minimum
total air change requirements and by careful selection of diffuser location and
performance, with proper attention to room construction features that can
affect distribution. Air-mixing effectiveness is also influenced by perimeter
envelope exposure and the temperature difference between supply and room air.
Additional information is available in Chapters 3 and 8.
1.7.3 Exhaust
of Contaminants and Odors
Exhaust systems provide for
removal of contaminants and odors from a facility, preferably as close to the
source of generation as possible. In addition, exhaust systems are used to
remove moisture, heat, and flammable particles or aerosols. Examples of source
exhaust in health care applications include the following:
Chemical fume hoods and certain
biological safety cabinets used in laboratories and similar applications where
health care workers must handle highly volatile or easily aerosolized materials
Special exhaust connections or
trunk ducts used in surgical applications to remove waste anesthesia gases or
the aerosolized particles in laser plumes
“Wet” X-ray film development
machines (now being rapidly replaced with digital equipment), which are
normally provided with exhaust duct connections for removal of development
chemical fumes
Cough-inducement booths or hoods
used particularly in the therapy for contagious respiratory disease
Kitchen and sterilizing
equipment that produce moisture and heat
When contaminants or odors
cannot practically be captured at the source, the space in which the
contaminant is generated should be exhausted. Rooms typically exhausted include
laboratories, soiled linen rooms, waste storage rooms, central sterile
decontamination (dirty processing), anesthesia storage rooms, PET scan, hot
laboratories (for work with radioactive materials), airborne infection
isolation (AII), and bronchoscopy. For potentially very-hazardous exhausts,
such as from radioisotope chemical fume hoods or disease isolation spaces,
codes or regulations may require HEPA filtration of the exhaust discharge,
particularly if the discharge is located too close to a pedestrian area or
outdoor air intake.
1.8
ENVIRONMENTAL CONTROL
1.8.1 The Role of Temperature and Relative
Humidity
As discussed in section 1.3,
temperature, and in some instances relative humidity, can be important in
establishing therapeutic conditions for patient treatment, and in maintaining a
comfortable environment for all of the building’s occupants.
Conditions of temperature and
relative humidity that would be considered comfortable for healthy individuals
dressed in normal clothing may be very uncomfortable for both patients and
health care workers, for a variety of reasons, including the following:
Patients in both clinical and inpatient
facilities may be very scantily clad or, in some instances, unclothed—and have
little or no control over their clothing.
In hospital settings, patients
are often exposed to a specific environment on a continuous basis, not merely
for short periods of time.
In a variety of cases of disease
or injury, patient metabolism, fever, or other conditions can interfere with
the body’s ability to regulate heat.
Health care workers often must
wear heavy protective coverings, as in surgery and the emergency department,
and engage in strenuous, stressful activities near heat-generating lights and
equipment.
1.8.2 Noise
Control
Noise control is of high
importance in the health care environment because of the negative impact of
high noise levels on patients and staff and the need to safeguard patient
privacy. The typical health care facility is already full of loud noises from a
variety of communications equipment, alarms, noisy operating hardware, and
other causes without the noise contribution from poorly designed or installed
HVAC equipment. High noise levels hinder patient healing largely through
interference with rest and sleep. In addition, loud noises degrade the health
care provider’s working environment, increase stress, and can cause dangerous
irritation and distraction during the performance of critical activities.
Sources of excessive HVAC noise include
direct transmission of
mechanical and/or medical equipment room noise to adjacent spaces;
ductborne noise generated by
fans and/or high air velocities in ducts, fittings, terminal equipment, or
diffusers and transmitted through ductwork to adjoining occupied spaces;
duct breakout noise, where noise
in ductwork penetrates the walls of the duct and enters occupied spaces;
duct rumble, a form of low-frequency
breakout noise caused by the acoustical response of ductwork to fan
noise—particularly high-aspect-ratio, poorly braced rectangular ductwork; and
vibrations from fans, dampers,
ductwork, etc.
Patient privacy can be
compromised when private conversations are intelligibly transmitted to
adjoining spaces. Frequent causes of this problem are inadequate acoustical
isolation properties of the construction elements separating rooms, inadequate
sound-dampening provisions in ductwork, and/or inadequate background room sound
pressure level. HVAC ductwork design and diffuser/register selection can
greatly mitigate the latter two concerns, by providing a minimum level of
background sound contribution from the air distribution system and by providing
effective attenuation in ductwork. Chapter 3 provides more detailed information
on the causes of, and solutions to, HVAC noise.
1.9 HVAC
SYSTEM HYGIENE
In addition to the general topic
of infection cause and control discussed previously, the designer must be aware
of the potential for infection risks that can arise through poor design or
maintenance of HVAC equipment. As explained in greater detail in Chapter 2,
infections acquired within the health care facility are referred to as
nosocomial infections, or health-care-acquired infections (HAI). Any location
where moisture and nutrient matter come together can become a reservoir for
growth of harmful microorganisms. Generally, hard surfaces (such as sheet
metal) require the presence of liquid water to support microbe growth, whereas
growth in porous materials may require only high relative humidity. Nutrient
materials are readily available from sources such as soil, environmental dust,
insects, animal dander and droppings, and other organic and inorganic matter.
The task of the HVAC designer is to minimize the opportunity for moisture and
nutrients to collect in the system, through proper design of equipment,
including adequate provisions for inspection and maintenance. Potential
high-risk conditions in an HVAC system include the following:
Outdoor air intakes located too
close to collected organic debris, such as wet leaves, animal nests, trash, wet
soil, grass clippings, or low areas where dust and moisture collect; this is a
particular concern with low-level intakes and a primary reason for
code-mandated separation requirements between intake and ground, or intake and
roof
Outdoor air intakes not properly
designed to exclude precipitation; examples are intakes without intake louvers
(or with improperly designed louvers) and intakes located where snow can form
drifts or splashing rain can enter
Improperly designed or installed
outdoor air intake opening ledges where the collected droppings of roosting
birds carry or support the growth of microorganisms
Improperly designed or installed
cooling-coil drain pans or drainage traps that prevent adequate condensate
drainage
Air-handling unit or
duct-mounted humidifiers not properly designed or installed to provide complete
evaporation before impingement on downstream equipment or fittings
Filters and permeable linings,
which collect dust, located too close to a moisture source, such as a cooling
coil or humidifier
Improper attention to
maintenance during design, resulting in air-handling components that cannot be
adequately accessed for inspection or cleaning
Designers must always bear in
mind that even properly designed equipment must be maintainable if it is to
remain in clean, operating condition. Chapter 3 provides additional information
regarding the proper design of HVAC system components to minimize the potential
for microbe growth.
1.10
FLEXIBILITY FOR FUTURE CHANGES
Changes in space use are common
in health care facilities, and periods of less than ten years between complete
remodelings are commonplace. The trend is normally toward more medical
equipment and increasing internal cooling loads. The initial design should
consider likely future changes, and the design team and owner should consider a
rational balance between providing for future contingencies and initial
investment costs. Future contingencies may be addressed by features such as
oversizing of ductwork and
piping;
provision of spare equipment
capacity (oversizing) for major plant, air-moving, or pumping equipment or
provision of plant/ floor space for future equipment installation; and
provision of interstitial
utility floors where maintenance and equipment modification or replacement can
occur with minimal impact on facility operation.
1.11
INTEGRATED DESIGN
1.11.1 General
To succeed, the HVAC design
process must be thoroughly coordinated with the other design disciplines. The
HVAC engineer’s involvement should begin no later than preconcept design and
continue until design completion. This chapter has addressed some of the design
features essential to good air quality, hygienic design, and comfort
conditioning; obtaining these features requires the HVAC designer’s early
influence on building arrangement and floor plan features that affect equipment
location and space availability. Early involvement and design coordination are
essential to ensure that
outdoor air intakes and building
exhausts are optimally located to avoid contamination of the building air
supply;
plant and equipment rooms are
well located in relation to the areas they serve, to enable economic sizing of
distribution equipment and air and water velocities well within noise
limitation guidelines;
plant and equipment rooms are
located so that equipment noise will not disrupt adjacent occupied spaces;
HVAC equipment room locations
are coordinated with electrical, communications, and plumbing equipment rooms
to minimize distribution equipment (ductwork, piping, cable trays, and conduit)
congestion and crossover, while providing adequate space for installation and
maintenance of these services;
sufficient vertical building
space is provided for the installation and maintenance of distribution
equipment of all trades; and
sufficient space is provided for
plant and equipment rooms and vertical utility chases, to enable proper
installation, operation, and maintenance of equipment, including provisions for
eventual equipment replacement.
1.11.2
Equipment Interface: “Make it Fit”
Because of the many engineering
systems that provide services in health care facilities, the need to provide
adequate access for future maintenance, and because criteria may restrict where
distribution equipment can be installed, the HVAC designer must carefully
coordinate the physical space requirements for equipment. Health care
facilities are served by a wide variety of fire protection, electrical power,
plumbing, medical gas, and telephone, data, nurse call, and other electronic
communication and monitoring systems. All of these must physically fit within
allowable distribution spaces along with HVAC ductwork and piping. Often, codes
or criteria restrict main utility distribution to circulation spaces to
minimize the need for maintenance personnel to enter occupied spaces and/or to
control noise. Codes also restrict certain utilities from passage over
electrical and communications spaces, exit enclosures, and certain critical
health care spaces, such as operating rooms.
It is the responsibility of
design engineers to verify that the equipment depicted in design drawings can
be installed in the spaces indicated, with sufficient space for maintenance
access, by a prudent contractor using standard construction practices and
reasonable judgment, according to the provisions of the construction contract.
When the designer knows that space is so limited as to require special
construction measures and/or limited or proprietary equipment selections, it is
wise to make this information known in the design documents. A prudent designer
depicts and dimensions the equipment on design drawings (including ductwork and
piping, and all major fittings and offsets required for coordination,
balancing, and operation) such that it could reasonably be installed as
depicted. These design responsibilities do not detract from the construction
contractor’s responsibility to properly coordinate the installation work
between trades and do not supplant his/her responsibility to execute detailed,
coordinated construction shop (installation) drawings.
Building information modeling
(BIM) collision-avoidance tools are increasingly being used to assist in the
spatial coordination of distribution equipment with architectural and
structural elements. Designers should be aware of their BIM software’s
capabilities and limitations in depicting maintenance clearances, as these must
typically be manually defined and input. Similar attention must be paid to the
correct modeling of gravity drainage, steam, and other sloped piping systems.
Many designers still accomplish systems coordination the “old fashioned way” by
a variety of methods that may include multidimensional overlays and
representative sectional views or sketches. Such sectional views should be
provided from at least two perspectives in each congested plant and equipment
room and at representative “crowded” locations in distribution areas throughout
the facility. Some building owners require submission of such
“proof-of-concept” documents to demonstrate satisfactory interdisciplinary
coordination.
1.11.3 Special
Considerations for Retrofit/Renovation
Designs for retrofit or renovation
of existing health care facilities, particularly when health care functions in
areas surrounding or adjacent to project work must continue during
construction, require special attention to factors that can affect patient
health and safety. Designs must include provisions to minimize the migration of
construction dust and debris into patient areas or the possibility of unplanned
interruptions of critical engineering services.
Construction work almost
invariably involves introduction or generation of substantial airborne dust or
debris, which, without appropriate barrier controls, may convey microbial and
other contaminants into patient care areas. Demolition activities, the
transport of debris and personnel traffic in and out of a facility can directly
introduce contaminants—as can disruption of existing HVAC equipment, removal of
barrier walls or partitions, and disturbance of building elements and equipment
within occupied areas. Project architects and engineers must work closely with
the owner’s infection control representative to help assess the potential risks
to the patient population during construction activities, and jointly identify
appropriate barrier controls and techniques. Typical barrier approaches can
include separation of construction areas by dust-tight temporary partitions,
exclusion of construction traffic from occupied areas, and isolation of duct
systems connecting construction with occupied spaces. In addition, negative
relative pressurization and exhaust of construction areas are usually required.
In cases of severe patient vulnerability, the use of supplemental HEPA
filtration units in patient rooms or other critical spaces may be considered.
Of equal concern, designers must
seek to minimize the possibility of unplanned service interruptions during the
construction project. Designers should become well acquainted with the existing
engineering systems and building conditions to be able to evaluate the impact
of new construction. Site investigations should always include inspection of
existing equipment plants, rooms, and other equipment and building areas with
reasonably available access. Maintenance personnel can often provide
information on concealed as-built conditions, and as-built drawings are often
available; in many cases, however, the latter are inaccurate or not up to date.
Predesign testing, adjusting, and balancing (TAB) of existing conditions is
advisable; otherwise, new design work will often be held responsible for
deficiencies in original equipment or system performance.
When as-built information is
lacking or suspect, designers should attempt to identify existing services that
are installed in, or are likely to be affected by, project work, to the extent
feasible under the scope of the design contract and the physical or operational
limitations of building access. Building owners should recognize the value of
accurate as-built information and, when not available from in-house sources,
contractually provide for more thorough investigations by the design team. It
is the designer’s responsibility to identify the nature of alterations of, or
extensions to, existing services and equipment, including temporary features,
and any required interim or final rebalancing, commissioning, or certification
services necessary to accommodate new building services while minimizing impact
to ongoing functions. This will often require the development of a detailed
phasing plan, developed in close coordination with the building owner. The goal
should be “no surprises”—no interruptions or diminishment of critical services
to occupied areas that are not planned and made known to the building owner
during the design process. Chapter 7 provides more information on this topic.
1.12 COMMISSIONING
Health care HVAC systems provide
critical functions that justify a comprehensive commissioning process that goes
beyond the level of quality oversight/control, static testing, and TAB
typically practiced on commercial facilities. Commissioning should begin with
concept design and continue through the project, with the active participation
of qualified commissioning professionals in development and review of
commissioning documents that define the responsibilities of all parties
involved, and clearly convey the scope and rigor of the commissioning process and
the owner’s project requirements (OPR). Among other features, proper
commissioning involves expert oversight of equipment and system startup,
prefunctional performance checks, functional performance testing, owner
training, and other activities overseen by a qualified representative of the
building owner, based on comprehensive specifications developed during the
design phase. A rigorous commissioning process will demonstrate that the
as-built HVAC system operates according to the owner’s requirements and the
designer’s intentions, by achieving the following objectives:
Providing assurance that
equipment and systems are properly installed and received adequate operational
checkout by the installation contractors
Verifying and documenting the
proper operation and performance of equipment and systems, to include operation
in part-load and failure modes
Establishing that performance
setpoints are achieved and optimized
Providing thorough documentation
of the commissioning process and results
Providing assurance that the
facility operating staff is adequately trained
Depending upon the size,
complexity, and budget for the project, the tasks involved in commissioning can
vary widely. Consequently, the commissioning process should be customized for
each project. It is worth repeating that the required scope and rigor of the
commissioning process must be clearly defined before award of the construction
contract, so that the necessary qualifications, responsibilities, and scope of
effort for all parties involved in construction phase commissioning are clearly
understood.
1.13 CONCLUSIONS
The design of HVAC systems for
health care facilities is a unique and challenging art and science—demanding
specialized experience and knowledge of the character of these high-stakes
facilities, the sensitivity and vulnerability of their populations, and the
complex interactions of the HVAC system with the other architectural and
engineering elements that make up the building. The design process requires
familiarity with a specialized and diverse set of criteria, regulations, codes,
and design standards, and the ability to weigh their application in the face of
an owner’s economic limitations associated with the business of health care
(addressed in detail in Chapter 9). This manual describes best practices for
the design of HVAC systems for health care facilities. It is not intended as a
code document, and readers should consider that even best practices, unless
codified, may be rejected by the building owner.
REFERENCES
ASHRAE. 2012. Advanced energy
design guide for large hospitals. Atlanta: ASHRAE.
BetterBricks. 2010. Energy in
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Alliance. Available at http://www.betterbricks.com/.
DOD. 2011. Unified facilities
criteria (UFC) design: Medical military facilities (UFC 4-510-01), Change
4, August 2011. Washington, DC: U.S. Department of Defense.
DOE. 2009. Department of Energy
announces the launch of the Hospital Energy Alliance to increase energy efficiency
in the healthcare sector, April 2009. Washington, DC: U.S. Department of
Energy. Available at
http://energy.gov/articles/department-energy-announces-launch-hospital-energy-alliance-increase-energy-efficiency.
EPA. ENERGY STAR® Program.
Washington, DC: U.S. Environmental Protection Agency. Available at
http://www.energystar.gov/.
ICC. 2012. International
building code® (IBC®). Washington, DC:
International Code Council.
NFPA. 2012. NFPA 101: Life
safety code®.
Quincy, MA: National Fire Protection Association.
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