[
Engineering Forum.
Alexander Delli Paoli, Jr.
The HVAC Process
Alexander Delli Paoli, Jr.
Welcome to “Engineering Forum.”
This feature discusses applied technical principles
associated with engineering topics that focus on usefulness to practitioners in validation and compliance.
We intend this column to be a resource for daily work
applications.
Engineering technology is a topic of great importance in contemporary pharmaceutical and medical
device manufacturing. Validation and compliance
professionals must become familiar with facilities,
equipment, utilities, and other systems at their sites.
Global regulatory agencies require more than just
compliance to procedures in the modern manufacturing organizations. They require understanding of
processes and topics controlled by site procedures.
Sound procedures, policies, and literally everything
involved in regulated manufacturing must be based
on scientific principles whenever possible, must be
appropriate for risk, and must be continually monitored and maintained. Outsourcing of manufacturing
and testing functions has further extended these
responsibilities.
Engineering topics are not generally well known
or understood beyond the engineering community.
Personnel resources have been reduced, and individual responsibility has increased. Those with limited background and experience may find themselves
involved in areas with which they have little expertise.
Further, the technical information supporting their
areas may be esoteric and incomprehensible for
those not trained in the field. We intend to address
engineering topics with these considerations in mind.
These topics will be discussed clearly and in a meaningful way so that our readers will be able to understand and apply the principles discussed in daily work
situations.
For more Author
information,
go to
gxpandjvt.com/bios
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The first series of articles will discuss HVAC processes for warehouses, offices, laboratories, cleanrooms, containment facilities, and other manufacturing environments. The series will also touch on
specialized applications such as containment hoods,
biological safety cabinets, and dust collection systems.
Subsequent articles will address each of these topics in
greater detail, driving toward a working familiarity of
HVAC systems and their typical challenges.
Reader comments, questions, and suggestions for
discussion topics are needed to help us fulfill the
column objective. Please send your comments and
suggestions to column coordinator Alex Delli Paoli
at [email protected] or to journal managing
editor Susan Haigney at [email protected].
KEY POINTS
The following key points are discussed:
•Understand the reason your site needs different types
of HVAC systems
•Recognize all the HVAC components and their
purpose
•Understand how all the components interact
•Be aware of the physics of air: Psychrometrics
•Assure proper safety measures are in place
•A system is only as good as its maintenance and
compliance to design criteria.
INTRODUCTION
Heating, ventilation, and air conditioning (HVAC) systems are critical to pharmaceutical and medical device
manufacturing. These systems comprise multiple components that are integrated in a reliable process to create
a sustainable environment.
This discussion provides an overview of the process
used to bring air from the randomly variable mixture of
[
ABOUT THE AUTHOR
Alex Delli Paoli, Jr., P.E., is managing director of Engineered Strategic Visions, Libertyville, IL, USA.
Engineered Strategic Visions, Inc. (www.engineervisions.com) is an engineering consulting firm specializing in project planning and management, manufacturing support, asset and energy management,
and other areas of expertise. He may be reached by e-mail at [email protected].
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Alexander Delli Paoli, Jr.
vapors and particles found in the atmosphere to a steady
state condition acceptable for the environment the system
serves. The following will be discussed:
•HVAC definition—the scope of HVAC and what
general areas are encompassed
•The process of HVAC—HVAC systems include multiple equipment that transforms variable air states
to achieve target attributes
•Why process the environment?—the reasons that
air must be processed
•Components and function of the air handler (e.g.,
the preheat coil and filters, cooling coil, return fan,
exhaust fan, and associated equipment)
•Applications (e.g., warehouses, offices and records
storage, laboratories, cleanrooms, containment facilities, and general manufacturing areas).
HVAC DEFINITION
HVAC is a hybrid engineering discipline based on
aspects of classical mechanical, electrical, and chemical engineering practices. It includes knowledge of fluid
mechanics, machine design, and instrument control. It
further includes a working knowledge of the physical
properties of several liquids and gases. Material compatibility knowledge is also important for avoiding chemical
interaction with dissimilar metals, incompatibility with
refrigerants, and other deleterious effects due to cleaning
agents used in the facilities served by the HVAC units.
Practical considerations such as physical layout and access
for maintenance along with a good sense of aesthetics
are also important to the discipline of HVAC.
HVAC started as a formal practice during the Industrial Revolution when it was recognized that mines and
factories needed to be ventilated (V) (i.e., air containing noxious fumes and particles needed to be replaced
with fresh breathable air). Heating (H) was also a need
beyond the home fireplace to warm shops and factories
in northern climates. Air conditioning (AC) became
practical with the invention of the mechanical refrigeration process. It was an obvious extension to H and
V. Occasionally, R for refrigeration is included when
refrigerators and freezers are involved in a project. This
is typically shown as HVAC/R.
THE PROCESS OF HVAC
Traditional textbook explanations of HVAC systems
often describe these systems as integrated pieces of
equipment (e.g., air handler, fans, ductwork) having
individual functions. These descriptions ignore the process of HVAC to produce a “product”—air with desired
temperature, humidity, particulate level, and other quality attributes.
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The HVAC process may be compared to a typical manufacturing process (see Figures 1 and 2). The manufacturing
process utilizes individual pieces of equipment to process
active drugs and excipients into a final pharmaceutical
product in commercial packaging. The HVAC process
utilizes multiple equipment components and operations
to convert incoming air to processed air that meets facility
needs. Most facilities require a broad scope of air quality.
For example, a facility might include sterile product manufacturing, non-sterile product manufacturing, warehouses, docks, offices, and other areas—each of which will
have differing HVAC requirements. Further, there may be
different requirements within a given area. For example,
a non-sterile manufacturing area may require rooms with
very low humidity to process moisture sensitive drugs.
The HVAC system and its component subsystems must
provide the required environmental conditions.
HVAC Process Comparison to
Manufacturing Process
The HVAC system process is generally similar to a product
manufacturing process. Both convert input materials
by means of process parameters into a final product
meeting required quality attributes. There are important
differences that the HVAC system must overcome to
accomplish its objectives. These include input material
considerations, process capability, and process changes.
Input materials. The manufacturing process converts
drugs and inactive materials to pharmaceutical products.
The incoming materials should be well controlled by
means of vendor approval and supply chain control. The
HVAC process converts air from the external environment
to air possessing the quality attributes required for the
respective areas in the site. The input air is uncontrolled,
may have unexpected content (e.g., fumes, particulates,
pollen, and insects) and has seasonal variation. Winter
air will have lower moisture content than summer air. Further, the summer humidity may approach 100% in tropical areas for extended periods during the rainy season.
Process capability. The manufacturing process
has defined process limits. These limits are usually not
exceeded because input materials are well controlled. In
contrast, the HVAC process may be challenged beyond
the limit of design capabilities depending on environmental variation.
Process changes. The manufacturing process is generally well established and remains relatively constant
throughout the product lifecycle. The process is often
approved by regulatory agencies and is not able to be
changed without regulatory approval. In contrast, the
HVAC process has significant seasonal variation requiring
cyclical heating and cooling. These are significant process
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Figure 1: Manufacturing process.
MANUFACTURING PROCESS
WHY PROCESS THE ENVIRONMENT?
API
Excipient
Excipient
Excipient
Manufacturing process unit operation
Equipment #1 (IQ, OQ, PQ)*
Equipment #2(IQ, OQ, PQ)
Equipment #3 (IQ, OQ, PQ)
Excipient
Excipient
Manufacturing process unit operation
Equipment #4 (IQ, OQ, PQ)
Manufacturing process unit operation
Equipment #5 (IQ, OQ, PQ)
Equipment #6 (IQ, OQ, PQ)
Bottles
Caps
Inserts
Packaging process unit operation
PRODUCT / PROCESS COMPLETED
* IQ=Installation qualification; OQ=Operations qualification; PQ=Performance qualification.
Figure 2: HVAC process.
Outside Air
Return Air Fan
Roughing Filters
Preheat Coil
Mix Air Streams, Preheat and Filtration
Filters
Cooling Coil
Humidifier
Intermediate Filtration, Moisture Content Adjustment
Supply Fan
Refined filters
Motive energy imparted to air, additional filtration
Supply air distribution ductwork
In-duct heating coils
Supply delivery devices (diffusers, terminal filters)
Trim air temperature, deliver and distribute to facility
Return air distribution ductwork
Collection devices (Fume hoods, etc.)
Exhaust air ductwork
Exhaust fan
HVAC PROCESS COMPLETED (cycle repeats)
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changes. Periodic checks to assure the HVAC systems
are operating as intended are key to consistent operation.
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Any manufacturing, testing, or storage facility and their
related processes strive for a steady state consistent environment to deliver reliable products to customers. Even
offices are expected to be consistent so as not to distract
employees from their responsibilities or create office
equipment failures.
HVAC Considerations
The following are major parameters to consider when
looking at a process and the environment’s impact:
•Temperature. Temperature is sensible heat. This
heat can be felt or sensed because it causes a rise or
fall in temperature.
• Humidity. Humidity is an indication of the level of
water vapor in the air. Humidity is typically expressed
as relative humidity. HVAC and facility professionals
utilize dew point to indicate moisture content. A psychrometric chart is a necessary tool for understanding
the current state of the air and water vapor mixture
(Figure 3). Humidity changes in controlled environments usually contribute to the cooling load of a facility. This load is called latent heat. Latent indicates a
phase change from vapor to liquid, or visa versa. At the
other end of the control demand is humidification. In
seasonally cooler climates, moisture must be added
to air to increase humidity to within desired limits.
•Particulate contamination. Particle load may
occur from the outside or from within the facility. The wind and the season can play big parts in
contributing to the amount of particulate in the air
being introduced into an HVAC system. Internal
particulate loading can come from people, corrugate,
facility materials of construction, and manufacturing
or testing contaminants. Particulate can be viable
or non-viable. Both have their potential hazards to
the facility environment.
•Vapor contamination. Vapor contamination can
come from internal and external sources similar to
particulate contamination. A site HVAC system near
a highway can draw in detectable levels of hydrocarbons. A diesel engine inadvertently operating
outside the intake of a HVAC system can bring odors
and vapors into warehouses, offices, laboratories,
and manufacturing areas served by the unit, causing discomfort or illness to the building occupants.
Improper amounts of outside ventilation air can
cause carbon dioxide build-up with resulting oxygen
deprivation concerns.
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Alexander Delli Paoli, Jr.
•Pressure. Air pressure is assumed to be
incompressible in most HVAC applications. This assumption comes into question when elevated pressure or vacuum
is needed in a process environment. Sites
located in higher elevations must also not
make the same assumptions that those
living nearer to sea level make about system component selection. Most component capacities are de-rated at higher
altitudes.
• Safety. Safety is an important system
capability often assumed or not adequately considered. Fire protection considerations, adequate ventilation for personnel,
fail-safe automatic controls, hazardous
fume and particulate containment
devices, and properly designed egress
are among many facility safety concerns.
Figure 3: Psychrometric chart (courtesy of Climate Solutions, copyright Trane).
There are other factors that affect the way
air is processed in an HVAC system, though
one cannot analyze a single cubic foot of air
to understand the impact of these design
characteristics. Future articles in this series
will address these factors in detail. The following are
some of these factors:
•Ratio of outside air (OA) to return (recirculated)
air (% OA)
•Amount of air moving through the HVAC system
relative to the amount of air needed to heat or cool
the facility
•Localized heat, humidity, and particulate issues
within a facility
•Efficiency of air distribution and circulation within
a facility.
Water Content in Air
Water must also be included in any discussion about
HVAC. Water is included because it is an effective heat
transport medium at temperatures at and above 100∘C
(steam) as well as at temperatures approaching the freezing point of 0∘C.
Water is often used in closed circuits transporting heat
between HVAC systems and remotely located equipment
such as water chillers to produce chilled water and boilers to make hot water and steam. It is also used in open
circuits to transport the rejected heat from water chillers to
large atmospheric heat exchangers called cooling towers.
Evaporative cooling is used in these towers by spraying
water into an airstream within the tower. This sensible
and latent heat transfer cools the water to near dew-point
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temperatures. The water is then returned to the water
chiller to take heat away from the facility. Open water
circuits require filtration to remove the same atmospheric
contaminants to which air intakes are exposed. Both open
and closed water circuits require treatment additives.
All HVAC systems using water in any form contain
additives to protect the piping and components from
temperature extremes, corrosion, and bioburden. This
article will not discuss further detail about additives. It
is important that validation and quality professionals
become familiar with the additives in the systems at
their site. The potential impact of additives should be
considered in any failure mode analyses performed.
AIR HANDLER
COMPONENTS AND FUNCTION
The central point of an HVAC system is the air handling
unit (AHU) or air handler. Figure 4 provides a schematic
drawing of an air handler. Air is shown moving from left
to right. This figure shows all the typical components
used in an air handler. There are many variations in this
type of equipment. The system described in Figure 4
will serve as an effective starting point. Components
discussed include the following:
•Preheat coil and filters
•Filters
•Cooling coil
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•Return fan
•Exhaust fan
•Other components including ductwork, dampers,
sensors, and smoke detectors.
Preheat Coil and Filters
Outside air (OA) and air returning (Return Air, RA)
from the facility served by the unit are combined at
the back end of the AHU and filtered to create air
at some intermediate level of temperature, humidity, and cleanliness (mixed air). Space is provided
between components within the air handler to allow
access by maintenance personnel. The air then passes
through a preheat coil (heat exchanger) to raise the
temperature of the air to a temperature that will not
expose subsequent components to freezing hazards.
The preheat coil is not required in warmer climates
where temperatures never go below the freezing point
of water. The preheat coil is usually heated by steam
or antifreeze-treated hot water.
Filters
The air then continues through a finer set of filters to
continue removal of finer particulates. Each successive
set of filters is more efficient that the previous set. This
is done to keep larger atmospheric dust particles from
plugging the finer downstream filter(s).
Cooling Coil
The air next passes through a cooling coil. As it passes
through this heat exchanger, the air temperature drops to
a prescribed temperature chosen so the air can effectively
cool the facility it is serving. The air will likely get to its
dew-point temperature during the cooling process. At
this point and as it continues to cool, the air has become
saturated with water vapor. Liquid water will form on the
cooling coil surfaces and run down the coil surfaces to a
drain pan. The water is then removed from the air handler
through a drain. The cool saturated air is then drawn
through a fan, which imparts the energy needed to generate the pressure necessary to drive the air through all the
Figure 4: Schematic diagram of a HVAC system.
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Alexander Delli Paoli, Jr.
air handler components and the ductwork distribution
system. At this point, the air is heated by fan as it passes
through the system. This raises the air temperature a few
degrees, bringing the air above its dew-point temperature
and avoiding condensation that could occur if the air
was still saturated. At the other extreme, if the humidity
of the air was very low as happens in cooler seasons in
northern climates, the dew-point temperature would
never be reached, and the HVAC control system could
detect the need to add moisture to the environment. A
humidifier using steam or atomized water would then
achieve the desired humidity level by adding this vapor
into the air stream.
Return Fan
A return fan is also shown on the schematic. It is common to have an HVAC system with only one fan. Systems
operating in a compliance-oriented industry tend to have
more components that create more pressure drops as the
air passes through each. Rather than having one fan that
gets larger and larger with a greater pressure demand, it
is desirable to use two fans—a return fan and a supply
fan. The return air fan draws the air through the return
side of the ductwork distribution system. The supply fan
draws air from the outside and also draws the mixed
air stream through all the air handler components. The
supply fan also drives the air through the supply ductwork distribution system. The two-fan arrangement
also offers a push-pull configuration that is desirable in
several applications.
Exhaust Fan
When fumes, particulate, or other contaminants are
generated in a facility, an exhaust system is required. The
typical components are fan filters, cyclone separators,
scrubbers, and a purpose-specific capture apparatus.
The apparatus can include fume hoods, biological safety
cabinets, and other custom-made enclosures all intended
to confine and conduct the contaminants to the exhaust
ductwork. Once in the ductwork, the contaminant-laden
air is treated in potentially many different ways. If the
contaminant is not an environmental hazard such as
simple particulate, the exhaust could go to the atmosphere with minimal processing. As the complexity and
hazardous nature of the exhaust air increases, differing
types and degrees of filtration and other treatments can
be applied.
The Rest of the System
Other system components are usually located in the
supply and return ductwork, including, but not limited
to, the following:
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•The actual ductwork. Ductwork must allow minimal
leakage to assure the intended volumes and condition of air is delivered. Improperly constructed ductwork can be noisy, creating rattling or “tin c­ anning”
when system adjustments happen. Above all, the
ductwork must be of the correct size and made of
materials compatible with the vapor stream flowing
within it. Typical ductwork is usually constructed on
galvanized sheet metal. High levels of water vapor
or corrosive vapors flowing through an exhaust duct
could dictate the need for an alternate material.
•Manual dampers for balancing airflow throughout
the air distribution system.
•Automatic dampers to control airflow in the system.
•Automatic control system sensors to measure temperature, humidity, airflow volume and air pressure
at key positions.
•Heating coils to warm air being delivered to specific
rooms for individual temperature control.
•Life safety components such as smoke detectors, heat
detectors, and fusible link fire dampers.
•Terminal filters where a cleanroom type environment is desired. These filters are typically of high
efficiency, and they are the last item the air passes
through as it is introduced to the clean room.
APPLICATIONS
HVAC systems are present in every facility and have a
wide range of applications. Some applications might seem
simple on the surface until regulatory implications and
unintended consequences are discussed. The subtleties
of each application may be touched upon in this article,
but will be addressed in greater depth in subsequent
articles in this series.
Warehouses
The word warehouse may suggest images of a large boxy
building with fork trucks running all around and truck
dock doors routinely open to the atmosphere. Perhaps
there is no issue ventilating the space with all that help
from nature, but it could be a real challenge to heat, cool,
and keep clean with the aforementioned openings to the
environment and potential sources of contamination.
Most warehouses operating in a regulated environment
are under much closer control. Truck docks are often
treated with close fitting dock door seals and localized
heating, cooling, and filtration as a first defense to keeping
the atmosphere out of the controlled environment. Pest
control measures are in place to keep rodents and flying
insects from penetrating too far before being intercepted.
Ceiling–mounted propeller fans move warm air from the
underside of the roof down, creating a circulation pattern
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that draws cooler air up. This allows for a reasonably uniform temperature distribution throughout the warehouse.
This is particularly important if the product being stored
must reside within restricted ­temperature limits.
Air handlers serving warehouses must have a first set
of filters to remove coarse atmospheric dust. A second
set of finer filters is often included in the air handler
to keep atmospheric dust fines from becoming visible
deposits on the materials and products stored in the
area. Heating and cooling coils will likely be present in
the air handler if the warehouse has operating limits for
temperature and humidity. Humidity is important to
control to keep the product packaging from developing
mold or other environmentally introduced blemishes.
The warehouse air handler will obviously need a supply
fan to drive the air through all its components and the
supply distribution ductwork. A return fan is often not
included unless the HVAC system has return distribution duct work.
The amount of outside air the air handler is required
to introduce to the warehouse facility is dependent on
the amount of exhaust air required, the minimum ventilation air required by local building codes, and the
number of gas-powered forklift trucks operating in the
building. Additional outside air may also be introduced
to pressurize the warehouse building to form another
barrier against atmospheric contaminants.
An exhaust system is definitely required over electric
forklift battery charging areas to capture hydrogen. Other
exhaust systems could also be needed to support warehouse operations requirements to keep fumes, particulate, and other potential hazards from being introduced
into the general building environment.
Office and Records Storage
HVAC systems serving office environments are usually
not captured in any product compliance regulations
unless samples to be ultimately sold are brought into
office areas for testing or inspection. This could also
apply to documentation storage areas. The areas used for
such functions could come under scrutiny, bringing the
entire air handler into the qualification and validation
arena. Baring that situation, a typical office HVAC system
includes two sets of filters, preheat and cooling coils, a
supply fan, supply and return air distribution systems,
and a return fan. Exhaust systems are required in toilets
and kitchens, and they may be required in break areas
and printing and reproduction areas.
Ventilation is generally specified by the governing local
building code. This can take the form of air changes of
outside air per hour or cubic feet per minute of outside air
per person occupying the facility. Either way, the build26
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ing manager should have a procedure for periodically
verifying that the proper ventilation rate is being met.
This could be done continuously with airflow measurement by the control system, or by periodic physical testand-balance reviews. In either method, a history record
should be maintained demonstrating a consistency across
reviews. This discipline applies to all HVAC systems with
a life-safety element, and not just office systems.
Laboratories
The basic laboratory HVAC system is similar to an office
HVAC system. Laboratories need a desk either in the
lab or in a segregated area adjacent to the lab. Laboratory facilities are usually served by an isolated HVAC
system dedicated to the laboratory environment. While
the desks and offices for lab personnel are often on the
lab system, it is not considered good practice to expose
personnel in general office areas to laboratory risks (e.g.,
solvent fumes and particulates) that are controlled in the
laboratory facilities.
Many different types of laboratory environments exist.
They can be wet or dry described by the type of activities
occurring in the facilities. Much of the electronics industry uses dry labs where testing and assembly occurs. They
have their own set of considerations for ventilation air
and exhaust containment. Wet labs typically use liquids
as the basis for their science. Sink and water sources are
located throughout to source water and allow personnel
to wash hands and have access to safety appliances such
as emergency eyewashes and safety showers.
Airflow in a laboratory is important. The following
are potentially conflicting purposes to be addressed with
the lab HVAC system:
•General circulation. Effective ventilation circulated
throughout air supplies and returns must be distributed across the lab in a way that promotes effective
currents and room-air-change-turnover to avoid
stagnant dead spots.
•Cooling of lab instrumentation. The air distribution
must deliver the correct quantity of air to the vicinity
of heat-producing lab instruments to keep both the
equipment and the lab occupants operating properly.
•Avoidance of stray air currents near containment
devices. Discharging air at relatively high velocities
near a fume hood or other containment device can
cause eddy currents that negate the collection airflow
of the device and introduce contaminants into the
lab. Attention to this detail should obviously be a
high priority.
•Room pressurization versus containment. It is
desirable to keep some labs at a positive air pressure relative to adjacent areas to keep potential stray
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Alexander Delli Paoli, Jr.
contaminants from entering the laboratory workspace. This desire is often in conflict with life safety
requirements dictating that exit corridors and other
evacuation routes should be pressurized to permit
safe egress from the facility. There is no one answer
to this conflict. The best answer is found when the
lab owners, the facility management, and local loss
prevention authorities meet and come to a sensible
compromise after evaluating all the risks.
Cleanrooms
The HVAC demand in cleanroom facilities is significant.
Often the amount of air being circulated has more to do
with room air change rate per hour than it does with the
heat load requirements. Air volume demands can range
from a historical “conventional” cleanroom with 20 air
changes per hour to complete unidirectional cross-flow
or down-flow airflow with room air changes occurring
several times per minute. The type of cleanroom style
is dependent on several factors.
The amount, source, and consequences of contamination must be understood. If the particulate generator(s)
can be isolated using containment devices, or if a critically
clean area can be isolated in a pressurized device, there
is a good chance a more conventional approach to the
cleanroom HVAC system can be taken. This helps minimize the size and operating costs of the system. Often
the biggest contamination source in a cleanroom is its
human occupants. Minimizing the number of people
in the room along with appropriate garments for those
that remain can help lessen the clean-up demands on
the HVAC system. If this is not possible and if the contamination control needs are great, it may be necessary
to go to a more complex cleanroom design.
Positive pressurization is usually desirable in cleanrooms to help keep the surrounding environment out.
Pressurization requires airflow through every door and
opening around the perimeter of the cleanroom, along
with unfound cracks and gaps that seem to occur in
cleanrooms from time to time. The air flowing out of
the facility must be replaced with outside air, putting
a greater demand on the air handler to process that
air. This typically means more frequent filter changes,
higher dehumidification loads on the cooling coils, and
higher demands on the site’s infrastructure supporting
the HVAC system.
Heat and humidity generation can be an issue in
a cleanroom. Heat and humidity generation must be
considered in conjunction with the placement of heat
generating equipment and the attire occupants must
wear. These garments often increase the propensity for
perspiration.
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The more a critical operation can be isolated in a
“mini” cleanroom environment, the less costly the
operation can become. This is especially true where a
specific process must be conducted in a cleanroom while
requiring containment for some recognized hazard.
Isolators are containment devices that can serve both
needs. While the cost of the isolator may seem high,
the overall cost of the facility may make it a worthwhile
investment. This is particularly true when trying to adapt
an existing facility and all its equipment and infrastructure to a new use.
Containment Facilities
Containment facilities are unique HVAC system applications that work in conjunction with the facilities’
physical layout, materials of construction, and operating procedures to create an environment that isolates
the object or process from the adjoining area. This is
typically more than a fume hood in a laboratory. It
includes facilities for potent drugs, biological hazards,
radiological hazards, explosion hazards, and many
other unique applications.
Non-Aseptic General
Manufacturing Facilities
Many manufacturing areas have elements of the facilities
described herein. Temperature requirements, humidity
restrictions, microbial controls, and other design and
operational requirements may be needed depending on
the type of product manufactured and associated processes. It is important to define the level of a controlled
environment before designing or modifying an HVAC
process to serve it.
SUMMARY
The reader should by now have related some aspect of
this discussion to their individual experiences. This
article is an overview intended to bring all readers to a
base level understanding of HVAC systems along with
typical applications containing anecdotal information.
All the topics discussed will be revisited in greater
detail in subsequent articles. We will discuss specific
applications, the functional nature of system components, validation, maintenance, operational consistency
and sustainability. All readers are encouraged to submit
questions to be addressed as the details unfold. JVT
ARTICLE ACRONYM LISTING
AHU
Air Handling Unit
HVAC Heating, Ventilation, and Air Conditioning
OAOutside Air
RAReturn Air
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