Cleveland Clinic Design Standards
MECHANICAL SYSTEMS DESIGN GUIDELINES
HVAC AIR DISTRIBUTION
PART I - GENERAL
1.1
SUMMARY
A.
This section addresses the general requirements for air handling distribution systems, including
air handlers, ductwork, ductwork accessories, terminal units, air devices, and stairwell
pressurization systems (if applicable to the project).
B.
Related Sections
1.
233113 – Metal Ducts
2.
233300 – Air Duct Accessories
3.
233413 – Axial HVAC Fans
4.
233416 – Centrifugal HVAC Fans
5.
233423 – HVAC Power Ventilators
6.
233433 – Air Curtains
7.
233723 – HVAC Gravity Ventilators
8.
234100 – Particulate Air Filtration
9.
234133 – High-Efficiency Particulate Filtration
10. 235100 – Breechings, Chimneys, and Stacks
11. 237313 – Modular Indoor Central-Station Air-Handling Units
12. 237413 – Packaged, Outdoor, Central-Station Air-Handling Units
13. 238123 – Computer-Room Air-Conditioners
1.2
HVAC AIR DISTRIBUTION REQUIREMENTS
A.
Air handling unit selection
ANSI/ASHRAE/IESNA 90.1.
and
performance
shall
comply
with
the
latest
B.
The quality and quantity of outside air must meet the latest ASHRAE Standard 62.1, the latest
Guidelines For Design and Construction of Hospitals and Outpatient Facilitates (FGI) which
includes ANSI/ASHRAE/ASHE Standard 170 requirements and must also maintain the
building pressurization reasonable positive (such as 5 to 15 percent net positive pressurization
(outside air - exhaust air)/total supply air]) depending on the building envelope
design/construction. Tighter buildings are eligible for less net pressurization, Architect and
Engineer to work together to determine the correct pressurization for the building. Please note
that if a building is connected to an adjacent building via skyway or tunnel the pressure
relationship between the two buildings should be reviewed and discussed.
C.
Air change rates, temperature and humidity shall comply at a minimum with the latest
Guidelines For Design and Construction of Hospitals and Outpatient Facilitates (FGI) which
includes ANSI/ASHRAE/ASHE Standard 170. Use local mechanical code for all areas not
defined in FGI. For energy conservation, spaces allowed to have unoccupied setpoints shall
have the sequence of operations written for automated setback, owner adjustable.
D.
Mechanical rooms must be large enough to allow for air handling unit coil pull space and full
space service clearance around the unit for filter replacement to accommodate both major and
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Cleveland Clinic Design Standards
MECHANICAL SYSTEMS DESIGN GUIDELINES
HVAC AIR DISTRIBUTION
minor repairs. A minimum clearance of 4 feet must be planned around the unit. The sides of the
units shall be provided with enough space for coil pull along the entire length of the unit.
Indicate the designated coil pull and maintenance clearance space on the Drawings.
E.
Each air handling unit fan shall be provided with a variable frequency drive (VFD). VFD’s
shall include either a by-pass switch or be configured in a manner that failure of one VFD does
not disable the entire air handling unit. Fan motor shall be high efficiency. Control shall be by
the duct static design pressure setpoint.
F.
Air handling unit fans shall have an efficiency rating where the ratio of the fan system power to
the supply fan airflow rate (main fan) of each HVAC system at design conditions shall not
exceed the allowable fan system power indicated in the latest ASHRAE Standard 90.1. Fans
shall be selected so that they are capable of meeting the design CFM at a max 60 Hz at normal
operation. Normal operation shall be no greater than 80% of the max wheel RPM.
G.
Fan arrays are preferred to use on air handling units and energy recovery units (ERU’s).
H.
Access doors (or panels) on the air handling unit sections shall always open against the positive
side of the door and shall not be blocked by internal filter casings or internal equipment
components. Micro switches or safety switch interlocks need to be provided at access doors or
panels on UV sections to protect maintenance personnel from possible injuries. Windows shall
be located 5’ above finished floor.
I.
Coordinate location of wall-mounted room temperature sensors with furniture and equipment,
so that sensor locations do not conflict with tall items of furniture/equipment.
J.
Each cooling coil shall not exceed 8 rows and 10 fins per inch.
K.
Design two (2) coils in a series arrangement if the cooling coil capacity requirement exceeds the
capability of an 8-row, 10 FPI coil. Chilled water shall be piped in series through both coils and
a 42” access section shall be provided between the two equally sized coils. Chilled water
velocity through the coil tubes should be 8 fps maximum. (The minimum ARI Standard 410
rating condition for water velocity through a coil is 1.0 fps).
L.
Maximum cooling coil discharge face velocity shall not exceed 400 fpm. Heating coil discharge
face velocity shall not exceed 800 fpm. Coils shall be selected to allow for an additional margin
of 20 percent cooling capacity for future renovations.
M.
Coil connections 2½” and larger must include bolted flange spools and be arranged to allow the
coils to be pulled and installed without having to remove the control valves. 2” and smaller
connections may be union connections. Provide strainers on inlet of the coils. Provide a pressure
and temperature gauge downstream of the cooling coil control valve. Control valve to be on
discharge side of coil.
N.
Electronic filters are not acceptable.
O.
The maximum shaft speed on any fan or pump shall be 2000 rpm.
P.
Self tension adjusters are not acceptable.
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MECHANICAL SYSTEMS DESIGN GUIDELINES
HVAC AIR DISTRIBUTION
Q.
All lab exhaust fans shall be provided with protective corrosion resistant coating.
R.
Variable-pitch and variable-inlet fans are not acceptable.
S.
VAV boxes shall be located outside of patient occupied spaces for ease for ease of maintenance.
T.
Stairwell Pressurization Fans:
1.
The IBC lists physical building height criteria, for determining when stairwell
pressurization fan system is required.
2.
The stairwell pressurization system shall meet or exceed latest edition of NFPA
requirements.
3.
On buildings over 7 stories should be evaluated for two fans for pressurization of each
building exit stairwell. One fan shall be located at the top of the stairwell and the other
fan shall be located near the bottom of stairwell.
4.
The fan shall be variable volume using a VFD and shall maintain positive static pressure
in each stairwell. The differential pressure across the stairwell access door shall not
exceed the maximum opening force as specified in the latest edition of NFPA 92A.
U.
Ductwork
1.
Low pressure ductwork is defined as ductwork subjected to velocities of 1600 fpm or
less, and operating pressure of 2 inches w.g. or less, positive or negative.
2.
Low-pressure ductwork required for the project shall include the following:
a.
Air-conditioning supply air systems downstream of terminal units and fan coil
units.
b.
Outside air intake plenums.
3.
Volume dampers shall be provided at all individual, low-pressure take-offs. Low pressure
take-offs shall be bellmouth or 45 degree boot tap.
4.
Medium and high-pressure ductwork is defined as ductwork subject to operating
pressures in excess of 2 inches w.g., positive or negative and up to 6 inches w.g. positive
or negative.
5.
Types of medium and high-pressure ductwork include the following:
a.
Air conditioning supply air systems from air handling unit discharge to terminal
units.
b.
Exhaust distribution systems.
6.
Construct elbows with radius of not less than 1-1/2 times width of duct on centerline.
Comply with SMACNA Standards. Use smooth radius elbows where feasible.
7.
Transform duct sizes gradually, not exceeding 20 degrees divergence and 30 degrees
convergence. Comply with SMACNA Standards.
8.
Ductwork Sizing: The following criteria will be utilized for sizing ductwork for the
various systems:
a.
Medium pressure supply ductwork upstream of air terminal units will be sized for
a maximum pressure drop of 0.15 inches of water per 100 feet of ductwork for
ducts carrying up to 12,000 CFM. For ductwork over 12,000 CFM, sizing will be
based on maintaining a maximum velocity of less than 2,000 feet per minute
(fpm). (Low pressure ductwork may be utilized in lieu of medium pressure duct for
energy conservation and sustainability).
b.
Low pressure supply ductwork between the terminal unit and grille/diffuser of air
terminal (Supply Air, Return Air or Exhaust Air) will be sized for a maximum
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MECHANICAL SYSTEMS DESIGN GUIDELINES
HVAC AIR DISTRIBUTION
9.
10.
11.
12.
13.
14.
15.
pressure drop of 0.08 inches of water per 100 feet of ductwork for ducts carrying
up to 8,000 CFM. For ductwork over 8,000 CFM, sizing will be based on
maintaining a maximum velocity of less than 1,500 feet per minute.
c.
Transfer openings and return air sound boots shall be sized for 500 fpm at the air
handler mechanical room wall and 300 fpm at all other locations.
Low-pressure ductwork will be utilized between the terminal unit and grille/diffuser to
transport supply air to the space and return/exhaust air from space.
Flexible runs of ductwork to air devices are not to exceed five (5) feet in length with no
kinks or crimps in the branch. Flexible duct to terminal units shall not exceed one (1)
foot.
All seams shall be sealed to ensure the minimum allowable leakage rate.
Non-metal rigid ductwork shall not be used except fiberglass underground.
Indicate manual air volume balancing devices in supply, return, and exhaust mains, and
branch mains.
All exterior supply and return ductwork shall be insulated double wall.
Lined ductwork is not acceptable on any new projects or equipment.
V.
Exhaust and Intake Louvers
1.
Coordinate louver selection with architectural drawings. To allow for future expansion
of the HVAC system ventilation requirements, the maximum design face velocity at the
louver face must not exceed a free area face velocity of 800 fpm on intake louvers and
1200 fpm on relief or exhaust louvers.
2.
All air intake louvers must include bird screen, and in some cases depending on the
location and height of the air intake, the louvers may need to include removable screens
with no smaller than ½” openings located on the leaving air side of the louver. This
requirement also applies to spaces such as boiler rooms and diesel generator rooms, etc,
where combustion air may be required.
3.
Air intake locations shall be coordinated with the building general exhaust system,
kitchen exhaust, plumbing vents, generator exhaust, grease traps, trash dumpsters, vehicle
exhaust, etc., to avoid introduction of undesirable odors into the building, under all
conditions.
4.
The bottom of all outside ventilation air intakes for occupants shall be located as high as
practical but not less than twelve (12) feet above ground. Intakes on top of buildings
shall be located no less than 3 feet above roof level. Select outside air intake louvers for a
maximum face velocity of 400 fpm using a free area of 50 percent.
5.
Due to potential entrainment of contaminated air or odors into outside air intake louvers,
AE to evaluate the need for a building study, to aid in finalizing the best locations for the
ventilation air intake louvers. Ventilation air intakes for occupants shall not be located
near potential locations where vehicles idle such as garage entrance and exits, loading
docks, trash compactors or near LN2 and CO2 bulk storage tanks.
W.
Energy Recovery Units
1.
The determination of energy recovery is based on the compliance of ASHRAE 90.1 or
ASHRAE 62.1 or actual energy recovery needs.
2.
Unless otherwise required to comply with applicable codes or standards, energy recovery
components should be evaluated by considering equipment installed cost, equipment life,
the time value of money, any utility avoided costs, and a simple payback of 5 years or
less.
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MECHANICAL SYSTEMS DESIGN GUIDELINES
HVAC AIR DISTRIBUTION
3.
4.
X.
All the major parameters of an energy recovery system should be connected to the
building automation system.
Refer to ASHRAE 170 for additional clarity.
Patient Treatment Air Handling Units
1.
Air handling systems shall be designed as single duct variable air volume (VAV)
distribution systems with supply and return ducts.
2.
Air handling units shall have a fan array system where if one fan goes off line the others
can ramp up to cover a minimum 80% of the air flow. Multiple supply and return air fans
or fan wall technology shall be incorporated in the unit design to achieve redundancy.
3.
VAV terminals with reheat shall always provide at a minimum the required air change
rates and critical pressure differentials with respect to adjoining spaces.
4.
Air handlers shall be designed to accommodate the pressure drop from 12” charcoal
filters based on Camfil Farr or AAF 24”x24”x12” filters.
5.
Coil drain pans shall be 316 stainless steel. Coils shall be mounted at a height so that
discharge of drain pan is located 12” minimum above finished floor. Drain pans shall be
individually piped and trapped with a discharge of 3/4” minimum union connection.
Cooling coil drain pan piping shall be copper. Cascading of drain pans is not allowed.
6.
A cost benefit analysis should be performed to determine if a mixed air temperature air
handling unit should be selected for 100% OA.
7.
Each VAV air handler may include, but not be limited to the following components for
air distribution systems:
a.
Inlet section.
b.
Return fan, centrifugal type. Fan speed is controlled by a VFD.
c.
Economizer section with air blender.
d.
Pre-filter section MERV 7 (30%) as rated by ASHRAE Standard 52.2-99.
e.
Energy recovery pre-heat coil.
f.
Access section
g.
Steam or hot water preheat coil; copper tubes, aluminum fins; maximum 10 fins
per inch; Integral face and bypass. Pre-heat coil discharge temperature sensor.
h.
Access section.
i.
Supply fan, centrifugal type (fan type may change due to fan array, review change
with Cleveland Clinic). Fan speed is controlled by a VFD.
j.
Chilled water-cooling coil; copper tubes, aluminum fins; maximum 8 rows,
maximum 10 fins per inch, desaturation coil (blow thru units only). Provide with
flow taps. Provide freezestat on entering face of cooling coil).
k.
Properly spaced ultra violet germicidal irradiation (UVGI) lamps shall be located
on the leaving air side of the cooling coil. Access section with micro switches on
door to enable unit.
l.
Access section.
m.
Mist eliminator (blow thru units only).
n.
Access section.
o.
Final filter section shall comply with the latest Guidelines For Design and
Construction of Hospitals and Outpatient Facilitates (FGI) which includes
ANSI/ASHRAE/ASHE Standard 170. (Units serving operating rooms shall have
HEPA filters)
p.
Access section.
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MECHANICAL SYSTEMS DESIGN GUIDELINES
HVAC AIR DISTRIBUTION
q.
8.
9.
10.
Steam humidifier, should be located after the final filters or at a distant sufficient
to be 100% evaporated prior to reaching the filter.
r.
Discharge section
s.
High static pressure and smoke detection shutdown control and reset capability.
High static pressure reset shall be push button type with LED indicator light.
Locate in a usable location.
t.
Instrument measurement taps for static pressure, temperature, etc.
Restrooms, janitors, and locker rooms in patient facilities are negative with respect to
adjacent spaces and corridors, and they are connected to the building’s general exhaust
fan system.
Design patient rooms for care and recuperation at proper outside ventilation and
recirculation air change rates. Patient restrooms are to be connected to the building’s
general exhaust fan system except for those located within an isolation room.
Design criteria, ventilation air rates and recirculation air rates for Intensive Care Rooms
(ICUs) shall comply with the latest Guidelines For Design and Construction of Hospitals
and Outpatient Facilitates (FGI) which includes ANSI/ASHRAE/ASHE Standard 170.
Y.
Airborne Infection Isolation Rooms:
1.
Rooms must be designed as once-through ventilation systems served with dedicated
redundant (N+1) exhaust air fan systems. The quantity of supply air to each isolation
room, shall meet the required supply and exhaust air offset to maintain the room at a
0.02” negative pressure per Cleveland Clinic Negative Isolation Room Standard and also
meet room total cooling and heating load requirements. The supply air VAV box shall
modulate to maintain negative pressure in the isolation room. Provide differential
pressure monitor with alarm points to building automation system.
2.
The exhaust airflow rate from the isolation room shall meet the minimum required air
change rate and modulate to maintain constant CFM offset exhaust airflow during all
modes of system operation. The patient private restroom shall also be considered as part
of the isolation room exhaust air requirement. The exhaust shall have a VAV box.
3.
For each project, the total exhaust from all of the combined isolation rooms should be
filtered with a bag-in and bag-out HEPA filter housing prior to being discharged to the
environment by an exhaust fan with a discharge 10 feet minimum above roof level. Refer
to the Isolation Room standard for the specific details on the exhaust fan system.
4.
VFD control of fans to maintain duct static pressure as filters load up.
Z.
Patient Protective Environment (PE) Rooms:
1.
Rooms must be designed at proper outside ventilation and recirculation air change rates,
and maintained at the required minimum positive pressure with respect to the corridor
and adjacent rooms or spaces per Cleveland Clinic requirements. Filter the supply air to
PE rooms using MERV 17 HEPA filter ceiling modules. Provide differential pressure
monitor with alarm points to building automation system.
2.
The quantity of supply air to each PE room shall meet the required supply offset to
maintain the room at a positive pressure with respect to adjacent spaces and the corridor
and to also meet the room’s cooling and heating load requirements. The supply air VAV
box and the return air VAV box shall modulate to maintain positive pressure in the space
to 0.01 positive.
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MECHANICAL SYSTEMS DESIGN GUIDELINES
HVAC AIR DISTRIBUTION
3.
The exhaust airflow rate from the patient restroom shall be included in the required air
change rate and to also maintain constant exhaust airflow during all modes of system
operation.
AA. General Operating Room (OR) Suites(including Orthopedic):
1.
Operating room suites shall be served by an air handling system that is dedicated to
serving only operating rooms and the surrounding spaces.
2.
The operating room air handling unit low temperature cooling coil shall be tied into the
low temperature chilled water loop where available. Verify tie in location and capacity
with Cleveland Clinic during design development.
3.
Suites must be designed at proper outside ventilation and recirculation air change rates,
and maintained at the required minimum positive pressure with respect to the corridor
and adjacent rooms or spaces per Cleveland Clinic requirements. Filter supply air to OR
Suites using MERV 17 HEPA filters in air handling unit or in ceiling modules. The
supply air VAV box and return air VAV box shall modulate to maintain 0.01” w.c.
positive pressure in the space. Air valves may be used in lieu of VAV boxes.
4.
The quantity of supply air to each OR Suite shall meet the required supply and return air
offset to maintain the room at a positive pressure with respect to adjacent spaces and to
also meet room total cooling and heating load requirements.
5.
The exhaust airflow rate from the OR Suite shall meet the minimum required air change
rate from FGI Guidelines
6.
Air Change Rates for operating rooms shall at a minimum comply with the latest
Guidelines For Design and Construction of Hospitals and Outpatient Facilitates (FGI)
which includes ANSI/ASHRAE/ASHE Standard 170.
7.
OR’s shall be designed with equipment that will allow for unoccupied setbacks and an
automated sequence of operations written for the setbacks.
8.
Humidity requirements for each OR Suite shall be individually maintained using a steam
distribution manifold installed in the supply duct downstream of the terminal unit reheat
coil. Access panels are to be placed in hard ceilings to gain access to the humidifiers for
maintenance purposes.
9.
A cost benefit analysis should be performed to determine if new operating rooms should
be designed with mechanical space directly above the operating rooms. The humidifiers
and VAV boxes serving the operating rooms shall be located in the mechanical space
above the operating rooms.
BB.
Imaging Procedure room:
1.
Rooms must be designed at proper outside ventilation and recirculation air change rates
of and maintained at the required minimum positive pressure with respect to the corridor
and adjacent rooms or spaces per Cleveland Clinic requirements. Filtration shall meet the
requirements of FGI guidelines (ASHRAE 170). .
2.
The quantity of supply air to each Imaging procedure room shall meet the required supply
and return air offset to maintain the room at a 0.01 positive pressure with respect to
adjacent spaces and also to meet room total cooling and heating load requirements.
3.
Humidity requirements for Imaging procedure room
shall be maintained and the
humidifier steam distribution manifold shall be installed downstream of the final filter at
the discharge of the air handling unit.
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MECHANICAL SYSTEMS DESIGN GUIDELINES
HVAC AIR DISTRIBUTION
CC.
Spaces that require specific pressure offsets (Typically: OR, Procedure Rooms, PE, AII, Sterile
Cleaning, etc.):
1.
The rooms shall be sealed and a room integrity test needs to occur.
2.
Room indicators shall be located in the spaces to verify proper ACH, temperature,
humidity, and differential pressure.
DD. Except for patient isolation rooms, which are totally exhausted, return air shall be ducted and
shall be considered as a design standard for patient care, patient treatment, examination rooms,
and protective environment rooms.
EE.
Duct sections shall be made of stainless steel where steam humidifiers are placed, and stainless
steel drain piping or tubing shall be placed at the bottom of the duct to prevent condensed steam
from remaining inside the supply air duct.
FF.
Duct humidifiers shall be provided with type 304 stainless steel for a minimum of 5 feet
downstream of the humidifier. Designer to verify the absorption distance for each application
and adjust the length of 304 stainless steel.
GG. Laboratory fume hood exhaust shall be type 316 with welded joints.
HH. Commercial dishwasher exhaust, steam sterilizer, and sterile washer exhaust shall be type 304
stainless steel with welded joints.
II.
Kitchen hood exhaust shall be 16 gauge black steel where concealed, and 18 gauge type 304
stainless steel, welded, grinded and polished to a No. 3 finish, where exposed.
JJ.
When secondary humidification is required in family health centers, steam generating canisters
are acceptable.
KK. Air handling units that are roof mounted shall be located on a structural steel platform or curb
mounted with ease of maintenance designed into the unit.
LL.
New VAV system designs shall use heating hot water reheat coils.
PART 2 - PRODUCTS
2.1
MANUFACTURERS: Refer to construction specifications for acceptable manufacturers.
*****
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