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SURGICAL SUITE TEMPERATURE AND HUMIDITY:
PROVIDING WHAT SURGEONS WANT VERSUS THE LIMITATION OF YOUR EQUIPMENT
Ronnie Moffitt PE, CEM
Principal Applications Engineer
Trane
Lexington, KY
Paper Presented July 21, 2008 at the American Society for Healthcare Engineering 45th Annual Conference
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Getting the Dew Point Temperature Required
Do your surgeons want the operating room temperature and humidity controlled to a
point that can not be achieved with your current system or infrastructure? There are
multiple reasons why the current air handling system can not deliver the air required to
meet the needs of the surgeons. The primary reason is the supply air dew point
temperature that can be delivered by the air handling system. The difficulty of achieving
the required dew point temperature is not regional. The extra cooling capacity required
by most systems is minimal. There are multiple ways to solve the problem. Since there
is more than one way to solve the problem, the question then becomes what is the
infrastructure impact of each option? If it physically can be achieved, then what is the
potential energy impact?
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Past Designs
Many past surgical room were designed around the AIA guideline. It recommends the
operating room air temperature be 68-75F with a 30-60% relative humidity. To get this
condition the air flow is dictated by a recommendation of 15 total air changes per hour,
ACH, with 3 air changes per hour with respect to outside air. Out of this
recommendation the typical room was designed for 15ACH with 20% outside air and
design target conditions for the room of 68F 50%RH. This temperature and relative
humidity equates to a design room dew point temperature of 48.7F. With so many air
changes per hour the supply air dew point temperature required was only slightly lower,
48F. This supply air dew point temperature could easily be achieved with a conventional
water coil being supply with 42-44F chilled water from the hospital chiller plant.
Cooling air down the air to 48F leaving the coil would achieve the 48F dew point
required to meet the humidity requirement. With the large amount of supply air (15
ACH), to maintain 68F temperature in the space, the supply air must be reheated to 5659F at design conditions to prevent overcooling of the space.
.
Figure 1
Psychrometric Plot of Room and AHU Supply Air Conditions
An operating room designed to the AIA guideline will require an
approximate 48F leaving air temperature off the cooling coil.
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Current Designs
Today there are often longer procedures, more gowning to wear, more people and
equipment in proximity of the surgeon. For surgeon comfort, cooler temperatures are
desired. There may also be procedures being performed that benefit from a lower room
temperature; one for example is the use of cements or adhesives that are aided by cooler
temperatures. Common temperatures requested for the operating room by the surgeons
have been lowered to 60-64F or even lower. The requirement is still in place to keep the
room at a target of 50% RH to reduce the risk of nosocomial infections. To keep the
room at 50% relative humidity with the air temperature at 60-64F will require the air to
be at a dew point temperature of 40-42F when delivered to the room. With the typical
hospital having chilled water at 42-44F, this new requirement is impossible to achieve
with what equipment is in place. A change in the HVAC system used needs to occur to
make this desired target.
Figure 2
Psychrometric Plot of Room and AHU Supply Air Conditions
An operating room designed to the common desired conditions will require
an approximate 42F leaving air temperature off the cooling coil.
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Change in HVAC Design
The set point in the operating room is going dictate how dry and cold the air needs to be
at the main air handler and cause changes required for the system. The air handling
equipment will most likely be serving multiple procedural rooms, scrub rooms and other
zones that support the surgical rooms. The example will focus on a single OR room to
help the reader see what may be required to retrofit from a previous design around the
AIA guideline, design “A”, versus going with typical new design conditions, design “B”.
Example:
Operating Room: 575ft^2 x 10ft high
14,400btu/hr Internal Sensible Load
1,600 btu/hr Internal Latent Load
Outside Air @Design: 83F 135gr/lbm
Conditioning of Air Delivered:
Supply Air Volume, Vsa = 15 ACH × 5750 ft3 / 60 = 1,438 cfm
Outside Air Volume, Voa = 0.20 x 1,44= 288 cfm
Return Air Volume, Vra = Vsa – Vra =1,150 cfm
Supply ΔT = 14400/ (1.085*1438) = Δ9.2F
Supply ΔW = 1,600/ (0.68 x 1438) = Δ1.6gr/lbm
Design “A”
Room Conditions = 68F 50%RH, 50.9gr/lbm
Supply Temperature = 58.8F
Supply Humidity = 49.3gr/lbm
Supply Air Dewpoint Temperature = 47.8F
Design “B”
Room Conditions = 62F 50%RH, 41.2 gr/lb Supply Temperature = 52.8F
Supply Humidity = 39.6gr/lbm
Supply Air Dewpoint Temperature = 42.1F
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Cool Reheat System
The starting point for Design “A” is a cool reheat system, the air at the central air handler is
cooled to 48F to dehumidify than reheated to 58.8F. Redesigning the system to
Design “B” and setting the room to 62F, will require the air handler to cool the air down to 40F
and reheat it to 53F. This requires a 4% increase in cooling capacity and a 4% reduction in
heating energy for each operating room. Though 4% more chilled water may be hard to obtain in
many cases, this looks like a minor impact on the infrastructure. However the dew point is
below what is achievable with 42-44F chilled water from the chiller plant. This system will
require an additional source of chilled water. The infrastructure changes include: adding a glycol
chiller, a new AHU with a second cooling coil and piping to a second cooling coil. The glycol
chiller does not have to be sized for the entire design load. As much cooling as possible would
still be accomplished by the central plant chilled water, with a new second coil fed by 36F
chilled glycol to help achieve the leaving air conditions required. Though there is only a small
increase in the cooling capacity required by the surgical suite. The energy use will be greater as
now 35% or higher of the cooling is now accomplished by an air cooled glycol chiller versus the
central plant chiller.
Air Flow Process Diagram Cool-Reheat
Figure 3
1150cfm
Supply
Air
68F
50%RH
51 gr/lbm
1438cfm
48F
98%RH
49 gr/lbm
42F CWS
Outside
Air
56F
73%RH
49 gr/lbm
288cfm
83F
135 gr/lbm
Cool and Reheat
Process for treating
air for operating
room for Design
“A” Conditions.
58.8F
67%RH
49 gr/lbm
48F DPT
What’s Needed
42F Chilled water
<180F Hot Water
180F HWS
Return
Air
Design “A”
Cooling
Coil
How Much per OR
55,700 btuh Cooling
12,800 btuh Heating
Supply
Fan
Heating
Coil
Air Flow Process Diagram Cool-Reheat
Outside
Air
288cfm
83F
135 gr/lbm
Figure4
Supply
Air
1438cfm
50F
98%RH
49 gr/lbm
42.5F
98%RH
39 gr/lbm
Cooling
Coil
Cooling
Coil
50F
74%RH
39 gr/lbm
Heating
Coil
52.8F
67%RH
39 gr/lbm
42F DPT
Cool and Reheat
Process for treating
air for operating
room for Design
“B” Conditions.
What’s Needed
42F Chilled Water
36F Chilled Glycol
<180F Hot Water
180F HWS
1150cfm
Design “B”
62F
50%RH
41 gr/lbm
36F CWS
Return
Air
42F CWS
<
Supply
Fan
How Much per OR
57,800 btuh Cooling
37,000btuh coil1
20,800btuh coil2
12,000 btuh Heating
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Active Desiccant System
Instead of using a glycol chiller to drop the dew point temperature past the chilled water
temperature, this could be done by using an active desiccant dehumidifier. The most common
system used for this application dehumidifies the outside air. The outside air is first pre-cooled
by a new chilled water coil then dehumidified further by a heat activated desiccant. The heat
activated desiccant rotor is typically regenerated by a direct fired gas heater or high pressure
steam that heats a second path of outside air flow. The regeneration air is heated above 180F.
This heated air heats the desiccant which changes the isotherm, and reduces the ability of the
desiccant to adsorb water vapor. This heat regenerates the desiccant to enable it to adsorb more
vapor as it rotates around to the cooled outside air. Versus the past design “A” this will require
about 4% more heating energy and reduce the cooling needed by 5%. The heat required will
now require an infrastructure change as natural gas piping and service is needed. Also piping for
additional cooling coil, a secondary outside air intake and an additional exhaust air outlet, an an
additional unit or adding a larger custom air handler which will have at least two fans. By
separating the air streams the cooling accomplished by the chiller is slightly reduced. However,
some of the dehumidification work is moved to the desiccant dehumidifier which has a COP<1.0
vs a COP>3.0 for the chiller. The added heat energy will require more energy usage by the OR
than the initial design “A”.
Figure5
PreCool Active Desiccant
Process for treating air for
operating room for Design “B”
Conditions.
What’s Needed
42F Chilled Water
Natural Gas Service
Exhaust Outlet
Secondary Outdoor Inlet
How Much per OR
52,700 btuh Cooling
23,500btuh coil1
29,200btuh coil2
13,200 btuh Heating
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Cool-Reheat System with Desiccant Wheel in Series
The next system uses a desiccant wheel in series to lower the dew point temperature. However,
it does not require high heat or a separate regeneration air stream. It utilizes the recirculated air
from the operating rooms to regenerate the wheel. This is possible because a different type of
desiccant is utilized. Using recirculated air also removes the introduction of an additional air
stream. The type III isotherm wheel has the ability to adsorb water vapor at high relative
humidity conditions. This affinity for water vapor quickly drops off at a lower relative humidity.
This allows for water vapor to be transferred with out adding regeneration heat. This system will
allow for an AHU with the same chilled water as in design “A” with still one coil, one fan and
one air path achieve the conditions for Design “B”. The air is dehumidified and cooled by the
cooling coil as in a cool reheat system. The air actually leaves the cooling coil at a temperature
actually higher than design “A”. After the cooling coil additional water vapor is removed by the
wheel and some heat is added from the adsorption process. The water vapor that is removed by
the wheel is added to the mixed air flow on the other side of the wheel. This occurs because it is
at a lower relative humidity. The water vapor transferred then takes a second pass at the cooling
coil and is removed. The end result is a 19% reduction in cooling capacity required and an 86%
reduction in heat required at new design condition versus the original design “A”. The
infrastructure changes are limited to a new AHU with a wheel. The operating rooms are taken
from past 68F 50%RH to the improved 62F 50%RH, at the same time the heat and cooling
required is reduced without changing the hospital infrastructure.
Air Flow Process Diagram Series Desiccant Wheel
Return
Air
1150cfm
62F
50%RH
41 gr/lbm
62F
74%RH
69 gr/lbm
288cfm
83F
135 gr/lbm
1438cfm
52.8
67%RH
39 gr/lbm
42F DPT
What’s Needed
42F Chilled Water
<180F Hot Water
52F
68%RH
39 gr/lbm
Heating
Coil
48F
97%RH
48 gr/lbm
65F
69 gr/lbm
42F CWS
Supply
Air
Figure6
Cool and Reheat w/
Series Desiccant
Wheel for treating
air for operating
room for Design
“B” Conditions.
Desiccant
Wheel
66F
63%RH
60 gr/lbm
Outside
Air
180F HWS
<
Cooling
Coil
Supply
Fan
How Much per OR
48,000 btuh Cooling
1,500 btuh Heating
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Summary
The more stringent conditions being expected by surgeons for operating rooms often drives the
infrastructure requirements and increases the energy usage for the hospital. There are different
ways to minimize the impact of these vital spaces. With new technologies, there are methods
that improve dehumidification capability. It may be possible to increase the dehumidification
performance of the system to meet new requirements without increasing the heating and cooling
required from the facility. This might be to the extent that the cooling and heating needed can be
reduced while at the same time improving the conditions in the surgical suite.
References
• Greim, C., D. Garrison, and R. Marchessault. “A Precision Operation.” Engineered
Systems 23(7). July 2006. pp 32-42.
• Moffitt, R. “Taking the Heat Out of Desiccants.” HPAC 79(3). March 2007. pp 20-34.
• Murphy, J. “Temperature and Humidity Control in Surgery Rooms.” ASHRAE Journal
48(6). June 2006. pp H18-H24.
• Murphy, J. and B. Bradley, “Advances in Desiccant-Based Dehumidification,” ADMAPN016-EN, Trane Engineers Newsletter.
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SURGICAL SUITE TEMPERATURE AND HUMIDITY:
PROVIDING WHAT SURGEONS WANT VERSUS THE
LIMITATION OF YOUR EQUIPMENT
Ronnie Moffitt, PE CEM
Principal Applications Engineer, Trane
45th Annual Conference & Technical Exhibition
SURGICAL SUITE TEMPERATURE AND HUMIDITY:
PROVIDING WHAT SURGEONS WANT VERSUS THE LIMITATION OF YOUR EQUIPMENT
Session Outline:
System Design
• Past Typical Operating Room Design
• Current Typical Operating Room Design
• Cool-Reheat
Cool Reheat Air Handling System
•Impact of Changing To Current Room Design
•Cool-Reheat System
•Active Desiccant System
•Cool-Reheat Series Desiccant
45th Annual Conference & Technical Exhibition
Ronnie Moffitt PE
SURGICAL SUITE TEMPERATURE AND HUMIDITY:
PAST OPERATING ROOM DESIGN
60%
50%
40%
30%
20%
10%
OR Room
Design
68F 50%
30
40
45th
50
60
70
80
Dry Bulb Temperature (F)
Annual Conference & Technical Exhibition
90
100
Ronnie Moffitt PE
110
200
190
180
170
160
150
140
130
120
110
100
90
80
70
60
50
40
30
20
10
120
Humidity Ratio
Grains/lbm
Altitude 0ft
90% 80% 70%
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SURGICAL SUITE TEMPERATURE AND HUMIDITY:
CURRENT OPERATING ROOM DESIGN
60%
50%
40%
30%
20%
10%
OR Room
Design
62F 50%
30
40
50
60
200
190
180
170
160
150
140
130
120
110
100
90
80
70
60
50
40
30
20
Humidity Ratio
Grains/lbm
Altitude 0ft
90% 80% 70%
10
70
80
Dry Bulb Temperature (F)
90
100
45th Annual Conference & Technical Exhibition
110
120
Ronnie Moffitt PE
SURGICAL SUITE TEMPERATURE AND HUMIDITY:
COOL REHEAT DEHUMIDIFICATION AND TEMPERING
RA
T
space
EA
T
space
RH
Central Air Handling Unit
C
OA
RH
H
H
H
SA
MA
Chilled Water
42-44F
45th Annual Conference & Technical Exhibition
Ronnie Moffitt PE
SURGICAL SUITE TEMPERATURE AND HUMIDITY:
Example: Design “A” 68F 50% Single Operating Room
RA
T
operating
room
RH
Central Air Handling Unit
C
OA
H
H
SA
MA
Chilled Water
42F
45th
Annual Conference & Technical Exhibition
Ronnie Moffitt PE
EA
T
space
RH
H
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SURGICAL SUITE TEMPERATURE AND HUMIDITY:
Example: Design “A” 68F 50% Single Operating Room
T
operating
room
RA
1,150cfm
RH
Central Air Handling Unit
C
H
3
5750ft
H
15ACH Total
SA
MA
OA
EA
1,438cfm
288cfm
3ACH Total
42F Chilled Water
45th Annual Conference & Technical Exhibition
Ronnie Moffitt PE
SURGICAL SUITE TEMPERATURE AND HUMIDITY:
Example: Design “A” 68F 50% Single Operating Room
68F
T
RH 50%
51gr/lbm
RA
1,150cfm
Central Air Handling Unit
C
Sensible Load
14,400btu/hr
H
Latent Load
1,600btu/hr
H
SA
MA
OA
EA
1,438cfm
288cfm
42F Chilled Water
58.8F
49 gr/lbm
47.8F Dew Point
45th Annual Conference & Technical Exhibition
Ronnie Moffitt PE
SURGICAL SUITE TEMPERATURE AND HUMIDITY:
CURRENT OPERATING ROOM DESIGN
60%
50%
40%
Outside Air
Dew Point
Design Day
30%
20%
Mixed Air
LVG Cool Coil
Return Air
Lvg Reheat
30
40
45th
50
10%
Supply Air
60
70
80
Dry Bulb Temperature (F)
Annual Conference & Technical Exhibition
90
100
Ronnie Moffitt PE
110
200
190
180
170
160
150
140
130
120
110
100
90
80
70
60
50
40
30
20
10
120
Humidity Ratio
Grains/lbm
Altitude 0ft
90% 80% 70%
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SURGICAL SUITE TEMPERATURE AND HUMIDITY:
Example: Design “B” 62F 50% Single Operating Room –Cool Reheat AHU
RA
1,150cfm
68F
51gr/lbm
C
1,438cfm
42F
CWS
H
58.8F
67%
49gr/lbm
47.5F DPT
180F
HWS
OA
SA
56F
49gr/lbm
47 5F DPT
47.5F
MA
288cfm
83F
135gr/lbm
Central Air Handling Unit
48F
98%
Required for Operating Room
Cooling Plant 55,700btu/hr
Heating Plant 12,800btu/hr
45th Annual Conference & Technical Exhibition
Ronnie Moffitt PE
SURGICAL SUITE TEMPERATURE AND HUMIDITY:
Example: Design “B” 62F 50% Single Operating Room
T
1,150cfm
Central Air Handling Unit
C
OA
62F
RH 50%
41gr/lbm
RA
EA
Sensible Load
14,400btu/hr
H
Latent Load
1,600btu/hr
H
SA
MA
1,438cfm
288cfm
42F Chilled Water
52.8F
39 gr/lbm
42.0F Dew Point
SURGICAL SUITE TEMPERATURE AND HUMIDITY:
Example: Design “B” 62F 50% Single Operating Room –Cool Reheat AHU
C
OA
288cfm
83F
135gr/lbm
MA
42.5F
98%
39gr/lbm
42F DPT
Central Air Handling Unit
50F
H
SA
1,438cfm
52.8F
67%
39gr/lbm
42F DPT
180F
HWS
1,150cfm
62F
41gr/lbm
42F
CWS
RA
Required for Operating Room
Cooling Plant 57,800btu/hr
Heating Plant 12,000btu/hr
Infrastructure Changes
Glycol Chiller
2nd Cooling Coil
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SURGICAL SUITE TEMPERATURE AND HUMIDITY:
Example: Design “B” 62F 50% Single Operating Room –Cool Reheat AHU
1,150cfm
62F
41gr/lbm
MA
OA
C
42F
CWS
288cfm
83F
135gr/lbm
52gr/lbm
42.5F
98%
SA
50F
1,438cfm
H
52.8F
67%
39gr/lbm
g
42F DPT
39gr/lbm
42F DPT
180F
HWS
C
Central Air Handling Unit
50F
98%
36F
CWS
RA
Infrastructure Changes
Glycol Chiller
2nd Cooling Coil
Required for Operating Room
Cooling Plant 37,000btu/hr
New Chiller 20,800btu/hr
Heating Plant 12,000btu/hr
SURGICAL SUITE TEMPERATURE AND HUMIDITY:
Active Desiccant Wheel
Heat-Activated Desiccant Wheel
EA
RG
OA
8 24 rph
8-24
h
SA
Process
Air
Heat used to dehumidify 2,250 to 3,000 Btu/lbmwater removed
45th Annual Conference & Technical Exhibition
Ronnie Moffitt PE
SURGICAL SUITE TEMPERATURE AND HUMIDITY:
Active Desiccant Isotherms
0.400
Type I Isotherms
50F
0.350
Desiccant %Weight Water
70F
0.300
90F
0.250
110F
0.200
130F
0.150
150F
170F
0.100
190F
0.050
210F
0.000
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
%RH Regeneration Air
Regeneration primary a function of temperature, Change in isotherm
45th Annual Conference & Technical Exhibition
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SURGICAL SUITE TEMPERATURE AND HUMIDITY:
Example: Design “B” 62F 50% Single Operating Room –Pretreat OA Active Desiccant
Natural Gas
EA
100cfm
OA
RA
205F
1,150cfm
62F
41gr/lbm
55F
C
64gr/lbm
C
OA
288cfm
94F
34gr/lbm
42F
CWS
42F
CWS
288cfm
83F
135gr/lbm
1,438cfm
52.8F
67%
39gr/lbm
g
42F DPT
39gr/lbm
42F DPT
MA
OA’
SA
50F
73%
45th Annual Conference & Technical Exhibition
Ronnie Moffitt PE
SURGICAL SUITE TEMPERATURE AND HUMIDITY:
CURRENT OPERATING ROOM DESIGN
60%
50%
40%
Outside Air
Dew Point
Design Day
30%
20%
LVG Cool Coil
Return Air
10%
Mixed Air
Lvg Cool Coil 2
30
40
Supply Air
50
60
Lvg Desiccant Wheel
70
80
Dry Bulb Temperature (F)
45th Annual Conference & Technical Exhibition
90
100
110
200
190
180
170
160
150
140
130
120
110
100
90
80
70
60
50
40
30
20
10
Humidity Ratio
Grains/lbm
Altitude 0ft
90% 80% 70%
120
Ronnie Moffitt PE
SURGICAL SUITE TEMPERATURE AND HUMIDITY:
Example: Design “B” 62F 50% Single Operating Room –Pretreat OA Active Desiccant
Natural Gas
100cfm
OA
RA
205F
C
C
OA
OA’
42F
CWS
288cfm
83F
135gr/lbm
1,150cfm
62F
41gr/lbm
MA
288cfm
94F
34gr/lbm
1,438cfm
52.8F
67%
39gr/lbm
g
42F DPT
39gr/lbm
42F DPT
Required for Operating Room
Cooling Plant 52,700btu/hr
Heating Plant 13,200btu/hr
45th Annual Conference & Technical Exhibition
SA
50F
73%
42F
CWS
EA
Infrastructure Changes
Natural Gas
2nd Cooling Coil
2nd Outside Inlet
2nd Exhaust outlet
2nd Unit or Tall AHU
Ronnie Moffitt PE
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SURGICAL SUITE TEMPERATURE AND HUMIDITY:
Cool-Reheat with Series Desiccant Wheel
Type III Desiccant Wheel
ΔW = +10 to 25gr
MA
50% RH
8-24 rph
98% RH
C
-
ΔW = 10 to 25gr
•Cooling Coil used for dehumidification
•Wheel enhances latent work done by coil
•Final Supply Air Dew Point Temperature << Coil LVG Temp
45th Annual Conference & Technical Exhibition
Ronnie Moffitt PE
SURGICAL SUITE TEMPERATURE AND HUMIDITY:
Type III Desiccant Isotherms
Type III Series Desiccant Wheel
MA
50% RH
CA
ΔW = +10 to 25gr
TMA
8-24 rph
98% RH
C
CA
-
ΔW = 10 to 25gr
MA
45th Annual Conference & Technical Exhibition
Ronnie Moffitt PE
SURGICAL SUITE TEMPERATURE AND HUMIDITY:
Example: Design “B” 62F 50% Single Operating Room –Cool Reheat AHU
OA
1,150cfm 62F 41gr/lbm
Central Air Handling Unit
66F
63%
MA60gr/lbm
SA
1 438cfm
1,438cfm
H
52F
68%
48F
97%
39gr/lbm
48gr/lbm
180F
HWS
52.8F
67%
39gr/lbm
42.0F DPT
62F
74%
69gr/lbm
C
42F
CWS
RA
288cfm
83F
135gr/lbm
TCA
Required for Operating Room
Cooling Plant 48,000btu/hr
Heating Plant 1,500btu/hr
45th Annual Conference & Technical Exhibition
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SURGICAL SUITE TEMPERATURE AND HUMIDITY:
CURRENT OPERATING ROOM DESIGN
60%
50%
40%
Outside Air
Dew Point
Design Day
30%
20%
LVG Regen
Mixed Air
LVG Cool Coil
10%
Return Air
Supply Air
200
190
180
170
160
150
140
130
120
110
100
90
80
70
60
50
40
30
20
Humidity Ratio
Grains/lbm
Altitude 0ft
90% 80% 70%
10
30
40
50
60
70
80
Dry Bulb Temperature (F)
90
45th Annual Conference & Technical Exhibition
100
110
120
Ronnie Moffitt PE
SURGICAL SUITE TEMPERATURE AND HUMIDITY:
Example: Design “B” 62F 50% Single Operating Room –Cool Reheat AHU
OA
SA
1 438cfm
1,438cfm
H
52.8F
67%
39gr/lbm
42.0F DPT
1,150cfm 62F 41gr/lbm
Central Air Handling Unit
66F
63%
MA60gr/lbm
62F
74%
69gr/lbm
52F
68%
48F
97%
39gr/lbm
48gr/lbm
C
42F
CWS
RA
288cfm
83F
135gr/lbm
Infrastructure Changes
Taller AHU
Required for Operating Room
Cooling Plant 48,000btu/hr
Heating Plant 1,500btu/hr
45th Annual Conference & Technical Exhibition
Ronnie Moffitt PE
SURGICAL SUITE TEMPERATURE AND HUMIDITY:
Case Study Data: Extending Achievable Dew Point
St. Vincent’s Hospital, Data was logged by University of Central Florida in collaboration with the Oak Ridge National Laboratory /
Department of Energy (Office of Distributed energy, within the Office of Energy Efficiency and Renewable Energy) for more
information go to http://www.sitepower.org/detail.php?id=120&category=5
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SURGICAL SUITE TEMPERATURE AND HUMIDITY:
Case Study Data: Extending Achievable Dew Point
5F or lower dew point
temperatures with same
chilled water
Typical Mixed Air
Conditions for
Surgical Suites
45th Annual Conference & Technical Exhibition
Ronnie Moffitt PE
SURGICAL SUITE TEMPERATURE AND HUMIDITY:
Operating Room Example Going From Design “A” To “B”
Going from 68F 50% to 62F 50%
Potential Building System Impact
Estimated Change in Required Capacity
Cooling
AHU Design
Cooling with Reheat
Active Desiccant
with Cooling
Cooling with Series
Desiccant
Heating
Infrastructure
Equipment
New AHU
Ducting
AHU Piping
Total
Central
Plant
Total
Central
Plant
New Cooling
/Heating Plants New AHU
4%
-33%
-4%
-4%
Glycol Chiller
Longer
Hot
Chilled Water or Natural
Water Steam
Gas
Inlet or
Outlets
No Change
-5%
-5%
4%
-100%
Gas Burner
Taller
/Longer
-19%
-19%
-89%
-89%
No Change
Taller
2 Coils
2 Coils
1Coil
No Change
No Change
None
Burner
New OA,
New EA
None
No Change
No Change
No Change
45th Annual Conference & Technical Exhibition
1Coil
Ronnie Moffitt PE
SURGICAL SUITE TEMPERATURE AND HUMIDITY:
Operating Room Example Going From Design “A” To “B”
Going from 68F 50% to 62F 50%
Potential Energy Impact
Estimated Change in Required Capacity
Cooling
Infrastructure
Equipment
Heating
AHU Design
Total
Central
Plant
Total
Cooling with Reheat
Active Desiccant
with Cooling
Cooling with Series
Desiccant
4%
-33%
-5%
-5%
-19%
-19%
Energy Impact
Central
Plant
New Cooling
/Heating Plants
-4%
-4%
Glycol Chiller
4%
-100%
Gas Burner
Desiccant Dehumidification vs Vapor Compression
-89%
-89%
No Change
Less Heat Energy, Less Cooling Energy at same KW/Ton
45th Annual Conference & Technical Exhibition
Higher combined KW/TON
Ronnie Moffitt PE
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SURGICAL SUITE TEMPERATURE AND HUMIDITY:
Operating Room Example Going From Design “A” To “B”
SURGICAL SUITE TEMPERATURE AND HUMIDITY:
PROVIDING WHAT SURGEONS WANT VERSUS THE LIMITATION OF YOUR EQUIPMENT
Conclusions:
Impact of Changing To Colder Operating Room
•More infrastructure impact vs cooling capacity
•Lower
Lower dew point temperature can make the
cooling required less efficient
•Series desiccant wheel can help achieve dew
point temperatures required with out hurting cooling
efficiency and lowering the capacity required
45th Annual Conference & Technical Exhibition
Ronnie Moffitt PE
SURGICAL SUITE TEMPERATURE AND HUMIDITY:
PROVIDING WHAT SURGEONS WANT VERSUS THE LIMITATION OF YOUR EQUIPMENT
Thank - You
?? Questions??
Additional References:
Greim, C., D. Garrison, and R. Marchessault. “A Precision Operation.” Engineered Systems
23(7). July 2006. pp 32-42.
Moffitt, R. “Taking the Heat Out of Desiccants.” HPAC 79(3). March 2007. pp 20-34.
Murphy, J. “Temperature and Humidity Control in Surgery Rooms.” ASHRAE Journal 48(6).
June 2006. pp H18-H24.
Murphy, J. and B. Bradley, “Advances in Desiccant-Based Dehumidification,” ADM-APN016EN, Trane Engineers Newsletter.
45th Annual Conference & Technical Exhibition
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