SURGICAL SUITE TEMPERATURE AND HUMIDITY: PROVIDING WHAT SURGEONS WANT VERSUS THE LIMITATION OF YOUR EQUIPMENT

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1 PROVIDING WAT SURGEONS WANT VERSUS TE LIMITATION OF YOUR EQUIPMENT Ronnie Moffitt PE, EM Principal Applications Engineer Trane Lexington, KY Paper Presented July 21, 2008 at the American Society for ealthcare Engineering 45 th Annual onference

2 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?

3 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, A, with 3 air changes per hour with respect to outside air. Out of this recommendation the typical room was designed for 15A with 20% outside air and design target conditions for the room of 68F 50%R. 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. ooling 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 A), to maintain 68F temperature in the space, the supply air must be reheated to 56-59F at design conditions to prevent overcooling of the space.. Figure 1 Psychrometric Plot of Room and AU Supply onditions An operating room designed to the AIA guideline will require an approximate 48F leaving air temperature off the cooling coil.

4 urrent 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. ommon 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% R 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- 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 VA system used needs to occur to make this desired target. Figure 2 Psychrometric Plot of Room and AU Supply onditions An operating room designed to the common desired conditions will require an approximate leaving air temperature off the cooling coil.

5 hange in VA 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 135gr/lbm onditioning of Delivered: Supply Volume, Vsa = 15 A 5750 ft3 / 60 = 1,438 cfm Outside Volume, Voa = 0.20 x 1,44= 288 cfm Return 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 onditions = 68F 50%R, 50.9gr/lbm Supply Temperature = 58.8F Supply umidity = 49.3gr/lbm Supply Dewpoint Temperature = 47.8F Design B Room onditions = 62F 50%R, 41.2 gr/lb Supply Temperature = 52.8F Supply umidity = 39.6gr/lbm Supply Dewpoint Temperature = 42.1F

6 ool 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. owever 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 AU 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. Flow Process Diagram ool-reheat Return 1150cfm Outside 135 gr/lbm 68F 50%R 51 gr/lbm WS ooling oil Design A 48F 98%R 49 gr/lbm eating oil 56F 73%R 49 gr/lbm 180F WS Supply 1438cfm Supply Fan 58.8F 67%R 49 gr/lbm 48F DPT Figure 3 ool and Reheat Process for treating air for operating room for Design A onditions. What s Needed hilled water <180F ot Water ow Much per OR 55,700 btuh ooling 12,800 btuh eating Return 1150cfm Outside 135 gr/lbm Flow Process Diagram ool-reheat 62F 50%R 41 gr/lbm WS ooling oil Design B 50F 98%R 49 gr/lbm 36F WS ooling oil 42.5F 98%R 39 gr/lbm eating oil 50F 74%R 39 gr/lbm 180F WS Supply 1438cfm Supply Fan 52.8F 67%R 39 gr/lbm DPT Figure4 ool and Reheat Process for treating air for operating room for Design B onditions. What s Needed hilled Water 36F hilled Glycol <180F ot Water ow Much per OR 57,800 btuh ooling 37,000btuh coil1 20,800btuh coil2 12,000 btuh eating

7 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. owever, some of the dehumidification work is moved to the desiccant dehumidifier which has a OP<1.0 vs a OP>3.0 for the chiller. The added heat energy will require more energy usage by the OR than the initial design A. Figure5 Preool Active Desiccant Process for treating air for operating room for Design B onditions. What s Needed hilled Water Natural Gas Service Exhaust Outlet Secondary Outdoor Inlet ow Much per OR 52,700 btuh ooling 23,500btuh coil1 29,200btuh coil2 13,200 btuh eating

8 ool-reheat System with Desiccant Wheel in Series The next system uses a desiccant wheel in series to lower the dew point temperature. owever, 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 AU 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 AU with a wheel. The operating rooms are taken from past 68F 50%R to the improved 62F 50%R, at the same time the heat and cooling required is reduced without changing the hospital infrastructure. Outside 135 gr/lbm Return 1150cfm Flow Process Diagram Series Desiccant Wheel 62F 50%R 41 gr/lbm 66F 63%R 60 gr/lbm Desiccant Wheel 62F 74%R 69 gr/lbm Figure6 ool and Reheat w/ Series Desiccant Wheel for treating air for operating room for Design B onditions. What s Needed hilled Water <180F ot Water Supply 1438cfm 52F 68%R 39 gr/lbm 48F 97%R 48 gr/lbm 65F 69 gr/lbm Supply Fan ow Much per OR 48,000 btuh ooling 1,500 btuh eating %R 39 gr/lbm DPT 180F WS eating oil WS ooling oil

9 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,., D. Garrison, and R. Marchessault. A Precision Operation. Engineered Systems 23(7). July pp Moffitt, R. Taking the eat Out of Desiccants. PA 79(3). March pp Murphy, J. Temperature and umidity ontrol in Surgery Rooms. ASE Journal 48(6). June pp Murphy, J. and B. Bradley, Advances in Desiccant-Based Dehumidification, ADM- APN016-EN, Trane Engineers Newsletter.

10 PROVIDING WAT SURGEONS WANT VERSUS TE LIMITATION OF YOUR EQUIPMENT Ronnie Moffitt, PE EM Principal Applications Engineer, Trane 45 th Annual onference & Technical Exhibition PROVIDING WAT SURGEONS WANT VERSUS TE LIMITATION OF YOUR EQUIPMENT Session Outline: System Design Past Typical Operating Room Design urrent Typical Operating Room Design ool-reheat andling System Impact of hanging To urrent Room Design ool-reheat System Active Desiccant System ool-reheat Series Desiccant PAST OPETING ROOM DESIGN OR Room Design 68F 50% 90% 80% 70% Altitude 0ft 60% 50% 40% 30% 20% 10% umidity Ratio Grains/lbm Dry Bulb Temperature (F)

11 URRENT OPETING ROOM DESIGN OR Room Design 62F 50% 90% 80% 70% Altitude 0ft 60% 50% 40% 30% 20% 10% umidity Ratio Grains/lbm Dry Bulb Temperature (F) OOL REEAT DEUMIDIFIATION AND TEMPERING T space R EA T space R entral andling Unit hilled Water 42-44F Example: Design A 68F 50% Single Operating Room entral andling Unit T operating room R EA T space R hilled Water

12 Example: Design A 68F 50% Single Operating Room 1,150cfm entral andling Unit hilled Water T operating room R EA 5750ft 3 15A Total 3A Total Example: Design A 68F 50% Single Operating Room 1,150cfm entral andling Unit 58.8F hilled Water 49 gr/lbm 47.8F Dew Point T 68F R 50% 51 51gr/lbm EA Sensible Load 14,400btu/hr Latent Load 1,600btu/hr URRENT OPETING ROOM DESIGN 90% 80% 70% Altitude 0ft 60% 50% % LVG ool oil Lvg Reheat Supply Mixed Return Outside Dew Point Design Day 30% 20% 10% umidity Ratio Grains/lbm Dry Bulb Temperature (F)

13 Example: Design B 62F 50% Single Operating Room ool Reheat AU 135gr/lbm 1,150cfm 68F 51gr/lbm 48F 56F 98% 49gr/lbm 47.5F DPT WS entral andling Unit 180F WS 58.8F 67% 49gr/lbm 47.5F DPT Required for Operating Room ooling Plant 55,700btu/hr eating Plant 12,800btu/hr Example: Design B 62F 50% Single Operating Room 1,150cfm entral andling Unit 52.8F hilled Water 39 gr/lbm 42.0F Dew Point T 62F R 50% 41 41gr/lbm EA Sensible Load 14,400btu/hr Latent Load 1,600btu/hr Example: Design B 62F 50% Single Operating Room ool Reheat AU 135gr/lbm 1,150cfm 62F 41gr/lbm 42.5F 98% DPT WS entral andling Unit Required for Operating Room ooling Plant 57,800btu/hr eating Plant 12,000btu/hr 50F 180F WS 52.8F 67% DPT Infrastructure hanges Glycol hiller 2 nd ooling oil

14 Example: Design B 62F 50% Single Operating Room ool Reheat AU 135gr/lbm 1,150cfm 62F 41gr/lbm 50F 98% 52gr/lbm 42.5F 98% DPT WS 36F WS Required for Operating Room ooling Plant 37,000btu/hr New hiller 20,800btu/hr eating Plant 12,000btu/hr entral andling Unit 50F 180F WS 52.8F 67% DPT Infrastructure hanges Glycol hiller 2 nd ooling oil Active Desiccant Wheel eat-activated Desiccant Wheel EA RG 8-24 rph Process eat used to dehumidify 2,250 to 3,000 Btu/lbm water removed Active Desiccant Isotherms %Weight Water Type I Isotherms F 70F 90F 110F 130F Desiccant % 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% %R Regeneration 150F 170F 190F 210F Regeneration primary a function of temperature, hange in isotherm

15 Example: Design B 62F 50% Single Operating Room Pretreat Active Desiccant EA 55F 64gr/lbm 135gr/lbm WS 100cfm 205F 94F 34gr/lbm Natural Gas 1,150cfm 62F 41gr/lbm 50F 73% DPT WS 52.8F 67% DPT URRENT OPETING ROOM DESIGN 90% 80% 70% Altitude 0ft 60% 50% % LVG ool oil Outside Dew Point Design Day 30% 20% umidity Ratio Grains/lbm Return 10% Lvg ool oil 2 Supply Mixed Lvg Desiccant Wheel Dry Bulb Temperature (F) Example: Design B 62F 50% Single Operating Room Pretreat Active Desiccant EA 135gr/lbm WS 100cfm 205F 94F 34gr/lbm Natural Gas 1,150cfm 62F 41gr/lbm Required for Operating Room ooling Plant 52,700btu/hr eating Plant 13,200btu/hr 50F 73% DPT WS 52.8F 67% DPT Infrastructure hanges Natural Gas 2 nd ooling oil 2 nd Outside Inlet 2 nd Exhaust outlet 2 nd Unit or Tall AU

16 ool-reheat with Series Desiccant Wheel Type III Desiccant Wheel 50% R ΔW = +10 to 25gr 8-24 rph ΔW = -10 to 25gr 98% R ooling oil used for dehumidification Wheel enhances latent work done by coil Final Supply Dew Point Temperature << oil LVG Temp Type III Desiccant Isotherms Type III Series Desiccant Wheel 50% R ΔW = +10 to 25gr A T A T 8-24 rph ΔW = -10 to 25gr 98% R A Example: Design B 62F 50% Single Operating Room ool Reheat AU 135gr/lbm 1,150cfm 62F 41gr/lbm 66F 63% 60gr/lbm entral andling Unit 62F 74% 69gr/lbm 52.8F 67% 42.0F DPT 180F WS 52F 68% Required for Operating Room ooling Plant 48,000btu/hr eating Plant 1,500btu/hr 48F 97% 48gr/lbm WS

17 URRENT OPETING ROOM DESIGN 90% 80% 70% Altitude 0ft 60% 50% % LVG Regen Outside Dew Point Design Day 30% 20% umidity Ratio Grains/lbm LVG ool oil Supply Mixed Return 10% Dry Bulb Temperature (F) Example: Design B 62F 50% Single Operating Room ool Reheat AU 135gr/lbm 1,150cfm 62F 41gr/lbm 66F 63% 60gr/lbm entral andling Unit 62F 74% 69gr/lbm 52.8F 67% 42.0F DPT 52F 68% Required for Operating Room ooling Plant 48,000btu/hr eating Plant 1,500btu/hr 48F 97% 48gr/lbm WS Infrastructure hanges Taller AU ase Study Data: Extending Achievable Dew Point St. Vincent s ospital, Data was logged by University of entral 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

18 ase Study Data: Extending Achievable Dew Point 5F or lower dew point temperatures with same chilled water Typical Mixed onditions for Surgical Suites Operating Room Example Going From Design A To B Going from 68F 50% to 62F 50% Potential Building System Impact Estimated hange in Required apacity Infrastructure AU Design ooling eating Equipment AU Piping ot entral entral New ooling hilled Water or Natural Total Plant Total Plant /eating Plants New AU Water Steam Gas New AU Ducting Inlet or Outlets No hange 1oil ooling with Reheat 4% -33% -4% -4% Glycol hiller Longer 2 oils No hange No hange Active Desiccant Taller New, New EA with ooling -5% -5% 4% -100% Gas Burner /Longer 2 oils None Burner ooling with Series No hange 1oil Desiccant -19% -19% -89% -89% No hange Taller None No hange No hange Operating Room Example Going From Design A To B Going from 68F 50% to 62F 50% Potential Energy Impact Estimated hange in Required apacity AU Design ooling Total Infrastructure eating Equipment entral entral New ooling Plant Plant /eating Plants Total Energy Impact ooling with Reheat 4% -33% -4% -4% Glycol hiller igher combined KW/TON Active Desiccant with ooling -5% -5% 4% -100% Gas Burner Desiccant Dehumidification vs Vapor ompression ooling with Series Desiccant -19% -19% -89% -89% No hange Less eat Energy, Less ooling Energy at same KW/Ton

19 Operating Room Example Going From Design A To B PROVIDING WAT SURGEONS WANT VERSUS TE LIMITATION OF YOUR EQUIPMENT onclusions: Impact of hanging To older Operating Room More infrastructure impact vs cooling capacity 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 PROVIDING WAT SURGEONS WANT VERSUS TE LIMITATION OF YOUR EQUIPMENT Thank - You?? Questions?? Additional References: Greim,., D. Garrison, and R. Marchessault. A Precision Operation. Engineered Systems 23(7). July pp Moffitt, R. Taking the eat Out of Desiccants. PA 79(3). March pp Murphy, J. Temperature and umidity ontrol in Surgery Rooms. ASE Journal 48(6). June pp Murphy, J. and B. Bradley, Advances in Desiccant-Based Dehumidification, ADM-APN016- EN, Trane Engineers Newsletter.