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  1. #1
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    Air conditioning for operating room


    Hi there,
    I would appreciate any help.
    I am designing an air-conditioning system for hospital operating room. The supply air must be completely fresh air with design ambient temp of 42C. Room design temp is 17C to 22C with 45 to 55% relative humidity.
    My questions are :
    1- The air conditioning system should be direct expansion or cold water system for better control purposes?
    2- What is the best control system? The room thermostat should control the water flow regulating valve or ? NOTE that because of required minimum of air change in the room, the fan must supply minimum quantity of air. i.e., the fan can not be switched off.

    Anybody having experience in this field please share.
    Thanks.
    Cheers


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    Re: Air conditioning for operating room

    Are you just conditioning the room through normal air terminals or is it going via a laminar flow hood in the theatre or both?

    I would prefer a chilled water system for stability unless you use multiple stage DX cooling.

    Also positive pressure must be maintained so barometric relief flaps will be required along with the extract system.
    Brian - Torquay, Devon, UK
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    They're starting to take it as a challenge...

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    Re: Air conditioning for operating room

    My only comment on this subject is based on the use of DX evaporators. If you consider using any type of VAV system on a DX system.... DON'T.

    The few AC systems I have seen where DX was used on a VAV system were a real mess.

    I think chilled water is a much better solution for this approach, since you will probably be using conventional HVAC equipment anyway.
    If all else fails, ask for help.


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    Re: Air conditioning for operating room

    Looking for work in maintenance, one application was a private hospital... thorny responsibility, system "engineer" designed... however a few thoughts from being shown around:
    1. 100% fresh air, filtered to highest standard at entry to system and HEPA+ before room, UV light bactericide, room kept at psitive pressure relative to surrounding areas (avoid entrance of contamination - doors must take this in to account) and run ventilation at HIGH while in use and LO otherwise to save energy.
    2. duct and evaporator cleanliness, avoidance of fungi etc and access for service, chemical dis-infection of drip tray always.
    3. temperature control RADICAL, before ops they heated the op. theatre to 40C+ with electric resistances in air flow then rapidly cooled it - if I remember correctly...: cant remember the exact reason why (probably shock kill bugs). Then careful control of Temp.: consider nervous, sweating doctors etc (latent), possibly a lot of electric equipment (sensible) etc
    4. In view of the above cooled water with a reserve cold water tank to smooth peak demands in system. This could help if your outside temperature fluctuates greatly day/night...
    Check out international suppliers of specialist equipment and read through the lines and medical journals on bugs and infections in hospitals.
    PS Let us know how it goes

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    Thumbs up Re: Air conditioning for operating room

    Quote Originally Posted by Brian_UK View Post
    Are you just conditioning the room through normal air terminals or is it going via a laminar flow hood in the theatre or both?
    Hi everybody,
    Thanks for your comments.

    Dear Brian, normal air terminals will be used.
    Any comments on controls? anybody?

    cheers
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    Re: Air conditioning for operating room

    Quote Originally Posted by lana View Post
    Hi there,
    I would appreciate any help.
    I am designing an air-conditioning system for hospital operating room. The supply air must be completely fresh air with design ambient temp of 42C. Room design temp is 17C to 22C with 45 to 55% relative humidity.
    What is the design ambient dewpoint?

    To reach your humidity target, you will need to maintain a coil leaving air wetbulb temperature of 6-7C. You will then need to reheat that air to achieve the desired room temperature. If/when the ambient dewpoint drops below 6-7C, you will also need to humidify that air.

    You will want a coil with maximum rows/minimum bypass factor to ensure sufficient humidity removal. Given minimum bypass factor, the leaving air wetbulb and drybulb temperatures (measured close to the coil) will roughly coincide.
    Last edited by Gary; 13-03-2007 at 03:24 PM.

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    Thumbs up Re: Air conditioning for operating room

    Quote Originally Posted by Gary View Post
    What is the design ambient dewpoint?

    To reach your humidity target, you will need to maintain a coil leaving air wetbulb temperature of 6-7C. You will then need to reheat that air to achieve the desired room temperature. If/when the ambient dewpoint drops below 6-7C, you will also need to humidify that air.

    You will want a coil with maximum rows/minimum bypass factor to ensure sufficient humidity removal. Given minimum bypass factor, the leaving air wetbulb and drybulb temperatures (measured close to the coil) will roughly coincide.
    Thanks Gary,
    Design WB in summer is 23C.
    I have designed the water cooling and heating coils also the Psyc. prosses is perfectly normal and achievable. All your points are considered and there is no problem at design point. My problem is the control. When the room temp is achieved then the thermostat must control something. As I mentioned before the fan can not be switched off therefore, I think that the theremostat mast control the water regulating valve to maintain the supply air temp.
    Another problem is during cold whether, which will make the water in cooling coil freez. So the main heating coil or elements must be installed before the cooling coil.
    This is what I think. Any comments will be appreciated.
    Cheers
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    Re: Air conditioning for operating room

    Quote Originally Posted by lana View Post
    Thanks Gary,
    Design WB in summer is 23C.
    I have designed the water cooling and heating coils also the Psyc. prosses is perfectly normal and achievable. All your points are considered and there is no problem at design point. My problem is the control. When the room temp is achieved then the thermostat must control something. As I mentioned before the fan can not be switched off therefore, I think that the theremostat mast control the water regulating valve to maintain the supply air temp.
    Another problem is during cold whether, which will make the water in cooling coil freez. So the main heating coil or elements must be installed before the cooling coil.
    This is what I think. Any comments will be appreciated.
    Cheers
    IMO, you will need to both preheat (to avoid freezing the coil) and reheat (to achieve room temperature target). Ideally, the preheat would be set to achieve the same 6-7C air temp (don't forget to install a freeze thermostat after the preheat) and the room thermostat/humidistat would control the reheat and the humidifier.

    preheat>freeze thermostat>preheat thermostat>
    chilled water coil>coil leaving air thermostat (controlling the chilled water regulating valve)>
    reheat>humidifier>room thermostat/humidistat (controlling the reheat and humidifier)

    Note: If there are times when there is a heavy latent load in the room, you may need to reduce the coil leaving air temperature to remove more moisture. If the humidity then drops below target, the humidistat/humidifier will compensate.
    Last edited by Gary; 13-03-2007 at 07:22 PM.

  9. #9
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    Re: Air conditioning for operating room

    As Gary says you will need some more coils.

    I feel that you should approach a reputable air handling manufacturer who will provide a design service for you. You seem to be a little short on the basic knowledge required for this project.

    Full air conditioning requires filtration, preheating, cooling, dehumidification, reheating, humidification, fine filtration etc.

    You are concerning yourself with controls when you don't know what to control just yet. Start at the beginning and work forward from there.
    Brian - Torquay, Devon, UK
    I have to stop saying "how stupid can you be?" to my co-workers.
    They're starting to take it as a challenge...

    BASIC MAINTENANCE. If it doesn't move and it should then use WD40. If it moves but it shouldn't then use Duct Tape.

  10. #10
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    Thumbs up Re: Air conditioning for operating room

    Quote Originally Posted by Brian_UK View Post
    Full air conditioning requires filtration, preheating, cooling, dehumidification, reheating, humidification, fine filtration etc.

    You are concerning yourself with controls when you don't know what to control just yet. Start at the beginning and work forward from there.
    Hi Brian,

    You are right BUT I have already designed and considered what you said. I was not sure to go with DX coil or water coil. By everything said here I went with water coil. There are many fine filtration and .... everything you mentioned.
    As Gary pointed out some control tips then I have pretty good idea what to do.
    Thanks everybody.
    Cheers
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    Re: Air conditioning for operating room

    Quote Originally Posted by lana View Post
    Hi Brian,

    You are right BUT I have already designed and considered what you said. I was not sure to go with DX coil or water coil. By everything said here I went with water coil. There are many fine filtration and .... everything you mentioned.
    As Gary pointed out some control tips then I have pretty good idea what to do.
    Thanks everybody.
    Cheers
    If you had decided to go with a DX coil, I would have recommended an EPR (Evaporator Pressure Regulator) valve to stabilize the coil leaving air temperature/humidity.

  12. #12
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    Re: Air conditioning for operating room

    Hi guys
    I usually prefer to use DIN 1946-4 as reference.
    And it seems Germans will replace it soon with new version.
    1- I suggest you to use cold water with brine because you will need 100% fresh air, if you have more then one rooms for each AHU.
    2- You need two control system. One is for temperature control with 3 way valfs in AHU and zone heaters in operating rooms.(for example operations for new borns require 26 C). Second control system shoul be air side. You should control volume of air with CAV s and inverter controlled fan.

    for more inf. you can contact me by msn

    coztemur@hotmail.com

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    Thumbs up Re: Air conditioning for operating room

    Quote Originally Posted by coztemur View Post
    Hi guys
    I usually prefer to use DIN 1946-4 as reference.
    And it seems Germans will replace it soon with new version.
    1- I suggest you to use cold water with brine because you will need 100% fresh air, if you have more then one rooms for each AHU.
    2- You need two control system. One is for temperature control with 3 way valfs in AHU and zone heaters in operating rooms.(for example operations for new borns require 26 C). Second control system shoul be air side. You should control volume of air with CAV s and inverter controlled fan.

    for more inf. you can contact me by msn

    coztemur@hotmail.com
    Thanks coztemur,
    There is one AHU for each room. I am going to use water coil with water flow regulating valve. For controls, I will use a pre-fabricated microprocessor control for temp. and humidity.
    Thanks anyway.
    Cheers,
    LANA
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  14. #14
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    Re: Air conditioning for operating room

    This may be too late to be of any assistance to your project but just in case.

    multiple AHU configurations cause havoc when establishing pressure cascades form ops room to peripheral areas.

    Air is generally introduced directly above the "slab" at a constant controlled temp which can be set from a SURGEONS panel (range of about 18c to 28c is more than enough).Careful that the air velocity doesnt exceed 1.5 m/s at head height. (double check velocity).

    the air is introduced here to ensure clean air aound the table and for comfort of surgeons.

    general conditions within the space should be controlled seperately.

    If you have any specifc questions about the your design I will try to advise.

    GOOD LUCK

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    Thumbs up Re: Air conditioning for operating room

    Thanks Trash101,

    My design is exactly as you described and the temp. range is the same (ASHRAE).

    Thanks for your advise. I will let you know if I need any help.
    Thanks a lot.
    Cheers
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    Re: Air conditioning for operating room

    I think I am a bit late on this. 17 to 22C DB and 45 to 55%RH is a wide band and you need not have to worry much, if you do the load calculation precisely. At the lower end of the DB limit, and corresponding RH of 55% (yet with in the limits), the DP is about 46.5F or 8C. This is almost the lower limit for chilled water system. For DPs below 45C, DX systems are preferred.

    I would go with a scheme of controlling chilled water flowrate by a humidistat and reheat by a thermostat.

    As you have HEPA filters in the system, it is prudent to go for a variable speed AHU with flow control (set at the minimum flowrate required). The HEPA pressure drops range from 25mm in clean condition to 75mm before replacement. Besides having significant optimisation of power consumption, the pressure balancing becomes easy.

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    Thumbs up Re: Air conditioning for operating room

    Hi Ravi,

    Thanks for reply.
    I am not going to use VAV system. I have decided to use constant air flow while the water flow would be regulated.
    Thanks a lot anyway.
    Cheers
    Lana
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    Re: Air conditioning for operating room

    Good choice I decided to use hydronic distrobution in my system for my house (No opperating room lol but lots of picky computers!) and by using a self balancing bypass type design to balance the heat demand to heat load, while keeping a heat bank (12Gallon water tank insulated)
    The V48AC-1C (May have been the V47---) would be ideal for the heating coil, it is a 3 way temp modulated water flow control valve, and they have wonderfull action! I love the valve series V46 is another nice one for condencing perposes.

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