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The Biomedical Engineering blog is the place for conversation and discussion about topics related to engineering principles of the medical field. Here, you'll find everything from discussions about emerging medical technologies to advances in medical research. The blog's owner, Chelsey H, is a graduate of Rensselaer Polytechnic Institute (RPI) with a degree in Biomedical Engineering.

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Can Displacement Ventilation Displace Disease?

Posted August 10, 2007 8:32 AM by Sharkles

Is it possible to create effective displacement ventilation in hospitals and medical buildings? This is precisely the question recently raised by two North American HVAC consulting firms hired to investigate the safety of using ventilation displacement techniques in place of traditional air displacement. The reasoning behind the investigation is of critical importance: to prevent the spread of airborne infections and contaminates. While traditional overhead ventilation mixes air supplied by an overhead diffuser to create a homogeneous environment, "the goal of displacement ventilation is to . . . carry contaminants directly up out of the occupied zone without mixing them." The good news is that displacement HVAC systems are a very real possibility. The bad news is that hospitals, like many health-care related facilities often run on tight budgets.

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#1

Re: Can Displacement Ventilation Displace Disease?

08/10/2007 11:02 AM

Everything has to go somewhere...

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#2

Re: Can Displacement Ventilation Displace Disease?

08/10/2007 6:57 PM

When they started using private rooms for everyone I thought they were providing a postive pressure flow from roof intakes down through the hall ways to the rooms and exhaust vents were provided in each room to prevent room to room contamination.

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#3
In reply to #2

Re: Can Displacement Ventilation Displace Disease?

08/11/2007 9:41 AM

I believe you are right. the critical zones are given the most negative pressures, and as such, leakage air will flow the critical zones, and then the contaminated air is controlled. Zones are supplied by individual AHU, and the supply and return volumes are basically matched. In the article, the one diagram shows a direct interspersing of return ducts with supply ducts with a one to one ratio. This is the design idea that elimates most of the mixing. Most systems have a many to one ratio of supply to return grills, and returns are often larger, and 'common'.

It makes sense that this system would be an improvement. I think it could be improved yet, with distribution through "Air Columns" and supply and return is channeled through floor and ceiling level diffusers, with matched volume.

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#4
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Re: Can Displacement Ventilation Displace Disease?

08/11/2007 1:39 PM

As I pointed out " I thought" that was what they were doing. I just remember that some engineers given demands for "Building Appearence" over function.

They are not being allowed to use cooling tower where water can be sprayed into the air and wash it before it enters the fresh air intakes because some committee does not want large structures on the roof. At a local V.A. Hospital in Johnson City, Tennessee they built the fresh air intake beside the emergency room.

They did not consider the ambulance that would park with desiel engines running espically in the winter and leave the vechiles running for long periods. The building design and placement made it nearly impossible to find a clean fresh air source as it is surrounded with parking lots that are extremely busy.

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#5

Re: Can Displacement Ventilation Displace Disease?

08/13/2007 4:28 PM

Im interested on where the contaminated air is sent to. If its just outside into the areas around the hospital , I think that would be a cause for concern.

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#6
In reply to #5

Re: Can Displacement Ventilation Displace Disease?

08/13/2007 11:21 PM

I worked as a contractor in a facility that created nuclear medical products. The building was desiged with concentric airflow zones, where each zone had a successively more negative pressure, such that all the air flowed to the 'hot' zones. Then the most negative areas were exhausted through a 'nuclear exhaust' which consisted of a large array of specialized filters, including hepa filters. The final result was that the output of the nuclear exhaust was actually lower in radioactivity than the natural background, making the facility a large air cleaner.

Even the doors in this place had differential pressure switches, which would alarm if a door stayed open, and created an imbalance in the pressure zones. Radioactivity tends to be an airborne contaminant. So does disease. Control the air, you control the contaminant. Thats how I think it works.

Chris

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#7
In reply to #6

Re: Can Displacement Ventilation Displace Disease?

08/14/2007 4:43 PM

When we design HVAC for pharmaceutical manufacturers the law requires clean air in, no cross over to different manufacturing rooms and clean air out. No cost spared here. In a hospital it may be more about economics, i.e. the strength of your health insurance. Keep those beds full! Not the cost of the building. Ask around and see how often budget on HEPA's is cut but an extra $250000 on the entrance to the facility is OK. Her in South Africa most hospitals are owned by doctors and health insurers. Go figure, bet it's the same over your way. You don't need a conference to work it out. You need someone who does not make a buck every time you sneeze. Apologies to the hand full of doctors who still put your health first, YOU are champions! Bush Driver - South Africa

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Anonymous Poster
#8
In reply to #6

Re: Can Displacement Ventilation Displace Disease?

08/15/2007 12:46 PM

Most hospital patient rooms are designed with an even air pressure relationship. However, hospitals do have "isolation" rooms for specific patients that may have TB or other air borne bacteria issues. The pressure relationship in the isolation room can be adjusted via pressure switch damper and fan speed control. The volume of outside air will be huge compared to todays standards. Air distribution systems will require complete reconfiguration. One thing to consider is the energy impact on the hospital but there are technologies available to help address that.

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#9

Re: Can Displacement Ventilation Displace Disease?

08/17/2007 8:10 PM

When I showed the article to our resident World expert on all things health - I received the following response.

These researchers should stick with the building types they know about and stay away from hospitals. Each hospital has an infection control manager and that person would be interested to know how a sub-floor space can be readily disinfected using an alcohol (say) based product. This action is needed after every patient has left that room. It's called terminal disinfection, an unfortunate choice of wording.

It's hard to beat simplicity. Simple split units provide maximum thermal comfort to each room. Easily disinfected. Filters thrown away. No large wall penetrations to upset pressure differentials. Outdoor air is admitted by a ducted system that is small and only conditioned to temper the outdoor air. No great penetrations involved. Exhaust similarly by straightforward ducting without any filters included as they complicate the disinfection process and are themselves contaminated and therefore a hazard to servicing personal.

I don't think the CFD investigators considered any of these practical aspects to air conditioning of isolation wards. The problem is that so many of our hospitals are similarly poorly designed and it is a wonder there are not many more nosocomial infections than there presently are. With a highly infectious agent such as SARS around, these facility shortcomings would be quickly found out.

I just hope that those involved in the concept of building infection control facilities use appropriate caution and query everything from every aspect as appropriate.

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Anonymous Poster
#10

Re: Can Displacement Ventilation Displace Disease?

09/20/2007 5:40 PM

The answer to your question is yes.

We use displacement through out hospitals especially in operating theatres in Europe.

As for running and installled costs it is much cheaper.

My mail is glen@comfortdesign.co.uk

web site www.lindabcomfort.dk

We have all the data you require.

Glen

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#11
In reply to #10

Re: Can Displacement Ventilation Displace Disease?

09/20/2007 6:16 PM

Firstly, I would agree that the operational costs of running the system would be greatly reduced over conventional systems and as consultants we have endorsed the use of the Hiross flexible space system www.flexiblespacesystem.com, which reflects the same, if not greater advantages as the system you described, and has been around for over a decade.

As to the use of displacement ventilation in operating theatres - You've got to be kidding....., I wouldn't endorse displacement or the flexible space type systems in a surgery where there was even the most minimal need for infection control (for Operating Theatres we recommend only 100% passthrough with HEPA and electrostatic on the supply and air scrub with terminal treatment of the exhaust). To achieve the static pressures necessary to push the air through a HEPA filter and an air scrubber at its rated flow rate, there is no advantage to considering displacement air distribution and once again to comply with requirements the cleaning and disinfection costs would be prohibitive. These would need to be included in any disclosure pertaining to cost benifits and impacts.

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#12
In reply to #11

Re: Can Displacement Ventilation Displace Disease?

10/03/2007 9:58 AM

It is not exactly like people are thinking. It saves lots of energy as well. As considering green building concept it reduces CO2 in the air. It may beatifically to a single patient in single room too. It may helpful to recover patient health faster then normal ventilation because it reduces airborne faster then normal mixing type ventilation.

It will be the only one accepted tomorrow's method of ventilation.

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#13
In reply to #12

Re: Can Displacement Ventilation Displace Disease?

10/03/2007 5:53 PM

Dear Guest - So you're back to the energy savings side and we've already agreed that this has merrit - just far removed from areas of infection control.

It is obvious from you post that you are trying to sell this old technology (I repeat it's been around for well over 20-years) as new technology.

While this forum should be used to provide information on emerging technologies and usage, it should not be used as a sales platform for an individual product by salesmen. Instead of stearing us to the product promotion website, it would be more beneficial to link to where these systems have been installed and the referees (say their skypeID) who are the hospital engineers managing these systems.

As there could be a number of individuals who are "Guests" and I'm assuming/attributing all of the "Guest" comments to a single individual, who should (If he wants the forum members to take him seriously) register as a forum member..

Doing a search of your suppliers website, I could find no reference to: operating theatre, infection, hospital etc. so would presume that these installations may not be endorsed or promoted by that supplier (and this would make a lot of sense, as they could be held liable for any infection transfer attributable to the inadequacies of this design).

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#14

Re: Can Displacement Ventilation Displace Disease?

12/09/2009 1:28 AM

Hello, I'd like to join in after 2 years. I want to start do some research, and now I would consider if we could use displacement ventilation in general wards and outpatient clinics. I know that we cannot use displacement ventilation in operation theare, but how about general wards and outpatient clinics?

I surfed the internet and find an abstract of a PhD research, saying:

The displacement ventilation shows obvious advantage in removing small airborne particles/droplets, but difficulty to carry larger droplets and their solid remains out of the room. The simulation results also show that the air flow mixed the droplets and dilute the concentration in the mixing and downward ventilated room as time goes on. With comparison, the downward ventilation set-up is recommended as it has equal ability in removing passive particles and lager droplets, moreover in this type ventilation set-up, the number of droplets attached less on the body of health care worker.

I don't know in daily life of general wards and outpatient clinics, what is the size range of the airborne particle between the sitting level (about 1.1m) and standing level (about 1.9). If anyone have some experience, please let me know. I'd like to see whether in general wards and outpatient clinics, if the displacement ventilation could move these particles away efficiently, that would be fine; or if they can only deposit on the ground, this is also good.

I am thinking .... and welcome to conact me and inspire me by :zhoubinwx@hotmail.com

Best regards

Bin

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Anonymous Poster
#15

Re: Can Displacement Ventilation Displace Disease?

08/09/2010 4:15 PM

Displacement ventilation may increase the chances of cross-infections. The studies recommending displacement did not address stratified "sneeze" or "chough" transients in the occupied zone.

Why endanger pateints lives for a fraction of energy? Many patients have very low white blood cell counts, and are prone to infection because their immune system is not functioning properly. Displacement stratification could increase the chance of a nurse contacting an infection and transmitting to other patients, because of the return air rises up from the patient to the caretaker.

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