Medical Gas Green Design

Posted on April 8, 2011

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I asked one of our healthcare plumbing engineers about some design ideas he encountered at the American Society of Plumbing Engineers (ASPE) Convention and Plumbing Expo last November.

He said sustainability in medical gas design is something that has been getting a lot of attention and offered some considerations for healthcare owners, facilities, maintenance and plant operators on their next renovation, addition or new construction project.

Here are ten sustainability ideas for medical gases from the ASPE Beacon Medaes’ presentation by Mark Allen:

  1. Reduce Usage.  Seems intuitive enough, but this can create serious savings for healthcare owners.  Liquified gases are very energy intensive to produce.  For example, 100 cf of oxygen or nitrogen requires 2kW to produce, while 100 cf of medical air requires about 0.5 kW.  In addition, transporting liquified gases is very expensive.  The less used, the greener.
  2. Consider Instrument Air in lieu of Nitrogen.  Instrument air is compressed air equivalent in pressure, dryness and cleanliness to nitrogen. Instrument Air (IAir) saves money on cylinder management (inventory, compressor system maintenance, cylinder rental costs, etc.) and the cost of the air itself is zero.  IAir is approved by NFPA and the Instrument Society of America as a sanctioned alternative as of 2002; it can be used anywhere nitrogen would and other applications where nitrogen would be too expensive (surgical tools, and pneumatic brakes / tables, inflating cuffs, lab air, etc.).
  3. Waste Anesthesia Gas Disposal (WAGD).  Five permitted methods exist via NFPA:  into medical system, into dedicated pump, into dedicated blower, Venturi or passive disposal. WAGD is about moving the gas, not producing a deep vacuum. For small volumes at high vacuums, use a pump; for large volumes at low vacuum, use a fan or blower.
  4. Air Dryers.  Consider the choice of refrigerated dryers versus dessicant dryers. A dessicant dryer uses purge air (~15% of inlet / 15% of 10Hp) and averages 9,723 kW / year, while a refrigerated dryer uses about .58kW compressor, or 5,080 kW / year—or nearly half as much energy per year.  Suggestion:  make purge proportional to usage.
  5. Oil-less Compressors / Pumps. Avoid need for oil-water separators, disposal and potential biohazard by using oil free or oil less compressors and vacuum pumps.
  6. Variable Speed (VSD) Vacuum Pumps. In the past VSD were too expensive for small horsepower; energy savings were not enough to justify cost; and most vacuum technologies do not benefit or accept VSD.  Some advantages:  consistency of vacuum, motor soft start, energy savings, lower exhaust temp’s and noise level, nigher altitude limitation. In addition, more air is moved at lower vacuums (greater efficiency) and most pumps / motors prefer to run continuously than start / stop (better reliability and reduced maintenance).  VSD choice has gray areas:  not adaptable to all pumps; some pumps most efficient at one particular speed; and VSD adds cost.
  7. Fix Outlet Waste. Gas lost from leaky outlets adds up to big money. For example, 2% leakage on 300 medical air outlets @ a .5 lpm leakage rate and prevailing prices is $17.89 / year.  3% leakage on 500 medical vacuum outlets @ 1 lpm leakage rate and prevailing prices is $38.89 / year. 2% leakage on 300 medical oxygen outlets @ .5 lpm leakage rate and prevailing prices is $378.88 / year. These expenses add up.
  8. Equipment Selection.  Poor quality makes problems worse; not all equipment is created equally.  Match equipment to your need, and purchase wisely—then maintain it.
  9. Test and Adjust.  Test for problems, then fix.  If no problem exists, save money and resources for real problems.
  10. Consider Xenon instead of Nitrous Oxide.  Nitrous oxide has 296x more environmental impact than an equivalent volume of carbon dioxide; yet medical use is less than 1% of all nitrous oxide emissions. Nitrous oxide use has been questioned for negative impact on patient outcomes. Xenon is a better anethetic gas:  has almost identical anethetic effects with no known side effects or negative environmental impact; however, it is 2,000x the price of Nitrous oxide.

I hope this helps for the facilities, procurement and clinical directors out there, as well as healthcare mechanical engineering designers.

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