Medical Vacuum System Design for Hospitals: Pressure, Diversity, Plant Sizing and Exhaust

Define the services and terminal units

List every terminal unit by room type: wards, ICU, theatres, recovery, emergency, endoscopy, neonatal and procedure rooms. Theatres and ICU use vacuum frequently and at higher flow than general wards. Count outlets per bed and per room, and note special loads such as surgical suction, chest drainage and continuous suction.

Related system elements are described in medical gas pipeline system components and the principles of a vacuum service in what a medical vacuum system is.

Pressure levels and performance

Vacuum levels are expressed as pressure below atmospheric and must be delivered at the terminal unit, not only at the plant. Standards such as HTM 02-01, ISO 7396-1 and NFPA 99 specify the minimum vacuum available at outlets and the flow per terminal for design, and values differ, so use the standard named in your contract. Keep in mind that the altitude and ambient temperature affect pump performance, so request the rating at your site conditions.

Pressure drop across the pipework must be controlled so that remote outlets still meet the minimum under peak demand, which is why pipe sizing and plant capacity are linked.

Diversity factors and demand calculation

Not all outlets are used at once. Standards give diversity factors that reduce connected demand to design demand, often with different factors for theatres, ICU and wards. Add known continuous loads separately. The result is the design flow in a unit such as Nm³/h or litres per minute that the plant must sustain at the specified vacuum level.

Check results with a second method, such as clinical estimate of simultaneous use in the busiest area, and document assumptions in the design report. A comparable method for gas supply appears in medical gas pipeline design.

Plant sizing and redundancy

A vacuum plant should have at least two pumps, each able to meet the design demand or a defined share of it according to the standard, so that service continues if one pump fails or is serviced. The plant includes a receiver, bacterial filters on the inlet side, controls and alarms. Pump type affects efficiency and servicing, as compared in medical vacuum pump types.

MZ Liberec's MIL's vacuum stations hold suction and flow automatically, include an antibacterial filter and secretion trap, and cover capacities from 6.4 to 632 Nm³/h. That range indicates the scale the manufacturer offers; the exact configuration should be matched to your calculated demand. See the MIL's vacuum stations.

Exhaust, filtration and plant room

Local legislation and facility guidelines may add requirements, so confirm with authorities such as DHA, DOH or MOHAP as appropriate.

• Filter the exhaust, because the air drawn from patients may be contaminated.
• Route the discharge to a safe outdoor location, away from air intakes, windows and walkways.
• Provide a drain or trap for liquid carryover and design the receiver for safe emptying.
• Provide ventilation for the plant room, since pumps generate heat and noise.
• Plan access for filter replacement and pump service.

Pipework, alarms and zoning

Vacuum pipework is usually sized with a slope towards the plant and is installed in a material approved by the standard, with isolation valves at each branch and zone. Vacuum alarms monitor level at the plant and in the area. A monitoring unit such as the MZU II can display pressure and flow for several gases, and the system can be tied into building management.

Maintenance planning should be part of the design brief; see vacuum system maintenance. To discuss a design brief with MZ Liberec products, contact Beckfinity.