Join us in Montreal on Oct 16 as HH Angus presents “Making a Super Hospital Work” at the Canadian Centre for Healthcare Facilities conference.

As the mechanical, electrical and security design engineers for CHUM, the HH Angus team has unique insight into what it took to successfully deliver the largest healthcare project in North America – the Centre hospitalier de l’Université de Montréal. Nick Stark, Marianne Lee and Phil Schuyler, principals of HH Angus and team leaders, will detail some of the key challenges and solutions for this mega hospital project. Conference attendees will also be able to tour public, clinical, mechanical and electrical facilities at CHUM.

Meeting  stringent standards while reducing energy use.

Hospitals face unique design challenges in meeting air handling requirements, none more so than the special requirements of operating rooms. As lighting systems and building  envelopes have become more energy efficient, it is air handling systems that increasingly  represent a hospital’s greatest energy consumer. But there are options to mitigate the energy demands of these systems.

Air handling systems are an important part of any building for maintaining occupant comfort. When it comes to hospitals, there are a series of special requirements that make ventilation systems critical to the delivery of healthcare.

Firstly, air handling systems are relied on to help protect occupants and adjacent  surroundings from infectious diseases and hazards created by equipment and processes. Many contaminants are generated which must be exhausted. In many areas of a hospital, the systems are designed so that air flows from clean to less clean areas to help protect staff and other occupants. A good example of this is Airborne Isolation Rooms where differential pressures must be monitored and alarmed.

Air handling systems are also a key component of the life safety strategy for managing smoke in a fire situation. A measure of the reliance on air handling is the requirement that ventilation systems must limit smoke concentration to allow operations to be safely concluded or for critical care patients to be safely transferred.

And now the rising level of patient acuity and the pressure of high utilization, with occupancy rates well above 100%, are putting even more pressure on HVAC systems. In Canada, CSA Standard Z317.2, Special  requirements for heating, ventilation, and air-conditioning (HVAC) systems in health care facilities, is referenced in most if not all Canadian Building Codes as good practice for the design, construction and operation of air handling systems. The latest edition was published in December 2015, and work  recently started on the next version due in 2020.

Operating rooms

Operating rooms and similar spaces where invasive procedures are performed have a number of particular air supply requirements:

  • Common practice for operating rooms is to supply a high volume of air at low velocity through laminar flow ceiling diffusers in the central area of the room with the intent of achieving a piston effect. The intent is for air to generally flow first past the patient and clean surgical staff before flowing to the outer portions of the room to the exhaust grilles. Studies have shown that 20 air changes per hour is effective; note, this is a far cry from the hundreds of air changes of a true laminar flow clean room.
  • The cleanliness of operating rooms is critical. Standards call for the supply air to be filtered to at least MERV 14, but many engineers and facility managers look to increase this to a higher level. HEPA filters, which are rated to 99.97% efficiency on 0.3 micron particles, have been adopted as the standard in many cases.
  • Staff generally prefer operating rooms be kept relatively cool as they are often gowned in multiple layers to minimize the possibility of infection. The premise that a wide range of temperatures is necessary to control the temperature of the patient, particularly during cardiac surgery, is not well founded. Blankets or pads that heat or cool are used to control the patient’s temperature.
  • There has been great debate over humidity in operating rooms. Many years ago the anaesthetics in use were flammable, and operating room  humidity was maintained between 50% and 60% to minimize the possibility of static electricity discharge. As anaesthetics became safer, the low end of the humidity range was reduced to 40%. The initial concern was that less humidity would cause drying at the surgical site; however, this condition was not observed. In the 2015 version of CSA Z317.2, the lower humidity limit was lowered to 30%, similar to most other spaces in a typical hospital.
  • Design engineers must carefully analyze the psychrometrics of air supplied to operating rooms over the possible range of temperature and humidity conditions. This is particularly true in the summer when cooling coils are relied on to dehumidify moist outdoor air. If this air is not dry enough, the relative humidity limit in operating rooms kept at a cool temperature will not be maintained. Enhanced cooling coils, lower chilled water temperatures, and desiccant moisture removal are some of the solutions.
An operating room inside the Centre hospitalier de l’Université de Montréal.

Energy efficiency

These high levels of ventilation and air cleanliness, coupled with stringent temperature and humidity control and around-the-clock operation, all contribute to high energy use in hospitals; however, there are a number of strategies that can help reduce energy use:

  • Moving air at lower velocities takes less energy, so air handling equipment and ductwork with a larger cross sectional area needs less fan power to move the air.
  • Variable volume air supply and exhaust is more complex in a hospital due to the requirement to maintain directional airflow between most rooms and departments. This generally requires that each individual room or group of rooms control both supply and exhaust air in tandem so pressure relationships can be maintained.
  • A number of methods of heat recovery, when correctly applied, have proved effective while maintaining the cleanliness of the air. Projects such as the Centre hospitalier de l’Université de Montréal (CHUM) and Royal Jubilee Hospital in Victoria used enthalpy heat recovery wheels on all air handling systems to transfer heating, humidity and cooling from the exhaust air to the supply air.
  • There is a misconception that air handling systems all need to operate 24 hours a day. This is true for a number of space types but, even in more critical spaces, there are opportunities to reduce the total air volume or volume of outdoor air when the spaces are not in use, as long as certain conditions are met. Less critical areas offer more flexibility to reduce airflows or setback temperature setpoints.
Interior of the Royal Jubilee Hospital in Victoria, where enthalpy heat recovery wheels are used on all air handling systems to transfer heating, humidity and cooling from the exhaust air to the supply air.

Published in the Canadian Consulting Engineer
January/February 2018 


Nick Stark, P.Eng., CED, LEED® AP, ICD.D

The Professional Engineers of Ontario and the Ontario Society of Professional Engineers have selected Nick Stark, P.Eng., CED, LEED® AP, ICD.D,  as this year’s recipient of the prestigious Medal for Engineering Excellence. Nick’s current role at HH Angus and Associates is Vice President – Knowledge Management, responsible for the overall information systems within HH Angus, as well as spearheading the design and management P3 hospital projects.

The Ontario Professional Engineers Awards program is presented jointly by PEO and OSPE, with industry awards in several categories. For the Engineering Excellence category, the evaluation is weighted 80% on work-related achievements, 15% on service to the profession, and 5% on service to society and the community.

Nick will receive the award at the PEO/OSPE gala in November. He responded, “I am honoured and humbled to be recognized by my peers in the engineering profession.”  Congratulations Nick!

Montreal mega-hospital project, CHUM (Centre Hospitalier de l’Université de Montréal) is featured as the cover story in this month’s issue of Canadian Consulting Engineer magazine. The story profiles the mechanical and electrical engineering for the project, as described by HH Angus Vice President and CHUM project lead, Nick Stark, P.Eng., LEED® AP, ICD.D. Also featured is the structural engineering by Pasquin St-Jean et associés.

Nick Stark’s article describes the complexity of engineering this enormous project (2.5 city blocks, 334,000m2), which is being delivered, financed and maintained by Collectif Santé Montréal.  The project replaces three hospitals in Montreal and includes a 20 storey acute care block, 772 beds, 39 operating rooms, and a full cancer centre.  CHUM is one of the largest P3 projects in North America. Phase 1 is scheduled to open by the end of 2016.

Click here for the abridged pdf.

Click here to read the full magazine.