Facility Ventilation

What is a Heating, Ventilation and Air Conditioning System?

A Heating, Ventilation and Air Conditioning (HVAC) system is the primary method in which ‘stale’ air is removed from buildings and replaced with ‘fresh’ air. The system also works to ensure comfortable air temperature, reduce the accumulation of moisture, odours and airborne particles in the air and improve the general comfort of occupants.

Most buildings have a degree of natural ventilation sources through open windows, doorways, etc. Natural ventilation relies on differences in air pressure, air currents provided by outside wind and other natural forces to circulate air.

Typically, as buildings increase in size, they will require a mechanical ventilation system to adequately refresh the air inside the building in order to ensure safety and comfort.

Key Elements

Each ventilation system is unique to the building it serves. Some ventilation systems are small and relatively simple in design, while others are complex with interrelated systems comprising of hundreds or even thousands of components which work in unison to achieve the ventilation requirements of its occupants.

Supply Air – all system components involved in drawing fresh air into a building from the outside.

Exhaust Air – all system parts involved with removing stale air from inside a building back to the outside.

Air Exchange – reflects the numbers of times that the volume of air in a space is changed per hour and is a key measurement of a ventilation system. As per CSA standards, the number of required air changes per hour (ACH) varies depending on the purpose of the room itself.

Return Air – in some cases, to improve efficiency or to retain building heat, the air within a building is recycled or “returned” from the exhaust system into the supply air system. Recycled air is carefully filtered to ensure cleanliness before circulating back into the building.

Filtration – at key junctures in the supply system, the return system and sometimes even the exhaust system, air is forced through special filters designed to remove odours and airborne particles from within the air. Different building needs will require a different level of filtration.

Humidification – in dry climates, the ventilation system will add moisture into the air to ensure a level of humidification which is more ideal for both comfort and healthy respiration. During warm summer months, the humidity in the air may need to be lowered.

Heating – during winter months, air within a building needs to be heated to ensure the comfort of building occupants. There are many different methods of heating air, ranging from radiant heaters located along the walls of building spaces to heating coils within the ventilation system itself which warm the air before it is circulated throughout the building.

Air Conditioning – during summer months, air may need to be cooled within a building in order to maintain comfort. Some health-care equipment also requires controlled temperatures to operate effectively. There are different methods of providing air conditioning to a building, but the ventilation system may also be used to cool the air while it is circulating in the building.

Zones – large buildings typically are divided into multiple zones. Each zone can be serviced by its own individual ventilation system. This is more efficient and effective than trying to have a single system circulating air through many kilometers of ducts to serve the needs of a building.

Building Management System (BMS) – many buildings have a central computerized management system which monitors and controls all aspects of the HVAC system. The BMS can centrally control all zones, but also works to regulate fan speeds, the amount of supply and exhaust air, the heating and cooling needs of the building, right down to the individual preferences for various locations in the building as monitored by local thermostats.

There are many other elements of ventilation systems designed to improve efficiency such as reduce noise and vibration, direct airflow, and remove moisture (which can contain bacteria).

General Considerations

Ventilation systems require continual monitoring and upkeep by knowledgeable and trained individuals. A regular schedule of maintenance is essential to ensure correct operation of all components of the system. Good systems have fail-safes and redundancies incorporated into the system such that a mechanical breakdown of one component is rarely noticeable by building occupants and does not compromise overall safety, however all components must be maintained proactively to ensure consistent operation.

Safety precautions must be in place to enable safe servicing of various components. These can include electrical lock-out procedures, confined space training, disposal techniques for contaminated filters, etc.

Ventilation systems require fresh air from outside to circulate throughout a building. Outside conditions such as high winds and dust, smoke from forest fires, or even nearby idling vehicles can place significant strain on a ventilation system.

Electrical outages can also impair the overall effectiveness of a building ventilation system. Key components—such as those which service operating rooms—may be supplied by emergency power generators, but it may not possible to supply emergency power to an entire ventilation system.

Limitations

When a building is constructed, the ventilation system is one of the first things which is built in place. The system typically runs throughout the entire structure of a building hidden behind walls, floors and ceiling spaces. As such, renovations and retrofits after a building is built become both difficult and expensive to complete. In some cases, the architecture of a building does not permit sufficient space to conduct renovations to add additional components to the system. This is typically the case with older buildings.

Ventilation science is a relatively recent development; modern ventilation systems are highly efficient and effective in providing comfort and safety to building occupants. These systems are constructed to a rigid set of standards for performance, particularly ventilation systems in health care facilities. However, these building standards are recent requirements for the construction of health care facilities. Buildings which were constructed prior to 2000 (approximately) may have been designed and built to a different ventilation standard. Likewise, buildings which were designed and built prior to the year 1980 may not have been required to adhere to any ventilation standard at all. Many older buildings have been improved and renovated to improve their ventilation, however not all of them have been improved to achieve modern ventilation standards.

How do you know if a Ventilation System is working as designed?

The primary measurement of the effectiveness of a ventilation system is the number of air exchanges per hour in any given space. This may be measured, but typically requires retaining a specialized third party vendor with both the knowledge and equipment to conduct such a measurement. The most modern health care facilities have reasonably measurement capabilities within the BMS system to provide similar knowledge.

All aspects of the HVAC system should be inspected, maintained and cleaned at a frequency that is sufficient to protect the health and safety of workers. Records should be kept of all inspections, maintenance and cleaning, including the individual who performed the duties. Records should be readily available to Occupational Health Committees.