HVAC Systems

The mechanical systems of a building largely relate to controlling the indoor environment of a building by means of heating, ventilation and air conditioning (HVAC). The goal is to provide thermal comfort and acceptable indoor air quality which changes depending on the occupancy type and usage of a building. This is typically achieved by controlling temperature and air pressure relationships between building spaces.

Heating systems are used for maintaining a higher indoor temperature than the outside temperature. Heating systems generate warmth for a building space which can be achieved by using a multitude of heating systems. Mechanical heating systems include, but are not limited to, central heating furnaces and boilers, heat pumps, direct space heaters, radiant floor heating systems, and ductless mini-split systems. The systems can be fueled by various solid fuels, liquids and gases.

Ventilation generally refers to the process of providing new fresh air (typically outside air) to remove and replace unconditioned old air of a building space. Natural means of ventilation can be achieved by simply opening a window or installing a wall vent. In mechanical systems, supply ventilation fans are used to draw in and force air into a building space. In addition, building ventilation exhaust systems are used to draw existing air out of a building space to make way for new air. The removal of air from a building ensures that steady flows of air changes occur, and helps to balance pressures within a building. Additionally, used air within a building can contain moisture, smells, dust, microbial matter and other pollutants. The removal and management of stale waste air is therefore important to ensure a comfortable and sanitary building environment. Supply and exhaust fans can be installed directly through a wall or roof. Supply fans are often contained within air handling units (AHUs) or rooftop units connected to ducts that penetrate the building enclosure, but can also be independent.

Air conditioning refers to the process of removing heat and moisture from within a building space. The purpose is to reduce ambient air temperature (i.e. cool the air), and a part of the air conditioning process reduces the humidity of the air. Removal of humidity dries the air which can have a negative impact on the building users, so on more modern advanced HVAC installations, humidity can be reintroduced to the conditioned air. Air conditioning can be achieved using a multitude of air conditioning systems including, but not limited to, through wall or window units, packaged terminal units, chilled water systems, mini-split systems, condenser units and de-humidifiers. Most air conditioning systems can operate on two cooling principles: the refrigeration cycle and evaporative cooling. The refrigeration cycle principal works by altering a refrigerant gas pressure (PSI) which in turns changes its temperature to provide cooling (and sometimes heating). Evaporative cooling works on the principal of reducing the temperature of a system by liquid evaporation, usually a condenser water loop connected to a cooling tower.

Mechanical systems should be inspected and maintained regularly to a provide reliable service. The mechanical systems form a critical component of a property and it is imperative that they are evaluated as part of the due diligence process. Failure of mechanical systems typically has significant business impacts that can often result in extended downtime and discomfort to occupants. Regular testing and maintenance is also essential on water-based mechanical systems which are susceptible to legionella, mold and organic growth which can be harmful (or deadly in the case of legionella) to human health.  The HVAC systems accounts for a large portion of a buildings energy use and it is therefore important to ensure the system is running at optimal efficiency to limit energy usage costs as much as possible.

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