dimax knowledge Base

  • A heat pump is a device that uses the refrigeration cycle for heat recovery. Normally thermal energy transfers from a hot body to a cold body. A heat pump uses external energy to transfer thermal energy in the opposite direction, that is to absorb heat and then reject it to ‘heat sink’. The simplest example […]
  • Variable Air Volume (VAV) Air Handling Systems use variable fan speeds to supply VAV boxes that are located in different zones of the building. The fan speed is controlled based on the discharge air static pressure downstream of the supply duct. In areas where the heating season is long, many VAVs may have electric or […]
  • Underground or enclosed parking structures require mechanical ventilation (exhaust fans) to displace any poisonous carbon monoxide produced by running vehicles.  The Ontario Building Code, as well as building codes in other jurisdictions, requires that exhaust fans run continuously 24/7 in such parking structures unless a carbon monoxide detection system is installed and maintained, in which […]
  • In order to assess whether or not the heat exchanger is performing properly, the medium needs to be flowing through both the Primary and Secondary sides.  The flow of medium should be somewhere close to the design flow rates, which are typically identified in the specification sheets of the heat exchanger.  This isn’t always easy […]
  • The purpose of a heat exchanger is to transfer heat from one medium to another.  Most often, heat exchangers transfer heat from water-to-water, air-to-air, water-to-air, or refrigerant-to-air.  An example of a water to air heat exchanger is a heating coil.  The two sides of the heat exchanger are referred to as Primary and Secondary. The […]
  • Dew point temperature is the temperature when the water vapour present in air begins to condense. The dew point can also be defined as the temperature at which the outside air becomes completely saturated with moisture. If the dew-point temperature is close to the dry bulb temperature –  the relative humidity is high If the […]
  • Dry bulb temperature is the temperature that is read by the sensing element on an ordinary temperature sensor or thermometer. Dry-bulb temperature does not take into account the effect of moisture in the air. The wet bulb temperature takes into account the effect of moisture in the air and its effect on the sensing element […]
  • When buildings are unoccupied and the equipment is off, the return/exhaust air ducts may still have air flow. This movement of air is known as a stack effect. The stack effect is due to the difference in the density of the air inside the building and outside the building. The density difference is caused by […]
  • In many buildings the exterior doors open outward to promote fast egress during an emergency situation.  If the air pressure inside the building is greater than outside, the air trying to escape the building will push its way out through any opening it can including exit doors.  This can cause the doors to stay open […]
  • AHUs with variable speed fans often feed into ductwork that have one or many control dampers that regulate the air flow coming out of the ductwork into the space. As these control dampers regulate open and close throughout the day to keep the space temperature at setpoint, it causes air pressure fluctuations in the ductwork. […]
  • An Air Handling Unit heats and/or cools and/or adds outside air as required to control the temperature within an enclosed space. AHUs always have a fan, and the fan can either be constant speed or variable. Some AHUs draw in their air from the enclosed space itself to heat or cool it, while others have […]
  • A Makeup Air Unit is like an Air Handling Unit, except that it draws in 100% outside air, then heats or cools it as necessary to satisfy the enclosed space it serves. Also see answer to: How does an AHU work?
  • An AHU is able to free cool when the outdoor air temperature is at or below the desired discharge air temperature. For an AHU to free cool it requires a set of dampers that can regulate what amount of outside air is drawn into the unit as well as what amount of inside air is […]
  • This could be a result of: The heating not working, which could be the result of a heating pump not working, or a control valve not opening, or a gas furnace not lighting The volume of air flowing through the heating coil or furnace is greater than it can accommodate The temperature of the air […]
  • This could be a result of: The cooling not working, which could be the result of a cooling pump not working, or a control valve not opening, or a compressor not operating, or a hot gas bypass cycle not functioning The volume of air flowing through the cooling coil greater than it can accommodate The […]
  • Supply air temperature setpoints often change (or reset) according to some other condition that affects the space being heated and cooled. For example, the supply air setpoint might reduce automatically to cause additional cooling to run when an increase in return air temperature is sensed. Similarly the supply air setpoint might increase automatically to cause […]
  • It could be a loss of power, or that a safety device has tripped, or that it was turned off by an automated device such as a timer or Building Automation System. To see if an automated device turned it off, check the automated device to see if it’s attempting to run the AHU or […]