Providing proper ventilation is a crucial component of multifamily building design due to its effects on occupant health and comfort. Ventilation ties the whole HVAC system together. Without ventilation, there is no way for the indoor air to refresh and re-oxygenate itself. What’s the right set of “lungs” to put in your building?
A Breath of Fresh Air
Indoor Air Quality (IAQ) refers to the air quality within and around buildings and structures, especially as it relates to the health and comfort of building occupants. Increasing the amount of outdoor air coming into the building helps to control pollutant levels, odors, temperature, humidity, and other factors that can impact the health and comfort of building occupants.
Ventilation can be classified into two subcategories: natural and mechanical ventilation.
Natural ventilation occurs as a result of natural forces, such as wind pressure or differences in air density, through intentional opens like windows and doors.
Ventilation requirements are covered in IMC section 402 and ASHRAE 62.2 – Ventilation and Acceptable Indoor Air Quality in Residential Buildings. The minimum openable area to the outdoors should be 4% of total floor area being ventilated. The specific approach and design of natural ventilation systems will vary based on building type and local climate. As per code, here are additional requirements:
Window Sizes: As per IMC section 402.2 and ASHRAE 62.2-2019 section 6.6.1, the minimum openable area to the outdoors should be 4% of the total floor area being ventilated. Windows should be sized in a way that the net openable area is equal to 4% of the total floor area.
If it is not possible to meet minimum openable area size, mechanical ventilation will be required.
- Bathroom Exhaust Required: As per ASHRAE 62.2-2019 section 5, a local mechanical exhaust system should be installed in each bathroom.
- Kitchen Exhaust: The recirculating hood can be used along with natural ventilation as long as the openable area is equal to 4% of the total floor area being ventilated.
Mechanical ventilation is relies on equipment that consumes power, supplying air to or removing air from an indoor space by powered equipment such as motor-driven fans and blowers.
Mechanical ventilation requirements are covered in IMC section 403 and ASHRAE 62.2-2019 section 4 dwelling unit ventilation. Energy codes such as ASHRAE Standard 90.1 – Energy Standard for Buildings Except for Low-Rise Residential Buildings often require air-to-air energy recovery for mechanical ventilation systems.
When Are Mechanical Ventilation Systems Required by Codes?
Ducted OA (outside air) to HVAC unit
A mechanical exhaust system, supply system, or combination thereof, should be installed to operate for a dwelling unit to provide continuous dwelling unit ventilation with an outdoor unit at a rate not less than specified in ASHRAE 62.2 section 4.1.1. This can be achieved by connecting the outside air duct to the AHU.
- ERV Units: Energy recovery ventilation is a very energy-efficient alternative, which is based on using the exhaust air to precondition the intake air and reduce the total cooling or heating load. It is important to note that ERV units may only meet the full HVAC load under specific temperature and humidity conditions. Otherwise, they must operate in conjunction with an air conditioner or heater.
- Whole House/Dwelling Unit Ventilation: A well-designed ventilation system will ensure adequate levels of air exchange, removal of pollutants and contaminants, and improvement of comfort levels in multifamily dwellings. Most importantly, the right ventilation systems means fresh air and indoor comfort.
BASE4 | Your MEP Experts!
Choosing which ventilation system to place in your multifamily project will depend on many aspects, including cost. The idea is to place a system that can create an ideal living environment for occupants while maintaining the budget. BASE4 is here to guide you on the correct choice for your project!
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