Certified HVAC Design: Adhering to Building Code Requirements & HRAI Guidelines for HVAC Design in Ontario
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Residential Ventilation Design is a primary component of HVAC Design. The Ontario building code prescribes natural and mechanical ventilation rates by which all projects must follow. The Ventilation Design specifies the required ventilation equipment including: bathroom exhaust fans, Heat Recovery Ventilators and Kitchen Exhaust Hoods.
Exhaust Fan location should be denoted on Duct Design Drawings, and specifications can be found on the Mechanical Ventilation Design Summary.
WHAT IS RESIDENTIAL VENTILATION DESIGN?
The terms and factors playing a direct role in Ventilation Design and Building System Performance:
Flue Gases
In the context of ventilation design, positive and negative pressure refer to the pressure difference between the inside and outside of a building. Positive pressure occurs when the air pressure inside the building is higher than the air pressure outside, while negative pressure occurs when the air pressure inside the building is lower than the air pressure outside.
Positive pressure can be beneficial for ventilation, as it can help to push stale, contaminated air out of the building and draw fresh, outside air in. This can help to improve indoor air quality and reduce the risk of air-borne contaminants entering the building. However, excessive positive pressure can also cause air leakage and energy loss, as air may escape through gaps and openings in the building envelope.
On the other hand, negative pressure can be problematic for ventilation, as it can cause air to be drawn into the building from outside. This can result in the infiltration of outdoor pollutants, such as vehicle exhaust or pollen, into the building. In addition, negative pressure can cause drafts and discomfort for building occupants.
HVAC designers must carefully balance positive and negative pressure in ventilation design to ensure that buildings have adequate air flow and air quality, while minimizing energy loss and other negative effects. This may involve the use of mechanical ventilation systems, such as exhaust fans or air-to-air heat exchangers, to control the pressure difference between the inside and outside of the building.
Should a Ventilation System be in Positive or Negative Pressure?
In the context of ventilation design, sensible efficiency refers to the percentage of heat that is transferred from the air to a space or object during the ventilation process. Sensible efficiency is typically expressed as a percentage, with a higher percentage indicating a more efficient transfer of heat.
Sensible efficiency is an important factor to consider in ventilation design, as it can affect the performance and energy efficiency of a ventilation system. A ventilation system with a high sensible efficiency can effectively transfer heat from the air to the space or object, resulting in improved indoor air quality and thermal comfort. On the other hand, a ventilation system with a low sensible efficiency may be less effective at controlling temperature and air quality, and may require more energy to operate.
To determine the sensible efficiency of a ventilation system, HVAC designers must consider several factors, including the temperature of the air, the temperature of the space or object, and the flow rate of the air. They may use calculation methods, such as the sensible heat ratio or the sensible heat gain, to estimate the sensible efficiency of the system.
By considering sensible efficiency in ventilation design, HVAC designers can ensure that buildings have effective and energy-efficient ventilation systems that provide optimal air quality and thermal comfort.
Sensible Efficiencies in Ventilation
In the context of ventilation design, total ventilation capacity refers to the maximum amount of air that a ventilation system can supply to a space. Total ventilation capacity is typically measured in cubic feet per minute (CFM) or cubic meters per second (m3/s).
Total ventilation capacity is an important factor to consider in ventilation design, as it determines the ability of the ventilation system to provide adequate air flow and air quality in a space. A ventilation system with a high total ventilation capacity can effectively remove stale, contaminated air and supply fresh, outside air to the space, improving indoor air quality and thermal comfort. On the other hand, a ventilation system with a low total ventilation capacity may be unable to provide adequate ventilation, leading to poor air quality and discomfort for building occupants.
To determine the total ventilation capacity of a ventilation system, HVAC designers must consider several factors, including the size and characteristics of the space, the number of occupants, and the air flow requirements of the system. They may use calculation methods, such as the air change rate or the ventilation rate, to estimate the total ventilation capacity of the system.
By considering total ventilation capacity in ventilation design, HVAC designers can ensure that buildings have effective and efficient ventilation systems that provide optimal air flow and air quality
Total Ventilation Capacity in Ventilation System
In the context of ventilation design, velocity, CFM, and Btu are important factors to consider when designing and sizing Ventilation Systems.
Velocity is a measure of the speed at which air flows through a ductwork. In ventilation design, velocity is typically expressed in feet per minute (ft/min) or meters per second (m/s). High velocities can cause air turbulence and noise, while low velocities can result in poor air distribution and reduced system efficiency. Therefore, HVAC designers must carefully balance velocity and other factors when designing ducts to ensure that the system performs optimally.
CFM, or cubic feet per minute, is a measure of the volume of air that flows through a duct. In duct design, CFM is used to calculate the size and capacity of ducts. Ducts that are too small can restrict air flow and reduce system efficiency, while ducts that are too large can be unnecessarily costly. HVAC designers must carefully calculate the required CFM for a given duct system based on the heating and cooling needs of the building.
Btu, or British thermal unit, is a unit of energy. In the context of ventilation design, Btu is used to calculate the amount of heat that is lost through exhaust. HVAC designers must ensure that the ducts are sized and insulated properly to prevent excessive heat loss or gain, in order to maximize the efficiency of the HVAC system.
Velocity, CFM and Btu
In the context of ventilation design, combustion air refers to the air that is supplied to a fuel-burning appliance, such as a furnace or water heater, to support the combustion process. Combustion air is necessary for the appliance to operate safely and efficiently, as it provides the oxygen required for the fuel to burn and the heat to be generated.
In buildings, combustion air is typically supplied from the outdoor air, through openings in the building envelope or mechanical ventilation systems. However, if the supply of combustion air is insufficient or contaminated, it can cause problems for the appliance, such as incomplete combustion, reduced efficiency, and increased emissions of pollutants.
To ensure the safe and efficient operation of fuel-burning appliances, HVAC designers must consider the supply of combustion air in ventilation design. This may involve providing adequate and properly located openings for the supply of combustion air, or using mechanical ventilation systems to provide a controlled supply of combustion air. In addition, HVAC designers must ensure that the supply of combustion air is not contaminated by other sources, such as exhaust vents or air-borne pollutants.
By considering combustion air in ventilation design, HVAC designers can help to ensure the safe and efficient operation of fuel-burning appliances, and protect the indoor air quality and thermal comfort of buildings.
Combustion Air & Ventilation
Condensation and ventilation are related in the context of building design and HVAC systems. Condensation occurs when moist air comes into contact with a surface that is at a lower temperature, causing the moisture in the air to form droplets on the surface. In buildings, condensation can occur on windows, walls, and other surfaces when the indoor air is too humid and the surfaces are too cold.
Ventilation is a process that involves the supply of fresh, outside air to a building and the removal of stale, contaminated air. In buildings, ventilation is typically provided by mechanical ventilation systems, such as exhaust fans or air-to-air heat exchangers. Ventilation is important for maintaining indoor air quality and thermal comfort, as well as reducing the risk of condensation and other moisture-related problems.
When designing HVAC systems for buildings, designers must carefully consider the relationship between condensation and ventilation. By providing adequate ventilation and controlling the humidity levels in the indoor air, designers can help to prevent condensation and the associated problems, such as mold growth and damage to building materials. This can help to ensure that buildings are comfortable and healthy for occupants, and free from moisture-related issues
Condensation and Ventilation
What is a Heat Recovery Ventilator?
A heat recovery ventilator (HRV) is a mechanical ventilation system that is used to remove exhaust air, and supply fresh outside air to a residential home, while recovering the energy potential of the exhaust air. They are often the principal exhaust fan for the home.
Unit(s) can be installed as fully ducted or as simplified connection. HRVs are used in all new homes and extensive renovations in Ontario.
What is a fully ducted HRV?
A fully ducted HRV has its' own independent distribution system (ducting) . Supply and return outlets are placed in locations across the home. Exhaust outlets may be used for many building code mechanical ventilation requirements including: bathroom exhaust fans, and kitchen exhaust hoods (with some limitations).
A simplified HRV uses a shared distribution system. This system employs the use of ductwork installed for the heating and cooling system. Supply and return ducts are attached to the duct system, and the HRV. Exhaust air is removed from the return air trunk, and fresh air is introduced to the supply side of the distribution system.
HRVs work by using a heat exchanger to transfer the heat from the outgoing, stale air to the incoming, fresh air (or vice versa in the cooing season) This allows the HRV to provide a supply of fresh air to the building, while minimizing heat loss and reducing the need for heating or cooling. Supply and exhaust air never mix within the system.
HRVs are typically installed as part of a building's HVAC system, and are controlled by thermostats or other sensors and switches. HRVs can be used in a variety of ventilation configurations, such as supply-only, exhaust-only, or balanced ventilation..
HRV Venting Code Ontario
9.32.3.4A of the Ontario Building Code specifies the minimum size of the homes principal exhaust fan. The size is determined by the number of sleeping quarters within the building. HVAC Designers use this along with HRAI Mechanical Ventilation Design Summary, to determine the Total Ventilation Capacity.
9.32.3.4B of the Ontario Building Code specifies the minimum size of the ducting attached to the homes principal exhaust fan. The size is determined by the number of sleeping quarters within the building. HVAC Designers use this along with the HRAI Digest, to size HRV Ducting.
Ducting can be sized via 9.32.3.4 B of the Ontario Building Code.
HRV ducting can be sized via 9.32.3.4 B of the Ontario Building Code.
Single or multiple exhaust ducts serving the principal exhaust fan required by Sentence (1) shall be sized according to Part 6 except that they may be sized according to Table 9.32.3.4.B. where,
(a) the longest total duct length, from intake grille to outdoor hood, does not exceed 12 m, and
(b) the number of elbows does not exceed 4,
but, in any case, they shall not be smaller than recommended by the manufacturer of the fan.
How do you size ducting for an HRV?
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