Proper ventilation and indoor air quality (IAQ) in buildings are crucial to the health of occupants, and this is especially true for homes, where we spend more than half of our lives inhabiting. Therefore, it is recommended by ASHRAE in its Standard 62.2-2016 - Ventilation and Acceptable Indoor Air Quality in Residential Buildings that homes receive a minimum air change rate of 0.35 air changes per hour (ACH), but not less than 15 CFM per person (7.07 l/s per person).
ASHRAE also suggests intermittent (occupant-controlled) exhaust capacities for kitchens and bathrooms to help control pollutant and moisture levels in those rooms.
ASHRAE also notes that "dwellings with tight enclosures may require supplemental ventilation supply for fuel-burning appliances, including fireplaces and mechanically exhausted appliances.
Ventilation
In the baseline model the ventilation strategy is specified for the entire project/home, at once, making the process straightforward.
To start out, confirm that the Baseline values People Outdoor Air Rate (CFM/Person) and Area Outdoor Air Rate (CFM/ft²), automated for the ventilation calculation method for the project-specific energy code, are correct. For example, the outdoor airflow rate (Vbz) specified by ASHRAE 62.2 is composed of people-related sources (Rp) and area-related sources (Ra). These values can be extracted from Table 6.2.2.1:
As shown in the table above, for residential dwelling units:
People Outdoor Air Rate = 5 cfm/person
Area Outdoor Air Rate = 0.06 cfm/ft²
Infiltration
Next, confirm that the Baseline Infiltration (CFM/ft²) rate specified is representative of the conditions desired for the home. Typically, a high infiltration rate will lead to higher an EUI for buildings in non-temperate climates. Since outdoor air leaking into a building constitutes a large part of the total space-conditioning load, in more extreme climates the impact becomes more pronounced. As a result, it is recommended by many global standards, such as Passive House, to make buildings as airtight as feasible, while considering the effect that this will have on indoor air quality and the mechanical ventilation systems that serve the building. A tighter enclosure must be accompanied by mechanical ventilation or a combination of mechanical and natural ventilation strategies to ensure there's an adequate supply of fresh outdoor air entering the home.
The platform uses EN 15242 Ventilation for buildings - Calculations methods for determination of air flow rates in buildings including infiltration as the methodology to calculate the impact of infiltration on building energy. Typical infiltration rates from EN 15242 Annex B Table B.1 for a pressure difference of 4 Pa are presented in this table:
Please note that infiltration rates are often reported at different pressures, such as 50Pa or 4Pa. To convert between different pressures the power law equation can be used.
Since a tighter enclosure leads to less heat loss it is a recommended energy saving strategy. To model the low leakage level adjust the infiltration rate to the designed value, for example:
Infiltration = 0.05 cfm/ft² (0.25 l/s/m²)
Existing homes typically have higher leakage levels; the older the home, the higher the infiltration. In this case, use the average or high leakage level infiltration rate from the table above to best simulate the conditions for your residential project.
Passive Ventilation
One of the unique features of residential buildings that distinguishes them from other building types is the ability to easily implement passive natural ventilation due to the abundance of operable windows. To simulate this, the Baseline page includes inputs Ventilation Type and Ventilation Control, which may be used to specify the set of conditions representative of a typical naturally ventilated home.
The input Ventilation Type has three options: Mechanical, Natural, and Combined. To simulate passive ventilation, choose either Natural or Combined, depending on what works best with the project's climate conditions. Homes in extremely hot or cold climates should not depend on natural ventilation and should instead be entirely Mechanical.
Natural ventilation relies entirely on the wind to naturally ventilate the home and is best for temperate climates. In coastal climates, many seaside buildings are designed with large ocean-facing windows to take advantage of cooling sea breezes. For drier climates, natural ventilation involves avoiding heat buildup during the day and ventilating at night.
Please note that a fully naturally ventilated building doesn't necessarily mean better indoor air quality. Poor atmospheric air quality resulting from forest fires, air pollution, etc. should be dealt with using supplemental air filtration devices when necessary.
Combined ventilation is a combination of both natural and mechanical ventilation, meaning that when the natural ventilation flow rate is too low, mechanical systems will activate. This option is best for non-temperate climates that experience a few temperate months where natural ventilation is possible.
Ventilation Control
The input Ventilation Control has three options: Demand Control Ventilation, Always-On, and Off During Unoccupied Hours. In order to best answer specify this input for homes or apartments, a series of assumptions must be made:
Homeowners have complete control of the thermostat and ventilation;
In almost all cases, the ventilation fan will not always be on. Homeowners typically activate the ventilation fans mostly when there's a need for heating or cooling;
Homes are assumed to always be occupied to some degree.
Given these assumptions, we recommend choosing Demand Control Ventilation as this best simulates the expected dynamic behavior.
Fan Energy
The input Specific Fan Power has four available options, all of which are described in the linked article. In most cases, residential buildings use either Local Ventilation (e.g. Window/Wall/Roof Units) or Other Local Units (Fan Coil Units) to ventilate the space, depending on what type of ventilation system is installed.