11/16/2015

Challenges to Ventilating Apartment Buildings

Apartment buildings that house multiple families come with unique challenges to ventilation, especially if the owners and tenants wish to keep the building energy efficient. If proper controls are not in place, air may be transferred from one apartment to another, making it more difficult to cycle out stale air. The stack effect, air flow, and external versus internal pressure also come into play.

Curtain Walls Can Allow Thermal Bridges and Air Leaks

The typical curtain wall construction used in many high rise apartment buildings may need to be altered to allow adequate ventilation while retaining energy efficiency. Steel framing often allows thermal bridges that leak heated or cooled air and breach the building envelope. In order for mechanical ventilation to work optimally-and to keep outdoor pollutants out-certain construction elements may need to be geared towards maintaining a tight building seal.

Stack Effect Can Impact Ventilation

Stack effect is the movement of air into and out of buildings resulting from a difference in air density between outdoor air and indoor air. Factors such as temperature and moisture differences may contribute to the stack effect. Additionally, in apartment buildings, stairwells and elevator shafts may contribute to the stack effect, while floors and partitions can mitigate it. Design considerations and mechanical ventilation may help to minimize the stack effect for best ventilation and efficiency.

Ventilation Increases Air Conditioning Needs

When an apartment building is designed to have a tight building seal that is in line with modern expectations and adequate ventilation is installed, it generally increases air conditioning needs. Cycling stale air out results in the cycling out of the air that has already been heated and humidified or cooled and dehumidified, increasing energy needs. A solution to this issue is to install individual ERV or HRV systems in units in order to decrease energy losses while maintaining adequate ventilation.

Holes or Air Leaks in Ducts Affect Building Seal

In many apartment buildings, there are air leaks around exchanges, exhaust points, and registers. There may also be holes in the ductwork that are difficult to detect without doing a whole-building inspection. In order to optimize ventilation in the building and to reduce energy losses, it is imperative to inspect ductwork and existing ventilation systems in order to detect and seal leaks and holes. In some cases, it may be necessary to replace older systems or shoddy ducts.

Roof Fan Issues Affect Indoor Air Quality

When roof fans are used to ventilate tall apartment buildings, it can help to utilize the natural building airflow in order to vent stale air, having an increased advantage during the summer when the warmest air is pushed up and out. Unfortunately, when a roof fan is shut off it can have a negative impact, allowing pollutants to cycle between units. When building owners shut off roof fans at night, it can result in extremely poor indoor air quality in units, as most units are occupied at night.

Dirt and Tenant Habits Impact Ventilation Systems

In many apartment buildings, air ducts may not be cleaned for years or ever throughout the life of the building. Dirt, grease, and other contaminants may clog ducts, reducing airflow and impacting air quality. In order to keep dust and allergens out, tenants may block registers, further reducing ventilation system effectiveness. By addressing these needs and keeping air ducts clean and free from obstruction, building owners help to ensure the health and well being of occupants.

Decentralized Solution to Challenges

One solution that may counter many of the issues presented by a centralized ventilation system and shared ducts is to install decentralized HRV or ERV spot balanced ventilation systems in individual units. This will help to optimize the fresh air flow in each apartment, mitigating inefficiencies and reducing concentrations of pollutants. This will also help to protect tenants in one unit from VOCs present in other units.