The coronavirus outbreak raised awareness about the importance of healthy building interiors. This is key in the residential sector, especially when there are elders or children present. To create indoor spaces that are safe from COVID-19, their MEP design must ensure a quick removal of germs from the air.
Each building is unique, but there are many general requirements that must be met to prevent the spread of viral particles:
- High ventilation rates, to prevent the accumulation of viral particles in the air.
- A smart ventilation layout, ensuring that air pollutants are removed at the source, and not distributed to other building areas.
- Efficient filtering, since viruses are among the smallest airborne particles.
- Reliable disinfection methods, to destroy any germs that are not removed with ventilation and filtering.
These measures increase energy consumption in residential buildings. However, this effect can be compensated with energy efficiency measures. An efficient HVAC design directly reduces the cost of COVID-19 prevention, but measures that target other building systems are also effective.
Design your next residential building project as a safe space against COVID.
According to ASHRAE, homes are currently the safest places to avoid a COVID infection. While the risk is still present, it can be mitigated with several design features.
Preventing COVID with Effective Ventilation Design
ASHRAE gives two main recommendations to design a ventilation system that helps prevent COVID. Buildings should be ventilated with as much outdoor air as possible, to quickly displace any indoor air that gets contaminated with viral particles. The ventilation system should also minimize recirculation and air exchange among building areas, so that viruses and other germs cannot spread indoors. Even when there are no viral particles present, effective ventilation improves indoor air quality.
The local weather may limit how much ventilation can be increased. For example, a high outdoor airflow during winter may overwhelm the existing heating system. The same can happen to air conditioning systems during summer, if too much warm air is allowed into the building.
Reducing air exchange between rooms and recirculation is also important, especially in a dwelling where occupants work in different places. Also, consider that patients with mild symptoms of COVID-19 are often instructed to recover at home, and the ventilation system should ensure that airborne viruses are removed at the source.
The additional ventilation required to help prevent COVID increases energy consumption, but there are ways to compensate for this.
- When allowed by weather conditions, a residential property can use an airside economizer to achieve “free cooling”. This is possible when outdoor air has a cool enough temperature to replace air conditioning.
- HVAC systems can also use an energy recovery ventilator or ERV. This device exchanges heat between the air supply and air exhaust, and depending on its design it may also increase humidity. The end result is a reduction of heating and cooling costs, without sacrificing thermal comfort or air quality.
The Role of Filter Ratings in COVID Prevention
ASHRAE recommends an air filter upgrade to help prevent COVID infection, and they recommend a minimum rating of MERV 14. Note that a higher filter rating poses more resistance to airflow, and additional fan capacity may be necessary. In a MEP design for a new residential construction, the air handler and filter capacities can be selected optimally. However, fan capacities must be checked before upgrading filters in existing homes or apartments, or the new filters may restrict airflow.
High-efficiency particulate air or HEPA filters are even more effective than MERV 16 (the highest MERV rating), capturing 99.97% of particles with a diameter of 0.3 microns. However, not all ventilation systems can handle them, and for this reason they are often used as portable air cleaners. These normally have a clean air delivery rate or CADR, which is expressed in cubic feet per minute (cfm). When a portable air cleaner is used, its CADR must be high enough for the room where it will be used.
Which Is the Best Air Purification Method Against Covid
Ventilation removes viral particles, while filtration captures them. However, when it comes to destroying airborne germs, the best addition for HVAC systems is ultraviolet germicidal irradiation or UVGI. There are many air purification methods available, but UVGI is recommended by health authorities like the CDC, and engineering organizations like ASHRAE.
Ultraviolet rays can kill germs by destroying their DNA, but the best effect is achieved with UV-C radiation, which has a wavelength of 200-280 nanometers. The highest germicidal effect is achieved at 254.7 nm, and UVGI systems should be as close to this value as possible.
Some UVGI systems are designed to be installed in air handlers or air ducts, eliminating germs in the air when it passes through. Other UVGI systems are smaller and portable, designed to clean objects or specific surfaces.
The COVID-19 outbreak has changed design practices in the construction industry, and this includes the residential sector. Four main principles are being applied: increased ventilation with outdoor air, independent ventilation for rooms to avoid recirculation and mixing, enhanced air filtering, and ultraviolet disinfection.
Prevention measures for COVID are easier to implement in a new MEP design, since they can be built into the project. However, existing HVAC systems can also be upgraded, ideally with the help of a qualified engineering firm.