LEED stands for Leadership in Energy and Environmental Design, one of the most popular certification frameworks for green buildings with sustainable systems that go well beyond HVAC. The certification was developed by the US Green Building Council (USGBC), and internationally it is managed by Green Business Certification Inc (GBCI).
Before a building can get this certification, it must earn points across several performance categories, which focus on its energy footprint and environmental impact. The maximum possible score is 110, and at least 40 points are required for certification. There are also Silver, Gold and Platinum levels at scores of 50, 60 and 80, respectively.
Two of the performance categories are Energy and Atmosphere (33 points), and Indoor Environmental Quality (16 points). Considering that demand controlled ventilation (DCV) offers both energy efficiency and air quality, it can help building owners earn points under both categories. A building can also earn points for using innovative solutions that are not covered in any of the categories. Therefore, being creative with energy efficiency and indoor air quality can pay off in the form of extra credits.
The LEED framework also includes mandatory requirements. These do not accumulate points, but the building cannot be certified unless it meets all of them. Just like with credits, DCV can contribute with the compliance of some mandatory requirements. Although there are many mandatory requirements, the following are the most relevant for DCV applications:
- Minimum Energy Performance: The LEED framework provides several compliance options, but all are based on ASHRAE requirements or equivalent standards with USGBC approval. Since DCV improves the efficiency of HVAC systems, it counts towards this requirement.
- Minimum Indoor Air Quality Performance: The ventilation systems must sustain the minimum outdoor air (OA) flow rate established in ASHRAE 62.1, or EN 15251 and EN 13779 as alternatives. A DCV system can be programmed to always keep the minimum OA supply.
Using DCV to Save Energy
Air conditioning and heating normally represent over 50% of energy consumption in residential and commercial settings. However, these building systems are not always used efficiently. Consider that heating and cooling equipment is sized for the maximum number of occupants, and the full design capacity is not required when the building is only at partial occupancy. This includes ventilation systems as well, since the nameplate cfm are only required with a full building.
Having a variable air volume (VAV) ventilation system is beneficial for heating and cooling efficiency. If the building is not equipped with occupancy sensors, a CO2 sensor can be used to track occupancy, and the OA flow rate (cfm) can be reduced accordingly. With less oa airflow, there is a reduced heating load in winter, and a reduced cooling load in summer.
Consider that the Leadership in Energy and Environmental Design framework establishes minimum performance requirements to make a DCV system compliant. The system must meet ASHRAE standards or local equivalents, and pollution sensors and CO2 sensor arrays must be installed between 3 and 6 feet above the floor.
An airside economizer can achieve synergy with a DCV system and boost efficiency. When weather conditions are adequate, this device can provide a suitable indoor air temperature without a heating or cooling input, using only airing.
Sensors of occupancy have many applications in energy efficiency. In addition to being used for airing control, they can also be combined with lighting controls to turn of the lights when there are no people around. LEED points are also available for lighting quality.
Improving Indoor Air Quality with DCV
Up to 2 points can be earned with enhanced indoor air quality strategies, and this includes keeping the accumulation of key air pollutants below the specified threshold values. Although a conventional DCV system responds to occupancy and not pollutants in particular, this can be modified with the right sensors.
An enhanced version of DCV not only responds to occupancy, but also pollutants like volatile organic compounds and particulate matter. When an increase in the concentration of these substances is detected, airflow can be increased as well. If this feature is kept active at all times when the building is occupied, a safe air supply is guaranteed for anyone inside.
DCV is strongly recommended for building owners seeking a LEED certification: it can help meet the mandatory requirements, and it also contributes to earning points across two of the performance categories.
Consider that this certification focuses on the impact – energy consumption, environmental impact and human-friendly indoor spaces. Since DCV helps with both energy efficiency and indoor air quality, it is aligned with some main goals of the LEED certification.