Energy efficiency and indoor air quality are desirable features in a building. Energy efficiency reduces the operating costs and environmental impact of buildings, while improved indoor air quality creates a healthier environment for occupants. Additionally, energy efficiency and IAQ can help score points toward a green building certification such as LEED. There is a common belief that energy efficiency has a negative impact on air quality and vice versa. However, both aspects can be improved along with smart design decisions.
HVAC systems are responsible for the majority of energy consumption in most residential and commercial buildings. Furthermore, indoor air quality depends heavily on HVAC performance. This means that good HVAC design is critical to achieving energy efficiency and IAQ in a construction project.
Reduce your energy bills and improve air quality.
Using ventilation effectively
Ventilation uses less energy than space heating and air conditioning. However, the amount of outside air supplied to a building affects heating and cooling loads. For example, if air handlers increase outdoor airflow on a hot summer day, the air conditioning system must work harder to compensate for the extra heat entering the building. The same applies to heating systems if ventilation is increased on a cold winter day.
According to the US Environmental Protection Agency, indoor air is typically 2 to 5 times more polluted than outdoor air, even in cities. Therefore, diluting indoor air with outdoor air is an effective way to reduce the concentration of atmospheric pollutants. As we spend 90% of our time indoors, maintaining indoor air quality is very important.
Lack of ventilation is detrimental to indoor air quality, but excessive ventilation represents a waste of energy. Ideally, a ventilation system should provide the right amount of air needed by a building. This can be achieved by meeting two design requirements:
- Measure indoor air pollutants and increase or decrease ventilation rates as needed.
- Ensure that the ventilation rate never decreases below the minimum values established in local building codes.
ASHRAE provides two methods for designing mechanical ventilation systems, the Ventilation Rate Procedure (VRP) and the Indoor Air Quality Procedure (IAQP). The VRP is based on prescriptive ventilation rates that were determined by ASHRAE after extensive laboratory testing. These fees are based on the type of building, its floor area and number of occupants. On the other hand, IAQP does not use prescriptive values and instead ventilation is controlled according to air quality measurements. IAQP has the potential to improve efficiency, as there is no minimum ventilation rate. However, many local building codes are based on the VRP because it is easier to use prescriptive values.
To optimize ventilation performance while meeting building codes, a hybrid design approach is possible. Minimum airflow rates are based on code requirements, but smart controls are used to adjust airflow based on air quality measurements. When ventilation rates are carefully controlled, building owners also save on heating and air conditioning.
Upgrading HVAC Systems to Improve Efficiency and IAQ
When energy efficiency measures are implemented without careful consideration, they can have a negative impact on indoor air quality. For example, if ventilation rates are arbitrarily reduced, indoor air pollutants may reach higher concentrations. However, with a professional energy audit, building owners can identify energy-saving measures that do not affect IAQ, or even measures that also improve IAQ.
Many ventilation systems are constant air volume (CAV) types, which means they always operate at full fan capacity. By converting them to variable air volume (VAV) systems, ventilation can be optimized with smart controls. Indoor air quality will not be impaired if ventilation control measures the concentration of atmospheric pollutants. The U.S. Environmental Protection Agency found that a ventilation upgrade from CAV to VAV can achieve annual energy savings of 10% to 21%.
Depending on the local climate, HVAC systems can also be improved with an air-side economizer or an energy recovery ventilator:
- An air-side economizer can determine when an increase in outside airflow will have the same cooling effect as an air conditioner. In these cases, the economizer supplies more outside air while reducing AC cooling output. Fans consume more energy to supply more air, but the air conditioning savings achieved are greater.
- An energy recovery ventilator exchanges heat and moisture between outside supply air and exhaust air. This measure can save on heating, cooling, humidification or dehumidification. When only heat is exchanged but not moisture, the system is called a heat recovery ventilator.
Airside economizers and ERVs are useful in buildings because they allow for greater ventilation while maintaining energy efficiency. However, the effectiveness of these measures changes depending on the local climate. It is recommended that professional energy modeling services study the performance of these measures before investing in them.
Improving indoor air quality is typically seen as a feel-good measure, but it also has a significant economic benefit. According to JLL Incorporated, one of the largest real estate companies in the world, payroll and other labor expenses are 10 times higher than utility bills in commercial buildings. This means that a 1% improvement in office productivity is comparable to a 10% improvement in energy efficiency and water efficiency. Because indoor air quality makes buildings healthier and more comfortable, it can directly improve productivity.
