Indoor Air Quality
Technology
Make-Up Air Units
Make-up air units are an essential part of a building’s mechanical system, providing high quality air while improving the efficiency of the heating and cooling system.
They save money by reducing drafts, dust and dirt entering a building. They also replace exhaust air that is expelled through kitchen and bathroom fans, and they reduce odours by supplying a continual flow of fresh, ventilated air.
Natural gas-fired make-up air units come in many sizes and offer a variety of features to suit any application. The guts of the unit is a heat exchanger, one or more fans, and a series of filters and dampers. Together they extract heat and moisture from the air and use it to heat incoming fresh air before sending it back into the building. It is the most efficient way to provide a supply of fresh air into a building.
Electronic controls are used to design the right air mixture for each setting. The unit can feed 100 per cent outdoor air into the building or it can mix outdoor air with recirculated indoor air, to reduce heating and cooling costs.
Several additional features can increase the efficiency and performance of the unit:
-
Heat reclaim coils, sometimes known as heat wheels, recover waste heat and reduce heating costs.
-
High efficiency filtration maintains air quality while automated controls regulate temperature and air quality to minimize energy consumption. Two-stage, modulating gas valves provide the most flexibility to match the unit’s output to the needs of the building.
Make-up air units can be installed indoors or on rooftops, depending on the application. Roof top installations generally work better for high-rise buildings, while in walk-up apartments the best choice often is a utility room or attic.
For a list of contractors that install make-up air units, click here.
The most efficient, high-tech way to provide good indoor air quality is either a Heat Recovery Ventilator (HRV) or an Energy Recovery Ventilator (ERV). Both provide fresh, outdoor air while also recovering the most energy possible from outgoing air. The recovered energy is used to heat the air entering the building, reducing costs and making the whole system operate more efficiently.
Both types of ventilators are ideal for buildings that are sealed for energy-saving purposes. Although tightly sealed buildings are good at reducing energy costs, they are not good at providing good indoor air quality. In fact, without some kind of ventilation strategy, a sealed building quickly becomes a “sick building” in which people feel sick or lethargic because the air they are breathing is stale and dry.
HRVs and ERVs can capture between 70 per cent and 80 per cent of the energy in air that is exiting the building. The HRV captures only heat; the ERV captures heat and moisture. In either case, the captured energy is mixed with incoming air at a ratio that is ideal for the building and the seasonal weather conditions to provide optimum air quality at the lowest possible cost.
Building operators often choose an ERV if they live in an area with consistently cold winter weather. It captures some of the water vapour in the air, so there is less water in the vapour to freeze and lock up the core and exhaust vent to the outdoors. This can happen with a HRV because all the moisture in the air is exhausted outdoors.
The core of the heat exchanger in either system usually is made of aluminum, resin-impregnated paper, plastic or a combination of all three. Plastic and aluminum are relatively good heat conductors and prevent the transfer of water vapour and contaminants from entering the incoming air. They also tend to last longer than other materials.
Properly designed ventilating systems should be able to move at least 1/3 of an air change per hour (ACH) or 15 cubic feet of air per minute (CFM) per person.