GREEN BUILDING

Energy & Atmosphere

Material Conservation

Sustainable Building

Water Conservation

Indoor Air Quality

Third-Party Raters

HVAC Equipment Sizing and Balanced Ventilation Systems

Heating and Cooling systems are more complicated than they appear and bring other structural factors into play during operation. A well-designed system is more efficient, more comfortable, and saves energy. Proper equipment and duct sizing or radiant tube placement is critical to optimum performance and efficiency. Houses with oversized equipment will be just as inefficient in operation as undersized equipment, and both will result in equipment failure in a shorter time frame. Computer modeling of heating and cooling loads for each individual house as well as careful duct sizing or radiant floor tubing placement is essential for optimum performance. Where possible, each area that can be closed off should have cold air returns, while other equipment such as bathroom fans and stove hoods should be an integral part of the ventilation plan. A humidistat can be as valuable as a thermostat in a well-designed house.

Particularly with tight houses, indoor air can hold up to 10 times the amount of pollutants as the air outside. Because it is important to continuously swap stale interior air for fresh exterior air, a ventilation system that delivers outside air is required for a healthy home. Exhaust systems rely primarily on the removal of stale air, but this will depressurize a home. Exterior air is then forced into the home through any number of areas where the house isn't sealed as well as drive air through the walls. With an attached garage, this is frequently the least sealed area, and the garage will usually have more air pollutants than inside the house. A depressurized home should be avoided.

A supply-based makeup air system will conversely pressurize a home. While considered better than a depressurized home, this should be avoided in Michigan because of its propensity to drive moist air through the walls in the winter, causing condensation and mold growth within the exterior wall cavities.

The best type of ventilation system for our location is a balanced ventilation system. This type of system brings in fresh air and exhausts stale air continuously while balancing pressure between the interior and exterior of a house. It can be as simple as drawing makeup air for a forced-air furnace from outside. This is not considered an efficient method however, as cold, dry winter air must then be heated and moisturized at a considerable cost of energy. A better solution for balanced ventilation is the use of an Energy Recovery Ventilator (ERV) or Heat Recovery Ventilator (HRV). ERV's exchange both heat and moisture from stale air to fresh air, while HRV's only exchange heat. For our location, which is mostly heating, HRV's can save energy, but humidification of incoming air is then a separate process to keep enough moisture in the air to remain comfortable. ERV's will retain some moisture in the air while exchanging heat, and will not require a separate humidifier, however the system itself is more expensive than an HRV and a separate humidifier. ERV's also remove water from the exterior air during the cooling season. Since a significant portion of the energy in cooling a building comes from moisture removal, an ERV is more efficient for air exchange in the cooling season. These systems can also incorporate HEPA filtration equipment to maintain interior air quality. While they must be maintained and have the filters changed occasionally, it is a worthwhile investment that will pay for itself over time with energy savings and result in a healthier home.