• Right-size and refresh HVAC:

  • Replacing an outdated mechanical system can have a dramatic impact on a home’s overall energy consumption. Legacy HVAC systems have multiple problems including; system over sizing and related cycling losses, combustion inefficiency, dilution air losses, poor combustion air supply, improperly sized ducts and insufficiently sealed (leaking) ducts. Distribution losses from leaking ducts alone amount to 5%-to-30% of the heat contained in the fuel being burned in the furnace or boiler.

    Improper system sizing is a common problem. Furnaces and boilers are designed to achieve their maximum efficiency at maximum output and load. When the heating load is less than the equipment output then the furnace or boiler cycles on and off, operating under a partial load. Numerous shorter cycles waste energy through greater off-cycle losses. Off-cycle losses occur when the heat exchanger in the furnace or boiler cools off. When the equipment recycles it must expend energy to bring the heat exchanger back up to temperature. System over sizing can occur as a result of improper heat-loss analysis by the original installer who may have used a “rule of thumb” approach to system sizing, or worse, the system may have been intentionally oversized in order to provide a reserve capacity or safety margin. Also, system over sizing can occur as a result of the homeowner dramatically altering the heat loss profile of the home through remodeling or through energy retrofitting.

    In a deep energy retrofit the performance of the building envelope is usually improved to the extent that the heat loss profile of the home is materially changed, requiring a reassessment of the size of the heating equipment. Also, in a retrofit many of the other inefficiencies, such as distribution losses, are also addressed and fixed allowing the furnace or boiler to operate more efficiently. When the retrofit is nearing completion, a very accurate measure of heat loss can be determined that, in part, uses the blower door test results and the heating equipment can be properly sized.

    Whole-house ventilation is one of the most important issues in residential energy efficiency. Most legacy homes are ventilated with ad hoc air leakage which has numerous problems, including: lack of total flow control; uneven ventilation; and, infiltration of unconditioned air. An important objective of a deep energy retrofit is to reduce the uncontrolled air infiltration and to control whole-house ventilation mechanically. The use of a balanced ventilation system that exhausts stale air and provides fresh air through a ducted distribution system does the best job of controlling pollutants in the home. Also, incorporating an energy recovery ventilator (ERV) allows the entering fresh air to recover the heat and moisture from the exhau