The most common complaint among heating and cooling equipment owners relates to uneven temperatures between different floors of a home or office. Air stratification is a layering effect where large air pockets with varying temperatures remain intact, regardless of the action of the central HVAC system.
In some homes, the temperature difference between a basement and the second level can vary by as much as 20 degrees. In these instances, occupants on the bottom floor are uncomfortably cold and turn up the thermostat. When the heat from the furnace enters the living area and rises, the people on the top floor may open windows to provide relief from the accumulated heat. In the summer, the pattern is repeated in reverse as the upper floor residents lower the thermostat while those on the bottom floor are uncomfortably cold.
The Stack Effect
Air stratification in a building results from a combination of buoyancy and something called the stack effect. Heated air is naturally driven upward by its inherent lighter density. In the winter, rising heat exits through the attic as the structure acts like a large chimney. Make-up air is recovered through gaps, penetrations and breeches in the building envelope. In the summer, hot air is drawn through the attic into the living area as higher pressure seeks out lower pressure. As the warm air enters the building, colder air is driven out through perimeter openings.
In both cases, the HVAC equipment must work harder and longer to condition the indoor air. This usually results in higher utility bills and reduced comfort for the occupants in the affected areas of the building.
Heating Tips and Air Movement Solutions
The majority of problems associated with uncomfortable multi-level homes and offices originate with a poor air distribution design and the selection of inadequately sized equipment. There are a variety of energy-saving tips that can help improve the comfort of the indoor environment while maximizing the efficiency of the central heating and cooling system.
Duct Design: In both new construction and replacement systems, a contractor should always design the duct network according to ACCA Manual D standards. These complex calculations account for any structural impediments that might affect system performance. Friction loss and static pressure directly impact the quantity and velocity of the air that circulates through the system. Proper duct design considers the dimensions of the building and provides enough movement to regularly mix the air from all the rooms in the home.
Equipment Selection: New equipment should always be sized according to ACCA Manual J standards. Contractors that use outdated rule-of-thumb formulas should be avoided. Oversized equipment will short cycle, resulting in stagnant pockets of stale air and poor humidity control. Undersized equipment lacks the capacity and blower volume to meet the load requirements of the building. Over time, excessive wear on system components can lead to premature failure. Properly sized equipment will provide the precise amount of air movement needed to keep any individual room from becoming stagnant or uncomfortable.
Return Air Grilles: Unfortunately, many builders look to reduce construction costs by eliminating HVAC system features that directly affect comfort. Return grilles draw air through the system and encourage air movement by balancing pressures. Those interested in heating tips to improve overall circulation and energy efficiency should consider adding a return air pathway in rooms that are drafty or unusually cold.
Duct and Perimeter Sealing: Loose building envelopes and leaky ductwork allow outdoor air to be drawn into the living area every time the HVAC system engages. This condition is a result of negative pressure and can dramatically impact indoor temperatures, especially when the outdoor temperature is severe. Sealing gaps and penetrations will improve efficiency and help maintain a consistent temperature throughout the building.
Air Balancing: Cheaper supply registers do not have a mechanism for controlling the volume of air that passes through the device. A double-deflection register with an opposed blade damper can be adjusted to provide a precise amount of air for greater comfort and enhanced air movement. Quality HVAC contractors have special equipment to balance the entire system for optimal performance.
Consult an HVAC Professional
Knowledgeable heating and air conditioning contractors understand air distribution science and can offer a variety of energy-saving tips to maximize indoor comfort and minimize monthly energy costs.
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