Duct systems can be a very sensible way to heat and cool and office space or a large home. They push air throughout the building, via ducts, and blow that air into the various rooms to ensure a consistent climate throughout the space. That is the concept behind them anyway.
Unfortunately, not all duct systems are as efficient as they could be, and often home owners or those working in the office buildings will complain about particularly hot or cold rooms. Worse yet, many find that the energy bills related to the less efficient duct systems are high.
There are a number of reasons why a duct system may be expending more energy than necessary. Some of these reasons can also explain the presence of cold- and hot spots.
Conduction is a big culprit. The air, as it moves through an uninsulated duct, will try to equalize with the temperature of the space outside the enclosure. Thus, as the air moves throughout the home, the rooms furthest from the heating or cooling source will receive less benefit than those closest to it. Proper insulation, of course, can help ebb this problem and improve energy efficiency of the system.
The fans in the duct work are also big energy users. When they are not running properly, the pressure in the ducts can become out of balance, resulting in too much- or too little air flow in particular areas of the building. Duct static pressure transducers are highly recommended. They will measure the amount of pressure in the HVAC ductwork, and, using this information, they can control the fan speed. The desired pressure is set at the time of installation, and the fans will run to maintain that preferred pressure. This can cut energy bills by ensuring that fans are only running when absolutely necessary.