HVAC GLOSSARY - G

---

Gas Sorption: Devices used to reduce levels of airborne gaseous compounds by passing the air through materials that extract the gases.

Geothermal Energy: Natural heat from within the earth, captured for production of electric power, space heating or industrial steam.

Geothermal Equipment: Heat pumps that use the ground to transfer heat to and from the refrigerant in the unit. The unit circulates water through a heat exchanger in the to a closed loop buried in the ground or by pumping water from a well through the unit.

Geothermal Gradient: The change in the earth's temperature with depth. As one goes deeper, the earth becomes hotter.

Global Climate Change:Gradual changing of global climates due to buildup of carbon dioxide and other greenhouse gases in the earth's atmosphere. Carbon dioxide produced by burning fossil fuels has reached levels greater than what can be absorbed by green plants and the seas.

Greenhouse Effect: The presence of trace atmospheric gases makes the earth warmer than would direct sunlight alone. These gases (carbon dioxide [CO2], methane [CH4], nitrous oxide [N2O], tropospheric ozone [O3], water vapor [H2O], and chlorofluorocarbons) allow visible light and ultraviolet light (shortwave radiation) to pass through the atmosphere and heat the earth's surface. This heat is re-radiated from the earth in the form of infrared energy (longwave radiation). The greenhouse gases absorb part of that energy before it escapes into space. Thus, the greenhouse effect allows solar radiation to penetrate but absorbs the infrared radiation returning to space. This process of trapping the longwave radiation specifically is known as the greenhouse effect. Scientists estimate that without the greenhouse effect, the earth's surface would be roughly 54 degrees Fahrenheit colder than it is today -- too cold to support life as we know it. (See Global Climate Change).

Greenhouse Effect (Relating to Buildings): The characteristic tendency of some transparent materials (such as glass) to transmit radiation with relatively short wavelengths (such as sunlight) and block radiation of longer wavelengths (such as heat). This tendency leads to a heat build-up within the space enclosed by such a material.

Grille: An air terminal device with multiple passages for the air. Grilles Coverings for the ducts where they open to the conditioned space. (Same as Registers).