Heating and Cooling Info From Warmair.net
Self-Contained Units
Self-contained or PTUs (packaged terminal units) are labeled as such because
all of the machinery (condenser, furnace, evaporator coil, and
blower) is contained in one large cabinet. The most common are
the rooftop units. Heating only, cooling only, or heating and
cooling can be obtained from these machines. Some manufactures
design them with interchangeable panels that allow ductwork to
be attached to the bottom for rooftop applications or to the sides
for outdoor location of the unit and through the wall ductwork.
Heat can be from any fuel (gas, oil, electricity, or heat pump), and air
conditioning will be electric. Designed originally for commercial
applications, their versatility has created a demand for residential
use and smaller, quieter machines are produced for the home. With
the help of a fresh air hood and enthalpy controls, air conditioning
demands can be met when outdoor air temperatures are low by means
of drawing fresh air in and ducting it to the space, reducing
the demand for electricity by keeping the compressor idle. As
the air temperature rises, the enthalpy control will mix fresh
air with re-circulated air as it turns the compressor on for needed
cooling.
Rooftop installations that are ducted out of the bottom require a curb, which not only
raises the unit up off the roof but has framework to support and
fasten the ductwork to.
The heat loss and gain calculator in this site can be used to size a unit,
but in commercial applications other major factors such as lighting,
fresh air, delivery doors, and machinery operating within the
space are critical, and therefore not recommended.
Copyright © 1999 Warmair.com, Inc.
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