Heating and Cooling Energy - Hydrogen and Fuel Cells: Advances in Transportation and Power - page 241

cooling demands of these different sectors may not occur at the same time
of the day, a single moderately sized system can meet the varying peaks of
the different sectors. If the ICES contains a short-term heat storage compo-
nent, such as a water tank, the system can operate continuously and at a
steady level around the clock with peak heat demand requirements drawn
from storage.
Conventional heating systems burn fossil fuels at high temperatures
to heat water to 120°F. Most district heating systems operate in the same
way. In these cases, when the hot water cools to 90°F or less, it is no longer
warm enough to supply heating. This remaining heat is eventually lost
to the environment. An ICES can recover this low-temperature heat that
would otherwise be wasted. This helps to increase system efficiency.
An ICES is often found to be economically competitive with con-
ventional heating systems such as furnaces and/or boilers in individual
buildings or district heating systems using fossil fuels. Capital costs are
a good deal higher than those of conventional systems, but ICESs have
lower energy requirements. Free environmental energy is substituted for
the burning of fossil fuels. In some ICESs, electricity consumption may
be greater than in conventional systems lacking heat pumps, but the total
consumption of all forms of energy is lower.
SOLAR DISTRICT HEATING
ACESs and ICESs rely on heat pumps and storage systems, and need
notable amounts of energy to operate. An annual storage solar district
heating system could supply most of a community's annual space heating
requirements with a minimum of nonrenewable energy.
An annual storage solar district heating system requires a heat store,
a collecting area and a distribution system. The storage can be either an in-
sulated earth pit or a below-ground concrete tank. Both have insulated con-
crete covers and are filled with water. Collectors are mounted on the cover
of the storage tank and are rotated during the day so they always face the
sun. During the summer, the collectors heat water for storage and for do-
mestic hot water. During the winter, the collecting system heats water that
is used directly for heating purposes. When additional heat is required, the
hot water stored in the storage tank or pit is used. Water is removed from
the top layers of the storage tank. The cooler used water is pumped back
through the collectors or into the bottom of the storage tank.
These systems cannot provide air conditioning so they are mostly