Environmental Engineering Reference
In-Depth Information
suited to northern climates. This is because over the course of a year even
northern locations such as Canada receive as much sunlight per square
foot as Saudi Arabia. The problem is that most of the sunlight falls in the
summer when it is not needed for heating. In annual solar storage the sys-
tem collects heat in the summer for use during the winter. A large rock
cavern in Sweden provides district heating for 550 dwellings.
A housing project at Herley, near Copenhagen in Denmark, uses a cen-
tral solar collector and a large insulated water tank buried in the ground.
Solar heat provides most of the space heating requirements for 92 housing
units. When the temperature of the heat store falls below 45°C, heat is trans-
ferred with a heat pump, powered by a gas engine, which boosts the tem-
perature to 55°C. This process continues until the temperature of the heat
store has fallen to 10°C, at the end of the heating season. Waste heat from
the engine is also delivered to the heating system, and a gas boiler is used
as a back-up. In summer, the main heating system is shut down and 90% of
the domestic hot water requirements of the housing units are provided by
additional solar collectors on each of the eight housing blocks. This type of
system can also be implemented by a gas furnace. All of these systems oper-
ate in latitudes far to the north of American cities.
An annual storage solar district heating system is capable of supply-
ing 90% of the annual heating requirements for the homes in a community.
Depending upon the climate zone, the required collector area per house
can range from 70 to 300 square feet. This can be reduced if residential heat
loads are lessened through increased weatherization and the addition of
passive solar features.
Solar district heating offers a number of advantages over conven-
tional single-residence active systems. The collectors can be set aside in
an open area and problems with access to the sun do not arise. The heat
storage capacity is not constrained by space limitations in any one build-
ing and the storage tank can be as large as necessary. Since the system is
equipped for annual storage, solar collection is not dependent on the day-
to-day weather conditions.
HYBRID COOLING
Hybrid cooling plants may use a number of different technologies
to provide cooling. These technologies include electric chillers, absorption
chillers, engine-drive and/or dual-drive chillers, thermal storage systems
and the use of a water-side economizer cycle. Most of these seek to pro-
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