Jökull - 01.12.1961, Síða 54

er above 100° C is preventecl from flashing and,
also, that the boreholes can be pumped according
to demand, at least to a certain degree. During
periods of heavy demand the pumping exceeds
the free flow of the holes. On the other hand,
the flow is below the free flow during periods of
low demand. In this manner the storing capacity
of the thermal area is utilized which is of great
economic importance. In fact, as will be dis-
cussed below, this appears to be the most ef-
ficient method of loadregulation.
This methocl is, however, relatively new in
Iceland ancl has to be tested in the long run.
At this juncture it appears aclvisable to limit
the pumping of the boreholes to a certain ratio
of the annual free flow. Over-pumping may lead
to an infiltration of cold water.
4. MAIN SUPPLY PIPE-LINES.
The great thermal areas in Krýsuvik and
Hengill which are located 30 km south re-
spectively 45 km east of Reykjavik are poten-
tial sources of natural steam at pressures up to
15 atm abs and high-temperature water up to
a temperature of 200° C, or possibly more. The
exploitation of these areas for heating in the
Reykjavik area involves the piping of low-press-
ure steam or high-temperature water over con-
siclerable distances. The question arises as to
the most efficient and economical piping system.
Three factors are of basic importance. First,
domestic heating constitutes the main market in
the Reykjavik area. Hot water is therefore to
be preferred as the medium distributed to the
consumers in the city. Second, the boreholes
produce wet steam with a water/steam ratio be-
tween 4 and 6. There are consequently large
quantities of liigh-temperature water available.
Third, the specific volume of low-pressure steam
is very unfavourable ancl implies large cross-
sections of the pipelines.
These factors iniply that hight-temperature
water is much to be preferred as the medium
for piping over distances more than a few kilo-
meters. Water temperature in the range 160 to
180° C or possibly up to 200° C are to be app-
lied. Heated surface water is to be preferred
to the thermal water due to the chemical im-
purities in the latter.
5. DISTRIBUTION SYSTEMS.
(a) Type of clistribution system.
Practically all houses in Iceland have central
heating systems. The systems in the smaller
houses burn gas-oil whereas the larger houses
use a lower grade of fuel oil. The central systems
are generally designed for a maximum riser
temperature of 60 to 80° C. This design temp-
erature is, however, considerably above the
real maximum occurring af ordinary conditions.
On the other hand, thermal water is available
from some of the thermal areas at temperatures
considerably above the maximum riser tempera-
ture.
This high-temperature water can be used for
domestic lieating in ordinary system in two ways.
Firstly, by means of two-pipe circulating systems
connected to the house systems either directly,
or indirectly through heat-exchangers. The
temperature of the outgoing water is controlled
by the the rate of circulation and is kept at a
maximum of 90° C. Secondly, by nteans of
one-pipe distribution systems connected indi-
rectly through heat exchangers to the house-
systems. The temperature in the riser is then
controllecl by automatic equipment which opera-
tes on the intake flow.
The application of lieat-exchangers has the
advantage that the house-systems are not ex-
posecl to the thermal water. Some thermal waters
are corrosive and form scale in pipes and radi-
ators. Tliis is rather serious mainly in the case
of the house-systems as the pipes are generally
built into the walls of the houses. Moreover,
the heat-excliangers may be necessary because of
pressure conditions.
On the other hand, the heat-exchangers re-
present additional investment and the efficiency
of the system may be slightly affected. In a single-
pipe system the temperature drop through the
exchanger is lost ancl this may reduce the over-
all system efficiency by as much as 5 to 10%.
In a two-pipe system, on the other liand, the
heat-exchangers do not induce losses to the
system if the effluent hot-water is applicable
in other heating systems.
The tap-water supply is of some importance.
The distribution of water with temperatures
above 100° C may make special heat-exchang-
ers either for the heating of tap-water or the
cooling of thermal water to tap-water tempera-
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