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tures. Moreover, the distribution of water 100° C
presents some difficulties as to the storage of
water for the regulation of the daily load vari-
ations.
The decision as to the type of system to be
preferred will in general depend on circum-
stances. At the conditions in Reykjavik a com-
bination of two-pipe and single-pipe systems
appears to be the most economical method of
distribution. The lreat content in the high-
temperature water at temperatures above 90° C
is utilized in areas of high consumption density
by means of two-pipe directly coupled systems.
The remaining available heat it conveyed to
single-pipe direct systems in areas with a rela-
tively low consumption density.
(b) Loacl regulation and heat-storage.
The demand on district heating systems varies
because of the daily rythm ancl also because of
variations in the outside temperature. Iceland
has a typical oceanic climate. The summer is
cool but the winter relatively mild. The annual
mean temperature is 4° C whereas the mean for
January is as high as zero °C. On the other
hand, the temperature is unstable and conside-
rable fluctuations are relatively frequent. But
teinperatures below minus 10° C are rare.
Experience obtained in the Reykjavik area
has shown that the heating systems have rarely
to meet the demand due to lower daily average
outside temperatures than about minus 6° C.
As a matter of course, the outside temperature
may for short intervals drop considerably be-
low minus 6° C, but the intervals are generally
not longer than a very few days at most. The
heat capacity of the walls of the houses prevents
the room temperature from responding com-
pletely to the variations of the outside tempera-
ture. Moreover, a somewhat lower inside tem-
perature can be tolerated for short intervals
occurring relatively rarely.
As the annual rnean temperature for the
Reykjavík area is about plus 4° C the maximum
daily average load on the district systems will be
about 70% above the annual mean load. A daily
variation corresponding to a maximum to rnean
load ratio of 1.3 is superimposed on this vari-
ation. The district systems have to be preparecl
for meeting the variations in the demand due to
these causes. Several methods are available.
Hot water storage in tanks appears to be the
most efficient way of meeting the daily variation.
Tlie volume of the tanks has at most to corre-
spond to about 20 to 25% of the total daily
consumption at the minimum outside tempera-
ture.
The long-period fluctuations can not be met
by means of waterstorage in tanks of the ordi-
nary type. The volume has to be of the order
of two per cent of the total annual flow which
is excessive for surface tanks. Underground stor-
age is a theoretical possibility which appears to
have some merits.
However, the two main methods of meeting
the long-period fluctuations are, firstly, a vari-
able pumping of the boreholes and secondly
the application of oil-fired booster heaters.
The application of pumps in the boreholes
has already been discussed. This method appe-
ars to be relatively inexpensive but it is at pre-
sent limited to borehole temperatures up to
150° C. Pumps of a special design are required
for higher temperatures. Hovever, this limit-
ation is not serious as the high-temperature
thermal areas have a very abundant supply of
tliermal water ancl pumping is largely unneces-
sary in these areas.
The application of oil-fired heaters in order
to boost the temperature of the water during
cold periods is a reladvely efficient method.
This method has been appliecl in the Reykjavik
Municipal District Heating Service. The maxi-
mum load to be carried by the thermal water
corresponds prefarably to an outside tempera-
ture of zero °C or slightly above. The addition-
al loacl at lower outside temperature is carried
by the booster heater.
6. DOMESTIC AND INDUSTRIAL HEAT-
ING IN THE REYKJAVIK AREA.
(a) Present distribution cosl.
During the first decade of operation the
Reykjavík Municipal District Heating Service
served approximately 30,000 inhabitants of
the city. The system depended almost entirely
on the Reykir thermal area as the source of
hot water. A double 14 inches i. d. pipeline
of a length of 16 km connects the thermal area
to the city.
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