The maximum load varies with the severity of
the weather, and reaches a value of 0.8 times the
total connected load in severe winters (-15 C).
About 85 per cent of the heat sold comes from
power-heat generation. For the fiscal year 1957/58
the total sale of heat was 783,000 . 106 kcal
( 3,121,000 . 106 Btu) and the total back-pressure
power generated 126 million kwh. Considerably
more power is generated when using warm-water
circulation, as will be apparent from Table II,
which gives average data for the year 1957/58 from
two of our plants.
Table II
Warm Water
Distribution
Steam
Distribution
Average steam pressure at
turbine throttle. . .... kg/cm2 110
110 45
Average steam pressure at
turbine throttle ...... c
504
504 380
Average back pressure at
turbine exhaust .......... kg/cm2 9. 7
9. 7 10.0
Average steam temperature
at turbine exhaust. C
266
266 275
Average circulating water
temperature
outgoing
returning ..
.... C
..C
80
58
Power generated per
106 kcal heat sold.
kwh net 340
162 110
The power generated is net, that is after subtracting all auxiliary power and power for circulating pumps and condensate pumps. The figures
for the 110 kg/cm2 plant will be improved, as the
heating load increases, as the plant is laid out to
supply about 200 per cent more heat than is sold
at present.
The climatic conditions in the country are
such that the normal heating season has a duration of about 250 days, from the latter part of
September to about the middle of May. Extreme
cold weather is unusual, heating systems normally
being calculated on the basis of a maximum outdoor temperature of -15 C (+ 5 F). The approximate load duration curve for the heating system
is shown in Fig. 4; it is apparent that maximum
loads are only short peaks, and that loads above
50 per cent of maximum are probable in less than
1,000 hours per year.
Heat Distribution System
Heat is supplied for house heating and for
industrial purposes. Until some years ago steam
only was used for distribution except in two small
areas; but when making the investigation mentioned before we came to the conclusion that
"145
Duration curve for district heatin9. toad.
%connected load according to contracts
100
90
80
70
\
60 \
50
~
4-0
~
30
~
20
..........
r--..........
10
aa 1000 2000 3000 4-000 5000 6000
--r--...t--
7000 8000 87" 60
FIG. 4-Duration Curve for District Heating Load.
warm-water distribution should be used as far as
possible. Warm water gives a simpler piping system than steam (less expansion and no drainage
problems), and the maintenance costs of the system
are smaller. With combined power-heat generation a further advantage is obtained with warm-water distribution, as the kwh generated for a
given amount of heat sold is about twice that
obtained with steam distribution (see Table II).
The principal objection to warm water has so far
been the question of metering; with the meters
now available this problem should be solved.
While warm water with the temperature used
here is satisfactory for house heating purposes,
usually it cannot meet all heat requirements of
industrial undertakings, hospitals, and hotels. To
take care of this group of customers, the existing
steam distribution is being maintained, and is also
being further extended into areas, in which there
is a reasonable demand for heat at a higher temperature. Warm-water distribution is used in
residential districts. Only one service is available
in a district.
Stearn System
Steam is sent out from the plant with a pressure
varying between 8 and about 15 kg/cm2 (114 and
213 psig) , depending on the heating load, in order
to get the largest possible back-pressure generation.
Certain minimum pressures must be kept at certain
points in the distribution system. In order to
reduce condensation in the mains, steam is sent out
with a certain degree of superheat.
Heating of buildings is always done by warm
water. The steam is, therefore, supplied to a heat
exchanger, in which the circulating water is heated
up to the desired temperature. A storage-type
heater is used for preparing hot service water.
