Condensate from the heaters is returned through
a condensate meter to a small storage tank and
pumped back to the power plant by an automatic
pump.
Where steam is supplied for industrial purposes, pure condensate is collected as far as possible
and pumped back to the power plant. In a few
cases where the danger of contamination is considered large, evaporator plants have been installed
at the customer, thus keeping the two systems
separated.
From our experience returning the condensate
to the power plants has been a paying proposition
so far as it is normally clean enough to be used as
boiler feed water. In the older plants up to 640
psig pressure this system has operated for a number
of years' with no difficulties. In the new high-pressure plant, llO kg/cmz (1562 psig), which has
been in operation now for six years, there has been
some difficulties in keeping the water clean enough,
mainly, we believe, due to the fact that so many
new heating lines have been placed in service. A
very close check must be kept on each returning
condensate line, and at the least sign of contamination the condensate is dumped until the fault
is located and corrected. To reduce the possible
loss of condensate we have in one section installed
two condensate lines for each outgoing steam
main, one line being used for condensate that is
believed to be clean under all cirmustances, and
the other for condensate that may be contaminated.
Our records for Svanemollevaerket show that for
the last year about 92 per cent of the condensate
was returned.
Warm Water System
The warm-water system is operated with an
outgoing temperature varying between 70 and
ll5 C ( 158 and 239 F) depending upon the
weather. The minimum temperature is determined
from the desired temperature of the warm-water
house service and may be carried for about half
the year. In mild winters the temperature need
not be above about 95 C (203 F) and even in
severe weather temperatures above 100 C (212 F)
will be necessary for short periods only.
The amount of heat sent out is regulated by
varying the temperature and the volume of water
circulated.
The water is circulated at such pressure that
it may be used directly in the radiators of the
houses; the maximum allowable pressure is 6. 5
kg/cmz (92 psig) and the mean pressure of the
system, i.e. the average of the pressure in the outgoing and returning pipes, measured at the station,
is kept at about 3. 5 kg/cmz (50 psig). In some
older installations the radiators are not capable
of withstanding the maximum pressure of 6. 5
kg/cmz with a reasonable degree of safety; in such
cases a pressure-reducing valve is installed. Radiators are now available, both in cast iron and steel
plate, which are tested at 10 kg/cmz ( 142 psig)
pressure, and which are used for all new installations served by district heating.
APRIL) 1959
Installation in a mulfistoM!/. "uileling witll p-,ump-, circulation.
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FIG. 5-lnstallation i·n a Multistory Building
with Pump Station Circulation.
Fig. 5 shows a diagram of the installation in a
multistory building with pump circulation. Water
from the district heating mains enter at A . A
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branch is taken off to the storage heater for house
service water and next the water enters the circulating system to the radiators. If the radiators are
of the old type, which may not be able to stand
the full pressure, a pressure-reducing valve (G) and
an automatic shut-off valve (H) are installed. This
last valve will shut off the line by increased pressure in case the pressure-reducing valve fails.
The temperature of the house service water is
regulated automatically by thermostats (Ez) in the
service-water tank and in the return line.
The temperature of the incoming water may
be higher than required for the water to the radiators, the system, therefore, is equipped with a
recirculating connection (C) through which the
returning water may be recirculated to regulate
the water temperature to the radiators. Regulation
is accomplished by a valve (E ) thermostatically
3
controlled by the temperature of the water to the
radiators. If desired, the system can be made fully
automatic, the temperature of the circulating water
being controlled by outside temperature and the
temperature of different sections of the building
(for instance, north and south side). As mentioned
before, water is sent out with a maximum temperature of 115 C (239 F). This relatively high temperature, which is too high for direct circulation, is
possible only because of this recirculating device.
The advantage of the system is that it enables an
increased cooling of the circulating water, thus
reducing-for a given sale of heat-the volume of
water circulated, the size of street mains as well
as the power for pumping. In the contracts it is
stipulated that the cooling' of the water, i.e. the
temperature difference between incoming and outgoing water, at the customer shall be at least 25 C
(45 F) and that the temperature of the return
water must not exceed 70 C ( 158 F). The return
water is metered at D and leaves the customer at
Az• Two meters are shown in the diagram, one
for winter and one for summer use. Fig. 6 shows
a photo of such an installation.
