IEEE Power & Energy Magazine - November/December 2021 - 99

ensure local stability of heat supplies,
local cooperative groups throughout
rural Denmark jointly financed and
managed local district heating plants.
In the small import-dependent country,
World War II-again-led to an
energy crisis. At some CHP plants,
heat-only boilers were constructed
as heat supply backup. After the war,
the existing district heating networks
were expanded to integrate this additional
heat production capacity. Coal
was still
the prioritized fuel
(see
" District Heating Technologies Improve "
and Figure 4).
1950s and 1960s:
The Welfare State and
Population Growth
In the decades after the war, many workers
and their families migrated to the cities
searching for work.
The Danish public sector grew in
the 1950s and 1960s, as did the role and
importance of the growing Danish welfare
state. All citizens, poor and rich,
District Heating
Technologies Improve
The very first district heating pipes
corroded easily. Insulation with min -
eral wool rectified this problem,
but this solution was expensive, and
therefore district heating was only
viable for large-scale end users such
as institutions and industry. In the
1960s, preinsulated district heating
pipes using a noncorrodible plastic
jacket provided the solution. Initially,
the heat tolerance of these pipes
was only about 90 °C. As this material-again-improved,
the heat
tolerance rose to approximately
120 °C. Some district heating suppliers
also advocated lower supply
temperatures in the 1960s. Lower
supply temperatures were subject
to less regulation and control. This
reduced the need for employees at
the heat generation plants and lowered
the price of district heating.
november/december 2021
were viewed as eligible for social welfare.
All through the country, municipal
institutions
were established.
Growing populations and urbanization
led to the growth of the suburbs,
and many of the new suburbs were
planned with district heating. Municipalities,
sometimes jointly, invested in
large centralized CHP plants. For the
end users, district heating provided
affordable, accessible, and convenient
heat supplies that required little in the
form of service and maintenance (Fi gures
5 and 6).
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.5 .6
1000
800
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R
600
500
400
200
300
300
200
TX-2
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13.8 - 0.48 kV
6%
100
80
60
40
50
20
30
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10
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4
5
6
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.1
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2
3
4
5 6 7 8 9 10
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4
5 6 7 8 9 10
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3
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5 6 7 8 9 100
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4
5 6 7 8 9 1000
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5 6 7 8 9 10000
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800
600
500
400
300
200
100
80
60
50
40
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1
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.08
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ieeepower & energy magazine
99
TIME IN SECONDS
17.58 1.90
18.71
0.15
TIME IN SECONDS
24.13
19.48
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IEEE Power & Energy Magazine - November/December 2021

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