The Substation; Abbreviations; Definitions - Honeywell AUTOMATIC CONTROL SI Edition Engineering Manual

The transfer medium is generally hot water at temperatures up
to 200 C and pressures up to 20 bars (2000 kPa). The optimum
operating conditions, temperature and pressure, depend on the
structure and dimensions of the network and the heat source. The
water temperature is generally limited to 130 C on the supply
side. In fact, many networks now keep the supply temperature
under 80 C allowing use of lower cost equipment and fewer safety
devices. See HOT WATER DISTRIBUTION SYSTEMS and
HIGH TEMPERATURE WATER HEATING SYSTEM
CONTROL.
Outdoor Air Temperature Control reduces the supply
temperature in a network with increasing outdoor temperature.
The Return Water Temperature in a DH Network is controlled
to not exceed either a fixed or variable temperature level.

THE SUBSTATION

Substations house heat exchangers which transfer the
required heat from the distribution network to individual
building heating networks (customer). In some cases, a large
heat exchanger station (HES) is required between different
types of networks. The HES transfers heat from high power
primary networks to smaller secondary networks with lower
temperatures and pressures.
A DH system only works efficiently if all components are
matched to one another. The heat source must deliver the
required heat at the lowest cost level, 365 days a year. Heat
demand as a function of the day of the week, time of day, and
weather conditions must be predicted in order to manage the
heat supply in the most efficient manor. In combined heat and
power (CHP) plants the electrical power generation must also
be considered.
Managing a system requires highly sophisticated dedicated
software and highly reliable control equipment. The software,
which includes demand prediction and total energy manage-
ment functions, plays an important role in the efficiency of
CHP systems.

ABBREVIATIONS

CHP — Combined Heat & Power.
DH — District Heating.
DHW — Domestic Hot Water.
ESD — Emergency Shut Down systems
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CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS
381
HES — Heat Exchanger Substation.
HEX — Heat Exchanger.
HTS — Heat Transfer Station.
OAT — Outdoor Air Temperature.
PRF — Primary Network Return Flow.
PSF — Primary Network Supply Flow.
RT — Return Water Temperature.
SRF — Secondary Network Return Flow.
SSF — Secondary Network Supply Flow.

DEFINITIONS

Booster Pump station: Maintains sections of a network (return
or supply pipe) in required pressure conditions. Used
in long networks or highly elevated sections.
Combined Heat & Power: Combines production of electricity
and heat for space (buildings) and processes (industrial)
Domestic Hot Water: Water controlled at a constant temp-
erature suitable for use in showers and hand washing
stations.
Differential Pressure Controller: Prevents too low or too high
hydraulic pressure at the building heat exchanger
substation. This improves the control performance of
the station.
Heat Exchanger Substation: Compact Station, controls the
radiator and DHW loop in a building.
Heat Exchanger: Also called a convertor, transfers heat from
the primary network to a secondary network.
Heat Surface Factor: A value corresponding to the
effectiveness of radiating surface. The value depends
upon the shape, size, and color.
Heat Transfer Station: Controls flow, pressure and temperature
in sections of a primary network.
Primary Network: Supply and return pipe for heating medium
(hot water or steam) from the heat/power plant to the
consumer heat exchanger.
Secondary Network: Supply and return pipe for heating
medium (actuator) from heat exchanger to radiators
or tabs.