Honeywell AUTOMATIC CONTROL Engineering Manual page 397

Functional principles:
The primary side consists of the supply and return lines, plus
necessary pressure reducing, regulating, and safety equipment.
This is self-regulating equipment which provides a given
differential pressure, absolute pressure reducing, and safety
close off functions.
The heat regulation unit (Fig. 130) provides the required
temperature by controlling the primary flow (A) or by mixing
the cooled return water with supply water (B). Different
configurations with two and three way valves can be used. In
the flow control configuration a fixed speed circulating pump
increases the pressure in the return line above the supply flow
pressure. In the temperature control configuration either a jet
pump or a three way valve is used.
SUPPLY LINE
RETURN LINE
CONTROL VALVE
A) FLOW CONTROL
Fig. 130. Two- And Three-Way Valve Configurations for a
Heat regulation Unit.
Jet pumps use the effect of injection, making a mechanical
pump unnecessary, thereby, saving electrical energy. However,
adapting and dimensioning jet pump applications to fit operating
conditions is difficult.
Control loops used in a direct substation:
– Supply flow temperature reset on outdoor air temperature.
– Return temperature limit.
– Time schedule functions.
– Night setback and frost protection.
CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS
THREE-WAY
MIXING VALVE
OR JET PUMP
CIRCULATING
PUMP
B) TEMPERATURE CONTROL
M11446
Small Substation For Multiple Family Buildings
Figure 131 shows a typical direct heat transfer substation.
DISTRIBUTION
TI
01
OUTSIDE AIR
PSF
PRF
Fig. 131. Small Direct Heat Transfer
Substation for Multiple Family Buildings
Table 9. Description of Figure 131 Reference Points.
Reference
TC Controller
TI 01 Outdoor air temperature sensor
TI 31 Room temperature
TIC 13 SSF temperature
Y 11 Actuator control valve PSF
Y 12 Circulating pump
387 ENGINEERING MANUAL OF AUTOMATIC CONTROL
SUBSTATION
CONSUMER
TC
TI
31
ROOM
Y
11
Y
12
TIC
13
M
SSF
Description
SRF
M11435