Honeywell AUTOMATIC CONTROL, Engineering Manual

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ENGINEERING MANUAL OF AUTOMATIC CONTROL
CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS
381
Fig. 122. Direct HTW to Domestic Hot Water.
Fig. 123. Indirect HTW to Domestic Hot Water.
In a storage converter, the tube bundle is immersed in the
bottom of a storage tank (shell) with capacity to provide for
large intermittent demands. There is little lag in transferring
heat from the tube bundle but because of the large capacity of
secondary water in the shell, the system provides more stable
control. Rate of change might be 20 to 50F per hour. Large
installations frequently employ a system circulating pump to
assure quick availability of hot water at remote usage points
and help eliminate stratification in the tank.
MULTIZONE SPACE-HEATING HTW
WATER CONVERTERS
Figure 124 shows a storage converter application. It is
controlled as a conventional converter with only the HTW valve
and pump interlock having special requirements because of
the heating medium.
Because the response rate of a storage converter is slow, the
storage capacity must be sufficient to supply any sudden
demands. Warm-up is the demand period where the converter
recovery rate becomes the determining factor for length of time
required for warm-up. Normally all other changes in a building
heating system are gradual.
HTW STEAM GENERATORS
Using the central HTW boilers for steam production is not
recommended. The HTW system is best used to produce steam
by locating steam generators at the point of need.
The steam generator (Fig. 125) is designed so that the
minimum water level covering the tubes takes up 60 percent or
less of the volume of the shell. The remaining 40 percent for
steam is sufficient to avoid water carry over. A water eliminator
at the steam exit removes most water from the steam.
Flash converters convert HTW to steam by reducing the
pressure. They are not satisfactory steam generators because
water is carried with the steam and control is less stable.
Control of a steam generator is simpler because pressure
changes are sensed immediately and corrections in valve position
are made quickly to maintain the desired steam pressure.
Fig. 124. HTW to HW Multizone Storage Converter.
TEMPERATURE CONTROL
STORAGE
CONVERTER
HTWR
HTWS
RELIEF VALVE
MAKE UP
WATER
120 ° F
C2585
TO
BUILDING
FROM
BUILDING
STORAGE
CONVERTER
PUMP
RELIEF VALVE
DOMESTIC
HOT WATER
TO BUILDING
MAKE UP
WATER
120 ° F
C2586
HTWR
SPACE HEATING CONVERTER
CONTROLS NOT SHOWN
SPACE
HEATING
LOAD
HTWS
TEMPERATURE
CONTROL
C2587
RELAY CLOSES
VALVE WHEN PUMP STOPS
(NOT REQUIRED TO
PREVENT FLASHING)
HIGH TEMPERATURE
WATER VALVE
HTWR HTWS
STORAGE
CONVERTER
HOT WATER
TEMPERATURE
CONTROL
TO PUMP INTERLOCK
AND/OR OUTDOOR
CONTROLLER
TO HOT WATER
CONVERTER
RESET SIGNAL
FROM OUTDOOR
CONTROLLER
HOT WATER
3-WAY ZONE
VALVE
PUMP
MANUAL
BALANCING
VALVE
TYPICAL ZONE
HWR
HWS
110-200 F
ZONE WATER
TEMPERATURE
CONTROLLER