CEMP-E
TI 810-11
30 November 1998
Figure 5-15i. DDC control system equipment for single-zone HVAC system without economizer control
mode.
Figure 5-15j. DDC control system I/O table and data terminal strip layout for single-zone HVAC system
without economizer control mode.
15. CONTROL SYSTEM VARIATIONS FOR DUAL STEAM VALVES. Generally when the size of a
steam control valve exceeds 65 mm (2-1/2 inches) (pipe size) or when there is a seasonal requirement
for low flow, two steam valves will be used to enhance control authority. Usually the valves are sized for
1/3 of the total flow and 2/3 of the total flow. The valve Kvs (Cvs) will be selected from available products
with one valve having a smaller Kv (Cv). The valves are then sequenced without a control signal
deadband. The control signal range available for operating the valves is to be split into two parts - one
third of the signal range (21 to 48 kPa (3 to 7 psi)) is used to modulate the smaller valve and two thirds
(48 to 103 kPa (7 to 15 psi)) of the signal range is used to modulate the larger valve. In the control
sequence, the smaller control valve opens first. The control system drawings affected are the schematic
and the equipment schedule. Figures 4-10a and 4-10c have been modified to show the required
changes and are shown as figures 5-16 and 5-17.
Figure 5-16. Schematic variations for dual steam valves.
Figure 5-17. Equipment schedule variations for dual steam valves.
16. CONTROL SYSTEM VARIATIONS FOR HYDRONIC SYSTEMS WITH BOILERS REQUIRING
CONSTANT FLOW. Figures 4-8a through 4-8j and 4-12a through 4-12j depict single building hydronic
systems which vary the flow through the boiler. However, some boilers will not tolerate low-flow
conditions. Figures 5-18a through 5-18j and 5-19a through 5-19j show variations of these systems which
maintain a constant flow rate through the boiler. The variations consist of adding an additional piping
loop around the boiler and an additional pump.
Figure 5-18a. Control system schematic for single building hydronic heating system with constant
volume hot water boiler loop.
Figure 5-18b. Control system ladder diagram for single building hydronic heating system with constant
volume hot water boiler loop.
Figure 5-18c. Control system equipment for single building hydronic heating system with constant
volume hot water boiler loop.
Figure 5-18d. Control panel interior door layout for single building hydronic heating system with constant
volume hot water boiler loop.
Figure 5-18e. Control panel back panel layout for single building hydronic heating system with constant
volume hot water boiler loop.
Figure 5-18f. Control panel terminal block layout for single building hydronic heating system with
constant volume hot water boiler loop.
5-9
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