AERCO SmartPlate - Manual (Page 22)

SmartPlate Installation, Operation & Maintenance Manual
CHAPTER 3 – FUNCTIONAL DESCRIPTION
Page 22 of 138 AERCO International, Inc.  100 Oritani Dr.  Blauvelt, NY 10913 OMM-0069_0E
PRI: 11/26/2013 Phone: 800-526-0288 SP-100
3.3 ELECTRONIC CONTROL OVERVIEW
The primary control mechanism for the ECS/SP is an Electronic Process Controller which is
installed in the Control Box. The Controller utilizes feed forward and PID (Proportional Integral
Derivative) algorithms to provide precise control of the Water Heater outlet temperature. Outlet
temperature control is accomplished by modulating the open/closed position of the MXG-461
Control Valve Actuator.
The Controller continuously monitors the Water Heater outlet temperature via a thermocouple
located in the outlet port. The Controller also receives a feed-forward signal from the
temperature sensor mounted in the mixed water manifold as shown in Figure 3-1. The mixed
water sensor monitors flow changes through the Water Heater and provides a feed-forward
signal to the Controller proportional to the change in flow. The mixed water temperature
provides an instantaneous feed-forward response for loads ranging from 0.5 Gpm to the
maximum Heater flow. The SmartPlate uses a cartridge circulator to create reliable mixed flow
conditions in the manifold.
The Controller provides a 0-to-10 VDC output signal to the MXG-461 Control Valve Actuator.
This 0 to 10 VDC signal proportionally modulates the Control Valve position from fully closed (0
VDC) to fully open (10 VDC). The control signal varies as necessary to maintain the setpoint
temperature programmed into the Controller. Under normal conditions, the SmartPlate Water
Heater outlet temperature is maintained within ±4°F of the desired setpoint based on a load
change of 50% or less. Surface-mount sensors and digital displays are also provided in the
ECS/SP Control System to monitor the supply and return water temperatures of the boiler
water.
3.4 OVER-TEMPERATURE CONTROL AND SAFETY FEATURES
The Control Box contains an Over-Temperature Switch which continuously monitors and
displays the outlet water temperature of the Heater via the input received from the thermocouple
installed in the hot water outlet port. Normally, the Over-Temperature Switch is set 20°F above
the setpoint temperature for the Water Heater. If the programmed over-temperature limit is
exceeded, the Over-Temperature Switch is activated. This in turn sounds an audible alarm,
disconnects power from the Control Valve Actuator moving the Control Valve to the full-bypass
position (B – AB). It should be noted that the Over-Temperature Switch has a slightly slower
response to temperature changes than the Temperature Controller. Therefore, slightly different
temperature readings may appear momentarily in their respective displays, particularly during
system start-up.
The Control Valve Actuator also incorporates a “Fail-Safe” feature which automatically closes
the Valve if there is a loss of the 0 to 10 VDC control signal or loss of input power. The 24 VAC
power supply transformer has an integral 3 amp circuit breaker to protect the Control Valve
electronics.