AERCO Packaged WaterWizard Steam-to-Water Heater - Manual (Page 17)

HE-110
1B+ II Water Wizard Water Heaters
OMM-0063_0B Installation, Operation & Maintenance Manual
AERCO International, Inc. • 100 Oritani Dr. • Blauvelt, New York 10913 • Phone: 800-526-0288
CHAPTER 4. PRINCIPLE OF OPERATION
The AERCO Helitherm Heat Exchanger (Heater) consists of three parts (see Figure 7);
1. Shell with Top and Bottom Heads
2. Coils assembled to Steam Riser and Condensate Return
3. Integral Demand Anticipator Temperature Control Unit
Cold Water (or other liquid) enters the heater through the inlet connection and Orifice in the
Bottom Head and strikes the Deflector. The Orifice serves to divert some Cold Water into the
Shut Tube, whereas the Deflector disperses the incoming Cold Water evenly into the bottom of
the Shell. The Cold Water in the Shell, then, flow upward among the Coils (heating surfaces)
and, heated, is discharged through the Check Valve and Hot Water Outlet Connection in the
Top Head.
Steam enters through the Control Valve and the Steam inlet connection in the Heater Bottom
and is fed through the Steam Riser to the inlet of each Heat Exchanger Coil unit as shown in
Figure 7. The Steam flows through these Coils units simultaneously in parallel and enters the
Condensate Return as Condensate. The Condensate is fed through the Sub-Cooling Coil unit
and leaves the Heater through the Condensate outlet connection in the Bottom Head of the
Heater. The Sub-Cooling Coil unit is included in the assembly to provide the maximum possible
condensing of the Steam, thus providing the greatest amount of heat transfer, the lowest
Condensate outlet temperature, and the greatest reduction in energy loss from flash steam.
As noted above, the Cold Water being heated flows through the Heater from bottom to top. In
addition, Heater Water, being of less density than Cold Water, migrates to the top of the Shell
by convection. These actions result in the hottest Water always being at the top of the Heater –
at the Heater outlet and at the How Water inlet to the Anticipator Temperature Sensing Tube –
See Figure 7.
Hot Water from the top of the Heater Shell enters the open end of the Sensing Tube and Cold
Water enters the Sensing Tube from the Shunt Tube at a rate proportional to the load (call for
Hot Water) on the Heater. The mixture of Hot and Cold Water in the Sensing Tube creates an
average temperature which necessarily will be cooler than the temperature of the Hot Water in
the top of the Heater Shell.
4.1. HEAT EXCHANGER OPERATION WITH PNEUMATIC CONTROL
The Temperature Sensing Element “reads” the average temperature of the Water in the
Sensing Tube at any given moment and signals the Water in the Sensing Tube at any given
moment and signals the Steam Control Valve to modulate between full open or closed as
necessary to maintain the required Heater Hot Water outlet temperature. With no demand or
load on the Heater, the Temperature Sensing Element reads only the temperature of the Water
in the top of the Heater and at the Heater outlet. If that Water is at the required outlet
temperature or above, the Sensing Element signals the Steam Control Valve to close.
However, the moment that there is a demand for Hot Water, Cold Water flows from the Shunt
Tube to mix with the Hot Water I the Sensing Tube, cooling the Sensing Element so that is
signals the Steam Control Valve to open. The need for Steam (heat) to the Coils is satisfied at
once, the incoming Cold Water passing over the Coils is heated, and the Hot Water outlet
temperature does not fall below that required.
The Demand Anticipator Temperature Control Unit, as its name implies, is constantly alert to
lead conditions and changes, as well as to changes in the temperature of the incoming Cold