System Schematics
Two basic flow schematics are applied to select ICE CHILLER® Thermal Storage Units. Figure 2 illustrates a single piping loop with the chiller installed upstream of the thermal storage equipment. This design allows the thermal storage system to operate in four of the five possible operating modes. They are Ice Build, Cooling-Ice Only, Cooling-Chiller Only and Cooling-Ice with Chiller.
Figure 2
For Figure 2 the following control logic is applied:
MODE |
CHILLER |
P-1 |
V-1 |
V-2 |
Ice Build |
On |
On |
A-B |
A-B |
Cooling - Ice Only |
On |
On |
Modulate |
A-C |
Cooling - Chiller Only |
On |
On |
A-C |
A-C |
Cooling - Ice With Chiller |
On |
On |
Modulate |
A-C |
Valve V-1 modulates in response to temperature sensor, TS-1. Valve V-2 could be positioned to either maintain a constant flow, less than P-1, or modulate in response to the return glycol temperature from the cooling load.
When the building loop contains chilled water, a heat exchanger must be installed to separate the glycol loop from the building’s chilled water loop. On applications where an existing water chiller is available, it can be installed in the chilled water loop to reduce the load on the thermal storage system.
This design should not be used when there is a requirement to build ice and provide cooling. This would require the cold return glycol from the thermal storage equipment be pumped to the cooling load or heat exchanger. Since the glycol temperature is below 32°F (0°C), the cooling coil or heat exchanger is subject to freezing. The flow schematic illustrated in Figure 3 details a primary/secondary pumping loop with the chiller located upstream of the thermal storage equipment. This design allows the system to operate in all five operating modes.
Figure 3
For Figure 3 the following control logic is applied:
MODE |
CHILLER |
P-1 |
P-2 |
V-1 |
Ice Build |
On |
On |
Off |
A-B |
Ice Build with Cooling |
On |
On |
On |
A-B |
Cooling - Ice Only |
Off |
On |
On |
Modulate |
Cooling - Chiller Only |
On |
On |
On |
A-C |
Cooling - Ice With Chiller |
On |
On |
On |
Modulate |
Valve V-1 and Valve V-2 modulate, depending on the operating mode, in response to temperature sensor, TS-1. The benefit provided by the primary/secondary pumping loop is that the system can build ice and provide cooling without fear of freezing a cooling coil or heat exchanger. This system design also allows for different flow rates in each of the pumping loops. When the flow rates in the pumping loops are different, the glycol flow rate in the primary loop should be greater than or equal to the glycol flow rate in the secondary loop. As in the single loop schematic, a heat exchanger and a base water chiller can be added to the system schematic.
Variations to these schematics are possible but these are the most common for ice storage systems. One variation positions the chiller downstream of the ice storage equipment. By positioning the chiller downstream of the ice, the chiller is used to maintain the required supply temperature. In Figures 2 and 3, the chiller is installed upstream of the ice. This offers two significant advantages compared to system designs that locate the chiller downstream of the ice. First, the chiller operates at higher glycol temperatures to precool the return glycol. This enables the chiller to operate at a higher capacity which reduces the amount of ice required. Second, since the chiller is operating at higher evaporator temperatures, the efficiency (kW/TR) of the chiller is improved. |
