Handbook of air conditioning and refrigeration / Shan K

31.8 CHAPTER THIRTY-ONE
FIGURE 31.3 Ice-on-coil, internal-melt ice storage tank.
(2285 kW). The chillers also provide direct cooling at a capacity less than 200 tons for refrigeration
loads that operate 24 h.
In this operating mode, the ice-on-coil, internal-melt storage tanks are charged. At the same
time, a 34°F (1.1°C) ethylene glycol solution is supplied to the air-handling units for nighttime
cooling. The DDC controller controls the ice storage system in the following operating sequence, as
shown in Fig. 31.2:
1. Open control valves CV-1, CV-2, CV-5, CV-6, CV-8, and CV-11; and close control valves CV-3,
CV-4, CV-6, CV-7, CV-9, and CV-10.
2. Reset the temperature of the glycol solution leaving the chiller T el to 22°F (� 5.6°C).
3. Reset the load limit of both chillers to 100 percent.
4. Start the chiller and condenser pumps. Chiller pumps operate at high speeds during ice making
to provide a higher flow rate and a high rate of heat transfer in the storage tanks as well as a
greater head to overcome the pressure drop for both the evaporator and the coils in the ice storage
tanks. Chiller pumps operate at low speeds in direct cooling mode.
5. Start chillers 1 and 2 following the lead/lag sequence.
6. After chillers are started, open control valves CV-3 and CV-7.
7. Start the building chilled water circulating pumps in sequence.