period three
System Variations
notes
Heat-Recovery Chiller Options
heat-recovery | auxiliary | | |
(dual) condenser | condenser | heat pump | |
◆ Second, full- | ◆ Second, smaller- | ◆ No extra | |
size condenser | size condenser | condenser | |
◆ Large heating | ◆ Preheating loads | ◆ Large base-heating | |
loads | ◆ Moderate | loads or continuous | |
| operation | |
◆ High hot-water | hot-water | |
temperatures | temperatures | ◆ High hot-water | |
◆ Controlled | ◆ Uncontrolled | temperatures | |
◆ Controlled | |
◆ Degrades | ◆ Improves chiller | |
chiller efficiency | efficiency | ◆ Good heating | |
| | efficiency | Figure 77 |
| | |
For water-cooled centrifugal chillers, there are generally three methods of implementing heat recovery.
The dual-condenser, or double-bundle, heat-recovery chiller contains a second, full-size condenser that is connected to a separate hot-water loop.
It is capable of more heat rejection and higher leaving-hot-water temperatures than an auxiliary condenser. The amount of heat rejected is controlled by varying the temperature or flow of water through the standard condenser. Chiller efficiency is degraded slightly in order to reach the higher condensing temperatures.
An auxiliary-condenser, heat-recovery chiller makes use of a second, but smaller, condenser bundle. It is not capable of rejecting as much heat as the dual-condenser chiller. Leaving hot-water temperatures are also lower, so it is often used to preheat water upstream of the primary heating equipment or water heater. It requires no additional controls, and actually improves chiller efficiency because of the extra heat-transfer surface for condensing.
A heat-pump chiller is a standard chiller (no extra shells are required) used and controlled primarily for the heat it can produce in the condenser. The evaporator is connected to the chilled-water loop, typically in the sidestream position discussed earlier, but it only removes enough heat from the chilled- water loop to handle the heating load served by its condenser. This application is useful in a multiple-chiller system where there is a base or year-round heating or process load, or where the quantity of heat required is significantly less than the cooling load. The heating efficiency of a heat-pump chiller is the highest of any heat-producing device.
