CenTraVac Liquid Chillers - 10/98 - Page 20

System Options — Auxiliary Condenser

The Trane auxiliary condenser option consists of a separate condenser connected in parallel with the standard condenser to provide simple heat recovery capability for applications where full heat recovery or high heating water temperatures are not required. Heat which normally would be rejected to the regular condenser water is picked up in the auxiliary condenser before the water enters the hot water heating system. Typical uses for this water include domestic water preheat, boiler makeup water preheat, and reheat air conditioning systems, as opposed to traditional heat recovery applications where higher temperature water is used to satisfy a building heating load, provide full heat input for domestic hot water, or provide the typically larger flow rates of hot water for process applications.

Benefits

Simplicity

No temperature controls are required. Auxiliary condensers are factory- mounted and tested.

Flexibility

Two auxiliary condenser sizes are available — standard and large. Either auxiliary condenser can be applied to any size CenTraVac^® .

Safe

Because the auxiliary condenser is a separate condenser, there is no possibility of cross contamination between the cooling tower water and the auxiliary condenser water circuits.

Efficient

Use of the auxiliary condenser option actually increases the chiller’s efficiency by increasing condenser heat transfer surface area and lowering the pressure differential the compressor must generate.

Decreased life cycle operating costs result through use of the auxiliary condenser option because heat, which normally would be rejected by the cooling tower circuit, is now used for building heating requirements.

Application

A simultaneous demand for heating and cooling is necessary to apply any heat recovery system. Common uses for heated water from an auxiliary condenser include domestic water preheat, reheat air conditioning systems, and boiler makeup water. Building use is not limited to the traditional heat recovery candidates. Schools, hospitals, office buildings, and hotels have all proved to be excellent applications for the auxiliary condenser option.

Controls

The auxiliary condenser was designed for simplicity of operation. Machine load, water flow rate, and temperature determine the amount of heat recovered. There are no controls needed for heating water temperature because no attempt is made to maintain a specific hot water temperature in or out of the auxiliary condenser.

Operation

The auxiliary condenser is a factory- mounted, separate, shell and tube heat exchanger available on water-cooled CenTraVac chillers.

Because hot refrigerant gas always migrates to the area of lowest temperature, auxiliary condenser operation is simple. As hot gas leaves the compressor, it is free to flow to the auxiliary condenser or the standard condenser. Since water entering the auxiliary condenser is normally colder than that entering the standard condenser, the auxiliary condenser will have a lower bundle temperature and will attract the refrigerant gas. The auxiliary condenser will recover as much heat as the machine cooling load, heating water temperature, and flow rate will allow. All remaining heat will automatically be rejected through the standard condenser to the atmosphere through the cooling tower. No controls are needed to balance heat rejection in the two condensers.

Good system design will include a heated water bypass to ensure that water does not circulate through the auxiliary condenser when the chiller is de-energized. There are several ways to bypass the auxiliary condenser. When the hot water system is installed as shown in the figure below, the bypass is automatic if the heating water pump is interlocked with the chiller compressor motor.

Another bypass arrangement is to install a diverting valve. When interlocked with the compressor motor, this valve diverts the heating water flow to the conventional heating system whenever the chiller is not operating. These are only examples of the many ways of accomplishing a bypass.

Contact your local Trane sales office for further specific information.

Table O-1 — Auxiliary Condenser Flow Limits and Connection Sizes