Chilled Water Systems Optimization Study

Oceanside, NY

 

The central plant at South Nassau Communities Hospital (SNCH) generates steam and chilled water for heating and cooling for the hospital.  Chilled water is generated at the central plant by two 750 ton two-stage absorbers and one 750 ton electric centrifugal chiller. The chilled water is distributed to the individual mechanical rooms in the hospital buildings through a network of distribution piping.

The configuration of the original chilled water system was a constant flow primary/secondary pumping system. Primary pumps are located at the central plant, and secondary pumps are located in the building mechanical rooms with hydraulic bridges.

SNCH constructed a new addition to the hospital (D-wing). After connecting D-wing to the central chilled water system, the system was having difficulties providing sufficient chilled water to all of the system users.

The Partners of CRC Engineering reviewed the existing system design as well as the D-wing addition and found that the chilled water system design for the D-wing addition was incompatible with the existing central chilled water systems. This was creating hydraulic problems for the overall system which resulted in some system users being starved of flow.

Based on review of the plant operating logs, the existing chilled water systems were experiencing temperature differentials of 4 to 6°F while the D-wing addition was operating with temperature differentials around 14°F. This was another symptom of the hydraulic problems.

A comprehensive survey of the existing system was performed and detailed piping flow schematics were developed of the existing systems. A hydraulic calculation was provided to verify that the primary pumps had sufficient capacity to serve the entire system without using the secondary pumps.

Schematics were developed for proposed modifications to the existing systems to convert the entire system from a primary/secondary pumping system to a primary system to make all the systems compatible. The secondary pumps at the buliding mechanical rooms were replaced with spool pieces and the hydraulic bridges were valved off.

In order to serve winter cooling loads and save energy, the feasibility of winterizing a cooling tower and the installation of a free cooling heat exchanger was reviewed.

Working closely with SNCH facilities staff, the proposed system modifications were implemented.

In addition to saving pumping energy by removing the secondary pumps at the building mechanical rooms, the modifications to the systems resulted in doubling the temperature differential from 4 to 6°F to about 12°F. Doubling the temperature differential reduces the required system chilled water flow by half; thus saving additional pumping energy at the primary pumps.