Achieving High Chilled Water Delta T Without Blending Station

Abstract

Typically a blending station is designed to ensure that its user is able to avoid low chilled water return temperature in the district cooling system. When the chilled water return temperature drops to a low limit, building return water is blended into building supply water to reduce primary chilled water flow and finally increase building chilled water return. However, the blending station will cause extra pump power and may cause humidity and temperature issues. Theoretical analysis has been conducted on the blending station performance. The results show that the blending station is not necessary in the building chilled water systems with 2-way modulation valves at end users. Actually the end user valve configuration and control mainly impacts building chilled water temperature. As soon as the water flow control is improved, the chilled water return temperature can be controlled without the blending stations. This paper presents actual system operation data and optimal control measures at three buildings which receive chilled water from a district cooling system.