Hot and Chilled Water Distribution
Stanford's Central Energy Facility (CEF) relies on hot and cold water for heating and cooling buildings and utilizes a heat recovery process to meet these campus needs.
How the Water Distribution System Works
Once created, the thermal, or heat, energy recovered from buildings and generated at the CEF must be distributed throughout campus. This impressive distribution system consists of underground piping that circulates from the CEF for more than 20 miles around campus.
First, the three heat recovery chillers (HRCs) send out 42°F chilled water to campus. When this water returns to the CEF, having served its purpose, it usually has heated up to around 56-60°F. This water must be chilled back down to 42°F so it can be used again for cooling. Concurrently, hot water at 160-170°F is being sent to buildings that need heat. When this water returns, it has usually dropped around 130°F. At this point, there is water at the CEF which needs to be chilled and water which needs to be heated. For efficiency, the heat removed in order to chill the cold water supply is used to heat up the hot water supply. With all the water returned to its correct temperature, it can be sent out again through the underground piping system.
This underground piping network is an extension of the CEF and the specifics of this network are as important as anything else to the functionality of the system as a whole. The network is made up of ductile iron piping with some small branch lines using PVC.
The peak cooling and heating loads for a building is related to its size. Typical building laterals are 4”- 6” which means peak cooling load is around 50 tons for smaller buildings, 800 tons for research centers and up to 2000-4000 tons for main hospitals. Peak heating loads also have a large range. The network must simultaneously handle small buildings, which draw less than 500k BTUs, and the campus swimming pools, which can draw up to 10 million BTUs.
This hot and chilled water enters each building underground and is funneled into the basement. There, the mechanical room equipment takes a measurement and then sends the water throughout the building using secondary pumps. Both the hot and chilled water systems are closed loop so that water makeup for leakage and treatment can be handled centrally at the CEF. After the water serves its purpose, it is brought back to CEF and the process starts again.
For more information, see the following animation: