User defined functions are similar to stored procedures. There are some limitations in terms of what you can and cannot do when developing user defined functions. You can review them by looking up user defined functions in the SQL Server 2000 Books Online help file.
The functions in ManagingEnergy serve the purpose of either gathering and calculating on data or returning a calculated value based on input. All udf's that are developed in the ManagingEnergy database should use the name prefix udf_.
When developing udf's the T-SQL code should be documented.