District Energy refers to the production and distribution of energy using one or more of the following technologies, which are subfields in the WWW Virtual Library:

• Cogeneration or Combined Heat and Power - The simultaneous production of heat and power through a single thermodynamic process.
• District Heating - The distribution of heat from one or more sources to multiple buildings.
• District Cooling - The distribution of cooling from one or more sources to multiple buildings.
• Energy Storage - The storage of thermal or electric energy.

Energy Efficiency is a very important factor in optimizing HVAC system. The following documents were prepared by Henry Manczyk, C.P.E., C.E.M., of Manczyk Energy Consulting, Rochester, New York:

• Energy Management Strategies in Response to Skyrocketing Energy Costs
• Sizing the Condensate Receiver and Pump for a Steam Boiler
• Estimating the Cost of Steam Loss through the Orifice of a Steam Trap
• Optimal Boiler Size and its Relationship to Seasonal Efficiency
• Refrigeration Chiller - Performance Analysis at Various Loads
• Hot Water Reset Schedule for Hydronic Systems
• Fourteen Basic Energy Conservation Measures to Reduce Energy Costs
• Energy Savings Through Retrofit From Constant-Volume Terminal Reheat to Variable Air Volume System
• Economic Analysis for an Energy Management System in a Commercial Type Office Building
• Life Cycle Cost Analysis - Selection of Heating Equipment
• Building Energy Auditing - Energy Conservation Program Presentation Prepared for the Department of Electrical Engineering, Silesian Technical University, Gliwice, Poland