Explain the concept of sustainability. 25-2. Describe a sustainable building. 25-3. What is the LEED program? 25-4. What is a CHP system and why is it efficient? 25-5. Identify and describe the three types of cogeneration systems. 25-6. Explain geothermal energy. 25-7. Describe direct use of geothermal energy. 25-8. Describe a geothermal heat pump. 25-9. Explain the direct use of geothermal energy and a geothermal heat pump. 25-10. Explain the fundamental components of a heat pump system: a. Ground loop b. Heat pump c. Air delivery system