1. Spring 2006  Harvard Science, A 52 FHA+MBM Lecture 18, 1 Science A 52 Lecture 18; April 17, 2006 Refrigeration a)Technical background b)Visit to the Chilled Water Plant

2. Spring 2006  Harvard Science, A 52 FHA+MBM Lecture 18, 2 Refrigeration Refrigeration is perhaps the largest single consumer of electrical power in the US. There is a very large central chilling plant below the Science Center that is electrical driven. We will visit the plant but we first need some material on how the refrigeration cycle works.

3. Spring 2006  Harvard Science, A 52 FHA+MBM Lecture 18, 3 Basics The refrigerant is the fluid that carries heat through the refrigeration cycle Most refrigerants are liquefiable vapors as the working fluid. Freon was such a substance - it had the property of boiling in the evaporator at a temperature below the temperature of the room or material to be cooled and then after the vapor is compressed it is cooled to a liquid again in the evaporator by rejecting heat to an external fluid at a higher temperature. At one time freon was a “wonder” fluid. Now we know better. Refrigeration can be though of as pumping or lifting heat from a low temperature and then rejecting it at a higher temperature.

4. Spring 2006  Harvard Science, A 52 FHA+MBM Lecture 18, 4 Refrigeration Cycle Mechanical refrigeration is a process that which changes the state of a volatile liquid in these four processes to vapor in the cooling stage - the Evaporator then raises the vapors to higher pressure and temperature in the Compressor to the heat rejection stage in which the vapors are condensed - in the Condenser The liquid is then returned to low pressure and temperature through the expansion And the cycle continues

5. Spring 2006  Harvard Science, A 52 FHA+MBM Lecture 18, 5 Refrigeration Definitions

6. Spring 2006  Harvard Science, A 52 FHA+MBM Lecture 18, 6 Basics - continued A TON DAY of refrigeration is the amount of heat required to melt a ton of ice - in other words the cooling resulting from allowing a ton of ice to melt at 32 degrees F -or the reverse -the amount of heat to be removed to freeze a ton of water (2,000 pounds) at 32 degrees F. A ton is commonly used as a the rate - a machine rated at X tons removes X times 12,000 BTU/h from the medium to be cooled. A ton day is then 24 hX12,000BTU/h =288,000 BTU

7. Spring 2006  Harvard Science, A 52 FHA+MBM Lecture 18, 7 Basics - continued If a refrigerating system - a window box AC unit removes - or lifts - 12,000 BTUs per hour from a room and rejects it to the outside air then the unit is said to have the capacity of one ton. Power is require to blow the room air by the evaporator, compress the refrigerant vapor, and blow outside air by the condenser.

8. Spring 2006  Harvard Science, A 52 FHA+MBM Lecture 18, 8 Basics - continued If the power required by the two fans and the compressor is a total of 1,000 watts then the EER of the unit is: 12,000 BTU/h 1,000 watts = 12.0 EER stands for Energy Efficiency Rating

9. Spring 2006  Harvard Science, A 52 FHA+MBM Lecture 18, 9 Now for a schematic of a typical mechanical refrigeration system

10. Spring 2006  Harvard Science, A 52 FHA+MBM Lecture 18, 10 The Basic Refrigeration System

11. Spring 2006  Harvard Science, A 52 FHA+MBM Lecture 18, 11 http://www.energystar.gov/ia/new_homes/ features/EstarAirConditioners1-17-01.pdf Energy use by HVAC Units The U.S. Environmental Protection Agency ENERGY STAR Program On average, air conditioning accounts for 15 percent of home energy use, but can increase to over 40 percent in hot and humid regions. Thus an effective air conditioning system is an important part of an energy-efficient home.

12. Spring 2006  Harvard Science, A 52 FHA+MBM Lecture 18, 12 http://www.eere.energy.gov/buildings/info/components/hvac/cooling/airconditioning.html#central Take a look at the DOE WEB site for data about home and Office Energy Efficiency This site worked at 10 am this morning and failed at 10:30. It may now be up.

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18. Spring 2006  Harvard Science, A 52 FHA+MBM Lecture 18, 18 According the DOE Energy Chart The conversion of primary energy to electrical energy Is done at a 30% average efficiency. Hence any diminution in electrical demand results in a substantial reduction in primary energy.