1 Refrigeration Cycle Video

Please watch these videos:

and answer the following questions:

  • Why doesn’t a refrigerator violate the second law of thermodynamics by moving heat from a cold mass to a hot mass?
  • What do you think the mechanisms of heat transfer are in the evaporator and condenser?
  • How is latent heat used in the refrigeration cycle?
  • How is the heat pump operation changed from heating to cooling?

2 Heat Pump Efficiency

What is the maximum possible efficiency for an air-source heat pump in the following conditions? The inside temperature is 70F, the outside temperature is 30F.

3 HSPF Energy Needs

You need to deliver 50 MMBTU of heating to a building with a heat pump with an HSPF of 10 BTU/Wh. How many kilowatt-hours of electricity are required?

4 SEER Energy Needs

You need to deliver 20 MMBTU of cooling to a building with a heat pump with a SEER rating of 20 BTU/Wh. How many kilowatt-hours of electricity are required?

5 HSPF and UA Energy Needs

You have a building with a UA value of 400 BTU/hr/degF in a climate with 2500 degF-days of heating needs. How many kWh of electricity are needed if you have a heat pump with an HSPF of 10?

6 SEER, HSPF, and Weather

Why do we need to know the weather temperature data to determine the SEER or the HSPF?

7 Plot the COP over temperature

Use a spreadsheet to plot the maximum COP (thermodynamic limit) of a heat pump in cooling and heating over a range of outdoor temperatures assuming a room temperature inside temperature.

Find the range of outdoor temperatures during the heating and cooling season. Use a heating air temperature of 90F and a cooling air temperature of 50F.

Plot the COP for heating and for cooling across this range of outdoor temperatures.

Assume that ground temperatures (for a ground-source heat pump) range from 60F to 70F. Plot the COP for heating and cooling for these ground temperatures.

8 Plot the energy use over temperature

For the air-source heat pumps in the question above, assume an inside air temperature of 20C and a UA value of 50 W/K. Plot the electrical power required to maintain the temperature difference at these different air temperatures.

Start by stating your strategy in bullet points.