The Residential (household) Sector in Singapore Contributes about 7% of Singapore’s CO2 Emissions, with Air Conditioning and Refrigeration Accounting for Most of the Emissions in That Sector: Thermodynamics Assignment, TP, Singapore

Assignment Narrative and Questions:

The residential (household) sector in Singapore contributes about 7% of Singapore’s CO2 emissions, with air conditioning and refrigeration accounting for most of the emissions in that sector.

There are about 1.4 million households in Singapore. You may assume that each household uses an air conditioning system that consumes 1 kW of electricity for an average of 8 hours a day,

Question 1

a. What could be the cost savings and CO2 emissions reductions for each household of switching to fans to provide thermal comfort at home?

b. What are possible reasons why such a switch may or may not be realistic for Singapore households.

c. Assuming that the average Coefficient of Performance (COP) of residential air conditioners is 3, how much heat (in kW) is rejected to the ambient by one air conditioner in the residential sector during hours of operation?

d. Assuming that the airflow used to take away this heat is 0.2 m3 /s, estimate the temperature rise that the air will experience?

e. Calculate the CO2 emissions resulting from air conditioning electricity use for the residential sector in Singapore.

f. Suggest possible ways for the GEF for power generation to be reduced.

Question 2.

a. Assuming that the air conditioner operates between 15 °C and 40 °C, what is the maximum theoretical COP of the air conditioning system?

b. If the rejected heat from the air conditioner at 40°C is used to provide the heat input to a reversible heat engine, what is the maximum theoretical thermal efficiency and power output (kW) of the heat engine, assuming that the ambient temperature is 30°C.

c. As an alternative to b., the rejected heat can be “upgraded” using a heat pump to provide hot water for homes. If the heat pump delivers hot water at 50°C, estimate how much hot water each household can produce daily from its air conditioning use.

d. Calculate the rate of entropy generation (kW/K) for the air conditioning system resulting from

(i) the heat rejection of the air conditioner taking place between 40°C and 30°C

(ii) the heat addition from the cooled room taking place between 15°C and 25°C

e. Discuss in practical (engineering) terms, how entropy generation arising from heat transfer across finite temperature differences can be reduced. Can such entropy generation be reduced to zero? Briefly explain your answer.

Question 3

a. Besides CO2 emissions from electricity use, non-CO2 Greenhouse Gases (GHGs) are emitted when hydrofluorocarbon (HFC) refrigerants are leaked or released into the atmosphere from air conditioners and refrigerators that use such refrigerants. Suggest/Describe several ways to significantly reduce non- CO2 GHGs emissions from air conditioning.

b. It is proposed to use district cooling systems to provide chilled water for air-conditioning to homes in Singapore. However, such centralized cooling systems typically have to operate at a lower refrigeration temperature to counter losses in distributing chilled water over a wide area.

Discuss if it is possible for district cooling systems to be more efficient than small household air conditioning units.