Consider the wintertime heating of a house with a furnace compared to addition o
ID: 1848618 • Letter: C
Question
Consider the wintertime heating of a house with a furnace compared to addition of Carnot heat engines/pumps. To compensate for heat losses to the surroundings, the house is maintained at a constant temperature T_house by a constant rate of heat transfer Q_house. The furnace operates at a constant temperature T_F, and with direct heat transfer, the heat required from the furnace, Q_F is equal to Q_house.
(a) Instead of direct heat transfer, if we utilize the surroundings, at T_S, as an additional heat source and include heat pump technology, Q_F may be reduced by generating work from a heat engine operating between T_F and T_S, then applying that work energy to a heat pump operating between T_S and T_house. Given that T_F=800K, T=293K, T_S=265K and Q_house=40kJ/h, determine Q_F utilizing heat pump technology. No other sources of energy may be used.
(b) Another option is to run a heat engine between T_F and T_house and the heat pump between T_S and T_house . Compare this method with part (a).
Explanation / Answer
1. First Law of Thermodynamics The first law of thermodynamics is often called the Law of Conservation of Energy. This law suggests that energy can be transferred from one system to another in many forms. Also, it can not be created or destroyed. Thus, the total amount of energy available in the Universe is constant. Einstein's famous equation (written below) describes the relationship between energy and matter: E = mc2 In the equation above, energy (E) is equal to matter (m) times the square of a constant (c). Einstein suggested that energy and matter are interchangeable. His equation also suggests that the quantity of energy and matter in the Universe is fixed. 2. Second Law of Thermodynamics Heat cannot be transfer from a colder to a hotter body. As a result of this fact of thermodynamics, natural processes that involve energy transfer must have one direction, and all natural processes are irreversible. This law also predicts that the entropy of an isolated system always increases with time. Entropy is the measure of the disorder or randomness of energy and matter in a system. Because of the second law of thermodynamics both energy and matter in the Universe are becoming less useful as time goes on. Perfect order in the Universe occurred the instant after the Big Bang when energy and matter and all of the forces of the Universe were unified.