Chapter 17, Problem 6P

We have exposed 1 kg of water, 1 kg of brick, and 1 kg of concrete each to a heat source that puts out 100 J every second. Assuming that all of the supplied energy goes to each material and they were all initially at the same temperature, which one of these materials will have a greater temperature rise after 10 s? We can answer this question using Equation as shown . We will first look up the values of the specific heat for water, brick, and concrete, which are cwater = 4180 J⁄kg K, cbrick = 960 J⁄kg K and cconcrete = 880 J⁄kg K . Now applying as shown , Ethermal = mc(Tfinal Tinitial) to each situation, it should be clear that although each material has the same amount of mass and is exposed to the same amount of thermal energy, the concrete will experience a higher temperature rise because it has the lowest heat capacity value among the three given materials.

A typical ceiling of a house consists of items shown in the accompanying table. Assume an inside room temperature of 21° C and an attic air temperature of −10° C, with an exposed area of 100 m2 . Calculate the heatloss through the ceiling.

For a building located in Madrid, Spain with annual heating degree-days (dd) of 4654, a heating load (heat loss) of 30,000 kj/h, and a design temperature difference of 30° C (20° C indoor), estimate the annual energy consumption. If the building is heated with a furnace with an efficiency of 92%, how muchgas is burned to keep the home at 20° C? State your assumptions.