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Question 4 1) A building engineer wants to design a heating system with cast iron column radiators for a two- floor residential building in winter. Calculate the number of radiator sections needed for the one-pipe arrangement with individual control. The design conditions are as follows: (1) The heating load of each floor is 5.0 kW at the design room temperature of 22 °C. (ii) The hot water supply temperature is 98 °C, and return temperature is 78 °C. The rated heating emission rate from each radiator section is 160 W when the difference between the mean water temperature in the radiator section and the room air temperature is 67.5 °C. The heat emission rate from the radiators is proportional to (tm-ta) 2 where tm is the mean hot water temperature at the inlet and outlet of the radiator and ta is the room air temperature. The hot water temperature drop across each radiator is 15 °C. You may assume one radiator with multiple sections serves one floor. (16 marks) 2) An air source heat pump is used for the residential building, and the chosen heat pump has a COP of 3.2 when the design outdoor temperature is 10 °C and the indoor temperature is 22 °C. If the outdoor temperature increases from 10 °C to 15 °C, will the COP of the air source heat pump increase or decrease? Briefly explain. (6 marks) 3) Why the earth ground can be used as a heat source for heat pumps? (3 marks) а