Working (formulas and short hand notation to explain what you are doing and why)

Question

Working (formulas and short hand notation to explain what you are doing and why)

would be greatly appreciated.

A boiler is used to provide space heating for a large residential apartment block that consists of 120 apartments. The space heating system works as a reticulated hot water loop. Hot water at 55 degree C is passed through radiators in each apartment and then returned to the boiler at 25 degree C where it is heated up again to 55 degree C. The boiler heats the water using the heat of combustion of natural gas with an overall efficiency of 70%. During the cold months of the year the apartments are maintained at 24 degree C and the maximum heat loss from each apartment due to air leaks and conduction through the walls is 2 kW. Draw a diagram of the process and label the streams. Calculate the maximum winter heating demand for the space heating system. How much natural gas in (g/s) is required by the space heating system? Useful data and formula: Density of water rho = 1 kg/L Heat capacity of water C = 4.2 kJ/kg. degree C Heating value of natural gas = 55 MJ/kg Average Molecule weight of natural gas is 19 g/mol water= rho , water C(Tout - Tin), NG = NG Delta Hcomb

Explanation / Answer

amount of water that should flow into an appartment to keep the room warm is

2 x 10^3 = M x 4.2 x 10^3 x 20

mass that should be heated for every second is

M = 1/42

amount of gasoline reqired for every second

70/100 x m x 55 x 10^6 = 1/42 x 4.2 x 10^3 x 20

m = 0.051

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