Question

Here is the energy analysis of the hydronic heating system depicted in the diagram.

The boiler plant consists of two identical boilers, each having the following characteristics:

• Fuel: natural gas

• Burner Type: on/off

• Rated Output = 85 kW

• Rated Efficiency, nFL = 80%

Boiler Plant Output Zone 1 Boiler 2 Heat Distribution Loop Zone 2 Output Boiler 1 pump Zone 3 Natural Gas Electricity motor

The boilers operate in a “Lead/Lag” arrangement, i.e., Boiler 1 operates first to meet the load (up to its capacity), and Boiler 2 operates as necessary to meet any remaining load.

The pump and motor have the following characteristics:

• Flow Rate = 15 L/s

• Pressure Rise = 160 kPa

• Pump Efficiency = 60%

• Motor Efficiency = 88%

a) Estimate the shaft power (W) required by the pump

b) Estimate the fuel consumption rate of the boiler plant (m3 /hr) during a moment when both boilers are cycled on. Assume the heat content of natural gas is 10.33 kWh/m3 .

c) Consider a period when the heat extraction rates from the loop are as follows: Zone 1 = 30 kW, Zone 2 = 12 kW, Zone 3 = 22 kW. Estimate the heat load to be met by each boiler (kW) during this period.

Answer 1

Son ܕ . Given charactuhc boilers:- 1.). fuel type : Natural gas (rog) 2.) bumes type : on/off 3.9 Raled Butput : Pout = 85 kW 4.) Rated effivenly: npr - 80% operating Boiley -2 starts when the Boiles - lag . Sunawon the load capacity Pump characlenchus 0-015 mols - flow Rate is 154/5 "Pump AP = 'Pump 160 kPa 2) Pressuge fise 3.) Pump efficiency 4.2 Motor efferinly npump 607, 881, motor as. Rise in Head due to Pump tha AP Pewares & 3 160x10 th 1000X9.84 Dh = 16.3098 m of watu. Power delieveged to wales - Puoles PgQAh -1000x9.81XD•015 X163098 Prater 2400 W

n pump Power deliever to wats. Powry at Shaft. Pirater Pchaft 2900 0.6 pump Pshaft 4000 W 4 kW Ane b) When both boiler age yeled on total power out from the boiler (Pout) 150 kw 2x85 Total Heat content of natural gas CV - 10.33 ku 10.33 kwh/ma tet, my is fuel consumphun rate of boiler plant- (Pour) Total MAL x cv 170 0.8 mitt X10.33 min 20.571 m/br Are.

2 Requiremunt :: Zone 1 30 kw Zone 2 12 lcw Zon 3 22 lcw total heat requirement 64 kw < Pout 85kW of each boiler only Boiley + operate for for this period. Heat load Boiler 64 kw Boites a 0 kw

Please forgive me for any calculation mistake and do comment for any short of queries.