Heating Running Costs - Page 1 2 3 4 5

 


 

 

Example 5

 

Compare the annual running cost for a domestic heating system using natural gas with LPG to heat a house with a total boiler output of 22 kW (75,000 BTU/hour).

DATA:

Plant operation: 7days per week, 10 hours per day, 39 week heating season.

Seasonal efficiency - 60%

Thermal efficiency of boilers - 80%

Part-load efficiency - 80%

The fuel costs used are from the Table of Fuel Costs in the Fuel Costs section in the Energy Sources pages of these notes.

Natural Gas cost 6.59 p/kWh (November 2008)

L.P.G. cost 8.30 p/kWh (November 2008)

 

 

 

Formulae:

 

 

 

 

 

 

 


 

 

 

 

Annual Energy Input (kJ) = (22 x 10 x (7 x 39weeks) x 3600 x 0.6 ) / ( 0.8 x 0.8 )

 

Annual Energy Input (kJ) = 202,702,500 kJ

 

 

 

Annual running cost (Natural Gas) () = (202,702,500 kJ x 6.59 p/kWh ) / ( 1000 x 3.6 x 100 )

 

Annual running cost (Natural Gas) () = 3,711

 

 

 

Annual running cost (LPG) () = (202,702,500 kJ x 8.30 p/kWh ) / ( 1000 x 3.6 x 100 )

 

Annual running cost (LPG) () = 4,673

 

 

Therefore using natural gas is 4,673 - 3,711 = 962 cheaper per annum.

 

 

 

Example 6

Calculate the annual running cost using oil firing for the average 160 m2 floor area house.

The average central heating requirement for a modern 160 m2 house is say; 30 W/m3 x 160 m2 floor area x 2.4 m high = 11,520 Watts

The average household uses a 120 litre hot water cylinder.

This needs 4,650 Watts (4.65 kW) of boiler power to heat up to 55oC from cold in 1.5 hours. (see Hot & Cold Water Hot Water Generation & Storage, page 2)

Also the annual energy requirement to heat a 120 litre hot water cylinder is given in Example 4, Hot & Cold Water Hot Water Generation & Storage, page 2 as 3849 kWh/ year.

 

Total boiler power required = 11,520 Watts + 4,650Watts = 16,170 Watts (16.17 kW)

 

DATA:

Central Heating Plant operation: 9 hours per day (average), 7 days per week x 39 weeks per year = 273 days / year.

Hot Water heating Plant operation: 7 hours per day, 365 days / year.

Oil fuel cost: 52.5 p/litre (14th April 2008)

Seasonal efficiency - 60%

Thermal efficiency of boiler - 80%

Part-load efficiency - 80%

 

 

 

 

 

 

 

 


=

 

 

Annual Energy Input Central Heating (kJ) = 95,528,160 kJ

 

Annual Energy Input Hot Water (kJ) = 3849 kWh/ year x 3.6 = 13,856 MJ = 13,856,000 kJ

 

 

Total Annual Energy Input (kJ) = 95,528,160 kJ + 13,856,000 kJ = 109,384,160 kJ

 

 

 

 

 

 

 

 


Annual fuel consumption (kg) =

 

 

 

Annual fuel consumption (kg) = 2404 kg

 

Convert to litres since price of oil is given in litres.

 

Mass = Volume x density

Volume = mass / density (the density of oil is 835 kg/m3)

Volume = 2404 / 835 = 2.879 m3

Volume = 2.879 x 1000 ( since 1000 litres = 1 m3)

Volume = 2879 litres.

 

 

Annual running cost (pence) = Annual fuel consumption x fuel cost in (p/l)

 

Annual running cost (pence) = 2879 x 52.5 (p/l)

 

Annual running cost = 1,511,475 pence = 1,512

 

 

The Data can be put in a Table for better understanding;

 

System

Boiler Power required (kW)

Percent of total Boiler Power

(%)

Annual Energy Input (kJ)

Annual Energy Input (kWh)

Percent of total

(%)

Annual

Running Cost (/yr)

Central Heating

11.52

71 %

95.528 x 106

26,536

87.3 %

1,320

Hot Water

4.65

29 %

13.856 x 106

3,849

12.7 %

192

Total

16.17

100 %

109.384 x 106

30,385

100 %

1,512

 

From the above Table it can be calculated that 1 kWh of energy (using oil firing) costs 0.0497 approximately 5.0p/kWh.

 

 

 


Heating Running Costs - Page 1 2 3 4 5