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Heating and Hot Water

The heating audit looks at improvements to the heating system as a whole.

Heat Loss compared to Radiator and Boiler Output

The table below is a summary of the heat losses for all the elements of the house.

Heat Loss  W/K
Walls 69.39
Floor 39.72
Roof 10.44
Windows 77.87
Ventilation 27
Total 224.42

When the temperature outside is -1 deg C and inside 20 deg C then the heating required, from calculation, is 21 x 224.42 = 4.7kW.

The back boiler and radiators both provide a heat output of approximately 12kW and so the heating system should, in theory, be able to cope comfortably. 

Energy Consumed by Boiler Pilot Light


Pilot Heat Input 210W = 0.210kW
Hours lit per year 24 x 365 = 8760
Units Consumed 0.210 x 8760 = 1839.6


Energy Required to Heat Hot Water Cylinder

 Storage Capacity of Hot Water Cylinder 80 litres = 80 kg
 Cold Water Feed Temperature 10 deg C
 Hot Water Storage Temperature 60 deg C
 Specific Heat Capacity of Water 4.2kJ/kg C

    
Energy Required to Heat Water = 80 x 4.2 x 50 = 16800 kJ

Number of Units = 16800 / 3600 = 4.67 units

Energy Lost in Hot Water Feed Pipe


The kitchen is one of the major users of hot water. However, this is some distance from the hot water tank and a considerable amount of water has to be drawn off before hot water is obtained at the storage temperature. 

 Pipe run length 20m
 Pipe inside diameter 20mm

Volume of water in pipe = 3.14 x (0.022 /4) x 20 = 0.00628 m3 = 6.28 Litres

If this volume of water is run off each time the tap is used to obtain really hot water.

Energy Lost in Hot Water Feed pipe = 6.28 x 4.2 x 50 = 1318.8 kJ

Number of Units = 1318.8 / 3600 = 0.37

If the tap is used 4 times a day, every day then the annual heat loss will be

4 x 365 x 0.37 = 540.2 kWh

Estimate gas used for hot water and cooking.

Gas is used to provide heating, hot water and cooking.

May, Jun, July gas consumption will be mainly hot water and cooking. The consumption for this period averaged for 2011 and 2012 was (1429 + 2085)/2 = 1757kWh. The immersion heater was switched off during this period.

Extrapolating for the year gives a consumption of 1757 x 4 = 7028kWh

Estimating that the consumption will be evenly split between cooking and hot water gives the cooking consumption as 3514kWh

The average of the total gas consumption for the full years 2011 and 2012 was 16216 kWh

The gas used for heating and hot water is therefore 16216 - 3514 = 12702 kWh

The gas used for heating alone is therefore 12702 -3514 = 9188 kWh