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PhD Thesis - Energy Systems Research Unit - University of Strathclyde

PhD Thesis - Energy Systems Research Unit - University of Strathclyde

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If a dedicated supply is used, for example a straw fired boiler, which runs<br />

continuously despite demand, the heat lost from the tank is calculated as before.<br />

The actual fuel consumption required to run the heater at maximum capacity<br />

must then be determined. If electricity is being used, the required supply rate<br />

(kW) is calculated using Equation 5.48.<br />

Supply = Power x Number x 100 (5.48)<br />

Efficiency<br />

where Supply = electricity supply rate (kW)<br />

Power = heater rated power (kW)<br />

Number = number <strong>of</strong> heaters<br />

Efficiency = heater efficiency (%)<br />

The actual required fuel consumption for gaseous, liquid and solid fuels may be<br />

calculated using Equations 5.33, 5.35 or 5.36 as appropriate, and multiplying the<br />

result by the number <strong>of</strong> heaters. If there is not enough fuel to run the heater at<br />

its rated capacity, the amount <strong>of</strong> heat which can be supplied with the available<br />

fuel is calculated, and the user is alerted that there was not enough fuel to run<br />

the heater at its maximum capacity.<br />

The amount <strong>of</strong> heat being supplied is then added to the storage tank. If this<br />

causes the amount stored to go above the maximum level, the excess heat is<br />

wasted. This wasted heat is calculated by subtracting the maximum storage<br />

level from the new storage level, which is then set at maximum.<br />

Whether using excess electricity and/or heat, or a dedicated supply, the stored<br />

hot water is then used to meet the demands for heat and/or hot water as desired.<br />

Figure 5.26 outlines this procedure.<br />

172

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