Energy Balances Check

Knowledge check

1. A boiler's fuel input, useful heat output, flue loss and blowdown loss are all measured or estimated directly. Casing loss is not directly measured. How is it found?
It's assumed to be zeroAs the residual: Fuel In − Useful Heat − Flue Loss − Blowdown LossBy multiplying the flue loss by a standard factorIt cannot be estimated without a thermal-imaging survey
2. In a steam system's energy balance, why does condensate typically return to the boiler carrying less energy than it left the point of use with?
Condensate loses mass on the way backSensible heat radiates from uninsulated or long condensate return pipework as it travels backThe boiler consumes the missing energy before the condensate arrivesCondensate always returns at the same enthalpy it left with; nothing is ever lost
3. Removing moisture from air in a cooling coil (dehumidification) requires cooling the air:
To exactly the target supply temperature, no furtherBelow its dew point, so water vapour condenses outAbove its dew point, so water evaporates fasterIt requires no cooling at all, only a change in air speed
4. In an HVAC energy balance, 'reheat' (warming dehumidified air back up to a comfortable supply temperature) represents:
Free energy recovered from the cooling processA genuine additional energy cost, on top of the cooling and dehumidification already doneA reduction in the coil's total loadEnergy that doesn't need to be counted in the balance
5. A boiler's own combustion efficiency and a wider 'fuel to point of use' efficiency for the same plant can legitimately differ because:
One of the two figures must be a measurement errorThey are balances drawn around two different boundaries, answering two different questionsEfficiency can only be defined one way; a difference always signals a faultWider boundaries always show identical numbers to narrower ones

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