Energy Efficiency and Balance Principles

1. Characteristics of Primary, Final, and Useful Energy

Understanding the fundamental definitions of energy is essential for analysis:

• Primary Energy (Ep): Energy extracted from nature in renewable or non-renewable forms.
• Final Energy (Ek): Energy purchased to fulfill demand, such as electricity, heat, or chemical fuel energy.
• Useful Energy (Eu): Energy required to support human life and activity, including mechanical work, heat, light, sound, and food chemical energy.

Example: Home Heating with Natural Gas

• Ep: Raw natural gas extracted from underground resources.
• Ek: Processed natural gas delivered via pipes.
• Eu: Actual heat transferred by a radiator to a room.

2. Energy Efficiency and Device Balance

The fundamental principle is Input = Output. The energy balance equation is defined as Ed = Eu + Ew, where Ed = Ew.

Energy Balance Equations

• Real Turbine: Gid + Qd = Giw + Ni
• Heat Exchanger (HEX): G1i1d + G2i2d = G1i1w + G2i2w + Qout
• Boiler: Mpal(ifpal + ichpal) + na(Mi)a = mp(iw - id) + nsp(Mi)sp + nst(Mi)st + Qout

Efficiency Calculations

• Direct Method: nek = (mp(iw - id)) / (mpal * wd)
• Indirect Method: nek = 1 - Σi (where Σi is the relative energy loss).

3. Indirect Method and Energy Losses

Relative losses (Σi) include physical enthalpy (Swf), chemical enthalpy (Swch), solid product enthalpy (Sstf), chemical solid product enthalpy (Sstch), and heat losses (Sot).

Example 1: Physical Enthalpy of Flue Gases

This represents the enthalpy of flue gases leaving the boiler. It depends primarily on the flue gas temperature (tsp > tot) and the volume of gases.

Example 2: Chemical Enthalpy of Flue Gases

The loss Sw_ch results from improper boiler operation, specifically the presence of combustible gaseous substances like [CO] in the flue gases.

4. Condensation Boiler Energy Balance

The energy balance for a condensation boiler follows the general form of the balance equation, accounting for the recovery of latent heat from flue gas condensation.

5. Efficiency at Final and Primary Energy Levels

For energy transportation, total efficiency is calculated as: Eff_total = ef1 * ef2 * ef3.

Example: Power Plant * Energy Transmission * Heat Pump. Here, Eff_primary is the power plant efficiency, and Eff_final is the heat pump efficiency.