CHP, DH and CHPDH: an introduction

Combined Heat and Power (CHP), sometimes referred to as cogeneration, is the simultaneous production of electricity and heat, both of which are utilised as produce, or, in the case of heat, stored for future use.

District Heating (DH) scheme provides instead heat from a central heat source to more than one building, dwelling or customer and a Combined Heat and Power District Heating (CHPDH) scheme, which combined both together, utilises the heat generated by the CHP plant as the source for heat, which would otherwise be vented into the atmosphere, and distributes it to buildings, dwellings or in general customers.

Figure 1. District heating network (left) and house interface unit (right) (R.Wiltshire 2011).

The main element of a CHP system is amachine that produces electricity and heat.

Usually, such a machine is a reciprocating engine or a turbine that can use as fuel: natural gas, biomass, biogas, coal, vegetable oil and other possible fuel.

The maximum electricity produced and fed into the grid by the CHP system over the primary energy of the fuel fed into the CHP system represents the electrical efficiencyof the CHP system. Equivalently, the maximum heat produced and recovered over the primary energy fed into the CHP system by means of the fuel represents the thermal efficiency of the CHP system.

For a CHP system is designed to recover most of the heat that is produced during the generation process in order to be utilised, CHP systems are said to possess the ability to recover most of the produced heat, achieving an energy efficiency of about 75% (Agency 2008), which is 24% higher than conventional generation.

Considering the fact that electricity cannot be stored economically and efficiently with the current status of technologies, there has been a lot of effort in these systems to recover and distribute most the heat.

Figure 2. Conventional system and CHP system: a comparison in terms of efficiency (Agency 2008).

Heat, also called thermal energy, is typically associated to a fluid and to a difference in temperature in the fluid.

A CHP system is able to exchange (by means of heat exchangers) most of the produced heat with other fluids and can then increase their temperatures as a tangible sign of exchanged heat.

This means that the possibility to have a DH scheme connected with the CHP system allows the latter to recover most of the produced heat.

The most diffused types of CHP systems are listed below as a comparison of CHP systems and their overall efficiencies (Agency 2008).

In the next article we will delve into the CHPDH technology and will provide a progressive understanding of the Anaconda technology of Cogenpower.

References

Agency, U.S. Environmental Protection. “Catalogue of CHP technologies.” Combined Heat and Power Partnership. 2008. 1-14.

R.Wiltshire. “Low temperature district energy systems.” 16th, Building Services, Mechanical and Building Industry Days, International Conference, 14-15 October. Debrecen, Hungary: International Conference, 14-15 October, 2011.

Written by Dr Francesco Vallone

Innovative resourceful CEO

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