J.M. Sala

Application of thermoeconomics to the allocation of environmental loads in the life cycle assessment of cogeneration plants

One of the most common problems arising from the application of life cycle assessment is the allocation of environmental loads in processes yielding several useful products. This is the case for cogeneration plants, and in general, for any energy plant producing more than one useful energy flow. Since traditional solutions to the problem are unsatisfactory, two new approaches for this kind of allocation are presented in this report, both of them based on thermoeconomics. In the first one, allocation is based on the exergetic cost of the products, so that the formation process of energy flows is taken into account. The second one, which has been called ‘method of the exergoenvironmental costs’, is a refined version of the first solution. It differs as each environmental vector is incorporated in the balance at the exact point in the plant where it comes into play. These methods are a generalisation of thermoeconomics, extending the applicability of its propositions to the allocation of environmental burdens. A comparison between the different allocation methods and a discussion pertaining to their suitability are made.

Heat transfer in a cylindrical geometry and application to reciprocating internal combustion engines

In many previous investigations, heat flux thorugh a wall has been studied when the system can be regarded as having a planar geometry. Traditionally, cylindrical coordinate systems, such as reciprocating internal combustion engines, have been approximated by planar geometries. In this work, we present an expression for the heat flux through the wall of a cylindrical chamber and establish conditions for which it can be approximated by a planar geometry. We have used the harmonic method to solve the heat equation with boundary conditions appropriate for a four-stroke internal combustion engine. These studies have bearing on engine efficiency and hence on energy conservation.

Ventilation requirements based on carbon dioxide concentration criteria: implications on IAQ and energy use

ABSTRACT Minimum airflow rates are either recommended or required based on the number of occupants, the intended use of the space or the floor plan area. This paper focuses on a new proposal for Spanish Technical Building Code based on limitations of the ventilation using the CO2 concentration as an indicator. The aim of the proposal is to introduce indoor air quality criteria in order to determine the design ventilation rates, and as a result, reduce the ventilation energy losses. Based on this proposal, the perceived indoor air quality in terms of the concentration of CO2 and other contaminants of concern is analysed through simulation. Maximum allowed area-based emission rates are defined for the indoor source contaminants. It was found that the minimum outdoor airflow rates based on maximum allowable CO2 concentrations would reduce heating demand by more than 25% when compared to the reference airflow rates. In addition, the influence of the airtightness of the envelope on the indoor air quality is analysed with regards to defining the corresponding maximum allowed area-based emission rates. As the envelope permeability increases, the maximum allowed area-based emission rates decrease for HCHO and total volatile organic compound, and should be around 27% lower comparing to the design case values.