Agriculture Reference

In-Depth Information

Figure 2.4
The building as a

control volume. Note the various

ways that contaminants can enter

the volume and the numerous

physical and chemical

mechanisms that can transform

the material that enters.

From U.S. Department of Energy,

Lawrence Berkley Laboratory,

http://eetd.lbl.gov/ied/ERA/

CalEx/partmatter.html, 2003.

The thermodynamics term for the description of the change of a system

from one state (e.g., equilibrium) to another is known as a
process
. Processes

may be reversible or irreversible, and they may be adiabatic (no gain or loss of

heat, so all energy transfers occur through work interactions). Other processes

include isometric (constant volume), isothermal (constant temperature), iso-

baric (constant pressure), isentropic (constant entropy), and isenthalpic (constant

enthalpy).

Thermodynamic terms are crucial to engineers, architects, and other design

professionals working collaboratively with them. For example, you may attend

a seminar or meeting where the engineer refers to conditions. Often, these are

of two types: initial conditions and boundary conditions. You may also hear

the terms
assumptions
,
constraints
,and
drivers
. These are all rooted in thermody-

namics. An
initial condition
is where we start. For example, differential equations

require an initial condition before calculating changes. A
boundary condition
is

imposed on the solutions of differential equations to fit the solutions to the

actual problem. In models, the boundary conditions describe what is expected

to occur along the edges of the simulation region. Thus, initial and boundary

conditions are similar to Figure 2.2. However, instead of the system within the

boundary, the region inside the boundary is what is explained by the differential

equation, and the boundary is where this is no longer valid (i.e., the bound-

ary value given along the boundary curve). Everything outside the boundary

is not explained by the differential equation, analogous to the thermodynamic

surroundings.
Constraints
are those factors that must be considered as part of what

could affect the energy transfer or changes within the boundaries.
Drivers
are

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