Corrected error in documentation.
Added documentation.
Bugfix for use of lambda_const

Replaced the use of Medium.lambda_const with
Medium.thermalConductivity(sta_default) as
lambda_const is not declared for all media.
This avoids a translation error if certain media are used.
Bugfix for #271

Corrected issue #271 which led to a compilation error if the heat
exchanger and the tank had different media.
Corrected wrong diameter.

Bug fix to correct diameter of PEX pipes.
Replaced abs() function.

Replaced the abs() function in the assignment of the parameter
nSegHexTan as the return value of abs() is a Real which causes a type
error during model check.
Removed unrequired public keyword
Fix for Dymola 2015 FD01 beta1 parameters

This changes the assignment of _T_a_start, _T_b_start and RTot to be in
the initial equation section as opposed to the parameter declaration.
This is needed to avoid an error during model check and translation in
Dymola 2015 FD01 beta1.
Improved documentation and expanded assignment.
Small editorial revisions
Moved declaration.

Moved declaration of compositeWall due to a bug in Dymola 2015 FD01
beta1.
Reverted replaceable change.

The replaceable keyword is needed in Dymola 2015 to allow assigning the
record from the GUI.
Added replaceable keyword.

This is need to assign data from the GUI through the pull down menu.
Avoided replaceable parameters

This simplifies the implementation by avoiding replaceable parameters
where they are not needed.
Changed assignment to use vector notation
Removed white spaces
Set start value to avoid conflicting start values.

Set start value for hPip(fluid(T)) to avoid
a warning about conflicting start values in Dymola 2015 FD01.
Removed invalid protected keyword.
Removed redundant connection
Removed access to conditional instance.