There are tens of thousands of existing dehumidification systems in operation today, many at their end of their useful life and in need of replacement. For example, an R22 system in operation today is very expensive to keep running, making it a prime candidate for replacement.
There is a tendency to simply replace the dehumidifier for the same exact unit. While that is certainly an option, this is really the time to assess the site and evaluate how the existing system performed and if it met the owner’s expectations. What was state of the art 15-20 years ago is very different to what is considered best practice today.
A complete audit is recommended. The pool might be used completely differently to its intended original design. Treat the audit as a new pool project and re-evaluate owner expectations. Once those expectations are established, shortcomings of the system can be considered for remediation.
The size and accessibility of the mechanical room will likely determine which equipment is ultimately selected. Manufacturers offer many different unit configurations in a variety of footprints: