We would recommend that you choose a reputable air conditioning manufacturer which may be more expensive that some unbranded makes, but from our experience this will offer you a more reliable piece of equipment in the long term. Established air conditioning makes in the UK such as Panasonic and Mitsubishi have the service back up and UK based infrastructure so property support you should it be required
There are number of major manufacturers that offer excellent products in the UK market such as Mitsubishi, Panasonic and Fujitsu. These manufacturers have a good UK support network and spares system should you ever need it. You may find a brand that is cheaper initially for the actual capitol equipment but then when a spare part is required a number of years later it cannot be obtained.
Panasonic offer a range of wall mounted systems called the Etherea range that are suited to server room cooling, This range has the option of fitting a hardwired remote control. We would always recommend that you choose a system that can have a hardwired controller fitted. The controller obviously cannot then be lost compared to a hand held controller, but more importantly can be configured so that parameters are password protected.
The Mitsubishi FDEN series under ceiling air conditioning units are another range that are frequently installed into server rooms. These models come in a wide range of outputs and can be ceiling mounted onto unistrut brackets physically under the ceiling, and hence a false ceiling void is not required. They are available in 3 phase options also for larger outputs with all models having a hardwired remote controller as standard.
Fujitsu like the other air conditioning manufacturers offer a complete range of systems that are similarly priced and of a similar quality.