From their information its seems that you are software guys doing porject in microsoft .NET technology. They want to interface & control some embedded hardware like control system for AC plant.

For you PC based DATA AQUISTION card /modules from Dynalog / National Instruments will be best option. These cards/modules are either pluggable type in motherboard slots or external box with RS-232/485/etthernet interface. These are having input for most type of sensors(temp, pressect) / voltage / current input / digital I/O. If you want some control then relay / solid state realy & other option are available.
These cards are supplied with full drivers library / interfaces /drivers for developing appl software in C, C++ , Visual Basic & lots other langa.