We've got several small portable data loggers that we use to monitor temperature, humidity, and co2. Ours are made by a company called hobo. I know the company also makes current data loggers. I believe they have a 15 channel data logger in the catalog. The advantage is you don't have to have a laptop tied up while you're doing the data collection and the software can calculate the "area under the curve" and give you total energy usage over many days or weeks.
You put the equipment in place and return later to dump the data onto your laptop where the report is generated.
Total cost: a few hundred dollars.
