I'm not a sysadmin, but an energy consultant and software developer, but there's a story from a datacenter, that I love to tell, because it shows how far you can take it if you're determined.
I attended a conference on green IT, and there was one guy from a consulting company in Bremen, Germany, who run their own datacenter inhouse for themselves and their clients. Not a huge one, but for the type of company, it was fairly large, maybe some 50 machines. Moreover, it was constantly growing.
One day, the CEO, who was giving the talk, lost his patience with the sysadmin requesting ever more powerful cooling and ventilation gear as their server room grew and grew. These devices started to draw as much on the budget as the servers themselves. Next time the admin wanted a cooling unit, he made the guy sit down and explain all he knew about why the server room has to be at 20 °C. It turned out that nobody really knew, so they started an extensive research.
First thing they realized was that the temperature on the hardware components is important, not the room temperature. So they compiled a list of all components they were using, and got detailed heat tolerance data from the manufacturers.
Next, they made sure they had constant realtime temperature readings from right on the components, at least for a large enough sample.
Now, they slowly started to allow the room temperature to go up, keeping an eye on the components' temperature. This alone made it possible to go up to 25-30 °C. When they were slowly approaching critical temperature on the components, these were still far hotter than the room, so they tried to improve air circulation and to turn up the ventilation units. The main idea was to go as far as possible on ventilation alone, because that's way cheaper than cooling.
This process went through a couple of iterations and they repeatedly refined and upgraded their ventilation system, while raising the average room temperature. When they got to 45 °C, they began to feel their safety margin was getting too small, and they couldn't improve the ventilation further. They took a step back to 40 °C and this is now the permanent operating temperature of the data center.
They draw the air for the ventilation from outside, which helps a lot in cold German winters. The cooling has only to be switched on at all on particularly hot summer days. In winter, they reuse the heat extracted from the data center to supplement the heating system. That way, the combined energy bill for power and heating for the whole company has gone down 80%.
The server room is now very hot, and very noisy, because of the strong ventilation. They had to put extra noise insulation on the walls, to not disturb the offices next door. Admins hardly ever enter the room, because it's not exactly a great working environment. For scheduled maintenance, they start to cool down the room two days before. In an emergency, the admins put on ear protection and change into swimming trunks (no kidding), before going in.