Mainframe computers used a lot of electricity, like 120AMPs, that is about 30KVA,
or thirty single-bar electric fires in one large room. If it was not cooled somehow,
it would get too hot for the computers to function - let alone the computer operators to work.
So there were air-conditioning plants. This is a view of PLANT B, installed in 1975,
for the installation of the IBM System 370/168, which in part had water-cooled circuitry.
You can see Jeff Craig and Kevin Renney, two air-conditioning technicians, who kept the plant going.
In the front are two compressor units, each having two compressors.
These compressed a refrigerant gas until it became a hot liquid
which then passed through a lot of small tubes surrounded by cold water.
This became warm as the refrigerant cooled.
The warm water was pumped up to cooling towers where the heat was transferred to the atmosphere.
The cooled liquid refrigerant under high pressure passed through a small orifice
where it expanded to become a gas, a very cold gas. This passed through tubes surrounded by a second
water cycle that was pumped through a bank of finned tubes through which the air from the computer room
was blown. The heat from the air went into the water, the air was cooled, the water warmed.
The warmed water transferred its heat to the cooled gas refrigerant
which was compressed to a hot liquid, which ...
The ductwork through which the air from the computer room flowed can just be seen behind the compressors.