Liquid-cooled broadcast transmitters have been around for a long time. In modern liquid-cooled designs, heat from the power amplifier modules is transferred through metal heat sinks to an “anti-freeze” fluid flowing through them. The heated liquid is pumped outdoors and through a heat exchanger with a fan blowing on it, much as in an automobile cooling system.
After a few years installing and working with liquid-cooled transmitters, my feelings about them are mixed. There are situations in which they make sense, but others where the downsides outweigh the ups. I’m sure there’s plenty of room for debate.
The installation of a liquid-cooled transmitter is much more complex than that of an air-cooled type. Important tasks include running hoses, putting on connectors, connecting pumps, installing heat exchangers (concrete pads?), leak testing and filling the system with fluid. Your maintenance program will involve the pumps, hoses, liquid tests, fans and heat exchangers.
Control and monitoring must consider the pressures and temperatures of the liquid and operational parameters of the variable speed pumps and fans. Most of this is monitored by a complex system, and cleaning and repairs of liquid technology require knowledge of such systems that a broadcast engineer may not already possess.
What’s the upside? The most obvious is removal of heat from the transmitter and less heat load in the building. About 67 percent of the heat of a transmitter is delivered outdoors to the heat exchangers.
Liquid cooling means less air must circulate through the building; operation can be cleaner and quieter.
Another major factor is the cost of electricity. We find many estimates of what power will cost us in the future, but it is unlikely to cost less.
Any good analysis of transmitter costs must include all relevant factors both internal and external. An analysis of building cooling needs in Tucson will not be useful for a transmitter site in Bangor.
Air conditioners have their own maintenance and upkeep issues including filter cleaning, recharging, fan motors and monitoring challenges.
Thought starters
Here are some questions with which to start:
Is the transmitter building already full and hot? Is there space adjacent to the building for heat exchangers? Can the heat exchangers be secured from vandalism?
Will there be significant savings in the costs of cooling the building by using liquid, or could you use readily available cool fresh or air-conditioned air?
Is altitude a factor? Air cooling requires more air moving through a transmitter to dissipate heat at higher elevations than at lower elevations.
Transmitter technological advancements come at an astounding rate. Improvements in the efficiency of power supplies, amplifiers and other components make any analysis done with older designs irrelevant. More efficiency means less heat loading. Liquid- and air-cooled designs create similar amounts of heat; the difference is how the heat is dissipated.
Kevin Haider of GatesAir recommends that when you are calculating electricity use and transmitter power, you should consider the possibility that you could add HD Radio channels at some point.
More HD means higher transmitter power and more heating load in the building, so you may wish to future-proof by designing a transmitter system and site that are robust enough to handle such changes without expensive facility upgrades. Haider suggests that liquid-cooled transmitters may fare better running near full power than equivalent air-cooled transmitters.
Liquid cooling is practical in an age where virtually every critical parameter can be monitored and controlled. But it’s important that someone who knows how to maintain the system is involved. A reliable engineer can pick up the basic skills, but do the research and consider how you will support your system.
And everyone I’ve talked to in this area strongly recommends that when it comes to the actual installation, bring in someone with experience in liquid cooling. While I like to handle projects myself, even I can tell that liquid cooling is not the time to “go it alone.”
I’ll return to this topic in more detail soon. Meanwhile, what’s your experience with fluid vs. air cooling? Drop us an email. Write to me via [email protected] with “Fluid Cooling” in the subject line.
The author wrote earlier this year about working with caps in a phase converter.
