Backup cooling

One of the issues that I have seen at many transmitter sites is inadequate cooling. Time was, when mostly tube transmitters were in use, a simple fan connected to a thermostat was all that was used to cool most transmitter sites.  Even then, however, that setup was lacking for several reasons.

Those reasons are:

  • The amount of cooling provided was limited by the amount of heat in the outside air.  On cool winter days, this is not a problem, but on hot, sticky summer days it could be.
  • No removal of humidity from the transmitter room was possible.  This often leads to excess oxidation, corrosion of metal parts, and so on.
  • No matter how much filtering was used, bugs, dirt, and other debris were sucked into the fan, making transmitter room cleaning a chore.

With solid-state transmitters, air conditioning is required.  Solid-state transmitter devices are far less rugged than tubes when it comes to heat.  In a high-heat situation,  a tube transmitter will keep running until its control circuits malfunction, or it catches on fire.  A solid-state transmitter will crash long before either of those things happen.

Air conditioners should be adequately sized for the heat load plus a little extra.  That information can be found in a previous post: A tale of two air conditioners.

As we all know, equipment malfunctions.  When an air conditioning system goes bad at a transmitter site, things start to happen fast if there is no backup.  That is when a backup cooling fan can save the day.  A good rule of thumb for sizing a cooling fan is to exchange the total volume of the transmitter room every two minutes accounting for resistance from louvers and intake openings.

3200 CFM cooling fan, WHUD transmitter site
3200 CFM cooling fan, WHUD transmitter site

This fan is connected to a 120-volt contact on a thermostat attached to the ceiling of the transmitter room.  The thermostat is set to 90 degrees, which gives a good bit of headroom for the air conditioners to maintain the room temperature while turning the fan on before the room gets too hot. It is also important to monitor the room temperature via remote control.  Having an alarm contact connected to the fan thermostat is also a good idea.

There is no such thing as too much backup.  Installing a louvered cooling fan affords a little bit of extra insurance.

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3 thoughts on “Backup cooling”

  1. Yeah, well. Let me just add that in the climate you are probably familiar with, hot is probably 35c.
    Here, we have the added joy of temps up to 48c, and fan cooling is most definitely not going to cut it.
    A stable environment is essential for the long term reliability of electronics. Non mil spec components are mostly rated to 35c or thereabouts. On a 45c day plus heat load from transmitters, stls etc the temp in a sealed building is going to zoom past that quickly.
    I’ve seen a room with nothing but computers (one was a mainframe or mini) and one a brand new NEC server for a netware network. Over a long weekend the AC died and on Tuesday when we opened the door the temp was over 55c. The ancient mini was still up and running, probably because it had huge forced air internal cooling that at least kept the air moving through. The NEC server had quietly died.

    Heat and cool cycles cause a range of problems, from ‘chip creep’ where IC’s and other socketed devices (even cards in pcs) gradually work their way out of the sockets due to thermal expansiona and contraction. This also leads to dry joints on pc boards and such.

    As you say, there is no such thing as too much air conditioning. Where there are computers and other solid state stuff as well, it’s not just nice to have, but critical. I refuse to work on delicate stuff unless it’s in a controlled environment, dripping sweat all over stuff you are working on is not an option.


  2. Geoff, In those climates, (for my US readers, 48C is 118F) redundant air conditions is the only way to go. Another recommendation for transmitter sites, have the transmitter cut back to 50% power if an air conditioner fails. I do not know what type of remote control equipment you use, but most of our sites use Burk ARC-16 with autopilot. If there is a high temperature alarm, we have the software configure to cut the transmitter back. With computer server rooms this is not an option.

  3. Don’t forget the other end of the temperature range. Many sites now include gear with internal hard drives (IBOC exciters, monitoring equipment, desktop computers, etc.) and the temp range for the drives is 0-40C if you’re lucky. Here in New England, temps often go below 0C during the winter, and hard drive failures are the unfortunate results. The oil in the bearings gets too thick and things don’t move like they should. Data gets written incorrectly and the system crashes. The old tube equipment didn’t care about sub-zero temps; it just kept generating heat and hummed merrily along. Not so with this new-fangled solid-state stuff.

    I know of one solid-state 1kw AM site that had no heat at all. In the winter the building basically got as cold as it was outside. The IBOC exciter used to die once a month, and needed a new hard drive two or three times a year. They had to install two 1500w room heaters to keep the building temp up to at least 5-10C, just to keep the hard drives and computes happy. So, the station used 1-2kw for the transmitter, and another 3kw for room heaters during the winter months. Not very efficient.

    Bob M.

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