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I'm facing a heat issue with a CCA 4000 FM that's currently venting the stack air outside and the daily temps have been exceeding 100 degrees. The Shack was quite leaky and the existing AC is not capable of providing enough cooling to consider recirculating the air....
My options are:
Opening the door and cooling with 100 degree air?
Venting the stack air into the room and cool it with more AC?
Most sites vent the stack and place air conditioning inside. This is not the most efficient way but this is the case at many sites. The transmitter draws air from the room, so it is sending the conditioned air out. This sounds like what you are doing. I replace the ac unit every 4 years or so.
One site uses outside air with good filters but they are on a hill and have lots of free air with flow. The old WNAP site has 2 20H series transmitters with a simple fan in the roof vent. 110 degrees in the room was typical during the summer. The CCA is good to 120 degrees. Your exciter or stl might have a problem. Some people have a rack separate from the transmitter room. Your exciter goes in the cooled room.
If you open it up with a large whole house fan and vent the stack air it might keep everything working well.
We have a Harris 10K in a frame building --about 16 X 8.
We use 3 tunnel type attic fans blowing in and three more blowing out. Thermostats on each one set to slightly different levels, so they don't all run except on the hottest days.
There's a hood built above the intake fans and a frame for furnace filters to keep most of the dust out. Works reasonably well, although the fine dust still comes in as well as the real small bugs. Transmitter seems happy. Exciter and other equipment is in a separate rack, we have a couple of 4" box fans blowing on the heat sinks of a pair of Moseley 606's used for other stations fed from this location.
Tube transmitters like lots of air blowing through them...doesn't seem to matter how warm that air is.
On the other hand, my one location with a Nautel 2.5 needs air conditioned air. That early V series just didn't allow for enough ventilation.
We run a similar system at one of our site's here in south texas, but we also have about 15 ton's of AC for the two HT-35CD's that are running in that room. I would just say to add more AC if you have the budget for it.
That said, its the only site we have that scenario in play the rest we condition and filter all the ar as to heep anything from coming back up the exhaust vent.
The transmitter is a CCA 4000 and I'm wondering about the blower's rating. I was told the unit was replaced a year ago and it might be the problem. Does anyone know how CCA spec'd the blower? I can't find a manual.
I bought an indoor/outdoor thermometer and taped the remote sensor to the PA exhaust duct and have the indoor sensor at the air intake and I now know that when the exhaust duct temperature reaches 112°, the power folds back to ~ 91%.
The range of readings
outside air / intake air / exhaust duct / % of power
105° / 95.3° / 112.1° / 91% with outside door closed and a small AC unit operating
105° / 97.5° / 116.7° / 91% with outside door open and no AC.
So I'm leaning to TomT's "lots of air blowing" logic... and now I'm wanting to know how much air volume???
I have been thinking about this all day and my current 'best bet' is to install a motel type AC wall unit close to the transmitter and duct the available air from this unit into the intake of the transmitter in order to blend this cool air with the outside air that is drawn by the transmitter's blower.
When you say "drawn by the transmitter's blower" that's part of the problem. You're asking the blower in the transmitter to keep the entire transmitter room at negative pressure and do the job of sucking air from outside the building.
Pressurize the room instead. Put a supply blower on the roof of the building with a filtered intake. Duct that blower down the outside wall so the air enters low in the room. Put a hood over the transmitter, with an exhaust fan (slightly lower CFM than the intake blower) to a roof outlet. Space it off the top of the transmitter so that if the exhaust fan fails the transmitter will not see an exhaust restriction. It looks like you'll need more AC anyway as the outside air temperature is just too hot to keep the transmitter within temperature limits. Remember that as your make-up air volume increases, so does your AC requirement as you need to cool that make-up air.
If you can seal off the entire room and run enough AC to cool the heat load of the transmitter, rack gear, and building solar load, that's by far the best method. You'll have a clean room and humidity control. If you go that route, either use redundant AC units or provide an exhaust blower and motorized intake louvers on a thermostat if the AC fails or can't keep up. I don't like the "motel-type" units... many of the newer ones tend not to restart after power failures or have combination remote control/thermostat units where the batteries eventually die. Just standard commercial condenser/evaporator type air conditioning seems to be best.
"Let the BARD Sing" or get a Compac. Put a couple on the wall, each large enough to carry the transmitter plus equipment heat load. Then close the room. As someone said, add an intake fan and air loaded louvers on a thermstat to cover A/C failures. You didn't specify location, but in the Southeast at least, up to a third of the A/C load is apparent load - humidity being removed. If you allow outside air in and try to cool it, you spend a lot of energy dehumidifying it. Closed, once the air drys out, the load is the transmitter heat output plus the equipment load plus infiltration. Paint the building white - particularly the roof - and the infiltration ain't much. We've found that there's little difference in cost recirculating vs cooling outside air. Things run cleaner as a side benefit.
A google search for CCA will get you Jerry's company which still has parts and can fix the CCAs. They aren't as efficient as a power grid tetrode setup, hence there will bhe a bit more heat thrown off for a given poawer level.
Absolutely. A nice dry air conditioned room is a great thing to have.
The other thing that amazes me is how few transmitter sites are insulated at all. I see concrete block buildings with metal roofs all the time, or wooden sheds. Enjoy throwing money out the window and still having a roasting building.
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