A tale of two air conditioners

It was a hot day, it was a cold day. The tube transmitter was running, the solid state (HD-1) transmitter was off the air. The books show that the company has deep pockets, but the accountant has short arms.  And so it goes.  In a sordid, yet familiar tale of leaping three quarters of the way across a river, the builders of this transmitter site seemed to think of everything except the cooling requirements for a 35 KW FM transmitter.

Instead of installing real commercial AC units, someone decided that 34,000 BTU window units were the way to go.  At one time, there were eight of those units, all single phase 240 volts sucking down gobs of power and freezing up when the outside temperature dropped below 40°F.  This was always a problem, but became more so when we took over the maintenance of this site.  When there was a full time engineer, his time, apparently, could be wasted running back and forth turning the window units on or off in the winter as required.  Now that a contract company is doing the work, it becomes cost prohibitive to require such things.

Therefore, the time had come to make a change.  To that end, six of the 34,000 BTU window units were removed from the building.  Two of the existing holes in the wall where used to create an emergency cooling system, consisting of a 4,292 CFM fan and a couple of shutters.  Two other holes were used for the new air conditioners and two holes were blocked up.  The remaining two window units were left in place in the combiner room, which is a separate cooling zone.

Bard 5 ton wall mount AC unit
Bard 5 ton wall mount AC unit and cooling fan shutter

The new AC’s are five ton wall mount Bard units.  These are three phase and should be more than enough to keep the transmitters cool.  Here is how I arrived at that conclusion:

  • The entire building load when the main transmitter is running at full power, without the transmitter room air conditioning, is 60 KW.
  • All of the building loads except the transmitters go through a single phase panel.
  • The load on the single phase panel is 10 KW, thus the transmitter load is 50 KW (this 10 KW is mostly the single phase AC units in the combiner room)
  • The TPO is 32 KW, therefore the transmitter is generating 18 KW of waste heat.
  • One watt hour = 3.412 BTU of energy, thus
  • 18,000 watt hours equals 61,416 BTUs
  • One ton = 12,000 BTU, thus
  • 61,416 BTU ÷ 12,000 BTU = 5.118 tons

That will take care of the main transmitter waste heat.  The HD transmitter generates another 4,000 watts of waste heat or 1.37 tons.  The combiner is an another room and doesn’t factor into the calculation.  The rest of the equipment is inconsequential, adding up to less than 100 watts.

The solar gain is more difficult to calculate, as it is based on the building structure, the type of construction and the heat gain (loss) through the walls and doors.  This building is concrete block, insulated, and has no windows.  It is unshaded, however it is painted a light color.  All in all, the solar gain should be less than two tons on a hot day.  Therefore the total AC load should be 8.25 tons or less.

Bard 5 ton wall mount AC unit
Bard 5 ton wall mount AC unit

All that is left now was to install the things.  Just pull up the truck and use a crane to lift them in place, except, no; that plan won’t work.  This is the transmitter site at the power plant and the 138 KV lines overhead precluded any lifting with a crane.  We instead had to build ramps and move the things around on large hand trucks.  One unit is installed on the rear of the building, the other on the front.  It required several days to make the ramps and four people to muscle the things into place.

The bottom air intake holes needed to be cut out for the new units.  Cutting into the concrete block while the BE FM 35A was running proved to be another challenge.  We used several sheets of plastic, shop vacs and extra air filters on the transmitters to keep the concrete dust out of the PA cavities and motor bearings.

Plan B cooling consists of a 4,292 CFM Venturi fan mounted on the rear wall of the building.  The fan is controlled by a ceiling mounted thermostat set to 95 degrees.  If the AC’s fail, the ceiling temperature will rise and the fan will turn on.

Transmitter site emergency cooling fan
Transmitter site emergency cooling fan

The room volume is about 3600 cubic feet, therefore this fan will change the room air about once every 60 seconds or so. It is not the best plan to move humid, potentially dirty outside air through a building, but it it keeps the station on the air while the main AC units are being repaired, then so be it.

The entire system went on line last week and is working well.

The Nautel VS-2.5 FM transmitter

This is cute. A small (VS allegedly stands for “Very Small”) integrated 2,500 watt FM transmitter.  This one we just finished installing as a backup transmitter for WSPK, on Mount Beacon, New York.

Nautel VS-2.5 FM Transmitter
Nautel VS-2.5 FM Transmitter

This site has a Nautel V-7.5 as the main transmitter.  That unit is very reliable, however, this transmitter site is non-accessible 4-5 months out of the year due to ice and snow.  The last time we had an off air emergency due to a crippling ice storm, it took an entire week to clear away all the downed trees so we could gain access to the site via snowmobile.  As such, every system needs dual or even triple redundancy.  Lack of said redundancy has lead to several prolonged outages in the past.

WSPK signal flow diagram
WSPK signal flow diagram

Last year, we were finally able to install a backup antenna after 63 years without one.  This year, it is time to upgrade the rest of the backup equipment.  The new auxiliary transmitter is connected directly to the auxiliary antenna via a five port coax switch.  This allows for use of the dummy load for testing when we are present, but removes a potential failure point in the coax switch.  There have been at least two incidences of the disk jockey accidentally transferring the transmitter into the dummy load when taking transmitter readings.  Hopefully this configuration will be fairly idiot proof.  I am making an interlock panel that will prevent both transmitters from being on the air at the same time.

Nautel VS 2.5 connections
Nautel VS 2.5 connections

This site is a work in progress.

The backup processor is at the transmitter site, the main processor is in the rack room at the studio.  This works well because the main processor occasionally looses its mind and needs to be rebooted.  It would be a significant pain to drive all the way up to the transmitter site just to reboot the processor.  It might not happen at all during the winter.  The back up processor has no mind so it is not an issue.

The VS transmitter is attractive because it has a built in exciter that accepts composite, AES or IP audio.  The exciter also has a built in Orban processor as an option.  Thus, if it really hit the fan, we could use the LAN extender to get the audio to the site.  Further, it could be addressed by any studio in the company WAN.  Which is cool, when you think about it.

Nautel continues to crank out innovative, dependable products and there is nothing wrong with that.

 

Mount Mansfield, highest point in Vermont

As alluded to in the previous post, I spent a fair amount of time at Mt. Mansfield last month. It is the highest point in the state of Vermont, topping out at 4,393 feet (1,339 M).  At the top, there is a large transmission facility that is home to WCAX-TV, WPTZ-TV, WVPS, WEZF, and several low power TV’s, NOAA weather radio, etc.  Next door, Vermont Public TV is housed in a separate building.  Here are a few pictures and descriptions.  First off all, Mount Mansfield is the home of Stowe Ski area.  They own the access road to the top of the mountain and are quite proud of it.  In the summer time, the toll for a car load of people is $26.00.

Mount Mansfield Toll Road gate
Mount Mansfield Toll Road gate

The transmitter building is below the actual peak.  This is one of the few transmitter sites that is manned 24/7, as such there is a working kitchen, bathroom, bunk rooms and so on.  I’d imagine it gets pretty deary up there in the wintertime, but perhaps not.

Mount Mansfield transmitter building
Mount Mansfield transmitter building

The transmitters are located along a long hallway.  WEZF and WVPS share a room, WCAX and WPTZ are in open bays as are the low power TVs.  NOAA weather radio and some other government transmitters are located over the garage.

WCAX digital TV transmitter
WCAX digital TV transmitter

All of the TV transmitters are new because of the recent conversion from analog to digital transmission.  WCAX is noted as channel three, which was their analog channel, they actually transmit on channel 22 with a power of 443 KW ERP.

WPTZ transmitter
WPTZ transmitter

Like WCAX, WPTZ was on channel five, it is now transmitting on channel 14 with 650 KW ERP.

The site is backed up by two 1.2 MW diesel generators, which can be paralleled with the commercial power grid, if needed, during peak demand times.  These generators also provide backup power for Stowe Ski area.   There is a 50 KW back up back up generator that runs all of the emergency transmitter cooling equipment if the two main backup generators fail.

Mount Mansfield generator
Mount Mansfield generator

All of this generating equipment requires a lot of fuel.

Transmitter building and fuel storage tanks
Transmitter building and fuel storage tanks

The TV and FM broadcast antennas are located just below the peak

Mount Mansfield TV and FM antennas
Mount Mansfield TV and FM antennas

I don’t recall which TV station belongs to which antenna. The FMs are combined into the four bay, three around panel antenna, this includes WVPS’s HD radio signal.

Mount Mansfield from the top looking west
Mount Mansfield from the top looking west

From the very top looking west into the aperture of the TV antennas.  I only stood there for as long as it took to get a good picture, then departed.  Off to the left of this view is the antenna for Vermont Public TV.

Mount Mansfield Vermont Public TV antenna
Mount Mansfield Vermont Public TV antenna

The transmission lines go down the hill on a large ice bridge.  An absolute necessity as the rime ice can sometimes accumulate several inches.

Mount Mansfield Ice Bridge
Mount Mansfield Ice Bridge

Tower base, which is the location of the highest RF concentration, according to the TV engineers.  I only lingered here to snap a few quick photos.

Mount Mansfield tower base
Mount Mansfield tower base

All of the STL antennas are mounted to the side of the transmitter building next to the living quarters.

Mount Mansfield STL antennas
Mount Mansfield STL antennas

On top of all that, as if that weren’t enough, there is the view.  I would also comment a bit on the weather.  In some cases, the site can be completely engulfed in a grey dull fog bank one minute, then the wind changes direction, the sun comes out and you see this:

Mount Mansfield morning
Mount Mansfield morning

I can think of worse things.

I regret that I didn’t have a better camera with me as several of the pertinent pictures came out blurry.  All of these pictures were taken with my cellphone camera, which works well, when it works.  It is also very convenient because it is almost always with me and I don’t have to remember to bring another gadget.  However, it this is going to be a semi-serious endeavor, I will have to take some of my earnings from these scribblings and buy a good camera.