Dog Days of Summer

That saying originates from Greek and Roman times, when Sirius, the Dog Star, aligned with the Sun during July and August and was though to bring extra heat to the earth.  The Dog Days are evil times; seas boil, wine turns sour, dogs grow mad, and all other creatures become languid; causing to man, among other diseases, burning fevers, hysterics, and phrensies.

Bad news, indeed.  Add to that; air conditioners fail, general managers become cranky, transmitters overheat causing damage to sensitive control circuits, which is even worse.

We shall be busy dealing with things like this:

AC condenser frozen dryer and piping
AC condenser frozen dryer and piping

Air conditioning condenser with low refrigerant. This unit either has a leak or was not charged properly. I would hazard the former.

AC condenser broken fan
AC condenser broken fan

Fan blade on condenser coil failed due to metal fatigue. I have seen this in more than one place.

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

These wall mount Bard AC units are pretty reliable, however, even they fail from time to time. The best course of action is to have a maintenance plan, a backup plan and the number of the best HVAC contractor that can be found.

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.

I Got The Air Conditioner Blues

Back in the day, when tube transmitters ruled the broadcast world, common practice was to have a big cooling fan moving outside air through the transmitter building connected to a thermostat.  Temperature swings of 30 to 40 degrees were common, however, the tube rigs could handle almost any temperature that didn’t melt plastic or freeze water.

Today’s solid state transmitters are not that rugged.  They like to have there rooms around 70 degrees +/- 10 degrees or so.  Not to mention the other computer controlled equipment commonly found at a transmitter site.  Things like air chain processors, STLs, remote controls, etc.  So, lots of air conditioning is the norm, and with lots of air conditioning comes lots of maintenance.

Air handler air filters need to be checked and replaced often.  Condenser coils seem to attract every type of flying debris on the planet and need to be cleaned once, possible twice per year depending on tree and weed species near the site.  Even with the preventative maintenance, occasionally things like this happen:

AC condenser frozen dryer and piping
AC condenser frozen dryer and piping

Of course, the entire cooling coil inside is frozen solid.

This condenser is low on refrigerant, causing icing problems.  It has a slow leak somewhere and is about to be replaced.  Other reasons for this happening are malfunctioning or non-existent low ambient kit on the condenser fan.  Sometimes less than knowledgeable persons will install a 5 ton unit designed to run throughout the year but not take into account the effect of moving below freezing air at high speed across the coils.  Insufficient air moving across the cooling coil will also cause this.  Insufficient air flow can be due to plugged air filters or clogged fan/blower blades.

This one is even better (same condenser unit):

AC condenser broken fan
AC condenser broken fan

The fan blade is sheared off and jammed into the condenser coil.  This happened during power transfer from generator power to commercial power.  Naturally, it was at 1 am in the morning after a pole mounted transformer had been replaced.  When the building transfered back to commercial power, I went outside to use the “bathroom” before my two hour drive back home.  I though I smelled something hot, you know that cooked paint/plastic smell, but couldn’t really track it down… the winds were kicking up and another thunderstorm was on the way.

The next afternoon, however, when the sun was up and the site was working on one air conditioner, the temperature alarm went off.  Upon arrival, I found the condenser breaker tripped, resetting it caused the building lights to dim.  The fan motor was shorted to case.  I would theorize the aluminum fan blade suffered from metal fatigue, likely because the blades were not balanced causing a vibration.  When the power transfer occurred, there was just the right combination of torque and centripetal force to cause the blade to rip, then lodge in the condenser coil.

The fan motor has replaced, but I think it is time to replace the whole condenser unit, which will be expensive.

AC&R Gauge set
AC&R Gauge set

I found having a set of gauges to check the head pressure and suction is a good diagnostic tool to quickly pinpoint problems with HVAC units.  This way, when the HVAC tech shows up, you can quickly point him in the right direction.