Yesterday, we were asked to look at a job and submit an estimate for a former Bell Telephone site. The commercial building has approximately 50,000 square feet of heated space. Bell Telephone stopped using the building around 1990, and it is currently occupied by five tenants; each tenant has approximately ten thousand square feet of usable space.

According to the original prints, the "Ma Bell" hydronic heating system was able provide different temperatures to different areas of the building. For example, the administrative offices were fitted with individual zone valves for each of the seven large offices. The rest of the offices were controlled with one thermostat (with a sensor) with a large pneumatic three-way valve. The machine shop temperature was controlled by a thermostat connected to a pneumatic three-way valve. The parts department had a separate three-way valve and pneumatic thermostat. The vehicle repair shop had a thermostat and another three-way zone valve. Finally, there was yet another zone for the enormous domestic hot water tank heat exchanger.

When we visited the site, we learned that approximately half of the building had had rooftop heating and cooling units installed. The original heating load for the boilers was a little more than one million BTUs. As was typical for this type of building in 1975, there were two boilers. Each cast iron boiler was sized to handle the load; the second boiler was redundant. There are three high head base mounted pumps: one was a backup and the other two were used for the four large zones. Another large inline pump was dedicated to the administrated offices; this zone was piped directly to the boiler supply header. I suspect the President or CEO wanted his office to be heated first with the hottest water. There was also a zone valve to divert water back to the boiler to prevent the boilers from condensing.

We spent a lot of time studying the system and learned how it had evolved over the last fifty years. If I had to guess, Bell wanted and was willing to pay for the best most reliable system money could buy. Pneumatic controls were at or near their peak in 1975. Honeywell used to have their own installers and maintenance people. Years later, some of the Honeywell pneumatic control guys taught a class or two I attended. Honeywell pneumatic was considered the "Cadillac" at the time. Unfortunately, the system has not been maintained and is currently in poor condition.

The boilers, burners and nearby boiler piping were removed by others before we arrived at the site. We know they were Weil McLain model 84 boilers based on the certificate and the prints. Most of the piping above the boilers, the base mounted pumps and expansion tank were in poor condition. We suspected that the boilers and base mounted pumps were leaking for some time. On a positive note, the pipe distribution system looked excellent.

As we looked up at all the piping, control valves, wiring and miles of pneumatic hose and copper tubing until our necks were aching, we came up with a plan:

• Remove the leaking and no longer functioning three-way pneumatic valves.
• Remove and replace the three leaking or missing base mounted pumps with more efficient inline models.
• Remove and replace the inline circulator pump (leaking and mounts sagging) with an efficient model.
• Remove the two-hundred-gallon overhead DHW tank and piping, as it has been abandoned for years. We were told the current residential forty-gallon gas fired water heater keeps up just fine. I’m guessing many of the tenants have their own DHW heaters -- especially the two private schools with little kids.
• Remove and replace the expansion tank with properly sized model.
• Provide and install a sequencing control designed for three boilers.
• Provide and install three small cast iron boilers, piped primary secondary into a large diameter supply and return headers.

We spent a lot of time studying the system and learned how it had evolved over the last fifty years. If I had to guess, Bell wanted and was willing to pay for the best most reliable system money could buy.

We considered installing condensing boilers for this project. Unfortunately, every aspect of the hydronic heating system requires high temperature boiler water. There is finned tube hot water baseboard in the administrative and general offices. The other area that is still heated by the boilers is the former vehicle repair area. This area is now used as a sports training area with large overhead doors with no insulation. There are a few hydronic unit heaters in this area.

On this job, the owner wanted to keep costs down and wanted a simple reliable system. I suspect condensing boilers would reduce fuel consumption during the moderate months, but may not be the best fit in the colder months; especially since the blower units appear to require 180-degree water temperature.

On this job, I was reminded of how this "cutting edge" system that was installed fifty years ago is now considered "old school." I can only imagine the amount of money Bell Telephone paid to have the original system installed. It is a shame that almost every component in the boiler room is outdated and nearly impossible to get parts for. I suspect that in less than twenty years, my successor (my son) will be saying the same thing.