by Robert M. Nordlund, PE, RS
Association Reserves, Inc.
We were recently on a site inspection for a luxury mountain timeshare. It was a relatively new property, and the engineer had plenty of tales of the “kinks” that he had to work out to get the facility running smoothly. The story of the garage goes like this.
Like most mountain resorts, the underground parking area is enclosed and heated. Here, the garage airspace was heated by one enormous heating unit instead of multiple smaller heaters. There was also a very powerful exhaust fan at the opposite end of the garage, to draw out automobile exhaust fumes and provide circulation through the garage when the heater was running. By design, the building’s four boilers (for heating, hot water, snowmelt, and pool/spa) were located in a large mechanical room within the heated garage. The clever architect designed the boiler system to draw their intake air from the heated garage airspace. This allowed the boilers to operate at maximum efficiency by using air that remained within a consistently warm temperature range, in contrast to the cold (inefficient) outside winter air. But during the first winter, all the boilers regularly shut down in the middle of the night, with the unfortunate consequence that there would be no building heat or hot water in the morning!
The puzzled building engineer decided to stand watch in the mechanical room overnight to determine the cause of the mysterious boiler shut down. What he found out early the next morning revealed a surprising chain of events!
In the middle of that cold winter night, the garage heating and exhaust system had finally been activated. But since the heating system had a two-minute warm-up delay, the first thing that happened was the exhaust system began sucking air from the garage, lowering the garage air pressure significantly. The dozing building engineer was awakened by the discomfort of his ears popping. The garage exhaust fan was so powerful that it was actually sucking air into the garage through each boiler’s chimney, reversing the airflow through the boilers, drawing flames into the mechanical room, and activating the automatic shutoff on three of the four boilers.
As the engineer jumped up to inspect the boilers for damage, he noticed that the pool boiler was still functioning. By then, two minutes had passed and the garage heater finally cycled on. His ears popped again as the garage re-pressurized, and he watched in dismay as a forceful stream of heated air blowing into the mechanical room from a vent adjacent to the pool boiler extinguished that one remaining flame!
What was the fix? The engineer placed the garage exhaust system on the same two-minute delay as the heating system, so both came on at the same time. Then he re-piped the air duct into the mechanical room to draw from cold “outside” air. Although using heated mechanical room air was a good idea in theory, the design was foiled by overly powerful garage heater and exhaust fan and resolved by a diligent and resourceful building engineer!