By Robert M. Nordlund, PE, RS
Association Reserves, Inc.
We were recently doing a site inspection for a luxury mountain timeshare. It was relatively new, 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 large (huge!) unit instead of multiple smaller heaters. There was also a very powerful single 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. All the boilers (for heating, hot water, snowmelt, and pool/spa) were in a large mechanical room in the garage. The architect designed all these boilers to draw their intake air from the heated garage airspace, so year-round the intake air for these units would stay within a consistent temperature range (so the boilers would never be forced to function using cold outside winter air). But in the first winter, all the boilers regularly shut down in the middle of the night, causing there to be no building heat or hot water in the morning. A real problem!
The resourceful building engineer decided to stand watch in the mechanical room overnight to see why all his boilers were shutting down. What he found out early the next morning was surprising chain of events!
While dozing, he was awakened by the discomfort of his ears popping. In the middle of that cold winter night the garage heating and exhaust system had finally turned on. But because the heating system had a two-minute warmup delay, the first thing that happened was the exhaust system began sucking air from the garage, significantly lowering the garage air pressure (enough to cause his ears to pop)! 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, causing each to shut off automatically. Inspecting the boilers for damage, he noticed only the pool boiler still functioning. But just then the garage heater finally cycled on. His ears popped again as the garage pressurized, while he watched in dismay as a forceful stream of heated air blowing into the mechanical room from a vent adjacent to the pool boiler blew out that one remaining flame!
What was the fix? The engineer put the garage exhaust system on the same two-minute delay as the heating system so both came on at the same time, and repiped the air duct into the mechanical room to draw from “outside” air. Heated mechanical room air, and a powerful garage heater and exhaust fan, were good ideas in theory, but in this case all those good ideas did not come together as a balanced or effective system.