Commercial HVAC in Alexandria.

Alexandria’s commercial buildings are older and tighter than most of Northern Virginia: restaurants and shops in the brick blocks around King Street and Old Town, offices and strip retail along Route 1 and Duke Street, and medical offices in the mid-rise buildings near Eisenhower Avenue. Old buildings mean small roofs, odd access and equipment squeezed in wherever it fit.

Two of our Alexandria calls were restaurants on rooftop units, and they tell the story. On one, power was dropping a phase and the disconnect had gone bad. While we were up there we found the heat exchanger was cracked, so we condemned the unit and shut the gas off. A cracked exchanger on a gas rooftop unit can push combustion gases into the air the kitchen and dining room breathe, and nobody gets to keep running it.

The other was a leak search on a 17.5-ton rooftop unit over a kitchen, a unit with four separate refrigerant circuits. A system that size doesn’t announce which circuit is leaking, so we pressurized with nitrogen and worked through the circuits until the leak showed up. It’s slow, and it’s the right way: guessing at a recharge on a four-circuit unit just burns refrigerant.

For Alexandria owners, the practical point is that the restaurant roof does a harder job than the office roof. Grease, heat and long hours wear out belts, bearings, contactors and heat exchangers faster, and a landlord who counts on a lease can lose a tenant to one bad week in July. A maintenance visit in spring and fall costs far less than a closed kitchen.