|
During the heating season the most difficult time to heat is when the outdoor temperature is fairly cool in the morning and then warm in the afternoon. The slang terminology for this is called "the in between weather". The most common reason why expansion tanks are full during this time is because of extreme expansion and contraction of the water throughout the boiler system. The boilers are called on for heat during the morning to warm things up, and then by afternoon they are shut down because the outdoor temperature is fairly warm, and the indoor space is becoming uncomfortably warm. At this point the boilers are off and they remain off for a long period of time. As the water cools off it also begins to contract so to speak, the water is made up of tiny little molecules, and the molecules cool off settle down and the spaces between them reduce as they cool. With this cooling of the water the system pressure drops, and in some cases especially on large systems, the pressure drops low enough that the systems' automatic water feeder starts to feed water into the system to compensate for the loss in pressure. Its now morning, the building is rather uncomfortably cool, so the boilers are started up. The burners fire and we begin to transfer vast amounts of heat energy into the water. As the molecules are warmed they begin to move more "vigorously" and the spaces between the molecules become much larger. As we heat, the water begins to expand, and system pressure starts to increase, the system was over filled when it was cool, and the expansion tank is trying to absorb or cushion this larger than normal volume hence becomes water logged and in some cases the relief valve on the boiler opens and dumps water until the system pressure is below the relief safety pressure setting.
|
|
