The problem with your sealed unit is fourfold:-
- As the unit heats it will expand under pressure, after a number of years of continious expanding and contracting the seal will eventually give way and the dry air will be expelled from the unit.
- As the unit cools it then sucks in cold moist air.
- The moisture is trapped as the unit re-seals.
- Once the desiccants are saturated the moist air when heated will rise and condense on the outer pane and in the colder weather will become foggy.
To solve this fourfold problem, we need to do just three things:
- We need to pressure equalise the unit by drilling two tiny holes, so that the seal on the unit doesn’t open when the sun comes out.
- We need to create an environment so that the moisture instead of turning into vapour when heated by the sun will evaporate.
- We need to install a tiny plug that will keep the air inside the unit to create a thermal barrier, but will also allow air to pass when placed under pressure.
The most common question we are asked is, will your pressure equalised unit have the same thermal value as a sealed unit? The answer is undoubtedly YES! Because dry still air is a poor conductor of heat, the thermal barrier is created by dry still air in between the two panes of glass. After the repair, when the unit is heated by the sun the moisture will evaporate on a daily basis, until both the desiccants and the unit are completely dry.
The two plugs are then installed and will hold the now dry air between the two panes and so create the thermal barrier.
However, when the unit is placed under pressure by the sun a minute amount of air will pass through the plugs out of the unit, therefore only a minute amount of air will re-enter the unit, the desiccants will grab that moisture so the air in the unit remains both dry and still.
The end result being that the unit maintains a stable thermal value and doesn’t produce condensation.