johnandrew70 said:
What i would like to know is why don't caravan manufacturers vent the fridge flue the same way as they do for the space heater, Surely this would be easy enough to do by boxing in a flue pipe right up to the ceiling,
I understand the ordinary fridge vents need to be there so that cool air circulates and cools the fins on the back but i could never understand why the flue had to be there as well. I am sure there is a reasonable explanation for this.
Hello John,
Damian has given you the finance directors answer, but the technical director would have two linked technical reasons:
The problem with small flames is they don't release a lot of heat and that means they are far more sensitive to external influences such as flue terminal temperature and length.
In a convection combustion tract you need enough heat in the products of combustion to keep them buoyant and thus intent on rising. If you increase the length of a flue, the increased surface area of the flue can cool the flue gasses more, and with the small flame of a fridge, it could easily cool enough to condense and baffle back.
You would have to increase the size of the flame just to drive the flue, and that will adversely affect the thermal efficiency, which by law must be more than 70%.
Interestingly, the original Truma/Carver 1800 series heaters managed to use the efficiency of the heat exchanger to cool the flue products enough to allow them to be ejected below the floor, they also condensed and could give gross efficiency of over 90%.
The same could not be done for the 3000/3600/5000 heaters as the flue products were too hot after they left the cast heat exchanger so they needed a continually rising flue to 'draw' the air and flue gasses through the heater.
Condensing domestic boilers achieve their improved efficiency by passing the flue products over additional heat exchangers, To do this and to overcome variable length flues they utilise forced air or blown combustion to drive the flue products.