I wasn't happy with the amount of space the rac used up in the MK1 version and airflow was whatever the rac fan provided, so a rethink was required, a bit of google, more reading, scratch a few ideas on paper, blah, blah.....
The kiln now looks like this
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MK2 builds on MK1 by adding an outer skin, under the floor and back, this gap provides a path for return air and it picks up the air off the rac.
The air is drawn thru the stack, down the front under the floor and up the back to the fans that sit on the top then down the back of the stack and thru the stack.
I mounted a fan in it's own box which sits on top of the fan plenum, I can add a further 2 fans but I dont think I'll need them, the fan plenum directs the air down the back of the stack, I also designed the back section so I can add a glass section to make it solar as well,(MK3)
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Here I am adding ribs to the underside of the floor, a rear view and front and rear curves that help the air turn the corners
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The heated air off the condensor enters the outer back skin via a centrally located hole and ducting
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One of the things I noticed with MK1 was that as the air became dryer and hotter the evaporator was unable to cool the air enough to condense any water thus negating the whole exercise, in MK2 I return some of the cooled air (~ 10 to 15%) back thru the evap to be further cooled, I have measured 0 to 7°C air temp off the evap (depends on kiln temp) so if I maintain a kiln temp of 35° and an air off evap temp of say 7° as moisture is removed my RH will drop to ~16% in the kiln
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With 2 fans and rac on a cooling cycle current draw is about 4 amps, this about 1Kw, when everything is upto temp the cooling cycle is on for about 10 to15mins in an hour, so for a domestic tariff of 20cents/kwhr it will cost about 20x.25 cents/hr to run

Pete