"A quick calculation tells us how much ventilation we should have.
5 air changes per hour (as taken from the table here for “shops, woodworking” and “factories, general”)
~450m³ volume
= 2,250 m³/hour
= 625 l/s
That’s a lot
Thing is, most buildings aren’t mechanically ventilated to anywhere near that amount. There’s a big gap between what is supposed to happen and what really does. IMO, we should get something we can afford and see how we do"
I say lets built one with the metrals we can get for free or very little and see how it works st the moment there’s just to many unknown factors then we know where we stand .
I can’t even guess at the efficiency of a diy heat exchanger made from old plastic
Does anyone know the required formulae to work out what kind of surface area we need common to both h compartments to get a good efficiency of heat transfer? Presumably we could then optionally put a heater on the inside side of the inlet? We’d also need some mechanism to extract condensate?
Thin copper tubing would probably work best laid in perpendicular crossing layers? Held in place by some kind of resin?
Normally heat recovery uses plate type and plastic semes very popular because of cost.
The heat exchanges in the equipment at work are tiny in comparison to the ones used for buildings but they are stanless steel . I think it is a size V cost thing .
corigated plastic (estate agents signs) or a copper or aluminium stack would seem like the way to go .
Water just falls out of the side and collects in the bottom of the box and to the drane
This was in the comments for the system in the link I shared.
Seems to make sense: more opportunity for heat to transfer across?
" “Counterflow” heat exchangers play a neat trick. Imagine that you have two pipes glued side-by-side. Exhaust comes in HOT from the left and goes right. Intake comes in COLD from the right and goes left.
On the very right edge, we have cooled HOT air warming the COLD air intake. On the very left edge, the HOT exhaust is warming the warmed COLD intake air. This lets us use the most heat possible in our mass flow. That’s how we get about 70% efficiency: Cool exhaust heats cold intake, hot exhaust heats warmed intake air."
Counerflow is more efficient but harder to make .
Cross flow is less effective but easy to make.
Two or three cross flow stacks will mostly be in counter flow so very high efficiency can be reached .
There cross flows with a 50% efficiency should give 87.5% when stacked up .
Most units i have seen are single stack cross flow and clame 70% .
We have room for a three stack system . Let’s build it out of scrap and see how well it works .
I am happy to donate the fans unfortunately they are the wrong type but will be fine for the first experiment
The simply of a cross flow stack and the easy exit for water and easy fitting ro the box wins it for me .and if you have more than one it is just as good .
But i do have an idea but we have to explain it with a cup of tea and a pencil and paper.
A 6’6’’ X 2’2’‘X 1’ box would house three 18’'sq sacks and fans it maximum efficiency should be 87.5% and the maximum airflow will be ??L/min .
It would be a lot bigger than any diy ones i have seen and we won’t know how much ait it can move until we build it . But it should have a 1.5 times higher capacity than the one in the link