DIY ventilation heat exchanger

pladijs · 01-27-13, 04:08 PM

Ham, Kostas, your posts will greatly help me with the construction of my unit, many thanks for your input...

Ham, you are very right about the 80-20 rule. But our goals were quite different. Mine was "get rid of peaks of humidity", due to no proper kitchen hood, no bathroom exaust, and clothes drying inside in winter time. All of that in a tiny appartment; not good. Given my inefficient heat exchanger that required some simple humidity based fan control. I does not make sense to have that unit on full power 24/7 and i dont want to switch it on and off every time i cook something or take a shower. Now adding 3 more sensors and hooking it up to wifi, that was just for fun. But it will allow me collect observations on hard-to-precict relationship between, say, fan speeds and efficiency, which might indeed deviate strongly in practice from what one might expect.

But now i decided to go for a larger unit after all... I think my control then will become as simple as "run at some fixed speed, unless RH<30 (switch to min) or RH>60 (switch to max)". Confession, I will add a mode for summertime, and an antri-freezup cycle when its gets really cold). Further confession: perhaps I will add a physical switch giving a choice between "auto" (the above rules), min (holidays), max (party mode, or badly burned food alert). My internal nerd is really taking over lately, and he looks forward bigtime to estimating the optimal fixed speeds of both fans using the collected data through running some regression analysis.

I won't pre or post heat, that question was just out of interest; why one would want to pre-heat rather than post-heat.

For filtration, I went for oversizing to limit the pressure drop. Those pocket filters have square square meters of filter surface. Their advertised pressure drops are very small at the flows our units are running at. They are a bit expensive; but I'd rather pay for a more expensive larger filter (giving clean air) rather than paying for electicity to push air through a smaller filter. I also live in a city, some quite busy roads near the house, I want to keep fine particles out.

I really want to avoid going for an oversized and possibly inefficient fan; but I'd need a ballpark figure of how much pressure there is to overcome. For the ducts, I can calculate a guesstimate using for example http://storedproducts.okstate.edu/Ae...Duct_Loss.aspx or similar tools

For a flow of 60CFM, for my immaculate straight tubing of about 16inch tubes with 0.11m(4.33 inch) diameter, that tool estimates 7Pa of pressure drop. Double that for the bends going into and out of the HRV itself. For my ridiculously oversized filter, I expect 5-10Pa at the max. The big unknown is the pressure drop to expect from a HR-unit like Kosta's. 10Pa, 20Pa, 50Pa, 200Pa? Beats me... But it hugely affects the choice of fan, obviously. I would really love to hear some of your insights on this before deciding on a fan; I am still a bit puzzled on the size of some of the fans you are using. Is it simply due to the fact that you have more air to push around, and some more relevant lenght of ducts?

I thought to go for a double "DISTANCED PP CORE", but I am surprised as well that it comes out so badly out of your tests, Kostas. Is this related to the flow resistance being much lower in one direction in that setup, and you happened to be sending the cold air through that direction in your tests? I am going to have a close look at all of your pictures and steal a lot of your ideas!

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01-27-13, 04:08 PM	#11
pladijs Lurking Renovator Join Date: Jan 2012 Location: belgium Posts: 13 Thanks: 2 Thanked 2 Times in 2 Posts	Ham, Kostas, your posts will greatly help me with the construction of my unit, many thanks for your input... Ham, you are very right about the 80-20 rule. But our goals were quite different. Mine was "get rid of peaks of humidity", due to no proper kitchen hood, no bathroom exaust, and clothes drying inside in winter time. All of that in a tiny appartment; not good. Given my inefficient heat exchanger that required some simple humidity based fan control. I does not make sense to have that unit on full power 24/7 and i dont want to switch it on and off every time i cook something or take a shower. Now adding 3 more sensors and hooking it up to wifi, that was just for fun. But it will allow me collect observations on hard-to-precict relationship between, say, fan speeds and efficiency, which might indeed deviate strongly in practice from what one might expect. But now i decided to go for a larger unit after all... I think my control then will become as simple as "run at some fixed speed, unless RH<30 (switch to min) or RH>60 (switch to max)". Confession, I will add a mode for summertime, and an antri-freezup cycle when its gets really cold). Further confession: perhaps I will add a physical switch giving a choice between "auto" (the above rules), min (holidays), max (party mode, or badly burned food alert). My internal nerd is really taking over lately, and he looks forward bigtime to estimating the optimal fixed speeds of both fans using the collected data through running some regression analysis. I won't pre or post heat, that question was just out of interest; why one would want to pre-heat rather than post-heat. For filtration, I went for oversizing to limit the pressure drop. Those pocket filters have square square meters of filter surface. Their advertised pressure drops are very small at the flows our units are running at. They are a bit expensive; but I'd rather pay for a more expensive larger filter (giving clean air) rather than paying for electicity to push air through a smaller filter. I also live in a city, some quite busy roads near the house, I want to keep fine particles out. I really want to avoid going for an oversized and possibly inefficient fan; but I'd need a ballpark figure of how much pressure there is to overcome. For the ducts, I can calculate a guesstimate using for example http://storedproducts.okstate.edu/Ae...Duct_Loss.aspx or similar tools For a flow of 60CFM, for my immaculate straight tubing of about 16inch tubes with 0.11m(4.33 inch) diameter, that tool estimates 7Pa of pressure drop. Double that for the bends going into and out of the HRV itself. For my ridiculously oversized filter, I expect 5-10Pa at the max. The big unknown is the pressure drop to expect from a HR-unit like Kosta's. 10Pa, 20Pa, 50Pa, 200Pa? Beats me... But it hugely affects the choice of fan, obviously. I would really love to hear some of your insights on this before deciding on a fan; I am still a bit puzzled on the size of some of the fans you are using. Is it simply due to the fact that you have more air to push around, and some more relevant lenght of ducts? I thought to go for a double "DISTANCED PP CORE", but I am surprised as well that it comes out so badly out of your tests, Kostas. Is this related to the flow resistance being much lower in one direction in that setup, and you happened to be sending the cold air through that direction in your tests? I am going to have a close look at all of your pictures and steal a lot of your ideas!