hi ashley here and today we are going to build a laminar flow hood so that i can have a sterile
environment for my mushroom grow we will be making a 24 inch by 24 inch flow hood and i decided to
go with the cash biomex hepa filter that has a 99.97 efficiency rating and a 0.3 micron filter
what that means is anything that's bigger than 0.3 microns gets filtered out i found this filter at a
local company called pci filtration services they gave me a great deal and i was also able to pick
it up so i saved on shipping then after countless hours of searching for a blower i decided to go
with the dayton 1tdu2 we want the velocity of the flow hood to be about 100 to 200 cubic feet per
minute because this should provide a laminar flow of clean air but not so much flow that it blows
things over and not so little flow that becomes turbulent if we look at the characteristics of
the blower's curve and the characteristics of the hepa filter's flow curve we can determine where
the blower will operate we know the hepa filter that i purchased has a test flow rate of 650 cubic
feet per minute which gives it a pressure drop of 0.9 inches of water and we found this information
on the label of the filter and the pre-filter has a pressure drop of 0.3 inches of water and
we found this information from a study on furnace filters and with this information we can plot a
few points of our hepa filter curve to see where the curve will intersect the blower's flow curve
okay let's look at the math to determine the approximate flow rate produced by the blower
first i want to mention that our hepa filter is 24 inches by 24 inches so that gives us four square
feet i will also be using a few variables fr for our flow rate and delta p for our pressure drop
first i must combine the two filters into a single line that can be plotted on the blower's graph
to do so i take the hepa filter's resistance and divide it by the flow rate and i got this
information from the flow data on the hepa filter that i purchased then we do the same thing with
the pre-filter using the figures that i found online adding these two figures together will give
us the combined resistance of the two filters now we can plot the pressure drop for any given flow
rate so let's go ahead and do that i purchased the dayton 1tdu and here's its specification sheet
and here is its flow curve on the graph and what i did is i went ahead and blew up this flow curve
or this graft in order to make it a little easier to see the first thing that we need
to do is plug in a few flow rates to find the pressure drop i will be using 260 780 and 1300
so if we look at the math we can plug in 260 780 and 1300 which at 260 we get a pressured up
of 0.51 at 780 we get a pressure drop of 1.5 and at 1300 we get a pressure drop of 1.9
now what we can do is we can plug these plots into our graph to find our hepa filter curve
so let's do the first one 260 and 0.5 is about right here
then 780 and 1.5 is about right here then 1300 and 1.9
is about right here we can also use our test flow data from the hepa filter which is 650 and
0.9 which is the 650 is about here and our 0.9 is about right here which is right on our flow curve
it's perfect then we can draw out the line of our flow curve which is not perfect sorry and we
notice that the hepa filter intersects with the blower's curve at 845 cubic feet per minute
and if we divide that by our four square feet we know it should be approximately 200 cubic feet
per minute which should be sufficient to create a laminar flow but also could be reduced if needed
now i just want to take a second to look at a smaller blower for comparison using the same data
as from above so i am looking at the dayton 1td 9 t9 1td t9 and here is its specification sheet
and i did the same thing and i went ahead and blew up the graph and we're going to be using the flow
rate points 160 480 and 800 and i'm doing the same math as before so i'm plugging in our flow rate
160 480 so at 160 that's 0.3 pressure drop at 480 it's 0.9 pressure drop 0.95 and at 800 we get 1.5
so now what we can do is we can plug those in so at 160 we are at point three right here
at 480 we're at point nine which is about here's eight 9
480 right here and then at 800 we're actually all the way up here off of the graph at 1.5
so if we make our lines which maybe i should use as more this time and do from here to here
from here to here and all the way up
there is the flow curve of our hepa filter then if we determine where it crosses the blower's curve
looks like it's around 400 cubic feet per minute and if we divide that by our four square feet
that gives us about 100 cubic feet per minute i believe that this blower would also be sufficient
as well as it will be able to create a laminar flow but i ended up going with the bigger blower
because i just wasn't sure if your flow rate is too fast you can always drill holes in the back
of the box to vent out some of the speed or add a flow straightener like honeycomb inside of the box
as for right now i believe this will give me a sufficient sterile environment so we're just
gonna go with it and now what you guys have all been waiting for let's build a laminar flow hood
so for our first step you will need to cut the four pieces that make up the main cabinet
the top and bottom pieces are 25 and a half inches by 24 inches and the side pieces are 25 and a half
inches by 25 and a half inches then sand down all the sides to smooth out any rough edges
second cut the 2x3 to 24 inches to use as a backing for the filter then measure back how thick
your filter is our filter is eleven and a half inches thick so that's how far we measured back
also make sure that your screws are not too long where they poke through the bottom
now fasten the two by three to the top and bottom pieces with wood screws
now we are ready to build our main box attach the sides with wood glue and wood screws
also you want to make sure that you pre-drill all of your holes
if you don't pre-drill your holes you could end up splitting the plywood we used four screws per side
now check to make sure your filter fits we want to try to prevent any air leakage around the filter
additionally we want the filter to be snug but
still be able to get in and out without force you think this is ever gonna get back in here
now it's time to add the blower
measure the hole to eight inches and three quarters by 5 inches and 9 16 or you can
just trace the top of the blower that's what we did then drill four pilot holes
big enough for a jigsaw and cut the holes with a jigsaw
and sand the edges
next we need to install the weather stripping this is used to seal the
space between the outlet of fan and the top of the box to prevent any air leakage
simply attach the weather stripping i had peel and stick it weather stripping so it made it really
easy i just used a pair of scissors to cut the correct length and then stuck it around the hole
now we need to add the plywood strips first cut three strips of three quarter inch plywood
measuring at five inches and nine sixteenths and one at eight inches and three quarters
then you will need to drill one hole in each side strip for a bolt to hold the blower in place next
clamp down the plywood strips to hold the weather stripping in place then fasten with wood screws
now it's time to attach the blower
first you will need to mark where the holes are going to be drilled on the blower
then carefully drill the holes in the side of the blower
and attach the blower to the top of the box we also added a small support shim
now we are ready to construct the pre-filter box cut the four pieces that make up the pre-filter
box the front and back measure to 16 and three-quarters by 24 and three-quarters and the
sides measure to 15 and one quarter by 16 inches and 16 and three quarters by 16 inches one side
is a little bit smaller so the filter can slide in you will also need to cut two plywood strips for
the filter rails to attach to the inside of the box then assemble and clamp the pieces together
and attach them with wood screws the purpose of the pre-filter is to remove the large particles
and contaminants in the air and extend the life of your hepa filter next attach the
filter rails to the pre-filter box then attach the pre-filter box to the top of the main cabinet
make sure that you get a snug fit around the blower
then use wood screws to attach the pre-filter box to the main cabinet
now it's time to wire the blower first punch out the little metal hole inside the wire box
then attach your wired armor cable to the blower's electrical
i just went by the diagram that was on the blower now it's time to add the switch drill
a one inch hole with a drill bit in front of really wherever you want we did it in front
because i didn't want to make the filter any wider than it had to be
then add the switch box
then wire the switch and add the face plate
next we need to install a few small plywood strips as backing for the back panel
now for the moment we've all been waiting for it's time to install the hepa filter
now carefully slide the filter into the box without forcing it it should be really snug
but you shouldn't have to force the filter into the the box just slide it in then silicone all of
the edges and crevices inside the box we need to try to prevent any air leakages then install the
back panel and fasten with wood screws around the outside of the box and silicone the back
finally cut the four front facing plywood strips and then fasten with wood screws
and now you have a sweet laminar flow hood thank you so much for watching and please subscribe