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OfflineGermanShaman
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Building a positive pressure Room
    #27872701 - 07/22/22 10:34 AM (1 year, 6 months ago)

Ok, So I built myself a LFH and am very pleased with the result.

Now for my next project, I am thinking about turning my growing area into a positive pressure room. The way I will achieve this is by pumping air into the room that has passed through a HEPA filter. 

I was thinking of buying a similar squirel cage fan, connecting a HEPA filter onto the output air flow and then port this into a vent at the bottom of the door to the growing room.

The fan will sit in a box that has a prefilter  on it and there will be pipe  about 120mm or so in diameter connected to the output. This will go into a connector to the vent. Since there will be more air blowing into the room than coming out the room will be maintained at a gentle positive pressure. There is also an air purifier inside the room but that just filters and circulates the air within the room.

What sort of Fan do I need to buy to ensure that there is enough air flow into the room.  I am sure the calculations are not as critical as they were for the LFH since I am not trying to create Laminar flow in the room.  Just clean air free of as as much contam as possible. I am looking at similar fans that will do the job and then will buy the other parts separatly.

Would love the thoughts of any experienced growers here.


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Offlinedeadmandave
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Re: Building a positive pressure Room [Re: GermanShaman]
    #27873283 - 07/22/22 06:26 PM (1 year, 6 months ago)

Since it's not critical to know the cfm I would salvage a furnace blower. They are powerful enough for HVAC in a house so should be plenty for one positive pressure room. Anyways that's a cheap way to get it done but doesn't really answer your question. What kind of work are you doing in this room?


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OfflineGermanShaman
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Re: Building a positive pressure Room [Re: deadmandave]
    #27873728 - 07/23/22 04:41 AM (1 year, 6 months ago)

What's the best way to salvage a furnace blower?  I am in Europe so I need to ensure that the voltage of the blower matches. I will also need to connect a control unit to it so that I can control the speed and hence the air flow.

The only thing that happens in the room is that grains in jars and bulk substrates are sitting being colonised.  The jars can sit anywhere really, its more the grain in bulk substrates  that I want to keep free of contam. My agar plates also sit in the same room but they are also sealed up.

What I really need to know is what kind of cfm I need to look for. I suppose its not that critical as its only going to be HEPA filtered air being pumped into the room.


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Offlinedeadmandave
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Re: Building a positive pressure Room [Re: GermanShaman]
    #27873873 - 07/23/22 08:44 AM (1 year, 6 months ago)

Just hit up the local HVAC people. Ask if they are replacing any furnaces and can you have the old one. The voltages will be the same as whatever is used in that area so probably the same as what you're using? But I'm not sure how houses in your area are wired nor what voltage you're trying to maintain.

I'm not sure what cfm you want, there's probably a way to calculate it based on how much air you want exiting the room. A fan speed controller will work most fans, but you can also block off parts of the air intake to accomplish the same thing.

Are you trying to keep fully colonized grain that's been added to bulk free of contam? Once it's been fully colonized it's already very contam resistant. Are you using sterilized substrate or pasteurized?


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OfflineGermanShaman
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Re: Building a positive pressure Room [Re: deadmandave]
    #27876365 - 07/25/22 08:28 AM (1 year, 6 months ago)

I dont think we have HVAC people or companies here in Europe.

In any case, I can pick up a new fan for about $100 or so. I'd be happy to pay that rather than have clean out an old fan and spend the time finding a supplier. The voltages here in Europe are 240v AC

how do I figure out how much air I want exiting out of the room?  I know the volume of the room and its not completely sealed.

Yes, I am trying to keep a room that has fully colonized grains  free of contam.  I have had issues with trich on bulk substrates. Have had far too many bulk grows succumb to trich and not fully colonize.  Just that extra step I suppose.


I use pasteurized bulk substrate not sterilized.


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InvisibleShroomintune
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Re: Building a positive pressure Room [Re: GermanShaman]
    #27887774 - 08/03/22 08:13 AM (1 year, 5 months ago)

Quote:

GermanShaman said:
I dont think we have HVAC people or companies here in Europe.




I’m sure you do, but they might have a different trade name. HVAC stands for Heating/Ventilation/Air conditioning, the tradesmen that install furnaces and ventilation equipment in homes and light industrial locations.


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Offlinedeadmandave
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Re: Building a positive pressure Room [Re: Shroomintune]
    #27888276 - 08/03/22 02:18 PM (1 year, 5 months ago)

If you're bulk subs are contaminating before fully colonized, I would reevaluate your pasteurization methods or double check that your spawn is clean.

Sorry I can't answer your air flow questions.


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OfflineEclipse3130
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Re: Building a positive pressure Room [Re: deadmandave] * 1
    #27891739 - 08/05/22 07:44 PM (1 year, 5 months ago)

Just a flowhood is needed and contam should never be an issue. I have my grow, flowhood, and spawn all in the same room and no positive pressure needed


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OfflineKemosabe
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Re: Building a positive pressure Room [Re: Eclipse3130]
    #27891838 - 08/05/22 09:00 PM (1 year, 5 months ago)

You can use a calculator like this one for the CFM. Looked quick seems to work accurately. But not sure it's entirely necessary unless you're fruiting in the room or maybe wanna replace the air with filtered air before working in there


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Offlinelivelogikal
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Re: Building a positive pressure Room [Re: GermanShaman]
    #28005645 - 10/18/22 11:18 PM (1 year, 3 months ago)

I feel like adding air movement to your flow hood room might defeat it's purpose. I make sure all air has become motionless after I turn off my stand alone HEPA filter. Sit and chill for a bit then get started. Unless you plan on turning off while using your fh, I wouldn't suggest this. How ever I've done the opposite neg pressure for marijuana. Lol


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OfflineTheUsualSuspect
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Re: Building a positive pressure Room [Re: livelogikal]
    #28005697 - 10/19/22 12:28 AM (1 year, 3 months ago)

While I would not try to talk you out of building a positive air pressure room, because that sounds cool, I dont think it will solve your contamination of bulk substrate.

I am certainly still learning, but it seems to me over and over if someone is having contamination isues its frequently in the grain prep.

Is your substrate contaminating before or after you add the grain?

Also, with pasteurization, too cold is bad and too hot is also bad. Maybe using a less nutrative bulk substrate might be worth a try, maybe coir and vermiculite.


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OfflineWalter_Wolf
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Re: Building a positive pressure Room [Re: GermanShaman] * 1
    #28323502 - 05/17/23 03:25 PM (8 months, 7 days ago)

I'm a little late to the party but maybe this is still relevant.

A quick online search gave me this numbers for overpressure demand in some random microbiology lab (can provide link):



So, this is approximtely (45 - 60 Pa) what you want to have in your clean room in my view. The level of sealing you are able to achieve for it and the total resistance from your filters will dictate the blower power and other specs you need.

I'm not able to calculate all this or suggest how to measure the overpressure value once you have the equipment, but it's the direction you need to take if you really need top notch setup I believe.

I'll ask around for some number crunching and see where it gets me. Will post back if it turns up interesting.

cheers

Edit: Link, see if it works

Link


Edited by Walter_Wolf (05/17/23 03:33 PM)


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