Co2 in the cider house

[Mike Lachelt]

Hi all,

I've installed an HRV system (heat recovery ventilation) in an effort to remove co2 from the cider house. But, even though the unit is rated to remove far more than ought to be necessary, Co2 is still noticeable and very unpleasant in the fermenting area. For now, we're flummoxed. My research included a very useful thread from this group, where I was able to verify facts about co2 production during fermentation. Here's the relevant information as it applies to our space:

Right now we're fermenting 12 x 1000L tanks, and the co2 levels are totally out of control.

We designed the system to easily handle 40 x 1000 L tanks, fermenting all at once, by appeal to the following sort of reasoning:

Assuming a maximum of 150g of sugar per liter, 40 tanks ought to produce a maximum of 6,000,000g of sugar, which ought to convert to no more than 3,000,000g of Co2.

Since 44g of Co2 = 24.47 L, this means 3,000,000g/44g*24.47L = 1,668,409L of Co2, or 58,394 cubic feet.

If we pretend all tanks were to ferment to dryness in a single day (which of course they won't), they would produce 58,394/1440, or 40.55 cubic feet per minute.

Yet the HRV unit we've installed is rated to remove and replace 179 cubic feet per minute!! The unit seems to be working, but the co2 build up is so bad I have to open all the doors in order to work! (The vents are located a couple inches above the floor, and there are two of them in a space sized L60x24Wx15H, and a third in an adjacent bottling area (no door), sized 20x40x10).

Could it be that even though our unit removes way more volume than necessary, the velocity is not sufficient? So, maybe reduce the diameter of the vents? Or, maybe there should be more vents in the space? But why?

Any thoughts about this would be truly appreciated!!

Thanks!

Mike

[Cornelius Traas]

Hello Mike,
I think your problem is in the calculation. When you converted to litres of CO2, this assumes the CO2 is liquid, which of course it is not. As a gas it will take up much more space than you have calculated. I am sure somebody with more knowledge of chemistry will get back with a more precise answer, so I add the following with a note of caution:
A quick scan of Google tells be that 1 kg of CO2 is equivalent to about 170 litres of CO2 gas.

On that measure your calculation underestimates the volume 170-fold:

Since 44g of Co2 = 24.47 L, this means 3,000,000g/44g*24.47L = 1,668,409L of Co2, or 58,394 cubic feet.

If we pretend all tanks were to ferment to dryness in a single day (which of course they won't), they would produce 58,394/1440, or 40.55 cubic feet per minute.

Cornelius Traas
The Apple Farm, Ireland.
T: @theapplefarmer
.

[Andrew Lea]

You say “Co2 is still noticeable and very unpleasant”..

I don’t want to sound naive, but just how are you assessing and measuring this? CO2 is pretty much odourless (which is why it is dangerous). Are you just noticing normal fermentation aromas?

Andrew

Wittenham Hill Cider Portal
www.cider.org.uk

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[Andrew Lea]

Standard gas laws teach that 1 gram mole of any gas occupies 22.4 litres in the vapour phase at STP. This equates to about 24 Litres at room temperature. The molecular weight of CO2 is 44. So that part of Mike’s calculation seems to be right to me. E. & O.E.

Andrew

Wittenham Hill Cider Portal
www.cider.org.uk

[Chris Schmidt]

HRV’s are low-speed, low-volume air exchange systems. I have the same setup in my cidery and there is always that fermentation smell, but my CO2 monitors are in the clear, so I know the HRV is working. A couple of thoughts:

- CO2 is odorless, so what are you actually smelling? But either way, HRV’s are supposed to improve indoor air quality, so something is amiss.
- decreasing the diameter of the vents will increase the sound transmission, whilst decreasing the volume of air exchange. My other business installs the occasional HRV system in basements, and we usually use 8” ducting for the main trunk, then branch out to 4”. Going bigger is better than going smaller. Smaller pipes also increase the wall friction level of the moving air, so it would reduce the effectiveness of the HRV. And as few elbows as possible.
- HRV’s work best in an air-tight building assembly. If your cidery is rather drafty, then the HRV won’t be all that effective. Less than 5 air-change-per-hour (ACH) ratings is the mimimum air tightness level for an HRV to work, so conducting a blower door test on the cidery would help to determine that. If this is the same Mike L I know that’s on SSI, then I can swing by with my blower door kit and check it for you. Otherwise, look for an home energy auditor in your area.
- based on your measurements, you have about 30,000 cubic feet of volume in your cidery, which means for a .5 ACH exchange rate (which is rather minimal) you would need to exchange 15,000 CFH, or 250 CFM. 1 ACH is probably where you should be for good indoor air quality, so you would need to exchange closer to 500 CFM. Which means your HRV is too small, or you need a 2nd HRV.
- you can do a simple test to determine the actually velocity of the air through the ducts. You’ll want to make sure that they are the same levels in the supply and return ducts, which is referred to as ‘balancing’ the HRV. You may not even be achieving the 178CFM your unit is rated for if its not balanced.
- glad to hear your return vents are near the floor level (CO2 is heavier than air) but are your supply ducts venting at higher levels?
- you could augment the HRV with a high speed extraction fan that is manually controlled, or even timer controlled. Of course, that may make a mess of your temperature control in the cidery.
- Stack effect will also mess up the HRV’s effectiveness. Stack effect is the warm rising within a building and escaping out the roof/attic etc.
- Vapo-rub under the nose, or a big bottle of Febreze???? :)

I suspect your biggest culprit is the large air space volume of the cidery….

[Mike Lachelt]

Hi again, Andrew!!

Good question. I definitely need to get a co2 meter to verify my impression. However, I do feel very confident that it is Co2. I'm not basing my judgment on aroma at all (and I'm aware it is odorless) but rather on the way it feels to breathe in the cidery. It feels as if there's a lack of oxygen, and if I hang out too long, I don't feel all that well and get a bit light headed. (Does fermentation produce anything besides Co2 that could contribute to these feelings?). This effect is something I've observed in different degrees, in response to the volume and stage of fermentation in the cidery, for the past few years. As a result I feel I'm quite sensitive when it comes to detection. I've only just installed the HRV unit as part of a renovation to our space, and I hoped that the days of running for the door were gone!

Mike

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[Andrew Lea]

Hmmm. I feel if you are getting those symptoms you really should get a CO2 meter or an alarm PDQ. Carbon dioxide asphyxiation can creep up on a person and overwhelm them. Of course fermentation produces loads of volatiles, but they are at quantitatively very minor levels compared to carbon dioxide and I doubt would give such effects.

Chris made some useful points about your ventilation system which are obviously well worth studying. Is there some way you could vent your fermentation tanks directly to the outside?

Andrew


Wittenham Hill Cider Portal
www.cider.org.uk

[Wes Cherry]

Can confirm. We have to wait a bit when opening the ciderhouse with active ferments.

Co2 makes carbonic acid in mucous membranes. At higher concentrations, definitely something you immediately *feel* before any cerebral effects.

Ventilation is a design parameter in our new ciderhouse design. Our mechanical engineer had specific recommended ratios of flow to volume for wineries. Can't find the #s on my phone though.

-'//es Cherry
Dragon's Head Cider
Vashon Island, Wa US
www.dragonsheadcider.com

[Tim]

Perfect ventilation, ferment outside.

 

Tim in Dorset

 

 

 

-----Original Message-----
From: cider-w...@googlegroups.com [mailto:cider-w...@googlegroups.com] On Behalf Of Wes Cherry
Sent: 20 October 2017 21:23
To: cider-w...@googlegroups.com
Subject: Re: [Cider Workshop] Co2 in the cider house

 

Can confirm.  We have to wait a bit when opening the ciderhouse with active ferments.

 

Co2 makes carbonic acid in mucous membranes.  At higher concentrations, definitely something you immediately *feel* before any cerebral effects.

 

Ventilation is a design parameter in our new ciderhouse design.  Our mechanical engineer had specific recommended ratios of flow to volume for wineries.   Can't find the #s on my phone though.

 

-'//es Cherry

Dragon's Head Cider

Vashon Island, Wa US

www.dragonsheadcider.com

 

 

 

 

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[Mike Lachelt]

Hi Chris! Yep, this is the same Mike you know who lives on SSI!! Thanks for your thoughts about my C02 troubles and for your offer to help! I didn't know you installed HRV's... I've inserted replies/comments into your text below:

>
> HRV’s are low-speed, low-volume air exchange systems. I have the same setup in my cidery and there is always that fermentation smell, but my CO2 monitors are in the clear, so I know the HRV is working. A couple of thoughts:
>
> - CO2 is odorless, so what are you actually smelling?

What I notice is that I can't breathe well, and if I hang out too long I get light headed. It's this sort of discomfort, rather than smell, that makes me think there's too much C02.

> But either way, HRV’s are supposed to improve indoor air quality, so something is amiss.
> - decreasing the diameter of the vents will increase the sound transmission, whilst decreasing the volume of air exchange. My other business installs the occasional HRV system in basements, and we usually use 8” ducting for the main trunk, then branch out to 4”.

Our pipes are 5" in diameter.

> Going bigger is better than going smaller. Smaller pipes also increase the wall friction level of the moving air, so it would reduce the effectiveness of the HRV. And as few elbows as possible.
> - HRV’s work best in an air-tight building assembly. If your cidery is rather drafty, then the HRV won’t be all that effective. Less than 5 air-change-per-hour (ACH) ratings is the mimimum air tightness level for an HRV to work, so conducting a blower door test on the cidery would help to determine that. If this is the same Mike L I know that’s on SSI, then I can swing by with my blower door kit and check it for you. Otherwise, look for an home energy auditor in your area.

Thanks for the offer! I didn't look into our air tightness level at all. I doubt the installer did either, but I'll ask him about it. He may be able to test it, so I'll check with him and get back to you!

> - based on your measurements, you have about 30,000 cubic feet of volume in your cidery, which means for a .5 ACH exchange rate (which is rather minimal) you would need to exchange 15,000 CFH, or 250 CFM. 1 ACH is probably where you should be for good indoor air quality, so you would need to exchange closer to 500 CFM. Which means your HRV is too small, or you need a 2nd HRV.

Hmm, this is very interesting. I bet you're right, but can I ask you to explain? Our approach was just to determine how much co2 would be created, and then to ensure that the HRV moves at least that much, with a good margin for error. (And as it is, the HRV must be moving about 20 times the volume that our tanks have been producing...and yet it's evidently not enough). My initial assumption was that we simply need a bigger unit, but the guy who installs it is quite reasonably hesitant to install a larger unit when it seems to him that the current unit should be easily doing the job. So I guess the question is: why do you think 500 CFM is required, even when it would seem 40 x 1000L tanks that cough up all their Co2 in one day (which they won't) would only produce 40.55 CFM! Again I feel sure you're right! But why? Do you think the C02 is escaping the vents by mixing with the air in the space (ie is this why you think the volume of our space is the culprit)? (We thought the C02 would hang out near the floor, and get sucked out via the low positioned vents, sort of like the way rising water would flow out of an overflow drain...)

> - you can do a simple test to determine the actually velocity of the air through the ducts. You’ll want to make sure that they are the same levels in the supply and return ducts, which is referred to as ‘balancing’ the HRV. You may not even be achieving the 178CFM your unit is rated for if its not balanced.

Good point I'll check on this.

> - glad to hear your return vents are near the floor level (CO2 is heavier than air) but are your supply ducts venting at higher levels?

Yes the supply vents are in the ceiling!

> - you could augment the HRV with a high speed extraction fan that is manually controlled, or even timer controlled. Of course, that may make a mess of your temperature control in the cidery.
> - Stack effect will also mess up the HRV’s effectiveness. Stack effect is the warm rising within a building and escaping out the roof/attic etc.
> - Vapo-rub under the nose, or a big bottle of Febreze???? :)
>
> I suspect your biggest culprit is the large air space volume of the cidery….
>
>

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[Mike Lachelt]

Venting directly outside would be the best way to go, but isn't practical for my set up (as far as I can tell). I think if I were using larger stainless fermenters, venting directly outdoors would be feasible. I've seen this done with a keg used as an airlock, with the output sent straight out the roof. But setting up blowoff tubes to multiple IBC tanks in a relatively small space, and connecting them all to a manifold that leads outside would be messy and tricky to work with! Anyway, that's the reasoning that had me looking into HRV's!

[Rod Calder-Potts]

I am not an expert in HRV but 2 points occur to me.

1/ As CO2 is heavier than air your exhaust vent would need to be fed at ground level.

2/    Doesn't HRV need a sealed room to work?

Rod Calder-Potts

[Mike Lachelt]

Wes, I'm *sort of* glad to hear I'm not the only one who's been dealing with Co2 in the old fashioned way! If you happen to come across those flow-to-volume #'s (or volume and flow to volume?), is be interested to see them. Mike

[Chris Schmidt]

Hey Mike;

If you’re feeling lightheaded, then you shouldn’t be working in there. Worksafe BC rules would apply also. Do you have a C02 meter? Acklands Grainger sells them, and you should have one mounted in your cidery anyway.

5” pipes, in my opinion, are too small for HRV’s. But if its a short run, then you might be ok. Hard to say without seeing your set up.

BC Building Code requires minimum ventilation guidelines. Worksafe BC has some more specific guidelines (which I don’t know off the top of my head). The one ACH rating is fairly standard for most homes to provide good indoor air quality. Non-occupied areas such as crawlspaces require .5ACH. Your cidery, with an HRV with 178cfm, means that in 60 minutes, you’re only getting .3ACH throughout the space - which is not enough.

C02, vapour, funny smells, etc will all diffuse throughout a space. Yes, C02 is heavier than air, but diffusion will still cause the CO2 molecules to spread throughout the entire space. That’s why one needs to achieve that ACH rates to ensure the entire space is mechanically vented properly. HRV’s added benefit is that they also retain heat energy, so you don’t puke all your heat out the vents. 

Anyway, if you want me to come over with the blower door kits, and HRV balancing testing equipment, let me know by emailing me. Or call my cell and I’m happy to answer any further questions.

Cheers!

[William Grote]

Depending on what country and state you are in, I would recommend putting in a few banks of LED grow lights and a hydroponic plant bed :-)

That notwithstanding, with 12 tanks, and I'm assuming blow off tubes from the top of the tanks to a bucket or similar container near the floor, make a small reasonably air tight container  with a door that seals - weather stripping- that encloses the bucket with a bulkhead for the tube, put it on a stand or tables that lifts it off the floor as high up the tank as you can manage, and run an additional tube from inside  the enclosure  to the outside, dropping down from the stand height so the tube gently slopes downward to the outside of your cider house.  Ive never used 1000 gallon tanks but Ive been around plenty during active fermentation, I don't see how this would add too much back up pressure as long as you used gravity and distance to your advantage?  Sure, 12 tubes, 12 enclosures, but no HVAC headache and you might save on heat?

I just built an enclosure for my 3D printer this week so I was in that frame of mind.

For whats its worth!  

Cheers