Heat Recovery Ventilation sizing

[Beerhippie]

Anyone here do HRV systems?

I have a problem--well, several, but let's just address this one:

We have a fermenter hall here at the brewery. Fermenters generate a LOT of CO2 gas during fermentation, which vents into the ferm. hall. Currently, we use an evacuation fan to keep the CO2 below OSHA standards.

This is a great way to waste heat in our climate. I'd like to install an HRV to try to recycle some of the lost heat, while keeping the CO2 within limits.

I have a CO2 monitor that has a relay output, so this would be automatic at a certain level.

Researching HRV sizing, I find a formula for residential use that I believe is some sort of base-line turnover of interior air--not necessarily ventilation to remove gas accumulation.

The formula used is (volume) X 5 CFM. Would this keep up with production of CO2 (sorry, the only guy here who knew the volume produced got himself fired)? Should I just double that factor?

 

[ericm]

Can you base the HRV off the CFM of the existing fan? May need to factor in ductwork as that will reduce flow.

Especially if it's triggered automatically then there's not much downside to oversizing it other than cost and size.

 

[Beerhippie]

Can you base the HRV off the CFM of the existing fan? May need to factor in ductwork as that will reduce flow.

Especially if it's triggered automatically then there's not much downside to oversizing it other than cost and size.

The evac fan we use was sized to remove malt dust from the brewhouse. I'm sure it's massively over-sized, as it creates a strong breeze throughout the building.

It's also located in a very inaccessible location (12' off the floor with no room for a ladder), so I can't easily read the data plate.

I need to diagram out the ductwork so I can see how to make it as short as possible, while keeping good separation between in and out.

I want to locate the HRV system itself where it's easy to access (see fan above) for maintenance.

I'm trying to find some numbers for CO2 production at high fermentation right now....

 

[Beerhippie]

Now the question is, if I decide to just "wing it", just how much to oversize? Twice?

I gotta justify expenses to the PTBs in the office.

 

[Dagny]

more info. room size and shape.

 

[Beerhippie]

I found the scrap of paper in a coat pocket with my notes!

10,120 ftsq.





That's looking east from the west entry of the room. Rectangular room, east-west long axis, two big entryways, open, one at each end. Single vaulted ceiling, 20 ft. high at center, 4/12 pitch.

I want to put the HRV unit on the south (right) wall. Possibly inlet on the south, outlet on the north walls. Ducting can run right under the catwalk.

Really hard to get a pic of that. I was using a 10mm ultra-wide lens. The room is, as you can see, full of fermenters and equipment.

 

[PCustoms]

Anyway to pull directly off the fermentation tank before the CO2 gets in the air?

Seems more effective, and should use a smaller fan/hrv (or potentially eliminate it).

 

[ericm]

If you know what type of sugar the yeast are eating and how much, you can calculate the amount of CO2: https://undergradsciencejournals.okstate.edu/index.php/JUBLI/article/viewFile/8728/1869.pdf

There's probably a way to go from starting and ending specific gravity measurements and volume to the amount of sugar.

 

[Beerhippie]

Anyway to pull directly off the fermentation tank before the CO2 gets in the air?

Seems more effective, and should use a smaller fan/hrv (or potentially eliminate it).

We tried that. One problem is that we overfill our fermenters, resulting in a lot of foam coming out the vent. I built a rather clever foam trap, but the brewers--damned conservative lot--wouldn't use it.

We also invested a big bag o' money in a fancy-*** system to capture and re-use the CO2 we produced--believe it or not breweries use a LOT of CO2--but that turned out to be a huge scam. It never worked from day one, and was about as funky a design as you could cobble together in a garage--but most folks here would probably cobble together one that worked. We finally got our money back, but everyone in the brewery and management had to sign an NDA to never reveal the maker or review their products.

If you know what type of sugar the yeast are eating and how much, you can calculate the amount of CO2: https://undergradsciencejournals.okstate.edu/index.php/JUBLI/article/viewFile/8728/1869.pdf

There's probably a way to go from starting and ending specific gravity measurements and volume to the amount of sugar.

Yes, I'm sure there is. I just need to find it. Our brewery chemist/microbio guy got in an argument with management and got his *** fired, so we're a little weak on that subject until we hire a new one.

 

[PCustoms]

We tried that. One problem is that we overfill our fermenters, resulting in a lot of foam coming out the vent. I built a rather clever foam trap, but the brewers--damned conservative lot--wouldn't use it.

We also invested a big bag o' money in a fancy-*** system to capture and re-use the CO2 we produced--believe it or not breweries use a LOT of CO2--but that turned out to be a huge scam. It never worked from day one, and was about as funky a design as you could cobble together in a garage--but most folks here would probably cobble together one that worked. We finally got our money back, but everyone in the brewery and management had to sign an NDA to never reveal the maker or review their products.

Hmmm....

Well I'm sure we can find a solution. I'll PM you my address, you can pay the consultation fees in beer.

 

[u3b3rg33k]

The evac fan we use was sized to remove malt dust from the brewhouse. I'm sure it's massively over-sized, as it creates a strong breeze throughout the building.

It's also located in a very inaccessible location (12' off the floor with no room for a ladder), so I can't easily read the data plate.

I need to diagram out the ductwork so I can see how to make it as short as possible, while keeping good separation between in and out.

I want to locate the HRV system itself where it's easy to access (see fan above) for maintenance.

I'm trying to find some numbers for CO2 production at high fermentation right now....

this is much easier to figure out than you're making it out to be.
option 1:
get a CO2 sensor with a readout.
find the volume of your space.
find the spec sheet for your fan. (a bonus)

start a timer, run the fan until CO2 levels are basically ambient.

wait until they're at the level you need to ventilate. stop the timer and fan.

"The actual amount of air changed in a well mixed ventilation scenario will be 63.2% after 1 hour and 1 ACH." https://en.wikipedia.org/wiki/Air_changes_per_hour#cite_note-bearg-3

you can rule-of-thumb your current fan's CFM with that info, roughly.


option 2: target ASHRAE/CDC's recommendation of 5ACH. there's plenty of large ERV/HRVs with summer bypasses (for when you DO want the cooling) as an add-on option.
You can meet target that with both an ERV and your primary RTU/DOAS/ whatever you have (what DO you have?).

if you've got an RTU with a fixed fresh air vent, upgrade it to a 100% economizer+ powered exhaust and put a CO2 sensor on it. both common Honeywell and Belimo controllers have 2-10v inputs for these standard sensors.

option 3: put a balloon over a tank vent and measure the peak gas production (i assume you know when it's the most active as the brewer). size a dedicated exhaust system for source control - this can also be an ERV/HRV because you need to replace what you exhaust out.

also, I would use an ERV instead unless you have a good reason for spec'ing an HRV.

 

[mike93lx]

How much are you spending to heat the space?

Are there utility rebates available in OR for energy savings projects? Those programs sometimes cover money for engineering the solution

 

[u3b3rg33k]

We tried that. One problem is that we overfill our fermenters, resulting in a lot of foam coming out the vent. I built a rather clever foam trap, but the brewers--damned conservative lot--wouldn't use it.

We also invested a big bag o' money in a fancy-*** system to capture and re-use the CO2 we produced--believe it or not breweries use a LOT of CO2--but that turned out to be a huge scam. It never worked from day one, and was about as funky a design as you could cobble together in a garage--but most folks here would probably cobble together one that worked. We finally got our money back, but everyone in the brewery and management had to sign an NDA to never reveal the maker or review their products.

Yes, I'm sure there is. I just need to find it. Our brewery chemist/microbio guy got in an argument with management and got his *** fired, so we're a little weak on that subject until we hire a new one.

in my experience, anything they have to do extra they won't do. you'd want an inlet near the vent, as close as you can get it, but far enough away to not be in the way. proximity does matter.

what PPM level are you targeting? IIRC most systems start modulating the OA at 800ppm, and go to 100% at 1500-2000ppm (most sensors hit 10V @ 2000ppm).

1989 edition of ASHRAE's ventilation standard, Standard 62 (subse-quently Standard 62.1), had a CO2 limit of 1000 ppmv, but this was removed from subsequent editions due to its common misinterpretation.

A.2 Health and Cognitive Effects of CO2 Exposure
Carbon dioxide is considered nontoxic at concentrations up to 5000 ppmv, which is the U.S. federal standard (Permissible Exposure Level) for workplaces set by the Occupational Safety and Health Administration (OSHA)

https://www.ashrae.org/file%20library/about/position%20documents/pd_indoorcarbondioxide_2022.pdf