Toilet Exhaust thru an ERV with a rotating wheel??

[michael333]

Hello,
I haven't been here in a while. I have an application where I'm currently exhausting 525 CFM @ .75 ESP from public restrooms and a janitor's closet through a energy recovery ventilator (ERV) with a static plate total heat exchanger (RenewAire). I'm bringing in 250 CFM @ .75 to 1.0 ESP of fresh outside air, via the same ERV, to ceiling cassettes in a VRF system. The 250 CFM of OA is not my total fresh make-up air. I also have a packaged RTU providing the necessary make-up for the 525 exhaust air for positive pressurization. Both airstreams are separated via the current ERV. My issue is the ERV is only (1) speed, unless I go with ECM motors. I don't want to go that route.
I'm thinking about switching to a ERV with a totol energy recovery wheel for this application.
My question: Am I allowed to use a wheel, since the airstreams (exhaust and incoming outside air) will not be totally separate like a static plate total heat exchanger?? Does the code allow this configuration, if the wheel has purging capability??

Thanks for any info/advice that you may give,
Michael333

 

[tys90]

As always, it depends on your local codes but the IMC only restricts the type of exhaust air stream used, not the type of energy recovery used. You cannot use energy recovery with:

Hazardous exhaust
Explosive/flammable exhaust
Smoke control systems
Kitchen hoods
Clothes dryer exhausts

However, if this is a hospital (I doubt it), there are different requirements that are more involved. In general though, bathroom and janitor room exhaust is acceptable through a wheel. Consult your local codes though.

 

[MTES93]

Look at ASHRAE 62.9. They classify "air" based on where it comes from. If local codes don't explicitly dictate, I use this ASHRAE standard as a basis of design.

Not sure what separation a total or sensible wheel gives you. And as I'm answering this from my so called smart phone I apologoze for any typs. SI equals SO. Crap in equals crap out.

Also. U sure u have enough air to warrant cost of ERV?

 

[trashcanman]

I would not. Last year I designed a couple of ERV systems for locker/toilet rooms. They used plate-frame exchangers, NOT WHEELS. I made sure of that. The client (schools) are very pleased with them and have no complaints. I would not take chances on the odor cross-contaminating the fresh makeup air.

 

[txdilbert]

I've used an energy recovery wheel for toilet exhaust. I like the latent benefits of the wheel over the plate. I think the cross-flow leakage rate is like 5% or less - mix that with 95% outside air and your return air stream and I don't think you would detect anything.

Ultimately, this is your call. If you are concerned about it, go with the plate setup.

 

[ChasBean1]

I’ve seen vendors of the enthalpy wheels claim less than 0.4% of cross contamination of exhaust airstream contaminants into the supply airstream. They do not typically devulge however particular contaminants that produce this rating (e.g. volatiles versus particulate — ammonia, sulfur, Arizona road dust, benzene, methane, etc.).

From what you’ve posted, it does not seem that your ERU optimizes ventilating air as it only recovers heat for about 40% of it, where the remaining 60% of the ventilating air still comes through the RTU. The ERU makeup air should supply 110 or so percent of the exhaust and the RTU can be set to full recirculation (as if it were a fan coil unit). This would depend on your system configuration.

 

[marcoh]

For toilet exhaust systems I have successfully used heat recovery wheels with 3A molecular coating in lieu of the more common desiccant materials. Also ensure the fans and pressures in the AHU are designed so that any leakage will leak from the clean air stream into the dirty air stream to eliminate contamination.

These systems only transfers small water molecules (which are < 3A in size) and not any other contaminnents (which are > 3A in size). These systems are also used and approved for use in labs and fume cupboards.

Below is an extract of the marketing from Semco

http://www.semcohvac.com/104

•3Å Molecular Sieve Desiccant Coating
◦The EXCLU-SIEVE wheel utilizes a 3Å molecular sieve desiccant coating to limit the risk of desiccant cross-contamination which would otherwise cause a portion of the exhaust air pollutants to be transferred, along with the water vapor, to the fresh air stream. The 3Å molecular sieve material utilized by SEMCO was developed specifically for “selective adsorption” and has been successfully used for decades by the petrochemical industry. Other desiccants like silica gel and oxidized aluminum cannot provide selective adsorption. Molecular sieves are structurally stable, chemically inert and have a strong affinity for water vapor. This strong affinity for water vapor produces the high rate of adsorption which provides superior latent transfer performance.

 

[ChasBean1]

Marcoh demonstrates above what is available. Incredibly awesome, but all the superlatives are based on the manufacturer's data. There is a bit of a conflict there. The manufacturer does not specify test conditions or what results are based on. Unbiased information is rare in this day and age...

 

[317069]

Michael
1- your exhaust is 575 cfm, is it total building exhaust?
2- ERV exhaust 575 cfm and bring in 250 cfm to VRF system, the difference is 50%, is it right?
3- your building exhaust 575 cfm, RTU and ERV bring in 575+250= 825 cfm of OA, is it right?
4- you are dealing with 575 cfm what benifet of changing equipments ( ERV OR weel) for such amount