ERV in garage with diesel trucks

[EnergyProfessional]

I'm designing a ventilation system of a garage. I'm considering an ERV wheel.
The garage houses diesel trucks. When the system runs the air should be relatively clean (up to 0.75 cfm/ft²) , there only will be limited idling. The garage has two oppsing overhead doors and is not longer than 200'. So the driving distance is relatively short. Trucks only drive in and out and park with engine off most of the time.

We do have some garages with ERV (flat plate). but we don't have long term experience, and in those locations we have local exhaust for the truck exhaust when they start (plymovent). So those garages are naturally much cleaner.

Now in this application we don't have local exhaust (plymovent). My conern is some diesel soot will settle on the ERV wheel. The wheel will have MERV 8 filter.
ERV wheels have some self-cleaning properties. If we just had dust, I would be less concerned. but diesel soot is a bit sticky.

My questions:
1. Do the "Best and Brightest" have experience and know of problems with ERV in diesel garages?
2. Would the B&B recommend a higher filter on exhaust side to protect the wheel? (I know, more pressure drop)

why an ERV? here the reasons:
- most our applications just have a direct-fired MAU on one side of the garage, and multiple roof and wall exhaust fans scattered around.
- this space has mezzanine that woudl not get ventilated well underneath with this approach. In addition my garage actually is two large areas with little opening in between.
- Ideally I only want two direct drive main fans for less service/maintenance, roof fans etc. are harder to maintain
- I may be limited to how muhc natural gas i can get, so the ERV would reduce load
- I also plan to modulate flow based on CO levels.

My ducting approach would be:
- have return duct above driving aisles (msot exhaust) to draw away from occupied surface
- supply fresh air at perimeter, under mezzanine.
- that way fresh air woudl flush out the corner / mezzanine pockets and the exhaust woudl have short path to the return duct without going through occupied areas.

Any advice appreciated.

 

[MintJulep]

I suspect that your concern about the soot is justified.

Why a wheel?

I'd suggest a cross-flow flat plate, with ducting arranged with access hatches on all four connections so that it can be blasted with coil cleaner and a hose at least once every so often.

 

[Drazen]

for your application, i only believe in water loop-air application, if cost can be justified.

 

[EnergyProfessional]

MintJulep: wheel seems more compact for that size. Most cores plate HX are not for such flows. in addition wheel is more efficient. I also think since the wheel turns into from clean to dirty airstream it can be cleaned a bit.
It sonds like you recommend an aluminum flat plate HX? WE typically use the Renewaire HX, but your suggestion of hosing them out wouldn't apply to the "paper" cores. Wha tmanufacturer woudl you recommend.
For wheel we usually use Semco. I haven't really foudn a sensitive-only wheel and know the Semco wheel is overkill as we don't use AC.

Drazen: you mean to have a glycol runaround loop from exhaust fan on one side of building to the MAU intake on other side? It would save ductwork if I use normal sidwall fans on one side of building and the MAU on the opposing side (but have to run pipes with glycol). Or do you mean both coils in one AHU, but use a coi l becasue it cna get cleaned better?

As far as cost goes, I'm doing an energy simulation. Obviously fluctuating natural gas prices make it diffficult to predict. With ERV I use more electricity (more dP), but less natural gas. Assuming my return flow needs good filters to protect the wheel, this is an added maintenace cost as well. There are other considerations, having extensive ductwork can cause conflicts. So far we only used ERV on smaller ~3,000 ft² garages. this one is 40,000 ft².

 

[SAK9]

Bypass ERV when CO level goes above certain level

 

[Drazen]

i did not know that exhaust and supply are much distant, but that actually give more justification to loop solution - piping is much less expensive than ducting and transmitting recovered energy via water is also easier to be made effective.

loop: one exchanger at exhaust, the other at supply, should seemingly be set as pre-heater for maximum efficiency.

 

[EnergyProfessional]

Drazen:
I think if i had air intake and exhaust clsoe to eahc other, I would have to have duct work inside the storage. Imagine 100'x 100 spaces. I supply fresh air on one end, and exhaust it from opposite end (or exahsut from multiple locations). With ho heat recovery, I don't need much ductwork.

now if I keep air intake and exhaust still separate, i need to run pipe for the glycol loop across the building. If I for some reason have air intake and exhaust next to each other, i need to run ductwork from one end of the building assuming i want to cross ventialte the entire space.

So if i do heat recovery, i have to either run duct, or pipe. My other cocnern with glycol loop is, efficiency is much lower since i need to transfer heat twice. ~50% maybe. a wheel can give me up to 80%. Obvioulsy the wheel will require ductwork since that will have air intake and exhaust next to each other.

another semi-related question is the optimum exhaust and supply location:
- our existing buildings typically have a exhasut fans at perimeter that draw air from within 18" of floor (for CO), in addition alrger buildigns have added roof exhausts. Supply typically is jsut on one end of the area, or near the center of a longer wall.
- woudl you recommend a different approach to have efficient flush out of the old air?
- I kind of think either only exhausting near floor (asssuming no people are in roof height anyway) would be good, supply air either coudl be central or ducted to different areas.

I read "indsutrial Ventialtion" manual and didn't find soem specifics for vehicle storages. Any advice aprpeciated.

i know my flowaret is given by code anyway, but with given cfm I want maximum ventilation efficiency.

 

[MintJulep]

Something like

http://www.venmarces.com/energy-recovery/flat-plate-exchangers

in either aluminum of polypro looks suitable. No recommendation other than they are high on the list of Google returns.

Passive device, and near commodity item. I suspect the name plate doesn't matter much and they are all made in the same factory in China anyway.

 

[cry22]

how many people in this place to warrant such an elaborate ERV system with ductwork? or run-around loop.
i'd go with the snorkel type used in fire houses connecting to muffler exhaust upon entry and exit of trucks.
And use Gas-fired radiant heat for such an application.
Ventilation is more likely handled by infiltration alone, unless you have an office space somewhere that needs to be handled separately.

gas-fred radiant heat is the most efficient system you can have in terms of energy conservation. 50% more efficient than an all-air system.

 

[EnergyProfessional]

So I almost completed my energy simulation and after dealing with all our utility rates (with summer, winter, demand, off, mid, and on-peak charges) it turns out using the heat recovery actually is more expensive due to higher electricity consumption. More pressure drop on intake, and quite a bit more pressure drop on exhaust due to need to filter. I didn't even include the added cost for ducting, and filter changes (obviously I would do that if I actually had energy cost savings to see if those savings are worth). Even if I assume 10% natural cost increase vs. 3% for electricity, I still don't get a positive net present value over 20 years. So, long story short, unless electricity gets much cheaper, or natural gas much more expensive, this doesn't seem to make economic sense. Good I did the comparison, really interesting. I still may have some final actual manufacturer changes regarding fan and motor sizes.... but I really don't expect a major change in the economic analysis. If someone uses LPG or oil to heat, this may be completely different, though.

Another thing I adjusted is to correctly enter my boiler OA temp reset, and efficiencies under partial load. when it is cold and high demand, my condensing boiler will have higher water temp and actually be less efficient than the direct fired MAU, which isn't affected by OAT.

I think I just supply air from MAU from one short end of the garage and exhaust it on the opposite wall. I would exhaust air from 18" above floor height. Supplied air will just get heated to space temp, so it doesn't rise or drop. Supply height would be little above 14' (I have a 14'mezzanine and 14'is vehicle clearance) Each space is ~100' x ~200' - 240'. So I hope to get away without roof fans (maintenance and leaks !!). That way I hope to flush out the breathing zone properly. Any advice greatly appreciated.

 

[11t]

I would think a water loop and coil would be the only rigorous maintainable design that would actually work. Even plate to plate is going to have internal issues with dust and soot. Just make sure it is designed such that there is a drain and you can easily get a pressure washer on it.

An enthalpy wheel seems like a very risky proposition with a lot of unknowns.

 

[11t]

What simulation tool do you use HerrKaLeun?

 

[EnergyProfessional]

cry22: point source exhaust on truck exhaust wouldn't be practical, and wouldn't take into account the exhaust for when they drive through the garage. We have that in fire stations, but there truck parks right in front of its designated overhead door. In that case the snorkel is attached right before it disengages when the fire truck is almost out of the door. when the fire truck comes back, no snorkel. but fire garages are very small and the open overhead door alone ventilates. However, code still requires the separate ventilation. Infiltration alone isn't code compliant and would not ventilate the core area well.

11t: I used Trane Trace. The runaround loop may be the easiest to maintain if I wash the coils, but the coils will add quite some pressure drop (like the wheel or core), and with the reduced efficiency they also may cost more to operate to make up for added fan energy. I haven't simulated it, though. A while ago I looked at that for a very small garage and was surprised how large the coils have to be to recover a decent amount of heat.

I kind of like the idea of exhausting air from the center of the space. In summer they keep the garage doors open all day, and I could just run the EF to ventilate (to save MAU wear and less fan energy). To ventilate all areas well I have the feeling I either need to exhaust from multiple points, or have to supply air to multiple points.
Somehow having an exhaust duct with multiple grilles along the drive aisle also seems to make sense since when the trucks drive, that is where the most dirt is in the air.

 

[11t]

Yeah I was referring more to what would actually work as opposed to what is or is not cost effective.

Modeling is great, I do a lot of it (but mainly in E+ since I'm a glutton for punishment), but it is very time consuming (at least to me) and I do my best to not further put myself in the hole by modeling something that isn't an option.