Solar Power Shed Project

[3RRL]

Hey Pat,
As usual, you bring up another relevant point to consider.
Rob, Have you any reason to suspect the thermal design of the generator installation is better than the advance site work that insured the trees were not in the way of the panels on the trackers?

I will definitely check into this one. The Outback control panels share the room with the generator. I was wondering if I could get the radiator fan to exhaust outwards? It would pull in fresh air through the opposite louvers and still cool the radiator, wouldn't it? It would also exhaust the room? What do you think?

 

[patrick_g]

Rob, The fire retardent paint is a good thing. I didn't us it myself. I elected to buy "water glass" to spray a lot of unpainted OSB and framing. Water glass is sodium silicate and has bene used for egg storage. Anyway it is commercially available and can be sprayed, brushed or rolled onto surfaces or cloth can be dipped in it. It will not make wood fire proof but it will prevent the wood from flaming. You could put a propane torch to treated wood and scorch it but when you remove the heat source there is no fire. It has been used to treat curtains in theaters.

Now, about your thermal design improvements... You want to exhaust pure hot, not mixture. Unfortunately influx is quite difuse compared to outflux in a fan's airflow. Take a vacuum cleaner and put the hose on the output side. How far away can you move a table tennis ball? (guite a ways!) ON the vacuum side how far away can you move the ball? (not very far at all.) Flow into and out of a fan is like that. Volume is the same but distribution of velocities is not.

What is it that you need to do? Have the hot air coming off the radiator leave the room without mixing with the room air. Are their a set of louvers or other centralized location where the hot air exits the genset? If yes, then make a plenum and duct to catch that air and direct it out of the bld. YOu might have to make a few small sheet metal and weather strip mods to plug major leaks.

If it were a genset with exposed radiator and no efficient containment possible of the effluent I'd suggest a reverse pitch fan and a custom shroud and ducting. You might need a mod to or improvement for the fan shroud. The idea is to contain the hot air, prevent it from mixing with room air, and directing it to the outside of the bld. Outside air will flow in your existing vents and provide plenty of fresh air to the bld when the unit runs.

This will lower the temp the other stuff is exposed to. Electronics and batteries last better when not overheated.

If you have a relatively direct path to duct the hot air out of the bld there will be little reduction in cooling airflow over the radiator. Even with some restriction it would be better than recycling the hot air through the room and back through the radiator again and again.

If it were only an issue of potential oveheating of the engine you would just put a duct between the input to the radiator and the outside. This woiuild give the engine ouitside air to cool it. Unfortunately this does not address the problem of overheating the inside of the bld and all the batteries and electronics.

If it were mine I would capture the hot air and direct it outside by whatever means were judged to be the most effective and practical whether it were a reverse fan blade or ductwork and a little sealing of the box the unit was in.

You can leave a "door" in the duct to allow the heat into the room if you anticipate wanting the heat in the room in winter if you are there running the genset and doing something.

My experience is that Onan dealers are not thermal design engineers. It won't hurt to talk to them but be prepared for bogus answers like, "we never had a problem." They may have literature or manuals with design consideratioins in them if you ask around. Since Onan has accessory shrouds for sale to fit their air cooled units maybe they have some standard sheet metal mods you can buy. Surely you aren't the only person to install a water cooled genset in an enclosed space. I don't know as all our gensets were air cooled even a big horizontally opposed 6 cyl Deutz unit which was specified by the project leader (and installed improperly like the Onans.)

I'm also involved in a solar installation now! (Yeah, right!) I'm taking the panels and charge controller off an old motorhome being removed from service to recycle as a batt charge sys for an electric fence charger.

Pat

 

[mwood]

New to this thread! Great project! I look forward to messing with some solar / wind stuff in a few years after we get some other more necessary things done to the house.

There are a couple of considerations that I think will be critical to cooling the genset properly as well as keeping any harmful gases out of the building as well (not really well versed on propane engines. Perhaps there are minimal harmful gases?)

Anyway, the whole goal is to provide enough airflow over the radiator to keep things running cool. You have some very good suggestions for that part. However, unless you have a ton of ventilation in the building already, you'll have to be careful not to create a vacuum as you start pushing air out of the building over the radiator. The best choice for this would be to run some form of fresh air intake from outside of the structure. Designed properly, it should provide most of the cooler outside air needed accross the radiator. Having some of the inside air of the building exhausting this way as well (perhaps 20% or so) would also help to keep the internal temp of the building down.

My concern is that without a proper supply of air, you're going to place the building under a vacuum and suck air from any and all cracks / crevices. With this comes dust and dust + electronics don't mix well. Having a dedicated intake of air will allow you some form of filtration if you so desire and keep the airflow patterns how you want them.

Sorry if this is somewhat long and confusing. Been a long week and while I can see the idea in my head, I'm having a hard time putting it down on paper.

Keep up the great project! I'll be curious to hear how well this system functions once you're using it under normal loads!

 

[patrick_g]

mwood, Hi, I couldn't tell for sure if you were commenting on my post (immediately preceeding yours, or not.)

Anyway, propane exhausts are pretty clean with low NOX and such which is why they use propane powered forklifts inside closed spaces but the exhaust of Rob's genset is plumbed out of his building.

Additionally he has air vents which will preclude the building imploding or sucking massive drafts through the cracks. Anyway after the initial draft through the cracks they wouldn't admit any more dust than the unfiltered vents he already has. (Rob, put furnace filters over your vents!)

My concern was that the heat in the air coming through the radiator is not directed out of the bld but is dumped inside the bld where there is an exponential mixing situation and the hot air is recycled through the radiator again and again. There is no reason to assume the hot air will be mixed with all the air in the bld. It might find a circulation path you don't want. Even if the radiator has a great margin of capacity to cool the engine in a hot room the electronics and batteries in the room would be happier if the room were cooler.

The only effective way to achieve that is to direct the air from the radiator into a duct and exhaust it out of the bld. There are always alternatives. You could remove the radiator and reinstall it in a plenum where the effluent were directed outside the bld envelope. This could be adequately supported by an electric fan such as is used to cool many modern autos. The issue is directing the hot air out of the bld instead of mixing it in with the air in the bld. The installed vents will exchange air but they are removing mixture not pure hot air and it is not a sure thing that they will do enough during a hot day with a long generator run. Lots of expensive stuff to gamble with and the fix isn't that difficult or expensive.

Pat

 

[mwood]

You seem much more familiar with his structure than I. I read all the posts and looked at the pictures, but somehow missed the vents!

I completely agree with your point. If there is enough ventilation already in the building, an additional fresh air intake isn't really needed -- as long as you get a desirable draft.

I completely agree that the only way to keep the engine cool enough is to force air over the radiator and then outside the building. Or, as Pat nicely said, move the radiator outside the building and install some form of fan.

Since you are spending around $100K on the setup, it makes sense to me to get some extensions to your radiator hoses and get the radiator mounted remotely with a fan. This will keep the engine from overheating. Even if you do this, I would still hook some form of fan up to the generator "ON" switch that cools the building. No doubt the engine itself will give off heat and those batteries aren't cheap!

Good luck and keep up the great thread! Very exciting to see someone actually going through with a completely off grid system!

 

[patrick_g]

Rob, You now have two software engineers in agreement that you need to get the heat out. If we had a third we could change a light bulb!

I'd just follow the $. If it is cheaper to remote the radiator than to mess with sheet metal then that is a good solution. If the radiator and its electric fan were mounted in a box mounted on the wall (big louver vent on the outside) then the room air would be exhausted through the radiator and fresh air would come in your vents to replace the exhausted air. Don't forget the furnace filters on the vents.

Pat

 

[mwood]

I'd just follow the $.

Good advice!

 

[Tig]

Rob, You now have two software engineers in agreement that you need to get the heat out. If we had a third we could change a light bulb!
Pat

Pat, need I remind you that the light bulb is a hardware issue and you should not be involved.

 

[3RRL]

Hi guys,
Looks like I got all the engineers on this project now. That should be interesting...hahaha...
OK, some very good points were made and I like the idea of:

1) Getting the radiator to suck up fresh cool air from the outside.
This has been seen to by placing the the radiator of the generator against this screened opening, allowing it to take in air directly from the outside. What you see here is the grill of the radiator showing through the screened opening.



2) I like the idea of taking the heated air and getting it out of the shed. You may not have seen it before, but this Cummins/Onan has an enclosed shroud. Here is a picture of it open and closed up. I will consider attaching an electric fan and exhaust from an opening in the enclosed shroud to suck the heat away made by the generator.





Those photos were taken before the generator was installed inside the shed. I want to see where the best place on the shroud would be to leach the hot air from? Then again, during this Winter, I may just add an electric turbine exhaust if I find the heat generated is not very much. I'll keep an eye out on that.

3) Remember that the batteries are separated from the generator. The shed is made up of 2 separate rooms, sealed off from each other.
Batteries are below where my wife is lounging on the loft.



4) I will add the heating/air filters over the louver screens. That is a good idea.

Thanks again for all the suggestions and continued input. Send me the bill...

 

[mwood]

Pat, need I remind you that the light bulb is a hardware issue and you should not be involved.

What we really need are a couple of System Engineers to coordinate meetings for the light bulb. They can interface between HW and SW to come to a conclusion -- maybe...