Off-grid Garn

[Clearlycountry]

Hi folks, new to the forum as a poster, but have been a silent follower now for a while.

We are looking at buying a Garn to heat our offgrid home & shop. When I built the place I put in radiant floor heating, but haven't gotten it hooked in as of yet. This last winters feeding of the woodstove has given me renewed motivation...

I was wondering if any of you are running a Garn on solar and how it's working out for you. There is no doubt in my mind these are great units, but what's got me a bit concerned is the blower energy consumption. The 1500 uses a 1/2HP and the 2000 a 3/4HP motor. Running this motor in the dead of winter for 4-5hrs is a big drain, on top of the circulation pumps, etc.

Any feedback would be greatly appreciated. Thanks,
Craig

 

[Nofossil]

I hope someone has actual power consumption numbers, but I'd be surprised if the power consumption wasn't a lot higher than other boilers. Of course, the heat output is a good deal higher as well.

That leads to my usual question: Do you need a boiler with that much output? If you're off-grid, I assume that you're looking at energy usage very carefully. Buying a boiler that's much larger than you need is not usually as efficient.

 

[Clearlycountry]

Hi Pyro, Yes, we are very closely tied to energy usage on everything, hence my post. Running the Garn 1500 for 4 hrs @9A is 4kwh of energy (5.3kwh for the 2000). During this time we either need to have lots of solar, or backup gen running to supply power for at least part of the time.

How are you running the EKO unit power since it too has blower(s)?

We need 100k btu total load worst case. It doesn't much matter whether it comes from a Garn, or EKO just doing the same thing two different ways i.e. built in storage vs external storage.

Thx,
Craig

 

[Hydronics]

Craig,
The EKO 25 & 40 have only one small fan.

 

[Nofossil]

The EKO 25 fan uses about 40 watts if I remember correctly, and the circ uses about 60. Zone valves use almost nothing, and my controller uses 5. I'm not off-grid, but I do have provisions for running off of battery backup.

 

[Jim K in PA]

Craig - welcome to the Boiler Room!

If you are able to run temps down to 120F or thereabouts for your radiant slab - your dwell time between burns for a GARN should be significant, perhaps 1-2 days. The 2000 has a real input rating of over 400k Btuh, so you should not need to run the fan for 4 hours in order to recharge the tank from 120-200 (1.2 million Btu into storage for a WHS2000). But, you are correct that the draft fan will be the biggest energy hog of that system, and if you are converting from DC to AC to run the fan, your conversion (in)efficiency is going to take a big bite out of your reserves, depending on how much electrical storage you have and your recovery rate. Are you purely solar?

The comparative analysis you need to make with any stove is the total energy input over time. The GARN will be a high load/short duration cycle, and an EKO or other unit will likely be a low load/longer duration cycle.

The output rating of the GARN is something that should be evaluated relative to the burn frequency and duration to recharge storage, not the energy load on the unit. This is one of the biggest differences in comparing a GARN system to other wood gasification furnace options. The GARN has enough output to simultaneously meet the building load AND recharge storage in a relatively short time. A GARN is really only oversized if you can't fit it in your building!

Best of luck with your research.

 

[Clearlycountry]

Jim K & Pyro, thanks. This is exactly what I was getting at with my question. Here are the #'s I'm using:

Example 1) EKO 25 & 880 gal of storage: 880gal is ~7336#'s & therefore requires ~586.9BTU to raise 80deg. @ 25K Btu, this would take 23.5hrs of burn time. @ 40W for blower, that is 940WHrs of elect per day of heat output. This assumes of course only pulling out 25kBtu/hr/day.

Example 2) Same calcs for a Garn 2000: ~1.2MBtu's & ~ 3Hrs run time @ ~4KWHrs. However @ 25KBtu/Hr, is 48Hrs of output.

So Garn uses twice as much electricity per unit of heat output to get the work done in one intense burst vs EKO as an example. This may actually be better for a solar home since I can do this during the daylight hours when we are making power. In winter when snow is on the panels, I have to run the genset each day for a while anyway. Fortunately, I have a Listeroid generator I use for battery charging that uses ~1Qt /hr of diesel or WVO @ 3KW load. I am also planning to use an LP boiler as backup, so it's an option to the generator, but uses more expensive fuel.

The only option left to look at is whether there is a more efficient motor and/or 240V motor to cut amps. Basically I just like the simplicity of the Garn units and we have tons of Juniper trees here, which are just considered large weeds.

Finally, Jim, I went through your pictorial. It was great and very much appreciated. You do nice work.

Do you guys have any other suggestions?

Thanks agan,
Craig

 

[flyingcow]

I didn't really understand the numbers, but the EKO should be able to recharge the 880gal tank in 6 hours, give or take. I'm using my tarm innova as a rough reference. I can take my 820 gal tank from 105 degrees to about 160 in one fill of the fire box. this takes about 4 hours+/-. The EKo 25 is a little smaller, I think. BUT I may have misread/not understood the #'s you posted.

 

[Jim K in PA]

Craig - I think your #s are a little off. The EKO 25 puts out about 85k Btuh according to Specs I found at Horizon. It also is rated at 50W consumption. If you are pulling out 25k Btuh, that leaves 60k Btuh to recharge storage. For 880 gallons and delta T of 80, you would need a burn of only 9.8 hours to recharge the tank. You would then get about 23.5 hours of draw time from the tank (80 delta T). Therefore total heat ouput would be 9.8+23.5=33.3 hours of heat. The EKO would use 50Wx~10 hours or .5Kwh to generate that 33.3 hours of heating

For the Garn, you have a 3 hour burn, which uses 3Kwh of electricity, and easily generates 425k Btuh with correct fuel. You would recharge the tank in that 3 hours, and supply your 25K Btuh load. You then get 48 hours of draw from storage. So, 3+48=51 hours of heat from 3 hours of electrical draw. That gives you 1.53 times the heating of the EKO, with an electrical draw that is 6 times that of the EKO.

What it will come down to is your ability to keep the EKO fed during the 10 hour burn, or longer if the load goes higher. The EKO 25 is probably a bit small for your load. If you are around to keep it fed, the EKO will be a better option from an electricity perspective unless you can generate 220V or 3-phase power to supply an alternate to the standard 120V GARN induction fan. But the GARN requires less operation and feeding time.

Glad you enjoyed the pictures.

 

[Nofossil]

The EKO 25 is a 25kW output, which translates to about 80,000 BTU/hr. In real life over the course of a burn, expect an average of 60-65k BTU/hr.

 

[Clearlycountry]

Jim, you are right. I used the wrong Btu output for the EKO 25. Guess I have too many boiler #'s floating around in my head at the moment. And, yes, it's a bit too small for our needs, we would jump to the 60 if we went the EKO route. Also, thanks for pointing out the boiler run time adding to the total.

So, theoretical's are interesting, but actuals are where rubber meets the road. During cold part of year we will pull closer to 50k/hr. Using an EKO 60 & same 880 as example, we could charge tank in 3.8Hrs, and run for 11.7 + 3.8 = 15Hrs. This is supplying zero BTU input to the shop slab.

Looks like the bottom line is this. Anyway I look at it, it's min 4hrs/day of run time on either unit during cold season. With the Garn I get more upside output and storage. It just means finding the power to do it. The EKO's look like nice units and review well, but it looks like I'll be running it continuously in the winter if I want to do both House & keep shop from freezing. During warmer months I can fire every other day during power availability.

So now, I've got this big chunk of extra steel pipe laying out in the shop: 10' by 36" x .625wall that I was going to make a boiler from. Might have to make into another tank...

I really appreciate you all taking time to look this over for me.

Craig

 

[Gooserider]

A couple of other factors...

1. I haven't looked at the numbers, but my understanding is that the EKO and similar boilers will draw essentially the same amount of power regardless of size, so oversizing would shorten your run-time and power consumption as long as you can get the excess production into your storage efficiently (Note that this might require bigger / more power hungry circs, but again it seems that upsizing a circ doesn't carry a big penalty compared to a small one...

2. Going to 240 for the same hp blower motor would NOT save energy - your amp draw would be less, but watts = Volts X Amps, so 120V x 2A is the same as 240V X 1A for instance. You WOULD possibly save a chunk going to a DC motor at whatever voltage your system runs at since that would save you the hit from inverter inefficiency - but then you would also need to be able to get the same voltage from your genset.

3. One other potential issue with the Garn that I see as less of one with the EKO, is the size of the demand... This would depend somewhat on your existing inverter capacity, but it would look to me like the amount the EKO draws would be within the range of what you'd need for the rest of your house anyway, so you wouldn't need to worry about adding supply capacity, or restricting other load uses to save power for the boiler... OTOH, When it's running the Garn looks like it would be drawing enough that you'd need to worry about either adding more supply capacity, or squeezing your other loads to free up the Garn juice...

I'm not a solar expert by any means, but my understanding is that inverters lose efficiency if not run close to full load, so you'd need to either have a dedicated unit for the Garn, or have lower conversion efficiency when the Garn wasn't running... Either way inverters looked like expensive items, and bigger ones looked like MUCH more expensive... Might be worth figuring that into your numbers if you haven't already...

Gooserider

 

[Clearlycountry]

Hi Gooserider. We've more or less established that the EKO is more efficient on the electricity usage, but that has to be weighed against the runtime and output. Given our usage model, it is pretty clear that the Garn will work better. e.g. running genset during winter am to charge batteries will be combined with boiler fire. Since Garn has 2 days supply and will most likely be fired daily, this will tie in nicely with battery charging time of ~2Hrs. Eventually, I'll also Hx tie the genset into the boiler and although only ~ 17KBTU, I have to cool it anyway so what the heck.

Our Solar system is pretty elaborate and if anyone is interested I would be happy to share more details. Essentially though, we can produce quite a bit of 240V power which is why I would go to 240V blower, (that and 240V makes motors work a little easier since you are running on 2 phases rather than just one). Running big loads on only one leg off the inverter (or genset for that matter) is something we have to keep an eye on.

I'm going to check with our local code people to verify any hidden issues, then place an order for the 2000 if all checks out. Maybe I'll follow Jim K's lead and take some pics along the way to share with you all.

Craig

 

[Gooserider]

Sounds good, long as it works for you, and it definitely sounds like you've looked at the stuff that matters...

Good luck with the install, and yes, you have the idea,

"WE LUVS PIKTURS :coolgrin:

Gooserider

 

[Jim K in PA]

I apologize if anyone got the impression from my post that using the higher voltage/lower amperage motor would use less energy. Goose is correct that total energy usage would be a wash. I was going with my silent assumption that the higher voltage unit would be more compatible with your solar setup.

BTW - the EKO 60 is a 100W unit, not a 50W unit. It is still a lot less than the GARN, but double the electric load of the smaller EKO.

Oh - and I think Listeroid CS diesels are WAAAAY cool! Is yours a single or a twin?

Best of luck with your setup.

 

[Clearlycountry]

Listeroid is a 6/1 w/ 5k ST head. I rebuilt it over the winter and it has just been sitting there quietly for too long. It should be up and running this fall. One of the nice things about these motors is they only plod along about 650RPM and burn about 1qt/hr@ 3kw load. It works really well for supplemental power for my machine shop and charging the batteries. The inverters load share with the generator, so they can be programmed to pull only what the genset can deliver, and then provide the rest themselves when needed.

On a different note, I wanted to pass along something I plan on doing this summer to ease the wood situation. We've always heated with wood and over the years I've gotten pretty tired of cutting, stacking, unstacking, wheelbarreling, restacking, etc. This year, I'm going to something new. If you've never seen a 275 gal paint tote, they look like a plastic cube surrounded by a galv tube framework. The local paint company here gives them away. I figure to cut the plastic container in half and use the top half for a bottom tray. Each is about 40" x 48 x 48 and can be moved with the forks on the tractor. They also stack vertically. Idea is just to pack all our wood in these as we cut/split/store, then park one by the furnace, and one by the house to feed the woodstove as needed. Here's an example of what they look like: (broken link removed)

Craig

 

[Gooserider]

Listeroid is a 6/1 w/ 5k ST head. I rebuilt it over the winter and it has just been sitting there quietly for too long. It should be up and running this fall. One of the nice things about these motors is they only plod along about 650RPM and burn about 1qt/hr@ 3kw load. It works really well for supplemental power for my machine shop and charging the batteries. The inverters load share with the generator, so they can be programmed to pull only what the genset can deliver, and then provide the rest themselves when needed.

On a different note, I wanted to pass along something I plan on doing this summer to ease the wood situation. We've always heated with wood and over the years I've gotten pretty tired of cutting, stacking, unstacking, wheelbarreling, restacking, etc. This year, I'm going to something new. If you've never seen a 275 gal paint tote, they look like a plastic cube surrounded by a galv tube framework. The local paint company here gives them away. I figure to cut the plastic container in half and use the top half for a bottom tray. Each is about 40" x 48 x 48 and can be moved with the forks on the tractor. They also stack vertically. Idea is just to pack all our wood in these as we cut/split/store, then park one by the furnace, and one by the house to feed the woodstove as needed. Here's an example of what they look like: (broken link removed)

Craig

The galvanized frame part looks OK, but I'd be a bit concerned about the plastic container - would it allow enough air circulation to let the wood season? The other possible concern would be the "weight loading" - the tanks and frames were designed for a liquid load, that would impose uniform strains all the way around. I don't know how it would be with firewood that is inherently going to put more of a non-uniform load on the frames because of the way it stacks... Might not be a problem at all, but I'd try testing a bit before spending a lot of money on a bunch of them, especially seeing how well they stack when full of wood...

Gooserider

 

[pybyr]

Listeroid is a 6/1 w/ 5k ST head. I rebuilt it over the winter and it has just been sitting there quietly for too long. It should be up and running this fall. One of the nice things about these motors is they only plod along about 650RPM and burn about 1qt/hr@ 3kw load.
Craig

Lister CS engines and their Listeroid-clone progeny are indeed a thing of extreme elegance in the sense that 'form follows function.' I've got a 6/1 Listeroid in my barn that I eventually intend to pair up with a good generator/ alternator. Originally I'd wanted to run it on used cooking oil as a residential-scale combined heat and power project, only to find that in my neck of the woods, demand for the UCO had already outstripped supply. It'll still make a great backup generator, and in the mean time, is ferrous art (large anachronistic metal objects seem to follow me home from time to time ).

 

[emesine]

ClearyCountry,

Where do you get your quote of 9A for the Garn 1200? Frequently power tools, etc. are rated for a certain amperage, but in practice the actual draw is much less. For instance, my power drill pulls 11 amps during the first 1/2 second of operation, but once it is up to speed it draws much less than 4 amps. I would make sure you have an accurate figure for the real life draw for the unit once the fan is up to speed. It might draw less than you are calculating. I don't own a Garn, so I don't know for sure.

Andrew