Garn Owners: Temperature Drop

[bpirger]

My quest for an outdoor gasifier setup continues. I find myself drawn to the Garn. My installation would have the Garn (1500) outdoors, sheltered in a Garn barn. I would insulate as much as possible...so minimum of R38 from the boiler metal shell to the outside walls. Likely higher.

I'm curious about what level of temperature drops Garn users see. Integral storage is a huge advantage of the GArn, but obviously dropping all the heat outside isn't ideal. I really want to keep the fire/mess outside.

What is the killer is the huge DeltaT, i.e. the huge thermal gradient to encourage temperature loss. We are talking over 200 degrees F here in temp differential (garn water to outside air temp) on cold winter days. So while the amount of temp drop will be very strongly garn barn dependent, I'm curious what people actually measure. I have in-floor radiant, so don't need water over 120 degrees (save for hot water), so I might imagine losing quite a bit of BTU's as I won't really use the high temperature water immediately.

A brief mention of "average" temperature drop in the winter (or whatever you have), in the summer days, as well as a brief mention of your insulation would be great. Others would storage, I'd be interested in hearing the same things for your storage system. 400 sqft. of Garn barn, insulated at R-40, with a temp differential of 100 degrees should be dropping 1000 BTUs/HR. I think the 1500 is 11000 BTUs/degree change....so this would be only a few degrees a day. I find that an unlikely achievble number. Just looking for data from experience....

Thanks!
Bruce

PS---> Would you buy a Garn again? Would you look at something different?

 

[RowCropRenegade]

I haven't fired my Garn in 3 weeks. My DHW isn't hooked up yet, so no need.

It was 120 degrees 3 weeks ago. Just ran out to see that it's still at 105.

Look up Heaterman for his insulation kit for the Garn. I call it a Garn Sweater. I'm very pleased with it.

 

[heaterman]

It sounds to me like you have a good plan in progress with the Garn in an insulated outbuilding. We have many running in the same scenario including some units that are in large unheated buildings where the indoor temp routinely drops below freezing. I have also seen them enclosed in such a nice fashion that the building used to house the Garn was also used as a family game room. Most of the Garns are enclosed in some type of a frame,drywalled and I have seen a variety of materials used to insulate them. About the only thing I would not recommend would be blown cellulose because of its propensity to absorb moisture.

As for standby heat loss, obviously there will be less if ambient temp is maintained at normal room temps. You are correct in thinking the greater the differential the greater the heat transfer all other things being equal. I can give you the following examples from my own experience and you may draw your own conclusions.

#1 Garn WHS2000 in a well insulated 14x24 room wrapped with the afore mentioned "heaterman sweater". This room is a shed roofed lean to attached to an uninsulated and unheated pole barn so for all practical purposes it is entirely exposed on all sides. The room construction has 6" in the walls and 12" in the ceiling with a 9x7 overhead door in the 14' west wall, a standard 3-0 x6-8 steel entry door on the south and a 2'x4' window on the north and east wall. The Garn is maintained by this owner at 140-180*. During standby periods when the Garn isn't actively burning the room temp will run between 70-80*. When it's firing the temp in the room will be driven up to about 85* mostly by the air discharge from the combustion motor. The exterior of the "Garn sweater" runs within 2-3* of the room temp so there is not much heat loss going on there.
I had a chance to observe long term heat loss when the owner and family went away for spring break the last of March this year. I went through shut down and switch over procedures with them on a Thursday afternoon before they left. The Garn was standing at roughly 165* and all circulation was killed at that point. The weather varied from about 15* to 40* while they were gone. They returned home on Sunday of the next week and the water temp was still at 105*. This would equate roughly to a standby loss of about 5,000 btu/hour if I remember my calculations correctly. Temp in the Garn room had fallen to about 65*.

#2. This Garn is installed in a 10x 20 insulated room and wrapped in a similar manner to the "Garn sweater". The difference is that the front 2' of the Garn is bulkheaded through the side wall and is exposed to ambient temp inside an uninsulated pole barn. While I didn't observe it personally, the owner claimed that during a period of three days he was gone the Garn dropped 90* starting at 200* and ending at 110* when he returned home. The heat was on but set to 50* in his house while they were gone. That figures out to about 21,000 btu's per hour. I would say his heat loss from the Garn itself could have been no more than 2-3000 btu/ hour because the heat load in his house would have been at least 18-19,000 given those conditions. That heat loss would also include anything lost in a 600' round trip of underground 1.5" pex tube.

As you can see from those examples, the standby loss can be reduced to very insignificant levels with a little forethought and planning. Standby heat loss becomes a problem only when a person fails to consider it in the system design. The advantage of having the heat exchanger integral to the storage as offered by the Garn design far outweighs the standby heat loss if a person just takes appropriate measures to deal with it.

Hope that sheds a little light on your question.

 

[emesine]

Once the fire goes out, cold air is going to blow through the firebox and up the flue, wasting heat. That's a problem with any unit where the storage is connected to the firebox. That and the storage with a garn is going to be in the wood shed, not in the house. Loss of heat from a storage unit in the wood shed is wasted. Loss of heat from a storage unit in the basment goes to heat your house. Even losing a degree or two per day means thousands of BTU (for a 1500 unit, each degree F is 12,000 BTU). I also worry about corrosion with an open system.

We did a wood gun in the wood shed with storage in the basement. Only time will tell whether we love our system or lament not doing a Garn. The Garn certainly has some CONSIDERABLE advantages, starting with the simplicity of having storage and boiler in one unit.

Just my thoughts....

 

[heaterman]

Once the fire goes out, cold air is going to blow through the firebox and up the flue, wasting heat. That's a problem with any unit where the storage is connected to the firebox. That and the storage with a garn is going to be in the wood shed, not in the house. Loss of heat from a storage unit in the wood shed is wasted. Loss of heat from a storage unit in the basment goes to heat your house. Even losing a degree or two per day means thousands of BTU (for a 1500 unit, each degree F is 12,000 BTU). I also worry about corrosion with an open system.

We did a wood gun in the wood shed with storage in the basement. Only time will tell whether we love our system or lament not doing a Garn. The Garn certainly has some CONSIDERABLE advantages, starting with the simplicity of having storage and boiler in one unit.

Just my thoughts....

Once the combustion blower shuts down there is very little if any air movement through the flues in a Garn because it is about 50' long and horizontal. Your point about any btu's lost being wasted in an uninhabited space is very true. For myself I would much rather waste a few btu's than have the wood and all that comes with it located in my basement. Locating the boiler section outside and the storage inside the house or other heated area does provide some reduction of standby loss but most of the units I have seen are not real great when it comes to insulation of the actual boiler. To each his own...........choose your poison and all that stuff

As for life expectancy on an open system, I have to say that when talking about a Garn, I see them lasting as long or longer than the sealed systems I run across. That is not saying however that all open systems are in that category. What I find is that the sealed systems, due to their design tend to fail from the fire side due to creosote and flue temp issues allowing condensation in the heate exchanger area. Open systems tend to fail from the water side which is much more controllable and manageable.

I looked at a pair of Garns this week that as near I can determine were made pre 1983. Serial number WHI1500-29 and WHI1500-44. One has a hole in the jacket which the owner just patched and the other is just fine. As near as I can tell neither of them had much in the line of water treatement over the years so I would say a 27+ year life span is not too bad.

 

[Como]

Wonder if there will be a Garn collectors club?

 

[heaterman]

Wonder if there will be a Garn collectors club?

The owner of those two jokingly asked me to call Dectra and see if they had any antique value........

Headed back to that job site tomorrow with the camera.

 

[Como]

Well if Dectra have a museum...

This begs the question what is the ideal structure. A given that the Garn needs to be insulated but I always assumed that an insulated building was implied as well.

I suppose you could locate the pumps etc somewhere else not subject to freezing.

For my situation I envisage a building containing all our mechanical, control etc equipment, I was contemplating a radiator as well but that sounds overkill.

You are going to lose heat keeping the door open to replenish wood supplies, unless it is a very big building. Or you can move wood really fast.