Tarm Question

[lawandorder]

So the new Tarm Solos all come with the Tarm loading unit which is the thermovar valve, pump assembly etc. that if I understand it correctly, automatically controls the supply/return temps. Is anyone with the older Tarm units looking to upgrade to the loading unit. If so why and do you think its worth the money etc.... Thanks

 

[kevindauch]

I bought my Solo 40 last year with the loading unit. It works as advertised, no problems. It is nice to be able to see the return temp from the load and the the return to the boiler.

 

[DaveBP]

If you can get the loading unit for the discounted price with the purchase of a new boiler it probably doesn't cost much more than all the separate components. Not everyone uses all those components (unions and isolation valves, particularly) in a DIYer install though. To just outright buy a loading unit as an upgrade to an existing Termovar or Danfoss type thermostatic return protection valve doesn't really bring much new to the system other than elegance. The loading unit does completely shut off supply water from recirculating once the return from storage is up to whatever temperature its thermostatic unit is set for. The regular Termovar valve always allows some recirculation but I'm not sure if that is a noticeable difference.

There are two types of Termovar loading units, though. The type Tarm USA (now BioheatUSA) has been importing does NOT have a bypass valve (they call it a backflow preventer) built into the casting that allows a pressurized storage tank to thermosiphon if power goes out and therefore acts as an emergency heat dump. This only works with pressurized storage installed at the right elevation and plumbed into the boiler to allow an actual thermosiphon to occur. Many systems are not hooked up appropriately. It can also scavenge the last heat after the fire has died down to where the draft fan stops but there is still residual heat in coals and refractory and let it thermosiphon into storage rather than go off up the chimney.

The type WITH the backflow preventer is not being imported for reasons which I can understand but I find disappointing. I would buy one of those in a New York minute if they were available. Perhaps if enough people called and inquired about getting one they would be more interested in supplying them.

 

[Chris Hoskin]

It's a good question lawandorder and I think DaveBP gave a great answer:

"To just outright buy a loading unit as an upgrade to an existing Termovar or Danfoss type thermostatic return protection valve doesn’t really bring much new to the system other than elegance. The loading unit does completely shut off supply water from recirculating once the return from storage is up to whatever temperature its thermostatic unit is set for. The regular Termovar valve always allows some recirculation but I’m not sure if that is a noticeable difference."

Also, just to clarify, we DO have the backflow preventer equiped loading units in stock. Normally these are sold along with a boiler, but we are happy to sell them alone and can easily ship UPS. $595.00 plus shipping. If you are interested call Brian in parts and he will be happy to take your order. Another excellent comment from DaveBP relating to this version of the loading unit:

"This only works with pressurized storage installed at the right elevation and plumbed into the boiler to allow an actual thermosiphon to occur. Many systems are not hooked up appropriately."

Please be sure your application is appropriate before relying on this component as a gravity heat dump.

thanks for the great comments DaveBP!

Chris

 

[DaveBP]

Also, just to clarify, we DO have the backflow preventer equiped loading units in stock. Normally these are sold along with a boiler, but we are happy to sell them alone and can easily ship UPS

Well now, that just makes my day and the next few, too.
I'm out the door late to work right now but I'll be calling tomorrow.

Thanks for the news, Chris.

 

[dogwood]

Dave BP,I am very close to purchasing a Solo Innova from BioHeatUSA and will doublecheck if the Termovar loading unit included has the backflow preventer. I'd seen pictures of it before online and didn't know it was available either. Would you mind explaining what the "right elevation for storage" means in order for the storage to work as a heat dump? I am going to follow Bioheat's PT3 schematic closely and have a 1000 gallon propane tank for storage. Any description of how the Termovar and storage would need to be plumbed in relation to each other would be greatly appreciated. I have 1.5 inch black iron pipe to use which should help in reducing head. It's not too for me late to make some plumbing modifications to get the advantages you describe. Thanks.

By the way I bellyached in another thread the other day about BioHeat not calling back or not being helpful to me trying to make a purchase. Chris and the salesperson/tech both made contact the next day, emailed installation manuals, schematics, quotes and other info which I was very pleased to receive. Seems like a good company to deal with. Thanks Chris.

Mike

 

[DaveBP]

Most people who use propane tanks probably use the stock pipe fittings for their systems. Seems so, anyway, from most of the posts on this forum. Most often those are all from the top. Drawing cooler water from the bottom requires using the dip tube that comes in at the top and goes down to the bottom. Using these fittings will form a heat trap that will inhibit the thermosiphon. You need to put the hot supply water directly into the top, that's the easy one. More importantly the cooler return water needs to come right out of the bottom without going up to the same level as the hot supply water coming in from the boiler.
You need to either use the drain fitting on the bottom, if you have one and it isn't so rusted from soil moisture that you can't get it unscrewed (mine are, people don't rake out the leaves from under their propane tanks). The other option is to weld another pipe fitting on there where it is close to the bottom and convenient to your piping layout. These fittings are often referred to as "Weld-o-lets". One good source is MSC:

http://www1.mscdirect.com/Tank-Flanges/Tank-Flanges/Components/s0002009329.HTML

Have a highly experienced welder do this if you are not one yourself.

The basic concept is that the cooler water from the bottom of the tank goes downhill (or at least level) to the boiler and the hot supply water from the boiler goes up to the top of the tank. For a propane tank lying horizontally this is probably going to mean elevating the tank some. The closer together the tank and boiler are, the better and larger pipe sizes will help, too. More elevation helps, too.

As a correction to what I said previously, Bioheat stocks the loading unit with the casting set up for inserting either a solid brass plate or the little flap that is the backflow preverter. You buy it with the solid plate installed and just ask them to include the little flap with your unit and then install it yourself.

True to my word, I called them up and ordered it right away. 23 hours later it was in my hands, regular ground rate.

 

[dogwood]

DaveBP, I do have a large drain fitting on the bottom of the tank that a machine shop was able to get the rusted plug out of. One of the threads on the tank was damaged in the process so I might have to get the new pipe welded in so it doesn't leak. Anyway, the tank inlet is currently planned to be roughly sixteen feet from the boiler. Is this way too far away for thermosiphoning to work. I could possibly change where I was going to locate the tank and boiler relative to each other if its worth the effort. The locations are only on paper at this point. How much higher would the tank inlet need to be from the boiler supply outlet for this to work effectively? And what might be a reasonable distance range for the tank to be away from the boiler for this to be effective? Our electricity goes out all the time around here, usually for short periods, sometimes for hours, and occasionally for days, so any added boiler overheat protection would likely come in handy.

Mike

 

[DaveBP]

Mike, I don't mean to present myself as an experienced professional boiler system guy. I'm just an enthusiastic relative newcomer to wood boilers with some physics and engineering background, enough to be enticed and confused but not always enough to recognize the difference.
It's not hard to get water to thermosiphon. In fact it can be too easy if you don't want it to. The big question is how fast will the setup carry heat away from the boiler. In order to function as an emergency heat dump, it needs to carry off all the heat the boiler produces that doesn't go up the chimney when the power is out or if the circulator failed. There are just too many variables to know for certain what will happen in precise BTU/hour terms. In northern Europe and Scandinavia where this type of setup is often used there might be some rules of thumb. One of the forum members from over there may be able to help if there are any design patterns to follow other than what I've presented.

This is probably why Bioheat doesn't advertise this function of the loading unit. Too many variables not under their control. Especially involving DIYers.

My goal would be to do everything possible to encourage thermosiphoning in the boiler/storage tank system and when you have everything running the way you want to, unplug the thing in mid burn and sit yourself down and watch those temperature gauges and stay some distance from the pressure relief vent. It's the only way to know if what you have done is good enough. And it would bestow great peace of mind to watch it and know that it will work. And if it isn't quite enough, well then it's that much less conventional dump capacity you'll need to add.

 

[dogwood]

Thanks DaveBP.

Mike