Need help with running a Hawken

[kleinchris]

Hi Guys, I need all the help I can get... let me give you my info before I get to the problem.

Hawken with two separate pumps on back of machine. Pumps are sized at 1 inch, I reduced down to 3/4 inch.
Each pump feeds a single stand-alone building.
Two buildings, one off each pump.
Building #1 has 1600 ft2 of in slab tubing.
Building #2 has 800 ft2 of in slab tubing plus two blower units.
Insulated lines with no water in corrugated conduit.
Highest temp ever measured on floor is 120. Water in OWB was at 155.
Highest water temp ever recorded is 165.
Average burn water temp is 110.
Stuffing this machine every two hours.
Wood is not perfect, but not green. About 20% punky
No damper, no fan control.

I'm burning a lot of wood for what seems like very little heat. I'm loading this thing every two hours! If I stuff it full at midnight, there's nothing but white ash in the chamber at 6 AM.

Any thoughts?

 

[maple1]

First suspect is your underground piping and heat loss there. You said corrugated which usually means wrapped which usually means not very good. You should accurately measure temps in & out of everything to get a better idea though. A good IR temp gun is a good tool for that, spray shiny surfaces with flat black paint first for better accuracy.

Edit: '20% punky' doesn't sound very good either.

 

[hondaracer2oo4]

You've got a host of issues going on I think.

1. Your underground lines feeding the slabs are only 3/4 pex? Where did you even find that?

2. How is your in slab radiant set up? I'm not a radiant guru but 120 degree slab temp sounds extreme.

3. You say you OWB is never over 165 degrees, why? You should be running the boiler at 180 or 185 as a high. You should un plug your pumps and let the boiler come up to temp before you put the building loads on it.

4. How long have you been working to bring the slabs up to temp? Should take a couple days.

5. Punky wood is like a marshmallow. It looks big but in reality it's all air with no substance. Probably 1/8 of the btus that you would get out of an equal size piece of seasoned hardwood.

How is your radiant set up with the manifolds etc? Flat plate heat exchangers keeping the owb and slabs separated? How is your air sealing and insulation in the 2400 sqft you are heating?

 

[maple1]

Is there lots of insulation under the slab?

Agreed on the host of issues comments, I think.

 

[hondaracer2oo4]

Good point, hopefully at least 2 inches of xps under and 2 inches of xps thermal break to the frost walls.

 

[kleinchris]

Answers and a question in italics

1. Your underground lines feeding the slabs are only 3/4 pex? Where did you even find that? Amazon

2. How is your in slab radiant set up? I'm not a radiant guru but 120 degree slab temp sounds extreme. 120 is the single hottest spot recorded on the floor. Average temp is 85.

3. You say you OWB is never over 165 degrees, why? Factory settings are at 165, but it struggles to get to that temp, with out pumps being off, I could never get to 185. You should be running the boiler at 180 or 185 as a high. You should un plug your pumps and let the boiler come up to temp before you put the building loads on it.

4. How long have you been working to bring the slabs up to temp? Should take a couple days. Weeks

5. Punky wood is like a marshmallow. It looks big but in reality it's all air with no substance. Probably 1/8 of the btus that you would get out of an equal size piece of seasoned hardwood.

How is your radiant set up with the manifolds etc? Flat plate heat exchangers keeping the owb and slabs separated? What is a flat plate heat exchanger.? Each buildind has its own pump and manifold. How is your air sealing and insulation in the 2400 sqft you are heating? Insulation of the buildings is very good. R-30 all around.

 

[hondaracer2oo4]

Ok so first off, I assume that the underground piping is some type of three wrap or similar product in a drain tile and I also assume it is a new install. Although a new install I would want to confirm that you aren't losing your heat between the boiler and the house because of ground water getting into that drain tile, that would kill all efficiency. You radiant manifolds should have a temp gauge going into the floor and returning that you can confirm you are getting whatever temp the boiler is at when it leaves.

Next what temp do you have your tempering valve set at to send water into the radiant slab

What is the differential on the boiler? You said 165 high, what temp does the blower kick back on again to bring the water back to 165? The problem with running this really low temp is that the boiler will start to sweat inside the firebox if the return water is below 150. So if you are sending water returning to the boiler below 150 you are causing condensation inside your firebox which is compounding your burning issues as well as causing corrosion. Most of us run at 160 low and 180 or 185 high. The boiler will run more efficiently up in these temps as well.

What do you have for insulation under the slab and for a thermal break between the slab itself and the frost walls?

You should really either forget about burning this punky wood or throw a piece or two at a time with the rest of your quality wood.

I think your major issues are two fold. First major issue is the wood you are burning likely has little heat content or BTUs and without the available BTUs you are not going to be able to rise the water temp.

Second problem I believe is that I think since you aren't sure what a flat plate hx is you are running a totally open system which is a problem for a couple reasons. First reason is that the water quality with junk in it from the owb jacket is going to get into the radiant system and cause sediment build up and corrosion issues, also you can have many issues with purging all the air from the loops in the system is open leading to zones in the floor that are air bound. Also the biggest problem with not keeping the two systems separate is that return water back to the boiler is going to be very cold causing shock to the boiler itself and running issues. You need to really have the systems seperated through a flat plate heat exchanger. This flat plate allows your to build a pressurized system on the radiant floor side and an open system on the owb side. On the radiant side you would have a mixing valve to mix the water down to somewhere around 100 degrees entering the floor and somewhere around 80 when it returns. The flat plate allows you to send 180 degree water from the boiler to the flat plate and then return to the boiler at 160 or somewhere there about(looking for around a 20 degree delta T(delta t = water temp drop) which will keep from shocking your boiler and allow it to run correctly. The picture below while not exactly your situation it is close enough. Your boiler in the diagram doesn;t need a expansion tank on it since it is an open system, it just needs a pump to pump to that flat plate heat exchanger. Now you could set it up like the pic shows with a loop and taking off the loop and sending to each slab or you can just use one pump on each outlet from the boiler(what I would do) and send it to the flat plate. The radiant side is what you want except you would also need a tempering valve added in there as well.

 

[kleinchris]

Ok so first off, I assume that the underground piping is some type of three wrap or similar product in a drain tile and I also assume it is a new install. Although a new install I would want to confirm that you aren't losing your heat between the boiler and the house because of ground water getting into that drain tile, that would kill all efficiency. You radiant manifolds should have a temp gauge going into the floor and returning that you can confirm you are getting whatever temp the boiler is at when it leaves.

Next what temp do you have your tempering valve set at to send water into the radiant slab

What is the differential on the boiler? You said 165 high, what temp does the blower kick back on again to bring the water back to 165? The problem with running this really low temp is that the boiler will start to sweat inside the firebox if the return water is below 150. So if you are sending water returning to the boiler below 150 you are causing condensation inside your firebox which is compounding your burning issues as well as causing corrosion. Most of us run at 160 low and 180 or 185 high. The boiler will run more efficiently up in these temps as well.

What do you have for insulation under the slab and for a thermal break between the slab itself and the frost walls?

You should really either forget about burning this punky wood or throw a piece or two at a time with the rest of your quality wood.

I think your major issues are two fold. First major issue is the wood you are burning likely has little heat content or BTUs and without the available BTUs you are not going to be able to rise the water temp.

Second problem I believe is that I think since you aren't sure what a flat plate hx is you are running a totally open system which is a problem for a couple reasons. First reason is that the water quality with junk in it from the owb jacket is going to get into the radiant system and cause sediment build up and corrosion issues, also you can have many issues with purging all the air from the loops in the system is open leading to zones in the floor that are air bound. Also the biggest problem with not keeping the two systems separate is that return water back to the boiler is going to be very cold causing shock to the boiler itself and running issues. You need to really have the systems seperated through a flat plate heat exchanger. This flat plate allows your to build a pressurized system on the radiant floor side and an open system on the owb side. On the radiant side you would have a mixing valve to mix the water down to somewhere around 100 degrees entering the floor and somewhere around 80 when it returns. The flat plate allows you to send 180 degree water from the boiler to the flat plate and then return to the boiler at 160 or somewhere there about(looking for around a 20 degree delta T(delta t = water temp drop) which will keep from shocking your boiler and allow it to run correctly. The picture below while not exactly your situation it is close enough. Your boiler in the diagram doesn;t need a expansion tank on it since it is an open system, it just needs a pump to pump to that flat plate heat exchanger. Now you could set it up like the pic shows with a loop and taking off the loop and sending to each slab or you can just use one pump on each outlet from the boiler(what I would do) and send it to the flat plate. The radiant side is what you want except you would also need a tempering valve added in there as well.
View attachment 192312

 

[kleinchris]

Honda- Im having a hard time getting accurate temp reading on the PEX, so I'm going to try the spray paint trick this week. But from what I'm reading now, I only have a 5 degree temp drop at the house. Lets say 130 leaving the boiler, 125 entering slab. Water returning to the boiler is in the 90's.

If I understand your last paragraph, it would lead me to believe that by dumping 90 degree water back into the tank, the owb will never be able to recover from that low temperature and leave me in the low temp purgatory. However, the exchanger will fix this issue?

Luckily, I already have a pressure tank and pump, all I would need is the exchanger. Actually, that's not true... I need to do this for each building.

Insulation under the slab is only rolled metalic bubble wrap, No frost walls, no frost. Average soil temp in winter is 62 degrees.

 

[hondaracer2oo4]

A good resource for you to read is radiant tec website. http://www.radiantec.com/. Explore the site. Lots of good info. Also just google radiant slab. Lots of info out there.

As far as the bubble wrap goes, people have mixed results, ultimately it is a very poor insulation. The frost walls also suck huge amount of the heat right out of the slab if you don't have a thermal break between the slab and the frost walls. Through radiation the heat that you are putting in the slab is sucked right out of it and transferred to the frost wall which is cold and exposed to the outside. Think of it as laying on a rock outside in the winter with no clothes on. Now put clothes and a jacket on( insulation and thermal break) it now isn't sucking the heat right out of you. The ground while 60 or so degrees is doing the same thing as the frost wall, sucking the heat right out of it. Hopefully you don't experience this to bad but this could likely be your issue not being able to heat the slab up, the heat is being sucked right out of it.

As far as isolating the two systems it is going to be better for both your slab piping because of sidement the crap. The boiler will also not be shocked by cold water which will cause the firebox to sweat and corrode.

 

[hondaracer2oo4]

Oh and if you are losing 5 degrees from the boiler to the house you are losing a ridiculous amount of btus before they get to the house. That would be from underground lines having ground water in the casing sucking all the heat out of the pipes before they reached the house. Probably burn an extra 5 or 6 cords per year if you are really losing 5 degrees.

 

[kleinchris]

Thanks to all with the replies- especially Honda who asked some key questions. I will run down the logic in head right now with bullet points, please point out if Im off track. For now, lets not concentrate on insulation and effeciency factors... Im in North Texas, this should be so much easier for me than you guys. There is no such thing as a frost zone here. Never snow on the ground.

CURRENTLY:

• My boiler runs at low temps and I am constantly feeding it. My stove came with a factory on at 150° off at 165°. Maybe lower preset temp than you guys because Im in Texas.
• Everybody I have talked to has said get your temp up! I should be running at on 170° and of at 185°.
• If I run my stove at 145°, lets say for 12 hours, house would get too warm, blower would never turn off, and I use to much firewood.
• If I ran boiler now, with current set up (no exchanger) at a higher temp (which I cant acheive anyways) house would get way too hot.
• Water from boiler runs directly to manifold, into house at 130°, back to manifold, back to boiler at 92°.
• Boiler cant produce enough heat to overcome the incoming 92° water.

IF I ADD HEAT EXCHANGER:

• I can supply constant water temp to house, and return more hot water to boiler.
• Boiler doesnt have to work as hard reheating incoming water.
• Boiler stays hot longer, blower comes on less, I burn less fuel.
• Water temp going to home is pressurized and temperature can be controlled at the exchanger.

Please give me your thoughts. Am I going in the right direction? And where can I pick up an exchanger?

 

[hondaracer2oo4]

Yes your on the right track. It would do you some good to go to radiant tec or google radiant slab heating just to learn everything you can. You are heating your slab WAY to hot right now. You should be sending it the lowest possible temp going in(90-95) and returning from the slab at 70-75. You achieve this through a mixing valve on the floor side of the system. The flat plate heat exchanger allows you to keep the two systems separate and only dump off only 20 degrees from the boiler. So if the boiler water going into the boiler side of the heat exchanger is 170 and it returns to the boiler at 150. Either eBay or outdoor furnace supply or just google flat plate heat exchanger. I have had good luck with outdoor furnace supply.

 

[maple1]

Your house shouldn't be getting too hot. When a thermostat gets up to temp, it should shut down the heating loops. Boiler temp & house temp should be independent of each other (as long as the boiler is making enough heat to meet the heat demand).

So sounds like you have a fundamental flaw somewhere, either in your piping layout, or controls, or both.

You should also have boiler protection plumbed in, somehow, so that boiler return water does not get below 140 or so. (Usually done with a boiler bypass loop). With those cold temps coming into the bottom of the boiler constantly, it increases creosote/firebox condensation dramatically, which also ups the corrosion potential a lot. Using a heat exchanger may help with that.

With no pictures of anything, we're kind of talking blind a bit.

 

[hondaracer2oo4]

I think he is overshooting so far because he is feeding the floor with 120 degree water which is causing the huge temp overshoot.

 

[maple1]

Could be.

I wonder if there is even a mixing valve in place? Might have missed it.

 

[hondaracer2oo4]

Yeah he does not have a mixing valve. I don't know who designed this system but it's evident they didn't have a clue what a radiant floor slab system consisted of. Water travels straight from owb to radiant manifold and returns right back to boiler.

 

[kleinchris]

I designed this system. I laid every foot of PEX, dug the trenches, and had to convince one concrete company that a PEX line in the slap would not compromise the strength of the slab. In North Texas, nobody has ever heard of heating a floor. It took the guys at Central Boiler about six weeks to return a call where I said "I want to buy one of your boilers." Six weeks. After shopping around again I decided to go with Hawken. They explained that they had never sold a boiler to the State of Texas, and they would forgive my shipping costs (about $1500) if I could forgive them not giving me an install and instruction on how to run it.
There are no engineers/firms/architects in Texas with extensive experience with OWB. There are no distributors here, my closest neighbor who owns an OWB might be 300 miles north.
This is why I'm coming to you guys. I need help here. Honda asked some good questions which got me to ask myself some questions. I am asking everybody else to keep asking questions to me.

Unfortunately I have my boiler shut down now and my windows open. 70°

 

[hondaracer2oo4]

Unfortunately you missed a bunch o key components you need to make a radiant slab work.

First think of it as two different systems. The owb is very simple. You put wood in it. It burns the wood and heats the water up to 180. There is one or two pumps mounted on the back pumping water 24/7 to each slab. When it gets to the slab it goes through a flat plate heat exchanger which exchanges heat with the water on the radiant side. It then heads back to the owb to e heated back up. That is the owb side. Very simple.

Second is the radiant slab side. The radiant slab side has a few key components. These components are the slab manifold which supply's and returns the water from the floor, you have an expansion tank, a spirovent, a tempering valve and a pump. The pump is kicked on when the thermostat calls for heat in the room. The tempering valve should be set to somewhere in the 90-95 degree range. Google radiant slab manifold and look at images. You should find plenty of diagrams. You are over shooting your thermostat because you are feeding the floor with 120 degree water. Also time will tell if the bubbly wrap is sufficient to insulate the slab from the ground or if it is just going to suck all te heat you put into it away.

 

[maple1]

When it gets to the slab it goes through a flat plate heat exchanger which exchanges heat with the water on the radiant side.

I would maybe add an 'almost' there:

'When it gets almost to the slab...'

(That might be getting picky )

 

[maple1]

You might have to re-do your underground piping also, at some point.

Don't think we got the full details on that - exactly what it is & how far the runs are. But 3/4" is not very big. Also don't know your piping layout & pump type/sizing etc..

(Don't get too discouraged - that boiler should be able to make all the heat you need as long as you give it a good diet).

 

[kleinchris]

The runs on the underground pumps are 75 feet each.

Here is another question: Hawkens website mentions specifically that the OWB water temp should only fall below 150° once per season during start up. Are there other opinions on this in the industry?

 

[hondaracer2oo4]

Are you asking if it's common knowledge that boilers need to be run or protected from dropping below 150'degrees? The reason for this is that the firebox will condense water on the inside of the firebox st temps below that causing rusting and corrosion in the firebox. You should be running your boiler with a minimum temp of 160 when it kicks back on the fan to heat back up. Most of us run 180 for a high. Central boiler requires a thermostatic protection valve to keep return water back to the boiler above 150.

 

[maple1]

The runs on the underground pumps are 75 feet each.

Here is another question: Hawkens website mentions specifically that the OWB water temp should only fall below 150° once per season during start up. Are there other opinions on this in the industry?

See post 14 re. boiler protection.

 

[kleinchris]

Heat exchanger arrived today, but I wanted to check with you guys to make sure I have a couple of thing right: The exchanger provides a physical separation between the boiler water and the house water, correct? And this is why I need a pump on the house side. right?