OWB Questions

[Nodak Andy]

Hey everyone, just had a couple questions for those of you using an OWB. First of a little background on me. My wife and I just built a new house. We are heating the house and DHW with a couple plate exchangers fed by the OWB. Our unit is a brand new Crown Royal Stoves 7400e. Love the boiler. It appears to be super efficient. We just started burning about 5 days ago and I am very pleased. Inside the house we have radiant floor heat for the basement, garage, and we ran the piping on the underside of the sub floor for the main floor and it works awesome. I'm using a 12 zone Cross Manifold for the majority of the house, and a taco 4 zone for the garage and 1 zone in the house.

Do you guys all run your circulating pump on the back of the boiler at full speed? Only reason I ask is the return temp going back to the boiler is only about 7-10 degrees cooler than the supply temperature. Does that seem right?
As far as heating the house goes, our system works VERY well. It just seems a little odd that theres such a small temperature difference from supply to return. We aren't living in the house yet, so I can't say how the DHW works. Hopefully by the weekend I will have the rest of the plumbing done and we can start moving in.

 

[CUCV]

The supply and return water temperatures will constantly be changing depending on outdoor temperature and what zones are calling at any given point and time. This delta T is much more constant with radiant heat as there is a slow constant draw instead of spikes. I don't know the specifics of your boiler but on my boiler they specify a certain speed for the boiler circulation pump as to alleviate hot spots within the boiler when it is firing. In the manual it specifies what speed different model boilers should be set at. I have long thought of using a variable speed pump to and from the boiler to drive electrically efficiency. I use one variable speed pump to service all my zones and really like it.

 

[lindnova]

I don't remember exactly what is normal, but 7-10 degrees sounds good. I think mine looses about 5 but my pipes are run together in insulated pvc and mingle temp on the way.

Many variables but generally it is better to have more water moving to keep the boiler from having hot spots.

Sounds like you have a good setup - do you use mixing valves to temper the water going into your floor? I didn't at first, but later added them to keep the in floor heat around 100° which works much better for an even heat on the floor and I'm sure helps expansion also. I put my Heatmor in in 2006 with a similar setup and other than working the bugs out in the first year all I need to do is feed it and keep up on ash and check the water annually. Except that my water is very hard and even with a iron filter and softener I need to de-scale the flat plate for DHW at least once a year when the pressure drops.

 

[dave_dj1]

I don't think that drop in temp is bad considering the amount of draw you have on it.
I'm of the "send the water through fast" camp I run a pretty good size circulator and it runs constantly. I have a HX in my hot air furnace, I have another HX built into the wall in the finished basement and a 10 plate for my domestic. I also have a short run to the OWB
55'

 

[Nodak Andy]

Thanks for the responses guys.
@lindnova I don't have a mixing valve in the floor loop yet. I've been kicking around the idea of putting one in. Thinking I probably will go ahead and put one in.

I have a 125k btu 20 plate exchanger for the DHW and a 175k btu 30 plate exchanger for the floor heat. There is a mixing valve installed for the DHW though. Once we get the plumbing done (hopefully by the weekend) I will see how the DHW works. I think it will work well though.

We had the temperature set for 71, but it was just too dang hot in the house. I had to take it down to 68 and now it's perfect. Once we get moved in I'll finish installing the rest of the Thermostats for Zone Control throughout the house garage. That'll make things run even smoother I think. Right now it's just 2- 6 loop zones which is a pretty large load anytime the T-stats call for heat. That being said, I'm pretty impressed with how little wood the system uses. We can go 30 hours easy before we need to refill the boiler. Thats using mostly cottonwood and pine rounds, with a few chunks of ash or oak to maintain a coal bed. Using rounds of cottonwood or pine really does make it last a lot longer instead of splits.

 

[cantoo]

I have an old Pacific Western owb. It's pretty huge and hold around 500 gallons of water. I heat 2 houses and a 24 x 56' shop with it including domestic hot water. The firebox has a 24 x 24" door and 54" deep. We never fill it full of wood as it just seems to burn up quicker. My splits are Ash, 32" long and about 8" diameter. In the morning we throw maybe 8 of these pieces in and then at night around 7 we put the same amount in. On Saturday and Sunday we use more wood as we are opening the big doors in the shop more often. During the day if the coals are getting piled up we might just rake them all foreword and let them burn down some. I think smaller quicker burns use less wood but haven't really tested it out much. During fall and springs we usually just burn poplar splits and cedar slabs off my bandsaw mill.

 

[NSMaple1]

I would definitely want a mixer on my floor loops. Water in there that is too hot could cause damage to floor materials. Dont think I would go above 120 or so.

 

[Nodak Andy]

I have ordered a mixing valve for the floor loop. We were finally able to get the water to the bathrooms and kitchen turned on last night. It appears the 125k btu plate exchanger I purchased for that isn't going to do the job. It has no problem maintaining a 125ish water temp if you only have 1 faucet running, but as soon as you fire up a second one it drops down to about 110. It doesn't appear it is even opening the mixing valve. I ordered a 225kbtu exchanger and will install that when it shows up. I'll save the 125k as a backup for the floor heat loop. I think it'd be more than sufficient for that.

For those of you running a plate exchanger for DHW, how many BTU is it rated for? I know 225k is probably way more than we need as it is just my wife, son and I in the house, but we may have a couple kids staying with us in the not so distant future so I want to make sure everything is going ot work out. Better to have it and not need it kind of thing I guess...

 

[Marley5]

Definitely gonna require mixing valve for floors or wear thick soled shoes. Lol
We have radiant through out, heating 4600 sq house and additional 30×30 garage set at 50*.
CB 5036 set at 165 - 175 constant flow pump at the boiler and thermostats for each floor and garage.
Yes, don't forget mixing valves for each room/floor with thermostat.
I've played with them and settled with an entry temp of 130* under concrete and exits at 110*.
Another one at your plate heat exchanger.
Amazed at the efficiency of radiant.

 

[NSMaple1]

Is the OWB your only source of DHW? Are you trying to run it as an on demand setup? Not an optimal setup, for me. I have an ordinary 80 gallon electric tank water heater. I use a 20 plate flat plate to heat it with wood when burning. Uses a small circulator on the DHW side to heat the tank up. All kinds of hot water doing that. Then if I dont burn for a while the elements simply take over when the tank temps drop. Burning wood all summer for DHW is a no thanks here.

 

[dave_dj1]

I only have a 10 plate for my domestic and it's the last thing in line and I have no problem with water temps at the valves. It is also hooked to a 40 gal water tank.

 

[Nodak Andy]

Is the OWB your only source of DHW? Are you trying to run it as an on demand setup? Not an optimal setup, for me. I have an ordinary 80 gallon electric tank water heater. I use a 20 plate flat plate to heat it with wood when burning. Uses a small circulator on the DHW side to heat the tank up. All kinds of hot water doing that. Then if I dont burn for a while the elements simply take over when the tank temps drop. Burning wood all summer for DHW is a no thanks here.

So to make sure I'm understaing this correctly, you've Tee'd off the hot and cold lines coming from the tank. The hot line I assume is the suction of a circulator pump, from the pump it goes through the plate exchanger and then back to the cold inlet line on the water heater. I've been thinking about this, and this seems like it would be the proper way to do it. I'd add a tempering valve between the inlet and outlet of the plate exchanger to keep the temp of the water in the water heater under control.

The way I'm envisioning this, the water heater could actually act as a backup heat source for the radiant floor heat loop as well... kick on the elements, circulate the hot water to the exchanger to put BTU's back into the Glycol which would then get sent to the next exchanger to drop btu's into the floor heat loops. probably wouldn't be super duper effective/efficient, but in an emergency situation it would probably suffice. Especially if we are leaving town for a couple days and basically just want to keep things from turning to ice... I think with the 175k btu plate exchanger I have for my floor loops it could possibly work pretty decent as a backup.

Thoughts or suggestions?

 

[NSMaple1]

My hot water heater is bottom entry. I have a T there and another one up high on the side at the T&P relief port. A small circulator (B&G Ecocirc) pulls from the bottom T, thru the load side of the flat plate, into the top T. Controlled by a Johnson A419 temp controller with the temp sensor set in against the bottom port as far into the tank insulation as I could get it. So when either the temp at the bottom of the tank gets below a certain temp, or someone turns a hot tap on so cold water starts running into the tank, the circ starts circulating to heat the tank water. You might be able to reverse that to heat the house heating water but not sure how you would control it and it would be $$ to run to heat your house. And if the tank temp gets above 150 or so it will trip the overheat breaker on it. I have an electric boiler for house heating backup if the fire goes out but havent used it in the couple years since we put mini splits in. It would use around $30/ day of electricity when heating the house.

 

[Nodak Andy]

Interesting. I'm not sure, but I'm thinking my idea will work. I'm going to give it a try, and if I need to I will add some controls to the unit after the fact. I have a spare grundfos pump laying around. When I install the new electric water heater I'll throw that pump in the mix(set on lowest setting) the way I described in post #12. Pull from the hot (outlet of the W.H.), push through plate exchanger and mixing valve(set to 130f) and then back into the inlet of the water tank. I don't see any reason why it wouldn't work. I'll even throw in a test to see how the system functions as a back up heater for the floor heat loop. I don't expect it to be super great, and probably won't be cheap to run that way as backup heat, but it'd do in a pinch for a couple days here and there I think.