In floor heating help

[borderboy1971]

I'm hoping someone can help me with my in floor heat. The shop is 60'x64' with 16' walls. The walls are 8" SIP panels rated at r32, the ceiling is blown in r50. There are 2 14x14 sectional doors rated at r25. There is r9 or r10 2" styro under the slab. (I haven't insulated the foundation wall yet). I put 15 loops of 1/2" pex (300 ft each) within the concrete stapled to the Styrofoam 12" spacing. Concrete is 5-6" thick. The south side wall has 6 3'x3' insulated windows. I believe the shop is extremely well insulated and quite air tight. Outside temps can get to minus 40c here. But typically run minus 20c to minus 30c during January and February. This is my first season with boiler operating and so far with temps down to minus 15c at night it has been ok but seems to use alot of fuel. Right now it burns about 5 gallons of diesel per day. (Due to south windows it pretty much doesn't run at all during the daytime). I'm trying to keep it at 60f. The boiler is a Burnham LE 74000btu that I put in myself. (Don't mind the messy boiler room or shop). I have one steibel pump feeding 15 loops. Can anyone tell me if the boiler is too small, too many loops on one pump, do I need a bypass circuit or is this just the way it's gonna be?

 

[Northislander]

Not sure if i'm missing something in your piping photo but that is a high temp boiler with radiant floor but i can't see any mixing or diverting valve.

 

[borderboy1971]

High temp? I'm guess so...it heats itself up to 130f then shuts down until 110ish. And yeah I didn't put in a mixing valve or divert valve. It's obvious that heating isn't my thing. What should I do?

 

[Northislander]

Here's a drawing i found with a 4-way mixing valve (this is the way i would) pipe a cast iron boiler which should probably be running around 180 degrees. At the low temps your running you are getting flue gas condensation that will rot out boiler heat exchanger prematurely. Disregard the indirect tank on the drawing

 

[borderboy1971]

Its around -15f outside right now and the boiler has been running steady now for over a day (non stop), and the boiler temp is only up to about 90f. The supply side of floor is about 85f and return side around 65f. The thermostat is using air temp which is around 58f. It seems like the boiler is struggling to get hot enough or there isnt enough flow or ???. I can set the boiler to a higher temp to shut off, but I don't think that will help anything since it's having a hard time reaching a low shut off temp now???

 

[Northislander]

Been a while since i was in school so someone else feel free to correct my rough calculations. Your boiler has approximately 270,000 lbs. of concrete to heat up not to mention the building space and overcome the heat loss. It will require approx. 50,000 btu to raise that concrete 1 degree considering your boiler probably caps out at a maximum output of 65,000 if it was piped correctly, as it's now piped it has to contend with the low return temps coming back to it reducing it's efficiency. it's going to take time to bring it up. Not sure how the circ. pump is wired but most cast iron boilers i've piped in the past if you used the boiler wiring harness the boiler wouldn't even allow the circ. to come on until boiler reaches a minimum temp approx. of 110 degrees.

 

[Jackfre]

You are going to rot out your boiler in pretty short order, the way that is piped. You need to be returning 140*f min.(please forgive the F designation. I'm American and not smart enough to use metric). You are asking a lot of that circulator. How did you size it? Actually that doesn't matter at this point. You need to put this on a Primary/Secondary piping system and you will need to add some controls for temperature. I would strongly suggest that you order Dan Holhan's excellent "Primary-Secondary Pumping Made Easy" Also, "Pumping Away" is excellent. These are well written and you don't need to be an engineer to profit from them. You have quite and investment there and you need to protect it. Also, the slab edge insulation, or lack of it is probably worth a couple gallons of oil a day. If you have an infra-red gun shoot the edge of the slab and you will see what I mean. You need to get on this right away to protect your boiler.

 

[Jackfre]

Also, on the burner side, how did you set it up? It is worth it to have a tech with a combustion analyzer set that system up.

 

[borderboy1971]

Regarding the burner side, I haven't touched anything with it regarding any settings. Oil fired techs are rare around here. Almost every place around here has natural gas. The few that don't usually run propane or an electric boiler. Our house is geothermal. Gas would cost me close to 30000 just to get it to my door.

I have swapped some wiring around and some settings so that the boiler now gets up to 180f then will start the circ pump. It only will circ for about 1 to 2 minutes before the circ shuts off and the boiler fires again to reheat. (Low temp setting at 140).

If I put a bypass in it to attempt to keep boiler above 140f, do you think the boiler will keep up? And do you think the fuel consumption will drop? I'm questioning now that it's too small.

I will check the foundation temp to see the difference. Unfortunately I can't dig around my foundation right now to insulate.

Thanks all for the help so far.

 

[Northislander]

borderboy You still need to change your piping so your low temp return does not go directly back in to the boiler. And 180 degree water does not go in to the slab. As Jackfre said you need prmary/secondary piping, there are several ways to accomplish this, the earlier drawing i posted is one.

 

[Jackfre]

Is the slab heating? Evenly? Depending upon how it is piped you may be getting flow through only a few zones. Get an IR gun and shoot the slab. You can control the return water temp with a tempering valve if need be, but I think you have bigger systemic issues that need analysis. I would suggest, by a pro and you need a burner tech. The likelihood that burner is running correctly, cleanly and efficiently is about zero. As pointed out, 180 to the slab is not good.

 

[borderboy1971]

I've got a heating guy lined up (I hope), to come and replumb my setup and hopefully get things working correctly. About a 2 week wait for him though. Ill let you all know how this turns out. Thanks again for all the help.

 

[yeldogt]

That's a low mass boiler and a quick look says it has outdoor reset capabilities -- did you get those controls? Sounds like you did not ? It looks like that boiler can take low temp water -- typically you have them set up with constant circulation with the circulator pumping away.

I think you have the circulator pumping towards the unit.

You need to see if it's actually circulating throughout all the pipes -- does all the floor seem equally warm?

With outdoor reset the pump runs all the time and the boiler goes on and off to maintain the water temp. The problem is what water temp do you need to heat the space ?

Did you do a heat load? You are getting about 60k out of the boiler ... I have a space with 1/2 you size and 1/2 the capacity and I can maintain the space ... but I get into the single digits for a day or two .. not down to your temps for weeks.

My guess is at -20 you are asking more than the boiler can deliver.


What's the firing rate of the burner -- using 5g a day does not seem excessive. That would only be 10 hours operation at .5.

 

[borderboy1971]

I thought I'd update where I'm at for anyone interested. Or for those that can help. I replumbed my boiler so that the circ pump is now pumping away from the unit and put in a valve to allow bypass fluid back to the boiler to keep boiler return hotter. I really now am thinking my boiler is too small. The valve that is pinched off is my bypass loop and I can barely pinch it off. If I pinch it off more the return temps on boiler are lower and then the boiler won't get up to tempurature. I currently have the boiler set at 160 outgoing and will restart at 130. The floor loop temps are approx 140 into floor and 50ish return. I think the boiler just can't build enough heat fast enough to work properly. It's keeping my shop at 65 as I've got the stat set there but on colder days (Not even cold yet), the boiler basically runs non stop during the night. The big south facing windows maintain pretty well through the day. (It will heat itself to 160 and shut off, but not long enough for exhaust fan to cool off and shut down).

P.s. don't mind the messy boiler setup, it's a work in progress.

 

[kj_mustang]

With that large a difference in the supply and return temps, I would be looking at the circulator pump. Is it sized correctly? What speed is it? How much gpm per loop do you have it runnning?