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Delta T

Started by Central Boiler 6048, February 25, 2015, 09:35:29 PM

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Central Boiler 6048

Hello I'm brand new to this forum, just signed up today. Hints my username you all can see that I have a cb 6048. I'm on my 4th month of burning wood and I love it so far. I installed everything myself this past summer. I'm heating a 1500 sq ft modular home with forced air, I'm also heating a 1970's butler building which is pretty much like a pole barn, its 40x70 2800 sq ft 13' high roof. I'm also heating it with a forced air suspended unit heater. I guess I can get to the topic, It's rather long. I am experiencing a real high delta on the zone going to my barn. LIKE 55 degrees. I did my research on my underground pipe which I used the cb thermopex 1 inch, however I thought I had everything figured out. Since I'm new to the owb I never figured in the proper gpm for my unit heater which is a 220K emitter from central boiler. I forgot to mention I keep the barn at around 42 degrees 24/7. My fan prop is spinning so fast that the air kinda has a cool touch to it, it still gives me my demand when needed. My boiler holds its water temp while the fan is on but after about 15 min of shutting off the water temp drops like 5-8 degrees. Did I screw up by not putting bigger pipe in the ground?  I'm 100' round trip and the unit hangs about 11' in the air. I also have like 10 90degree elbows in the loop. I'm running a 007 taco pump. I know I will never get 220000 btu from the emitter, I would be happy with 130000-150000. I'm thinking about putting a lower rpm motor on my fan prop to make my delta go down. Would this help me out? Would I burn less wood if my delta was lower?  Any comments would be much appreciated. Thanks

thecfarm

Central Boiler 6048,welcome to the forum. I am not in the know about what you asked,but I have the same pump,taco 007 and I have only about a 20 foot run and it's all straight. But I have no idea what you would need. Hang on,there are others that know what you need.
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Dave Shepard

Do you have two separate zones off of the boiler? One for the house, and one for the Butler building? I am using the 1" CB Pex from my 6048 to the house and it delivers all the heat I need with an 009, which is less gpm than an 007. On the house side of the heat exchanger, I have a large Delta T. Outgoing is usually 168, with the return often as low as 130, and after going through the Modine heater in the garage, under 100. I have a huge exchanger, so it heats it right back up. I don't think there is anything wrong with your system if the boiler is maintaining it's temperature and your zones are at the temp you want.
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Central Boiler 6048

Yes I have two separate zones one for the house and one for the building. I have reviewed bigger underground pipe and I am realizing obviously it can carry more Volume which would be higher GPM? I'm just trying to get more heat off my heat exchanger. I would love to know how many BTUs I'm currently throwing out. The problem is when I want to go work in there and bump the temperature up 10-15° I'm thinking it would take a long time? Did you say your return temperature is sometimes 100°?
My Delta on my house is around 23 to 25 which I think is about right?

Dave Shepard

Yes, my return temp can be quite low after going through the house and the Modine. In the pic, the vertical gray pipe on the left is the return from the house. It goes up to the Modine, and returns to the upper left elbow on the exchanger. The exchanger is in the garage. The 007 I'm using on the house side of the exchaner isn't moving enough heat. I suspect that with about about 90 feet of run, that even though it has a higher gpm than an 009, that there must be too much resistance on that circuit. I'd like to switch everything to 011's, as they are high flow and high head pumps. The Modine can suck almost 40 degrees out of the return water when it's running. It is a large heater meant for a warehouse, so it doesn't run for very long, maybe five minutes once an hour.



 
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hedgerow

Is the building your heating the one in your sig picture one with almost a flat roof or is this like a pole shed with no ceiling. Sounds like you better put a divider in the building and heat less of it or call the spray foam guy and get that building insulated. Your going to get tired of cutting wood. It will take a lot of wood to heat that much building. One inch pipe is plenty big to heat that. It would be easier to heat with in floor and a lot of insulation. My shop is in a pole building with a ceiling it is 30 by 60 with 16 ceiling and it is spray foamed with in floor and I have a forced air unit hooked to the Garn so if I want a little more heat I kick it on. It takes a lot of wood when the temp is in the teens and stays there. I have 450 ft of one inch to my house two supply and two return and we run three furnances with that and heat our hot water also. The one inch works fine. I do run two pumps on each line one at the Garn and one in the house.   

Holmes

 To get 150,000 btu's [15gpm] thru your piping , you need an 0011 [18 gpm] or 0013  [23 gpm] circulator.
Think like a farmer.

doctorb

When you send that cool water back to the 6048, you're making it work pretty hard to keep the water temp in the OWB high enough to have the furnace cycle on and off.  with your current set-up, does your stove run constantly or can it raise the temp up to the idle point?
My father once said, "This is my son who wanted to grow up and become a doctor.  So far, he's only become a doctor."

Central Boiler 6048

The Butler building has a flat roof with pretty decent insulation all around. It is a steel structure building. Yes my boiler does keep up with it, it also can get back up to the idle temp which is 185. Every time the barn unit cycles the boiler temperature doesn't move which is a good thing however about 10 to 15 minutes after it does it will drop the water temp down 7-8 degrees which gets it closer to the low point that is 174. I think the problem is the blower motor is rated for 18 to 20 gallons per minute which would give me 200,000 BTUs I'm thinking about getting a electric motor at 1140 RPMs with the same prop to lower the air flow which I hope would reduce my Delta. I know lower CFM is lower BTUs but I'm just trying to match my GPM? I did my calculations on my pipe length and elbows and with the central boiler hydronic's book it says with the equivalent length and a 007 I should be around 6 gallons per minute?  Thanks

garret

The flow design software I wrote shows 15 GPM BUT at 30 ft of head for 100 ft RT and 10-1" ells to get 150K btu through 1" PEX.  That's a lot of pump and wasted electricity.  At a delta T of 30, 10 GPM and 14.8 ft.
E-Classic 2400 comfortably heating 4,200 sq.ft. and unlimited DHW, Off-grid, Photovoltaic-powered pumps in gloomy SW PA , 34 t splitter, numerous Husky chainsaws

Holmes

  I see the 007 maxes  out at 10' head. I doubt you are getting 6 gpm flow.  A 009 will get you 7 gpm with the head loss you have.  If you are going to spend money on a motor it might be better spent on a larger circulator.  It appears you have the heat you need sitting in the boiler and it is not getting delivered to the house and barn. Do you have 1 circulator or 2, 1 for each building?
Think like a farmer.

Central Boiler 6048

I have two pumps they are both 007. I was looking at a 014 pump. I was told 1 inch thermopex has a max flow of 8 gpm? I think I'm getting the heat deliver to my house okay. I would like to try a bigger pump and a electric motor but that would be around 400-500 dollers. I've already spent 900 on the total unit. In my Central Boiler book it says that a O14 Pump would give me around 8 to 9 GPM? I have around 60 foot of pipe in the ground then it enters my barn then I have around 38 foot of 1 inch pex going to the unit which is around 11 foot high. The equivalent length for my emitter is 50 foot +12 90° elbows would be around a 200 foot total length? Does that math sound right? That is pump and return included

doctorb

I am sure it's not too feasible now, but would 1 1/4" pipe solve this problem and decrease the delta T?
My father once said, "This is my son who wanted to grow up and become a doctor.  So far, he's only become a doctor."

Central Boiler 6048

I think it would but I really don't feel like tearing out my pipe and redoing everything. One problem that I have realized is The 1 inch pex that central uses in there thermopex in not a true 1 inch ID. It's 7/8 of a inch. I think I'm going to have to make the best out of what I got? The problem is the bigger circulators cost so much I hate to try one and it not make much difference.

Dave Shepard

The PEX pipe is supposed to flow like 1", so you can use 1" values for calculating flow rates. If you have a long run and a lot of restrictions, that equates to higher head, even if it isn't really higher elevation wise, so you may need a higher head pump, like an 011, to achieve the 6-8 gallons per minute that CB says the 1" will move. An 007 is not a high head pump. If your house and shop are being heated, then why are you trying to move more heat?
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Central Boiler 6048

I am just trying to get the most BTUs that I can get out of my 220K. And I think if I can reduce that Delta it would be more heat. My pump is mounted to the boiler which means it sits about 5 foot off the ground, The barn is ground level with the boiler. Is 1 gallon per minute equal to around 10,000 BTUs? The Butler building in previous years has been heated with 130 K propane heater. When I turn it on the temperature rises twice as fast as the boiler unit and the heat coming off of it is alout warmer.  Do you think my 007 is out of it's head range? Is that one of the reasons I have a higher Delta?

Dave Shepard

I suspect it is, but I don't know the math to calculate it.
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LittleJohn

6048, a few question since I am somewhat familiar with the CB

* Did you install the thermostatic by-pass between the OWB and the structure? (It diverts water back to boiler if temp is less than 140F, to reduce condensation)
* What are water temps going into and out of water to air HE, and the FPHE (all ports)

And a few answers:
...you are getting approximately 10k BTU/hr for every 1 GPM, assuming that your delta T is 20F
...also, 1" Pex maxs out at about 14gpm (@ 8ft/s -> which is FAST, and may cause turbulance in pipe or erosion in metal fitting) along with a delta of 20f; its about 140k btu/hr.  At 8gpm (puts you at about 4ft/s, much safer water velocity), and delta of 20, about 80k BTU

General formula for heat loss is:
BTU = GPM x Delta T (F) x 500
So if you know GPM & Delta T, just do the math

Central Boiler 6048

No I did not install the thermastatic valve, I have it sitting on the shelf. I can give you my delta which is 55 degrees. That's 180 water temp going to the emitter. As far as my gpm I'm going off the central boiler book. I'm guessing 5-6 gpm. Am I only getting 60000 Btu?

Holmes

The numbers show you are not getting 5 to 6 gpm with an 007 circulator.  If you were you would be getting 50 to 60,000 btu's . Head has no bearing on height, it is friction of the fluid traveling thru the pipe and fittings.
The lack of flow will give you a higher delta T. The emitter is sucking all the heat out of the water as it slowly moves thru the coil.
I agree with garrett's head numbers and a high delta t is ok. I think a pump that would get you 8 to 10 gpm at 15' of head will get your barn warmer , faster.
Think like a farmer.

Gary_C

Quote from: Central Boiler 6048 on February 27, 2015, 10:29:49 AM
I am just trying to get the most BTUs that I can get out of my 220K. And I think if I can reduce that Delta it would be more heat.

If you reduce the delta T, you will get LESS heat unless you increase the flow. A high delta T means the heat exchanger is doing a good job. So why do you want to reduce that efficiency?
Never take life seriously. Nobody gets out alive anyway.

Central Boiler 6048

Holmes,
Do you think it's worth trying a 009 pump before I go and buy a lower rpm blower motor? The 009 would have the head I need but a max gpm of 10.

Holmes

Yes That should help a lot.
Think like a farmer.

Central Boiler 6048

Gary C,
I thought that a lower delta would help me out? What I'm trying to do here is make the heat cfm from my emitter to be hotter. Now it's just warm with a cool touch. Is it worth trying a 009 pump? Wouldn't slowing down the cfm from my fan make the delta go down? I'm assuming if I did that I would get more BTUs? I could be wrong. Like I said I am a rookie at this and just want to get the most out of the system as possible. Have alout of money tied up in it!

Dave Shepard

I wouldn't monkey with the fan. To get more btus you need more volume. The 009 with it's higher head will be better able to overcome the frictional losses of the long run and the many fittings, but I can't say for sure how much more.
Wood-Mizer LT40HDD51-WR Wireless, Kubota L48, Honda Rincon 650, TJ208 G-S, and a 60"LogRite!

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