Help with Math for Base Board

[flyingcow]

I have an 8ft section of BB in my upstairs bathroom. That puts out 500/600btu's per ft at 175f water? 4/4500btu's of out put? If i run 135f water thru it, whats my btu output going to be? Just a rough idea, it may vary a bit.

The reason for this question is my builder/installer, nearly two decades ago, installed this BB in my upstairs bathroom. But, it's piped into my 1st floor zone. So during the day and night, setback T-stat allows bathroom to cool off pretty good. It's a good sized bathroom, has washer/dryer in it. What i've been thinking about is tying this BB into my radiant floor loop, that serves my kitchen. There is an extra connection on the manifold. Be a fairly easy thing to accomplish. That would give me a continuous flow into bathroom, 24/7. The room is on the west side of house, and can get cooled off pretty easily. I thought about putting a panel rad or cast iron rad in there, but would like to try this first.

Any thoughts?

 

[NE WOOD BURNER]

550/175= x/135 x=424

30% is what I was told to use for sizing so x=385

theoretically speaking.

 

[henfruit]

You can go on line. They have charts that will give you this info.

 

[NE WOOD BURNER]

You can go on line. They have charts that will give you this info.

he did. he came to the hearth! its a great place for any question. LOL

 

[Karl_northwind]

According to my slant fin table, for 3/4" element (that has 2x2" fins at about 3/16" spacing for comparison to yours) 135 F water will deliver about 300 Btu/ft. longer runs will need more flow rate, but there you have it.

 

[PassionForFire&Water]

Just an example
At 130F you have 260F per foot.
Water Flow does not make much a difference

 

[Karl_northwind]

Just an example
At 130F you have 260F per foot.
Water Flow does not make much a difference

my point was that that BTU number is not consistent over long runs of fin tube element. the water temp drop towards the end of a 30 or 40 ft run is substantial, and upping the flow rate from 1 gpm to 4 gpm will have significant impacts to the heat output on the far end of that run. especially important should the run go thru multiple rooms, like the described application.

karl

 

[kopeck]

As others have said Slant/fin and Sun-Temp have some nice charts on their sites.

The "Pro" that installed most of my heating system used the "Put as long a run as humanly possible on an exterior wall" method, no math needed other then the use of tape measure!

*sigh*

K

 

[maple1]

As others have said Slant/fin and Sun-Temp have some nice charts on their sites.

The "Pro" that installed most of my heating system used the "Put as long a run as humanly possible on an exterior wall" method, no math needed other then the use of tape measure!

*sigh*

K

I think that's way better than the alternative, at least.

Then with the use of a VS circ pump like an Alpha, and throttling zone flows as needed to get even heat distribution zone to zone, and maybe closing some shutters at the start of the zone & leaving end ones open, there are lots of tuning possibilities.

I think mine was designed with more rads than needed too, but I'm thankful for that now.

 

[flyingcow]

You can go on line. They have charts that will give you this info.

Never been online, tell me how to do it.

 

[henfruit]

Just as easy to go to a manufactures web site and get accurate answers to your question, rather than quess

 

[NE WOOD BURNER]

I would try it as it easy to do. If it don't work I would go with a panel radiator that way you can put the thermo control on it and you will be hook into the 24/7 loop already. IMHO

If you are computer challenged you can practice your pointing and clicking with a few games of solitaire!

 

[kopeck]

I think that's way better than the alternative, at least.
Then with the use of a VS circ pump like an Alpha, and throttling zone flows as needed to get even heat distribution zone to zone, and maybe closing some shutters at the start of the zone & leaving end ones open, there are lots of tuning possibilities.
I think mine was designed with more rads than needed too, but I'm thankful for that now.

Yeah, more really doesn't hurt, some of it's really over kill though and other rooms really don't have enough. That being said I stay warm, even in the deep freezes we've had this year.


K

 

[kopeck]

Never been online, tell me how to do it.

I hear you need to talk to Al Gore, he's the one that know all about that new fangled internet thing.

K

 

[Bob Rohr]

I have an 8ft section of BB in my upstairs bathroom. That puts out 500/600btu's per ft at 175f water? 4/4500btu's of out put? If i run 135f water thru it, whats my btu output going to be? Just a rough idea, it may vary a bit.

The reason for this question is my builder/installer, nearly two decades ago, installed this BB in my upstairs bathroom. But, it's piped into my 1st floor zone. So during the day and night, setback T-stat allows bathroom to cool off pretty good. It's a good sized bathroom, has washer/dryer in it. What i've been thinking about is tying this BB into my radiant floor loop, that serves my kitchen. There is an extra connection on the manifold. Be a fairly easy thing to accomplish. That would give me a continuous flow into bathroom, 24/7. The room is on the west side of house, and can get cooled off pretty easily. I thought about putting a panel rad or cast iron rad in there, but would like to try this first.

Any thoughts?

Unless that board is very first on the loop it may not see the temperature that the boiler is providing. Measure the temperature going into the board, and the temperature at the other end, add the two, divide by 2. That gives you the average temperature across the element. Use the output table from the manufacture to see the actual output at that average temperature.

Boards at the end of a series loop will see much lower temperature and have a lower output, often times designers calculate that temperature drop and size the boards accordingly.

Most baseboard has dampers and you might adjust down the first ones to get more output to the last ones, balancing the system so to speak.

An electric heated towel rack is a nice addition to an under-heated bath, and may be a simple fix.

 

[flyingcow]

Thanks Bob, good advice. I shake my head when someone states the obvious. That is the info I need to help me. Would an IR thermometer be ok to use?

 

[Bob Rohr]

Thanks Bob, good advice. I shake my head when someone states the obvious. That is the info I need to help me. Would an IR thermometer be ok to use?

Yes, use a black marker to "color" the pipe and get an accurate reading, shinny surfaces don't read as well.

Here is an output graph for typical 3/4 fin tube.

If you REALLY want the math, here is a link to Idronics 8 also which drills down on baseboard output, remember the air temperature as well as the fluid temperature plays into the output.

It's always about the ∆T in heat transfer both the wet, and air side of emitters

http://www.caleffi.us/en_US/caleffi/Details/Magazines/pdf/idronics_8_us.pdf

 

[flyingcow]

thanks

 

[tom in maine]

Baseboard heaters operate by convection. The housing enhances this.
If you want to play with minimal cost, you can make a new housing to go around the fin tube. The taller it is, the better it convects, just like a chimney. It also performs better with lower temperature water.
Now it is just a matter of making something that looks good. But it is mostly a woodworking project!

 

[flyingcow]

I had that in mind today Tom. I had to reinstall some ho baseboard today. Looks to be a few inches taller.

 

[Bob Rohr]

thanks

If you are trying to reduce the temperatures to you baseboards, series piping is not a good match. Better to parallal or homerun heat emitters if you are planning around lower supply temperatures. At lower supply temperatures you will run out of fizz at the emitters at the end of the line.

Progressive hydronic designers have 120F as a goal for design temperatures these days. This allows may types of heat sources to power the system, like heat pumps and thermal solar. It also leverages storage. But the heat emitters need to match the low operating temperatures. More surface area like panel rads, or oversized fins on the tube. Or forced convection, adding a small fan to move more air across the heat emitter. Large radiant surfaces with tight tube spacing is another option.

A common misunderstanding is that the boiler controls the temperature that the system operates at. Water temperature in the distribution will only rise to the point where thermal equilibrium is reached. The controls on the boiler are really there to "limit" temperature, not assure operating temperature in the distribution.

In fact the distribution is what dictates the temperature the systems distribution operates at. The concept is thermal equilibrium. A good explanation and graphic on how that all plays out starts on page 51 of this journal.

http://www.caleffi.us/en_US/caleffi/Details/Magazines/pdf/idronics_12_us.pdf

 

[flyingcow]

Once I get a chance to measure the Delta T chances are I will be hooking this 8ft piece of BB directly to my manifold off of the staple up system. This runs about 130. I think the continuous flow will make the room warmer. If I have to I can put a trv on it.

 

[jeffesonm]

If you are trying to reduce the temperatures to you baseboards, series piping is not a good match. Better to parallal or homerun heat emitters if you are planning around lower supply temperatures. At lower supply temperatures you will run out of fizz at the emitters at the end of the line.
Progressive hydronic designers have 120F as a goal for design temperatures these days. This allows may types of heat sources to power the system, like heat pumps and thermal solar. It also leverages storage. But the heat emitters need to match the low operating temperatures. More surface area like panel rads, or oversized fins on the tube. Or forced convection, adding a small fan to move more air across the heat emitter. Large radiant surfaces with tight tube spacing is another option.

I am trying to crunch some numbers on how low I can run my baseboard supply temperatures and stay warm. Is 20 degrees deltaT still a good assumption for running baseboards with lower temp water (100-150)?