Calculating baseboard requirements


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Old 09-15-06, 06:28 PM
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Calculating baseboard requirements

I'm in the process of enclosing our back porch. It's about 26' x 10' and sits 9' in the air over nothing. The walls are 2x4 framing, the ceiling 2x6 and the floor 2x8. I'm having foam sprayed into the ceiling, floor and walls. Three of the walls have windows and there are 4 skylights. The fourth wall is attached to the house. I have a copy of the book Modern Hydronic Heating, which I don't understand, which came with the software Hydronics Design Studio, which I don't understand much better. I fumbled through it, however and came up with this:
http://i103.photobucket.com/albums/m123/longaville/porchheatloss2.jpg

http://i103.photobucket.com/albums/m123/longaville/baseboard2.jpg

I'd appreciate it any comments on these results and if the baseboard requirements seem accurate.

Thanks,
 
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Old 09-16-06, 07:10 AM
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Given what you describe, your location and outdoor design temp, the heat loss seems a bit (possibly at lot) low (the 7500 BTU/hr). However, most of the inputs look about right. R19 walls, R3 windows and doors, R35 ceiling and floors. I don't think you can get R19 in 2x4s without spraying. Are these values given to you by the insulation contractor? Is this icynene (sp?) foam?

Ah, how high are the ceilings? Your room volume at 1280 cu ft is too low. A 26x10 room with 8 ft ceilings has a volume of 2080 cu ft. That will definitely affect your heat loss.

What brand/specs for the windows and skylights? How many and how big?

What did you use for baseboard sizing/output?

I can plug this into my software, maybe tonight, and see what I come up with. Not sure why you're using 150F supply water? Typical is 180F. What kind of heating system for the rest of the house and how is it set up?

BTW, the Siegenthaler software is IMHO about the best there is without going to really really high end commercial stuff.

Ok, time to go catch some dinner.
 
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Old 09-16-06, 07:35 AM
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Baseboard

I too noticed the supply temperature to the baseboard at 150 but the outlet temperature was 147 & a flow rate of 5.5 GPM using a B&G 100 circulator & 16 feet of baseboard?????
A 3 drop thru 16 feet of baseboard sure isn't going to give you much heat.
 
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Old 09-16-06, 01:56 PM
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The 3F delta-T is probably about right for that flow rate through 16 ft of baseboard. Consider that a typical loop strives for a 20F dT. Just for example: a loop has 64 ft of element, 4 pieces of element at 16 ft each. If dT is 3F per element, that's 12F temp drop. Add another few degrees for piping losses, etc. and you're probably close to 16-18F. Not bad. The transfer rate will also be in part a function of the temp difference between the room and the supply water. Plus at 150F fin-tube baseboard isn't yielding much output (~400 BTU/ft @ 150F vs. ~600 BTU/ft @ 180F).

I'm also guessing that the loop shown is not a real loop, but just an approximation to illustrate the baseboard. That's probably why the flow rate is relatively high.

berone, how did you make up the loop diagram?

Also noticed that the ACH is set for .2. More typical is .35. 0.2 would be a very tight structure.
 
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Old 09-17-06, 03:51 PM
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Huh?

Just barely hanging on to what you guys are talking about, but I'm starting to get it. Thanks for your guidance - I found the errors in the input and corrected it. (the ceiling was sloping down to 2'6" instead of up to 10'4") I also changed the water temperature to 170 which is where we kept it last year. Here are the revised screen shots:
http://i103.photobucket.com/albums/m123/longaville/porchheatloss3.jpg

http://i103.photobucket.com/albums/m123/longaville/baseboard3.jpg

I changed the ACH to .35 after I redid this. It didn't affect the length of baseboard needed.
I didn't create the baseboard drawing - it was the default background for the program on that page. I think it's just a generic to show the components.

The windows are Andersen 400 series casements, all from 2'6" to 3' by 5'. The skylights are Velux VS deck mounted, 30" x 46". 2 are fixed, 2 venting.

We are having the insulation sprayed. It's Sealection 500 and the R values are what the contractor told me (near as I can recall).

What I can accommodate from a design standpoint in the room is 8 3' long baseboards. (Actually I'm going to build my own into the window seats that will be surrounding the room) (That's my own enclosures, not the elements). That will bring the radiators around the 3 exposed walls, leaving a space for the door. From what I'm seeing, even with the revised numbers, 24' should be enough to do the job. This room will be a separate zone unto itself, so I don't have to worry about balancing these units with the rest of the house.

The original plan was to do radiant in the floor, but the specs I was coming up with made me question if it would produce enough heat in my application. Once I thought of building the rads into the baseboard that seemed like a better choice in terms of producing adequate heat as well as cost and ease of installation.

Thanks for the help. Please let me know if I'm overlooking anything else.
 
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Old 09-17-06, 05:00 PM
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Sunrooms are tough to do with radiant. Lots of windows, usually 3 exposed walls, etc. Good choice going baseboard.

24 ft should be fine. If you are building them into seating, make sure you follow manufacturer specs on how much air space they need to naturally convect effectively.

We've been swapping out old windows, replacing with Andersen 400 series casements. We really like them.

FWIW if you really upped the ACH, it might change the heating element. ACH, or air changes per hour, is a measure of infiltration, i.e., leaks around doors and windows. Your spray in insulation should really keep the infiltration down.

Sounds like a good project. Good luck.

When you are ready to talk about setting up the near-boiler piping for your new zone, stop on back. Valves vs. pumps, loop length, etc. are all things that are easy to get right, kind of a pain to get wrong.
 
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Old 09-18-06, 02:28 PM
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Thanks for the help.
I'll post when I'm ready to layout the rest of the zone.
 
 

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