question for you heating/plumbing experts...

[fletcher0780]

Here's a quick description of my heating system:

-3000 sq. ft. 7 year old log home with radiant floor heat at 70* (4 zones + hot water)
-Detached 3 car garage with radiant floor heat at 50*
-800 sq. ft. apartment above garage with baseboard heat at 70*

All heating zones are effectively run off a 100K BTU buderous oil boiler

I installed a Shaver 290, 265K BTU outdoor wood boiler this year and a 250K BTU water to water heat exchanger. When the temp dips below 10* for three days or more, I start to lose heat in the apartment (drops to 60* at night, but only after 3-4 days of COLD weather). My oil boiler could keep everything warm, but it also provided 195* to the heating system, The best I can get out of my heat exchanger is 175* to 180* tops. One thing I did notice is the baseboard loop in the apartment is run by a little Taco 007 pump. Would increasing GPM by installing a larger pump get more heat into the apartment? What other options do I have? Should I add more baseboard?

 

[trialanderror]

check this out, it'll give you a ballpark figure

http://www.heatexchangersonline.com/airtowater.htm


then look at this and do some crazy math.

http://www.taco-hvac.com/uploads/FileLibrary/SelectingCirculators.pdf

if in doubt, go bigger in any situation. I put a 200k unit in my moms house, which is easily heated by a 120k unit. but, i can get the same heat from using a 200k unit at 130F instead of 180F. *BUT* if for some reason i really need the BTU, i can just fire the boiler harder and up the temp. Always over-estimate. Better to have it and not need it then to need it and not have it...

GPM is your friend. do the head and pipe flow loss math...

 

[fletcher0780]

Thanks for the info on the taco pumps. I'm not sure what to do with the HX info you provided, mine is a water to water setup that ties my wood boiler into my oil boiler. I know everything I have can be heated with my 100K BTU oil boiler, so I played it safe and went 2.5 times that on the wood boiler and water to water heat exchanger.

 

[trialanderror]

if your gpm is too low, then the water will cool much quicker if your application is calling for heat (shower, washing dishes, etc if your using water towater)

if you can afford it, install a water temp gauge at each zone's suplly and each zone's return ( or after the HX)

temp guages will tell the story if your drawing more BTU then what the water can carry to the application.


(drunk tyops, sorry)

 

[fletcher0780]

My heat exchanger temps look good, I'm just thinking the 007 pump running the apartment baseboard heat isn't enough. All the other zones work well at even the coldest sustained outdoor temps. I was hoping that moving 170* water faster (wood boiler wit ??? pump) would equal moving 190* water slower (oil boiler with 007 pump)

 

[trialanderror]

it would. if you have more displacement to dissipate the heat then you could get by with either lower GPM or lower water temp ( but not both at once)

 

[BIG BEAM]

BB heat doesn't make many BTU's when it drops below 170* and at 140* it doesn't make much heat at all.The oil boiler makes 100K all the time and the wood boiler will go up and down in BTU's.
DON

 

[AOD]

Sounds like you need to kick your water temps up in the real cold weather. You're probably losing a lot of heat into the ground through the interconnecting piping and you only notice it when it gets super cold.

Remember, BTU's = GPM x 500 x delta T. Most baseboard zones are meant to run on a 20° delta T, anything less than that and you can't move heat.

 

[fletcher0780]

so basically the only answer is to bump up the temp, increased flow or additional baseboard won't help? If I have the wood boiler at 175-185*, I get 172-182* on the A side of the heat exchanger and 165-175 on the B side. I guess I need my OWB up around 200* to get my B side temps where they need to be.

 

[mtfallsmikey]

All good points....the HX for the oil boiler might be your weak spot tho...how many ft. of BB are in the apt., how many zones?...600 BTU/ft. @ 180 deg. is a good baseline.

 

[fletcher0780]

mtfallsmikey, I was hoping you'd reply. I've got about 25 ft of baseboard in the apartment with one zone. Do they rate baseboard at a lower temp? ie 450 BTU/ft at 160*? or is 180* the recommended temp? I can swap out the pump or add more baseboard easier than trying to get my OWB to try and keep the water at 200*. 185* is really pushing it when it's real cold out, but that is an entirely different issue that I'll be addressing this spring/summer.

 

[projectsho89]

Fletch,

You can get answers to most of your questions at www.slantfin.com They're one of the larger manufactures of baseboards - perhaps yours is one of their products.

Pick out which baseboard you're interested in checking out, then follow the link to the Literature Library. Select the product your're checking out and select the ratings chart. It will show you a table of BTU ouputs at various water temps and GPM rates.

One thing to look out for is that when water velocity is increased, you can run into two problems: Increased water noise and the water may move too fast to effectively "give up" enough BTUs to safisfy your requirements.

Steve

 

[mtfallsmikey]

Yes they do...here is an example of Slant Fin Fine Line 30 series BB specs

4 gpm: 180 deg=610 BTU/ft
160 deg=480 BTU/ft.
140 deg=340 BTU/ft.

1 GPM: 180 deg= 580 BTU/ft
160 deg=450 BTU/ft
140 deg=320 BTU/ft

 

[fletcher0780]

great info guys, thanks. It seams that I can overcome the low water temp problem by adding more baseboard to increase the BTU output to the apartment. I may also be able to replace the 007 with a larger pump and move more water though the existing baseboard overcoming the lower supply temperature.

I wish I just did radiant floor heat for every thing, this is my only baseboard zone out of seven zones (including hot water) and the only one that gives me problems. I know that radiant floor requires lower supply temperature and that's why I have no problem with the other zones.

So just doing very rough math is 25ft of baseboard at 180* effectively heats the apartment that equals 15,250 BTU's, using the example mtfallsmikey provided. So if the supply temp is cut down to 160* I would need 32ft of baseboard, or an additional 7ft (28% more) to get the same 15,250 BTU's. I know BTU numbers provided may not be the same as my particular brand of baseboard, but the general theory should be correct I think. It seams reasonable to think that being 28% short on baseboard would cause the apartment temperature to drop during extended periods of very cold weather.

Now the next question, is it reasonable to assume a larger pump could overcome the shortage of baseboard, or is 28% deficiency too much to overcome with increased flow? Perhaps I should just buy 10ft of baseboard and give it a go. Now would be the time to do it before I sheetrock my garage ceiling.

 

[BIG BEAM]

I would go with more BB.Putting in a 011 pump won't give you a 28% gain.More like 5%.You'd be best off with 10' or 12' more BB.Once you drain the system putting in a little more BB is EZ.Even 15' wouldn't be overkill.
DON

Also carpet and furniture have an effect on BB.I use 500 BTU's per foot as a number.What the BB produces in a lab is only what it produces in a lab not in the real world.2 or 3 years worth of dust and the lab numbers go out the window.

 

[fletcher0780]

OK, thanks. Is there anything I missed? The apartment has a full dormer on one side and a sloping wall/ceiling (upstairs of a cape garage) on the other. The main room of the apartment has 25ft of available space at the bottom of the sloped wall/ceiling where I can add more baseboard.

 

[mtfallsmikey]

Easy on that pump size, my son!...Look at PShoe's comment.....3/4" pipe only rated for 4 gpm anyway....actually might look at a SMALLER pump....a 007 can blast a lot of water thru a loop. Done a heat loss lately on that thar apt.??...you can do that from slant fin's website too...

 

[fletcher0780]

I did the calculations with their heat loss, at 0* outside and supply of 180* I need 29ft of multi/pak 80, when I go down to 160* I need 38ft of multi/pak 80. Looks like my best bet is to add another 10-15ft of baseboard. Thanks for the info and that calculator.