Temp drop ???

Ed Lentz

OK I'm one of those HO that likes to DIY, I even have posted pix of my system here and gotten some help. I have an upstairs BB loop of about 100' of copper and in that length about 24' of Slant Fin 15. The loop is supplied with a Taco 007. I have read here that I probably should have about a 20 degree drop from the supply to the return from the BB. All the vents are open at the top of the BB. I am getting about 5 degrees. Here's the question: How do I get to that magical 20 degrees? Can I partially shut my iso valve at the pump, or is there a way to slow the pump down (I've read lately about a guy using a fan controller to slow the pump).
Or am I really just getting anal? The room heats up nicely, just wondering if I am as efficient as I can be. BTW, my supply temp is 150.

Thanks
Ed

Dave_22

hmm..

The first question would be what type of boiler and if it has protection for too cold of a return temp. If it doesn't, return temps under 140 degrees should be avoided. You will start condensing and could do damage.

Uni R

20 truly is magical

One way to help would be to let your house get really really cold and then measure it while it is recovering with 210 degree water!


Seriously, I'll bet your normal operational delta T is even higher than mine and I don't lose sleep over mine. I'd say you're being anal. How is the comfort level across the heated space? That's a more important question.

Weezbo

may i make another suggestion....

consider puting a temp probe and t on the return .and a taco I series zone valve on that zone ....

hr

You've got it backwards, slowing the pump down

decreases the baseboard output! Do the math, if you supply at 150° and return at 145 you're average temperature in the bb is 147.5

Slow the pump down and the 150 supply 130 return equates to 140 average teperature innthe baseboard.

Does 140 or 147 temperature give off more heat??? Unfortunatly this bb output chart doesn't go low enough to show you S&R numbers.

The faster the flow through baseboard the greater the output! Same with fan convectors, same with radiant tube circuits.

Look to any baseboard output graph. This is a Slant Fin Series 80 chart.

1 gpm (slow flow) gives 730 BTU/ foot at 180°.

Increase the pump speed (and gpm flow) to 4 gpm and you get 770 btu / foot at 180°.

Notice however the pressure drop difference. Faster flow equates to higher pressure drop.

Also at some point around 4 fps the noise and pipe/ fitting wear becomes a concern, in addition to more pump head and hp required for higher flow rates.

So you get to a point where it doesn't make sense to flow to fast.

Slowing flow to let the fluid "linger" in the pipes longer does not increase output

hot rod

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Ed Lentz

OK then I guess I am tilting at something that is already straight. BTW my boiler is a Crown AWI series. It does keep the space comfortable even in the coldest weather. So I'll leave enough alone then. Thanks everyone for your comments.

Ed

Mark Eatherton1

So...

You're comfortable RIGHT? Then don't lose any sleep over the 20 degree delta T. It's a reference point used in the design and engineering of systems and is RARELY seen in the field. WHen your system needs it, it may extract enough heat to creat GREAATER than a 20 degree delta T.

NO to worry, unless you're not comfortable, then worry like the dickens:-)

ME