Baseboard Zone Circulation

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Old 05-01-12, 04:24 PM
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Baseboard Zone Circulation

thought this should be posted separately from my other thread so as to keep from muddying the waters.

Have an issue - my wife complains - well, about her office being cold even when the heat is on. This room is the last one in this particular zone & it's the furthest away from the boiler ~70 feet (ranch house). The piping is 1/2" Cu, total head for this loop is 21 feet which includes 111 ft of pipe & 31 feet baseboard. The room before it has a in-the-wall heater with fan that's 2.5' higher than the baseboards.

There are 3 zones with 1 Taco 007 doing all the pumping. Tested to see how well the room heats up not really fast, but only as long as the other 2 zones aren't calling for heat. Otherwise, wait but you're going to get cold feet!

As an FYI, this all the baseboard & supply piping are 1/2". The return 'manifold' which is centerline and uses Tee junctions for the zone returns is a 56' run back to the return side of the boiler.

So, consensus time:
1. go with zone pumps instead of zone valves?
2. upsize this zone to 3/4" (alot of copper but would use pex instead)
3. upsize the return manifold to 1"?
4. ????
 
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Old 05-02-12, 07:35 AM
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Not an expert, but I sure have learned a lot when I started looking into my boiler system.

- You said your rads are connected via two tees (putting the rad in parrallel with the mainline/manifold)?
If this is correct, have you checked the rad for air?
In theory, the rad in that room should be at ~ the same temp as the mainline at that point in the circuit.

- If your system has your rads in parrallel to the mainline loop (sorry, don't know the correct terminology), what size is the mainline if your thinking of upsizing it to 1"?
My system is running 2" copper pipe for the two zone loops (talking of expensive).

- Is the rad above or below the mainline?
 
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Old 05-02-12, 08:56 PM
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All the zones pipe into a 3/4" cu pipe return that runs 56 ft back to the return side of boiler

one section is connected at the other end with 1/2" to 3/4" 90 elbow - this is the one im thinking of upsizing to 1". The other 2 sections tie in with tee's, 1/2" in to 3/4".

The radiators in each zone are in series
the zones are parallel to each other.
 
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Old 05-03-12, 06:10 AM
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Originally Posted by Thors Twins
All the zones pipe into a 3/4" cu pipe return that runs 56 ft back to the return side of boiler

one section is connected at the other end with 1/2" to 3/4" 90 elbow - this is the one im thinking of upsizing to 1". The other 2 sections tie in with tee's, 1/2" in to 3/4".

The radiators in each zone are in series
the zones are parallel to each other.
See the bolded text in your quote. This is your problem.

I had a bit of a brain fart when I was first looking into my hotwater system as I was having issues with air in the rads. Was looking at reconfiguring it to the rads in series and one of resident experts here on the forum gave me a kick in the butt, which made me realize my mistake.

Looking at one zone (particularly the one with the wife's office).
Hot water leaves the boiler and goes through the first rad in the series. That rad is designed to take the heat from the water, and transfer some of it to the air in that first room, leaving the water in the pipe just a bit cooler (bet your first room is good and hot).
The hot water goes from the first rad into the second, with the same effect (water is again, a bit cooler on the exit of the rad due to the heat transfer).
If you where to compare the input temp of that last rad to the input heat of the first one, you will notice a fair difference.

Here is a quick CAD sketch of a series setup and a parrallel setup which should help give you an idea of what I am talking about. The bottom setup is how mine is setup which balances the water temp a bit better then series and allows for the first rad/room to be close to or the same as the last rad/room in the loop. (please note, not to scale in any way shape or form. Image rotated to allow better viewing.)
 
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Old 05-03-12, 07:36 AM
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Oh boy!

Just out of curiosity - the water leaving the heater is cooler and is tying back into the pipe, doesn't this cool the water also?

I suppose the best set up is a distribution manifold

Looks like I've a bit of work to do!

Thanks for your insight, Mike.
 
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Old 05-03-12, 09:54 AM
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Thors Twins,
Yes the return feed from the rad will be cooler then the water in the loop, but the impact is less then cooling your entire suply with the rad fins.

One thing I should have mentioned which I failed to do (and it's not visible in such a small picture), is that my system has a 2" copper pipe for the main loop, and the rads are 3/4" (? need to verify). So in theory, my returning cooler water is a lower volume then the main feed.
 
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Old 05-03-12, 11:10 AM
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I hate to double post, but I thought I would add a close up of the parrallel rad setup sketch.
I don't know the technical term for it, but here is how mine is setup (rad above the loop (note, not to scale in anyway).
Name:  RadSetup.jpg
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You'll notice the two little tabs on the right hand tee. This is a builtin reducer within the tee which adds a bit of back preasure. This will force some water to travel up into the rad.
From the reading I have done, generally only one of these special tees (don't remember the technical name) is used, and generally on the return end of the rad.

Also noted from my reading, if the rad is physically located below the loop, two of these special tees are used (one on the feed, and one on the return).

Someone with more technical background in this industry may want to fill in the technical stuff and/or correct me of any mistakes.
 
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Old 05-03-12, 06:20 PM
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That is called a 'diverter-tee' or monoflow system. Not in vogue any more. Many reasons. Not worth getting into here.

The half-inch piping is most of the problem. Too much head (resistance), low flow rate, plus series emitters means end of the loop gets not much heat.

If you have access from below, a simple fix would be to either

a) home run each room's emitter(s) from a near-boiler manifold, or

b) repipe to a two pipe, reverse return system

You could very likely do all that in 1/2 piping.

You could do either with PEX (oxygen barrier PEX, of course). Keep one pump and zone valves.
 
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Old 05-06-12, 05:42 PM
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Going by your calculation of 21 ft head, not sure how you came up with that, the pump would be too small and you cannot carry 18k+ btu's in 1/2" pipe.
Here is a link to a pipe size/btu chart.
btu_pipe Btu
If you have already calculated the equievelent feet of pipe and came up with the total of 142 (111 + 31 ft element), than the pump head is about 4.5 ft head not 21.
Pump sizing
Circulator Pump Sizing
If this is the most resistant of the three loops the pump will be big enough. The fanned convector is going to have a rating that will need to be added to the 18K before pipe is resized.
 
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Old 04-23-13, 03:19 AM
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Revisiting

I'd like to revisit this topic...i know it's been 1 year, but now the heating season is coming to an end and have to figure out exactly what needs to be done.

The house stayed warm all winter long, but I still need to optimize the zone piping.

The mono-flow T system:
any good reason not to do this?
i've calculated headloss, etc. and would need 3/4" Cu or Pex, use the monoflow t's & regular t's as needed and keep the 1/2" convectors. doing this eliminates the added cost and labor of going to 3/4" convectors.

As far as zone returns...
All the zones pipe into a 3/4" cu pipe return that runs 56 ft back to the return side of boiler

I have a pre-fab'd supply manifold, 1-1/4" with the circulators coming of of that. Should I have a similar return manifold of 1-1/4" on the boiler return and have all the zones return to that manifold? Or can I ditch the 3/4" return pipe & increase that same run to 1" or 1-1/4" Pex?
 
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