Vertical rise in hydronic baseboard system?


  #1  
Old 04-29-06, 03:27 PM
biver
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Vertical rise in hydronic baseboard system?

I have a ranch with hydronic baseboard from an oil-fired furnace in the basement. The ground floor heating is one zone, split into two loops, each loop having its own TACO circulator pump (each has 1/25 HP). There is also a basment zone.

I am considering renovations that would have a chunk of my baseboard ripped out and moved, and it would then be connected via a PEX branch that would go through a ceiling (really, there's no other way to get heat to the exterior wall, which is the only place there's a good amount of wall space).

I am wondering if adding the 8' vertical rise to the previously all-horizontal system is going to be ok. If there is the slightest risk that the pump will not be able to handle it, I will look up specs for these pumps, unless someone knows offhand.

(Oh, the loop that would be changed would have about 10-15 feet of baseboard left unchanged, with about 10 feet of high capacity in the new area)

Any help is appreciated.
 
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Old 04-29-06, 05:47 PM
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Circulator size

It sounds like a Taco 007 should be able to handle the loop with no problems but just to be sure you should calculate the head & required flow.
 
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Old 04-29-06, 06:54 PM
biver
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Does a "bump" count as head?

According to the specs, this pump's flow goes to zero at about 11 feet. thats not good, considering its about 5 ft below floor level already, and I'm talking about taking it up to 8 ft above floor level and then back down to the baseboard, and then back over the hump again for the return.

But does it really count as "head" if its just an 8 ft bump in the supply, down to a baseboard then an 8 ft bump in the return???

In a dynamic system, won't the water at the top of the hill be pushing the water at the bottom of the hill in front of it, and as it falls won't it help pull the water behind it?

In saying "dynamic", I recognize that the pump has to get things going in the first place, and it might lack the power (sigh)
 
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Old 04-30-06, 09:08 AM
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Feet of head

Either Taco's or Bell & Gossett's web site has a "how to" on calculating head & required flow. I'm not sure which site it was but I think it was B&G's.
 
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Old 04-30-06, 12:54 PM
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What is the upper temperature/pressure limit for PEX?

I would be really concerned about using PEX tubing. Baseboard convectors use water at 140 to 190 degrees with most systems engineered to operate at 180-190 degrees during the coldest weather.

The high-temperature cutout on the boiler would need to be set to the maximum working temperature (at maximum system pressure) of the PEX tubing.
 
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Old 05-01-06, 07:47 AM
biver
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PEX limits, definition of head

PEX seems to be rated at various PSI's depending on the temperature. My boiler's upper limit is probably around 190, and I think the corresponding MAX PSI for this temp is around 80. Right now my boiler is reading 175F and 5 PSI, though I am not sure if the pressure is directly from my closed loop system.

I looked up head in a plumbers dictionary and it said "height". Is there some different definition? I'll look on B&G's site.


Thanks.
 
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Old 05-01-06, 08:29 AM
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calculating flow and head

Here's a step by step to do it right:

http://www.taco-hvac.com/uploads/Fil...irculators.pdf

This is a piece of cake to do in Excel. I have a spreadsheet if you want to PM me I can send it.

Briefly, head has little to do with vertical height, and much to do with the resistance to flow imparted by the tubing, fittings, valves, etc.

Basically, you need to figure the head (resistance) at a flow rate sufficient to keep air bubbles entrained and deliver the heat to the baseboard. That's 2-4 feet/sec or in 3/4" copper about 3.2-6.5 gpm. PEX will be a little different, but the link above gives you values for PEX.

From the 11ft comment, sounds like you have a Taco 007. Great little pump, can probably do what you need. I run one that circulates through two zones in a 2-story house.

Do not use the various "rules of thumb" for calculating head and flow that you might find at the B&G site, for example. (For head it's something like measure the longest loop, multiply by 1.5, then multiply by 0.04, etc.) Those are from a bygone era when the alternative to crude guestimation with a rule of thumb was that you had to sit down with a pencil and a slide rule to do it right. These "rules" can lead to spectacularly wrong results.

If your zones are done with individual circulators, then you should be able to make whatever changes to this zone you need, then size the pump appropriately if the existing one is not adequate. I'll guess that you'll find the existing pump to be just fine.

And don't forget to do a heat loss calculation on the various rooms you're adding/modifying to make sure the radiation is sized correctly.
 

Last edited by xiphias; 05-01-06 at 10:14 AM.
 

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