Rheostat on Taco 003 Pump??

Rheostat on Taco 003 Pump??

PostBy: traderfjp On: Tue Sep 09, 2008 12:11 am

Hi,

I have a copper coil in my oil fired boiler. I'm running the hot water from my Bock tank through the coils to keep my how water heater from firing as much. I have a Taco 003 bronze pump for circulation. I'm wondering if I should put a rheostat on the circulator to slow down the flow for better heat transfer? The coil is made from 1/2" pipe while everything off the HW tank to the coil is 3/4" copper. The tank to coil is only about 3 feet away. Here are the specs on the pump: Drive TypeDirect Face to Face Dimension (In.)4 13/32 Full Load Amps0.43 GPM @ 1 Ft. of Head6 GPM @ 2 Ft. of Head5 GPM @ 4 Ft. of Head1.5 HP1/40 ImpellerNoryl (R) Length (In.)5 1/8 Max. Temp. (F)220 Max. Working Pressure (PSI)145 Phase1 Pump Body MaterialBronze Thermal ProtectionImpedance Voltage115 Width (In.)3 5/16 Weight5.00
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traderfjp
 
Stove/Furnace Make: Alaska
Stove/Furnace Model: Channing 3

Re: Rheostat on Taco 003 Pump??

PostBy: Yanche On: Tue Sep 09, 2008 12:37 am

No. You cannot control the rotor speed with a rheostat on permanent split phase capacitor motor. You can reduce the flow by putting a restriction in the piping, i.e. a valve, ideally a flow control valve.
Yanche
 
Stoker Coal Boiler: Alternate Heating Systems S-130
Coal Size/Type: Anthracite Pea

Re: Rheostat on Taco 003 Pump??

PostBy: Freddy On: Tue Sep 09, 2008 3:45 am

What Yanche said....but.... might you actually transfer more BTUs with the faster moving water? Heat transfer is a factor of difference in heat. The faster moving water stays cooler so you might actually move more heat than if it went slower but got hotter? I'm just guessing a bit here, but food for thought.
Freddy
 
Stoker Coal Boiler: Axeman Anderson 130 (pea)
Hot Air Coal Stoker Stove: Reading piece o' junk in the barn (rice)
Coal Size/Type: Pea size, Superior, deep mined


Re: Rheostat on Taco 003 Pump??

PostBy: Yanche On: Tue Sep 09, 2008 9:46 am

The best heat transfer occurs when you have turbulent fluid flow in the pipe. This breaks down the boundary wall of fluid just inside of the pipe ID. Many pipe style heat exchangers use a twisted and/or holed copper strip in the pipe to force turbulent flow. The poorest heat transfer occurs with large pipe diameters and low flow rates. For the small pipe diameters in stove heat exchanger, a high flow velocity will surely cause turbulent flow. If you are using even the smallest circulator to pump the water to a tank and the piping run is relatively short you will surely have sufficient flow velocity to create turbulent flow. The opposite of turbulent flow is laminar flow.

There's a good example of both types from a guy smoking a cigarette here:

http://en.wikipedia.org/wiki/Turbulence
Yanche
 
Stoker Coal Boiler: Alternate Heating Systems S-130
Coal Size/Type: Anthracite Pea

Re: Rheostat on Taco 003 Pump??

PostBy: Freddy On: Tue Sep 09, 2008 12:55 pm

Good info!

I have a question on this topic... I'm planning on using the DHW coil in my boiler to supply heat for my infloor radiant heat. Right now it has a 007 pump near the oil boiler for the radiant. I'm venturing a guess when I ask that pump to now pump an extra 150 feet and go through the coil, it will not do the job. It might, but might not. So, might I add a second 007 to that loop, perhaps put it near the coil? Or would it make more sense to change the pump to a 0010?
Freddy
 
Stoker Coal Boiler: Axeman Anderson 130 (pea)
Hot Air Coal Stoker Stove: Reading piece o' junk in the barn (rice)
Coal Size/Type: Pea size, Superior, deep mined

Re: Rheostat on Taco 003 Pump??

PostBy: Yanche On: Tue Sep 09, 2008 2:04 pm

Freddy, It would make sense to design your heating system and not guess at all. Why would you want to use the domestic hot water coil in the boiler to supply your radiant heat emitter? Doesn't make sense. What's wrong with the boiler water? To size a circulator you determine system resistance. Total up all the piping resistance and the equivalent resistance of the fittings and plot a system curve. Then determine the flow rate needed to move the needed BTU's. Next select a circulator the does the job.
Yanche
 
Stoker Coal Boiler: Alternate Heating Systems S-130
Coal Size/Type: Anthracite Pea

Re: Rheostat on Taco 003 Pump??

PostBy: Freddy On: Tue Sep 09, 2008 3:23 pm

I do have a reason for wanting to use the coil for the infloor. My radiant tubing is Entran II made by Goodyear. When we built this house they had not invented pex al pex. The tubing can permiate oxygen and corrode system components. By using the hot water coil I'm keeping the radiant water in a less corrosive enviorment. The coil is copper, tubing pex al pex, and the rest of the piping is copper. By doing it this way I keep the oxygen impregnated water out of the Axeman. The only thing that can rust is the 007 pump.

I can add up the piping and fittings, but how would we guess at the resistance of the coil? It totals approxamately, 150 feet of 1" pex al pex, 100 feet of 3/4" copper, 800 feet of 3/8" ID rubber tube, a 3/4" mixing valve, 8 1/2" tees, 20ish 3/4" elbows, and the hot water coil. Remove the Pex and a 007 has been doing the job for 13 winters.

I'm sure you've figured out I'm kind of a seat of the pants guy. I make things work, and usually well, but sometimes it takes a few tries. I'd be happy to do it right the first time, but don't have that knowledge in my brain.
Freddy
 
Stoker Coal Boiler: Axeman Anderson 130 (pea)
Hot Air Coal Stoker Stove: Reading piece o' junk in the barn (rice)
Coal Size/Type: Pea size, Superior, deep mined

Re: Rheostat on Taco 003 Pump??

PostBy: Sting On: Tue Sep 09, 2008 3:47 pm

Freddy wrote:What Yanche said....but.... might you actually transfer more BTUs with the faster moving water?



Freddy,

FFFFFFlow produces or reduces Delta T

Too much and there isn't enough differential in supply and return. If there is no differential then the radiation of the load didn't have a chance to extract the available energy of the liquid.

Too little flow and what? the opposite effect is in play.

Both cause a detrimental result to operation efficiency and human comfort in the load!
Sting
 
Other Heating: BurnHAM=NG-gas

Re: Rheostat on Taco 003 Pump??

PostBy: Freddy On: Tue Sep 09, 2008 4:06 pm

I always thought Delta T was simply the temperature difference. Flow may effect the temperature, changing the Delta T at a different rate, but until the temperature changes doesn't the Delta T stay the same? Or, does Delta T relate to things other than temp?
Freddy
 
Stoker Coal Boiler: Axeman Anderson 130 (pea)
Hot Air Coal Stoker Stove: Reading piece o' junk in the barn (rice)
Coal Size/Type: Pea size, Superior, deep mined

Re: Rheostat on Taco 003 Pump??

PostBy: Yanche On: Tue Sep 09, 2008 4:28 pm

Freddy wrote: I can add up the piping and fittings, but how would we guess at the resistance of the coil? It totals approxamately, 150 feet of 1" pex al pex, 100 feet of 3/4" copper, 800 feet of 3/8" ID rubber tube, a 3/4" mixing valve, 8 1/2" tees, 20ish 3/4" elbows, and the hot water coil.
What's in series and what's in parallel? A simple piping sketch would be helpful.
Yanche
 
Stoker Coal Boiler: Alternate Heating Systems S-130
Coal Size/Type: Anthracite Pea

Re: Rheostat on Taco 003 Pump??

PostBy: Sting On: Tue Sep 09, 2008 5:25 pm

Freddy wrote:I always thought Delta T was simply the temperature difference. Flow may effect the temperature, changing the Delta T at a different rate, but until the temperature changes doesn't the Delta T stay the same? Or, does Delta T relate to things other than temp?



Yes it is almost that simple - the temperature difference

now --- how do we chance the temperature difference of the supply and return? or --> how do we change Delta T?

....... with flow. What else can you change? One thing - You can change the supply temperature out by cranking the boiler to make hotter water - but does that change the Delta T? NO - the return water still returns with a exponentially higher temperature. What did you do by that - you burned more coal --- :oops:

Read more regarding system balance - another of Dans sermons in wet system care - custody - and control.
Sting
 
Other Heating: BurnHAM=NG-gas

Re: Rheostat on Taco 003 Pump??

PostBy: Freddy On: Tue Sep 09, 2008 8:57 pm

The piping I mentioned is just the radiant loop from the coal boiler with the oil boiler valved out of the picture. The sketch just shows half coming, half going with four loops of the Entran coming off the 3/4" copper header. I left the mixing valve (and all the tees & ells) out of the sketch.

Sting wrote:You can change the supply temperature out by cranking the boiler to make hotter water - but does that change the Delta T? NO


I think "yes"... it changes the difference in temp between the boiler water and the domestic water.
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Freddy
 
Stoker Coal Boiler: Axeman Anderson 130 (pea)
Hot Air Coal Stoker Stove: Reading piece o' junk in the barn (rice)
Coal Size/Type: Pea size, Superior, deep mined

Re: Rheostat on Taco 003 Pump??

PostBy: Sting On: Tue Sep 09, 2008 9:58 pm

I don't need to argue this

our moderator will not tolerate it

I am sure you will find your way!
Sting
 
Other Heating: BurnHAM=NG-gas

Re: Rheostat on Taco 003 Pump??

PostBy: LsFarm On: Wed Sep 10, 2008 3:57 pm

The way I understand it, Delta-T is temperature differential.. so if the water in the DHW tank is say 50*, and the water circulating in the coil in the tank is 150*, then the Delta-T is 100*.

If the water is circulating slow enough in the coil that it enters at 150*, but returns to the boiler at 100*, then the Delta-T is variable, and the amount of heat transfered from the coil to the water is less from the cooler part of the coil. If the water leaving the coil returning to the boiler is the same temp as the DHW , then there is at least some of the coil not tranfering any heat into the DHW, this system need either faster circulation or hotter input temperature to make the coil more efficient.

If the water is circulating fast enough in the coil that the water temp is constant through the entire coil, then the Delta-T is constant, and the amount of heat transfered to the DHW is the same for the entire length of the coil... The heat transfer is at maximum.. this it difficult to achieve, because the flow rate would be very high in a coil.

This is an ongoing discussion in the automotive world too,, Some people believe that you must slow down the circulation of the coolant in a radiator to make the radiator more efficient.. But if the entire radiator surface is at the same maximum temperature, then the Delta-T is at maximum over the entire radiator surface,, shedding the maximum amount of heat into the ambient air. This is acheivable in an automotive radiator, because of the volume of water that can circulate through the tubes..



Greg L.
LsFarm
 
Stoker Coal Boiler: Axeman Anderson 260
Hand Fed Coal Boiler: Self-built 'Big Bertha' SS Boiler
Baseburners & Antiques: Keystone 11, Art Garland


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