General Pump flow question

d0eby

I have an outdoor wood burner, that has a taco 007-f5 pump in 1 inch pipe, to make a dry loop into the house and back out to burner. I have 3 zones in the house which are also using taco 007-f5 pumps for each zone. I'm not getting enough heat when temperature gets really low. Can i put a bigger pump on my main floor zone to try to get more flow and get more heat, or will it pull to much water being bigger than the pump that supplies it. The water coming in is very hot, and the return water temperature is probably around 10 degrees lower before the return. i have tried turning off the other 2 zones, so just the main zone i want heat in was on. It didnt effect the temperature in that zone at all.

Jamie Hall

Pumps in series do not necessarily increase flow -- it depends on the pumps and the system characteristics.

That said, if your delta T in to out is only 10 degrees, you are getting close to as much heat from your emitters as they can deliver. You may not have enough emitter capacity.

hot_rod

depends a bit on how you have it piped also. Is there a heat exchanger between the OWF and inside?

What size furnace?

what is the total length of the loop to the boiler? Many fittings in that loop?

Most often the constipation is in the 1” loop from the OWF to the building.

d0eby

1 inch pex for about a 40 ft run underground into house, makes a loop then back to wood burner.
off the loop, there are 3 zone controllers and pumps, 1 for each floor of the house. they are pex lines to fin copper pipe radiators. wood burner has a 200 gallon water tank, that is set at 195 degrees. Pretty sure the size of the burner isnt the problem.
I never temped the water coming into the house, but i cant even hold the pex, its too hot. I believe the temperature of the water coming in is fine.
no heat exchanger, just straigth pex and copper pipe to radiators.
i know the right answer is put more radiators in, but it works until outside temp gets to below 28. I was hoping moving a little more water would get me that little bit more heat i need to work in lower temps outside.

mattmia2

1" pex is about 3/4" id. if you can push your delta t up by using something like panel radiators or ci radiators, something that still has good output at low temps, you can move more heat through that tubing.

EdTheHeaterMan

Does your OWS connect to a regular Gas or Oil boiler indoors, or do you have only the wood stove. 1" PEX will move a little less Gallon Per Minute (GPM) that copper tubing. 1" copper tubing will move about 80,000 BTU per hour when there is a 20° difference between the supply and the return if you move 8 GPM. So using a taco 007F pump on a 40 ft total distance of pipe might have a pump head pressure of about 5. (40 ft supply and return = 80 ft.). the rule of thumb for pump head pressure is
80 ft + 50% more = 120 ft equivalent length. x .04 = 4.8 (about 5 ft head pressure)
If we look at the pump curve for the Taco 007F (it is #5 curve on the graph) we see that at 5' head the pump will move 11 GPM. We also know that 1" copper will only move about 8 GPM. So the smaller pipe diameter will restrict the flow, increasing the friction loss, and perhaps only move 7 GPM. That means that if you are moving 7 GPM with a 20° temperature difference, your boiler will transmit 70,000 BTUh. If you are moving 7 GPM and the temperature difference is only 10° then you are only moving 35,000 BTUh.

By the way, 120° is about the maximum temperature you can still hold your hand on before it is too hot. If you have 130° or 190°, that is a big difference to measure without a thermometer. Holding your hand on the pipe won't give you the temperature difference. So I believe you are going to need a couple of thermometers to strap on to those pipes.

The bottom line is that if the water is moving too fast, the water can not absorb the heat from the boiler. If the water is moving thru the radiators too fast the radiators may not have enough time to transmit all the heat to the rooms. You may not need a bigger pump, you may need to slow the GPM down so the boiler can put more heat into the water going to the house. and you may need to slow down the GPM so the radiators can let more heat leave the radiators and get into the rooms.

If there is a valve anywhere in the system, try slowly closing the valve and watch the water temperature in the pipes get hotter. That may be your answer. You want a higher temperature difference, and slower moving water should get you there.

If you go too slow then you will have a problem in the other direction. Not getting all the heat into the rooms fast enough. Try to get your temperature difference as close to 20° as you can. That will get you where you need to be. If that does not work, then your pipe size is wrong, you need bigger pipes.

hot_rod

I really hope Eds tongue is firmly in cheek when he make statements like this

The bottom line is that if the water is moving too fast, the water can not absorb the heat from the boiler. If the water is moving thru the radiators too fast the radiators may not have enough time to transmit all the heat to the rooms. You may not need a bigger pump, you may need to slow the GPM down so the boiler can put more heat into the water going to the house. and you may need to slow down the GPM so the radiators can let more heat leave the radiators and get into the rooms.

If there is a valve anywhere in the system, try slowly closing the valve and watch the water temperature in the pipes get hotter. That may be your answer. You want a higher temperature difference, and slower moving water should get you there.

If you go too slow then you will have a problem in the other direction. Not getting all the heat into the rooms fast enough. Try to get your temperature difference as close to 20° as you can. That will get you where you need to be. If that does not work, then your pipe size is wrong, you need bigger pipes.

The faster fluid flows through a heat emitter the hotter the emitter and the higher the output. This is shown by the hydronic formula shown below, also by the output charts available with the fin tube baseboard in you home.

There are defined maximum flow rates for the piping used. In hydronics 2-4, some say 5 fps is the acceptable range. Some heat will transfer all the way down to small flow rates, 1/2 gpm even, see the flow curve in the slide below.

Yes it will take more pumping power to get the additional output as flow resistance increases with flow increase. And at the top of the curve the additional flow increases do not add much to the output, probably not worth chasing. Which is why the fin tube output charts show 1 and 4 gpm as max. design recommendations.

The faster flow = higher output is true in fin tube, radiant tube, fan coils, and in my opinion some, maybe many cast iron radiators.

The same is true for boilers, solar collectors, heat pumps, etc. The faster the flow, up to pipe design limits, the more heat energy is transferred. The formula again output= 500 (f) (∆t) Keep increasing the (f) flow rate in this formula, what happens to the answer.

20 ∆T operation, or design is a number pulled out of thin air for hydronic design. It makes the math easy is the only selling point.

I highly doubt a 007 is over-pumping your boiler or fin tube loop. I'd suggest a high head circ on the OWF to increase output, through undersized tube.

leonz

d0eby said:

I have an outdoor wood burner, that has a taco 007-f5 pump in 1 inch pipe, to make a dry loop into the house and back out to burner.

I have 3 zones in the house which are also using taco 007-f5 pumps for each zone. I'm not getting enough heat when temperature gets really low.

Can I put a bigger pump on my main floor zone to try to get more flow and get more heat, or will it pull to much water being bigger than the pump that supplies it.

The water coming in is very hot, and the return water temperature is probably around 10 degrees lower before the return. i have tried turning off the other 2 zones, so just the main zone I want heat in was on. It didn't effect the temperature in that zone at all.

================================================================

What brand of outdoor wood boiler do you have?

What is its water volume?

Is it an open system or closed system?

Being a former wood and coal burning boiler owner I can sympathize with what you are experiencing.
I have baseboard heat and I absolutely hate it as it has very little thermal mass to store and shed heat.

Can you provide us with pictures of your zone controls and the circulator?

What type of underground pex for your heating system is installed and how deep is it buried?

With your TACO circulator you have the option of installing a smaller pump cartridge to slow the flow down and allow the forest eater to heat the water in the boiler hotter and longer before it is pushed to the home.

For now, I would invest in the smallest pump cartridge for your TACO circulator being the 00-3B and go from there based on only what you have told us.

You will need to have all the numbers from the circulator identification plate with you when you visit a plumbing supply store to purchase a cartridge or a much smaller circulator which would allow you to keep the one you have now as a spare.

Short of that you may need to think about investing in hot water storage and using a small circulator with the 00-3B cartridge to move water from the boiler to the storage tank and back to the boiler and a second circulator for the home heating loops and just valving off all three zones allowing you to slow the flow to the unoccupied zones.

Using salvaged hot water radiators from a house wreckers salvage yard will provide you with greater thermal mass in gallons and they will provide greater heat energy at a lower temperature.

hot_rod

Show me @ leonz how replacing his 007 with an 003 through 1" pex and fin tube emitters increases his heat output. Start with this formula, use the pump curves also.
500 flow ∆T

Ed estimates 5' head, how many gpm will the 003 provide at 5'?

Im guessing his boiler is at least 120,000. Maybe even 250,000
Bigger is better for OWF according to the salesmen.

leonz

Hello Bob,

I would want to find out what cartridges are in the circulators before I did
any math on this.

With 4 circulators and only 200 gallons in the reservoir that leaves a tiny bit of
basic math to do this and perhaps a great deal of cavitation as we do not know
what size cartridges are in the 4 circulators.

If they designed and built these things the right way with 3 pass smoke boxes
they would burn cleanly and also have a lot of water in thermal mass like the
Garn units.


It all comes down to money.

hot_rod

leonz said:

Hello Bob,

I would want to find out what cartridges are in the circulators before I did
any math on this.

With 4 circulators and only 200 gallons in the reservoir that leaves a tiny bit of
basic math to do this and perhaps a great deal of cavitation as we do not know
what size cartridges are in the 4 circulators.

If they designed and built these things the right way with 3 pass smoke boxes
they would burn cleanly and also have a lot of water in thermal mass like the
Garn units.


It all comes down to money.

No you are not getting off the hook that easily You suggested

With your TACO circulator you have the option of installing a smaller pump cartridge to slow the flow down and allow the forest eater to heat the water in the boiler hotter and longer before it is pushed to the home.

For now, I would invest in the smallest pump cartridge for your TACO circulator being the 00-3B and go from there based on only what you have told us.


The math as I see it:

I want to move 70,000 btu from my boiler to the house, running a 20∆
Rearrange the basic formula Q= 500(flow) ∆t to this:

flow= Q divided by 500 (∆t)

70,000 divided by (500X20)= 7 gpm to move 70,000. Agree?

We have 80' 1" pex with maybe a few ells. Use the PPI calculator I have head of 4.9'. So my pump spec to move 70K from the boiler to the house is 7 gpm at 5'

Attached is the curve for a 003. I don't think you can replace a 007 cartridge with a 003, so a new circulator would be needed.

I'm not seeing how you plan on moving 7 gpm, 70,000 btu/ hr through 80' of 1" pex with a 003??

The bottom line, reducing flow through the boiler or fin tube will not increase output. And if it were true would not residential package boilers, millions of them over the years, ship with 003 instead of 007's?

leonz

Hello Bob,
Part of me wants to see him put in a boiler bypass valve and a mixing valve to blend the water down to
165-170 degrees Fahrenheit to see if that helps.

hot_rod

Maybe the op will return and better explain what his “dry loop” is

Are loads parallel to the loop? In series? As primary secondary closely spaced tees?

leonz

Hello Bob,

I am not sure, but I think he ment he has a hot water loop between the home and forest eater where the 3 zones draw from the single 1inch line coming from the boiler to heat each loop with the cool water return for all three heating loops connected to the boilers return to sump line.

d0eby

i will try to clear up all the questions so i can get a good answer.
pictures are of the dry loop i was describing, comes in to house after 40ft underground run from woodburner. Water 200gallons at wood burner at 192 temperature. 1 taco pump 007-f5, pushing from woodburner. Temperature with no heat being called, all valves closed. going back out dry loop at 185. When i turn on heat for main floor only, taco 007-f5 pushing water around copper pipe, with just fins on them for radiators . dry loop return temperature is at 178. I currently am only heating the main floor that i am trying to get the most heat too. 2 other zones, the thermostat is set low that they don't turn on.
This is just for heating, not hot water heater also.

So my main question is will a faster pump, create more heat. Should i put bigger pump at woodburner or on the main floor loop that i need more heat on.

hot_rod

The missing answer is how many gallons per minute you need to move through the loop?
You have 80’ tube in the ground, 10’ in the room, at least 7 elbows, so here is what the pressure drop would be for a 10 gpm flow. 14.9’ of head, which the 007 cannot provide

7 gpm would be around 7’ which is where the 007 will provide

If you need or want more flow (heat) then you need more flow, a larger pump. And yes it moves the fluid faster to increase the heat delivery.

If you want your truck to go faster down the road do you let up on the gas? Or give it more gas? Same applies to moving fluid, more power, gpm, more work or energy moved.

Do you know the heat load of the home? That would be another way to determine the gpm you need. 10- 12 gpm will. Be about all you can safely move through the piping “dry loop” you have.

Although I would argue it is a wet loop🤭

d0eby

can i put the bigger pump on the inside zone i need hotter. it would be a lot easier to change the pump there, than out at the wood burner.

hot_rod

Your "dry loop" is the conveyer belt. If not enough flow, energy, heat is on the belt, you will not get more to the heat zones.

Ideally you would know or calculate how many gpm every circulator needs. The "loop" needs to be able to supply all the zones operating at once.

If all the zones require 10- 12 whatever gpm and the loop only can supply 7, guess what.

Assume your 3 zone pumps can move 5-6 gpm each, call it 15 gpm total. But your loop pump is only moving 7 gpm

You can try robbing Peter to pay Paul, increase the zone pump size or speed, but from what you show and describe Peter doesn't have any more to give.

Its possible if only one zone, maybe two are calling you are covered. But I think you want to cover all 3 zones?

Just from past posts and personal experience with those boilers, most often is is the lack of the loops ability to get the heat into the building.

But without any info on your system, load size or boiler size, it all a guess