Central Boiler 6048 Pump Choice?

[LegendsCreekFarm]

Its been ages since I posted but I joined here originally for advice on what boiler to buy. I ended up buying a Central Boiler 6048 and I really love it. I finished installing it a few weeks ago and have it plumbed up to my home and its working great.

To prepare for winter I need to finish hooking it up to my workshop. I ran the underground thermopex differently to my workshop because of my set up so I have no idea what Taco pump to get. I always buy Taco.

My boiler is sitting near my workshop. My line runs from the boiler, underground to my shop, through the floor of the shop and up to the rafters, and then 40 feet to the middle where it meets the forced air boiler. The pex is 1". Total pex run round trip is no more than 200 feet. There will be 2 elbows, but possibly 4. I plan on mounting the pump near the rafters in my shop, but then the pump will be mounted higher than the boiler by just a few feet. The heat exchanger I got is 230k BTU, that is the amount I need, and the size that fits in my plenum.

I want to get the correct pump but don't know much about head calc with the elbows and everything, and was hoping for some input. I want to make sure I move the right amount of water. Any suggestions will be much appreciated.

 

[hondaracer2oo4]

(broken link removed to https://www.taco-hvac.com/uploads/FileLibrary/SelectingCirculators.pdf)

That is how to size your circ. It seems overwhelming at first but just go step by step through the document. If you have any questions on a specific part of the document we can help.

 

[hondaracer2oo4]

By the way you will find some rather alarming news when you learn how to calculate the headloss. You will find that you won't actually be able to move more than about 80k btu per hour through 1 inch pex efficiently. You will be fine though, your workshop would have to be alarming large and non insulated to actually require 230k btu per hour.

 

[LegendsCreekFarm]

I reviewed the Taco file you sent. Thank you for that. But it didn't make much sense to me which is why I was hoping for some advice.

I understand about the 1" pex but I am not worried about it. I am certain the boiler will heat everything I need it to.

 

[hondaracer2oo4]

You know all of the specs of the system so you are the best person to do the actual calcs. Plus you learn how your system works. So step 1 is figuring out what you want for gpm to hit a certain Btu that you are trying to achieve. So let's look at what you are trying to get for a btu out of the system. Since you can only get 70-80k btus out of 1 inch pipe let's use that number for the btu that you are trying to achieve. Plug that number in to step 1 and tell us what you come up with. Then work on step 2.

 

[vtwoodheater]

By the way you will find some rather alarming news when you learn how to calculate the headloss. You will find that you won't actually be able to move more than about 80k btu per hour through 1 inch pex efficiently. You will be fine though, your workshop would have to be alarming large and non insulated to actually require 230k btu per hour.

yup. 80K BTU max through 1" pipe. My suggestion would be a Taco Viridian pump. Set it for 20degree delta. That way it will run at 3 watts when nothing is needed, and variable speed all the time to deliver the proper amount of water for the load. (up to 80K btu/hr.)

 

[LegendsCreekFarm]

yup. 80K BTU max through 1" pipe. My suggestion would be a Taco Viridian pump. Set it for 20degree delta. That way it will run at 3 watts when nothing is needed, and variable speed all the time to deliver the proper amount of water for the load. (up to 80K btu/hr.)

Thank you very much for the pump suggestion. I am familiar with the Viridian. Its an ECM I believe correct? I do have brand new Taco bumblebee also, that is an ECM variable speed and I believe the Viridian replaced it as they don't make them anymore. If I were to go with a pump that isn't variable speed would there be one that would be best suited?

 

[hondaracer2oo4]

You need to calculate your head to find out what pump will meet your needs. If you don't you will either not get enough btus and be upset with the performance of your heating Eqiupment, you will be upset with your needlessly high electric bill or you will maybe find yourself somewhere in the middle. Do yourself a favor and dedicate 30 mins to calc for yourself the headloss. It will help you understand how your system works.

 

[vtwoodheater]

Calculate your head loss, then look at a Viridian pump chart. I used a Viridian pump for 2 years with my OWB, I am now using it to feed my house from my pressurized storage. The Delta T feature is phenomenal. Major power savings.

 

[Bob Rohr]

If you are pumping from the boiler, thru the pex AND a air coil, you need the pressure drop of that coil in the calculation. Everything in the circuit, tube, valves, fittings and any heat emitters are all in the head calc.

The coil manufacturer should have a pressure drop chart, more pressure drop as you try the flow more GPM, of course.

You may be looking at a 0014.

Taco does build a special pump for OWF it is not a wet rotor type pump to keep the motor out of potential crappy water.

 

[LegendsCreekFarm]

Thank you for the input. I am looking at the Taco chart to make my calculations. I finally have some time to go over it but before I can make the calculations I have a question.

First, you said that 1" pex will only allow 80k BTU coming in. I bought a 230k btu water to air heat exchanger. Should I be using the 230k or the 80k in my calculations for pump choice?

If all I can get is 80k, then shouldn't i be looking for a pump for 80k as opposed to 230k?

Thanks!

 

[hondaracer2oo4]

So the way that they rate your heat exchanger is that it can move so many gpm through it with typically a temp drop of 20 degrees from the inlet to the outlet at 180 degrees. That is what btus is representing. So many degrees extracted per hour. But since your 1 inch pipe won't be able to deliver the number of gpm required to obtain that number it won't be possible. I would guess that you need about 18 gpm through that heat exchanger to get those btus. Your 1 inch pex can only move 7-8 efficiently before it gets turbulent and the friction loss is very high causing a high head condition. Go through the taco instructions step by step and ask questions if you have them. Have you done a heat loss calculation for your building to know how much it needs? If not I would just shoot for max that you can get out of 1 inch pipe which is about 75k btu. You will need to call the heat exchanger company and ask them what the head loss is at 7 gpm.

 

[LegendsCreekFarm]

Thanks again for the info! I did read through the instructions and did the math. Calculating everything with 80k BTU, without adding in loss from the exchanger, I got 17.5 for head, with about 7 or 8 gpm. Once I get the numbers for the exchanger, I can add it in and it will bring the number up on the head. It looks like a Taco 0014 with my current calculations but I can't order the pump until I get the info about the exchanger. If it goes up, the only other pump that will do the job is a 0011, which I happen to have a brand new spare of. I won't use it until I know exactly which pump is best for the job.

 

[hondaracer2oo4]

I figure that the exchanger will probably add very little head flowing at only 7-8 gpm if it is rated at 230k btu. I commend you on working out the head yourself. It really helps you to learn how the system works I think.

 

[Bob Rohr]

I came up with about the same numbers you did, at 7.5 gpm flow the 0014 is spot on, the 0011 is a higher head, a bit overkill, but if you already have one...

 

[LegendsCreekFarm]

I was thinking the same thing. As I am still learning about how to make these calculations I wasn't sure the 0011 would be too much overkill. I am waiting to hear back from the heat exchanger manufacturer about the gpm loss, I will factor that into the original calculation and it should give me a better idea. I may end up using the 0011 for my workshop, but I need to also hook up my guest house which I think will be spot on for needing a 0014, but I still need to do the calculations.

 

[Bob Rohr]

I was thinking the same thing. As I am still learning about how to make these calculations I wasn't sure the 0011 would be too much overkill. I am waiting to hear back from the heat exchanger manufacturer about the gpm loss, I will factor that into the original calculation and it should give me a better idea. I may end up using the 0011 for my workshop, but I need to also hook up my guest house which I think will be spot on for needing a 0014, but I still need to do the calculations.

If you over pump you can end up with high velocity, noise and wear. Or add a balancing valve to "throttle" the flow to the desired rate, best to get the pump selection close as possible, manufacturers offer many choices.

If money is no object the Grundfos Magna is an incredible pump with unlimited adjustability, for medium and larger pumping jobs.

I agree the coil probably does not add a lot of head. The heat output of the coil is based on both temperature of the fluid, and the airflow CFM. The performance specs from the manufacturer should show those relationships.

If you plan on expanding, the larger pump may be needed. You will need to recalculate as you add on. if the new components are low pressure drop, you need more gpm not head. I think the Taco wood boiler pump leans more toward high flow (gpm), a low slope pump curve.

 

[heaterman]

"I plan on mounting the pump near the rafters in my shop,"

The location of your pump may prove problematic given that your Central is an open or unpressurized system.
Installing the pump above the water line means no static head pressure on the pump inlet. ....this is a bad thing for little wet rotor pumps.
Once it cavitates, and it surely will given the circumstances due to zero suction head, it will form air bubbles around the rotor and overheat/meltdown.
You would be better off with one of their close coupled pumps in the 2400 series if there is not other option for location. The 2400-10 would probably do it.
The pump will still cavitate but you'll lose only the impeller rather than the whole pump.

(broken link removed to http://flopro.taco-hvac.com/products/water_circulation_pumps__circulators/in-line_pumps/2400_series_high_capacity_circulators/index.html)

We use this series for almost all open system applications.

 

[LegendsCreekFarm]

I didn't consider that and I'm glad you brought it up heaterman. Would I still have the problem if I lowered the pump to below the water line of the boiler, but the pex still goes up and runs along the rafters?

 

[hondaracer2oo4]

You will have the cavitation issue unless the pump is always fed with water on the suction side either by gravity or another pump pushing water to it. Why aren't you putting the pump on the boiler?

 

[LegendsCreekFarm]

I won't be putting my pumps at the boiler because its much easier to service them in the buildings where they connect to my boilers. Its also much warmer.

 

[hondaracer2oo4]

Yes I understand it's easier to replace the pump in a warm building but you are going to run into issues with possible cavitation. The longer of a pull through 1 inch pipe to the inlet side of the pump the more chances for cavitation. The pump will be plenty warm enough next to the boiler. I have run the same pump for 6 years with no issues.

 

[LegendsCreekFarm]

My neighbor has the same boiler I bought. He said the biggest mistake he made was putting his pump at the boiler. He has had to replace cartridges in freezing weather, etc. I decided its better for my set up to keep them in the buildings, I just need to make sure to get the correct pumps!

 

[maple1]

My neighbor has the same boiler I bought. He said the biggest mistake he made was putting his pump at the boiler. He has had to replace cartridges in freezing weather, etc. I decided its better for my set up to keep them in the buildings, I just need to make sure to get the correct pumps!

The thing is, they're circulators, and not pumps - per se. One thing a circ won't do well, for example - or maybe even not at all depending on the situation, is move an air bubble through itself. The bubble might get to the circ, then it can stop at the impeller/rotor. That makes it very tricky if the circ is at a high spot, even if it has the right amount of inlet pressure. So there are a few things to be sure about - inlet pressure likely being the main one. Did your neighbor ever move his pump or try it somewhere else?

 

[Bob Rohr]

water at sea level boils at 212F, at higher elevations at lower temperature, at 9000 feet in Colorado for example water boils at 195F

Vapor pressure is the term that refers to the pressure required to prevent boiling. We know at sea level the atmospheric pressure is 14.7 psi.

So any condition that allows causes the fluid temperature to increase, or the pressure to drop below vapor pressure will cause boiling. See graph below.

In an open system the only pressure on the pump is the water level above it. If the pump is low on the boiler, maybe 5 feet of head = about 1.9 psi. So that pump runs at a very fine line as far as cavitation. Suppose the boiler overheats to 211F, now the vapor pressure needs to increase to prevent that steam flash.

I would guess you neighbor has had some run away temperature (boiling) conditions in his systems causing pump failures. Look up the pump spec from the manufacturer, at 190F they want about 5 feet of head to eliminate cavitation potential.

Raising your pump above the level of the water in the boiler puts it in a sub atmospheric condition when it powers off. You could in fact experience steam flash, and vapor locking.

Here is some reading to help demonstrate the concept of vapor pressure as it relates to OWF.