Garn It!

[slowzuki]

Hi Robert! There is some madness to pump selection. For your main circulator feeding the HX the following would apply.

1) Find out how many gpm we need on the HX to obtain the desired performance.
2) Figure out pressure drop in HX and system piping at the gpm picked in step 1 from the circulator to HX back to tank.
3) Look at pump curves, mark a point showing the gpm and ft of pressure drop.
4) Curves above this point will provide adequate performance, but, eliminate any pumps that are at the extremes of their curves ie you don't want to be running a monster pump at near stall conditions or making pump run out to the extreme limits of its capacity.
5) If you still have several pumps left at this point, check the power use and efficiency and go for the least power/most efficient.

The hardest thing is finding the pressure drop. You will need to use a Hazen-Williams headloss calculator. There are online ones. You also need to have pipe measurements and fitting counts.

For common pump sizes there will be models available from each brand. Do you like chevy or ford basically at that point!


OH, if you want to implement an outdoor reset mixing type setup right from the start using the HX pump, you will need a VS pump. That will reduce your selection of available pumps.

 

[rvtgr8]

Okay, this is the latest drawing done to help me figure out pipe sizes, fittings and flow rate. I am having little luck figuring the correct heat exchanger size. Using rudimentary figures and GEA software, I keep finding a HX much smaller than the ones I have been talking to members about. Quite frankly, I do not know what I am doing because the software is pretty straight forward, so I must be plugging in the wrong numbers. There is a hell of a lot of difference between the twenty plate that it is telling me to consider and the 70 plate that I thought I needed.

The drawing is a little funky in that it shows that I am going to put the circulator on the primary loop outside of the boiler. That is correct. I just do not have the room inside the boiler room to put both the manifold and the exchanger. It is a plus in that it rids me of a couple of elbows. Any thoughts?

 

[Jim K in PA]

Robert,

The way you have shown it, the pump is in the wrong place, IMO. You are not building an primary/secondary piping system, based on this drawing. You are showing a manifold system. Given the size of the load on the house loop, I would use a dedicated pump for that loop, as well as all the other loops. They can be sized according to each load, and controlled independantly.

Your piping losses are going to be minimal, given the small amount of pipe you are showing. The HX will be the single biggest component of head loss on the house loop. For my house loop, with over 250' total piping distance, plus an undersized HX (20 plate), my Grundfos UPS 26-99 is more than adequate. It is a high head, medium flow pump, smaller than the 43-44. I have it set on medium 24/7 right now, but will be adding a variable speed controller to it, as it can often run much slower than it does (but sometimes needs to pump faster under higher loads).

At the moment GEA wont let me log into the sizing software. However, the closer you make the target output temp to the input temp, the bigger the HX will get. As I described previously, my 20 plate HX is actually working fine - at average loads. With peak loads, my delta Ts get extreme, and increasing the pumping rate results in greater head loss (more resistance). Also, as the GARN water cools, I cannot get as much heat out of the small HX as is available. That is, if my GARN input temp is 150, I can't get much more than about 140-142 out of the HX. My oil furnace cut in is set at 140, so that is when it starts to fire to supplement the GARN (and I HATE burning oil!). With a bigger HX, I should be able to let the supply temps dip below 150 and still keep the house side above 140.

Personally? I think you should plumb the supply side out to the utility room in 2" pipe and branch off the manifold with 1.5" for the greenhouse loop, 1.25" for the house loop, and 1" for the hot tub loop. Put a 26-99 on the house loop, and a 15-58 on the hot tub loop. Greenhouse pump to be determined later. Use a 50 plate HX for the house loop and a 20 plate for the hot tub loop. Greenhouse can be in series, or use a seperate 90 plate HX.

 

[rvtgr8]

Jim,

Is this what you were referring to, with these pumps? Would a Tekmar 356 be a good control for this setup?

Robert

 

[timerak]

I use a Tekmar 356 on my heat exchanger feed pump. Its the ticket if your doing radiant. It's controlled by the mix temp on the house side of the heat ex. (mix temp is set by outdoor sensor) Mix temp stays constant wheather storage temp is 180 F or 120 F. I think I paid about $255 locally. It was the cheapest way to do what I required.
Tim....

 

[Jim K in PA]

Robert - yes, that is the configuration I was suggesting. With manifolds, you only need to pull/push water through the legs that need it, so you don't need a "primary" pump. As long as there are check valves on the other legs or in the other pumps, you should not get reversion through the return leg.

I think the 26-99 will be plenty for the house leg, and you will likely be able to run it on low speed and still meet your demand. The Grundfos (broken link removed) put your house HX load right at the upper end of the 15-58, so going with the larger pump will reduce it's duty cycle and let it have a longer life.

As for controls, the 356 would be something to consider for the pump on the house side of the HX (as Tim suggested above), not the GARN side. However, I would operate your GARN side pump for a while and monitor S/R temps and see if a variable speed controller might be worthwhile. There are pumps available from Wilo and TACO that have integral VS controllers, however, they are more expensive, and you are trying to work within a budget. The three speed pump gives you some control at lesser cost. You can add a Tekmar 157 later to vary the speed according to demand on the HX. For now, just add a relay to bring the 26-99 up whenever the existing circulator comes on.

 

[timerak]

Robert and Jim:

The last schematic I saw indicates that the secondary side of the heat ex is the secondary/mix loop. I didn't see a tempering valve/scheme anywhere else in the system. Therefore the pump on the primary side of the heat ex would be the injection pump for generating a controlled tempered mix for the radiant. It could be controlled by a 357 or 157. Is there a third loop/mixing valve/injection scheme that will do tempering that is not drawn?

Tim....

 

[Jim K in PA]

Robert and Jim:

The last schematic I saw indicates that the secondary side of the heat ex is the secondary/mix loop. I didn't see a tempering valve/scheme anywhere else in the system. Therefore the pump on the primary side of the heat ex would be the injection pump for generating a controlled tempered mix for the radiant. It could be controlled by a 357 or 157. Is there a third loop/mixing valve/injection scheme that will do tempering that is not drawn?

Tim....

Tim - you are correct, there is no mixing valve on his radiant system at this time. The original installer has his existing propane fired (high mass, not a mod-con) boiler ranging from 140-180 (I think - it is several pages back) with these temps running through the floor loops. Robert also has an indirect DWH running off of one of the zones. He will need the higher water temps for the DWH, unless he runs a seperate loop from the GARN through another small HX and supplies heat to the indirect that way (or seperates it from the radiant zones). I was trying to help him get his GARN up and running with a limited budget, and this first stage may have to omit water tempering via pumps, controllers, or mixing valves.

 

[rvtgr8]

Boiler Enthusiasts,

I cannot thank you enough for your valued opinions on my project. It is a tribute to the spirit of common cause and genuine friendliness that this site is so successful.

Jim, thanks for the clarification.

I know the house side of the system will probably need a mixing valve. Does anyone know of one that would be sufficient for my system. I have some cash left in my budget, and if I do not spend it on the boiler, it will probably go on something frivolous like food. hh: In addition, would the Tekmar 356 be a fit with the mixer? I assume that it would, but I have been known to be pretty thick.

Robert

 

[rvtgr8]

I have been doing some research and was surprised to see the the Taco Iseries automated mixing valves do not go up to the 1.25" pipe size that I will need. Is the Tekmar 712 mixer a pretty good mixing valve? How absolutely necessary would the actuating motor for this be? If I am out there being a heating geek and salivating all over my equipment as I anticipate, can't I just manually adjust it, or would not spending the extra $250 coupled with the fact that I will already have a Tekmar 356 controller be an insult to the Gasification spirits? :bug:

Robert

 

[slowzuki]

Hi Robert and Jim back on board, I'm internet free on weekends.

Robert, I'd say don't worry about the mixing valve for now. Jim and I are both recommending using the pump that supplies the HX as the tempering device. By using a controller or intelligent pump that watches the output of the HX on the house side, it will adjust the pump speed to hit a given temp.

This saves trying to get a mixing valve setup and is a lot simpler/reliable. If you can't afford the variable speed pump or controller, the 3 speed pump is essentially a 3 position mixing valve. Warm weather it runs on the slowest speed, cold its set to the fastest speed.

 

[rvtgr8]

Slowzuki,

Thanks for the PM. I really appreciate your attention to my situation. My current situation is a waiting game. My thread on Pex Supply speaks volumes on just how important having a good source for parts can be to a project. I do not have enough cash to double purchase every item that Pex Supply does not include in one of my orders. I have called them. They say they have the parts and will ship immediately. Does the shipment arrive? No. Has it shipped? Apparently not or I would have a tracking number. So I am on hold, unable to move forward. If I cancel and reorder, it can be a real hassle with my card company. I made another mistake by not doing my homework on Pex Supply. Lesson learned. I will wait one more day and then cancel and reorder through a more honorable company.

When the stuff comes, or I sandcast my own, I will be in touch for your invaluable opinion on the install. You, Jim K and others are truly the only bright spot in this rather dismal project.

Robert

 

[Jim K in PA]

Hang in there Robert. The momentum is building, and you will be up and running before the year is out . . . :lol: Sorry - couldn't resist. You may recall from my blog, I had delays every step of the way, from the delay in delivery of the GARN through the PEX tubing, pumps, PEX fittings, proprietary PEX tools, ad nauseum. Keep the faith.