Too much head

[heaterman]

LeonMSPT,

Thanks for the overheating explanation !

That scenario is exactly why/how I started my posting last month on tha fact that a circ. pump can be too much/large for a boiler (even though all the postings I had seen previously stated that's it better to have a little bigger pump.)

I have an EKO40 system (with 1,000 gallons of pressuized storage) with approx. 30' of 1-1/4" copper for the primary piping.

I had been burning it approx. 1.5 months (Nov/Dec 2008) before I realized (and then perfromed the calculations) that my pump was moving the water way too fast though my boiler and thus it was not removing the heat away from the boiler in an efficient manner.

I had a Taco 010 3 speed pump which I had been operating on HIGH (using approx. 125 watts of power).

After I did the calculations I found out that I had a system which only had 4' of head (due the large cooper tubing I used in the primary loop).

Thus, I immeditely changed the circ. pump to LOW speed (which operates the Taco 010 just like a 007 and uses approx. 75 watts of power) and my heat transfer into the tanks went from 52K BTU/HR to 103K BTU/HR.

I was able to prove the old saying that "you can't get something for nothing" is not true.

Actually, I was able to get 2X the BTU's for 50 watts less power

Hope this helps !

NWM

NWM, I agree with your figures and the bigger piping is a definite plus in these boiler setups. One thing that I am having a problem with in this post is that your circulator is moving water to fast through your boiler to extract heat from the boiler right? I got a few question to ask. 1. when you were charging/ heating on high speed, what was the burn like- was it cycling or burning full out? 2. do you have a temp gauges on the supply and return into the mixing valve or boiler and if yes what was the temp span between high and low flow?


I guess what I'm picturing is that its not a problem of moving water to fast through the boiler but a case of hot water cumming back to soon from storage maybe a short cycling problem in the plumbing

I know, correct me cause I am probably wrong. I burn a garn style so I don't do the burn/pump/charge.

Ummmmm........ BTU transfer is a function of pounds per minute x degree of temp drop. Thus........ 10 pounds of fluid dropped 10* is the same as 20 pounds of fluid dropped 5* or 40 pounds of fluid dropped 2.5*. What some people misconstrue as "moving too fast to drop off the heat" as I heard one old timer explain, is not exactly correct. Now, as Garnification has said, you can run into heat transfer problems if inadequate flow is causing the burner to shut down due to high limit scenarios but I guess I'm not following how too much flow causes a slowing down of heat transfer. More flow through a HX of a given size will simply mean a lower Temp rise but actually the same amount of BTU's. A classic example of this is a pool heat exchanger which typically has a delta T of only a few degrees on the pool side but transfers mucho BTU's because the pool side flow is maybe upwards of 40-50GPM. I'm going to quiz one of the techs at AIC the next time I talk with them.

 

[brad068]

Heater, I think you and me are on the same page. The only reason that I can think that you don't want excess speed through a boiler is in a small fuel oil or NG boiler which usually have a max design transfer and flow in which case a hydro separator would need to be used or a variable speed circ.

Heater I think that we got ruined by the basic effective simplicity of the garn :coolsmirk:

 

[LeonMSPT]

Heat transfer isn't "instant". A unit of time is necessary for heat to get from the material containing the water, into the water. If the water is passing the heat exchanger at a rate that is faster than the unit of time, less of the heat will get into the water. Result?

According to Ron Beck...

"If the flow is too fast, the water passing through the boiler won't pick up enough Btu (heat). When this happens, you will be working with a lower Delta-T."

http://contractormag.com/hydronics/cm_column_491/

"Ron Beck is a training manager for Burnham Hydronics with 25 years of trouble-shooting experience."

There's quite a few experts out there who remain convinced that the flow rate has to be within specifications in order to work. I'm no expert, but I am inclined to work within their parameters when spending my money, or making recommendations to others about it.

Learning bunches today. Many thanks.

 

[brad068]

I agree 100% with you and Ron. But... we are comparing apples to oranges here. The boilers he is talking about is a basic on demand type condensing and non which need the exact flow a temp to operate properly and maintain warranty. As heaterman stated the btu transfer is the same but what Ron is saying is that with water moving to fast the water will strip the heat to quickly and not let the boiler get up to proper operating temp thus condensation will form in the flues deteriorating the boiler. The exact flow and span( delta-T) is a set parameter to protect the boiler. Remember on demand with low water volume capacity.

Now on the wood boiler setup NWM is charging a tank and heating at the same time some of the time which the boiler is putting out more than the demand is. The wood boiler can handle more flow through it as long as the return temp is above 140*F or so. If this wasn't the case they wouldn't have to weld 1.5" or 2" bungs in the boilers. The only thing that will change is that the span from supply/return will be lower with a higher flow circ.

One benefit that I can see with a lower flow circ is that if a load circuit is calling for heat when the boiler is charging the higher temp would be there sooner to satisfy the demand quicker for instants, baseboard. On a closed loop system of course

 

[taxidermist]

Well my internet was down so I missed all of this...Just wanted you to know I can still heat my house very well with my set up. My boiler is oversized to heat my pole barn in the future. We just had temps as low as -11 overnight and I was still only burning 2 times a day. As you know we are all blocking off nozzles and cutting fans so we basically are cutting down the BTU for our boilers.


Thanks to all that replied

Eric maybe you should make Heatermans post on pipe sixe a sticky to keep people who are buying from the same supplier I did from making the same mistake.

Thank you,
Rob

 

[LeonMSPT]

It's a good thing people are smart, and can figure out ways to make things work that aren't perfect... so many things out there aren't. Talked with a guy yesterday and showed him the calculations. "Yeah, but the suppliers don't carry the larger PEX, and they tell everybody it's more expensive and hard to deal with."

Yeah. It's harder to jack up your car and put a full sized spare tired on it when it's got a flat. But try going down the highway at 75 miles an hour with that little wheelbarrow tire most cars come with now. If they're so good, why not throw four of them on and go for it. Bound to be cheaper than four regular tires.

 

[rkusek]

I have been looking for this post. Getting ready to finish underground pex to the house and it had some good data that others may find useful.