Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.
hydronic heat exchanger water flow path
Tom M.
Member Posts: 237
The water enters in the bottom left of the front section and the lower push nipples are in a row behind that tapping. The water exits at the top right of the front section and the sections are connected there by the large push nipples (5" or larger) where the tankless coil is located. These rows of push nipples act as manifolds. When the pump runs, there is a pressure difference between the bottom push nipple location and the top and water will therefore flow through each section.
Another feature of this design is gravity flow when the heating pump is not running. If there is a call for hot water, the cold water enters the inner coil of the tankless heater. This helps to cool the temperature probe to get the burner started quickly. As domestic water is heated, boiler water is cooled and becomes heavier. This heavier water will move down the right leg of the boiler, across the bottom, will then be pushed up the left leg by the heavy cool water that follows it. It then goes across the heat exchange surface where it is heated and back to the coil where it transfers the heat to the domestic.
Another feature of this design is gravity flow when the heating pump is not running. If there is a call for hot water, the cold water enters the inner coil of the tankless heater. This helps to cool the temperature probe to get the burner started quickly. As domestic water is heated, boiler water is cooled and becomes heavier. This heavier water will move down the right leg of the boiler, across the bottom, will then be pushed up the left leg by the heavy cool water that follows it. It then goes across the heat exchange surface where it is heated and back to the coil where it transfers the heat to the domestic.
0
Comments
-
hydronic heat exchanger water flow path
this is a boilers 101 question - except that i havent taken that many apprt.
is the water flow path in all cast iron hydronic heat exchangers serpentine?, ie the segments are connected alternating plugged and open, forcing the water to go through all the segments, or are some open at both ends, and your have to put the return at one end, and the discharge at the other end, in order to guarantee full water passage? - i have a customer with an old hydrotherm, in which the return is at the bottom, and the discharge is at the top, of the same end of the boiler, - however their manual shows, it's supposed to be piped at opposite ends. note the brochure on their new equivalent boilers, shows the flow to be serpentine - tnx - kal0 -
The typical sectional boiler
has all of the sections connected to each other in two places. The sections are joined with either push nipples or gaskets which are aligned with each other. The supply and return tappings are usually each near one of the push nipple locations. If you could see inside with the boiler assembled, the series of push nipples would look like a manifold to supply flow to the sections. In the case you describe, there should not be a problem with the return entering the same end of the boiler as long as the tapping that is used is directly across from the other tapping and therefore in line with the push nipples. If it is not, there could be a cold spot across the bottom of the section or the water could "short circuit" right to the supply tapping and overheat the other sections. Many manufacturers (Weil -McLain, Utica, Burnham, Peerless, Slant/Fin, others) put the supply and return ports in the front section for convenience but the flow is maintained through the other sections by this manifold effect. Hope this helps.0 -
i have seen what you describe in cut-away diagrams on the net - and they seem to go straight through, i don't see why the water would flow around the casting when it could just go straight through the connection points - especially in my customer's old hydrotherm where the segments are horizontal with finn-tubes in the center over the fire and the water flows from bottom to top
urls where i find pictures
http://www.uticaboilers.com/pdf/PEG.pdf
http://www.bills-heating.com/bodnar/Boilers.htm
http://www.slantfin.com/quality.html -- they have it rigged to fource flow through all the sections
http://www.newyorkerboiler.com/Io/M24200R2(CLW)web.pdf -- tubes at oposite ends - again fourced circulation
http://www.buderus.net/literature/GA124-IOM-01.pdf -- page 70
0 -
i must be stupid - cause i still don't get why the water doesn't go in the bottom of the first section and out the top of the first section especially on a boiler like Buderus, (http://www.buderus.net/literature/G115-CB-01.pdf) that can only be entered an exited from the same end, the only explanation i could come up with is that the inertia of the water flowing into the bottom at speed, makes it jet straight across rather than turn and go up, the flow straight up might also be restricted by baffles in the cast, though i doubt that, since it would cause the water to cavitate, and get turbulent, and a non-laminar flowing fluid does not exchange heat with it's contact surface as efficiently as laminar flowing one would, i have not as yet found any engineering design info on this subject on the net, the manufactures may each be holding on to their trade secrets, it must take a lot of casts to get it right.0 -
Don't look too deep
If you have a flow rate that laminar flow is a problem with, and heating the building is not happening because of it, you have some other problems in your design, also.
If you flow slowly enough to be within the accepted velocity of the piping, and use a flow rate that allows a 20° F. rise through the boiler, you will not have a problem.
You are absolutely correct in that the boiler will have hot and cool spots, to the point of making perking noises, if you flow through the boiler too fast. Most systems aren't designed for flow rates that fast, and if they are, a bypass around the boiler for the added flow is recommended, to keep the boiler temperature rise near 20° to 40°.
You see, the system designer makes sure the flow rate is such that your described problem is not an issue.
Conversely, some systems with mixing valves and zones can return water so cool, and so slowly (on "one zone only" cycles) that you can see over 100° F. rise through the boiler. It can perk and rumble at the top of the heat exchanger before the limit probe in the middle shuts it off. Look at it like this, if you are seeing 90° return water, and 190° supply water, and the limit is halfway between the two, what do you set the limit to, to prevent the outlet water from boiling?
Put a small, pumped bypass zone in, run it every time another zone runs, and the Temperature differential across the boiler becomes less, the boiler is protected from condensing, and the noises stop. Flow rates are important, just as you described.
This debate is interesting, and I look forward to discussing this more, as I'm sure I didn't touch on some of what you want to talk about.
Noel0 -
I's not really a debate, I have a lot more engineering smarts then experiance smarts, so on new installs i use a primary/secondary-closly-spaced-tee show - because this is the new school of thought, and in that environment everything is easy to control, however, when i get into a repair/retrofit of an old system where i am trying to diagnose a problem like execive carbon buildup even though there seems to be plenty of air - that i get stuck. I tought that maybe there were cold spots in the heat exchanger because of the way it was piped - also in that system there are three zones with no zone valves, it's an all or nothing system, who knows what the temprature rise across the boiler is at a 5am start.
A two day I=B=R course is comming to my neighborhood in two weeks, i am trying to fit my schedule to it, cause it never hurts to learn again about somthing you already know from an inteligent teacher, you always get a different slant on things, one good idea is easly worth the $400 cost, and you get to network and ask questions0 -
I=B=R course
You are sooo right. I took the course again last year. I keep the book with me when I'm at work.
Noel0
This discussion has been closed.
Categories
- All Categories
- 86.5K THE MAIN WALL
- 3.1K A-C, Heat Pumps & Refrigeration
- 53 Biomass
- 423 Carbon Monoxide Awareness
- 96 Chimneys & Flues
- 2K Domestic Hot Water
- 5.5K Gas Heating
- 101 Geothermal
- 157 Indoor-Air Quality
- 3.5K Oil Heating
- 64 Pipe Deterioration
- 928 Plumbing
- 6.1K Radiant Heating
- 384 Solar
- 15.2K Strictly Steam
- 3.3K Thermostats and Controls
- 54 Water Quality
- 42 Industry Classes
- 48 Job Opportunities
- 17 Recall Announcements