What is the proper flow through sidearm

[4492011]

Hi I am installing a sidearm exchanger for heating domestic hotwater, I am seeing that the hot water from the boiler enters the bottom of the sidearm, but reading a couple of posts other people are entering the hot water from the boiler at the top of the sidearm so which is it hot boiler water at the top or the bottom?

 

[MNfarmer]

If I was going to hook one up I would run the hot boiler water in the bottom, that's how most of them are that I've seen.

 

[itn]

bottom

 

[Mister Twister]

Everything I read says you should always put the feed in the bottom and the return out the top on any heat exchanger. I think it is to keep from getting any trapped air pockets. Good luck with the insall.

 

[Crofter]

Hot feed from the boiler into the top of the sidearm exchanger and out the bottom same as radiator on your car. That is normal thermosiphon flow in the cooling off mode; as the liquid cools it gets heavier and sinks.(same as your car). The flow in the domestic water side of the sidearm exchanger will be in the opposite direction going in the bottom cool and rising as it heats and discharges out the top back into the hw storage tank. This will give the best heat exchange and is the natural flow direction. If the boiler water is pressure circulated it can work with feed in the bottom but is not optimum or standard.

 

[4492011]

Hot feed from the boiler into the top of the sidearm exchanger and out the bottom same as radiator on your car. That is normal thermosiphon flow in the cooling off mode; as the liquid cools it gets heavier and sinks.(same as your car). The flow in the domestic water side of the sidearm exchanger will be in the opposite direction going in the bottom cool and rising as it heats and discharges out the top back into the hw storage tank. This will give the best heat exchange and is the natural flow direction. If the boiler water is pressure circulated it can work with feed in the bottom but is not optimum or standard.

Thanks that is what I thought , I forgot to say that most of the time my pump does not run my house just naturally convects my boiler is inside within 5 feet of the hot water heater, the only time the pump comes on is twice a day when I am having a hot fire to burn cresote off, and it reaches the upper limit. I am hoping that I will not need another pump just for hot water.

 

[mga]

i guess it depends whom you talk to......


http://www.**********/econtent/index.php?ACT=24&fid=21&aid=5443_fHKIhy1NubIVrOs3cXMe&board_id=1


http://www.**********/econtent/index.php?ACT=24&fid=21&aid=5535_ryE1Fvy6djd7pskRsi00&board_id=1

http://**********/econtent/index.php/forums/viewthread/8168/

 

[mtfallsmikey]

I was confused

When I bought the Heil hydrocoils...supply in top port, return in bottom, was spec'd in the install manual....made no sense then, but does now.

 

[Crofter]

If you want to use the effect of natural thermosiphon and wish to take advantage of the discharge to the domestic hot water being in contact with the highest temperature boiler water (best heat transfer) , there is no choice. Also if your circulating pump is in the return line piping, not much choice either. You should never depend on flow to disperse air locks unless the piping is graded up to the boiler at all points of flow. Independant venting is necessary.

MGA, you are right about opinions differing, but in at least some cases, only one is proper.

I was adding a bunch of plate coil tank heaters to an existing glycol heating system at a refinery and discovered that the flow to the existing unit space heaters in the building were hooked up wrong (fed from the bottom) I asked the engineer if he wanted the additions hooked up correctly or to match his existing units. That was a fun moment!
In that particular system there was high pressure differential between feed and return and no consideration for thermo siphoning, so it was only a minor efficiency deal but it would have been interesting to chase the paper work and see where the original screw up occurred.

 

[4492011]

The circulating pump is on the return side, but if thre is no check valve in the pump that should not make a difference where it is should it ? My boiler is in the basement and the hot water heater is aproximately elevated 5 inches above the boiler.

 

[mga]

If you want to use the effect of natural thermosiphon and wish to take advantage of the discharge to the domestic hot water being in contact with the highest temperature boiler water (best heat transfer) , there is no choice. Also if your circulating pump is in the return line piping, not much choice either. You should never depend on flow to disperse air locks unless the piping is graded up to the boiler at all points of flow. Independant venting is necessary.

MGA, you are right about opinions differing, but in at least some cases, only one is proper.

I was adding a bunch of plate coil tank heaters to an existing glycol heating system at a refinery and discovered that the flow to the existing unit space heaters in the building were hooked up wrong (fed from the bottom) I asked the engineer if he wanted the additions hooked up correctly or to match his existing units. That was a fun moment!
In that particular system there was high pressure differential between feed and return and no consideration for thermo siphoning, so it was only a minor efficiency deal but it would have been interesting to chase the paper work and see where the original screw up occurred.

you obviously are knowledgable with steam heat, and i'm not questioning your experience, but, every sidearm exchanger that i looked at shows them feeding in thru the bottom.

for example, Timber Ridge shows a diagram how theirs is installed here:

i imagine the reasoning behind this is because it helps with the convection of water from the tank. whereas, if the hottest water entered thru the top it would cool as it went downward, defeating the principle behind convection.

 

[MS-310]

It works both ways I have hooked up over 200 or so of them....THE BEST WAY IS THE HOT IN TO THE BOTTOM>>>>>> trust me and the other outdoor wood boiler guys.....CB, heatsource1, heatmore, Freeheat,empire,and every other wood boiler tells them to hook up the hot to the bottom of the side arm.

 

[MS-310]

you obviously are knowledgable with steam heat, and i'm not questioning your experience, but, every sidearm exchanger that i looked at shows them feeding in thru the bottom.

for example, Timber Ridge shows a diagram how theirs is installed here:

i imagine the reasoning behind this is because it helps with the convection of water from the tank. whereas, if the hottest water entered thru the top it would cool as it went downward, defeating the principle behind convection.

+1 you have it all the way right!!!!

 

[Crofter]

Like I said it will only work with forced circulation and will not work at all by convection unless the hot feed goes to the top of the exchanger. You will also have the domestic water leaving the heat exchanger limited to the temperature of the exit temperature of the boiler water from the exchanger, instead of potentially at the temperature of the boiler temperature feed water. (no counter flow of exchange liquids). I see some people have some misconceptions about how thermo siphon convection works. I see the poster wants his system to work mostly by convection without being dependant upon the circulating pump! The cooled water from the exchanger is denser than the boiler water so it will flow into the boiler and the lighter hot water from the top of the boiler will flow out to replace the cooling and sinking water in the sidearm exchanger. That is how that works. If the water was being heated it would become less dense and rise, which is exactly what happens to the domestic water side of the exchanger. Where hot liquid is giving up heat instead of receiving and becoming denser in the process, the natural flow is opposite direction (downward)
The pressure differential so created is very small in comparison to what the circulating pump can create so it will not prevent the system from working, but if you are dependant solely on natural convection flow the sidearm exchanger must be fed from the top. If your piping is all up and down and all over the place it must be force fed and is dead when you lose power. I do not see any explanation why those manufacturers choose to hook up in that manner that causes flow deliberately counter to thermo convection, so I am all ears. Trying to operate without high point bleed valves might be a possible reason but that is a guess on my part.

 

[mga]

so, what you're saying is that when no circulator is being used, then the reverse would be standard installation than the diagram i showed?

i'm asking to learn something here...not to challenge you.

 

[Crofter]

so, what you're saying is that when no circulator is being used, then the reverse would be standard installation than the diagram i showed?

i'm asking to learn something here...not to challenge you.

Yes, I would say so. The flow in the cooling off part of a thermosiphon convective flow loop is a bit counter intuitive to our more usual association with heated water rising as it is being heated; the flow on the DW side is as expected, upward, but the hot boiler water is being cooled off and becoming denser as it gives up heat to the domestic water side of the exchanger so the natural flow is downward on the BW side of the exchanger. The water sinks as it becomes heavier than the hot water in the boiler so it flows into the boiler and displaces lighter hot water out.

If there is high flow and little heat dissipation through the boiler water side of the exchanger the effect of the loss of counter flow efficiency is probably of minute concern too in a forced circulation system.

One household system I have worked on both on repairing the boiler and on the piping was originally conceived to work on thermosiphon, which it did, but the line loss even in two inch graded pipe runs would not create enough flow to maintain heat in extreme cold so we added a circulating pump but had to be carefull not to disrupt the convection that he wished to maintain so he could maintain reasonable heat if the power went off. The boiler water and heating system is glycol/water so he has to have a sidearm exchanger for his domestic hot water.
With the high flow circulated systems mentioned, I guess it is no concern; they are mostly dead in the water if the power goes off but I am curious as to the technical reason for feeding the sidearm exchangers from the bottom. Actually I think the code calls for double isolation from boiler water to potable water so I think the exchanger should be a little more involved than shown. My experience is more in oil refinery and other industrial installations so maybe I am missing something here.

 

[MS-310]

Nice point.....But you have to pump water to the house...so you are pumping water in to the side arm. Yes if your where to pump the drinking water in the side arm then you would want to flow the water in to the top.....


If you are doing a normal hook up with a normal side arm you need to put it on the bottom. It works the Best!

your dead in the water when you lose power....No way for the hot water to be pumped in the house....

For being code, you need to use a UL lister side arm.... In MI.

 

[4492011]

Nice point.....But you have to pump water to the house...so you are pumping water in to the side arm. Yes if your where to pump the drinking water in the side arm then you would want to flow the water in to the top.....


If you are doing a normal hook up with a normal side arm you need to put it on the bottom. It works the Best!

your dead in the water when you lose power....No way for the hot water to be pumped in the house....

For being code, you need to use a UL lister side arm.... In MI.

My boiler is in the basement and it naturally convects all the time. The only time my pump runs is twice a day when I have a hot fire to burn cresote off at that point it reaches the upper safety limit and turns on. I have ran my boiler lots of times without power I just keep an eye on amount of wood I put in to make sure it does not get to the upper limit. I really do not want to put a pump for heating the domestic hot water. I am hoping it will thermosiphon like the rest of the house. That is the reason for the post to make sure I do everything I can to accomplish this.

 

[MS-310]

Well if I would of read post #6 I wouldnt have to type....LOL I thought from your first post it was a OWB.....Ok ...Dam I fell :censored: dumb....LOL

 

[4492011]

Not a problem we all do that at times. I will let you know how it turns out when it gets cold, I am going to try going into the top of the side arm and see what happens. Thanks everyone for the replies