Why is the Return On the Top

CMadatMe

I came across the attached today and as a hydronics guy of course I wanted to know the science behind it. While it's named a low loss header I just can't grasp the science behind it.



Normally on a LLH supply is top and return is bottom. I have the math for that which is also attached. How would you figure supply side system temp for this? If you look at a true LLH it basically gives a mix. Colder water back to the boiler warmer water rising and mixing with boiler water giving you a supply temp different from boiler temp. With this strategy cold water would be falling, Would the math just be reversed? How would you figure supply water temp?



Also one of the benefits the lit gives you is that this is like a low loss header in the fact that it acts as a catcher of debris and sediment. If the return is at the top and the debris or sediment falls to the bottom what long term effect could that have on the dhw or system pump? Would that sediment or debris be pulled in to them? Would you pull the check out of the dhw pump and use a separate flow check?

I'm asking because this is a very neat concept and I want to understand and be able to figure the science on what happens inside with water temps based on flow rates. The thoughts about possible pump problems also has me curious.



ME this is right up your ally. I figured you'd have a good opinion on this.

meplumber

Not sure this helps.

I am not sure if this helps Chris.



At a hydronics/fluid dynamics class I attended a while back, we discussed the physics of heat transfer in "semi-open" vessels like Viessman's low loss header.  It appeared to not matter top or bottom as long as you employ counterflow.  With the boiler entering at the opposite side as the returning water from the system.  So if the boiler supply is bottom left, then the system return should enter top right and vice versa.



The size and water holding capacity seem to matter though.  There was a "breaking" point once the size of the vessel got pretty large.  In the sizes that we see most of the low loss headers/hydraulic separators it did not effect transfer.



I'm not a scientist or engineer, just a lowly basement dweller.  Probably not the answer that you were looking for, just my $.02 worth. 

CMadatMe

The Math

I here what your saying. I thank you for the reply and your dweller sense makes sense. I'm curious as to the math to figure out system side water temp and also any possible effects the pumps might see from debris/sediment as it falls from the return at the top. Especially in cast rads or cast board systems.

Jean-David Beyer

I found this description easier to understand.

See bottom of page 2 of this. It is clearer than the pictures you posted.



https://encrypted.google.com/url?sa=t&source=web&cd=3&ved=0CBoQFjAC&url=http%3A%2F%2Fwww.caleffi.us%2Fhr_HR%2FTechnical_brochures%2F01076%2F01076.pdf&ei=NLOCTf6bBPC10QG3g7nYCA&usg=AFQjCNHZtS2ZtZA4YH87u9ax8_-O1A0W4w&sig2=5F5FJ0Bx8jW6AWI_fDnJEg

CMadatMe

Thanks

I have this and also the idronics manual. The actual closer match to the LLH in question is the Hydro-Link on page 19 at the bottom of the attached. But again supply is top return is bottom and the opposite on the header in question. So is the anwser the math is just reveresed? I don't know. Cold air falls, hot air rises. The same effect happens in a LLH cold water stays at the bottom warmer water rises to give a mix effect. With the return at the top does colder water fall to the bottom towards the supply and warmer water head back to the boiler?

Gordy

Hydro link section

http://www.caleffi.us/en_US/caleffi/Details/Magazines/pdf/idronics_1_us.pdf



Maybe this will help



Gordy

Gordy

Ooopsy

 Posting the same time.

CMadatMe

Thanks Gordy

It's the closet I can also find to the Peerless. Still though on the Peerless return is at the top and supply the bottom. The opposite of these..I'm also curious as to sediment/debris heading towards the pumps as it falls from the top to the bottom.

Gordy

Closley space ts

 Really that is what the seperator no mater the configuration is based on the way I have come to understand the seperators.  Its just a question of the flows to get the right mix to the port.

Gordy

Sorry

 I can't be more help....Its hard for me to really see the attachment in your initial post.  I agree with what you are saying. Maybe this particular manufacture is trying to be a little different, and this is their way of doing it who knows.  Good question though in my opinion.



 Does that particular configuration lend itself better to peerless boiler piping?

CMadatMe

Return

But in a separator the returns are at the bottom. Importnat because the coldest water stays there and warmer water rises to the mix. If at the top wouldn't the colder water fall and warmer water head to the boiler?

Gordy

Thinking

 What you are saying is true when system is off. Hot, and cold water has its way inside the seperator.  But while running I would think flows would over come that tendancy. The boiler may see a slug of warm water at initial start, and the sytem side a slug of cold....minimal though I would think.

CMadatMe

Don't Know

Haven't had a chance to ask them. Going to call them tomorrow though.

Jean-David Beyer

terminology

Just as there seems to be some disagreement on what is the primary and what is the secondary in P-S piping,I have observed disagreement on what is supply and what is return in systems where a boiler is used to heat a space.



Thus, when it seems to matter, I call the loop in a P-S system with a boiler in it the boiler loop, and the loop with the space to be heated the load loop.



Similarly, some look at things from the point of view of the boiler, where they call the tap to the boiler where the cooled water enters the boiler the supply, and the tap where the hot water returns to the heated space the return.



Now these seem equally valid, but since neither is in universal use, there can be confusion unless face to face discussions are done, preferably with a blackboard so pointing can be easily done.



Is that wat is going on here?



Let me call the hot water out of a boiler the supply, and the cool water return the return.

Let me assume the boiler is on the left in the Caleffi pictures, and the load on the right.



Then it seems to me that the hot water supply enters from the boiler to the TOP LEFT of the LLH and exits the TOP RIGHT of the LLH. The cool water enters the BOTTOM RIGHT of the LLH and exits the BOTTOM LEFT of the LLH to return to the boiler.



Is that what we are all understanding?

Mark Eatherton

Can't see...

I tried going to Peerless' web site to no avail.



Got a link, or send me an email with attachment so's I can see :-)



ME

CMadatMe

No link

This was a copy from a copies that was made and left out at the counter of one of the branches. I just happen to see it.

hot_rod

the mix

would be the same as long as there is flow through it. You could lay it on it' side and still have the blend, regardless of supply and return connections, as long as they are across from one another.



I'm not sure about air removal? A true 3 purpose device will have an extended "media" to help with air and dirt at top and bottom.



Air does "remove" best the the warmest spot in the system. With the domed top and air vent up there I would think that would be the best connection for boiler supply.



hr

CMadatMe

The Blend

The blend is really the question HR. Since the cooler water is at the top and the hottest water at the bottom would the same math as given on a traditional hydro sepearator be the same?

What about the indirect zone in this case? Would it not see blended water?



I'm sorry for all the can't see the pic clearly. I had to scan it. I do not have a PDF of this.

hot_rod

Maybe

it would be fun to "watch" the operation of a separator with an infrared camera Maybe they have tested that device with both piping options and decided the performance is the same?



I agree the blend would not be a problem. Most important is the hot flows are across from one another regardless of top or bottom connections being used.



All things considered, IF the device has an air elimination baffle or media at the top 1/2 then I feel it's best performance for all the benefits it offers, separation as well as air, and dirt removal then I like top connections for hot supply, bottom connections for return.



Check out this video for a clear view and explanation of the "separation" concept. With the audio added you get a better understanding of header based piping compared to separation.



hr





www.caleffi.us/caleffi/en_US/Site/Products/Product_videos/index.sdo#

CMadatMe

Spoke To them

Its just a hollow piece of copper. They already are making a change in it. I didn't notice this but there was a spot for a LWCO in it. There changing that.  The tech agreed that there would be blending but didn't have the math. If someone from Peerless engineering peers in...Please provide the math for this. The DWH spot could be used other things...

jp_2

Here's the Math

never mine, this apparently is not correct......



F4/T4 - F3/T3 = F1/T1 - F2/T2



or



T4/F4 - T3/F3 = T1/F1 - T2/F2



I KEEP THE ERROR but,  here's the correction:



(F4 x T4)  -  (F3 x T3) = (F1 x T1)  -  (F2 x T2)



or



F4T4 - F3T3 = F1T1 - F2T2



basically  A - B = C - D.  what the radiator gives off, the boiler must supply.



you can move things around and figure out whatever you need.  remember 9th grade algebra?



since the boiler flow in and out is the same, and the branch in and out is the same, they simplified the equation.

CMadatMe

You Would

Have to define the forumla as it pertains to the in's and out's of the header. What is T4, F4. Here is my reason for wanting the math.



The concept is great for mutiple zones with radiant. On a condensing boiler I would take my supply and return from the boiler side anyway. If I have a single temp radiant system with 2 zones same water temp my header is done for me here. It make the install a breeze in the labor end. Same goes for radiant and panel rads. It may easy the cost of a job. Ten degrees in the difference between the supply ports of the DHW and System side could make a huge difference in design. Same could also be said of a cast iron or cast rad zone and a fin-tube zone.



The thought process of this could bring great advantages in system cost in alot of systems that are using condensing boilers. Plus I'm a wet head and I need to know how it works.

jp_2

equation defined

the definitions for T4 F4 come straight from the little color diagram you posted.



the letters are the same from the diagram too, so there should be no confusion.



I kept everything the same as in the diagram.