TT-110 to p/s or not

JIMBO_2

Installing a new TT-110 in a house with piping from the 1940s, including 2" headers for supply & return running across the basement and feeding the 1st and 2nd floor CI radiators (10 of them).  TT said I do not have to pipe in a primary/secondary loop if I do not want to.  But will the system run better, more efficiently, with or without p/s piping?  It will also have a 40-gal indirect as well as outside air reset.  I certainly don't mind piping in a loop and pump, but is it worth it?

TonyS

No need to waste electric

that is one of the benefits of the TT.  Pump right through, Lower temps in the boiler for better condensation and half the electric consumption. 

EricAune

Flow through the boiler

As with most mod/cons, primary/secondary is recommended by TT to maintain proper flow through the heat exchanger. 



Be sure to calculate head loss through the system along with your system flow requirements and match the pump sized needed to satisfy the boiler flow requirements. 

TonyS

With 2 inch mains and

cast iron rads. Im sure you will have no problem with the grundfos 3 speed supplied on the unit.

JIMBO_2

But is that "best"?

With the size of the headers, being fed by the 1" supply & return from the boiler. Is it efficient and effective feeding ALL that pipe before and after  the radiators?  I cannot help but wonder if I should have come off the boiler with 1-1/4 or 1-1/2" pipe to connect to the 2 inch headers, rather than the 1".  Any ideas?  Then again, how about the circ pump?  Is less circ pressure better than more?  Or am I looking for a specific delta-T?   Say 20^?  30^?  

TonyS

The system was probably

gravity and is piped in 2 pipe direct return. The rule of thumb for converting pipe size is 1/2 the pipe size and drop one pipe size. So 2"= 3/4. So your 1' will be more than adequate. Your boiler is only 100,000 out so you only need to move 10 per minute max at 20 degree delta t. You dont need 2" pipe to do that. Is this system still direct return or was it coverted to reverse return?

JIMBO_2

Now you have me

The piping comes out of the boiler and into a (bull headed) tee, feeding 2" black pipe going toward opposite ends of the basement.  The return does exactly the same coming back to the boiler.  Ihave always been told NOT to pipe the supply into the bull of a tee, but this has been in opperation for about 50 years, so I left it.  Reverse return?  The return flows from both ends of the tee, bangs head-on into the other side returning into this tee and then both join to flow through the bull of the tee and into the new TT-110.  Reverse return? 

TonyS

From the boiler follow

the supply to the T and out of the T, any side you like, until you come to the first T that feeds a radiator, follow the line to the radiator, through the radiator and then the return line from that radiator back to the main return. If that return main goes directly back to the boiler, the same distance as the supply did, it is a 2 pipe direct return. What you really want is a 2 pipe reverse return. Water is lazy, if it can go 10 feet through the first radiator hook it through a big cast iron radiator and right back to the boiler, there really isnt any reason for it to go all the way back to the last radiator. Ideally want you want to do is make it equal distance to and back from each radiator, you do this by reversing the return. First radiator to get water is now the last radiator back. Because you have Ts bullnosed off the boiler I am going to assume the boiler is centrally located near the middle of the home. You probably have 5 radiator in the front of the boiler and 5 in the rear. When they are like this the problem isnt so pronounced as it would be if the boiler was in the front of the house and the mains extended all the way to the rear, this is when the rear radiators dont get hot at all. If all the radiators get hot in your case and no one is complaining about cold rads or overheated rooms you can leave it, but to really make the job right you should reverse the return so the flow is balanced. This can be a hard sell when the customer doesnt feel the problem. Usually depending on the job I will break out the bullnosed Ts and put ball valves on either side to balance the flow between mains. In Dans book 'PUMPING AWAY' he has a ladder diagram of a direct return and reverse return system. 

NRT_Rob

use P/S when needed

and "when needed" means when your GPM/head requirements are too high for system with the boiler heat exchanger pressure drop and the pump you are using (internal, for that boiler).



otherwise, install a pressure bypass for your minimal flow requirements (assuming radiators are TRVed or that there is any other possible way you could have total system flow below the min flow of the boiler).. which you'd need for the secondary circuit in any case... and go primary. saving a pump is great if you can do it.



and big pipes are known as "long, skinny buffer tanks". they are awesome. be glad they are there. but insulate them in cold space.

JIMBO_2

Thanks, Tony

Okay, this system is pretty much as you described.  The 2" headers, say east and west sides of the house, tee off for the 1st floor rads with 1" pipe up, and 3/4" pipe up to the 2nd floor, gradually reducing size to the last radiator on the branch.  The return pipe gradually increases coming back.  What do you think would make this system more efficient?  I am open to any idea or suggestion you care to offer.  Jim

TonyS

I would install

a TT  Prestige, just like your doing, piped right through. The prestige has alot of parameters for you to adjust but the factory wont give you the control supplement unless you go to their school in NJ. I dont know if you have ever been there, but it is really worth going.  It usually cost about 150 bucks for 2 days. That includes the hotel and the food. A limo into Philadelphia for a feast... the whole deal and then they give you 100 bucks off your next prestige. They really go over all the parameters and they have working units on the wall. Anyway its well worth it. But anyway radiators on old gravity systems were never made to run at 180, usually 140-150 on design day is enough, so set your outdoor reset accordingly and that thing will be condensing on all but the coldest days. Also a couple of well placed TRV;s in some rooms they want a little cooler can save bucks. Show some pics when your done. Take care

CMadatMe

If this isn't a job

for the New Viessmann Vitodens 200 I don't know what is. You have already picked the boiler but in this case I would look at using a Calefi Hydro Seperator.

JIMBO_2

Interesting

It's a funny thing, after closer examination I discovered the headers are NOT the same length.  The one side reduces quickly down to 1-1.4 after only 6 feet away from the bullheaded tee.  The other runs double that before reducing down.  I find it ironic that we are presently piping a NYC public school that utilizes a reverse return on the secondary hot water system.  I'm piping it, but I did think it a bit "odd."  I have never really run across a reverse return before.  But, if it might help the system function better, I am all for trying to rearrange the piping to make it work.  Have you any suggestions? 

TonyS

Reverse return is an excellent system

because it deliver the same temperature water to every radiator. Most guys Ive seen, when they size baseboard use the 170 degree water temp to figure how much board they need in each room. This is only true when using a reverse return, when using a monoflow or loop system they neglect the fact the water is getting consecutively cooler and cooler as it exits each radiator and never figure this into their calculations. Reverse returns get the bad rap that they cost more in pipe to put in, when in reality if you have to keep adding more and more cast iron board to each room, at todays prices it gets alot closer. When I use to do school work they were always piped in reverse return.

JIMBO_2

Thank you

It does sound very interssting.  As I look up at the existing return piping, I see that it too reduces in size as it continues to the last tee on each side of the basement.  As I understand it, I would disconnect the return piping at the last tee, as well as at the first tee, capping it at the first.  And then run a new pipe up to the original returrn piping at the farthest tee to the supply pipe leading back to the boiler, where I disconected the closest tee.  But might it increase the system's efficiency noticably?  I mean, will it be worth the work, in the long run?  It sounds logical to me.  I'll have to go back and take a good look at what might be needed to accomplish this.