Old building DHW recirc system

Timco

The Barbara Worth. 1920's. 40 units, 3 stories, all enclosed.



DHW line goes supply down the east side in 1.5" and a recirc line back from both sides in 1/2" that several units' tubs pull from.



Found a UPS 15-35SFC installed and swapped in a bronze 0014 and got 10-15* better in a few minutes, but still way sub standard on the far end and down the west side. 107* max.



Also found the remnants of an old bronze series 100 B&G. Could it be in this case I do actually need a bit more pump? Neither return seems to be hotter than the other, and isolating one side does let the other side get hotter but slightly and it takes a while.



Both returns hit a 3/4 tee then down to the recirc pump in 3/4 before mixing with the cold water supply.



Hope everyone is well!



Tim

hot_rod

balance valves?

usually with two returns there are balance valves, could these have been turned down or mis-adjusted?



Does it have a 3 way thermostatic valve at the DHW tank? Anything else been replaced?



The piping for a recirc is a bit different when a 3 way thermostatic is used.

Timco

Info

No balance valves, no 3-way. Straight out of the tanks and back.

hot_rod

maybe

a single handle faucet crossing C to H? A small 15-35 or the old Series 100 should be plenty of pump.



You are correct the pump just needs to move enough flow so the farthest fixture sees warm enough water. Really just overcoming the heat loss in the loop. Often times 1gpm is enough flow with enough head to overcome the pressure drop in the loop.



Something else has changed in the piping. Maybe an apt has a cross over of some sort from a tenant installed device? Meth lab?

Timco

Single handle faucets..

Can someone help me grasp in what circumstances single handle fixtures effect a recirc system like this? My returns both got really hot after I replaced all the plugged pipe around the return then one side got cool, felt mixed.

Timco

Found issue

There is a spring check on the suction of the pump. If the pump is running it is open. If there is a large enough call for hot water, cold make up water cheats backwards against the pump and into the hot recirc line! Should I dump off my recirc somewhere else or rearrange the check system? If I choke the iso flange off enough it doesn't Backflow but I loose recirc capacity.

Steve Whitbeck

erosion

You need to read the other post about the return line erosion.

That is WAY too big of a pump - You will destroy the piping.

Timco

Size

So the 15-35 or the 0014 are too big? The 15-35 is 3 speed.



Any thoughts on the recirc termination? Maybe move it from the hot water makeup to the to the hot water supply?

hot_rod

got a drawing of that piping?

I'm not sure a spring check on the suction of a recirc is a good idea? It could induce cavatation. The recirc needs to go thru the tank to supply a constant temperature as the loop temperature drops.



The 15-35 should be about right, 3- 4 gpm at 7-8 ft head.



With no faucets flowing, if you can do that, maybe a 5-10° drop from supp[y to return.



It's a hydronic loop, really, you need to assure the most distant faucet has adequate temperature. If the return loop is un-insulated it will loss temperature from the last fixture to the tank. Check the temperature at the last fixture. State code may indicate the required temperature, I think 110- 120° is common.



What temperature is the tank set for? I'm surprised there is not a thermostatic valve required for a building like that.

Timco

Drawings

I'll post pics and a schematic later.



3 Lochinvar tanks in parallel, 1.5 out and a .5 back from each side really is all I can see. At the return termination it ties into the cold water makeup line that feeds all 3 tanks in parallel. On some hot water calls the cold water is drawn backwards through the pump and mixes in the recirc line. It's that Backflow or mixing I need to stop. The temps on my returns are great now since I found nearly totally blocked iron pipe in both directions. With that removed it is recirculating great. Uninsulated iron pipe. Lots of heat loss.



Since I was asked to deal with the recirc issue I have not checked tank temps yet. I'll do that as part of my checklist today before wrapping up. Camus mod con is making the DHW.