poor system performance

ptm

The performance of our radiant system has diminished since install two years ago. Temperature recovery in the building (a hangar) is poor. Lately the 80' by 80' buildling could only get to 60 degrees. we got our own transfer pump and purged the lines and got some air out of the lines. There are two air seperators on the system (at the boiler and primary header). We found some lines (333' of pex in each of 8 loops times 3 headers each with its own Taco circulator) had diminshed flow. A week later we re-purged the lines and those flowed well but other lines had little flow. We suspected the 0014 Taco pumps were too small to get good flow and replaced them with model 0011s. We then got the heat up to temp (69) in the hangar but continue to have poor flow in some lines. When we start to purge a line it may flow good and them taper off to little or almost no flow. we are trying to determine why selected lines don't flow and why we are getting some air formation in the lines. 

kcopp

tell us more....

about your system. Boiler? fuel? What type of tubing (brand, size, o2 barrier on it or not) Was  the slab insulated underneath and at the edge and how thick? performance degradation issues  that I have seen are usually from a system w/ either no or an inferior o2 barrier on the pipe that causes the ferrous components to break down....

icesailor

Poor Performance:

It sounds like a developing problem with the install of the tubing. Like you have a case of the squisheys under the slab. Did I read correctly that the tube is under 10" of sand? or is there 10" of sand with the tube on top? It would be better off if it is on top of insulation and the concrete encases the tube or a slight layer of sand is over the tube. If it is 10" below the slab under 10" of sand, I think that there is a probability that the tube is squished and oval.

The fact that you say that you have flow for a while when you purge and then it slows down leads me to believe this. When you start the flow, you have static pressure. When you purge, it will go to flow pressure. How clean is the water coming back?

Where I work, a contractor builder set himself as "The Green Builder" specializing in Green houses. He built a number of specialized houses with geothermal and solar. He bought all his materials from an Internet supply company that did the design and supplied the equipment. Water PEX for all the heat, steel pipes connected to wall hung boilers and iron circulators. After a year or two, the systems stopped working. The fluid looked like chocolate syrup and flowed about the same way. All the iron circulators were failing.

Using a higher head circulator now in place of what was there in the beginning just shows that restrictions have developed.

In my opinion, once the system is purged of air and working, no air should ever get into the system unless allowed in mechanically. If it can't get in mechanically, it must be getting in through the tubing.

I would blow out the circuit lines that are affected with air into a 5 gallon bucket. Check the color. If it gets grungy, and the air starts to come, and the air and water mix is black and dirty, it is probably sediment that has settled to the bottom of the pipe and restricting the flow. If so, blow all the circuits to clean them out. If you get the crud out, it may work better.

I've seen this before.

Gordy

Pex size? And Pics of system

   At 333' per loop what size is the pex? Agree with others you need to determine if pex has O2 barrier, Condition of water purged from loops, What were the conditions of the changed out circs? Did the system have glycol, assume now it does not since purged. Type of boiler HX has the condition of the HX been compromised if the pex is NOT O2 barrier.



  I would power purge every loop, good flow or not. You may be chasing debris around the system. Analyse water condition, install a strainer.  If Pex is not O2 then an HX will have to be used to isolate the boiler from the system, and SS, or bronze pumps used at the stations.



 Gordy

ptm

system specs

The system is a slab on grade. The pex (1/2") was stapled to the insulation board before the concrete pour (6" thick). There is 4' of sandy compacted fill beneath the insulation. I believe the pex was O2 barrier type--I can't read the labeling any more. The boiler is a Weil Mclain ultra plus gas fired unit. The system is 50% glycol but the pH has dropped and is acidic--the water/glycol is clear.

Gordy

PH

Need to get the system water balance to between 7.0-8.5. The HX on the ultra is aluminum.

kcopp

You say...

you added glycol and its an W-M Ultra boiler.... What type/brand/ exact name of glycol?