Wirsbo hePEX failure revisited

clammy

install your mixing valve on a thermal drop and you could add a manual reset high temp limit on the outlet of your circ to give you a good safty margin maybe limit you max temp to 150 .Adding a 30 lb relief to your closed loop is a must peace clammy

James Bates

Wirsbo spec limits

had TWO failures here in last two weeks in 10 year old Wirsbo hePEX radiant Floor heat tubing. Actually only first one was Wirsbo. Wirsbo-hePEX ½” SDR9 100PSI/180* - 80PSI/200* ASTM F876 HAUSER UB06941212….IT burst like a lateral split seam in middle of return (COLD) leg to boiler. Feeder hePEX was strung beam to beam across the basement ceiling using large staples with the plastic insulators. Heat source is Trane two pipe steam system taken off the Weil Mclain 572 steam boiler DHW coil. Aquastat had been set to 160*F but after the first hePEX burst was reduced to 140*F…What I am guessing is that when the boiler chugs for an hour building steam first thing in the morning (the Tstat is setback to 55*F at night from 65*F in day) the boiler water is reaching almost 220*F to generate steam at the (present) 3PSI steam (formerly 5 to 8 PSI steam) and I am also guessing that the water pressure in this area runs about 80-90PSI.. What I find is strange is , ASSuming combination water pressure/temperature stressing, why did the failure happen in the (cold) return leg of the open air radiating return leg??? Would not the return temperature have dropped substantially from an assumed 220*F start point at boiler DHW coil 20 feet of air radiating source feed tubing in basement then the radiant floor (12x12 foot with 3 exposed walls, well insulated) and THEN exiting into the basement on COLD return leg back to boiler??It is the cold return that burst.
This basement feed run was then replaced with ½ inch copper with the appropriate pex couplers BUT….. the repair tech came up short on the HOT supply leg of copper and for last 8 inches before the pex splice he spliced in some white colored tubing, Guess what??? That burst a week after the repair. Actually literally bubble melted a nice ¼ inch hole (see pics). In this case I do not know the rating, simply the tech gave assurance that “IT WOULD WORK”. Temperature across the exposed uninsulated copper pipe after 20 foot run in basement should have dropped, but by how much??? Our solution is to use a tempering valve to drop the water temp to 140*F to 160*F then feed to the radiant floor. Any other suggested (prefered) procedures for feeding radiant heat floor ??? Alfred/Jim

kk_2

Why would the PEX be exposed to the 80-90PSI that you say the water pressure is in the area? Isn't this a closed system fed off a PRV? If not, how is it set up?

Sounds like you need a temperature controlled mixing valve, especially if you're really hitting 220F. Yikes!

Just a guess but I bet that "white colored tubing" was not rated for the temps/pressures the Wirsbo tubing was.

Dan Foley

Pex Failure

I too have used a tankless coil off of a steam boiler to supply a small radiant or baseboard zone. You must set up up properly for it to work. An aquastat will not act as a high limit when the boiler is steaming so a mixing device is required with radiant. You also must have an expansion tank, air separator and 30# relief valve the same as you would on a boiler. Do you have any photos of the mechanicals?

I would think that the relief valve would open long before the tubing failed. Maybe the relief valve has failed? As to why the "cold return" burst - cold is a relative term when your supply is going out at 220*. -DF

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James Bates

tempering CLOSED LOOP ???

This radiant closed loop is literaly hooked straight off the steam boiler tankless coil with a circulator and thermostat, PERIOD....NO seperate pressure safety valve (boiler has one) but it has an expansion tank.My question is:: water tempering valves for Domestic Hot Water via Watts or Taco valves "ADDS" cold water into the OVERhot water stream because it CAN....That is, you have opened the hot water faucet, some volume of hot water is LEAVING the house pipe "loop" thereby allowing COLD water to enter and mix to temper the temperature. HOWEVER, the "CLOSED" loop radiant heat is exactly that, totaly CLOSED, so even if you interject a tempering valve, there is NOT one drop of hot water LEAVING the loop in order for COLD water to enter the loop. So (question) how do you temper superheated water off a steam boiler tankless DHW coil??? Any diagrams? Explanations on the technical procedure? Tnx for your help. Alfred/Jim PS: sorry, no photos. The weird missmosh of incorrect piping would only boggle you mind anyway .lol..

Dan Foley

Mixing Device

Jim,

I used the term mixing device as you could use several different options such as a 3-way motorized valve, a 3-way thermostatic valve or even injection mixing if you desired. The systems I have installed were relatively small radiant zones so Iopted for the thermostatic mixing valve. Danfoss, Sparco, Taco, Honeywell all have valves available. The idea is to blend some return water with the hot supply off of the tankless to temper the water feeding the radiant zone.

If you are operating a closed loop hydronic system without a pressure relief valve, I hope your liability insurance is current! In all seriuosness, you MUST have a separate 30# relief valve for the radiant zone. The boiler relief is isolated from the tankless coil and will not protect the radiant zone from over pressure. This is most likely the cause of the pex failure. You might also want to check the expansion tank to see if it is sized properly. I have some piping diagrams at the office that I can post tomorrow. -DF

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adayton_2

Mixing Radiant Cold Return

into its own tempering valve I now understand. Thanks Dan. During the bursts of near steam heat out the coil the tempering valve will merely be restricting that coils hot output and recirculating more of its own cold return water. Eureka!!! :-). I look forward to viewing your diagrams.
One more question though is that the design limits for the best tempering valves is 200 to 210*F HOT input. The specs even go so far as to require a "heat drop loop" specifically to drop some of the input heat (Watts and others). Since there is the potential for temperatures up to aprox. 215*F (give or take a bit) from the hour long steam build up to 3 PSI on each cycle I was thinking of putting a short piece of standard finned radiator pipe (8 inch long) in the heat drop loop to be assured the temperature drop to the tempering valve. If post install temperature measurments indicate to large a drop I can always cover/insulate part of this heat drop radiator adjusting as needed. What do you think of that idea? Thanks for your help.
Alfred

adayton_2

Thermal Drop

I understand a thermal drop. I wanted to make the temperature DROP even bigger b4 super hot water slams the tempering valve. I would like to insert a short stock finned hot water radiator section in the thermal drop loop. Does this sound ok?? alfred