Presure in Hydronic heat system

Discussion in 'HVAC Heating & Cooling' started by Duaner, Jan 4, 2009.

  1. Duaner

    Duaner New Member

    Messages:
    5
    Hi
    I am a DIY homeowner, I installed pex pipe in my garage floor 4 zone loops. I dont have gas so I am using an electric water heater to heat the water. I have the zones connected to a manifold, a 3 speed circ pump, pressure reducing valv and double check on incoming water supply, expansion tank near water heater and check valves on the circ lines. I also have a combo temp/pressure gage on supple and return loops. the supply loop is 120 degrees F return loop 110 degrees F on low speed. My problem is the normal pressure of t he system when pump is not running is around 40 psi. when I run the pump the system pressure climbs to where it exceeds the readings of the guage and pegs at the center of the temp gauge.
    What do I need to do to control the pressure in the system?

    Thanks
    Duane
  2. nhmaster

    nhmaster Master Plumber

    Messages:
    3,189
    Location:
    S. Maine
    Not sure what you used for a pressure reducing valve but it should have been something like a Watts S1156F or the Tack equivilant. These come factory set at 15 lbs which is about what you want for pressure. If you are getting a drastic increase in pressure when the circulator runs, you have the circulator mounted in the wrong place. It should be on the supply, pumping away from the tank (tward the zones) and past the expansion tank and fill valve.
  3. Duaner

    Duaner New Member

    Messages:
    5
    The pressure valve is f1201 25-75 psi .
    Pump is mounted on the verticle supply side of the zone loops
    The expansion tank is near water heater on supply side of pump
    I also have an automatic air relief at the high point of system
  4. Duaner

    Duaner New Member

    Messages:
    5
    Does orientation of expansion tank matter? I have it installed so the writing on the tank is correct, pipe fitting at top air valve at bottom.
  5. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    22,332
    Location:
    New England
    The orientation of an expansion tank doesn't matter, and the way you have it makes it easier to replace when it fails without getting a showerbath. Note, if the pressure jumps while heating, it could be the tank has failed or lost its charge.
  6. alternety

    alternety Like an engineer

    Messages:
    671
    Location:
    Washington
    When you say the pressure is 40 lbs, what exactly do you mean. You have two gauges. Are you reporting both of them at 40 lbs; the difference between the two is 40 lbs. If they are both showing 40 lbs with the circulator off, you have put in too much pressure and need to bleed some. With a sealed system you will not need to add water. Also check to see if you set up the pressure tank properly.

    If both gauges track each other but go off-scale when you turn the pump on, I am not sure what would cause that. Heating the water with a properly sized and operating expansion tank should not cause that kind of pressure increase. Again, investigate the tank. No valve turned off, pressure, size based on system water volume.

    If the gauges do not track each other and only one goes high, your pump is too big for the amount of tubing in the system and is causing a pressure drop across the load.

    If the latter, you can fix it by properly sizing the circulator or adding a pressure bypass to the system. This is done to stabilize pressure when zones open and close. Do you have separate control valves on the Zones? If not your pump is too big for the system. If you do run the zones independently (and since you say there are check valves in the loops, I assume you are) you need the bypass. A bypass is probably cheaper than a new pump. Ideally the pump should provide just the amount of flow needed to supply all loops at once. But even if it too big the bypass will deal with it.

    You may have both problems. Overfilled system and too large a pump.

    A side note. Since it is in a garage, if you are in an area that freezes, you should have properly formulated antifreeze in it. Not automobile stuff.
  7. rmelo99

    rmelo99 Network Engineer

    Messages:
    349
    Location:
    Connecticut
    What about the PRV? I thought those typically blow at 30PSI. Do you have one?

    If so what is it rated at and how come it doesn't purge water at the 40PSI?
  8. nhmaster

    nhmaster Master Plumber

    Messages:
    3,189
    Location:
    S. Maine
    You have the wrong fill valve to start with. Pressure should be between 12 and 15 lbs. The valve you need is a Watts S1156F or the equivalant Taco, Wilkins or Calleffi product. The expansion tank should be installed in the feed pipe before the circulator and the fill valve should be tee'd in just above the tank.
  9. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,332
    Location:
    New England
    He probably didn't change the WH T&P valve for one designed for hydronic heating, either. My personal perspective is that a WH is a lousy way to get hydronic heating, but some people are proponents. I think a boiler is better.

    As stated, with a properly set up system, the pressure should be in the area of one atmosphere (15 pounds) or so. The expansion tank should be precharged with that pressure, and unless you are creating steam because the controls aren't working OR the expansion tank is big enough for the volume of water you have, the pressure should not change much - a pound or so maybe, if that in between cycles.

    If the pump is on and the flow is restricted, the pressure can go up on the pump outlet (and since it is a closed system, it will reflect at the inlet as well if there is any flow.
  10. Duaner

    Duaner New Member

    Messages:
    5
    1st off THANK YOU ALL for the responses. I have just found this forum and it haas been a great source of info. I am a SR Electrical Inspector in Seattle, WA and will try to help out in your electrical forum.

    Jadnashua- I am going to replace the expansion tank. I bought it just under a year ago it is a pft-12 precharge pressure 40psi.

    Alternety-the 40lbs is what is read on the guage. pressures seem to be equal going into zone loops and returning from zone loops. How do I set up pressure tank properly?
    The pump is Groundfes type ups 15-45 psi 3 speed p/n 59890247. I told he counter guy at the parts house what I was using the pump for. I pretty sure he gave me a fairly common boiler pump.

    Overfilling could be it!! I just have the water valve on feeding the system, so it takes all the water it needs to fill the system. how do I determine how much water the system needs? Should suppy valve be off once system fills?

    Freezing not much of a concern here in Washington, been here 15 years this is first year temp was below freezing for more than a few days.


    Rmelo99---The PRV on the water tank is stock w/ tank. Should I change this?

    Nhmaster----- I will attempt to find this lower pressure fill valve



    Thanks Again Everyone
    Duane
  11. alternety

    alternety Like an engineer

    Messages:
    671
    Location:
    Washington
    Do all the things that people have said about positioning of components within the circuit. It matters.

    The precharge pressure on the expansion tank is wrong. As people above have pointed out system pressure should be around 15 lb. That means the air pressure in the bladder needs to be set at about that pressure. The system has to be depressurized when that is set. I believe you have the tank mounted hanging down. Take it off and drain it to set pressure. That way the setting is good and you can make sure the blatter is intact. If you get any water out of the air valve when you release air pressure the bladder has a hole and the tank must be replaced. Someone else should comment on this but I suspect you don't have to replace the expansion tank if the bladder is OK - just reset the pressure.

    40 lbs on BOTH gauges with the system cold is what would be expected with the fill valve set to 40 lbs. After you drain some water and set the tank bladder to 15 psi refill the system. If you have replaced the fill valve with one providing the correct pressure, just turn on fill. If you have not done this (and you really should; if for no other reason than the next owner filling it wrong) just slowly let in water when it is near full until the pressure guage shows 15 lbs. This would get it filled if you can't get a new pressure regulator and need heat. Let out air from the valve you placed at a high point. Run it for a while with all circuits open and let out air until none comes out. Any air left in the systemis left will get caught by the extractor I think you said you had in the system (if not add one). And get the correct pressure relief valve. That is not an option. You need it.

    The pressure tank volume must be sufficient to deal with the volume of water "created" created by heating the volume of water in the tank. The arithmetic uses change in temperature, volume of water in the system, and the coefficient of expansion of water. Or there is probably a table published by the tank vendor. I am sure someone here can easilly tell you what size is necessary. For this you will need the volume of the tank and piping (the length and inside diameter of the total of the tubing you are using). This will get you volume in the pipe. There may still be a problem with too much pump. Again there are calculations. To get it right you need to know what volume of water at what temperature is needed to put the required energy into the garage to equal the heat losses at the design temperature. Make sure the tubing is the right size to handle the flow. Then size the pump. Of course the water heater must be able to provide sufficient BTUs.

    You don't need to keep the makup valve turned on. Unless you get a leak, it is not going to use water. Boilers use low water sensors and high temperature cutoffs to protect the system for this type of things. The PRV will keep it from blowing up. If you lose the water it will liekly burn out the heater elements and pump. If it leaks and you have the fill valve on, it is an infinite amount of water to show up somewhere.

    If the slab has not thoroughly cured you should probably bring the water temperature up gradually over a few days.

    You should probably be able to get to the plumbing store now that the streets are back.
  12. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,332
    Location:
    New England
    There should be both a backflow preventor and a autofill valve for easiest operation but you can fill manually. You MUST have the backflow preventor, though, when connecting potable water with stagnent hydronic systems. The autofill valve will keep the cold pressure at around 15 pounds unless the expansion tank is shot. If you have 40 pounds in the expansion tank, after heating cycles, it will push back and provide 40 pounds pressure in a full system, it needs to be reset as indicated. A PRV isn't what you need inside of the system, there is a T&P valve on the WH (or there SHOULD be). Normally, this would have much higher pressure relief settings than used in hydronic systems to accommodate normal water supply pressures, and probably should be replaced with one for hydronic. A typical boiler might run as hot as 200-degrees, while a residential WH normally can't. A hydronic T&P valve trips at something like 30-pounds and 220-degrees (don't quote me on this - those are not exact - I dont' remember the actual numbers).
  13. Duaner

    Duaner New Member

    Messages:
    5
    Thanks for all the good advice. It will take me a week or so to gather the parts and impliment. I will post back here the results

    Duane
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