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Hot Water Heating System

Rich P
Rich P Member Posts: 6
Help!! We maintain a large research and development facility with a hot water heating system which is comprised of the following: a closed loop system with approxiametly 30 % propylene glycol added to the loop. The loop temperture is held relatively concstant at 140-180 degrees depending on outside air condtions as selected by the hot water reset controller. The heat source is a steam to hot water shell and tube exchanger. The equipment varies from 3 central station air handlers, all operating with a 100% outdoor air, hot and chilled water coils, (4 pipe system), 3 way diverting valves respectively and set to deliver 55 degree air to the lab spaces in the building. Located in the labs are a total of 25 reheat coils, each with it's own space control and 3 way diverting valve. Our problem is we want to keep the make-up water to the system off in order not to dilute the glycol content beyond a required protection level once the system is pressurized to between 12-14 psig. This system seemed to hold this pressure for many years and functioned properly with the make-up water closed until recently when we noticed a pressure drop from 14 psig. down to 5 psig. in a matter of one week.the system heat exchanger has been replaced, we have inspected all piping, valves, coils, pumps and any other connecting components and found no leaks!! The vertical expansion tank air charging valve has been checked and no bladder problems have been found although we did recharge the tank with air to 14psig. The air seperator vent is not passing liquid and all seems to be normal. We shut down the circulator pump, pressurized the sytem with make-up water to 14psig., bled all air at are high points and restore operation only to find in approxiametly one week that out system pressure slowly drops to around 4psig., when we repeat the process to prevent pump cavatation and flow loss to our highest coils. If this is a closed looped system where is our pressure going? Please Help!!


  • jim lockard
    jim lockard Member Posts: 1,059
    I'm thinking

    Rich --That some where you have a leak. Keep looking. Best Wishes J.Lockard
  • Steamhead
    Steamhead Member Posts: 16,732
    Isolate the different parts of the system

    and pressurize them. You'll know when you have found the leaky portion.

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    EBEBRATT-Ed Member Posts: 15,344

    If you keep losing pressure you must have a leak. What is the height from lowest to highest point of the system?? Are you maintaining adequate pressure when initaly filled?

    If you can't find any leak I would suspect expansion tank problems. To check the air charge you must drain the water side of the expansion tank and keep it isolated or disconnected from the system. Check the air pressure and recharge if necessary and allow 1psi of air for every 28" of system height and then add 5psi to this figure to insure adequate pressure at the top of the loop. After determining this pressure reconnect the water side and fill to the same pressure as the air side. Install a gage in the air side if possible (but you cannot get a correct reading with the water side pressurized)

    Is it possible you have a coil leak and the water is going down the condensate drain??

    I had an apartment bldg. with a similar problem. The system kept loosing pressure and they kept adding water and no leak was found--It was the expansion tank not pressureized to the fill pressure.

    Good luck let us know what you find

  • Al Letellier
    Al Letellier Member Posts: 781
    system pressure leak

    If you have a leak and can't find it, isolate and test your heat exchangers. A small leak in the tube bundle or in one of the head gaskets could be the culprit. If your anit-freeze solution is colored in any way, it would show up in the boiler water at some point.

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  • Rich P
    Rich P Member Posts: 6
    Pressure Loss

    Thanks for all the good advice. My problem is the original installers did not put in an isolation valve between the expansion tank and the system. Is there an alternate method to recharging the tank without draining the water side. I'm looking for a short cut here. I can assure you there are no leaks! I reinspected all coils, the heat exchanger and all piping. If there is no alternate method I'll have to schedule a shut down and cut one in.

    As a newcomer to the wall I just have a few questions: 1st- How many problems can you post before you become a pain in the a...
    2nd- It seems that this site is more geared toward residential instead of commercial-industrial, is that correct?
    3rd- Who fields these questions and when do I get to talk to the Big Kahuna himself Dan?? Thanks for all your help!!
    EBEBRATT-Ed Member Posts: 15,344


    If you didn't find any leaks then the problem is almost surely expansion tank related. There is no alternative to draining and installing a valve.

    We had an apartment building that drove the customer crazy with the same type of problem. They were convinced they had a leak and even went to the expence of digging up underground piping. Isolating the expansion tank and pressurizing the air to the correct value solved their problem. They needed to run 40psi on their system do to the height of the building. The original installer installed the tank and left pressurized at 15 psi

    I don't know what pressure you need because I don't know your building height. But on this job 25 psi (40-15) made a hudge difference in the way the system operated.

    If you need more than 15 psi and they didn't think to install a valve it is certain that they didn't increase the tank pressure.

    Good luck,
  • Ben_5
    Ben_5 Member Posts: 1

    What is the formula to calculate the BTU's to heat
    a home with a hydronic system.Considering room size,
    windows, doors, and outside insulated walls.
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