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  1. #1
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    May 2017
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    What is an acceptable backpressure on the return well line for open system?

    The system is a Bosh 3 ton residential HVAC.. either its undersized or a little low on efficiency as it does well below 90% out side.. then wont hold the temp below 80... so question is what is an acceptable back pressure on the well return water line... and if its excessive can that cause lower return water and lower the efficiency...
    Also does anyone have any other ideas on how to measure water flow thru the system.. i have use the catch it in a 5 gal bucket and time it.. but of couse that will not be that accurate unless i know what the back pressure is and make sure the water into the bucket has to exceed the backpressure currently in place.. else the free flowing water with no backpressure will be more than the flow that would be passing when it working against backpressure...
    The only other method i have heard of is measuring the pressure drop across the input coil.. but that will be pretty inaccurate unless the gauges are super accurate since my guess is the difference will be only a very tiny difference..
    Thoughts, ideas, suggestions..
    1. For acceptable backpress range in return line..
    2. for good method to determine flow thru system w/o a fancy flow meter..

  2. #2
    Join Date
    Apr 2003
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    St. Louis
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    Since the pump is down in the well suction head would e determine by the difference between water level and how much further underwater it is. 2.3' per lb. so if the pump in 23 feet under = 10 lbs. If you would time a 5 gallon bucket on the return side close at the well head it should get you close. It use to be when using city water 2 gpm per ton.
    The unit what are the in and out water temps, supply return temps.

  3. #3
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    May 2017
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    Thread Starter
    Thanks for that Servicefitter..
    Just for additional information in my case the pump is not in the well.. I have a well with an above ground pump... with an operating pressusre of around 40 psi..with a backpressure of 30 psi.. and with my Train it gives a chart to compare the difference in inlet and outlet pressure and a chart to tell what the flow is but with my Bosch i have not found a chart for that..

  4. #4
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    Apr 2003
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    St. Louis
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    Whats your water temp in and out, in cooling should be around 10*, air temp across the air handle?

  5. #5
    Join Date
    May 2017
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    Thread Starter
    Quote Originally Posted by servicefitter View Post
    Whats your water temp in and out, in cooling should be around 10*, air temp across the air handle?
    Just checked it again.. 80 water temp in and 77 water temp out.. but the only way i can check is a digitial ray gun at the copper fitting of the pt ports.. but of course doing much better now since the temp rarely goes above 75 degrees now.. due to temps dropping down for winter...
    I don't have the pt port temp gages.. but the contractor had used them and said its fine.. however fine does not tell me what he read... probably means he did not want me to know since it may not be right.... LOL. but my water temp range seems ok.. I know for fact the water flow is way high.. but doubt that water temp or water flow is my problem.... want to say undesize but for my square feet and the tonnage is ballpark.. but we still have no manual reading.. so have no idea if the load is correct or if the venting is right as none of the Manual measusrements were done before install and still ahve not been done..

    Still runs about 40 inlet pressure with outlet pressure around 30 psi for 10 psi backpressure..
    but we water is set way high since all water valves are full open.. no throttling at all... Contractor and Trane still trying to resolve the issue but contractor has not been very helpful.. he says its all good.

  6. #6
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    May 2017
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    Thread Starter
    quote: If you would time a 5 gallon bucket on the return side close at the well head it should get you close. /quote
    Just reread an earlier comment about measuring the flow with a 5 gallon bucket.. Wondering how accurate that would be since you are not considering the backpressure which can drastically lower the overall flow rate.. For example if i open the line as it heads back to the well to see how much flow i get to fill a bucket.. of course it would be way more than it would if the return line had to overcome 35 psi of backpressure since i have just opened the line wide open into the bucket.. NO backpressure.. I suppose i could open the valve only a small amount to catch water while restricting the return at the 35psi level and be more accurate but i am sure opening the valve to fill the bucket but hold the backpressure that is sees normally will lower the flow into the bucket significantly... so not sure how accurate that would be..
    But anyway i tested that before and it gives in the ballpark of 8-9 gallons per minute.... when in fact my system needs only about 6 gpm.... and i am sure i am way over flowing since all my valves are full open.. meaning the flow is currently set the move as much water as the pump is capable of with the 35 psi backpressure... but backpressure is not the problem as i have temp dumped the return to the yard. with Zero back pressusre with no noticable change..

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