Need Info on sizing the loop system and pump

Discussion in 'General Discussions' started by Mr. Buzzard, Apr 16, 2018.

  1. Mr. Buzzard

    Mr. Buzzard New Member

    I am installing two 1.5 ton heat pumps in our home with the coils in a pond. If I am reading correctly each needs 900 feet of coil. The pumps are plumbed for half inch pipe. I need someone with more knowledge than I to advise me on the size and length of the pipe for the coil and the pump or pumps.
    Again if I am correct they will seldom if ever run at the same time. One in the basement, the other on the main floor.

    Thanks
    Averett
     
  2. nc73

    nc73 Member

    Not sure where you got your info but it's more like 2 coils of 300ft for each, so 600 total (2 coils each to provide turbulence for better heat extraction). 900 total shouldn't hurt. Heat pumps, if sized properly should run for extended periods, short cycles are bad. So yes there is a good chance that both will run at the same time. Some will tell you that you need a pro, blah blah. It's a good idea if you have the cash. You'll do fine on your own, but in your case you need to do more research.

     
  3. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader

    This forum is pretty good at not telling people they need a pro. But then you get the free information and the responding value just provided in some cases. This draws us out. Cunningham's Law.
     
    ChrisJ likes this.
  4. Mr. Buzzard

    Mr. Buzzard New Member

    Thanks for the advice. I am researching. This is just part of the research. I am in the newspaper industry and already know you can prove absolutely anything on the internet. I also know many forums like this are self correcting. If someone gives incorrect advice someone else will comment. I could spend weeks learning how to calculate what I need but since I will only be doing this once it seems unnecessary when there are people who already know. I put in a passive geo-thermal in the 1970's and it worked great for what I wanted which was keeping my shop above freezing and below 80 degrees. It lasted almost 40 years.
    Is there a chart to size coils? I know I over built way back then but everything I used was free.
    Thanks
    Buzzard.
     
  5. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    Your post is confusing: 2 coils of 300ft for each heat pump? 600ft total for both heat pumps? Or 900 total for both heat pumps because it does not hurt?

    "....but it's more like 2 coils of 300ft for each."
    Or is it now 2 coils of 300ft for each heat pump, for 1,200 ft total for both heat pumps?

    What size diameter of coils? How deep is the pond? how large is the pond? Is the pipe spread out or coiled up?
     
  6. Mr. Buzzard

    Mr. Buzzard New Member

    Thanks for the response. I was confused by that response also. Here is my situation. I have two 1.5 ton units. I plan to put one on each floor. My pond is an acre with about half at 8-12 feet deep and is 200 feet from the house. I don't think it matters but the house is 12 feet higher than the pond. According to the math I only need 1.5 tons total but got a great deal on the units. Since the house is a basement and two floors I was going to put one up and one down. I've done this before with an open system and have no idea how to size the coils.
    I need to know what I need in the way of coils, size and length and configuration.
    Thanks for the help.
    Buzzard
     
  7. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    You are looking at about 9 gpm when both units are running. Yes, they will run simultaneously, which is what you have to account for. 4 circuits (loops) at 400 ft length each with 3/4" SDR 11 pipe should cover you for all occasions. Use methanol for antifreeze, 15% by weight. Let us know if you use anything else.

    Use 1.25" for your pipe to and from the pond, I would assume 250' total to the middle of the pond where it is 8-12' deep. Elevation difference between pond and house does not matter in a closed system. Total pressure drop for the loop is 16.8ft/hd, so you should get by with a single small variable speed pump.
     
  8. Mr. Buzzard

    Mr. Buzzard New Member

    Thanks. I was also wondering if I should take advantage of the 100 feet between the pond and house. Since I will have to bury the lines anyway, I can easily dig a 3' wide 6 foot deep ditch for the 100 feet and put coils in it. I could put a coil on each side for a total of 600 feet of coil with the rest in the pond. What do you think?
    Thanks
    Buzzard
     
  9. moey

    moey Member

    The ground is colder then the pond it would not make much sense.
     
  10. ChrisJ

    ChrisJ Active Member Forum Leader

    To get the low pressure drop that Doc says, you need to run the large diameter pipe out to the loop field.

    At the four 3/4" loops you set up a 2 part manifold, 1 for supply of brine and 1 for return of brine.
     
  11. Mr. Buzzard

    Mr. Buzzard New Member

    Thanks Chris.
    So what Doc was saying is run the 1.25 to the pond. Then split it to each of the four coils and return it in an 1.25
    Thanks
     
  12. ChrisJ

    ChrisJ Active Member Forum Leader

    If you do some research using the term "reverse return header" you will see what we are talking about.
     
  13. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader

    No. The ground is colder than the pond in summer (good thing) and warmer than the pond in winter (good thing).
     
  14. moey

    moey Member

    Yea thats true thanks. I forget some folks actually use the A/C. Too cold where I live our A/C is on for a couple days a year.
     

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