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  1. #1
    Join Date
    Jun 2008
    Posts
    47

    Geothermal: Vertical Loop sizing in SE Pa

    I'm in the process of getting quotes for a geothermal install and as usual, there are as many ideas as possibilities. A couple questions have come up that I'd like some opinions on from anyone in the SE Pa (Philadelphia area)...

    A heat load analysis shows that I need around 10 Tons capacity (1 5-ton and 2 2.5 ton) units.

    1. I was told a total of 1500 feet if vertical bore? Does this sound correct? Similarly, 6900 ft if horizontal.....

    2. in doing this, is it best to have each unit with separate feeds from the ground loops into the house? For example, three pairs of incoming lines (one for each unit)?

    3. is there any value to having extra vertical bores? Does this impact the water pump requirements?

    My expectation is that our load calcs area assuming that we want to not-require our backup/emergency oil heat..... is that a reasonable expectation for this area?

  2. #2
    Join Date
    Nov 2007
    Posts
    86
    1500ft of borehole should be sufficient, although that may be the minimum requirement.
    That works out to 150ft per ton. Be sure that this is enough to reject the heat from the envelope during peak cooling, if not, you may not be comfortable during the hottest, most humid days of the summer. If your ground heat exchanger is not large enough for the very coldest days, your backup may come on a bit more than otherwise. That may be no big deal – but if you’re uncomfortable during a heat wave – that is a big deal! You probably require a larger ground heat exchanger for cooling than for heating.

    I would prefer 3 separate systems, 1-150 foot borehole per ton (minimum); in a parallel configuration using reverse return headers.

    Just like the heat load calcs for the house, the numbers have to be run for the ground heat exchanger to be sure you’ll be getting what’s being promised. It’s only simple when it’s designed, installed & all running properly. To get there someone has to know what they’re dong!

    I’d loose the oil heating system and go for electric plenum resistance heaters. It’s cleaner, safer, more eco-friendly, price stable and you’ll gain more space in your mechanical room; getting rid of that oil tank – now that’s priceless (Especially when it’s time to cash out. Who wants an oil system anyway?).



    IMO

    SR

  3. #3
    Join Date
    Apr 2005
    Location
    NE PA
    Posts
    698
    I would agree that 1500' seems about right. However this needs to be done in multiple holes. The next big factor your installer will do is calculate the pressure drops and associated line sizes. There are multiple combinations that will work. You may end up with 5 holes with 1" line, all in parallel. In general drilling is by the foot and whatever the combination, the cost will be about the same.

    paul

  4. #4
    Join Date
    Feb 2007
    Location
    out in the country
    Posts
    633
    I'm not an expert on sizing loops by any means. But I believe the number of feet of bore hole depends on the diameter of the pipe they use in the hole.


    When we installed them we always oversized our loops, the aux. strips never ran as aux. only as emergency. In the summer loop temps remain lower. And winter loop temps remain higher. Loop capacity is always important.


    If you have seperate feeds coming into the house each with its own pump, one for each system, then one pump or loop has an issue you will still have heat/cool in the rest if your house and you may have spent more money but you will be happy because you have heat/cool. However if you have one large loop and one large pump, you may spend less on the install, but if the pump or loop fails you have no cool/heat until the repairs are made.
    I never let schooling interfere with my education... Mark Twain

  5. #5
    Join Date
    Jun 2008
    Posts
    47
    thanks.

    Looks like 8 or 9 bore holes, 1500 feet total line, but separated for each unit coming into the basement. They will likely feed Climatemaster Tranquility 27 units. It sounds like I need to just make sure that we have enough capacity in the loop for heat, as I would prefer a solution for our area that allows me to stay away from the emergency/backup.

  6. #6
    Join Date
    Jan 2008
    Posts
    16

    150 Holes

    We do a fair amount of geothermal in the Greater Cincinnati area. We use one 150' hole per ton of air conditioning. I would definately put a 10 KW heater in for back up. Remember the units are sized on the heating load vs. the cooling. If you used a 2 stage variable speed unit humidity removal should not be a problem. Good luck

  7. #7
    Join Date
    Mar 2003
    Location
    PA/DE area
    Posts
    1,535
    We do alot of GEO in SE and size loop pipe via GIZMO and try to stay off back up for less then 200 hours.Where do you live in PA?
    It's NOT the BRAND,it's the company that installs it!!!!!

  8. #8
    Join Date
    Jun 2008
    Posts
    47
    Near Quakertown

  9. #9
    Join Date
    Mar 2003
    Location
    PA/DE area
    Posts
    1,535
    Alittle far from us,we handle CHESCO,DELCO and New Castle County DE.We are also 150ft per ton in our neck of PA.We install FHP and Water Furnace.
    It's NOT the BRAND,it's the company that installs it!!!!!

  10. #10

    Loop Sizing

    Just doing some calculations of my own - can't run any of the loop sizing software `cause I am using a mac... however, am I understanding correctly that using a larger diameter pipe in the vertical loop will decrease the necessary depth of the well? For instance, living up here in Canada, they were telling me to drill 200' per ton, using 3/4" tubing.... if I go bigger, say to 1.5" pipe, would that be better? Thanks all.

  11. #11
    Join Date
    Jun 2008
    Posts
    47
    I'm waiting for our installer (who is depending pretty heavily on ClimateMaster) for the final design, but from what I understand, approx 1500 feet for ten tons will be used here. they are planning 3 loops (1 5-ton, 2 2.5 ton) using 1" piping.... approx 150ft vertical bore per ton.

    We are in SE Pa and in approx 6000 sqft. Currently have oil backup on older air-to-air system.... moving to geothermal to avoid oil as much as possible. Once I get the final heat load and design recommendations for our install, I'll post for comment.

  12. #12
    Join Date
    Mar 2003
    Location
    PA/DE area
    Posts
    1,535
    ask for loop design print out.
    It's NOT the BRAND,it's the company that installs it!!!!!

  13. #13

    Also in SE PA

    I am just starting to investigate geothermal options for my existing home. Current system is heat pump which is over 25 yrs old... it is HORRIBLE.

    I would love some recommendations on the contractors you are dealing with.

    Thanks!
    InSearchOf... answers

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