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  1. #1
    Join Date
    Aug 2012
    Location
    Central Virginia
    Posts
    43

    Sizing water source system to replace aging 4 ton + 1.5 ton system

    Greetings!

    I have been reading a lot here and finally took the plunge to register. Great forum with a wealth of information!

    My house was built in 1997 and still has the original primary HVAC system which consists of a Trane 4 ton XE1000 10 SEER outdoor unit coupled with a Trane XE90 120,000 BTU (5ton) LP fired furnace, which supposedly has a 90+ AFUE rating.

    In 2002 I added a Carrier 38TKB 1.5 ton system to the 2nd floor with an attic mounted air handler with a 5kw electric heating element. 2nd floor had electric baseboard hear and window mounted AC units when I purchased the house in 1999 as the 2nd owner.

    Today the 2nd floor is not being used much except for when guests are in town, but I have 2 daughters (16 months a 1 week old), that will take over the upstairs when they get older. So I envision a future with lots of hot water, heat and cooling consumption from upstairs...

    Without even running the upstairs system, my monthly electric bill hits $500/month during the hot July and August months, compared to less than half that during the winter month. On the other hand, I burn through about 800 gallons of propane annually and at $2.85/gal currently, that works out to about $2,280 per year.

    I have a Polaris water heater (LP fired) and radiant floor heat in the master bath and half the basement. When I moved into the house in 2000, the basement was unfinished, so presumably the original system was not sized for it being finished.

    Here are the floor plans of my house with glass surface area, etc:

    1st floor:



    2nd floor:



    Basement:



    In total, there is 4,346 sq. ft. of conditioned living space (including the shop in the basement) and 543 sq. ft. of glass.

    I'm working with a well respected local company that is a Waterfurnace "GeoPro Master Dealer". They are working on quoting me both a 5 series and 7 series for the primary and an Envision Split system for the upstairs.

    They have already given me the recommended horizontal loop specs, which are as follows:

    6 ton capacity
    900 feet of trench
    5.5 feet deep
    2.5 feet wide
    4 pipes / 2 loops in each
    Each trench 8-10 feet apart for a total loop length of 3,600 feet, which works out to 600 feet per ton

    I was thinking of doing 4 trenches 225 feet each.

    Does it look like I'm on the right track given my house size and configuration? I own a backhoe attachment for my tractor (10.5 feet digging capability and 6000lbs break out force, so not one of those small ones). I plan to do the trenching and back filling myself as well as any electrical work, but will leave the rest to the dealer.

    Would it make sense to have the 5/7 series and Envision Split system share a single loop, or should I dedicate some loops for the primary system and some for the split system? Shared would be preferred I would think as that would mean only a single circulation pump and a larger overall ground loop to supply the not always identical loads of the 2 systems.

    Does it sound like I'm on the right track?

    One last thing, the loop field slopes down from the house quite significantly, but that should not matter, as long as I maintain the 5.5 feet depth, right?

    Thanks!

  2. #2
    Join Date
    Mar 2007
    Location
    Cedar Rapids, Iowa
    Posts
    119
    Two systems on a single loop should have their own pumps. They should be piped as shown, this will insure proper flow through the units without short cucling between them.

    BergyName:  Dual Heat Pump Deadhead Layout.jpg
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  3. #3
    Join Date
    Aug 2012
    Location
    Central Virginia
    Posts
    43
    Thanks Bergy! It will be interesting to see if that is also the design they recommend.

    Peter

  4. #4
    Join Date
    Aug 2012
    Location
    Central Virginia
    Posts
    43
    I looked at the GIS map of my house and drew in the loop trenches (in blue). There are a couple of obstacles. In yellow is the water line to the shop, and in red are the 400A power lines to the house and shop. I think I can just miss the water and house power lines, but there is no way to avoid crossing the power lines to the shop. I'll have miss utility come out and mark the power lines.



    And here's an actual shot of the area:



    As you can see, I'm already in the process of clearing out the pines although I have been just using a stump grinder to get rid of the stumps. I guess I'll have fun digging up the complete stumps where the trenches are going to be.

    I wonder if there will be any code issues with running the loops underneath power lines?

  5. #5
    Join Date
    Aug 2012
    Location
    Central Virginia
    Posts
    43
    Hmm, how many posts are needed before you can edit your own posts?

    Anyway, based on my measurements, it makes the most sense for me to do 5 180ft trenches, which is what I'm showing above, and the lay down 2 loops in each, for the 3,600 total loop length.

  6. #6
    Join Date
    Aug 2012
    Location
    Central Virginia
    Posts
    43
    I forgot to mention that I pay just over $0.11 per KWh. My consumption last month was 4473KWh. Here's my consumption over the last 12 months (Ignore October, they must have had a glitch in their system).


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