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  1. #1
    Join Date
    Apr 2005
    Posts
    21

    Equipment Sizing for Geothermal

    I recently solicited proposals for a geothermal system for my new home. I provided the house plans and other needed information so that both installers could run J calcualtions. There is nothing unique about the home design...ranch with a walk-out lower level, 3 bedrooms and about 3,200 sq.ft Both companies are well established, reputable players in the local HVAC marketplace. One quoted a 3 ton Waterfurnace system and the other a 5 ton Carrier system.

    With the sophisticated tools available today and considering how long contractors have been doing these calculations, for the life of me I can't understand how the results can vary so much. I hate to think that I should be hiring a consultant to give me an unbiased and (hopefully) accurate analysis for what would seem to be a simple project.

    Any tips on how to evaluate which installer's sizing I should trust, if either one?

  2. #2
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,170
    Tell them what the other said and see what the response is. I usually think the lower bid is more accurate. Dealers aren't going to take a chance and undersize. They usually oversize since you won't know the difference unless you have humidity issues. New contruction you ought to put some money into a tight home, maybe some foam insulation, etc. Will save on the juice bill for decades to come.

  3. #3
    Join Date
    Apr 2005
    Posts
    21
    Point well taken. On the other hand, could it be that the installer proposing the 3 ton unit is doing so to get his quoted price down?

    Construction will be 2x6 walls with dense pack cellulose (Nuwool).

  4. #4
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,287
    Quote Originally Posted by batman71 View Post
    I recently solicited proposals for a geothermal system for my new home. I provided the house plans and other needed information so that both installers could run J calcualtions. There is nothing unique about the home design...ranch with a walk-out lower level, 3 bedrooms and about 3,200 sq.ft

    hiring a consultant to give me an unbiased and (hopefully) accurate analysis for what would seem to be a simple project.
    What is the heating load?
    ++++++ Cooling Load?

    Walk-out lower level is somewhat unique. One certainly does not see them Everyday.

    Is the 3,200 square feet .. 1,600 sq feet on each level?
    How much of the lower level is exposed to the outside air?
    What is the r-value of the wall (provide type of wall and insulation) that is exposed to the outside air?

    Is the ceiling insulation foam or blown in / amount?

    How much windows surface area faces in each direction? U and SHGC values?

    Location ? Mexico - U.S. - Canada or Europe?
    Load depends on the state and city.
    i.e. Northern CA and Southern CA are more than 500 miles apart and entirely different climates.

    OR
    just send me PDFs of house plans and BOM. Address in my profile.

    - THAT SIMPLE _ Project only takes about 2 to 4 hours as a Block (whole house) Load on a 2 story residence. Maybe 10 or 20 hours for the room-by-room design. One should have this completed about 3 months prior to start of construction.
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  5. #5
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,287
    Quote Originally Posted by batman71 View Post
    Point well taken. On the other hand, could it be that the installer proposing the 3 ton unit is doing so to get his quoted price down?

    Construction will be 2x6 walls with dense pack cellulose (Nuwool).
    http://www.nuwool.com/Products/Cellu...gySavings.aspx

    What is the quoted savings from NuWool?
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  6. #6
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,074
    1 may be sizing to the cooling load, while the other is sizing to the heating load.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  7. #7
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    Location makes a big difference. Sometimes you need to size Geothermal for heating and either sacrifice humidity control in summer, or look into a while house dehumidifier.

    Ideally geothermal targeted water source heat pumps would recognize this issue and integrate hot as reheat coils in their units for humidity control and even start offering larger standard units like 6 and 7.5 tons for the residential market.

    Pretty common for a geothermal home to be a big cool & clammy in the summer due to poor humidity control.

  8. #8
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    Quote Originally Posted by dan sw fl View Post
    http://www.nuwool.com/Products/Cellu...gySavings.aspx

    What is the quoted savings from NuWool?
    My own personal opinoin, I hate cellulose. To many potential issues with moisture. Being dense pack, it might not settle so much, but it will settle some eventually. I don't like fiberglass because it's R value drops off fast if the structure isn't air tight. Foam or even ICF walls structures are the way to go. Just my biased opinion.

  9. #9
    Join Date
    Jul 2004
    Location
    Massachusetts
    Posts
    6,837
    We've done a lot of geo systems and always size for heating at 98% factor. That is, the coldest weather 98% of the time. The bottom 2% is short term and can be handled with aux heating. That said, we always install either multiple 1-stage systems or 2-stage units to help accommodate the difference between winter heating and summer cooling. Cooling is generally about 50% of heating in our area. Now our prayers have been answer with modulating compressors. ClimateMaster now has a modulating unit and I'm sure others do or will shortly. With modulation, you can size for heating and easily accommodate all the cooling needs with good humidity control as well. I suspect 3-tons is the cooling load and 5-tons is the heating load, as stated by beenthere. As such, I'd go with the 5-ton systems, 2-stage or modulating. If you go 3-tons with a 5-ton heating load, you'll be paying a lot more for heat with the aux electric heaters. That's generally not the preference for geo systems.
    If YOU want change, YOU have to first change.

    If you are waiting for the 'other guy' to change first, just remember, you're the 'other guy's' other guy. To continue to expect real change when you keep acting the same way as always, is folly. Won't happen. Real change will only happen when a majority of the people change the way they vote!

  10. #10
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,287
    Quote Originally Posted by motoguy128 View Post
    Ideally geothermal targeted water source heat pumps would ... .. and even start offering larger standard units like 6 and 7.5 tons for the residential market.
    I F a residence actually needed > 5 tons, it ALSO REQUIRES 2 Units simply due to Air Distribution / Ducting issues.
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  11. #11
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    Quote Originally Posted by dan sw fl View Post
    I F a residence actually needed > 5 tons, it ALSO REQUIRES 2 Units simply due to Air Distribution / Ducting issues.
    In the north, a 80k BTU furnace is pretty common, that's 6.5 ton of heating if you don't want heat strips coming on. That size home won't be unusually large. We have plenty of 7.5 and 10 ton water source commercial units at my work. Why not in residential. With the increased efficiencies on the newer units, you should still be able to get up to 7.5 ton with a 230VAC single phase system. You could also do 2 or 3 stage with 2 compressors.

  12. #12
    Join Date
    Feb 2009
    Location
    Portland OR
    Posts
    1,991
    Quote Originally Posted by skippedover View Post
    Now our prayers have been answer with modulating compressors. ClimateMaster now has a modulating unit and I'm sure others do or will shortly. With modulation, you can size for heating and easily accommodate all the cooling needs with good humidity control as well.
    Try and buy the tranquility 40, they are over a year away from actual ship date from everything I have heard. If you want a modulating system get a WaterFurnace 7 series the ONLY modulating geothermal system available to buy today(I bought one Friday and put it in this Thursday) and the most efficient at 41EER and up to 6COP at 50% load. If you are in Portland call me and I can quote a system being the areas only geopro dealer.

    Another design consideration is BTU capacity and actual not rated EWT. Most geothermal systems are rated for at most 36,000 BTUS(assuming 3 ton) if EWT is 50+ yet actual loop temps can get into the 35 degree range providing only 29,000 BTUs, some will account for this with a larger unit and others just don't understand actual vs rated capacity.
    Check out my YouTube channel - http://www.youtube.com/user/skyheating1 We have customer testimonials, product reviews and more!
    Like us on FACEBOOK if you like our advice here!

  13. #13
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,436
    Quote Originally Posted by batman71 View Post
    I recently solicited proposals for a geothermal system for my new home. I provided the house plans and other needed information so that both installers could run J calcualtions. There is nothing unique about the home design...ranch with a walk-out lower level, 3 bedrooms and about 3,200 sq.ft Both companies are well established, reputable players in the local HVAC marketplace. One quoted a 3 ton Waterfurnace system and the other a 5 ton Carrier system.

    With the sophisticated tools available today and considering how long contractors have been doing these calculations, for the life of me I can't understand how the results can vary so much. I hate to think that I should be hiring a consultant to give me an unbiased and (hopefully) accurate analysis for what would seem to be a simple project.

    Any tips on how to evaluate which installer's sizing I should trust, if either one?

    No mention of fresh air ventilation? Climate? These are critical issues. Are you concerned about humidity control through the 4 seasons?
    Regards TB
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

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