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  1. #1
    Join Date
    Dec 2009
    Posts
    24

    Geo bids/load calculations

    Bids have been all over the place. Finally got to look at load calculations and I think I now understand. With one exception the load cals are close. How the bidders use the load cals is what is different. Some bidders are using the cooling load as a basis for equipment needs. Others are using the full heat load in order to ensure that heat strips are not used. Designing to heat load means that in cooling mode the equipment is greatly over sized. The contractor said not to worry, we will set up your equipment to run cooling only on the first stage. But I am paying for a two stage system! The folks who bid based on cooling load are sizing the unit to run well in cooling but the unit is not producing enough heat without back up. Both camps are set in their positions, "this is how we bid".
    As the consumer, buying a do all heat solution, I will find myself paying for cooling equipment I will not use, higher operating costs. One contractor said each ton more than I need will cost me about $15/month. Too small and I pay for expensive back up heat. I am about to throw in the towel and go with a seer 19 air source. Any advice?
    Thanks

  2. #2
    Join Date
    Apr 2008
    Location
    Northwest Arkansas via Chicago Area via Straight Up from There on Lake Superior
    Posts
    1,411
    Quote Originally Posted by hammerone View Post
    ...

    The contractor said not to worry, we will set up your equipment to run cooling only on the first stage. But I am paying for a two stage system!

    ...

    As the consumer, buying a do all heat solution, I will find myself paying for cooling equipment I will not use, higher operating costs. One contractor said each ton more than I need will cost me about $15/month. Too small and I pay for expensive back up heat. I am about to throw in the towel and go with a seer 19 air source. Any advice?
    Thanks
    I wouldn't let any contractor defeat the 2-stage design of my system.

    Does that $15/month extra include the extra well cost for the larger system - doubt it. I found that each ton of geo is VERY expensive. How often would the heat strips be on if you design for 80-90% of the heating load? What would it cost in your area to run them compared to that extra geo tonnage?

    Do the numbers with all tax credits and manufacturer rebates that seem rare for geo for both the geo and HP (DFHP?). What's the payback period? You going to stay for a while? I couldn't make geo work for the total amount of energy we use, but then we set heating low and cooling high so it's what uour energy life style is.

  3. #3
    Join Date
    Feb 2010
    Location
    The midwest.
    Posts
    663
    Quote Originally Posted by hammerone View Post
    Bids have been all over the place. Finally got to look at load calculations and I think I now understand. With one exception the load cals are close. How the bidders use the load cals is what is different. Some bidders are using the cooling load as a basis for equipment needs. Others are using the full heat load in order to ensure that heat strips are not used. Designing to heat load means that in cooling mode the equipment is greatly over sized. The contractor said not to worry, we will set up your equipment to run cooling only on the first stage. But I am paying for a two stage system! The folks who bid based on cooling load are sizing the unit to run well in cooling but the unit is not producing enough heat without back up. Both camps are set in their positions, "this is how we bid".
    As the consumer, buying a do all heat solution, I will find myself paying for cooling equipment I will not use, higher operating costs. One contractor said each ton more than I need will cost me about $15/month. Too small and I pay for expensive back up heat. I am about to throw in the towel and go with a seer 19 air source. Any advice?
    Thanks
    Where do you live? Another option would be to go with a "split" geothermal system. This can save a lot of money. The problem with geo (in cold climates) is sizing for the heating and thus oversizing the cooling. The 2-stage helps only if it will stage.
    The bottom line is getting someone that knows what they are doing. I have heard of some many horror stories.

  4. #4
    Join Date
    Feb 2005
    Location
    Idaho Falls, ID
    Posts
    39
    Are any of you bids for Waterfurnace? if so get them to do a design with GeoLink design studio.

  5. #5
    Join Date
    Dec 2009
    Posts
    24
    Thanks for all of your replies. The $15 a ton/month is additional operating cost due to the larger compressor/air handler. The latest bid is for 100% geo heat pump @ 5 degrees. The contractor said he has to allow for ground temp drop due to heat extraction. Said to expect ground heat to be 50 degrees @ start of heating season and down to 35 degrees by February thereby lowering efficiency of equipment. Thanks for you suggestion on Water Furnace. One bidder is a Water Furnace dealer who provided me with Load Calculation. I think I am getting good calculations problem is, they are, in my opinion over designing for heat load. Help me. Is a design for 100% geo heat @5 degree temp reasonable? No heat strips used. My baseline for geo payback calculations are two new Carrier Infinity, SEER 19 units 3T and 4T.

  6. #6
    Join Date
    Sep 2005
    Location
    Texas
    Posts
    2,793
    Quote Originally Posted by hammerone View Post
    Bids have been all over the place. Finally got to look at load calculations and I think I now understand. With one exception the load cals are close. How the bidders use the load cals is what is different. Some bidders are using the cooling load as a basis for equipment needs. Others are using the full heat load in order to ensure that heat strips are not used. Designing to heat load means that in cooling mode the equipment is greatly over sized. The contractor said not to worry, we will set up your equipment to run cooling only on the first stage. But I am paying for a two stage system! The folks who bid based on cooling load are sizing the unit to run well in cooling but the unit is not producing enough heat without back up. Both camps are set in their positions, "this is how we bid".
    As the consumer, buying a do all heat solution, I will find myself paying for cooling equipment I will not use, higher operating costs. One contractor said each ton more than I need will cost me about $15/month. Too small and I pay for expensive back up heat. I am about to throw in the towel and go with a seer 19 air source. Any advice?
    Thanks
    the equipment has to be sized for the larger of the two loads. heat loss is typically larger than heat gain

  7. #7
    Join Date
    Feb 2010
    Location
    The midwest.
    Posts
    663
    Quote Originally Posted by hammerone View Post
    Thanks for all of your replies. The $15 a ton/month is additional operating cost due to the larger compressor/air handler. The latest bid is for 100% geo heat pump @ 5 degrees. The contractor said he has to allow for ground temp drop due to heat extraction. Said to expect ground heat to be 50 degrees @ start of heating season and down to 35 degrees by February thereby lowering efficiency of equipment. Thanks for you suggestion on Water Furnace. One bidder is a Water Furnace dealer who provided me with Load Calculation. I think I am getting good calculations problem is, they are, in my opinion over designing for heat load. Help me. Is a design for 100% geo heat @5 degree temp reasonable? No heat strips used. My baseline for geo payback calculations are two new Carrier Infinity, SEER 19 units 3T and 4T.
    Remember with air source heat pumps, they work efficiently to about 30 degrees.
    Then you'll be on back-up heat.
    There is more to geothermal than just a direct pay back. Geo adds greatly to the resale of the home.
    Not to mention the possibility of the Obama skunks taxing us for our carbon footprint in the future.

  8. #8
    Join Date
    Jan 2002
    Location
    East Grand Forks, MN
    Posts
    1,373

    Right way

    Quote Originally Posted by hammerone View Post
    Bids have been all over the place. Finally got to look at load calculations and I think I now understand. With one exception the load cals are close. How the bidders use the load cals is what is different. Some bidders are using the cooling load as a basis for equipment needs. Others are using the full heat load in order to ensure that heat strips are not used.
    Sizing any equipment is by the cooling load, no matter what!


    Designing to heat load means that in cooling mode the equipment is greatly over sized. The contractor said not to worry, we will set up your equipment to run cooling only on the first stage.
    It is better to size a two stage unit with a 5% or more of operation of the second stage compressor. So it's okay to size a system with the one stage compressor running the majority of the time.


    But I am paying for a two stage system! The folks who bid based on cooling load are sizing the unit to run well in cooling but the unit is not producing enough heat without back up.
    I sized the system so that the supplement heat will not operate more than 10% for the season!


    Both camps are set in their positions, "this is how we bid".
    As the consumer, buying a do all heat solution, I will find myself paying for cooling equipment I will not use, higher operating costs.
    This is not true concerning higher operating cost compared to other types of systems. Geo systems always came out lower than any other type of systems, sometimes not much lower but still lower.


    One contractor said each ton more than I need will cost me about $15/month. Too small and I pay for expensive back up heat. I am about to throw in the towel and go with a seer 19 air source. Any advice?
    Thanks
    Get a quality proposal with numbers to back up their claims: operating cost etc..
    Perhaps maybe you should talked to some of their clients with Geo and ask how their equipment are operating; are their operating cost reasonable??

  9. #9
    Join Date
    Feb 2005
    Location
    Idaho Falls, ID
    Posts
    39
    Hammerone
    Your WaterFurnace dealer should be able to take the load calcs and use them in the GeoLink design studio along with all other information specific to your project. Then they can print out reports showing the economics, & proformance of each of the different size of unit's.

  10. #10
    Join Date
    Dec 2009
    Posts
    24
    Thanks for all of your replies. Finally got closure on this. Lost a bidder in the process. Solved by adding more insulation to the basement walls. Thanks again.

  11. #11
    Join Date
    Feb 2002
    Posts
    516
    Quote Originally Posted by air2spare View Post
    the equipment has to be sized for the larger of the two loads. heat loss is typically larger than heat gain
    NO, NO, NO!!!!!! Especially here in the humid South, and especially with single stage compressors. If the equipment (HP) is sized for the heat load, then the cooling is grossly oversized. You will be able to pull the indoor temperature down, and in a short time, when the ambient temperatures are less than ASHRAE design temps. However, the indoor comfort (and that's what our customers are buying) will suffer because the cooling system will not run long enough to pull the indoor humidity down to a comfortable range-normally 45-50% RH. Also, the oversized system won't run very much, ie; the run cycles will be short. Therefore the indoor temperatures are on a roller coaster. One can slightly oversize with a two stage compressor system using a variable speed indoor blower and a thermostat that has a dehumidifying control feature. But this can also cause condensation problems with the ductwork located in the humid attic.

  12. #12
    Join Date
    Jun 2006
    Location
    Republic
    Posts
    16
    In cold climates, size the unit for heating, some of the extreme weather may require heat strips, but the overall cost and efficiency will be better.

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