Thinking of a Geothermal system w/hydronic gas backup
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  1. #1
    Join Date
    Dec 2010
    Posts
    93

    Thinking of a Geothermal system w/hydronic gas backup

    I currently have a 3200 Sq. Ft. house with Natural Gas heat for first floor and a heat pump in the attic for second floor. House was built in 2002. HVAC is original and was never serviced by previous owners.

    Current setup: 2nd floor (1400 Sq ft) heat pump is a 13 Seer Goodman unit (2 ton) connected to a 2.5 ton attic air handler with 2 - 4.5KW strips backup. Honeywell VisionPro 8000 Thermostat.

    1st floor (1800 Sq. ft) is 92% Goodman gas furnace with 3 ton standard AC unit. Honeywell IAQ Thermostat

    Current system handles house well (comfortable, keeps up fine). House is very well insulated for Maryland. (Heat pump looses refrigerant, gas furnace had a cracked secondary combustion chamber) - looking to replace both systems .... last month 3000KW electric usage, natural gas usage not that bad (also covers fireplace, hot water heater and stove).

    My yard size (4 acres - wide open) would support a Geothermal system (horizontal system may be preferred due to cost and efficiency). Soil is clay.

    I am considering a system with one combination geothermal unit/air handler for the 1st floor (~3 ton unit in basement) and a second split system with geothermal unit in basement (~2 ton) with air handler in attic.

    For backup, I am considering a high-effeciancy gas boiler that would be zoned and connected to a hydronic coil in the basement air handler and another hydronic coil in the attic air handler.

    Another option would be to install high efficiency gas furnaces as the backup to the geothermal systems (instead of the hydronic systems).

    Looking for pros/cons of such systems.

    Our local HVAC company can install any/all of these (our choice).

    Current Heat Pump system w/electric backup is sufficient but expensive to run during December through February with the temps here in Maryland.

    Thanks in advance for suggestions/ideas.

  2. #2
    Join Date
    Jul 2004
    Location
    Massachusetts
    Posts
    6,829
    If your local company is prepared to install any of the systems, I'm a little surprised that you on this site asking for input. It would seem that your installing contractor could more accurately answer your questions. But since you are here, I've attached a couple of more expansive documents to help you get started on the project.

    Selecting the right company is of paramount importance. The company you select should be capable of both sizing, installing, maintaining and servicing all aspects of your system. Absent a company with all that capability comes the inevitable finger pointing when something doesn't work properly.

    There are no real negatives to the type of system you've proposed from my perspective. The type of earth coupling selected should be judged on scene by the soil type. Cost of installation will, of course, depend on the type of coupling installed. In our area we're blessed with enough water to be able to do standing column wells. While not the least expensive installation, they are almost bulletproof in designing them and they're good for life as long as they're to the proper depth. Ultimately they also extract the highest efficiencies from the equipment.

    The amount of supplemental heat you'll need will depend totally on the size of the earth coupling and the amount of heat that design will support. You can supplement with full Btu's to heat the home in the event of an equipment failure (geo equipment, that is) or you can supplement with just what's needed to pick-up where the geo is forecast to be inadequate. I recommend not trying to size to the very coldest day ever anticipated as this will lead to oversizing the equipment and giving you less than satisfactory cooling performance in the summer.

    Whether you go with warmed water in the winter and chilled water in the summer (water-to-water systems) or water-to-air conventional systems will also make a difference in the cost of the systems. So you've got a lot of decisions to make and you'll really want a knowledable company to help you with those decisions.
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  3. #3
    Join Date
    Dec 2010
    Posts
    93
    My HVAC company did not want to steer me towards any particular setup. They provided me with several options that would work with our house.

    Due to very acidic water in the area (requires an acid neutralizer), two different well drillers cautioned us against an open system due to amount of conditioning that would be required to keep a system from deteriorating.

    I ended up going with a hybrid system (3 stage gas furnace with a heat pump). Main unit was installed on Thursday (after a Manual-J and much discussion, we downsized the furnace from the previous system - went with a 3 ton air Heat Pump (same as before) but an 80K BTU 3 stage 96% furnace (versus the 100K BTU 92% single stage furnace we had). This system will be responsible for the first floor and basement (when we finish it).

    As for the top floor, our HVAC installer will be here Tuesday - we are still discussing sizing for our top floor .... that will be a gas/heat pump system as well. Our current system is barely adequate for AC and expensive to operate for heat. Natural gas solves the heat part, but the current AC unit may have been undersized .... I'll have to take another look at the Manual J and discuss with our HVAC company about adjustments to it for the Cathedral ceiling in the master bedroom/bathroom and the 3 sky lights upstairs.

    I obtained information from DOE that allowed us to enter utility rates for the area (gas and electric) to obtain cost per 1M BTUs of heat. Geothermal was cheapest to operate, but Natural Gas was within 10% of Geothermal. Fine Home Building had an article about Geothermal and basically stated that many of the efficiency numbers were a bit overstated versus what people actually were seeing with Geothermal units. I spoke with some local residents that had Geothermal systems and even though they were happy with them, they all stated that their typical energy consumption was a bit higher than predicted in the winter. Summer consumption was generally what they expected.

  4. #4
    Join Date
    Mar 2011
    Location
    Virginia
    Posts
    93
    I would also look at a Daiken Altherma system and possibly look at solar hot water heat. You can incorporate a backup boiler like Triangle tube in to the loop which would cover any needed supplemental heat requirements.

  5. #5
    Join Date
    Mar 2011
    Posts
    31

    Unhappy bad choice

    Quote Originally Posted by chloeourdog View Post
    My HVAC company did not want to steer me towards any particular setup. They provided me with several options that would work with our house.

    Due to very acidic water in the area (requires an acid neutralizer), two different well drillers cautioned us against an open system due to amount of conditioning that would be required to keep a system from deteriorating.

    I ended up going with a hybrid system (3 stage gas furnace with a heat pump). Main unit was installed on Thursday (after a Manual-J and much discussion, we downsized the furnace from the previous system - went with a 3 ton air Heat Pump (same as before) but an 80K BTU 3 stage 96% furnace (versus the 100K BTU 92% single stage furnace we had). This system will be responsible for the first floor and basement (when we finish it).

    As for the top floor, our HVAC installer will be here Tuesday - we are still discussing sizing for our top floor .... that will be a gas/heat pump system as well. Our current system is barely adequate for AC and expensive to operate for heat. Natural gas solves the heat part, but the current AC unit may have been undersized .... I'll have to take another look at the Manual J and discuss with our HVAC company about adjustments to it for the Cathedral ceiling in the master bedroom/bathroom and the 3 sky lights upstairs.

    I obtained information from DOE that allowed us to enter utility rates for the area (gas and electric) to obtain cost per 1M BTUs of heat. Geothermal was cheapest to operate, but Natural Gas was within 10% of Geothermal. Fine Home Building had an article about Geothermal and basically stated that many of the efficiency numbers were a bit overstated versus what people actually were seeing with Geothermal units. I spoke with some local residents that had Geothermal systems and even though they were happy with them, they all stated that their typical energy consumption was a bit higher than predicted in the winter. Summer consumption was generally what they expected.
    Should have gone with a 6 ton Waterfurnace and whistled all the way to the bank.
    My utility costs are 75%cheaper with geo vs. natural gas.

  6. #6
    Join Date
    Dec 2011
    Location
    USA
    Posts
    66
    You have air heat now and going to hydronic is very expensive, but very comfortable. It can be done just order the geo without the electric backup and put a relay in to bring on the boiler. I would rather see you size it correctly and the backup will very rarely run.

  7. #7
    Join Date
    Jan 2013
    Location
    Henry county,ky
    Posts
    81
    Here's another twist, or option. Use a instantaneous water heater piped to a water coil for backup heat. Not only would you heat with hot water, you could also heat you domestic water and use your current water heater as a storage tank for hot water. Get a geo unit with a desuperheater and have it hooked into the tank as well. The system I piped like this works very well.

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