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Geothermal Heat Pump Systems

Discussion in 'Environmental Discussion' started by iplug, Aug 2, 2015.

  1. iplug

    iplug Senior Member

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    Many here have solar, so wanted to discuss another potential home energy/efficiency improvement: geothermal heat pump systems.

    In terms of cost and environmental benefits, thoughts?

    Here’s my situation. We live in the greater Sacramento area on PG&E (high electricity rates, but mitigated by solar). We have hot dry summers and mild winters where daytime highs rarely drop below freezing. For heating, we have a natural gas furnace. Our AC system is 13 years old and therefore there is a good chance it will need to be replaced within the next few years.

    One thing to consider is the 30% federal tax credit set to expire at the end of next year. Another is that because dirty electricity sources are a part of the grid, the system may not necessarily be “greener” than what it replaces. This problem is worse in some regions than others. But States like California are among the cleanest and both California and the nation will continue to get cleaner over the years (apparently the White House is to release more aggressive targets tomorrow).

    Anyone who has converted to a geothermal heat pump system and can discuss kWh, system and electricity costs, etc. would be especially helpful.
     
  2. bwilson4web

    bwilson4web BMW i3 and Model 3

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    When I looked at it about 5 years ago, the problem was the two wells: one to source and the other to sink. The cost was >> the expected savings.

    In California, you may have water table issues.

    Regardless, GOOD LUCK!
    Bob Wilson
     
  3. Trollbait

    Trollbait It's a D&D thing

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    Instead of wells, it can be done with a trench, but that will tear up the entire yard. Which I imagine might be too small in California.
     
  4. bwilson4web

    bwilson4web BMW i3 and Model 3

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    I my case, we have two large trees providing shade in the afternoon. I'd rather have the trees than tear up their roots.

    I had considered using the pool as the heat sink . . . still do.

    Bob Wilson
     
  5. iplug

    iplug Senior Member

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    Yes, we're on 1/3 of an acre (larger lot compared to the average suburban Californian lot), but still would have to go with the more expensive vertical well system (as opposed to horizontal).

    With heating the average U.S. home producing roughly the same amount of CO2 as cooling it, would be nice to diminish this carbon footprint after one installs more affordable PV solar.


    Natural gas is significantly more affordable than electricity here, so it would likely take many years to recover the initial costs, if ever.
     
  6. bwilson4web

    bwilson4web BMW i3 and Model 3

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    I'm replacing our 20 year old, pilot lit, gas furnace with a high efficiency unit in the Fall. Already had the first estimator out and just going with electronic ignition will be a blessing. But I'm also having them take out the old evaporator that is probably matted with 20 years of crud. It will initially be a heat-only system.

    For the house, I'm using self-constructed, zone using portable A/C units. They are small enough, affordable, and only cool the spaces I want cooled. But in the Fall, I'll have a couple of permanent, zone units put in. If we still have any money left, I may go back and put in a small, footprint heat-pump above the new gas heater. But this time it will have cleaning ports.

    I'm OK with a heat-pump to take out humidity and handle light duty HVAC chores as long as I have the option of using electricity or gas. But I am NOT going to get back on that central air conditioning monopoly ever again.

    Bob Wilson
     
  7. Trollbait

    Trollbait It's a D&D thing

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    And you would have a heated pool outside of winter. win win:D
    Southern California isn't the average US home. I'd say most of your energy use is going towards cooling. A high efficiency AC unit, or even air source heat pump could give you most of the gains of geothermal for lower cost. You could even go with a heat pump water heater(or heat the water off the HVAC heat pump) if that is now natural gas. If it is time for some interior redesign, a wood pellet stove could reduce your natural gas use for heating.
    How much more affordable? The 30% tax credit also applies to residential fuel cells. These reform natural gas for fuel, but a cogen unit that provides heat and hot water can be over 90%, maybe 95%, efficient. For electric alone, they are much better than the most power plants using natural gas, and even better than the latest CCGT ones.
     
  8. drysider

    drysider Active Member

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    Actually, in winter you would have a cold pool of water. It would, however, be hot in the summer.

    You can get systems that use a single well with a heat exchanger under the water line. There are some environmental issues you will have to work out, though.
     
  9. iplug

    iplug Senior Member

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    We're in Northern California, but still our balance is tipped significantly more towards heating, probably ~3:1 heating:cooling energy used. However, natural gas is so cheap that it still costs less for us to heat than cool the house. From a purely cost opportunity standpoint, you are probably right that an air source heat pump is more cost effective than a geothermal one.

    We spent $625 on natural gas in the last 12 months after all taxes and fees. That comes out to only $0.047/kWh. On the standard rate plan here without solar, the neighbors pay about $0.20-0.30 per kWh for electricity. On our solar rate plan, were are currently net zero, and generate more peak than non-peak electricity, so we have a long way to go with $0.00-0.12 per kWh if we need a few thousand kWh in excess each year.

    Here are my back of the envelope energy calculations:

    Current:
    Natural Gas (furnace >> water heater + range): 454 therms last year (13,300 kWh)
    Electricity use (pool pump > AC > other): 11,500 kWh/yr

    Total: 24,800 kWh

    Geothermal Heat Pump System Predicted:
    Heating (assuming COP of ~3): 4,400 kWh
    Remaining non-heating electricity use (AC uses ~1/3 of current electricity and EER ~25): 9,600 kWh/yr
    Total: 14,000 kWh

    So in our situation we would eat the large up front costs for a geothermal heat pump system. After that, we might save a few hundred dollars yearly, but the greener impact may be more significant on the heating side.
     
  10. Trollbait

    Trollbait It's a D&D thing

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    And thus "heated outside of winter":)
    If the pool doesn't have a deep end, it might not work very well for winter heating(of the house).
    I see single digit Fahrenheit temps every winter, Northern California is still on the mild side of average;), and their are some air heat pumps that can work down to that level.
    How old, what type is your gas furnance and water heater now? If they are as old as your current AC, you can reduce your NG use with upgrades, but using them as back up to a heat pump, the current ones will use less to begin with.
    If geothermal isn't going to be a financial burden, and you are net zero with PVs, I'd go with it.
     
  11. wjtracy

    wjtracy Senior Member

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    If you Google hydrogen house you get a guy in NJ who was on 60-minutes he did the geothermal might have some figure$
     
  12. iplug

    iplug Senior Member

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    I requested a local contractor give us an estimate. Our central AC (EER ~13-14), central natural gas furnace (efficiency ~95%?), and natural gas water heater are all 13 years old (house built in 2002).

    Worst case scenario, we could replace the AC with a dual fuel air heat pump for not too much more than replacing with a newer AC unit. The dual fuel heat air heat pump could be augmented by the existing natural gas furnace if needed for lower temps and as you mentioned capture the "waste" extra hot water to the existing gas water heater or to a supplemental hot water holding tank during the summer.
     
  13. iplug

    iplug Senior Member

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    Saw one of the videos someone posted on another thread, impressive setup. There are probably some specific figures posted elsewhere, good point.
     
  14. wjtracy

    wjtracy Senior Member

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    Amazing how cheap the nat gas is by your calcs, and normally residential customers pay at least 4x to 5x the cost at the well. Residential customers unfortunately do not get a chance to participate fully in the low price of nat gas because the utilities add on a whole lot for their overhead and maintenance.
     
  15. Trollbait

    Trollbait It's a D&D thing

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    These are probably the most basic type then; the builder isn't going to spend more unless forced.

    A basic gas water heater has the chimney going up through the the center of the tank. This transfers more heat to the water than having it out side of the tank like a pot on the stove. Then there is the blower type. The chimney has baffles or coils to extend the time it spends surrounded by the water tank. So more heat transfer to the water, but the exhaust gases need heat to rise up and out. They've now lost enough that they start slowing down, and so a blower is on top of the tank to suck them out. Condensing types go a step further in their chimney coiling. The exhaust gases lose enough heat to the water tank that the combustion water vapor condenses out in the pipes.

    The condensing types are in the 98+% efficiency range. They used to be pricy to install, not because of the unit's additional cost, but because the basic steel pipes for the exhaust can't stand up to the extra moisture. So they used stainless, but newer units can use PVC now.

    Whatever you do that involves keeping the water heater tank, be sure to check the sacrificial anodes in the tank. They are just magnesium, or another metal I can't recall, rods. Their entire existence is to corrode away. By doing so, any exposed steel of the tank doesn't rust, and then leak instead. Replace the anodes regularly, and the tank will last virtually forever. The longer warrantied tanks just have more or thicker anodes, and perhaps more insulation.
     
  16. austingreen

    austingreen Senior Member

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    In texas with the hot summers there can be big fuel savings, but construction costs on existing houses are high. Sacramento is much milder, so even though it sounds like your construction costs may be much lower than ours, so will the fuel savings. Get a big for geothermal and see if its worth it, otherwise most cases here pv + efficient air conditioner are less expensive for existing construction, but geothermal works well for our schools and new houses.

    Good Luck
     
  17. fuzzy1

    fuzzy1 Senior Member

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    Late next week, I'll be watching over the conversion of dad's house from a central wood furnace to a ground source heat pump. This is driven mostly by geriatric issues, as he is no longer able to stoke the old furnace on the needed schedule. I'll be able to give better feedback next month, and more next spring after his first heating season with it.

    Natural gas is not available. Any other fossil fuel (oil, propane) would have to be trucked in, and would be hideously expensive with that century old house. The local utility talked him out of direct electric resistance decades ago, back when they were still promoting such for new construction.

    Carbon-wise, this is a step backwards, That old biomass fuel is generally considered to already be within the atmospheric carbon cycle, thus not a contributor to AGW. His woodlands produce far more dead trees than he can use for fuel and fenceposts and farm lumber combined. But air quality-wise, shutting down that antique emitter of dense smoke will be a giant leap forward.
    We will have 5 trenches, 10 feet apart, 300 feet long, buried in a hay field just in front of the house. Haven't yet selected between just below the septic drain field or off to the side. Bedrock depth may drive the final choice.
     
    #17 fuzzy1, Aug 11, 2015
    Last edited: Aug 11, 2015
  18. fuzzy1

    fuzzy1 Senior Member

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