Why No High End Split Geo Equipment?

Discussion in 'General Discussions' started by Alexander Wood, Jan 7, 2018.

  1. tl;dr: Why doesn't anyone make a variable speed split geothermal system with a COP over 5.0?

    I don't have geo, but I've been looking at various heating sources and what each costs to operate. Here in Connecticut, I have either had, or know someone who uses oil, gas, cordwood, wood pellets, air source heat pumps, propane, and electric baseboard. Basically, we have some of everything, not a lot of natural gas lines, and relatively high electric rates (they recently went DOWN to about $0.18/kwh).

    In my research, I have come to the conclusion that heat pumps of some type or cordwood are the most economically viable ways to generate some or all of the heat needed based on the fuel prices and equipment efficiency, which I have tabulated in a spreadsheet.

    In looking at heat pumps, I have looked at the following equipment as examples of high performing examples of each technology:

    Mini ASHP: Mitsubishi H2i
    Split ASHP: Carrier Greenspeed
    Geo packaged: Waterfurnace Series 7
    Geo split: Carrier Infinity
    Geo hydronic: Climatemaster Tranquility

    Those are not necessarily the only high performing options for each type, but examples of equipment that performs near the top of the range of the available technology.

    Based on that conclusion, and the cost of installation, I can't see a way to justify putting ductwork into a house that doesn't already have it, or, in most situations, re-doing ductwork that is only suitable for heating in order to make it work for cooling. In these situations, it seems to me that the Mini ASHP is by far the most viable option in terms of cost and efficiency, with an existing gas, oil, or propane system running as supplemental if the Mini ASHP is smaller than <85% of the calculated design load, in which case, it would need assistance, and running as an offline backup that can be fired up if the Mini ASHP breaks when the Mini ASHP is 85% or larger of the calculated design load. Design calcs have a fudge factor, plus they assume grandma has the heat blasting at 70, when it's 2F outside in CT, so realistically, you can push things right to the edge with a heat pump if you have a backup system, say oil hot water baseboard.

    So this begs the question: why doesn't anyone make a Mini Geothermal HP, replacing the outdoor unit of a system like the Mitsubishi with a WSHP like a split WSHP system? Is there just a market mis-match between people who want a low up front cost, versus ones who want to spend the dough on a geo system?

    So my next musing is when you've got ductwork in a house already that is suitable for heat and AC. If your envelope is pretty tight with relatively small loads, and you've got a big zone of FHA fed from a furnace in the basement, great, packaged WSHP for you. Waterfurnace and Climatemaster have examples of all the latest technology of ECM fans, variable speed compressors, and everything put together putting out COPs in excess of 5.0. Here in CT, you've got to have a really, really good COP to justify the up front cost of geo at $0.18/kwh. You also have to size the system to carry nearly 100% of the design load, as electric strips running at $0.18/kwh are very, very painful, unless you have an oil or gas hot water system to fall back on.

    However, I can imagine a LOT of situations where a packaged WSHP isn't going to work, and a split WSHP is what you need:

    1. Remote air handlers or furnaces.
    2. Where it doesn't make sense to size the geo to design loads, but to use a furnace or hydronic coil for backup.
    3. Houses with a bunch of air handlers running smaller zones.

    I have seen all of these situations, in houses that currently have gas furnaces or oil hydro air. There really isn't a good product for them to convert to geo right now. The split geo heat pumps that are out there today don't have the variable speed compressors and really high COPs that the packaged systems have, and are a really tough sell compared to a high end Split ASHP, like Carrier Greenspeed, which can be just plopped in place with a new furnace or ahu to give heat pump savings with hydronic or gas furnace backup heat.

    So my question is, why doesn't anyone make a high end variable-speed geothermal split system that can achieve a COP over 5?

    There shouldn't be any difference in the physics compared to a packaged system, other than the length of the refrigerant line. If they need a special fan or airflow configuration to make it work, they could build their own air handler with the option to put either a hydronic coil or electric strips in, as well as their own two-stage furnace with ECM blower. Further, this type of product should either be available in, or be able to be capped out in software to as small as 1.5 or 2 tons. This way, geothermal could be installed at a much lower up front cost, and still provide 90%+ of the heat to a building over the course of the season, with an oil or gas boiler or furnace doing back-up duty.

    I'm most surprised that Carrier hasn't staked this market out, as they have the Greenspeed/Evolution Extreme heat pumps, and the associated furnace and air handler line. If they transplanted the Greenspeed technology into the form factor of the Carrier Infinity WSHP, it would be a pretty unique, and very useful product for geo conversions.
  2. Another situation where you would want a split geo system would be for power outages, another thread discussed this recently. With a modest generator, you can run a boiler or furnace and associated equipment, a WSHP is a much larger load, and the toaster strips are a massive load, and very problematic for a geo installation, which most likely doesn't have natural gas available, so you'd be burning through your LP supply very quickly.
  3. viveksunderam

    viveksunderam New Member

    I'm surprised that you didn't get an answer to your query above given the knowledge in this forum. Also, I'm interested in that spreadsheet you mention at the beginning of your first post.
  4. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    Waterfurnace just introduced a 7 series split....
    Alexander Wood and viveksunderam like this.
  5. Terry Hewitt

    Terry Hewitt New Member

    Mr. Wood, you are comparing apples to oranges even in CT. if the envelope of your house is tight hands down geothermal would be your best bet for your money. Retrofits are more expensive when compared to a new house with a geothermal system installed. There are several kinds of geothermal units available such as water to water geothermal room radiators, where you should start and find out what is necessary to have a unit installed in your residence. A little backup heat from strip heat to electric boilers would make your geothermal unit run more efficiently than trying to make the unit do the complete heating load. The moral to your story is do it right or do not do it at all.
  6. viveksunderam

    viveksunderam New Member

    Does anyone have any further information on this? I've not seen any information on the 7 series split online. Any brochures / links you could point me to?
    Alexander Wood likes this.
  7. Excellent point. A propane furnace or oil hydro air system would run just fine off of your garden variety portable generator. Most boilers are oversized anyway, combined with envelope improvements to make it oversized, you could heat the house up at near-design conditions even with the generator running only intermittently. Running a WSHP with a COP of 5.0 off of a standby generator would be roughly the same as just burning the LP gas, but it requires a much larger generator and ATS versus a small portable unit or partial circuit standby to run the furnace or boiler. These types of installations that are in more rural/exurban areas are also more likely to have extended power outages.
  8. I haven't updated it in quite some time, but I just calculate the costs per million BTU for various fuels. I use the rated equipment efficiency, assuming that none of them are getting that efficiency, and all are falling short of their rated efficiency by a similar margin. The heat pump to combustion comparisons may be a little off, since the performance is all seasonally averaged, and may not properly account for different speeds on a variable speed setup.


    I compare the following systems for space heat:

    Natural Gas
    Cord Wood
    Electric Res
    Mini ASHP
    Split ASHP
    GT Package
    GT Split
    GT Hydro

    I compare the following systems for hot water:

    NG Tankless
    NG Tank
    LP Tankless
    Oil Indirect
    Oil Tank
    Electric Res
    Heat Pump
  9. I can't find it. Do you have a link? That could be a game-changer for Geo retrofits if it gets to market.
  10. For new construction, geothermal doesn't make any sense. If you're retrofitting an older house that was well built, sure, geothermal could be great. For new construction, you're much better off doing double-walled dense-pack cellulose and triple-pane construction to get your design loads down under 5 BTU per square foot, at which point it's much cheaper to heat the whole thing with a couple of mini-splits. This company has figured it all out for CT, and determined that the Mitsubishi units are the best bet so they can spend more on building a good envelope: https://www.lehtodesignbuild.com/

    For retrofits, electric resistance heating is horrendously expensive, and that's why a split system would be much better. If you can size the WSHP to 65% or more of the design load, you will only use the oil or gas system a few days a year, especially since the design load calculations are BS anyway. Many winters the GSHP system will get through the whole winter without using the backup at all, especially if the owners want to play around with it a bit.

    The other issue I've seen is that with houses built in the last few decades is that their design load is really determined by wind, not temperature, as they are well insulated, but fiberglass batt insulation doesn't do a great job at air sealing. They'll use a fraction of their design capacity at 0F with no wind, but if it's 5F with high wind, the heating system is cranking. For example, a 3800 square foot house built in 2000 to code with a design load of 65K BTU/hr actually needs about 55K BTU/hr of heat in the worst late evening winter conditions and would run all but a couple of days per year with 2 2 ton WSHPs, one feeding each AHU. A hybrid system would effectively provide full redundancy (at least you're not going to freeze anything up if the boiler goes, conversely, if a WSHP fails, the boiler can take over), and the ability to run the boiler and AHUs with a small portable generator. The boiler could remain in use for other zones or hot water - or not.

    The next step, which doesn't exist yet, would be to have an incentive for homeowners to have their Wi-Fi thermostat connected to the smart grid, so that when the natural gas pipelines start running out of capacity during an extreme cold snap, the houses can just burn fuel oil or LP directly instead of having to burn vast quantities of fuel oil at plants like Merrimack Station, which burned thousands of tons of fuel oil at a massive cost in the 2017-2018 cold snap. If that was implemented at grid scale with a lot of hybrid systems, mostly ASHP/furnace or ASHP/boiler, then it could make an impact on the grid. Toaster strips just make that grid-level problems far worse when the GSHPs can't keep up.

    EDIT: Some of that stuff, like oil hydro air, and pipeline capacity doesn't really apply outside of the Northeast, but hybrid systems themselves can be used with gas furnaces anywhere that geothermal heating makes sense. Down South, it probably makes more sense to just put Carrier Greenspeed in and set it for heat pump only mode.
  11. To attempt to answer my own question in the OP, I'm guessing that the market for mini-splits tends to be too mid-market, or in smaller, older homes on lots where GSHPs aren't practical to justify building a GSHP mini-split. However, I would think that a Carrier Greenspeed split GSHP would make a LOT of sense, since the higher end market tends to be more ducted, and it would drop nicely into a lot of retrofit applications. We've got a lot of higher end houses in New England with 2, 3, and 4 zone oil hydro air that would retrofit quite nicely with 1.5 or 2 ton variable speed GSHPs, but they'd have to have a COP over 5 and an EER over 40 to be worthwhile compared to Carrier Greenspeed.
  12. Anyone have any thoughts on this? I still can't find anything about a Series 7 split system.
  13. viveksunderam

    viveksunderam New Member

    I heard from an installer that they had an event where they showed a demonstration unit this summer, and told the installer that the units would be available for sale next summer. He thought, based on history, that it would take them 2 years to come to market.
  14. Nice! That would really be a game changer in geo retrofits.
  15. viveksunderam

    viveksunderam New Member

  16. So that's the unit. And it's partly a game changer. However, there are still a number of applications that it appears it will not cover. It appears that you have to use it with their air handler, which does not, as far as I can tell, have provisions for installing the 7 series refrigeration coil on a gas furnace, with a hydronic coil, and/or in a Unico small duct system. These are the applications where a Series 7 would really shine in terms of flexibility, even though the split system itself will cover some applications.
  17. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    Samsung makes a water source HP with multiple heads
  18. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    Not sure if I agree here. Just saw this. We are building a lot of net zero houses, new construction, and geo makes a lot of sense. The key is to size the geo systems, so electric strip heat never turns on. This is where the variable speed systems shine.
    waterpirate and Deuce like this.
  19. I found those online, and they have a neat lineup, but they are for commercial and large multi-family, not for SFUs.
  20. So several years ago I talked to the owner of the company I linked to there, and he has run all the numbers, there is no economic case, at least in Connecticut for geothermal in a newly built NZEH. Once you have a design load below 5 BTU/sq.ft, you're using so little heating energy that installing an expensive geothermal system with ductwork all over the place is far more expensive than putting in a minisplit on each floor and calling it a day. He has installed geothermal for customers who want it, or for very large custom projects where cost is not a primary concern, but it's inherently overkill to put in an expensive ducted 36,000 BTU geo system when you're building a 2,000 square foot house and you have a design load of 6,000-8,000 BTU, when you could easily handle the load with a pair of 12,000 BTU Mitsubishi Mini-splits, one downstairs for heat, and one upstairs for AC. Add a heat pump water heater in the basement, that handles DHW and dehumidifying the basement.

    The other problem is that when you get into geo, the cost of a NZEH goes well above that of a "typical" poorly built home with a scorched air furnasty and central A/C, versus using a pair of mini-splits saves tens of thousands of dollars in HVAC costs that can mostly or fully offset the additional cost of properly building an energy efficient envelope with 12" walls, triple-pane windows, excellent air sealing, and 24" of insulation above the heated envelope.

    Now that equation might change in a significantly colder climate than Connecticut, although there have been many successful uses of ASHPs in Maine and even Canada.

    I don't see a good argument for installing geo in new construction when the envelope can be built to modern good building practices (roughly triple code or more), whereas geo makes a lot of sense in retrofit applications and renovations.

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