2-stage DX Geothermal Heat PUmps
Last Post 22 Jan 2019 02:08 PM by teshj314. 67 Replies.
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Dana1User is Offline
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15 Jun 2017 06:45 PM
Posted By docjenser on 15 Jun 2017 02:24 PM
Posted By anon on 14 Jun 2017 05:05 PM
Mini splits have pretty much destroyed the geothermal market.


Not sure if that is the case, but I would agree that the discontinuation of tax credits and the falling prices of natural gas had a noticeable impact on the geo industry. But long term I do not see any alternative to geo in cold climate. Given the state of the technology, and assuming that electrically driven heat pumps are widely implemented, one thing is certain: Mini splits will destroy grid reliability due to their peak demand in cold climate.


The notion that air source heat pumps "...will destroy grid reliabilty..." is absolutely NOT certain. In fact it's a red herring, as big a red herring as the notion that distributed solar is a threat to grid reliability. It may be a threat to some business models, but not to the reliability of the grid.

ALL electric heating systems (including resistance heaters and GSHPs) increase their duty cycle and thus the grid load when the average heat load in the region increases. The fact that with ASHP systems the power per BTU/h increases non-linearly with falling air temperatures is a difference, but not a sufficient distinction to really matter very much for the grid. The curve is still a very a smooth transition, and a manageable one.

Undersized heat pumps (GSHP or ASHP) that switch-in several kilowatts of heat strip when the load vs. capacity threshold is crossed presents a far more drastic and disruptive non-linearity. People that use overnight setbacks and fire-up the heating in the AM deliver a nonlinearity even bigger than heat strips kicking on. But even that isn't a threat to grid reliability. There are now lots of tools in the grid-stabilization tool kit, and more being installed every day. Grid batteries are poised to oblitherate the capacity factors of even the existing fleet of gas or oil fired peakers on operating cost, but demand-response markets (still small, but developing quickly, now that FERC Order 745 was upheld by the US Supreme Court) is cheaper still. A Wi-Fi thermostat and Wi-Fi water heater participating in demand response markets can time-shift lots of load to smooth the ramp rates, and can even provide frequency & voltage control ancillary services to the grid. As more distributed resource demand response aggregators get into the game the spinning reserves requirements will drop precipitously, and the grid will become MORE stable, not less.

It's now possible to hang a Wi-Fi thermostat onto mini-split remote controls, to even let the mini-split contribute as a distributed grid resource for stabilizing the grid. This guy has the right type of thermostats on his three mini-splits but SFAIK Georgia Power doesn't have programs to allow them to be used that way:

http://www.greenbuildingadvisor.com/blogs/dept/green-building-curmudgeon/done-well-almost

Bottom line, I'm not even a tiny bit worried about heat pumps (mini-split or other) being a threat to the grid in any climate.
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15 Jun 2017 06:52 PM
I really don't understand how mini-splits of destroyed the geothermal HP market.

If you are referring to a VRF system, where multiple indoor units can be piped back to the outdoor unit, then maybe.

But mini-splits, are at best a retrofit application where existing equipment is no longer able to adequately condition a space, and the client is left with little option other than to locate a wallmount, ceiling mount, or cassette in the space to cover the loads.

I will agree that the elimination of the 30% federal tax credit essentially killed the drive and fervor, experienced in my AO between 2008 to 2016, to install geothermal heat pump systems.

However, new construction and proper renovations/addition construction are still installing GHP.

But my question, and the theme of this thread, is how are the 2-stage DX geothermal systems operating, based on the 2016-2017 winter?

This thread ended up with a manufacturer's rep, who I believe is no longer with the manufacturer, arguing Fourier’s law was the answer to every DX doubter's questions.

I simply noted that the winter of 2015-2016 in my AO was extremely mild, and if there were any 2-stage DX equipment installed during this time, the winter of 2016-2017 would be a more typical heating system to collect data and review.

And, just my opinion, I can't see how any one would really desire having their interior peppered with wall-mounted units, or ceiling units, and choose mini-splits over a properly engineered forced air heating and cooling system.

And if mini-splits are the answer for Heating and AC, then how do you size them appropriately (especially considering Climate Zone 5)?

1) Size for cooling and engage a supplemental source of heating upon encountering temperatures of diminished output?
2) Oversize the compressors and rely on inverter technology to cover the heating load and ramp down during the cooling season.

Geothermal Heat Pumps are, to my knowledge, the only refigeration/compressor technology available that allows an individual case by case to design the heat exchanger to cover the entire heating and cooling loads.
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15 Jun 2017 08:09 PM
"But mini-splits, are at best a retrofit application where existing equipment is no longer able to adequately condition a space... "

"I can't see how any one would really desire having their interior peppered with wall-mounted units, or ceiling units, and choose mini-splits over a properly engineered forced air heating and cooling system. "

BS

Mini-splits are becoming a go-to solution for smaller houses even in colder climates, since they're cheap and can right-sized for very modest loads. I'm aware of a ~3000' of code-min new house in my area (Massachusetts, zone 5) where the clients opted for 4 ton multi-split solution , which came in at $ 15K (raw cost, before MA utiltiy rebates kicked in) and was ~$10K less than the quote for a ducted hot air propane furnace + 3 ton split-AC system, and a HELUVA lot less than the 4 ton GreenSpeed w/ heat strip quote (which was nearing GSHP proportions!)

It was not a retrofit, not a compromise, but the client's choice based lifecycle costs. It's not superinsulated or super-tight, but it's not a super-lossy house either. They have a wood stove for when the power goes down in a nor'easter (which happens a couple of times per decade in that neighborhood), and the wood stove can turn half the house into a sauna at any outdoor temp if they wanted to. They're pretty happy with their decision (even though I had advised them to do the bedroom half the house with a single mini-ducted unit rather than oversized half-ton heads.) It's the quietest and most comfortable system they have ever lived with. YMMV The couple is in their 60s, with one teenager still in the house, and the occasional 20-something sometimes boomerang child. This wasn't their first house or first heating system.

In climate zone 5 it's usually appropriate to size them for the 99% heat load and the extended temperature capacity tables. It's worth running the cooling load numbers too, but that is usually more than covered if sized for the heat load. At zone 5 type 99% outside design temps the efficiency in the high end of the modulation range is under 2, but they're not losing much capacity or efficiency below that at the 99.6% outside design temps. Sizing exactly to the 99% load is rarely possible, and the next size up usually covers the 99.6% design load. It's really not worth worrying about what happens below that temperature- it needs to be below that temperature for more than just a couple of hours to actually lose ground, and most people can figure out if they need to leave the game computer on to have enough auxilliary heat to cover the difference if it starts to lose ground.

But mini-splits are not really what's destroying the geo biz.

"Geothermal Heat Pumps are, to my knowledge, the only refigeration/compressor technology available that allows an individual case by case to design the heat exchanger to cover the entire heating and cooling loads."

That is also part of the design risk that the client takes on- every system is a custom design, and not all designers have equal experience or competence.

Modulating reversible air source chillers with individually size hydro air coils can be set up to handle both heating & cooling in a micro-zoned manner. eg. Chiltrix: http://www.chiltrix.com/

They have capacity tables that extend to negative double-digits, and it doesn't take rocket-science designers to get it to work in a zone 5 climate.

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15 Jun 2017 08:54 PM
Dana1,

To each his own then. If a ductless/low profile mini split is the answer, then I say design and install it.

I've looked into the Spacepak version of the ASHP/reverisble chiller, and saw that I needed 1.5x the capacity of the load in the equipment to match the heating design points.

I'll admit that my opinion on mini-splits is based on aesthetics, and I'm entitled to my opinion.

But, and not to be snarky, what does your fervor towards mini-splits have to do with my question in this thread?



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15 Jun 2017 10:45 PM
I wouldn't exactly call it a mini-split fervor, only trying to counter some broad brush statements. After 7 pages this thread has drifted into some side alleys, to be sure.

I initially got sucked down mini-split alley by anon's assertion that...

................ "Mini splits have pretty much destroyed the geothermal market."

That's an assertion I find utterly preposterous! Even if SOME people are indeed buying mini-split and satisfied with them (even in substantially-sized houses), it's not really what's putting pressure on the GSHP market.

Making broad assertions about where the different technologies are appropriate or not invites a rebuttal when existence proofs to the contrary abound, but it wasn't my intent to try to take over the thread or sell you on a mini-split solution. Phrases like "... at best a retrofit..." or "...the only refigeration/compressor technology available that..." invite the counterexamples, as does docjensers' bizarre assertion that " Mini splits will destroy grid reliability..." .

I'm not trying to convince you that these are better than a GSHP solution for you, only that the GSHP chauvinism expressed isn't necessarily well founded, and mis-statements of fact about other solutions aren't really warranted.

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16 Jun 2017 04:14 PM
Understood.

All technologies have their use and applications for sure.

Rarely have I ever been asked to design an HVAC system that incorporated mulitple min-splits into a project, rather a VRF system to me seems more suitable.

Obviously the challenge, as I am aware of to date, is that VRF's usually enter the realm at 6 tons, and require 3 phase electrical. Obviously there are ways around providing single phase to three phase equipment, but I generally do not go in that direction if need be.

The pressure within the GSHP market is several factors: First Costs, ROI, and finally, the reputation that the GSHP market has garnered from unsatisfactory installations.

For the last factor, that obviously lies on the successful bidding contractor's abilities, and the fact that the owner hired them. Unfortunately, that is on them. Unfortunately the internet and its reviews are forever.

I'm going to re-use your phrase "GSHP chauvenism" as it seems accurate with Geothermal Expert/Installers in my AO.

I'm purely a fan and advocate of any refigeration/compressor technology that is successful in delivering comfort at proposed efficiency and costs, regardless of the source.

This thread was created to discuss the the DX market, manufacturer's, and 'advancement' in technologies. From my experience, there is in fact a limitation in application that can be put on a DX Geothermal design. My number one comment is to describe a DX compressor's HX as one that is "unitary" in that it can not be shared or connected to any other DX geothermal equipment.

Water Source allows for connection to a "plant" or "manifolded" heat exchanger; therefore numerous compressors can be connected, and all can benefit from a designed performance.

I really am curious to see "real world performance" data on these 2-stage DX compressors to see how they operated to handle the loads, and more importantly, how did the ground respond?

Knowing how the 2-stage equipment functions from a controls perspective, I am anticipating that the ground was abused.

Regards,

teshj314
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16 Jun 2017 09:46 PM
You got a point, we are getting off topic here, so I started a new thread.

ccASHP vs GSHP.
http://www.greenbuildingtalk.com/Forums/tabid/53/aff/13/aft/84552/afv/topic/Default.aspx
www.buffalogeothermalheating.com
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22 Jan 2019 02:08 PM
Well, Earthlinked out Lakeland, FLA is D-E-A-D.......

Apparently a successful DX Geo installer/contractor purchased what was left of ETI and moved the operation out to Ohio.

Earthlinked = Waterless Geothermal as manufactured by Total Green Mfg.

Which, is hilarious considering their was/is a DX geothermal contractor calling themselves Total Green, LLC who has laid to waste so many DX geothermal projects in the NYS area.
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