www.greenss.net
New Member
Posts:16
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| 01 Dec 2011 08:19 AM |
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I am trying to find out if this makes more sense for the consumer in the long run. A mini split tied to a pv system compared to geothermal. Which is going to save you more on utility's and be more environmentally friendly? Both would qualify for 30% tax credit. Looking for your thoughts. Thanks! |
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| Brian Shier<br>Green Structure Supply LLC |
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HHH
New Member
Posts:81
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| 01 Dec 2011 12:59 PM |
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The mini-split does not qualify for the 30% tax credit from the federal gov.  |
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www.greenss.net
New Member
Posts:16
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| 01 Dec 2011 01:20 PM |
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The mini split would be covered up to $1500 with a max of $500 for tax credit. The PV system would be covered with the 30% tax credit that has no maximum limit. Just like geothermal. |
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| Brian Shier<br>Green Structure Supply LLC |
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engineer
Veteran Member
Posts:2749
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| 04 Dec 2011 12:08 AM |
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Minisplits shine when no ductwork is needed.If the project's objective may be met with one or more blower units hung high on the wall(s) of the rooms to be conditioned, then yes, minis may be the right answer. |
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Curt Kinder <br><br>
The truth is incontrovertible. Malice may attack it, ignorance may deride it, but in the end, there it is - Winston Churchill <br><br><a href="http://www.greenersolutionsair.com">www.greenersolutionsair.com</a>
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www.greenss.net
New Member
Posts:16
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| 04 Dec 2011 07:20 AM |
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Thanks Curt for the info. I am wondering why it would not work with a traditional air handler and duct work? |
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| Brian Shier<br>Green Structure Supply LLC |
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SkyHeating
Basic Member
Posts:203
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| 04 Dec 2011 04:17 PM |
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You can do a mini-split with ductwork, but when you add ductwork you loose efficiency. Also the numbers for efficiency are deceiving. A mini split is rated at a 47 degree outdoor air temperature. There are low heating models but they are what we call a 1:1 system meaning 1 outdoor and one indoor instead of a whole house unit that may be 1:4 one outdoor to 4 indoor. A geothermal unit does not base its efficiency on outdoor temperatures. Also you quoted $1,500 for a ductless system, how do you figure? The federal tax credit is $500 and is a maximum of up to $300 per outdoor unit, so you would need at least two units to meet that cap. Second from what I remember these units have to be installed retrofit, not into existing construction, so depending on your circumstance it may vary.
Where are you located and what are you trying to accomplish should be the first questions that need to be answered, then how big is the house and how much property do you have. |
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Visit my Youtube channel for product reviews and customer testimonials http://www.youtube.com/user/skyheating1
http://www.welserver.com/WEL0626/
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www.greenss.net
New Member
Posts:16
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| 05 Dec 2011 05:48 AM |
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Thanks Sky Heating and Cooling for correcting the tax credit info. We should probably not even consider a credit on the mini split. Most likely not going to be renewed. I was hoping to hear from someone that works with mini splits on a ragular bases. Anybody? |
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| Brian Shier<br>Green Structure Supply LLC |
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SkyHeating
Basic Member
Posts:203
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| 07 Dec 2011 02:53 PM |
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I work with Mini splits on a regular basis. I am putting in 15 systems this month mostly Daikin 2 and 3 port with the occasional one port system. I have some buildings in Portland Or downtown area that have 44 Mitsubishi units in them.
A ductless is not more efficient, it may be more cost effective in many circumstances but more efficient no. |
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Visit my Youtube channel for product reviews and customer testimonials http://www.youtube.com/user/skyheating1
http://www.welserver.com/WEL0626/
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tinoue
New Member
Posts:96
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| 07 Dec 2011 03:15 PM |
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In practice, I've found that there are a number of real-life variables that make mini-splits better than GSHP in a variety of situations. I wouldn't claim either system a winner in all situations.
In particular, as you start adding up the inefficiencies present in real-world centrally ducted systems, you find any system loses.
- 20%-30% duct losses are typical in broad based measurements across thousands of homes
- Duct friction losses, leading to an increase in energy required to power central air handlers compared to ductless systems
Then there are GSHP related issues
- Pumping energy - highly variable depending on loop configuration but in the range of 3%-5% of system capacity
- Actual ground loop temperature can be much lower than ideal (i.e. 32-35F instead of 45F) due to inadequate loop design/sizing/conditions.
While it is possible to do an excellent GSHP installation, with very tight ductwork, all contained in the conditioned space of the home, large ground loops, properly grouted, etc., it is not guaranteed, especially with so many hacks installing GSHP systems these days. OTOH, a mini-split has far fewer components and is therefore much more likely to perform near manufacturers specifications.
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joe.ami
Veteran Member
Posts:4377
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| 08 Dec 2011 09:30 AM |
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Posted By tinoue on 07 Dec 2011 03:15 PM
In practice, I've found that there are a number of real-life variables that make mini-splits better than GSHP in a variety of situations. I wouldn't claim either system a winner in all situations.
In particular, as you start adding up the inefficiencies present in real-world centrally ducted systems, you find any system loses.
- 20%-30% duct losses are typical in broad based measurements across thousands of homes
- Duct friction losses, leading to an increase in energy required to power central air handlers compared to ductless systems
Then there are GSHP related issues
- Pumping energy - highly variable depending on loop configuration but in the range of 3%-5% of system capacity
- Actual ground loop temperature can be much lower than ideal (i.e. 32-35F instead of 45F) due to inadequate loop design/sizing/conditions.
While it is possible to do an excellent GSHP installation, with very tight ductwork, all contained in the conditioned space of the home, large ground loops, properly grouted, etc., it is not guaranteed, especially with so many hacks installing GSHP systems these days. OTOH, a mini-split has far fewer components and is therefore much more likely to perform near manufacturers specifications.
That is an incredibly lop sidded assertion which neglects to consider:
1) Ductless is not a good fit in all aps.
2) Ductless can be more expensive if many rooms are partitioned off.
3) Hacks are more likely in mini-splits as it is closer to conventional HVAC work and an inexperienced tech may "try it out".
There are applications where ductless makes sense,but there are applications where ducts are required.
So to the original question are mini splits more efficient than geo? The answer is -seldom, but it often makes more economic sense not to pick geo. |
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Joe Hardin
www.amicontracting.com
We Dig Comfort!
www.doityourselfgeothermal.com
Dig Your Own Comfort! |
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www.greenss.net
New Member
Posts:16
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| 08 Dec 2011 04:19 PM |
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I feel like we are forgetting to figuare in the solar aspect. I am still not seeing a strong argument yet. I really appreciat everyone's expertise. |
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| Brian Shier<br>Green Structure Supply LLC |
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ICFHybrid
Veteran Member
Posts:3039
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| 08 Dec 2011 08:21 PM |
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Assuming you can do net metering, the solar panels stand on their own merit.
Right now, the energy payback time for PV panels is somewhere between 2 and 4 years. That means that they will generate as much energy in a few years as it takes to produce them in the first place. Obviously, their useful life is much, much longer than that, meaning that they are truly renewable energy.
The economic payback period is a bit more, somewhere between 7 and 20 years, depending on tax breaks and subsidies. |
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joe.ami
Veteran Member
Posts:4377
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| 09 Dec 2011 08:11 AM |
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Posted By www.greenss.net on 08 Dec 2011 04:19 PM
I feel like we are forgetting to figuare in the solar aspect. I am still not seeing a strong argument yet. I really appreciat everyone's expertise. PV solar will help offset electrical expense regardless of heating/cooling system. Did not forget to "figure" it, it is simply a non-factor in a discussion of efficiency differences between geo and mini splits. If you are asking which is better for your home and we have to choose between geo by itself or minisplit with PV we'd need more info about the job. Tax credits being what they are however, geo with PV may not have a higher net cost than splits with PV. |
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Joe Hardin
www.amicontracting.com
We Dig Comfort!
www.doityourselfgeothermal.com
Dig Your Own Comfort! |
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Dana1
Senior Member
Posts:6991
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| 13 Dec 2011 12:15 PM |
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Posted By SkyHeating on 07 Dec 2011 02:53 PM
I work with Mini splits on a regular basis. I am putting in 15 systems this month mostly Daikin 2 and 3 port with the occasional one port system. I have some buildings in Portland Or downtown area that have 44 Mitsubishi units in them.
A ductless is not more efficient, it may be more cost effective in many circumstances but more efficient no.
That would be at odds with ongoing field studies in your area being conducted/contracted for by the BPA. When air-handler power is factored in it's hard to break a COP of ~2 for a seasonal average on a ducted residential system, whereas a 2x oversized ductless can average better than 3. This is true even when the ducts are sealed, and located fully within conditioned space. If ducts are outside of conditioned space or leaky the true system efficiency takes a hit from duct losses too, independently of what would show up an a COP power measurement of the unit. COP measured at the compressor to interior coil will run about the same for ductless v.s. ducted though. |
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jonr
Senior Member
Posts:5341
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| 13 Dec 2011 06:05 PM |
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I would add that unless all interior doors are kept open, ducts (even perfectly sealed, interior ones) tend to pressurize/depressurize rooms. This adds to infiltration/ex-filtration and also reduces net efficiency.
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joe.ami
Veteran Member
Posts:4377
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| 14 Dec 2011 08:32 AM |
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Why would we use a study that cites efficiency of "2X oversized" equipment? Does the study offer a comparison with 2x oversized ducts and ducted equipment. I've found while running countless op cost comparisons that larger (oversized) equipment boasts better efficiencies regardless of technology.
.....This is a far cry however from suggesting it is economically sensible to significantly oversize a furnace or heat pump as there is start up cost consequence and sometimes back door costs (higher cooling or hot water production expense).
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Joe Hardin
www.amicontracting.com
We Dig Comfort!
www.doityourselfgeothermal.com
Dig Your Own Comfort! |
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ICFHybrid
Veteran Member
Posts:3039
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| 14 Dec 2011 12:06 PM |
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Why would we use a study that cites efficiency of "2X oversized" equipment? I think that talking about "2X oversized" heat pumps might be a response to those who say that heat pumps fail to put out rated heat at low outside temperatures. One strategy that might be suggested in such a case is to "oversize" the heat pump equipment in order to increase the output at those low temperatures. "Aha!" Say the detractors. "Oversizing the equipment is wasteful and leads to lower operating efficiencies…", which is true, but what I think is being pointed out is that you can oversize ductless minis and still come up with efficiencies higher than some other ducted options. Does the study offer a comparison with 2x oversized ducts and ducted equipment. No. I think it is commonly understood that oversizing ducting causes significant inefficiencies which would push the ducted options even more to the uncompetitive side. there is start up cost consequence and sometimes back door costs (higher cooling or hot water production expense). You know, I think the BPA studies looked at year-round performance which included the cooling seasons. I think another BPA comment called the ductless heat pump performance "...remarkable during part-load operation", if that helps any. |
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jonr
Senior Member
Posts:5341
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| 14 Dec 2011 02:52 PM |
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I think it is commonly understood that oversizing ducting causes significant inefficiencies Can you explain the physics of this? |
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Dana1
Senior Member
Posts:6991
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| 14 Dec 2011 06:36 PM |
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Duct oversizing (within reason) causing lower efficiency would be news to me too. Oversizing minis is more efficient due to the fact that peak efficiency occurs in the lower ~1/3 of the compressor speed (an similarly with the variable speed on the interior units.) If you "right size" the system suffers a double hit on efficiency- the compressor has to run near max speed to handle the load and the delta-T is also higher due to the cooler air temp. joe- The mini-split testing contracted for by the BPA didn't cite a 2x oversizing, it tested both heating & cooling efficiency at different loads and varying compressor speeds, comparing them to the manufacturers published efficiency specs at temp. The part-load efficiency at low compressor speeds is phenomenal, often exceeding manufacturer's spec. This is true both in heating and cooling modes. Do be able to get enough heat out of it on design day and still have an average compressor speed in the 1/3 or lower range calls for oversizing them by something like 2x, but it's a squishy oversizing number. Since they are fully modulating systems with more than a 3:1 turn down range, 2x oversizing will never short-cycle the beast in to lower efficiency the way a bang-bang single speed or simple minded 2-speed would. At 4x oversizing it would probably hurt, but 4x oversizing with a inverter-drive mini-split probably isn't even an option for any house that isn't already approaching PassiveHouse levels. But a very tight well insulated house in a temperate climate (such as Portland OR), could easily have a design condition heat load of less than 18K, and a fully modulating 2.5-3ton mini-split will run extremely efficiently at the design condition load, and even better on the average load. Part of that BPA sponsored has been integrated into this document. Take a look at figure 5, p10, and note the difference in COP at 30F between min compressor & fan speed vs. at max compressor & fan. Design temps in Portland are in the low 20s F and the January average temp is ~41F. If you "right size" it for the load at 22F you probably won't do better than a COP of 3 for a seasonal average, but if you oversize it 2x you'll probably hit 4 or better. (The tiny Mitsubshi tested in that docment didn't fare quite as well, but similar work on other makes & models look more like the Fujitsu in terms of speed vs. COP.) |
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ICFHybrid
Veteran Member
Posts:3039
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| 14 Dec 2011 07:41 PM |
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Can you explain the physics of this? If they are in unconditioned spaces there is more heat loss. |
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