http://www.greenbuildingtalk.com/Forums/tabid/53/aff/13/aft/79922/afv/topic/afpgj/3/Default.aspx

Posted By Dana1 on 07 Mar 2012 02:17 PM
On new construction you get the choice of what to spend the efficiency-money on, and when you look at the difference in system costs between a 3-4 ton geo compared to what it takes to get the design condtion loads under 2-tons and use inverter-drive air-source (hydronic or split-system "mini-split") that uses the same or LESS kwh/annum the results are not a given. Average winter outdoor temps affect the equation considerably when looking at air source, though, since ASHP output at the outdoor design temp may not always cut it.

But in places with -5C <==>0C average temps and 99th percentile outside design temps of -20C or higher there are hydronic air-source systems that can fill the bill at half the cost of geo, and nearly the same efficiency (notably, the Daikin Altherma series: http://www.daikinac.com/residential/altherma.asp?sec=products&page=53 ) In places where the average winter temps are 0C or higher, with a low-temp slab the system efficiencies of best-in-class air source can exceed that of geo when the full system power (including all pumping) of the geo is factored in. As "canned systems" there is far less system design cost & risk as compared to geo. So if another $20K of building envelope upgrades gets you there...

Building envelope efficieny is downright cheap on new construction if one takes the time to do iterative designs and apply the cost savings of the smaller/cheaper/less-risky mechanical systems to the building envelope.

This is in response to the above threads and others where the case were made for air sourced heatpump in cold climates. Having replaced just recently 2 air sourced heatpumps with geo, I question the practicality and efficiency of air sourced heat pumps in cold climates. While the technology sounds great and seems to work well in a dry testing lab at sub freezing temperatures, it really becomes problematic when low ambient temperature occur together with high humidity conditions, or rain. The outdoor coil's is below ambient temperature (inorder to transfer heat into the refrigerant circuit) and will freeze the water particles on the coil. The unit will go into defrost mode, at lower outside temperatures quite frequently, essentially going into A/C mode, taking heat out of the house, counteracting efficiency. Now the electric resistance heater kicks in and has to make up not only for the heat loss of the building but also for the energy needed to defrost the outside coil.
At cold temperatures, defrost cycles a few times per hour.

Now, an other typical weather condition would be a snowstorm dumping a couple feet of snow. How do you think the outside coil will work under those conditions.

So what am I missing here. Doesn't one want a heating system which works reliable and efficient under cold weather condition when you need it most? Without the efficiency further deprived by the defrost cycle. Which works well in a lab or in Arizona might be more challenging in cold weather climate

essentially going into A/C mode, taking heat out of the house

Sounds dramatic, but the fact is that defrost cycles are accomplished seamlessly, without affecting the comfort levels inside the house. Don't know what types of air source heat pumps you "just replaced", but the newer, more efficient air source pumps operate down to below 0F, even in the "humid" conditions you describe. Daikin, for example (such as Dana1 mentions above), publishes "integrated values" which show the performance taking into consideration the defrost cycles. In milder climates, where you don't get the deep sub-zero temps, the air-source heat pumps are the way to go. Couple them with low-temp radiant floor heating and you have a very comfortable and efficient system without troublesome ground loops.

What ICFHybrid said about defrost cycles on mini-split type technology- they have NO resistance heaters anywhere in the system, and reverse flow to achieve defrost.

My mother claims to have never noticed or even observed the defrost cycles on her Mitsubishi mini-split in her foggy-dew Puget Sound climate (and I guarantee you they are FREQUENT in a 35F-40F & rainy winter climate.) Hers is not instrumented and I've yet to do a careful analysis of her billing, but the gross analysis points to an average COP greater than 3.5. It may be hard to get more precise than that, since the (now abandoned) ducted electric hot air furnace had return ducts outside the thermal envelope of the house. Whatever, her heating bill is now something like 20% of what it had been. There's no way the mini-split is averaging a COP of 5 with average temps in the 30s, but it might at low speed when it's north of 45F. The mean January temp there is ~38F, the 99th percentile design temp ~22F.

NRT.Rob (posts on the radiant forum here) has real-world instrumented performance data on the Altherma in slab-radiant applications, in a place snowy Maine with 99th percentile design temps in negative single-digits, mean January temp ~+20F. IIRC it had been exceeding expectations on average COP, possibly due to the very-low-temp radiant design &/or moderate oversizing of the compressor to the load leading to lower average compressor speed (=higher COP, with these beasties.)

In general the compressors work just fine in snow (my mother had a record 2 foot dump this season), but it's best not to locate them where burial by roof-avalanche is possiblity without a least a mini-shed or wall-mounting it high enough under roof overhangs:

http://media.photobucket.com/image/recent/Xringer/NCL/Sanyo-1.jpg

http://uphillhouse.files.wordpress.com/2011/07/ashp-1-2.jpg

and not:

http://www.tensionnot.com/pictures/images/Snow/Frozen-Split-AC.jpg

http://fourthickwalls.files.wordpress.com/2010/12/dsc_00031.jpg

This is not an unforseeable and difficult to rectify problem. Low-energy house builders have been installing them in snowy Vermont/New Hampshire/Maine for years now.

I didn't mention- after a $1.2K subsidy from the utility the INSTALLED COST of my mother's mini-split is under $3.5K, which wouldn't even buy you a decent DESIGN for 1.5-2 ton geo.   Even if a perfectly-designed geo system might edge it out on performance (which it would, in some cases) the difference in lifecycle cost wouldn't make sense in an economic analysis.

This will be the case in most areas where the heating design temps are in positive double digits, and often in situations with even lower design temps.  Design temps in my area are in low positive single digits, and the economic rationale for low-tonnage geo vs. ductless mini-splits has gotten real thin, even with substantial subsidy for geo, and nearly none for mini-splits.  Where there's a performance advantage to geo it doesn't usually make up for the cost multiplier over the life of the system, even with 15-20cent electricity.  The insulation & air sealing that can be purchased with even the post-subsidy cost difference is usually a far better investment, and the net power use lower.

It will get even more interesting when CO2-refrigerant hydronic air source heat pumps get here, with an even lower operating temp and higher operating delta-Ts.  (Sanyo is currently selling them in Europe for both low-temp hydronic space heating and commercial hot water heating.)

Posted By ICFHybrid on 15 Mar 2012 09:51 AM
...without troublesome ground loops.

Our installer had no trouble whatsoever installing our ground loops.  He was experienced and had proper equipment.  In three years of operating our system, I have had no trouble whatsoever with our ground loops.  What was your personal experience with "troublesome ground loops" again?  Do you have any geothermal experience whatsoever?

Posted By Dana1 on 15 Mar 2012 11:17 AM
My mother claims to have never noticed or even observed the defrost cycles
on her Mitsubishi mini-split in her foggy-dew Puget Sound climate ...

Uhh, are you really equating the climates of Puget Sound and the Philly 'burbs?

...REALLY?

Looby

http://www.furnacecompare.com/heat-pumps/daikin/reviews/

http://www.refrigeration-engineer.com/forums/archive/index.php/t-29823.html

http://forums.moneysavingexpert.com/showthread.php?t=2968958

http://forums.moneysavingexpert.com/showthread.php?t=3403593

http://www.navitron.org.uk/forum/index.php?topic=13449.0

Keep in mind, these are an accumulation of anecdotes, not data. The fact that some low energy builders might put them in for years does not mean that they work very well. I understand that you can do measure to protect them from snow cover. I see the lower installation costs, and the lower lifecycle costs, and no question that they are the way to go in above 30F climates. Most of the above reports are from the UK, with much warmer weather than continental US climate. And even the Pudget Sound climate is somewhat more suitable. Anyone here with deep winter experience?

Who would want to put mini splits into an average 2 story colonial or similar house anyway? What, like 4 or 5 or even more indoor units ... Really?and god forbid if you wanted to shut a door and freeze in that back bedroom. Lets keep the system comparisons to houses with ducting or underslab who likely need to stay that way. Most won't switch to mini-splits for many reasons even though they are great for certain applications and their efficiencies are very good. Your beating the mini split drum to death on a GEO forum...

In any event...Geo wins over air source on straight up efficiency, but it costs more, so an analysis is needed. Both system are good, but there are many variables that need to be considered. If you are going to stay in the house a long time (>8-10 years), geo will likely be better if your site variables will accomodate it. If you are short term, air source will win. If you go geo, you need a good contractor, which is not quite as important with air source, so that may make air source a lowerr risk and time investment on the homeowner. True COP is likely close to 3.5 for geo and 2.5 for air source in heat dominated climates like the north east. This is once you include losses for loop pumping for geo and defrost for Air source.

Chris

If memory serves, Dmaceld on this thread put a Daikin inside unit in a sealed, conditioned crawl space where it heats and cools his entire house. In a similar approach, I am putting an inside unit in a sealed vertical shaft that moves air between floors in my passive solar house. I've been looking at SEER 18, inverter models priced under $1k.

Posted By Looby on 15 Mar 2012 02:01 PM

Posted By Dana1 on 15 Mar 2012 11:17 AM
My mother claims to have never noticed or even observed the defrost cycles
on her Mitsubishi mini-split in her foggy-dew Puget Sound climate ...

Uhh, are you really equating the climates of Puget Sound and the Philly 'burbs?

...REALLY?

Looby

Really!

From a heating design temp and annual heating degree day point of view they're far more similar than different:

Outside design temps are within 10F of one another, and well into the reasonable operating temps of mini-split air source heat pump.   Compare Bellingham or Bremerton WA to Philly's 99th percentile numbers.  Seattle has a ~4600 HDD heating season to Philly's 4700HDD, need I go on? I'm not making it up. 

Yes, Philly has a lower average January temp than most Puget sound locations, but it's not 30F lower, not even 20F- it's less than 10 degrees.  Graph it on Weatherspark, if you like. The mean January temp in Wayne PA is about 33F, the mean January temp in Port Orchard is about 39F. BFD.

Outside design temps here in central MA are 10F or more colder than suburban Philly, (look up Worcester, Springfield) and people are heating with mini-splits here. (I'm not making that up either.)  If it works here, it surely works in Wayne PA.

Posted By chrisbiker on 15 Mar 2012 02:41 PM
Who would want to put mini splits into an average 2 story colonial or similar house anyway? What, like 4 or 5 or even more indoor units ... Really?and god forbid if you wanted to shut a door and freeze in that back bedroom. Lets keep the system comparisons to houses with ducting or underslab who likely need to stay that way. Most won't switch to mini-splits for many reasons even though they are great for certain applications and their efficiencies are very good. Your beating the mini split drum to death on a GEO forum...

In any event...Geo wins over air source on straight up efficiency, but it costs more, so an analysis is needed. Both system are good, but there are many variables that need to be considered. If you are going to stay in the house a long time (>8-10 years), geo will likely be better if your site variables will accomodate it. If you are short term, air source will win. If you go geo, you need a good contractor, which is not quite as important with air source, so that may make air source a lowerr risk and time investment on the homeowner. True COP is likely close to 3.5 for geo and 2.5 for air source in heat dominated climates like the north east. This is once you include losses for loop pumping for geo and defrost for Air source.

Chris

Those COP estimates work from central MA to southern NH and even southern ME, but both average and outside design temps in Wayne PA (from the thread that prompted docjenser to start this one) are considerably warmer than in southern New England- you'll beat 3 with a ductless Wayne, even if you only make 2.5 in Worcester.

Mea culpa if I'm pointing out that the cost differential isn't always rational from a price/performance perspective or a lifecycle cost perspective ESPECIALLY in a US zone 4 climate like SE PA. 

I'm currently responding to a thread titled "air source versus ground source in heat dominated climate", and make no apology.

Posted By Dana1 on 15 Mar 2012 04:55 PM
Graph it on Weatherspark, if you like.

Roger. Wilco.

The mean January temp in Wayne PA is about 33F...
the mean January temp in Port Orchard is about 39F.
BFD.

One of docjenser's primary (and as yet unanswered) arguments was the
issue of freezing HX coils in air-source systems at low ambient temps.

The Weatherspark graphs clearly demonstrate that freezing conditions are
the norm in the Philly 'burbs throughout Dec, Jan, Feb -- but rather unusual
around Puget Sound, even on the coldest day of winter.

...so, yes, it's quite a pronounced BFD,

Looby

What was your personal experience with "troublesome ground loops" again?

I presume you can read the threads involving troublesome ground loops right here on GBT the same as I can.

Posted By ICFHybrid on 15 Mar 2012 07:16 PM

Our installer had no trouble whatsoever installing our ground loops.  He was experienced and had proper equipment.  In three years of operating our system, I have had no trouble whatsoever with our ground loops.  What was your personal experience with "troublesome ground loops" again?  Do you have any geothermal experience whatsoever?

I presume you can read the threads involving troublesome ground loops right here on GBT the same as I can.

So, in your mind problems listed in help forums are representative of an entire industry.  Makes sense.   

Second request -
What was your personal experience with "troublesome ground loops"?  None?
Do you have any geothermal experience whatsoever?  None?

I think all agree both are viable technologies but comparing a minin split to a central geo is like comparing a space heater to a furnace. While both have their uses, their paths rarely cross.
If you want to compare multiple mini splits to a central furnace then it is 3K times........one for evry room or zone or....?
and what better place to preach minis than a geo forum?

Posted By Dana1 on 15 Mar 2012 04:55 PM

Posted By Looby on 15 Mar 2012 02:01 PM

Posted By Dana1 on 15 Mar 2012 11:17 AM
My mother claims to have never noticed or even observed the defrost cycles
on her Mitsubishi mini-split in her foggy-dew Puget Sound climate ...

Uhh, are you really equating the climates of Puget Sound and the Philly 'burbs?

...REALLY?

Looby

Really!

From a heating design temp and annual heating degree day point of view they're far more similar than different:

Outside design temps are within 10F of one another, and well into the reasonable operating temps of mini-split air source heat pump.   Compare Bellingham or Bremerton WA to Philly's 99th percentile numbers.  Seattle has a ~4600 HDD heating season to Philly's 4700HDD, need I go on? I'm not making it up. 

Yes, Philly has a lower average January temp than most Puget sound locations, but it's not 30F lower, not even 20F- it's less than 10 degrees.  Graph it on Weatherspark, if you like. The mean January temp in Wayne PA is about 33F, the mean January temp in Port Orchard is about 39F. BFD.

Outside design temps here in central MA are 10F or more colder than suburban Philly, (look up Worcester, Springfield) and people are heating with mini-splits here. (I'm not making that up either.)  If it works here, it surely works in Wayne PA.

One of the points is that both locations might have the same total heating degree days for the whole year, however, Philly spikes more down to more extreme temps way below freezing, while the Puget sound is influenced much more by the pacific ocean and keeps the temp relatively stable, usually slightly above freezing. Again, what works well in the Puget sound with above freezing temps does not have to work in regions with more extreme temperature dips.

So, in your mind problems listed in help forums are representative of an entire industry.

It's not just in my mind. The problems "listed" here definitely come from the geothermal industry.

Don't bother asking again geome, the artful dodger will simply misrepresent the question though the answer is self evident.

FWIW in the context of the thread I still maintain its silly to compare a minisplit to a central heat pump. Let's try a geo console eh?

Posted By ICFHybrid on 16 Mar 2012 02:13 AM

So, in your mind problems listed in help forums are representative of an entire industry.

It's not just in my mind. The problems "listed" here definitely come from the geothermal industry.

While most loop problems here come from incorrect installations, the are not many things which are more reliable than a correctly installed HDPE ground loop. Freezing HX coils in air-sourced HPs in cold climate appear to be a conceptual issue, although the HP manufactures are getting better in controlling it.

Don't bother asking again geome, the artful dodger will simply misrepresent the question though the answer is self evident.

My "personal experience" which seems to fascinate Gomer so much has no bearing whatsoever on the discussion here.

FWIW in the context of the thread I still maintain its silly to compare a minisplit to a central heat pump

Maybe you didn't realize that the Daikin Altherma unit Dana1 referenced above is not a minisplit.