Posted By jonr on 20 Mar 2012 08:55 AM
... over-sized heat exchangers are more efficient.

In thermodynamics, larger and less intense is ALWAYS "more
efficient" -- especially when being powered by the ubiquitous
"frictionless, weightless pistons" of Thermo-101 textbook fame.

Of course, at some point (after the frosh textbooks) there's
a course on engineering economics, or common sense, or
somesuch -- where we (well, some of us) learn that HXs the
size of Montana tend to be kinda spendy ...and ROIs tend to
diminish rapidly.

Executive summary: You pay for what you get.

Looby

Posted By docjenser on 20 Mar 2012 04:16 AM

Posted By Dana1 on 16 Mar 2012 02:29 PM
In regards to COP increases with modest oversizing, see figure 5, page 10 of this document.  

At 17F at mid speed it hits COP about 0.5 higher than running fully flat out. 

At 35F at low speed it hits a COP about 0.5 higher than running at mid-speed

In the sample location under discussion the  outside design temp is 15F, the average mid-winter temp about 33F.

If  25%-50% oversized for the heat load at 15F it will run between low and mid-speed at 33F, and between mid and high speed at the 15F design temp.

If sized exactly for meeting the heat load at 15F it'll only pull a COP of 2.1 at design temp rather than 2.5+, and at the average 33F winter temp would only pull 3.5 compared to 4+.  If oversizing a half-ton is even possible, it's worth it.

If you grossly oversized it (which is hard to do, if you have anything but a super-insulated house) you'd get a COP of nearly 5 at 35F by only running at low speed, but between the wind chill of the higher cfm  blowers on the interior heads  at min-flow and the short-cycling, would make it less comfortable.  These are fully modulating systems, but the turndown ratio isn't infinite.   When oversizing a ductless for higher efficiency 50% would be about the limit of what makes sense from a comfort/effciciency point of view.  br />

First I was looking at the document you had cited. And figure 5, page10. It compares a 1 ton heatpump under certain load conditions. it shows that the same heatpump with the same compressor load runs more efficient, because the power to run the fan higher outpaces the higher efficiency with higher air flow. So what is new? That does not mean that if you now take another, larger unit (oversized) that it will run more efficient.
PLus there is so much inconsistency in the figure, that I actually question the results and the accuracy of the measurements.
Lets say the intermediate compressor with the low fan at 47F has higher COP that the same intermediate compressor with low fan at 63F. Makes no sense.
Or there is no difference for high compressor/high fan between 7F and 17F. Very unusual.

The next report you throw in starts with "Now that this horse has been kicked thoroughly to death and then some" and you cite a engineerings bureau report to NYSERDA which describes a house with an air source heatpump system with a gas backup, which now means you are paying for 2 systems upfront (page 19). It makes the point that the heatpump itself is not able to keep up with the house load at lower outside temperature, thus the need for the additional furnace. The best here is that this is not meassured performance, but calculated by the engineering bureau based on manufactures' data provided and the bin data. Even further, certain things like the frequency of defrost cycles are "assumed". None of that is data, it is not even an anecdote!

Please check things you cite as evidence before you post them so we can take them for granted.

So, you don't like evidence like measurements (especially when they seem paradoxical or not every data point is easily explained)...

...nor do you like theoretic projections unless accompanied by anecdotes.  It's not rocket science to estimate defrost cycles based on weather history dew points & heat loads, but have it your way.

Anecedote 1: My uncle's heating power use on Whidbey Island is slightly less than what the heat-load tool projected for geo. He's heating with a ~50% oversized mini-split.

Anecdote 2:  My mother is using about 1/5 the power per HDD for heating  post mini-split than she had been using resistance heating forced-air, despite using a constant temp control strategy with the mini-split vs. 10F overnight setback strategy with the prior system, with a unit ~25% oversized for the load.

But those are mere anecdotes- they're not instrumented not even separately metered, way too fuzzy to be called "evidence".

You admonish me to check the evidence before posting(which I generally DO), yet you're happy to make assertions that minisplits lose huge efficiency to use of resistance defrost heaters (a component that that doesn't actually exist in any mini-split that I'm aware of), then post a picture of an ice-storm encrusted compressor unit improperly installed in the open as evidence that the mini-split defrost somehow can't keep up or are somehow so problematic that they cannot or should not be used in heating dominated climates.

More anecdotes:  While traveling earlier this week I at a restaurant in a ski-tourism town (Stowe VT) that was heated and cooled by a 2-ton Fujitsu, properly installed with a small shed roof protecting it from heavy snowfalls.  I stayed in a condo at ~1k' of altitude at a ski area (Smuggler's Notch VT) a few doors down from a ~750' condo heated with 2-head 20K Mitsubishi multi-split, (MXZ-2A 20NA), with the compressor politely protected from roof-avalanches & snowdrift by the back deck. (Other units in the building were heated with ~25-30K propane wall-furnaces, but that unit clearly was not, with no exhaust vents or regular/meter in evidence.) These are locations with negative double-digit design temps and annual snowfalls in excess of 200" .   Apparently the news that you can't run these things without them icing up or getting clogged with snow or ice has yet to reach snow country.

You also assert regarding my cited document with the ducted air source heat pump with gas-fired backup is "...paying for 2 systems upfront (page 19)", while  in the second sentence on page 19 the unit it's stated:

" The Belmonte Challenge home installed a high efficiency, dual fuel heat pump to provide space heating and cooling."

...which reads like a single system to me.  If that counts as "...paying for 2 systems upfront...",  a geo unit with auxilliary strip backup counts as two systems upfront too.

So yes, usually do read the stuff that I cite, sometime I read it in great detail. No, not all evidence is perfect or fully explained, but I don't view test data that seems paradoxical or difficult as completely useless, even if it begs for further testing to figure out the outliers. The folks at Ecotope (rightly) published what they measured rather than penciling  in something that may have been more intuitively obvious.  The error bars may be wide, but the trends are fairly clear. 

"" The Belmonte Challenge home installed a high efficiency, dual fuel heat pump to provide space heating and cooling."

...which reads like a single system to me. If that counts as "...paying for 2 systems upfront...", a geo unit with auxilliary strip backup counts as two systems upfront too."

It's more than semantical in this context- dual fuel suggests two different heating appliances i.e. air source heat pump and gas or oil furnace. Package geo systems are not dual fuel with electric auxiliary added which is a relatively inexpensive feature (about 1/10 the cost of a 95% furnace). Central ASHPs and mini splits require purchase of furnace or air handler with or without gas or electric back-up and may or may not be dual fuel. Some situations require no auxiliary for either system (ask Curt how many auxiliary coils he sells).

I again think we stray from honest discussion when we compare mini splits to any central heating/cooling system but folks seem to want to interchange ASHPs and mini-splits. Where all have there uses, design and application should be case by case.
Some of the new mini-splits are unfortunately getting their growth stunted by the same kind of band wagon guys geo suffers through with every new tax credit.

We do not include aux strips with geo systems. Our heating loads are generally equal to or less than our cooling loads, though we are at or near design cooling load far more often than heating.

Some may argue that we thus deprive ourselves of important backup capability, but no one dies or experiences frozen pipes here if heat fails, especially in the typical house getting geo (ICF + Spray Foam)

While minisplits are truly wonderful, highly advanced systems, they do not meet residential requirements down here with the exception of very small simple studio or efficiency apartments or enclosed "Florida" rooms, typically added after main home construction and not accessible to the main duct system.

The problem with minisplits here is that they are not able to reach small rooms needing conditioning - baths, WICs, pantries, laundries, commode closets, etc, whereas it costs me <$100 to run a 4" flex duct into those spaces, including a balancing damper to ensure they get only the 10-25 CFM needed.

Posted By engineer on 23 Mar 2012 02:06 AM
While minisplits are truly wonderful, highly advanced systems, they do not meet residential requirements down here with the exception of very small simple studio or efficiency apartments or enclosed "Florida" rooms, typically added after main home construction and not accessible to the main duct system.

The problem with minisplits here is that they are not able to reach small rooms needing conditioning - baths, WICs, pantries, laundries, commode closets, etc, whereas it costs me <$100 to run a 4" flex duct into those spaces, including a balancing damper to ensure they get only the 10-25 CFM needed.

Well put.  I'm so tired of reading all these fantastic posts about how mini-splits are the holy grail.  I wish this GEO forum would stay more on topic and be less combative with other technologies always being touted as suitable option over GEO for the typical home.   Just not so in most cases.

The problem with minisplits here is that they are not able to reach small rooms needing conditioning - baths, WICs, pantries, laundries, commode closets, etc,

As I posted once before, those rooms are preferred locations for HRV exhaust ducting. That arrangement draws conditioned air into the room and exhausts it as opposed to pushing it back out into the house when you have a heated duct in there. I'm glad you noted the use of balancing dampers as I've noticed those rooms are often way too warm when heated directly.

And as I posted before, no one says you can't add ducts to a minisplit -- by installing the indoor unit in a conditioned crawl space, by putting it in a great room from which air is drawn off by low-speed continuous fan, by buying a ducted version of the minisplit, or by any combination of the above.

Dana's point is that you get to choose how to spend your money in new construction. If you do it right, you won't need conventional hvac of any flavor.

Posted By chrisbiker on 23 Mar 2012 08:31 AM
I wish this GEO forum would stay more on topic and be less combative with other technologies always being touted as suitable option over GEO for the typical home.

Agreed.  There is an "Alert" button in the upper right corner of replies.  This informs the moderator that a post is "Off Topic".  There are also other selections including "Trolling".  If the moderator gets enough of these messages, perhaps some action will be taken.  I would encourage all members to use it.

Posted By toddm on 23 Mar 2012 10:03 AM
And as I posted before, no one says you can't add ducts to a minisplit -- by installing the indoor unit in a conditioned crawl space, by putting it in a great room from which air is drawn off by low-speed continuous fan, by buying a ducted version of the minisplit, or by any combination of the above.

Dana's point is that you get to choose how to spend your money in new construction. If you do it right, you won't need conventional hvac of any flavor.

The point you miss is when you add ducts and fans to mini splits efficiency plunges while cost rises rapidly. Not sure of your crawl space plan, but likely not suitable for those fettered with following the code.

Posted By chrisbiker on 23 Mar 2012 08:31 AM Well put.  I'm so tired of reading all these fantastic posts about how mini-splits are the holy grail.  I wish this GEO forum would stay more on topic and be less combative with other technologies always being touted as suitable option over GEO for the typical home.   Just not so in most cases.

I have asked before why people would pick the geo-centric section of these forums to suggest it is inferior to other technologies. Perhaps mods should open a mini-split forum for those smitten with the technology. Perhaps it would attract a few pros with real world experience vs stary eyed consumers with limited anecdotal experience in the Pac NW. By and large the pros here do not suggest ASHPs are unviable technology, simply that the uses aren't as versatile as some think.

docjenser started this thread after finding some pix of iced up and snowed over ASHP units so I am not sure how this is off topic. Maybe the trick is to start an argument you can win. Low speed continuous air movement costs me ~50 watts/hr. It should work in a high mass house because the delta t among rooms from hour to hour is tiny, absent big inputs of heat or cold. If it doesn't work I am out $1k. If it does, the life cycle cost will be a fraction of geo even if it runs at a COP of 1. (The COP in a trickle charge use of inverter ASHPs should rival geo.) Dmaceld on this site got a CO in Idaho using his crawl space as a forced air plenum.

Depending on what code is enforced and the education of the inspector, a crawl may be a plenum. Those areas governed by the ICC permit the crawl to be a return air plenum only.

Incidently areas governed by the ICC also require an "an automatic heating system" to provide 68* in all occupied space. While your plan is cute and potentially doable it is still not an option for those of us governed by codes. It would permit you to use multiple mini splits or ASHP on air handler or furnace with duct system etc. it would not permit you to duct a ductless system. You aint gonna find that app in man. D.

BTW who the heck wants a heating and cooling system that can't recover large temp swings in a reasonable amount of time. Certainly not my customers; ah but again the fetters of the real world......

If you want to tout the strengths of a "ductless" mini split, why not select applications in it's wheel house, not mutations of it's purpose.

By and large the pros here do not suggest ASHPs are unviable technology, simply that the uses aren't as versatile as some think.

The same might be said for either side, as both Dana and I have supported geo source heat pumps on numerous occasions. It's only the individuals who sell the units who seem to feel so embattled.

Toddm correctly noted how this thread began, so all the claims about being "off-topic" are rather disingenuous.

Posted By geome on 17 Mar 2012 10:17 PM

Posted By ICFHybrid on 17 Mar 2012 01:20 PM
Even though I have accessible acreage on this build, I am pleased that I don't have to have a ground loop. It just adds another layer of issues.

Posted By ICFHybrid on 08 Feb 2011 05:49 PM

BTW, I do own a geothermal system and have now installed the field all by my lonesome in the bitchiest weather in recent history.

ICFHybrid, lie or withhold pertinent information much?

Perhaps you would enlighten everyone as to the troublesome loop problems you experienced by installing your own loop with your personally subcontracted, piecemeal, geothermal help which you spoke so highly of (from a cost saving standpoint) in the thread "Why do Geothermal Systems cost so much"?

Second request. 

"The same might be said for either side, as both Dana and I have supported geo source heat pumps on numerous occasions. It's only the individuals who sell the units who seem to feel so embattled."

Not sure I follow. Are you suggesting that the pros here (on a geo forum) have the gall to imply geo is a superior product in many applications. OMG! Course I can't think of any of the pros here who haven't suggested a different tech from time to time depending on the application.

I think I'll re-suggest ASHPs get their own forum. The advancements in the technology are worthy of it and it would benefit from contribution by pros who prefer it.

For the record, in the thread that prompted this thread I was talking up spending the serious cash on tightening up and better insulating the house to reduce the heat load first, and THEN looking at the bang/buck going with geo vs. a Daikin Altherma (air-to-water based on inverter drive mini-split compressors) or even a mini/multi-split solution. The location in question (Wayne PA) has a 99% design temp of +15F, and a winter average temp of over +30F, a climate in which the average system efficiency of this better-class of ductless air-source would be comparable to geo. The size of the 1920s vintage house was a ~2500' two story, size & shape where it seems likely that the heat load at design temp could be brought down to under 3 tons, possibly 2 tons for less than the installed price difference between a 2 ton Altherma and a 4 ton geo, and with half or 2/3 the load the Altherma would use considerably less power to boot. (Similar efficiency, lower load.)

I really DON'T have anything against geo, but when push comes to shove I'd rather people spend their money wisely, and rare is the 1920s vintage house that can't be made tighter for the kind of money we're talking. In colder places & bigger heat loads, in buildings with few or no retrofit options geo truly stands out.

I was surprised at first to see a number of places in northern VT (US climate zone 6) heating with mini-splits, but perhaps I shouldn't have been. Design temps may be in negative digits (negative double-digits at altitude), but mid-winter averages are in the teens. I suspect the seasonal average COP would only run about 2.0-2.2 in those areas, but since the gas-grid isn't well developed, that's still going to be significantly cheaper to heat with than propane or oil. Electric baseboards to cover the deficit when it's -20F out isn't a very expensive backup either. As long as the output of the air source heat pump at the winter average winter temp more than covers the heat load at that temp, performance will be reasonable. But the lower the average outside temp, the smaller/tighter/higher-R the place has to be for that to be the case: A sub-1000' ski area condo, no problem. A 3500' colonial, maybe not, unless you're looking at PassiveHouse type tightness & R values. I haven't seen mini-split compressors cozied up to any of the latter.

But with a super-insulatoin approach it can be done pretty handily. This 3000' house is about 5 miles away from mine, heated with a 3-head 2.5 ton multi-split:

http://www.greenbuildingadvisor.com/blogs/dept/green-building-news/matt-beaton-s-full-court-passivhaus-press

The outside design temp at that location is about +5F, average January temp something like +23-25F. At 2.5 tons it's way overkill for the actual loads, but they wanted 3 zones.

I'd be happy to see a forum for air source heat pumps, but that wouldn't stop me from sticking my head in here and chatting up the cost/benefit of putting the money into reducing the heat load first on projects like the one in Wayne PA and seeing if it wouldn't end up with lower overall power use using less expensive mechanicals for the same cash outlay.

Second request.

How many houses do you own?

Posted By geome on 23 Mar 2012 01:12 PM
ICFHybrid, lie or withhold pertinent information much?

Posted By ICFHybrid on 24 Mar 2012 12:21 AM

Second request.

How many houses do you own?

Stalling for more time to make up a believable answer, huh?  Your credibility is already shot.

Dana I agree with insulation and load reduction. You and Curt have been large part of my education in that regard. So was a problem in the field when reliable software didn't seem so reliable any more (blower door test revealed major softspots in insulation.....).
I will add alert to your last post as a Yea toward ASHP forum- I think it's time.

For those who don't know....Daiken curiously makes water source products and owns McQuay so I'm gonna guess they don't think air source is the only answer.

I used to support the notion of an ASHP section, but I'm not too sure about that anymore.

For example, if an ASHP section did exist, which section would the OP have posted in and what was the purpose of it?

As Dana points out, the existence of separate sections wouldn't stop him from weighing in on issues that come up in either section and I'm sure that goes for a number of others, me included.

The ones who seem to be calling the loudest for separate sections are the "pros" who appear to think that they might get their own sandbox to play in and control which is not the purpose of GBT at all. This exists to have an open dialog on all these issues. If you have some single-minded promotion in mind, I'm sure all of you have an advertising budget which you can use as you see fit.