I am building a log home in eastern N.C. We will be running mini splits throughout. I was recommended to also install a whole house dehumidifier and air filter. I can see the benefit in moving the air through the house and preventing stale air in certain rooms as there is no central air system. If I do a single return in the center of the house do I then look to run ducts to the corners of the house? Also I am doing a sealed crawlspace below. Should I condition it? Should I let the dehumidifier suck in air from the crawlspace?

Whew ! you will get a page ful l...
there are several log home , sealing to oversize the heating pages around here!

However, I do not see how you will heat hot water too...  and how big? How insulated?

BUNDLE: HVAC-HW 9hot water system selected yet? Heat pumps since the 60's have heated HW, and later in cooling for savings. 
Priority HW with a GT System; Also can be with mini splits but a significant 2-ton single GeoThermal with 100% Priority HW in Cooling mode- as recovered heat (loop pumps off line then) can also be programmed for SPECIAL DeHumidification too, and eliminate buying another dehumidifier
a little noisier AIR-Ht-P HW heaters runs like a dehumidifier need heighth if not the Hydro-Temp (,com) or others similarly like it

a little ducting will get your corners with say 6-to 8 runs on a 2-ton, set ~ 700 cfm to 900 on a higher choice, one bigger filter for air cleaning too.

From that 2 or 3T GT: Forced Air and WITH / same unit , one box, ---If you want a fancoil zone, the HYDRO-TEMP makes a unit with HYDROZONE also which you can send HW or Chilled fluids (shared with air-coil, and blower shuts off while fluid zone is called, too) - to another fancoil(s) of many designs, some look like consoles on walls. Or you can order a w:w unit and minisplits and still do most of that too. Enertech adv in directory has TETCO full HW systems, and more. 4-zone controller is built in OEM

JP
www.GEOPros.com


I see the alternatives coming: but programming air speeds by temperatures, selecting say 100 deg at the registers or just 350 cfm per ton (that is compressor ton in the box--- watch rated units "tons" and ask what's in the box, since ALL must be Energy Star Compliant for tax credits) 350 cfm/ton in cooling, separately programmed, can wring the water out a fast as the best that you will ever need. (Palm(TM) programmer, logs, to 9 sensors.

Why not just make sure the minisplit system you use has a dehumidification mode?  Most inverter driven minisplits that I have researched do, and I would expect they can be programmed to shift into dehumidifier mode under certain conditions, such as time of day or when cooling/heating setpoint is reached.

Most whole house dehumidifiers are designed to work with a standard central ducted air conditioner.  A multi zone inverter driven minisplit system is a completely different dynamic due to the variable speed of the compressor, the size of the coils in the head units, and some, at least, use a pulse width modulating expansion valve that create an additional degree of freedom.  Not the same animal.

Thanks to you both. GTJP I would love to have gone GT but budget sent me to Fulitsu mini splits - can do it myself and units run $1500 and they can get 25 seer. Am seriously looking into a heat pump WH. Also will check specs of Minisplits for DeHumidification function. I want to do a sealed, conditioned crawlspace. Am thinking to draw air form inside house into whole house filter then into crawl space and back into house. My concern is smell from under house crawlspace air. Any thoughts?

Sealed crawl spaces in my area (dry Colorado) do not have any smell, and therefore are not like the old vented crawl spaces. Does your sealed crawl space have a smell? Maybe it is not yet constructed, but hopefully it will be dry and mostly odor-free.

A disadvantage of the minisplits is that they do not have ducting, so it is hard to arrange for airflow through the crawl space. I have a ducted natural gas furnace, and the heat recovery ventilator (HRV) uses the same ducting for the outlet side of the HRV. The stale air inlets for the HRV are on opposite ends of the crawl space to make sure that there is airflow from the house and through the crawl space and then the stale air is exhausted. What is used more commonly here (in homes without HRVs) is an exhaust fan in the crawl space, so house air flows through the crawl space and is exhausted. With either of these two arrangements, any smells from the crawl space are not blown back into the house.

If your minisplit is for both heating and cooling, I assume that when in cooling mode, it will certainly be dehumidifying the air. As the air cools, physics says that the water vapor will condense, and the minisplit will have some provision for draining that water.

Dehumidification mode on most mini-splits is a cooling-only, but Daikin Quaternity can dehumidify in heating mode as well. See: http://www.daikinac.com/residential/productsUnits20-humidity.asp?sec=products&page=55

With a vapor-barrier in the crawlspace floor and a sealed-insulated crawlspace wall, the bulk of the humidity issues will be from air-leakage in summer, and occupant-activity (breathing/bathing/cooking). The logs themselves can buffer a significant amount of moisture, so long as the roof overhangs are big enough to prevent a lot of direct rain or splash-back. It's not clear that a whole house dehumidifier would ever be necessary, but an ERV ventilation system is a good idea, which would tend to even-up room to room humidity differences. In cooling mode all mini-splits will be dehumidifying, even when not explicitly set to dehumidification mode.

Take the money you would have spent on a whole house dehumidifier and plow it into ERV. In winters most log homes are leaky enough (read "too leaky") that dry air is more of an issue than air that is too humid. In the shoulder seasons one can either use a standalone 70pint or larger room dehumidifier places in the crawlspace, set up to drain into a sump (or a condensate pump arrangement) if moisture levels rise too high before it's a true cooling season, or you can buy into Daikin Quaternity mini-split technology (which has better dehumidistat control than any standalone.)

The crawlspace will likely be the coolest spot in the house in summer so unless there is good air communication with the rest of the house it will tend to have the highest RH. But with an ERV feeding it even a modest amount of ventilation air it's humidity will pretty much track with the rest of the house, despite the incomplete drying of the ventilation air by the ERV. If you keep the rest of the place at 50% RH or lower in summer, with ERV ventilation it's unlikely that the crawlspace would hit mold-inducing levels.

And in eastern NC it's definitely ERV, not HRV that you should be looking at- your summertime dew points can be quite high at times, and ERV will cut roughly half the moisture out of the ventilation air, relieving the latent load on the mini-splits.

Thanks for the input. While researching I found this link that puts me off the value of an ERV. Check it out and see what you think. http://www.greenbuildingadvisor.com/blogs/dept/musings/hrv-or-erv
It seems that the only time I should be worried about humidity is during summer and so why introduce outside air that brings in moisture - like you said the log cabin is not likely to be that tight. So if instead I set a DH in the crawlspace and draw air from the downstairs rooms into the crawlspace I will be conditioning the crawlspace and removing the moisture. I can then vent the dehumidified air to the upstairs to get good circulation and provide the vacuum to draw the air from downstairs in. I'm an amateur here so feel free to tell me I don't know what I am talking about and point me in the better way. Brian

Posted By kiwielectric on 06 May 2012 07:31 PM
Thanks for the input. While researching I found this link that puts me off the value of an ERV. Check it out and see what you think. http://www.greenbuildingadvisor.com/blogs/dept/musings/hrv-or-erv
It seems that the only time I should be worried about humidity is during summer and so why introduce outside air that brings in moisture - like you said the log cabin is not likely to be that tight. So if instead I set a DH in the crawlspace and draw air from the downstairs rooms into the crawlspace I will be conditioning the crawlspace and removing the moisture. I can then vent the dehumidified air to the upstairs to get good circulation and provide the vacuum to draw the air from downstairs in. I'm an amateur here so feel free to tell me I don't know what I am talking about and point me in the better way. Brian

The dew points in summer can be QUITE high in summer, in NC and cutting out half the humidity in the ventilation stream cuts the load on your standalone dehumidifier.  The dehumidifier raises the temperature of the air in the house with every pint of humidity taken out, so it really does count on both comfort and energy use.

In winter the outdoor air is dry, and at high ventilation rates with an HRV (or leaky house) it can be come uncomfortably dry, or even unhealthy.  By recovering half the humidity in the ventilation air you moderate that wintertime effect, reducing or eliminating the need to add humidity to the air to keep it above 25% RH.  Adding humidity reduces the air temperature, so retaining some of the humidity in the ventilation air reduces the heating load.

If you lived in the Rocky Mountain west where summertime dew points are low an HRV makes more sense than ERV (though some would still want it for the wintertime dryness issue.) But anywhere in the southeastern US ERV is the higher-comfort/lower-energy-use way to go.

Where ever you live, building the house as air-tight as possible is an important comfort and energy-use consideration.  Log houses are notoriously difficult to make ultra-tight, but that doesn't mean throwing your hands up in defeat is the right response.

Now how big is it all anyway?
if it is over a crawl space and if it is possible that I am assuming you would have a 1400-1700 sq ft log home with a vaulted ceiling as well and some upper level half taken space to make it a 2000-2400 "log home-----
If that is close, or larger, a dehumidifying and cooling hot water-heat-pump over tank, has an initial benefit. But where would the noisier HW-maker go? I have looked at some costs PA-WVa etc:
if you have a decision made and the system is in DIY and you just finished setting the thermostats and HW setting-----
HW air Ht-Pump over tank fit in place with some expectation of maintenance in plumbing in all fittings @ $ 1800 (cheap) then insulate lines

http://www.homeenergy.org/show/article/nav/hotwater/page/7/id/1315 etech

PERHAPS you could look at:
http://klimaire.com/product.htm 16-to-20seer Minis which have exactly the same drop off in performance in humid winter 15 deg freeze ups as the very high Mits-Z ~ COP can be just 1.8 at 15 above. but see if you can have a situation like that ever of your exacting conditions by calling a few manufacturers. It was interesting to hear from Klimaire their real world examples of the freeze-thaw cyclic loss in COP of any air source heat pump. A 1993 DOE study of NOX gas emissions reporting showed what is still the real world issues of today: Air Heat Pumps are still about 34 to 42 percent less effective than a GSHP to 5 above and even 12 above of what is of today, a standard 2012 COP minimum set by the Energy Star requirements for a tax credit .

WHOLESALE say 4) 9000 and 3-tons machine [for only less than 20,000 btuh if it gets below 25 degrees] and fittings (and a CFC license that is to be, really.....) DIY as an installed job with a CFC EPA buddy @ $ 5000- 6000  x 1.5 I believe, because of but after calling about the heating performances at 15 degrees, it really appears that that same 34% to 42% UP-SIZING is still required over a proper GSHP., after all things considered, what is the back-up to the Air Ht Pumps for you comparing to a supplement (if any) in a few winters with GSHP? DIY a 3-ton GSHP duct work is inexpensive. I mean of I would be able to do with of 8 runs of 7" flex or 6" metal piping and a great return air and air in the basement recirculating.

research is easy here and it is about Mitsu also:
http://www.squidoo.com/air-source-heat-pumps-for-cold-weather

http://welserver.com/WEL0457/ DIY

http://welserver.com/WEL1000/ radiant and other

welserver.com  and at their home pages "balloons" you really can pick from many, you might call the other companies to get some of this old information you will be able to benefit from

I am sure geo H.P. would be great but you have to add up costs. Doing the mini splits DIY will cost us about $8500 for the house. It is about 2800 sq ft with vaulted ceilings. That's four 9 BTU units and two 12 BTU units - fujitsu 25 seer rated. And no ducts to run. If we went with the geothermal its a lot more work and the water here is deep down and full of minerals so would have to get closed loop wells drilled. Then have to get the cost of the geo system. And after that we are not much better off with efficiency. Even if it ended up costing just $10,000 more for the geothermal system we would never recover that cost if the system lasted for 2 lifetimes - O.K. maybe after 100 years we would break even. Also with mini splits each room is individually controlled - a great benefit for a 4 bedroom 2 story home. The disadvantage of the minis is that if it does get really cold - below 20 degrees we might need to plug in some heaters. But with Thousands saved on the install and weather that cold pretty rare here that is still a better option or better yet put an extra blanket on the bed.
Here's a question for you. If we were going geothermal could you put it in a conditioned crawlspace or would it create a moisture problem?

Posted By kiwielectric on 26 May 2012 07:54 PM
1) I am sure geo H.P. would be great but you have to add up costs. Doing the mini splits DIY will cost us about $8500 for the house. It is about 2800 sq ft with vaulted ceilings. That's four 9 BTU units and two 12 BTU units - fujitsu 25 seer rated. And no ducts to run.
2) If we went with the geothermal its a lot more work and the water here is deep down and full of minerals so would have to get closed loop wells drilled. Then have to get the cost of the geo system.
3) And after that we are not much better off with efficiency.
4) Even if it ended up costing just $10,000 more for the geothermal system we would never recover that cost if the system lasted for 2 lifetimes - O.K. maybe after 100 years we would break even.
5) Also with mini splits each room is individually controlled - a great benefit for a 4 bedroom 2 story home.
6) The disadvantage of the minis is that if it does get really cold - below 20 degrees we might need to plug in some heaters. But with Thousands saved on the install and weather that cold pretty rare here that is still a better option or better yet put an extra blanket on the bed.
7) Here's a question for you. If we were going geothermal could you put it in a conditioned crawlspace or would it create a moisture problem?

1) Sooooo really, 9 units with both ends, tax, line-set, condensate disposal for less than $1,000 each. Hmmm, well since we wanna skip a few details, the last DIY geo kit I sold was $9,500 (course the homeowner had some loops already, did his own digging etc).
2) If you go with anything ducted it will be more work for more space conditioning. For example you mention 6 splits for a 4 bedroom house. Are we to believe you only have 2 other rooms in the house or that you won't be directly conditioning some?  Course more work = more product, more even temps, more comfort etc. You mention wells and bad water in your AO, is a horizontal loop system not doable? Let us not forget water is not bad everywhere nor is airsource good everywhere.  
3) Depending on where you are at the efficiency boost can be quite significant (~1 COP).
4) Maybe maybe not depends on a lot of factors, If you were already going to spend $8,500, then at 10k more the geo is $18,500 less 30% tax credit ~5,500 the geo is actually $4,500 more. Your thinking the geo is only $45/yr less to operate? Maybe depends on where you are at.
5) With your minisplit proposal, each room with a minisplit is individually controlled. Some rooms are only conditioned by accident.
6) So the disadvantage of minis is they can't heat your house when it's cold? The disadvantage to your space heater theory is it may not comply with code (depending on design temps).
7) Geo can go anywhere any other appliance can.

Look there is no technology that doesn't have it's wheelhouse. Air source is definately better in some areas than others as is geo. If nat gas is available then little is more cost effective to heat your home.
If you do it yourself, a nat gas furnace and regular central air or airsource split unit would be cheaper than your minisplits and heat every room.

Why do people always tout ducts as a disadvantage? Don't you want heat to every room? Aren't you governed by a code that requires it? Some here suggest adding ducts to distribute conditioned air from mini-splits?! Isn't that now a ducted system?
If you want a real comparison for minisplits, look up console geos. They cost about the same as your minisplits and sip water. How 'bout gas fired space heaters? They are even cheaper than your minisplits.

If you wanna compare technologies, compare apples to apples- ducted or not.

I have 2 different projects currently where (after the tax credit) geo is cheaper to install. Annual savings for both jobs is approaching 2K so even were there no tax credits pay back would be 5 ish years. True everywhere? Absolutely not, but what is true everywhere is that a ducted system in forced air heating and cooling will always deliver better than unducted if we are talking a single unit with multiple rooms.

Call me crazy, but 5 tons of mini-split capacity seems like extreme overkill for any 2800' house, even if it is an air-leaky thermally so-so log house.

And six of anything is just plain silly- if ductless, go with multi-splits (and maybe just one, two only if you have to.) But if subsidized geo isn't a big cost adder, the potential boost in efficiency may be worth it. Vetting the geo designer would be important though, since the as-built efficiency could end up no better than a mini-splits, whereas mini-splits are "systems in a can", and the primary determinant of average performance is the average outdoor air temperature (and to a lesser degree, average winter dew points: high dew-points=higher defrost duty-cycle=lower heating capacity). In eastern NC you'll average in the mid to high 3s for seasonal COP with better-class mini-splits, which would be about the same performance of lesser-quality geo system designs. If it's going to cost more it had better perform better, yet there are many existence-proofs of under performing geo despite the higher attainable performance when best-practices are used.

I can't imagine that 5 tons of mini-split wouldn't be able to keep up below 20F though. I'm fairly confident that I could heat my ~2400' (+ 1500' of semi-conditioned basement) 1920s timber-framed house comfortably with a 4-ton 3- head multi-split at a design temp of +5F if I had to, but being on the gas-grid there's no reason to go there. This house is full-dimension 2x4s 16" o.c., with retrofitted cellulose in about 85% of the wall area, 2x6 rafters with R20 batts in some, open cell foam in others, definitely not superinsulated, antique double-hungs + storm windows throughout, but reasonably tight for it's ilk. Using the boiler efficiency and fuel use to measure the heat load the heat load is a bit shy of 3 tons @ +5F, and as I slowly upgrade the place I'm confident I'll bring it under 2.5 tons eventually.

I have a relative in the northwest heating about 2500' of living space in a 1980s code-min house with a single head 2-ton mini-split, in an area with a heating design temp of about 20F (but it gets down to +15F at least once, most winters.) The heating design temps in eastern NC are also around 20F, but the average winter temps are higher (and wintertime dew points lower) than in the Puget Sound area, so average mini-split performance will be better on both efficiency and capacity than he's getting. (And he's no tough pioneer willing to freeze to save a buck, and his wife wouldn't allow it even if he were. :-) )

In a tight moderate-R (~R30, whole-wall) house with decent better-than code windows, in an NC climate you could probably heat point-source style in reasonable comfort with a 1-ton, like this guy:

http://blog.energysmiths.com/2012/03/winter-temperature-data.html

If you zoom in on the graph you'll note that yes, it did get down to about 65F when it hit +12F one night, but if he cared he could have thrown a stick in the wood-stove. Looks like he sets it around 68F, but sees modest but comfortable overshoots from passive solar gains through windows.

http://thrivingonlowcarbon.typepad.com/.a/6a014e86fffc67970d0168e8dd528a970c-pi

Before spending $8500 on way too many mini-splits or geo, consider seriously what 2" of closed cell foam would do for you. Log homes are cute, but they suck from air leakage and thermal performance points of view. Air-sealing with R12 in foam to a leaky log structure does more for comfort than any mere heating system would. With high-R (or even moderate-R) walls the notion that it needs micro-zoning on a room-by-room basis is just plain wrong. In a tight moderate-R house heated with mini-splits the ventilation system design can reasonably balance temps without increasing power use if you think and design carefully, placing the mini-split heads and ventilation supply registers in rooms where the bigger loads are, and putting the ventilation exhaust registers in the other spaces. (Marc Rosenbaum's house in the link above does not even use that strategy, since it was originally heated with an oil-fired boiler and zoned-baseboard heating. Yet the delta-Ts between the heated room and the rest of the house are reasonably well bounded.)

Putting geothermal (or anything else) in a conditioned crawlspace does not create a moisture problem. Moisture problems come in three flavors:

Bulk water intrusion (hopefully it's graded and drained properly)...

...condensation (which won't happen if you've insulated the crawlspace properly- including R5 or more foam on the crawlspace floor, so that the crawl tracks the temperature and humidity of the first floor)...

...and water vapor diffusion (which is handled by ground vapor-barriers and properly selected foundation insulation materials using semi-permeable rigid or spray foam between the foundation wall and any fiber insulation, and leaving the fiber insulation fully vapor permeable but air tight- no facers.)

The definition of a conditioned crawlspace means those details have been attended to. If you place mechanical systems in the crawlspace you'd use the same condensate handling methods during the cooling season that you'd use when placing them elswhere. The biggest moisture threat to the crawlspace would be from plumbing leak.

Ducts done to Manual-D perfection are not necessarily a disadvantage, but when implemented at "typical" leakage and balance they drive outdoor air infiltration, lose performance to unconditioned/semi-conditioned space, and in all instances take power to drive, reducing the net COP of the system. The performance of even the best inverter-drive ducted split-system air source system is a the mercy of the duct designer/installer, and usually can't touch mini-splits for whole system efficiency. But the notion that one must separately provide"... heat to every room..." only applies to fairly low-performance buildings (arguably this is one, if it's a typical log house), as is the notion that there is a "...code that requires it...". Many high-performance house work just fine with point-source heating. Ventilation air to every room is important in a very tight house, but the incidental leakage rates of log homes are atrocious. But it's the heating cooling load of that air leakage that argues in favor of separately delivered heating/cooling to that room, not necessarily code. In most of NC a tight R13 + 5 c.i. with code-min windows could be designed to do just fine withoutsupply ducts to every room with a bit of forethought to the ventilation system, but with R20 + 10 c.i. construction (~R25 whole-wall) and better windows it could be treated in more of a point-source fashion.

But tradition (and sometimes code) still treats the building envelope and mechanical systems separately, even though it's been demonstrated that better overall performance can be delivered at lower cost when the building & systems are designed with some synergy & feedback using energy use modeling tools. It doesn't need to be anywhere near PassiveHouse levels of thermal & air leakage performance before ducts to every partitioned space become superfluous. A 3-family deep energy retrofit I've been advising on ~R40 whole-wall insulation levels with ~U0.20 windows, and uses the ERV system to assist in balancing the room-to-room temps to the bedrooms & bath, with only a 1.5 ton single-head mini per apartment as point source heat, located in the kitchen/dining/living area (separated by open archways rather than doored off from one another.) The partition walls are ~R2.5-ish, by design the ventilation air-stream balances the most of heat loss out of the bedroom window, and the delta-T between a 70F common area and a bedroom at the +5F outside design temp comes in at just a bit shy of 4.5F in simulation, and that's only if there's nobody in the bedroom and the door is closed. When occupied with even at 1 person occupancy the "human-space heater" effect balances it even further. (I get bigger delta-Ts than between rooms in the ducted air zone in my house, but mine is an antique with much higher U-values for both walls & windows, and the ducts were installed before Manual-D was invented.)

I'm assuming this house is off the gas-grid, or the notion of using mini-splits for heating wouldn't even be on the table, since gas heating equipment & fuel is so cheap. Condensing propane would be relatively cheap to install, but far more expensive to use.

There is too much lip service paid to residential "code requirements" in order to support traditional methods of heating and cooling . Is there something about "code" that limits ductless applications?

"Educated inspectors" are those who know more than the letter of the code. They know the intent of the code such that they can understand how you don't have to have a dedicated heat source in every "room".

What is the energy code definition of "room" as it pertains to residential construction, anyhoo? I've got no heat in my pantry which is bigger than many peoples' kitchens. Is that a code violation?

As Dana points out, when building envelopes improve, we no longer have to have a duct register in every room in order to hold comfortable temperatures.

It's tough to improve log homes to a high performance standard, and are destined to disappear as a construction method where <3ACH/50 air tightness is required per IRC2012. But in a climate as mild as eastern NC you probably don't need a heating/cooling unit or duct in every room, if you're judicious about placing them in rooms/spaces with the highest heating & cooling loads, even with log house.