Posted By Bob I on 02 Jul 2012 02:52 PM
I should have mentioned that the house has a number of south facing windows which contribute to the heat gain. This house was 2x6 walls with cellulose and 2" of XPS on the exterior. Cap is a flat attic with R-60 cellulose. Basement has 2" closed cell spray foam and R-21 fiberglass on the walls and R-20 under the slab. the slab is completely thermally broken. My next generation of homes will have double 2x4 walls with cellulose, the same basement setup and either an R-60 flat attic or R-60 slopes using TJI rafters and triple glazed windows. The majority of the air leakage (<1.0) seems to have been the (standard) Therma True doors so we're going to multi point lock system as a tighter alternative.

I've used direct vent high performance gas (propane) boilers and furnaces for thirty years; good product. The difference is that in a very tight superinsulated house the temps are consistent throughout the house, so you really do not need ductwork. The ideal would be a minisplit and enough PV to run it. (and at $500 per year you wouldn't need a very big system.) A ducted FHA system would run 12-15K; a minisplit 5K. The owner had been dreaming of a geo system for years, so that's what we installed. Bottom line: get the heat loss - and air tightness down first, then decide on the heat source, then how to power it.

The real issue with sill seal is that you spend $.10/LF, you get an effective value of between -0- and .01. It's junk. Accept that and move on. I design the houses to be built by good, average framers. They tape the ZIP sheathing which I can see; I handle all the other air sealing issues.

Gee, Bob. You've really got me thinking about the minisplit option with net-metered PV to offset some electric costs. You mentioned it to me last fall when we met but I was leaning towards a low-temp baseboard that would be conducive to solar hot water in the future. But the minisplits would take care of heating and AC in a relatively simple installation. With a wood backup (which I was planning anyway), it might be the way to go for me. 100% output down to +5 degrees is nothing to complain about either. I've been reading in many other posts that tightly insulated/sealed houses have much more even temps and no need for ductwork, which plays in favor of a minisplit. I could probably get away with 2 heads on the inside. Have you run into any code issues with inspectors, e.g. requiring backup heat? How many $$ worth of PV would be involved in the 1500 sq ft house you originally talked about?

HI steveusaaf
These folks used 4000 KW for the six month period. Using May & June as an average for non - heated months, they used slightly less than 1400 KW for heat for the six months. I don't know how many panels it would take to cover that on an annual basis, but you could find out easily. Also can't answer your question about building inspectors. In NH, each town has it's own inspector and they are all different. Backup heat, where required can be baseboard electric, which is accepted by everyone as a heating source. They might want some confirmation of your calculations, though.

This is a new technology for almost everyone, but I was very impressed at the NESEA Buidling Energy Show in Boston in March (Best place for info on these buildings!) how many progressive builders are using them and how happy they are with them.

You may have read this, but there is a growing feeling that the days of solar hot water has passed and that solar PV is the way to go. I don't have enough knowledge of either to advocate either way, but PV is getting cheaper and in terms of heat, heat pumps are becoming more efficient.

I think active solar-thermal is dead or dying from a space heating point of view, but probably not for hot water. With a ~15% post-inverter efficiency for the PV, and an annual average COP of 3 for a mini-split the net efficiency is still less than 45% for the collector, but the relatively simplicity and modular aspects of both the PV and heating systems make it more reliable, with lower design-risk than traditional active solar thermal heating.

Solar PV provides a more premium-value output per square foot of roof area, but even coupled with a heat-pump water heater that draws it's heat from conditioned space it's net-efficiency as a heater isn't really as efficient as hydronic active solar for domestic hot water. The hybrid designs (SunDrum, etc) that marry PV to a solar thermal panel can maximize total utility of the roof area, but (of course) for a price.

Marc Rosenbaum wrote a piece recently for Building Science Advisor (I think) where he discussed the relative merits of heat pump water heaters in various situations - superinsulated houses with minisplits, older inefficent houses. etc. Well worth finding & reading.

active solar-thermal is

quite alive for using a 10x 4 sheet of 24 ga galv duct metal to get nearly 8x3 air solar collection...
1.1/2" poly like c-tex for back and sides inner walls
3 layer window screening (baked 500 deg, OEM )
stretched inside under TFE clear layer barrier,
under solar glaze or filon-like (yellows in a few years, lasted near 22 years)

In Dayton OH  over 3000 btuh, normal (perpendicular) to the sun , usu set ~ 51 to 49 deg off grade...

4 systems of 6 to date since 1980 are operational, pleated-air-filtered, all flex duct in attics, all high return air grills contributing to air rotation...
?-1 gone, other: bro-in law enjoyed 200 annual gas bills since 1980 to 300 abouts in 2010 , 1700sq ft , replaced w/ new roof in upgrade to home value instead of current costly solar air cert collectors, even at breaks.

DIY is best or get a sheetmetal shop to build the old SOLSTAR(tm) 1980's version w/ more thickness to the insulation. 55 to 110 cfm per collector with 2 speed blowers was best, by second 110 snap disc "sophisticated" controller; first @ 100 "on", to a common "fancenter" or 24v induction relay on a pig-tale for a plug-in disconnect, through a switch.

6 collectors was too big for 2800 sqft ranch, generally getting 85 degree rooms in feb... standard OLD INSULATED STRUCTURES.

:)

Posted By Lee Dodge on 01 Jul 2012 01:30 PM
Joe,

I know this is a tricky question, but what would typical costs be for a heating-only system without hot water for a the 1500 sq. ft. one-story ranch described above in New Hampshire (or in your area) for the following:
1. hot-air furnace with ducting
2. minisplit (single outdoor unit, with two or three indoor units?)
3. geothermal

Sorry, just noticed this. If we are talking new build:
1 & 2 likely 8-10K and water to air geo as little as 18K with duct system and ground loops.

Posted By steveusaf on 16 Jul 2012 05:12 PM

I've been reading in many other posts that tightly insulated/sealed houses have much more even temps and no need for ductwork, which plays in favor of a minisplit. I could probably get away with 2 heads on the inside. Have you run into any code issues with inspectors, e.g. requiring backup heat? How many $$ worth of PV would be involved in the 1500 sq ft house you originally talked about?

Mini splits work well, but their application is not as universal as some here suggest. Consult with your local building authority to see if they have a "central heating" requirement. If they do mini-splits do not always qualify.
If the mini-splits do qualify, then no "back-up heat would be required.
That said, the multi-headed mini splits and inverter systems discussed often run as much as a ducted system once installed.

My building inspector was pretty enthusiastic about my one head minisplit. So am I. It's mounted about 10 feet from the west wall in an open floor plan of about 1k sf (roughly 20x50), with a den and bath on the east wall. I can't distinguish any temperature difference, even in the bath when the door is closed. Mine is a high mass house, so the cold air drops to the concrete slab and rolls through the ground floor. We set it on dehumidify but typically turn it off at night because it gets too cold. Have to confess we did use AC on the day it was 99 with a dew point of 74. Your results may vary.

I paid $1,000 for an (oversized) two-ton Fedders, $150 for the line set and $350 for insulation. http://www.ebay.com/itm/18000-BTU-FEDDERS-Inverter-Ductless-Mini-Split-Heat-Pump-Air-Conditioner-18-SEER-/120940756055?pt=Air_Conditioner&hash=item1c28a17c57

Haven't got a power bill yet

Yes, it's off the Internet, Joe. But it lasts a fourth as long as your $8-$10k version, I am money ahead, eh?

Good heavens. $350 for installation.

Todd,
Did you notice this line before you started disagreeing with me: "Mini splits work well, but their application is not as universal as some here suggest."
the keys to your project are
1) modest home (so 18000 btus is adequate)
2) open floor plan so one delivery point gets it done
3) modest load (more than minimum insulated house)
4) code official on board
5) zoning (Heck there's not one township in my county that permits 1kSF homes at this time)

These conditions are not universal, and that is my point.

I also object to constant apples and oranges comparisons of minisplits. People talk about Daikens and Fedders 18000btu and 36000btu, one or multihead systems as though they are all interchangable. the last Daiken I priced cost 5 times what you paid (36000btu 18 seer) so yeah installation with electrical and mechanical permits was easily 8K.

I conceded that minis are great in some applications, why are you defensive about that? Are you bullishly unable to concede that there are applications where they are not the best fit?

You missed the key difference in my home, Joe The minisplit is auxiliary hvac. While it could meet my 25k btu/hr design day heating requirement, recovering from cool downs in a high mass house (vacations, bitter cold, power outages) requires a much bigger hammer. In my case, that would be a 20kW wood stove boiler plumbed to radiant floors. Since radiant is more comfortable and wood is free where I live, I'd expect my mini to run from, say, March to October, and sporadically at that if solar hot water handles shoulder season heating. Gotta say, if I were starting over, I'd be severely tempted by the <$5k it would cost to marry a minisplit with a radiant wood stove.

To clarify, the $350 installation bought connection, pump down and start up. I set the inside and outside units. Electrical was included in the overall bid for the house.

Mini-splits/multi-splits are not universal solutions, but with highly insulated houses (R30 whole-wall R, R33 foundation, R60 attic, etc) like the one described in the post that started this thread they're pretty broadly applicable.

Point-source heating quickly became passe' with the advent of centralized steam heating in the late 19th century, but that was an era of zero insulation, leaky houses and low-performance windows. At current code-min R/U point source heating can work pretty well, given a good layout. At ~2x code-min performance (like Bob's low-heating cost house) it doesn't need an ideal layout to work well, just some forethought to the head placements. Most recent PassiveHouse examples built in MA have 1-2 head ductless as the primary heating and cooling- one head per floor. Even at half the typical PassiveHouse R-values it usually works if the windows are up to snuff (which may be the Achilles heel of going ductless Bob's NH house, but the cost delta of better windows would probably have been less than the cost delta between ductless & geo.) I'm sure it's possible to design or find high-R examples where it doesn't work, but those would be the exceptions proving the rule.

I agree. This year we're going to the next level with all triple glazed windows (U=.20) for comfort as well as insulation value.