MiniSpilt or PV
I am building a single story house in the Pacific NorthWest which is 1800sq ft. I am using Pretty Good House/PassivHaus principles. The house will be well sealed and insulated, it will use good quality glazing for some solar gain.
I had been planning on using a MiniSpilt to heat the house. Only electricity is avaiable.
I just had the design modelled by a consultant using the PHPP software and although it doesn’t quite meet the PassivHaus standard it is Pretty Good. One sidenote here that I haven’t heard before, I am finding it very hard to get close to PassiveHaus standards with a single level home because of the total floor/wall/roof area.
The models show that I will need 3500KwHrs of electricity to heat the house and no cooling will be required. This is fairly low. I will be putting in the infrastructure for a PV array so the basic cost is covered.
The minisplit seems to be between $5 and $7K installed while heaters are a few hundred dollars.
For $5k I could add about 1.5 – 2Kwatts to the PV array at the prices I anticipate when I build the house. PV install would be mid-2014. This would produce about half of the electricy I will need for heating.
My question is this. Should I use a minisplit with two heads in the house or use simple baseboard heaters with additional PV cabaility.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
Stephen,
It sounds like the math still favors the minisplit, which should be three times as efficient as electric resistance heat. But the electric resistance heat is simpler ... it will last longer ... and it will require less maintenance.
Readers, keep your eye on these numbers. It's only a matter of time before these two lines cross.
Martin, Thanks. I kind of anticipated your answer. For me it is not purely about cost. Comfort, simplicity, reliability and lower maintenance are important factors. This is why I am on the fence on this issue. I don't mind spending a bit extra for these, it isn't a large amount in the overall cost of the project.
The mini-split pricing seems about 2x on the high side for a very low-load single story house. (I have close relatives in the PNW heating & cooling with 1.5-2 ton mini-splits that came in well under $5K installed, before any subsidies, under $4K after PSE kick-backs.) At near-PassiveHouse loads you'd probably be looking at a 3/4-ton, which would usually be well under $4K or even under $3K.
Better mini-splits are running better than 300% efficiency on the west side of the Cascades, but only average a COP of 2.7-2.8 in the foothills of the Bitterroot in ID, so it sort of depends exactly where you live. (see: http://neea.org/docs/reports/ductless-heat-pump-impact-process-evaluation-field-metering-report.pdf?sfvrsn=18 )
If the annual output of a 1.5-2kw PV array delivers half your heating energy using resistance heating, a ~1kw array would cover ALL of it if you're heating with a mini-split. It's not necessarily an either/or kind of deal. If you find the $3-4K mini-split that covers it (and they ARE out there- if not, DIY isn't out of the question here!) and you can buy a 1kw PV array for $4K it's a similar money and it's covering 100% of the heating energy, not 50%.
What's your 99% outside design temp, and your peak heating load?
http://www.energystar.gov/ia/partners/bldrs_lenders_raters/downloads/Outdoor_Design_Conditions_508.pdf
Most 3/4 ton mini-splits can deliver ~12,000 BTU/hr heating @ +17F, and the internet-pricing is about $1500 even for some pretty-good ones. One-tons run ~$1700-1800. Installation does not take a rocket science education, but it's a good idea to read up on it first, and maybe have a qualified tech commission it if you're a ten-left-thumbs type of DIYer.
BTW: The discussion I'm more accustomed to having isn't deciding between PV and mini-splits, but between ground source heat pumps and a high-R house w/mini-split. You have the high-R house already under design and live in an area that gets very good efficiency out of low-cost mini-splits.
I just noticed that you were looking at a dual-head multi-split rather than a mini-split solution (which may explain the $5-7K, but even then...) which isn't usually necessary in high-R houses. Many Net-Zero houses in New England heat with one head per floor, at R-values well under PassiveHouse levels.
There is a 2-story + full basement PassiveHouse about five crow-miles from my house heated with a 2.5 ton 2-head multi-split, but they run it in cooling mode most of the time due to excessive plug-load use in their house full of teenaged video-game enthusiasts. But it's one head per floor (none in the basement) with very few room-to-room comfort issues other than overheating the play room during extended during video game parties. See:
http://www.passivehouse.us/phc2011/2011%20Presentations%20PDF/Panish,%20Paul%20-%20Ad-Hoc%20Passive%20House%20-%20The%20Beaton%20Residence.pdf
Dana
Thanks for the feedback. I've downloaded the links you provided and will read through them.
Steve