Design opinions...

Tom_133

I have a new potential project coming up that I am seeking some different opinions.



Its a 3000sqft home built in the 70's with electric heat thru out. Its basically a big box basically with a shed roof over the whole thing. The bedrooms are downstairs, the living space is up. They would like to gut the upstairs living space and put in some heat, (of course the budget dictates) they don't want to do a boiler right now.



My first thought was cover the south facing shed roof with PV solar panels and dump it into the grid to offset electrical heat costs and perhaps a pellet or gas stove to supplement.



Architect thinks mini split with coil in ducting (more electrical costs) with the benefits of AC in summer.



Anyone ever run into this very vague and convoluted setup before?

SWEI

PV and electric resistance heat

will never pencil out, unless (maybe) you have something akin to a German feed-in tariff.  A multi-head mini-split is a good idea, especially if there is a cooling load.

Tom_133

I hear that..

I am with you on the PV, I was hoping to just have it constantly (all summer) dumping juice back in the grid and giving the customer a credit so that it helps offset the winter bill.



I will need more than just mini split when its -30 for a week though, correct?

bob_46

Tom

It sounds like the original builder read Rex Robert"s " Your Engineered House "

The first thing you need to do is an accurate heat loss. What fuels are available ?

Tom_133

Good Call

Hard at work on it now, but I also have the plague. So it may need to wait until next week.

It is almost exactly 3000sqft, 1250 on a cold crawl space and 600 over a cold garage, and 1176 is above the bedrooms. I think it's going to need a good radiant design and plenty of insulation upgrades through out. It only has LP, and oil available and they really wanna get as eco friendly as possible.



H

Zman

Options

The payback on PV is essentially never. Check out the pvwatts calculator on the doe site. The last one I did worked out to 17 years. By the time you figure in the degradation of the panels and the cost to relocate when you inevitably have to reroof it just doesn't work.



If you are seeing -30 temps air to air heat pumps are out.



I think you are on the right track with super insulating. I also see a boiler as having a decent payback over electric. Check out this calculator from doe http://www.eia.gov/neic/experts/heatcalc.xls



Carl

SWEI

minus 30

Means either a GSHP or burning something with carbon in it.



I'd get into that crawlspace and put a whole bunch of plates under the floor if at all possible.  What kind of subfloor?  You might look at the new Watts FlexPlates, which will tolerate less-than-perfect surfaces far better than extruded aluminum plates will.



I assume the garage is slab on grade?



Where is the house located?

CMadatMe

What's The

Heat loss?

Tom_133

chris.

Im still sort of working on the heat loss, I have been sick all week and this is getting back burner treatment, Im seeing around 100K btu's before the insulation and window upgrades. The outside design temp is -6. It is a perfect candidate for radiant on both floors. The homeowner is a musician who is away ALOT. I was really hoping for just some spit balling of ideas, so keep them coming I always enjoy different opions



The garage is slab on grade and the crawl space is cold but may be getting foam insulation.

NRT_Rob

not to disagree with other posters

but I'm gonna. we're net zero with PV and even without our additional grant, just the 30% federal payback was less than 15 years. in our case we had a 6 year payback. where are you? local incentives may change it too.



If you're going to go with offsetting with PV heat pumps are a must though unless the load is tiny. We are using air source in a -4 deg F area and it works great. we're Daikin Altherma powering radiant heating/cooling (does have built in 6kw electric element, our heat load is 33kBTU/hr at design).



minisplits are a great option as well for many people. all air source are especially great if they are "away a lot" because cooler water temps/air temps really help COP!



GSHP pretty much only if you can "pump and dump".



100kBTU for a 3000 sq ft house ... either this house is horribly insulated or your numbers are high. with electric installed I doubt that it was horribly insulated... this was energy crunch time, it's probably very well insulated? in any case I would expect 60kBTU or lower in MOST cases.