Solar Off-Grid "workshop" shed heating options?

[SPFycool]

Hey guys. In Spring, I converted my 12'x12' storage shed to a Solar powered workshop. It has worked great through spring and Summer and I barely even tap the power that is generated by the panels on most days. Essentially, the batteries stay on float about 95% of the time on sunny days. My usage is typically less than 500Wh as I normally use battery operated tools and just recharge when done with intermittent power tools using up to 12A for a few minutes at a time.

Solar: 730W (2 365w LG NeON 60-cell Mono)
Batteries: 24V 210Ah (4x6V Golf Cart batteries)
Inverter: XYZ 2000W/4000W peak Sine w/remote (LINK)

Now, Winter is coming and i'd like to continue using the workshop to some degree. With the colder temps and shorter days, i'm trying to determine the best way to heat the space to 50-60 deg F only when i'm actually planing to be out in the shed. This time of year i'm likely to be working in there after dark, so will rely on the battery SoC.

I'm located in New England, so temps can drop to 0F a few times during winter, but typically 20-30F. Currently adding foam board insulation to the walls and roof rafters to try to reduce draftiness.

I have a remote controlled inverter that I use to turn on/off from the house roughly 60ft away.

Option 1: Electric heater set to a timer or low thermostat setting (50-60F). Turn on/off manually via remote.
Pros: inexpensive, simple, reliable, safe
Cons: Could drain batteries if not careful

Option 2: Propane tank heater
Pros: Simple, Effective
Cons: Potentially unsafe, propane costs.

Option 3: Solar heating during daytime/sunny weather (soda can heater with solar powered fan)
Pros: Inexpensive, doesn't rely on gas or electric for heat
Cons: Effective only in full sun during daytime. Requires lots of insulation/air sealing to be effective at all.

Any other options i've missed?

PS: Hardwiring to the house is not an option right now do to the layout of my property.

[bcroe]

Propane is the way to go. Before trying anything electric, you need to work out an energy
budget of just how many KWH you will be using. I was able to do this on my house based
on gallons of propane used, and 27KWH for resistive heat will provide the equivalent of
one gallon of propane burned in a high efficiency furnace. To make things really effective,
I use mini split heat pumps to multiply heat per KWH by up to 4, depending on the weather.

A 300 foot array manages to do mine on net metering, summer energy is saved for winter.
With a reserve of some 13,000 KWH, batteries are not a possibility. Bruce Roe

[Mike90250]

Kerosene/diesel fan jet heater ? (torpedo heater,

https://www.garagejournal.com/forum/showthread.php?t=75961&page=3

Or a BBQ propane tank IR burner ?

[PNPmacnab]

700W is not much, but it sounds like it will be wasted much of the day. PV heating would be a start to take some of the chill off and prevent condensation. It is a shame to waste it. I run directly off PV panel voltage (60V) with a specialized control and and an oil finned heater that runs about 400W at that voltage. Never run off the battery. I vote tor a 8KW diesel parking heater for less than $150.

[SPFycool]

Propane is the way to go. Before trying anything electric, you need to work out an energy
budget of just how many KWH you will be using.

That's the main question i've been asking myself. I don't have a set schedule and how much heat I need is based on weather conditions of the day. Has anyone used one of the little "Mr Buddy" propane heaters? I have a bunch of 1lb tanks and also the hose to connect to my 20lb grill tank. I'm thinking this would be the easiest and least expensive route to start with.

700W is not much, but it sounds like it will be wasted much of the day. PV heating would be a start to take some of the chill off and prevent condensation. It is a shame to waste it. I run directly off PV panel voltage (60V) with a specialized control and and an oil finned heater that runs about 400W at that voltage.

Very good point and this is what I was originally thinking. I waste so much PV energy when my batteries are at float during the day. I have been able to keep my batteries topped up using only 1 panel until now. I'm only now connecting the 2nd panel due to the shorter days. If there was an easy way to use the 2nd panel to connect direct to a heater, that would be fantastic. Voltage would be up to 40V though, so I would need some sort of buck converter to step down to power a DC heater. I also have an old 30w 18V panel that can be used to power a fan to circulate air around. I was going to use this panel for the pop can heater fan if I went that route.

Obviously on the not-so-sunny days, I would still need an alternate heat source, which I think the propane heater would still work great.

[bcroe]

One thing to consider, is that your propane heater is big enough to turn on
from completely cold, and quickly reach working temp. This will allow using
no heat at all the rest of the time, probably a huge energy saving. Ran that
way a decade here, till I got heat pumps. Bruce Roe

[J.P.M.]

FWIW:

Adding insulation will reduced the heat load but sealing up the cracks and tightening up the building envelope - which insulation may do some of - will do a better job of reducing drafts and also work with insulation to reduce the heat load even more. Sealing will cost less for materials than insulation but will take more time to do. The real PITA with sealing is in the details. Think of it as you would if you were trying to stop a water leak. The devil is in the details.

Insulation to reduce conduction heat transfer, and sealing to reduce infiltration and associated heat transfer are related but mostly separate issues.

Face any foil to the warm side of the insulation and seal the warm side so that the outside of the walls/ceiling of the structure is "looser" than the inside. Reason: Sealing the warm side (in cold(er) climates) will tend to make/keep the space between the inside and outside surfaces dryer and so have a better chance of staying dryer by circulating dryer air from the outside. Colder (outside) surfaces that are tighter than harm (inside) surfaces will tend to trap and then condense water vapor. That will cause problems.

For building heat loss/load: Get/Do an est. of the building heat load at design temp. for your area. I'd suggest using 2 air changes/hr. for the infiltration portion of that load.

Add: If using unvented fossil fuel/combustion heat sources: Always vent. Do. not use salamander type heaters or unvented devices in enclosed areas., For appropriate/code allowable fossil fuel fired equipment, use outside air for combustion and vent according to building code requirements.

Size the heating equip. accordingly.

If using elec. resistance as a heat source, use 300 W heating requirement for every 1,000 BTU/hr. of the design heat load you calculate.

[SPFycool]

Thanks for the tip! I am focusing on sealing over insulation R-value. I'm just using 1/2" R3.3 foam board and using cans of spray foam to seal the edges and around the wall studs. Since it's only a shed that I will just be using for a few hours in at any given time, i'm not worried about it staying warm overnight, just comfortable while it's occupied. There are 2 large vents at the peak on both sides I plan to keep open to promote air flow as well as cut a small intake hole near the floor.

Is there any benefit to using less/more insulation on the South facing side of the Shed and vice versa on the North side?

[J.P.M.]

Thanks for the tip! I am focusing on sealing over insulation R-value. I'm just using 1/2" R3.3 foam board and using cans of spray foam to seal the edges and around the wall studs. Since it's only a shed that I will just be using for a few hours in at any given time, i'm not worried about it staying warm overnight, just comfortable while it's occupied. There are 2 large vents at the peak on both sides I plan to keep open to promote air flow as well as cut a small intake hole near the floor.

Is there any benefit to using less/more insulation on the South facing side of the Shed and vice versa on the North side?

You're welcome. Understood.

Depending on heating cost, if it was me, and for the likely ~ equal labor/time involved, I might consider 1" vs. half inch insulation and in any case use closed cell blueboard. BTW, from some work I've done, I found/measured that an "R" rating > ~ 4 for any rigid foam board is overly optimistic. Mfgs. usually/often/commonly add an R of ~ 1 to the total thickness R value for each foil face.

Also, if polyurethane and depending on origin, know that if it burns, some polyurethane foam formulations may liberate cyanide gas, but that likelihood seems to be decreasing moving forward. Some building codes disallow it for that reason. Also, if the cheap, open cell white stuff, whatever the R value starts out at, it will deteriorate over time by 10 % or more.

I read about such things many times and proved most of them to myself (except the cyanide gas stuff) the hard way by 1st effort cheaping out and soon after learning the "buy cheap, buy twice" principle. Now, because I won't live long enough to make all the mistakes on my own, I know enough to learn from the mistakes of others.

Probably not much real benefit to more/less insulation as f(wall orientation). Adding a window to the south face may make things a bit more cheery and also add some passive solar heat during sunny periods. If that's a choice, I'd add a piece of whatever wall insulation you wind up using as (re)moveable window insulation for use when the sun isn't shining or to reduce unwanted heat gain when it's warm.

Take what you want of the above. Scrap the rest.

[Ampster]

Is there any benefit to using less/more insulation on the South facing side of the Shed and vice versa on the North side?

Maybe. Paint South side it black to get winter heat and have big overhang in summer. I have seen some passive solar using insulated South facing windows and dark surfaces inside. More clothes is probably cheaper. LOL.

[J.P.M.]

Maybe. Paint South side it black to get winter heat and have big overhang in summer. I have seen some passive solar using insulated South facing windows and dark surfaces inside. More clothes is probably cheaper. LOL.

The exterior color of an insulated wall has little effect on the heat transmission. I did that to my first home in Buffalo and over 7 yrs. the difference was smaller than I could measure. I'd SAWG the improvement to be of the order of a few % or less.

FWIW, on dark surfaces and passive solar design, making the heavy surfaces (floors, hard furniture, etc.) dark and the light weight surfaces like curtains, soft furniture, etc. light colored helps avoid overheating. Passive solar design is a lot more than a bunch of south facing fenestration, lots of thermal mass and super insulation.

[SPFycool]

I picked up the little 9000btu Mr Buddy heater last night and performed some tests. So far, seems to work fairly well. Temps dropped quick and by the time I made it out there at 6pm, the outside temps were in the low-mid 20's F. Inside the shed was between 28-30F. Using an infrared thermometer there was ablout a 5 degree difference between the insulated and uninsulated sections (I'm only about 1/2 way done sealing and insulating). The insulation i'm using is Dow Super Tuff-R 1/2" Polyiso board with foil facing on 1 side and vapor barrier on the other.

With the heater on the high setting (9k BTU), it took the chill out within 45 minutes. I only ran it for about 90 minutes total and temps rose to about 50F. The last 30 minutes were pretty comfortable. If I wasn't opening and closing the door every 15-20mins, i'm sure it will get nice and toasty in there after I finish the air sealing/insulation..

Cost-wise, I think this is most cost effective solution that will work regardless of time of day and conditions. 2 Hrs at 9kBTU's burns roughly 1lb of Propane. Hooked up to a 20lb tank should last me about a month based on my estimated usage. I have 2 tanks to rotate, so this should work well. Just need to shop around for the most economical fill station nearby.

The Shed does have a small South-facing window that does seem to help on the Sunny days. I may paint the interior lower sections and floor a darker color and the upper half white. Should allow for some solar heating during the day and help with lighting.

PS: In my haste to get some of the insulation installed, I placed the boards with foil facing out (exterior). I have the bottom half foamed in. Is it worth cutting out the spray foam and flipping the boards around at this point? Will it even make a notable difference?

[Mike90250]

> PS: In my haste to get some of the insulation installed, I placed the boards with foil facing out (exterior). I have the bottom half foamed in. Is it worth cutting out the spray foam and flipping the boards around at this point? Will it even make a notable difference?

Just get a couple more foam boards and install them foil facing in, glue (with approved glue) to the existing boards
Thats what I'd do.

[J.P.M.]

PS: In my haste to get some of the insulation installed, I placed the boards with foil facing out (exterior). I have the bottom half foamed in. Is it worth cutting out the spray foam and flipping the boards around at this point? Will it even make a notable difference?

As long as there is not a lot of water vapor or moisture generation going on in the shed, I'd probably not worry a lot about it as long as you have good, and I mean attention to detail, nitty gritty, immaculate, sealing. Attention to detail is the gospel when sealing. By sealing, what you really want to prevent is moist air from getting behind the insulation and into inaccessible areas, cooling down, and then having the water vapor in the now colder but still moist air, condense, leading to problems of smell, mold, rot, bugs, etc. over time.

The sealing will also make things less drafty and go a long way toward reducing heat loss/gain, but the often overlooked goal of eliminating possible water vapor condensation sites is very important.

If you're working in the shed near the insulation that has the shiny side facing in, you may notice that area may "feel" a bit warmer than the area with the less shiny side facing in, but that's about all, and even that would be, IMO, a close call. That (possible) perception of more warmth is the result of the greater surface reflectivity of your own body heat and also part of the reason the mfg. claims a higher R value for the insulating "system" which includes an R value for the reflectivity.

BTW, the shiny foil facing is also a vapor barrier.