Modular Solar Workshop
Imagine a morning sun sliding through your bedroom window and gently waking you after a satisfying sleep. A sparrow lands on your wild bird food dispenser and starts singing as the scent of geranium mixed with the aroma of tomato blossoms makes its way from the solar greenhouse below. You don’t have to get up but you want to. Orders for more apple chips are filling your inbox, but you’ll deal with them later. You must have that morning sun heat shower to start your day. The collectors are not yet hot, but there’s still plenty of heat inside the heat storage vault. The mulch digester is working better now since you’ve connected it with the solar workshop vault. Extracting methane from hot wet mulch was not so difficult, but finding a practical way to move the leftovers to the compost bin was a challenge. As you cook your breakfast of rolled oats flavored with dried apples, strawberries and bananas you wonder….
“Was it worth the trouble”, you wonder?
AND then you smile…
The
concept
A solar heated workshop may not be right
for everyone but if your property receives sufficient sunlight this sustainable
energy workshop might be right for you. Bigger is better when it comes to solar,
but affordability is also important. MTD solar collectors can be manufactured
for less than $4/ sq ft. so a 400 sq ft. array can be assembled for $1600 and
the 16 plastic drums used for heat storage can often be salvaged from food
processing plants at no cost. More conventional drain back systems pump water to
the bottom of collectors while trickle down systems like this trickles water
down through the tops of the collector array. Sixteen 2’x12’ Modified Trickle Down
collectors can harvest more than 300,000 BTU’s per day in most
This top view demonstrates the overall solar heating concept. Notice that the heat storage drums are isolated from the shop inside their own insulated storage vault built against the North wall. The proximity of stored heat to the shop facilitates forced hot air or radiant floor heating. Both methods have their advantages and disadvantages.
CHOOSING
A BUILDING SITE
Choose a location with a good southern exposure that’s higher than
the surrounding terrain. You will not be happy if your shop fills with water
after the first rainstorm. If you
decide to use some stored workshop heat for your home DHW system plan a trench
that will connect ¾” PEX from the heat exchange platform to your home hot
water system.
SUB
SOIL PREPARATION
After settling on a workshop site you
should hire an excavator to scrape off loose loom and get down to solid sub
soil. After the loom has been removed level the sub soil and fill the excavated
area with sand. The top level of
sand should be about level with ground level
FOOTING
More time should be spent with the footing
than the workshop floor because the weight of the shop rests on the 8” x16”
footing. If 2x8x16 planks are used for the framing materials they may be reused
when it comes time to install the shop ceiling joists. I recommend keeping the
top of the footing about 3” above ground level. After the 2x8 planks for the
forms are removed line the outside of the footing with 2” strips of solid
insulation.
HEAT
STORAGE VAULT PAD
It’s best to pour the footing and the
floor separately but you could still pour a 3” deep cement pad for the heat
storage vault at the same time the footing is poured.
FLOOR
Placing solid insulation under the cement
workshop floor is not entirely necessary. Dry gravel under the floor may be used
as an insulator. Cover the gravel with plastic before pouring cement otherwise
the insulating properties of the gravel will be lost forever.
CEMENT
BLOCKS
Cement blocks are easy to lay once the footing and floor are poured.
Mortar the corner cement blocks in place and then stretch a level line between
the corners. Just follow the line and the blocks will look great. Be sure to
install anchor bolts about every 10 feet and fill the hollow of the blocks with
insulation.
SHOP
STUD WALLS
Secure a bottom sill plate to the cement blocks with the anchor
bolts. Now install the stud walls on top of the bottom sill. Someone could help
raise the walls, but you seem to know what you’re doing and I bet you could do
it without any help. After all the stud walls are in position lock them in place
with overlapping top sill plates. Keep the studs plumb and the sills level. If
you do this the work will be easier and your Momma will be proud.
CEILING
JOISTS
Finish the stud wall framing before assembling the heat storage vault
First install the 2x8x16 ceiling joists AND give the building inspector a piece
of your famous blueberry pie if he gives you a hard time.
RIDGE
ROOF
Almost done! Let’s frame the ridge roof
with 2x6x12s and take a break for lunch. A ridge roof is less expensive than a
truss roof plus it will allow for valuable loft space.
SOFFITS
Frame out soffit extensions to leave a
hollow area under the eves. This is where the drain from the gutter will pass
under the top of the sill plate.
Once the shop is complete the heat storage vault may be assembled, but don’t mount the collectors yet. The heat storage vault should first be completed. Keeping the TDM moist is a good idea, so keep the collectors off the roof until the heat storage facility is ready to go. This will extend collector life expectancy. Remember the “Trickle Down Mat” collects heat and the drums inside the vault store heat. Without heat storage drums all you have is a nice looking shop.
VAULT
PLATFORM
Storage drums are placed on the heat
transfer platform last. Build the outside vault stud walls so they may be easily
removed. After the vault is finished the drums are connected in series with 2”
rubber boots and 2” PVC pipes. You will not be able to daisy chain the drums
with a vault wall in the way. OK…Let’s now focus on preparing the insulated
vault platform. If a Domestic Hot Water system is needed you’ll need a
concrete slab upon which the drums rest to extract heat.
There are many ways to extract heat from the drums of hot water but I
believe this method is most practical. A network of copper tubes connected in
parallel will transfer more heat than a serpentine PEX tube so let’s use
copper for DHW heat extraction. The heat storage vault platform is built on top
of the 3” cement pad that we mentioned earlier. Let’s take a closer look at
the cement pad and the copper tubes that run through the heat transfer platform.
This platform
is framed with 2x6 timbers and rests on cement blocks. The frame is packed with
insulation (solid and fiberglass) and capped with a ½” plywood lid. 2x4 sill
plates line the perimeter of the platform. Wire mesh is stapled to the plywood
before the copper tubes are laid out with a 2” space between them. After the
tubes are in position the cement platform is poured inside the 2x4 perimeter. Be
sure to protect the copper with polyurethane before pouring cement on it. Cement
can corrode copper over a period of time. A thin protective coating will extend
the life expectancy of your heat storage vault into the next century. A well
constructed level platform works will be worth your efforts. Keep the drums at
least 3” away from the inside walls of the vault to allow air circulation. A
top view of the heat transfer platform concept is illustrated below.
HEAT STORAGE: A dip tube heat transfer system is illustrated below. Notice how heat stratification is maintained. The coldest water is taken from the bottom of a drum with the help of a dip tube. This cold water is then deposited near the top of the adjacent drum. In this manner solar heated water is trapped within the multi-drum system. The coldest water from the last drum is then returned to the collectors to gather more heat.
These 60 gallon drums have been connected through the tops, but they may also be connected through the sides. I am now recommending side drum connections with a diminished flow velocity to reduce turbulence and increase heat stratification. Water having the same flow rate will have a greater flow velocity through small diameter orifices. To mitigate high velocity turbulence large diameter orifices should be used to transport heated water through the multi-drum storage system. High velocity water causes turbulence within the drums which in turn decreases heat stratification which decreases collector efficiency. In other words large diameter connecting pipes and large orifices connecting the drums increase collector efficiency.
The drum units may be pre-assembled in this manner. Two 2.7” holes are drilled through the sides of each drum toward the center of the sides. It is very important to keep the holes at a standard location in each drum. One 2”x 28” PVC pipe may be used in each drum, but before inserting the PVC pipe through the drum a top notch and bottom notch are cut out and the center part of the PVC (black line) is plugged so that hot water entering the drum is directed to the top and cold water leaving the drum is pulled from the bottom. The large notch cut into the PVC slows down the velocity of water. By lowering the forces of turbulence the delicate forces of convection currents are encouraged and the process of separating hot water from cold water is facilitated. Now all we have to do is finish framing and finish insulating the heat storage chamber before we retire for the day. An even better arrangements of storage tanks might look like this:
A few cross supports should be used to hold the walls together and a 3” slab of solid insulation should be used as an inner lid above the drums. A shed roof on hinges is also a good idea. We don’t want the storage vault to fill with rain water. Four tons will be quite sufficient.
THREE POSSIBILITIES
1. Push or pull cold shop air through the heat storage vault with a fan.
2. Regulate the flow of hot convection air currents from the heat storage vault with louvers.
3. Last but not least…Radiant floor heating
A radiant floor heating system provides an ideal method for regulating shop temperature although there are concerns in cold climates where freezing may be a problem. If you decide to heat your shop floor with solar heated water be sure to insulate the outside of the footing as mentioned before and drop in a mat of solid insulation before pouring cement. Of course the sub floor should still be level and tamped down Don’t forget about the steel flooring mesh and re-rods used to hold the PEX in place while pouring the floor. Also notice the two circulator pumps. Since heat is concentrated in the end drums hot water is circulated from the end drums and returned to the coldest drums located toward the center of the storage vault.
More information about MTD solar heating is available on line, but it’s actually easier to build MTD collectors than explain how they are built. MTD collector starter kits with construction guides are available. They facilitate the hands on experience needed to become an MTD pro.
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