Solar controls

Wayco Wayne_2

for my churches Yurt project. We are going to install a radiant floor in a concrete slab and heat it with a Wall hung munchkin. This is the simple part. Now The Board of the Church, run by a bunch of old hippies, wants to add 3 or 4 Solar panels and an 80 gallon storage tank donated by someone who had one in his basement not being used. Since this is not much storage I would want to store as much as possible in the slab during the week when the building is unoccupied. I figured put a constant circ system circulator on the manifolds and turn it on and off by an outdoor stat. Then have the munchkin and the storage tank both injecting heat into this primary loop kind of like they were 2 boilers, but one is the so;ar hot water tank. I would run the munckin on a night set back stat during the week and program the stat to only run when it got very cold and bring up the temp Sat night before church. I would want to let the Solar run whenever there is heat availible to store it in the slab, but set a linmit so we don't over heat the space. Are ther any Tekmar controls that could do this for me, or any other controls for that matter. WW

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Paul Pollets

Thermomax

try the thermomax smt400 controller. Thermomax has an office in New Jersey. See their website at www.thermomax.com

If you're west of the Missisippi, I can hook you up with a local dealer (I buy from an Idaho dealer)

Their advice is first rate. Mahjouri, the director of the US division, has a PHd in electrical engineering. He's a world-class expert on solar controls and applications.



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Uni R

Major dilemma

The sun is the best source of energy on this planet. That said, it's seldom easy to extract and manage the heat. We need one of the hydronic math gurus to say how many BTUs can be stored in 80 gallons of water at whatever temp it can reach. My guess is that it is a drop in the bucket compared to what that slab needs to get ready over Saturday night. With the added costs, complexities and system risks, it might be hard to make a case for adding it, given that the savings are probably slim to unmeasurable in the grand scheme of things.

Wayco Wayne_2

Thanks for the replys

The way I see it my control dilema is I will have 2 heat sources with 2 different functions. One is only to be used when necessary (the boiler) and the other to be used whenever availible (the solar) That way we can store solar heat in the slab during unoccupied times since our storage with a solar tank is so small. I may just go with 2 different programable tstats.

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Nron_9

solar control

tekmar 155 is there only solar contol but you can combine them to get want you want for slab control

hr

A Yurt?

What is the load? I helped a gal (hippie) construct a yurt once. It was a stick and canvas deal in the mountains above Park City. I hope your's is constructed better.

Sticks and canvas are poor insulators, and not good with snow loads

The control you want is a differental control. For the money I like the Goldline, available in the Graingers catalog.

Use some in conjunction with setpoint controls to fire the back up. One fires the solar pump when the panels are warmer than the storage. The other could be wired to fire the boiler when the tank drops to a certain temperature.

If the panels and tank are free, and you can supply the labor Why not.

Buying this stuff new, and installing it may not pay back, but in your case...

Keep in mind winter time solar will not be a strong, or warm as what you will see this time of year. Dead of winter I see around 90-100°

You won't store a lot of BTU's in that temperature range in 80 gallons. But it is still a fun energy source to play with. Pipe it with the ability to add storage capacity, if more insulated tanks come your way.

What is their DHW load. Lot more bang for you bucks in that arena, as it is a year 'round load. Free hot showers, for all parishioners at the YURT! Or a Yurt solar powered soaking tub.

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S Davis

Tekmar 363

You might want to look at a Tekmar 363, It will pull heat from a storage tank and control a boiler.
Also boiler and floor reset in the same control.

S Davis

Wayco Wayne_2

Yeah!

A yurt. It's not made of canvas. Its a pre fab kit that will be assembled on top of a round concrete slab. It will be 35 feet in diameter and the side verticle walls are 10 feet. Then the roof will be cone shaped with a 6 foot skylight in the top that can be opened. 75 percent of the Walls have windows that can be opened. It will be used as a meeting hall for my church on some land out in the woods that they bought last year. Yeah were a bunch of old hippies. What can I say. These days instead of passing doobies we're passing the collection plate. Such is life. Oh yeah, I figured the heat loss at 35000 at 10 degrees outside temp. Slab will have 1 inch syrofoam on the sides and insultarp on the bottom. 6 loops of 5/8 Multicore tubing to a manifold fed by a constant circ pump and fed by the storage tank and or the boiler, a wall hung Munchkin T50. WW

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Arthur

Church heating

Taking 1 btu as 1lbs of water delta 1 degree,
1 Gall imp = 10 lbs, 1 US galls = 8.5 lbs.
A 80 gall tank at say 180 degrees at delta 80 (the temp you would want to put into the slab = 100 degrees)
80 x 80 x 10 (imp galls) = 64,000 btus/3412 = 18 kws.
But using US galls, 80 x 80 x 8.5 = 54,400 btus/3412 = 15 kws.c
18 kws will not go very far heating a church even a very small church!
It would possible use up all that heat in no time overnight and you would have start from scratch the next morning. even if you stored it and then only dropped it into the slab the next morning it wouldn't go far. The cost of the control would possibly be more that the so called saving they would(hope) to get.

Wayco Wayne_2

Yep!

We're not so much being practical as much as having fun with solar. The Yurt won't be occupied much during the week so we figured any heat we got from the solar would be gravy. I know the 80 gallon storage isn't much. Thats why I would just pump it straight into the slab and store it there. WW

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hr

Still sounds fun!

with that roof configuration where would you mount the solar collectors. Connecting them together would be a fun piping exercise. Need a copper bender?

What about mechanical room space?

Also consider the shading from the trees, if this is in the woods, before embarking on a serious solar project.

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Wayco Wayne_2

There

is no Domestic water needs. The only water line to the structure is for filling the boiler and system. The trees that are there will lose their leaves in the Winter. The roof that I described as cone shaped is actually beveled as it goes around and would fit some panels nicely and each one would get a turn facing the sun as it travels. I recommended a draindown system so we wont be baking our glycol during off times. We've got a free tank and a good price on some used collectors. Were not putting much money into it. Just playing around. If a windfall hits us one day we'll look at installing some vacuum tube collectors. Yowsah! (Someday never comes) WW

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hr

Storage, storage, storage!

The problem I forsee is solar gain overheating with all that glass, and the need to harvest and store the solar for the overnight (non sunny) portion of the day.

I don't think you would want to store the slab with much more than a temperature that would be comfortable to walk on. Certainly would not want to charge it to 120 and try to cool it down for use on meeting days.

Once I did a solar room with a black tile floor. A setpoint control would circulate water to storage when the floor hit a certain temperature. I lost track of the job it was a DIYer mainly. The concept made sense.

I suppose if you wanted to store solar energy in the slab and ground below, an uninsulated slab might work better. Remember the old rock storage beds from old Mothers Earth News articles

However if you wanted to heat with fossil fuel that uninsulated slab would work against you.

I still feel shoving bonus BTU's into well insulated storage would be the best option, considering the materials you already have.

Use Siggys design software to run buffer tank sizing "what ifs" It will tell you how far 80 gallons of various temperature water will take you

The heatloss program will allow you to calculate that shape building, also, with the clever area calculator feature.

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