Heat for small shop

Morris Dovey, wrote the following at or about 6/7/2007 9:20 PM:

Any idea how impressive that is to us dorks who are paying into the grid? That's incredible, Morris. If you don't mind saying, what was the cost of those "Panels of Madison County."

That's close to what I use in my shop. I think the high output mode on the Dayton is 17.5kBTU

I can understand the necessity for the ceiling fan as we have cathedral ceilings in the kitchen and family room. Certainly helps to balance the heat from the wood stove out there.

It certainly does make a point. No magic, but the output is way more than what I ever would have guessed for those two panels in that sized structure.

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Unquestionably Confused
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Unquestionably Confused wrote: | Morris Dovey, wrote the following at or about 6/7/2007 9:20 PM:

|| That shop is 30' x 40' - so floor space will be a bit less than || 1200 sq ft. A comfortable daytime temperature is anything in || excess of 72F. If there's a run of especially sunny days, the || owner will probably need to open windows during the day to keep || the temperature in the 70's. | | Any idea how impressive that is to us dorks who are paying into the | grid? That's incredible, Morris. If you don't mind saying, | what was the cost of those "Panels of Madison County."

It's not a "Bad Thing" to pay into the grid - it's only bad to pay in more than is needful. Solar energy isn't a panacea, but in some applications it does offer solid economic advantage.

I don't mind saying - but I say it at

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so no one finds an old price in the archive and gets PO'd because I ask 'em to write a check for more than what they'd found.

The sun does deliver an impressive amount of energy to our little planet. I've knocked myself out to produce a design to capture everything from low-frequency EM through UV, and it seems to pay off (most notably in the IR range). If you haven't seen the plot of solar energy distribution by wavelength, you might find

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interesting.

|| I don't remember - I think he told me that it's a 20kBtu heater. || Food for thought: in the solar context, his ceiling fan will be || even more important than his unit heater. | | That's close to what I use in my shop. I think the high output | mode on the Dayton is 17.5kBTU | | I can understand the necessity for the ceiling fan as we have | cathedral ceilings in the kitchen and family room. Certainly helps | to balance the heat from the wood stove out there.

In this shop, the insulated 6" concrete slab acts as a big thermal "flywheel". Since warmed air "wants" to stay up near the ceiling, the fan is necessary to shoot it down to warm the floor. When the sun sets and the solar panel shuts down, the heat stored in the floor radiates as IR to extend the daily comfort period and prevent the shop temperature from dropping anywhere near the freezing range overnight.

|| Always glad to do that - on the other hand, one of the purposes of || that web page is to demonstrate the total absence of magic. On the || third hand, there's more to the design than meets the eye. | | It certainly does make a point. No magic, but the output is way | more than what I ever would have guessed for those two panels in | that sized structure.

The structure is well-sealed and well-insulated, which is important regardless of heating system. If you stand a full arm's length away from these panels at noon on the winter solstice, these totally passive panels will blow your hair back - if you have hair

It's important to panel efficiency to get the heat out of the panel as quickly as possible. By designing to maximimize capture bandwidth and to maximize the volume of air flowing through the panel, the panel operates at a lower temperature and delivers more heat. Operating the panel at a lower temperature reduces the black body (IR) radiation back through the glazing, and lowers conductive losses through the panel body. It's a balancing act, but as you home in on the balance point, panel performance does seem to peak spectacularly.

-- Morris Dovey DeSoto Solar DeSoto, Iowa USA

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Morris Dovey

Morris Dovey, wrote the following at or about 6/8/2007 6:07 PM:>

Sorry about that, found the price list after the question went out. Damn! ~$3200 for a unit to heat that place. Let's see now... Gotta be what? >$2000 for a decent FANG unit, ductwork and install and you get to keep paying and paying to keep it fueled and running vs what solar offers. Damn that's a hard one - not!

Again, I guess I'm somewhat surprised that the concrete (insulated or not) comes into play that much. Would expect it, I guess, from basking in the direct sunlight behind a wall of windows, etc. but not so much with the air above circulating over it.

Yeah, I still have enough to blow around with a convertible and probably with one of your panels as well. What really blows me away though is your system. Thanks for sharing your knowledge.

Okay, that explains why the high efficiency panels are "more better" though they are operating at 140 degrees vs the discontinued economy panels that were running at 160 degrees.

Reply to
Unquestionably Confused

Lot's of good replies so far. MY .02: Do NOT use any heater that runs on propane, fuel oil, etc that vent into the shop. Safety aside, they ALL generate a lot of water, which will rust everything. Your main goal is to warm yourself, but right behind it is to produce a non-condensing environment for you shop's equipment. That requires some heat above ambient all the time. When your equipment is cold and the air warms up, water condenses out of the air onto those cold surfaces and you get rust.

No one has mentioned warming the floor. I don't know about you, but my feet and lower legs are my main problem when standing in a shop. DO get a heater that has a blower so the floor area can be warmed, not just the top 4 feet of the shop. I use counter-flow (extermally vented) propane furnaces in my shops and they are great. I work several days a month in a shop that has one of those ceiling mounted heaters and it is miserable, as far as I am concerned. It is often 95 degrees 7 feet off the floor and 50 degress or less 2 feet off the floor.

Pete Stanaitis

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THOMAS CLEVELAND wrote:

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spaco

Unquestionably Confused wrote: | Morris Dovey, wrote the following at or about 6/8/2007 6:07 PM:>

|| In this shop, the insulated 6" concrete slab acts as a big thermal || "flywheel". Since warmed air "wants" to stay up near the ceiling, || the fan is necessary to shoot it down to warm the floor. When the || sun sets and the solar panel shuts down, the heat stored in the || floor radiates as IR to extend the daily comfort period and || prevent the shop temperature from dropping anywhere near the || freezing range overnight. | | Again, I guess I'm somewhat surprised that the concrete (insulated | or not) comes into play that much. Would expect it, I guess, from | basking in the direct sunlight behind a wall of windows, etc. but | not so much with the air above circulating over it.

Normally (without the fan) the slab would not play such an important role. The ceiling fan provides a whole collection of benefits, and it's difficult to say that any one of them is more important than the others.

By pushing the warm air away from the ceiling, it helps to reduce conductive losses through the ceiling.

By mixing the warm air with the cooler air below it reduces stratification and evens out the heat distribution throughout the shop to make the whole more comfortable.

The continuous flow of warm air on the insulated slab warms raises its temperature (stores energy in it) so that the it will begin giving up its heat to the air as soon as the air temperature drops below that of the slab. If the slab were left cold, it would still take some energy from the air that touched it, but it would warm less and might continue absorbing heat well beyond the point where the air felt chilly.

|| It's important to panel efficiency to get the heat out of the || panel as quickly as possible. By designing to maximimize capture || bandwidth and to maximize the volume of air flowing through the || panel, the panel operates at a lower temperature and delivers more || heat. Operating the panel at a lower temperature reduces the black || body (IR) radiation back through the glazing, and lowers || conductive losses through the panel body. It's a balancing act, || but as you home in on the balance point, panel performance does || seem to peak spectacularly. | | Okay, that explains why the high efficiency panels are "more better" | though they are operating at 140 degrees vs the discontinued economy | panels that were running at 160 degrees.

Exactly! The concept you've grasped is of the utmost importance - that heat (energy) and temperature are _not_ synonyms.

My current aim is to lower that 140F to 120F for a 6'-tall panel without major cost increase. The Madison County installation won't quite make it but I'm getting closer with every design iteration. Interestingly, I'm not sure that achieving that goal will necessarily produce a more efficient /system/.

-- Morris Dovey DeSoto Solar DeSoto, Iowa USA

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Reply to
Morris Dovey

| No one has mentioned warming the floor. I don't know about you, | but my feet and lower legs are my main problem when standing in a | shop. DO get a heater that has a blower so the floor area can be | warmed, not just the top 4 feet of the shop.

Pete...

One solution to this problem is to install an inexpensive ceiling fan (the "ceiling huggers" are best) and run it at low speed to use the warm air near the ceiling to warm the floor. Not only will it provide greater comfort, but it'll allow you to use less fuel.

-- Morris Dovey DeSoto Solar DeSoto, Iowa USA

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Reply to
Morris Dovey

How about a hybrid system? Would not adding, say, a low-cost (operation) axial/muffin fan with a rheostat allow you to tweak the internal temperature?

In your scheme of things that'd be cheating, I know, but... I'm just thinking aloud here. Even from a testing/design aspect you'd at least be able to see if the 120F would be more efficient, no?

Reply to
Unquestionably Confused

|| My current aim is to lower that 140F to 120F for a 6'-tall panel || without major cost increase. The Madison County installation won't || quite make it but I'm getting closer with every design iteration. || Interestingly, I'm not sure that achieving that goal will || necessarily produce a more efficient /system/. | | How about a hybrid system? Would not adding, say, a low-cost | (operation) axial/muffin fan with a rheostat allow you to tweak the | internal temperature? | | In your scheme of things that'd be cheating, I know, but... I'm | just thinking aloud here. Even from a testing/design aspect you'd | at least be able to see if the 120F would be more efficient, no?

I don't consider fans cheating - but insist that they not actually /impede/ operation of the panel.

At this point, the best of the axial/muffin fans (I have a small collection of not-so-cheap fans of a variety of types brought in by well-meaning friends) and all except the very largest (1/2 HP and up) act more as obstructions than enhancements to the airflow - even when running full-bore.

Although it's not an issue involving "cheating", I really do prefer the absolutely silent operation of the purely convectional operation.

I can boost the natural convection (lower temperature) by "streamlining" the interior plenums - rounding all the interior angles in the plenums, providing still smoother internal surfaces, etc. - but from where the design is today, all of these represent significant increases in labor and/or material costs.

The system question is: "What is the optimal discharge temperature that provides a comfortable environment for humans yet allows maximum _coincidental_ heat storage in a typical installation?"

The question contains a hidden twist in that excess heat can be discarded without impacting operational costs in any way - with an additional consideration that the discard mechanism can be used to control humidity.

It's the "typical installation" that's the unknown here. I don't need fans - what I really need is a variety of solar-heatable /structures/ to test. :-)

-- Morris Dovey DeSoto Solar DeSoto, Iowa USA

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Morris Dovey

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