Author Topic: Is there a Mechanical/Industrial Engineer in the House ?  (Read 8168 times)

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Offline Weisshaupt

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Is there a Mechanical/Industrial Engineer in the House ?
« on: May 04, 2011, 07:42:11 PM »
I am an EE by training, so ask me to solve thermodynamic fluid equations and I fail miserably. I am trying to figure out the best/most economic way to build an unheatedshed to house the batts and inverter for the PV system.  It doesn't need to be big - 8x8 or 8x10 - 

I was thinking of trying to excavate into the hill and build a ICF concrete building to try and use the high R value (20+)  of the ICF  concrete and the temperature averaging charateristics of the soil (  1 foot down, the soils temperature reflects the WEEKLY average of surface temps  -and deepe tends to be around 54 degrees)
The Inverter shouldn't  get any hotter than 70 degrees and really the batteries shouldn't get any colder than 60 - I was was going to use a Solar hot water system to release heat into the battery box in the winter, and use that same tank of water as an additional thermal mass to keep the shed cool in the summer  - so largely its like a root cellar, but I want to keep it at 70 instead of 54 --   The theory here is of course its easier to keep a building at 70 F if its buried in a hill because the temp differential is 20 -30  instead of 100 ( Lowest recorded temp is -50F, -10F is NOT unusual in January) But it looks like the cost of the thing is going to be closer to $4-5K  even when I do a lot of the work myself.  The alternative is to build a 2x6 shedabove grade..With the right Furring you can get the wall close to an R 20  insulatvie value,  but I will be dealing with the temp differential of 70  to -10  (or more) - cost of building that structure will be more like $1-2K --  but I don't have the match to do a proper analysis of it makes sense to go the more expensive route.  The Hot Water system I am looking at is a DYI that should keep 180 gallons of water in an insulated tank at above 100 F - even on the coldest days - so that is the heat source to be rn through a heat exchanger.  The inverter also produces some heat,  and the  batterys can ( and should) be enclosed in a smaller box - but there won't be a lot of airspace in it..

Anyone have experiece with this sort of thing? Is the underground shed overkill?
 


Offline John Florida

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Re: Is there a Mechanical/Industrial Engineer in the House ?
« Reply #1 on: May 04, 2011, 08:35:58 PM »
You need to remember that some might not know what an ICF is.so we'll clear that up right now.
Eco-Block Training -- Part 4 Assemble/Cut Standard Forms

 If you have a hill available you may think about using that rather than going down into the ground.The reason I say that is that you now may have a moisture problem or a out and out water problem which is harder to deal with than going into a hill.

 Am I on the right track for you?
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Offline John Florida

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Re: Is there a Mechanical/Industrial Engineer in the House ?
« Reply #2 on: May 04, 2011, 08:42:02 PM »
If you do above ground 2x6 framing and use spray foam insulation to would end up with an R rating of 38.5 based on a 5 1/2 inch cavity and using an isolation foam that gives you R7 to the inch.

 Now if you have a lumber mill close by the rough sawn lumber would be a full 6 inches instead of a 5 1/2 inch board. that would give you an R42 wall.
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Offline Weisshaupt

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Re: Is there a Mechanical/Industrial Engineer in the House ?
« Reply #3 on: May 04, 2011, 10:16:41 PM »
If you do above ground 2x6 framing and use spray foam insulation to would end up with an R rating of 38.5 based on a 5 1/2 inch cavity and using an isolation foam that gives you R7 to the inch.

 Now if you have a lumber mill close by the rough sawn lumber would be a full 6 inches instead of a 5 1/2 inch board. that would give you an R42 wall.

The problem with the stick built walls is you have to account for the R-value of the whole assembly, and not just the cavity.. (same for ICF really -its the largely continueout nature of the insulation in ICF that makes it so good - whereas studs between the drywall and outside sheath also communicate heat and force breaks in the insulation.. 
http://www.homeenergy.org/archive/hem.dis.anl.gov/eehem/99/991110.html

there are ways to mitigate this with 2x6 construction by minimizing the areas of stud contact and the drywall contact.
http://www.builditsolar.com/Projects/Conservation/MooneyWall/MooneyWall.htm

which will bring it up to ICF range..

My real question I am try to answer is understanding the effective  temperature loss difference having 3 walls buried in a hill with temperatures between 54 and 20 on the other side, and a temp of -10 in air on the other side of the 4th wall, and a structure where all 4 walls are exposed to that outside temp of -10.  if its a 5 or 10% difference then its probably NOT worth spending twice the price for it.  IF its 80%-100% difference, then maybe it is.. just trying to figure out the value/cost curve.



Offline John Florida

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Re: Is there a Mechanical/Industrial Engineer in the House ?
« Reply #4 on: May 04, 2011, 10:38:09 PM »
If you do above ground 2x6 framing and use spray foam insulation to would end up with an R rating of 38.5 based on a 5 1/2 inch cavity and using an isolation foam that gives you R7 to the inch.

 Now if you have a lumber mill close by the rough sawn lumber would be a full 6 inches instead of a 5 1/2 inch board. that would give you an R42 wall.

The problem with the stick built walls is you have to account for the R-value of the whole assembly, and not just the cavity.. (same for ICF really -its the largely continueout nature of the insulation in ICF that makes it so good - whereas studs between the drywall and outside sheath also communicate heat and force breaks in the insulation.. 
http://www.homeenergy.org/archive/hem.dis.anl.gov/eehem/99/991110.html

there are ways to mitigate this with 2x6 construction by minimizing the areas of stud contact and the drywall contact.
http://www.builditsolar.com/Projects/Conservation/MooneyWall/MooneyWall.htm

which will bring it up to ICF range..

My real question I am try to answer is understanding the effective  temperature loss difference having 3 walls buried in a hill with temperatures between 54 and 20 on the other side, and a temp of -10 in air on the other side of the 4th wall, and a structure where all 4 walls are exposed to that outside temp of -10.  if its a 5 or 10% difference then its probably NOT worth spending twice the price for it.  IF its 80%-100% difference, then maybe it is.. just trying to figure out the value/cost curve.




 then the only way to do it is to price it all out from digging a hole to insulating the roof. Stch built will win out even if you use sheet foam insulation under the siding and sheetrock. Which would raise the R factor even more. But the question I can't answer is tha the insulation value is of a 2x6 there has to be a value to it or log homes wouldn't work without insulation and I think we can agree that they do work.( I would never own one but they do work.
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Offline trapeze

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Re: Is there a Mechanical/Industrial Engineer in the House ?
« Reply #5 on: May 04, 2011, 11:15:39 PM »
What you need to do is perform a comparative heat loss calculation of the two different structures using the weather data for your location and an indoor design temperature of 65F (the midpoint between your acceptable high of 70F and your acceptable low of 60F).

The heat given off by the equipment is irrelevant for the comparative analysis because that heat gain is the same for both designs. What you really need to know is 1) which design costs more to build...you sound as if you have a pretty good idea already and, 2) what your cost is to add the required amount of heat to maintain your indoor design temperature. That is the purpose of a heat loss calculation - to size a heating appliance to match the loss.

Contact a mechanical engineer if you want the calculation done precisely. It will cost a couple of hundred bucks or so for a design that is this simple. You could also contact a heating/air-conditioning contractor and hire them to do the calculation but they might not give you the level of accuracy that you are looking for and it might end up costing you about the same amount as the PE. Personally, I would go for the PE because he (or she) will probably throw in some advice on heating for the same price. And the heating advice will be unbiased since (unlike a contractor) they aren't trying to sell you a system.

There are also some free online heat loss calculators out there but they probably won't give you the level of detail you are looking for.

So, what you want is the combination of the building structure and heating system that will yield the lowest overall cost. If the more expensive building has a lower operating cost that will pay back the difference between it and the cheaper building in five years or less then that's probably the best option. If the payback is greater than five years then it's probably better to go the other way.

Anyway...that's my advice and it's worth every penny I'm charging for it.
« Last Edit: May 04, 2011, 11:22:44 PM by trapeze »
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Offline John Florida

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Re: Is there a Mechanical/Industrial Engineer in the House ?
« Reply #6 on: May 05, 2011, 08:00:57 PM »
Post and beam construction would eliminate the stud problem
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Offline Weisshaupt

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Re: Is there a Mechanical/Industrial Engineer in the House ?
« Reply #7 on: May 06, 2011, 04:30:25 PM »
Post and beam construction would eliminate the stud problem

Glad I have people around to hit me in the head  with a Pole and a  Beam, or I would never have thought of doing it.
You are too right, this is the perfect application for that type of construction.. but for some reason I just assumed Stud walls ... sad really.
Old and set in my ways already.

 Thanks JF..

Offline trapeze

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Re: Is there a Mechanical/Industrial Engineer in the House ?
« Reply #8 on: May 06, 2011, 05:09:33 PM »
I don't know if you have considered it or not but a 2x6 wall (2x6 top and bottom plates) that has staggered 2x4 studs (every other one is flush to one side of the wall) will have no thermal conductivity through the studs. This uses less board feet than a double wall (2 - 2x4 walls separated by x inches and completely filled with insulation). Makes for good sound suppression, too.



Also consider cellulose insulation. It has roughly the same R-value per inch as foam for less of an installed cost. As a bonus, cellulose is non-toxic and thus, less deadly when burned. And, properly installed, cellulose is flame retardant.

Another option wound be SIP panel construction which also has no thermal conductivity via studs because SIPs have no studs, just styrofoam fill. SIPs are available in different thicknesses/R-values.

Both cellulose insulated frame walls and SIP walls have low to zero infiltration as well.

One place you might want to take a look at is this one for overall energy efficient construction of small structures (like residences).
« Last Edit: May 06, 2011, 05:14:07 PM by trapeze »
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Offline John Florida

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Re: Is there a Mechanical/Industrial Engineer in the House ?
« Reply #9 on: May 06, 2011, 05:26:19 PM »
I don't know if you have considered it or not but a 2x6 wall (2x6 top and bottom plates) that has staggered 2x4 studs (every other one is flush to one side of the wall) will have no thermal conductivity through the studs. This uses less board feet than a double wall (2 - 2x4 walls separated by x inches and completely filled with insulation). Makes for good sound suppression, too.



Also consider cellulose insulation. It has roughly the same R-value per inch as foam for less of an installed cost. As a bonus, cellulose is non-toxic and thus, less deadly when burned. And, properly installed, cellulose is flame retardant.

Another option wound be SIP panel construction which also has no thermal conductivity via studs because SIPs have no studs, just styrofoam fill. SIPs are available in different thicknesses/R-values.

Both cellulose insulated frame walls and SIP walls have low to zero infiltration as well.

One place you might want to take a look at is this one for overall energy efficient construction of small structures (like residences).


 Trap I've see that type of framing bu in standard consrtucion material it creates problems with nail spacing. A standard sheet of plywood is as we know 4x8' and accepted construction framing is 2x4 spaced 16" on center. Or 2x6 spaced 24"on center.

 The style wall you just showed eats lumber because most state will still only allow those spreads and now you have to use more wood than you need to. Remember that has to be an inspection on all the work he's doing so you can't just slide with it.

 Oh  If you could get me to a link on the R values of blown in insulation I need to do some reading on that.
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Offline John Florida

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Re: Is there a Mechanical/Industrial Engineer in the House ?
« Reply #10 on: May 06, 2011, 05:28:06 PM »
Post and beam construction would eliminate the stud problem

Glad I have people around to hit me in the head  with a Pole and a  Beam, or I would never have thought of doing it.
You are too right, this is the perfect application for that type of construction.. but for some reason I just assumed Stud walls ... sad really.
Old and set in my ways already.

 Thanks JF..


 No sweat But i'll be honest I just don't like the idea of all those electronics under ground just as a humidity stand point.
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Offline trapeze

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Re: Is there a Mechanical/Industrial Engineer in the House ?
« Reply #11 on: May 07, 2011, 01:22:08 AM »

 Trap I've see that type of framing bu in standard consrtucion material it creates problems with nail spacing. A standard sheet of plywood is as we know 4x8' and accepted construction framing is 2x4 spaced 16" on center. Or 2x6 spaced 24"on center.

 The style wall you just showed eats lumber because most state will still only allow those spreads and now you have to use more wood than you need to. Remember that has to be an inspection on all the work he's doing so you can't just slide with it.

 Oh  If you could get me to a link on the R values of blown in insulation I need to do some reading on that.

JF:

Yes, of course you have to space 16 OC on both sides of the wall for both exterior sheathing and interior drywall.

This type of framing is cost effective in that it has a substantially lower operating cost for the structure. First cost is high (although it can be lower than some others) but the payback is fast through lower utility costs during all seasons. Besides, the original post had the structure size at between 64 and 80 square feet so utilizing this framing style for that small an area isn't such a big deal.

Cellulose insulation can be as much as R-4/inch. Compared to urethane foam at R-5/inch, that's pretty good especially when you take into account the significantly higher installation cost of urethane. Also take into account that urethane has substantially worse specs than cellulose in regard to flame spread and total smoke generated. Cellulose is treated with a fire retardant and has an installed 1 hour fire rating. Here is your link.

One other thing...ICFs are great, especially for below grade type work but proper installation is critical. A short wall typical of pier and beam construction is hard to screw up but basement walls (which is what would essentially be needed in a hillside application) are prone to voids in the concrete pour due to the greater height of the wall. Stirring or vibrating during the pour is good but no guarantee of a void free ICF wall (or any other formed concrete wall for that matter). Water proofing a below grade wall is also tricky and water will always find a way if a way exists. A French drain around the below grade portion will be helpful but no guarantee, either, of a leak free wall. And depending on the local water table a hillside application is every bit as likely to have water issues as a full basement.

I also wouldn't hesitate to pour the floor with 1.5 to 2 inches of foam board underneath. It's cheap and makes interior temperature control easier.

As to humidity...that's a function of two things. First is the relative humidity level of the air. Second is dew point. Electronic equipment (usually we are talking about computer rooms) has an ideal relative humidity range of 45% to 55%. Higher levels of relative humidity lead to corrosion related electronic failures. Lower levels lead to static electricity related electronic failures. The only way to know for sure if this is going to be a problem is to build it and then measure. The inverter can probably stand up to more extreme humidity conditions than computer room equipment.

Using a solar/hydro collector for this small space is probably the best way to go. If it was me, I would pour four or five inches of concrete on top of 2 inches of foam board (with 2 inches of edge insulation) and run 1/2 inch PEX tubing (closely spaced) through the slab. A mixing valve with an outside air reset controller will keep the heating water temperature at the appropriate setting. A tiny circulating pump controlled by a thermostat rounds out the system. Combined with an appropriately insulated building envelope this will probably give you the best temperature control in the heating season. Below grade during the cooling season will (depending on location) probably not require any mechanical cooling.

« Last Edit: May 07, 2011, 01:44:21 AM by trapeze »
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Offline Weisshaupt

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Re: Is there a Mechanical/Industrial Engineer in the House ?
« Reply #12 on: May 07, 2011, 08:42:28 AM »
No sweat But i'll be honest I just don't like the idea of all those electronics under ground just as a humidity stand point.

Humidity? Whats that? This is High Colorado Mountain Plateau :>)
I am picking up perfectly good fire wood  thats been on the ground 12+ years.

Its possible I could get some condensation from the coolness of  the ground, but it might even be a good thing- I have had capacitors dry up...and you could get that to happen in any tight well insualted building.

Still haven't fully decided which to do. Above ground makes the DC lines much shorter, and simplifies much of the trenching requirements, and overall works better and cheaper  if I can keep temperatures at around 70 in there year round. Ambient high in the summer will be 80 , so the major factor will be heating, not cooling. The inverters will give off some heat in operation, and the only space that MUST be heated is the battery box (2x4x3 ) or so. ( Battery selection is another whole painI am struggling with ) -- I am looking at doing a insulated concrete pad as the floor and doing ambient heat/cooling of the shed using solar heated water in the winter, and then using the cooler water as a heat sink ( if required) in the summer -of course thats another damn electrical load to  run the pump. 

The good news is that the structure itself will not neeed to be inspected -( any building under 120 sq ft, the county doesn't care about)- so staggered studs could also be used cost effectively .  From what I have seen of Pole Barn construction, you basically have horizontal staggered studs instead of vertical, so I don't see it matters that much..

 The state will be inspecting the electrical/solar install.

 

Offline John Florida

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Re: Is there a Mechanical/Industrial Engineer in the House ?
« Reply #13 on: May 07, 2011, 10:36:15 AM »

 Trap I've see that type of framing bu in standard consrtucion material it creates problems with nail spacing. A standard sheet of plywood is as we know 4x8' and accepted construction framing is 2x4 spaced 16" on center. Or 2x6 spaced 24"on center.

 The style wall you just showed eats lumber because most state will still only allow those spreads and now you have to use more wood than you need to. Remember that has to be an inspection on all the work he's doing so you can't just slide with it.

 Oh  If you could get me to a link on the R values of blown in insulation I need to do some reading on that.

JF:

Yes, of course you have to space 16 OC on both sides of the wall for both exterior sheathing and interior drywall.

This type of framing is cost effective in that it has a substantially lower operating cost for the structure. First cost is high (although it can be lower than some others) but the payback is fast through lower utility costs during all seasons. Besides, the original post had the structure size at between 64 and 80 square feet so utilizing this framing style for that small an area isn't such a big deal.

Cellulose insulation can be as much as R-4/inch. Compared to urethane foam at R-5/inch, that's pretty good especially when you take into account the significantly higher installation cost of urethane. Also take into account that urethane has substantially worse specs than cellulose in regard to flame spread and total smoke generated. Cellulose is treated with a fire retardant and has an installed 1 hour fire rating. Here is your link.

One other thing...ICFs are great, especially for below grade type work but proper installation is critical. A short wall typical of pier and beam construction is hard to screw up but basement walls (which is what would essentially be needed in a hillside application) are prone to voids in the concrete pour due to the greater height of the wall. Stirring or vibrating during the pour is good but no guarantee of a void free ICF wall (or any other formed concrete wall for that matter). Water proofing a below grade wall is also tricky and water will always find a way if a way exists. A French drain around the below grade portion will be helpful but no guarantee, either, of a leak free wall. And depending on the local water table a hillside application is every bit as likely to have water issues as a full basement.

I also wouldn't hesitate to pour the floor with 1.5 to 2 inches of foam board underneath. It's cheap and makes interior temperature control easier.

As to humidity...that's a function of two things. First is the relative humidity level of the air. Second is dew point. Electronic equipment (usually we are talking about computer rooms) has an ideal relative humidity range of 45% to 55%. Higher levels of relative humidity lead to corrosion related electronic failures. Lower levels lead to static electricity related electronic failures. The only way to know for sure if this is going to be a problem is to build it and then measure. The inverter can probably stand up to more extreme humidity conditions than computer room equipment.

Using a solar/hydro collector for this small space is probably the best way to go. If it was me, I would pour four or five inches of concrete on top of 2 inches of foam board (with 2 inches of edge insulation) and run 1/2 inch PEX tubing (closely spaced) through the slab. A mixing valve with an outside air reset controller will keep the heating water temperature at the appropriate setting. A tiny circulating pump controlled by a thermostat rounds out the system. Combined with an appropriately insulated building envelope this will probably give you the best temperature control in the heating season. Below grade during the cooling season will (depending on location) probably not require any mechanical cooling.



 I was basing the framing costs on a whole house not the shed were talking about here and you're right what the hell can it cost in extra studs. As for the cellulose insulation I had not looked at it in years that's why I wanted the link. The last time I looked at it it was dry blown in and the big problem was that it didn't stay where you put it in the sense that it settled in the walls and left big  gaps at the top of the stud walls so It was useless to me.This new stuff looks much better and it does cost a hell of a lot less. As to the R values there are foams that claim R7 to the inch but the cost is a big factor too.

 Thanks for the link.
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Offline trapeze

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Re: Is there a Mechanical/Industrial Engineer in the House ?
« Reply #14 on: May 09, 2011, 10:53:26 PM »
I forgot to mention that the infloor system will also need a storage tank. A fifty gallon electric water heater is a cheap insulated tank. You don't connect the electricity, of course.
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Offline Weisshaupt

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Re: Is there a Mechanical/Industrial Engineer in the House ?
« Reply #15 on: May 10, 2011, 01:36:22 PM »
I forgot to mention that the infloor system will also need a storage tank. A fifty gallon electric water heater is a cheap insulated tank. You don't connect the electricity, of course.

Yeah, another area where I need additional research in order to do the math - In really cold conditions(-30F)  you can expect your solar water to still reach around 100F during the day - and in normal conditions  140-160F  isn't  unusual - but how much water at  120 degrees (and pump electricity) do  I need  to keep a large mass ( concrete and  3000 lbs of lead batteries) at 70F I am not sure how to figure out. The mass of the batteries is so large that they might not track the shed or concrete temps very well, which is fine because that may mean only a small of heat really needs to be input - problem is the batts have to be vented to the outside whenever they are actively charging and producing H2 -- the alternative is getting AGM batts. they are about 80% of the price of the lead batts, but can't cycle as deep, and will last about 1/3 as long. Of course when the batts are producing H2 they are also creating their own heat as part of the charging process
 
In the end this may be a lot of trial and error.  A lot of the DYI solar hot water systems I have seen use a re-enforced wood  insulated box with a pond liner.  3x3x3 box is almost 200 gallons of water storage- and there is no reason that the system needs to be pressurized - just needs a pump strong enough to push the water through the pex in the concrete at a rate such that the water coming back into the tank is at the target slab temp. All allows mwe to use a drain back solar collector - which will help prevent freezing at night.

Offline John Florida

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Re: Is there a Mechanical/Industrial Engineer in the House ?
« Reply #16 on: May 10, 2011, 06:54:25 PM »
Are you sure that hot water is the way you want to go? Maybe you might want to look at hot air with a heat sink under the slab to release heat at night through the floor?? I'm just tossing things our there.
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Offline Weisshaupt

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Re: Is there a Mechanical/Industrial Engineer in the House ?
« Reply #17 on: May 11, 2011, 03:12:55 PM »
Are you sure that hot water is the way you want to go? Maybe you might want to look at hot air with a heat sink under the slab to release heat at night through the floor?? I'm just tossing things our there.

Hey, I am never sure about anything till I have put enough work into it that its too costly to change  ;D

The greeenhouse we are putting in works on the pirinciple you propose-- it uses a solar fan to move hot air from the top of the greenhouse into the ground during the day, and that heat insulates and protects the greenhouse from loosing too much heat through the uninsulated  floor at night. There is alos a 1200 gallon water tank in there as a thermal mass - to moderate the temps a bit so it absorbe extra heat dring the day, and puts it off at night.

the thing about air it is it has this nasty tendency to try and escape when you heat it up. Water works well as a Thermal Battery because it can be heated up, stored, and then moved easily elsewhere (say into a concrete mass) when needed - It is possible of course to do a heat exchange operation with air in the same manner - but air takes on and gives up heat a bit too easily because its a gas. In the greenhouse you care about the overall temps - of air and soil.  IN the battery instance, I really only care about that big hunk of lead and electrolyte being warm - however.. my direct contact with the concrete plan for heat transfer plan is flawed..

Been talking with a SeaBee friend of mine.. He built a lot of Solar Shed installations in Desert storm.. said that the batteries in direct contact with the concrete would discharge completely and go bad at an unusual rate.  I know a lot of people will tell me its a myth,  but he saw it with his own eyes and offered a reasonable explanation for it. .. the concrete acts as a heat sink and will either heat up/cool down the part of the battery in contact with it, relative to the top of the cell. THis leads to stratification of the electroyte - which results in a voltage difference between top and bottom of the plate-- and an eddy currrent then discharges the battery- the higher the difference in temps, the faster the drain. So in a thin wall shed in the desert, the air at the top of the battery would rise quickly to be 120 degrees, while the concrete would take longer to heat up, and the reverse at night, and it would destroy the batts.

So if I do this, I pretty much have to rely on heating the air around the battery, so the whole cell remains at an even temp. So I need to raise the batts of the floor and then heat up the floor and possibly the sides and do what I can to mitigate heat loss via the vent system . (http://zephyrvent.com/)

Offline John Florida

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Re: Is there a Mechanical/Industrial Engineer in the House ?
« Reply #18 on: May 11, 2011, 04:14:49 PM »
 Why not shelve the batteries so that only a small part of them touches what you use as a rack type deal so the air flows all around them inside a box with air flowing in and out your venting system. Constant air flow or on a timer on a fan so it cycles every so many minutes hours whatever you decide.
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Offline trapeze

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Re: Is there a Mechanical/Industrial Engineer in the House ?
« Reply #19 on: May 13, 2011, 12:53:08 AM »
Are you sure that hot water is the way you want to go? Maybe you might want to look at hot air with a heat sink under the slab to release heat at night through the floor?? I'm just tossing things our there.

Water holds heat better than air. Higher density. Concrete (insulated from the ground) is the same. Heat it up and it stores the heat quite nicely, releasing it slowly to the conditioned space. Air heats up quickly but sheds heat just as fast.

Hydro solar collectors are the way to go. Use water with a high ratio of propylene glycol and no drain down is needed.

You have to have some pressure in the system or it will not pump. Not a problem with a closed loop. Pressure it up with a garden hose and a pressure regulator set to 15 psi and you are set. Need an expansion tank, too, to deal with the variance in water temperature between day and night.

Worst case is you need a hot water backup. Use a propane water heater where the gas comes on when the tank temp fall below, say, 80F. Sunlight does the lion's share of the work and the gas would kick in during the middle of the night for a few minutes. Or invest in more storage tanks for the solar HW. Might have to add space to accommodate them but that's always the problem with solar: storage. Hydro or PV, it's always storage that's the problem.
« Last Edit: May 13, 2011, 12:59:29 AM by trapeze »
In a doomsday scenario, hippies will be among the first casualties. So not everything about doomsday will be bad.