dc hvac systems

[bridget]

With building codes being whatv they are around here, we are required to put in an hvac system. We are planning to run on dc power(still working on code problems for that). Does any one know of an hvac system that is designed for dc power? Or is the only option to use a passive sytem with a dc fan attached and timer?

[henjulfox]

Bridget,

I once had a camper trailer that had a small propane furnace that ran on 12VDC. No idea how "code" would like it...

-Henry

[TAH]

The code lets you wire for DC?

[stephent]

yeah--the code (US--NEC) allows and even has a lot of "got-too's"/shalls and requirements for DC systems.

Specifically mentions Solar/wind/other forms of generated electric.

It's usually specific but sometimes a bit confusing for leisurely reading, but it's certainly there.

Grid-tie and stand alone systems.

A passive cool-tube system or with a fan would work or even a swamp-cooler type system would work if ambient humidity is low enough.  Local codes sometimes are rather rigid--local inspectors/authorities are sometimes in-flexable as to alternatives too.

Hopefully an alternative you find will be acceptable.

[whatsnext]

Unless you plan on never selling the place I think I would just buy inverters and wire the house normally. The next owner may not want a DC system.

John...

[bridget]

I don't plan on ever selling my home. Plus the wiring is the same(heavier guage), just different recepatcles and there are dual purpose breakers, so just the incoming would have to be changed.  I realize it is a unusual even with alternative power, but I know dc is more efficient and that is what we are wanting to do, we are trying to work with inspectors as much as we can and so far haven't had any major road blocks, but Im sure there will be some.

I was wondering if there are any hvac systems in place already for remote locations, like gov't sites etc that any one might have ideas for. we probably will do the passive  fan system if we can't find one.

[pepa]

hi bridget, i am building a central unit that has ice making/hvac as part of the system. i am using the idea of a solar icemaker that i found on the web. my system will use heat from an oil burner insted of solar but the principle is the same. this setup would be good with your all dc system. see june/july 1996 home power #53 sorry i don't know how to make a link to the sight but you will find it interesting, hope this helps, pepa

[bridget]

ok , now any ideas on an hrv system as well, again looking for dc if possible.

[altosack]

Be careful how you define "efficiency". Yes, not inverting DC is more efficient electrically, but that does not always translate into you getting more of what you want for how much DC you put into it. For example, I challenge you to find a DC blender that will be as efficient as a cheap AC one driven by an inverter, and DC CFLs are quite expensive and there is very little selection available.

I want my refrigerator and some lights to be DC so a failed inverter doesn't put me out of commission, but using AC for many other things will save you money unless you are very frugal and forego most of the stuff most USians take for granted. If this is where you are on your personal path, I commend you; however, be honest with yourself, get second opinions, and do much research before you decide to forego AC entirely.

My recommendation is to have both AC and DC runs in your house and use the most efficient one for each appliance you have. This will also make it easier to pass code; in fact, why don't you make them all AC, pass inspections, and then change the ones you want to DC ? No questions asked is a good way to go.

For a DC HVAC system that will pass code (i.e., is UL or CSA listed), good luck. I have heard of people putting in one or two electric baseboard heaters because this is the cheapest thing to do. The electrical inspectors don't even care that your RE system could never in a million years power it. As long as it's stamped (UL, or whatever) and they can check it off on their list, they are happy.

Don't get me wrong, I don't think all electrical inspectors are no good. However, even the good ones do not have the time to research every non-standard thing you present to them, and once they see some things that are questionable in their experience, they will look all the harder at everything else, which you do not want. If you do decide to go all DC, have a long talk with the actual inspector who will do the work before you even get started. If you have to change things mid-stream, it will not be an enjoyable experience.

Best of luck,

Dave

[TAH]

Do you need a commercial device? If so you could buy an AC unit and change the motor. If you want to build one it is a box, air to air heat echanger and a fan. I used an intercooler from a Volvo semi and put it in a box with a fan to force air out and let the negative preasure bring the return in.

[vawtman]

Hello Bridget

 Where are you from?Just wondering what codes are used in the boonies?What is going to supply the dc?Thanks

[bridget]

We live near Perth Ontario Canada. I'm not completley sure of the code requirements, but my understanding is that it is permissable and ac requirements apply as far as number of receptacles and locations, the place I may run into trouble is the ground fault and arch fault receptacles, I'm not sure what is available in dc. But so far my  search has been good. I am having trouble talking with an actual inspector... they ESA here is protective of their inspectors before a permit is issued. So the next step is to get a permit and get some questions answered.

We plan to use solar and wind with a deisel generator backup.

I think we have revised our ideas on the heating system and are going with a woodstove and radiant heat, less complicated. Now we just need to figure out the hrv system that is still required.

[GaryGary]

Hi,

On the AC side of HVAC, there are some 12VDC listed here:

http://www.builditsolar.com/Projects/Cooling/passive_cooling.htm#Active

(down the page a ways -- these are evap coolers made for PV systems)

For the heating side, could you use one (or more) of the propane heaters that mount on a wall, and do not use a fan at all?  I don't think that they have any kind of electrical connection at all(?)  Or wood?

Gary

[luckeydog]

try this website http://www.backwoodssolar.com/newsletter/articles.htm

[MaxtorD]

here is a site that has 24v and 48v HVAC systems.  check out the dealer links to get some more info on them.  I have seen a few dealers that have these systems that are not listed on this site.  anyway here is the link...

http://www.solcool.net/