Double stud wall construction-anybody seen it/done it?

[jimbom]

JimboM:

How do you heat the house and get hot water from the same water heater?

Good question. What I am about to write is not condoned by any building code that I know of. Any public health officials skip this comment. Same for any water treatment operators.

The floor loop is tapped directly into the bottom and top of the water heater. The floor loop water is pumped through the water heater as needed. The water that heats the floor could be giving a shower in the next instant. The hot water tank temperature is set to medium temperature on the dial. Nothing extremely hot or anything out of the ordinary.

Do not do this at home unless you are comfortable with the methods to keep pathogens from growing in fresh water. Not to recommend anyone do this, but the key is to keep the water in the floor loop circulating at all times. My judgment was this would prevent health hazard from the water. We have been doing it since 1990/91 and no trouble to date. This includes when the floor is drawing no water from the tank.

There are a lot of smart people on this forum and I know the arguments against this. I agree with those and do not recommend this type of system for use in any application.

 

[jimbom]

JimboM:
I'm in the same boat when it comes to solar. I just scrounged a brand new controller, but I've been looking for a tank for a long time.

I found a propane tank on the cheap. The safeties, fill point, and other hardware had been removed. It was in good shape, had two coats of paint on the exterior and no apparent rust.

As a bonus, when I called the number in the ad, I recognized the voice. Our kids had played baseball together all the way through high school and we know each other very well. He had obtained three neutered tanks from a propane company in some sort of barter deal. I was the first to respond to his ad and he steered me to the best tank and loaned me a trailer from his business to take it home on. It weighs 900 pounds. I used the Ozark forklift to get it off the trailer. All you need is a tie down strap and a tree. You tie the tank to the tree and drive the trailer from under the tank.

Now that I know propane tanks become excess, I might start with propane companies to find a tank. Also, good would be areas where they are currently installing natural gas systems. When we did that here in 1992, almost everyone switched. The local propane guy still has ~1000 tanks out on his farm. Will not let go of a single one. They show up on Google earth. Do not know what he is thinking. Must have something to do with taxes or liability or something not apparent to a layman.

I on the other hand do not yet have a controller. Such is the life of comshaw artists. Between honey-do jobs today, I was looking at thermistors and thermocouples on the net. They are very reasonable. My thinking is I will put those in when I put things together and then monitor with hand held meters until I can figure out the best operating scheme. Then I will know better what I need my control system to do. Meantime, I will be the controller.

 

[GaryGary]

Hi,
One inexpensive way to build a tank for solar systems is to use a plywood box that is framed with 2 by lumber and lined with EPDM rubber roofing membrane. For non-pressurized drain back system this works well. The design may seem a little goofy, but this design goes back to the 70's, and has a very good track record. I've heard from people who are just changing out their original EPDM liner for tanks that were installed back in the 80's. Tanks up to 800 or so gallons are easy to do in this way.
One nice thing about these tanks is that the when the EPDM liner does go out it can be replaced and you are then good for another couple decades. They also work out for spaces with limited access, as they can be passed through the access in pieces and assembled in place.

The tanks need to be insulated, and the best place to put the insulation is inside the plywood before the EPDM goes in. At least the first layer of insulation needs to be the polyiso type of rigid foam board insulation -- most lumber yards carry polyiso, but may not know it by that name -- ordinary Styrofoam won't take the temperatures. The insulation turns out to be the most expensive part of the tank.

For solar space heating applications, you can just pump the hot water right out of the tank, around your floor loop, and right back into the tank -- no heat exchanger normally needed. For heating domestic hot water, you do need a heat exchanger to transfer the heat stored in the tank to the potable hot water -- I use a 300 ft coil of 1 inch PEX for this -- it serves as both a pre-heater and a heat exchanger. Using a smaller coil of copper pipe is also common.

These are the details on my 180 gallon tank:
http://www.builditsolar.com/Experimental/PEXColDHW/TankConstruction.htm

Another scheme is to use multiple 50 gallon plastic drums for heat storage -- there are some temperature limits, but a number of people have successfully done this. The JC-SolarHomes website has a lot of info on this scheme.

On the controller front, you can still get the Goldline GL30 for about $90 if you look around, and John Canivan at JC-Solarhomes makes a kit differential controller. Might also Google "Shem controller" -- this is a China imitation of the Steca type controller. I was given one to try, and its been working on my space heating system for all of this season with no problems -- not sure what they cost, but I think fairly cheap.


Gary

 

[Trouthead]

I built and have lived in a double walled house since 1980. I would never build a house any other way, but I would change some ways of doing it. I used 2x4 studes with fiberglass batts vertically in the outer and inner walls, and fiberglass batts horizontally in the inner wall. For sure in the future I would spray foam the outer stud wall and then most likely use either blown in fiberglass or cellulose. My ceiling has R-65 worth of cellulose, and my roof trusses have a kicker built into them to set the roof above the outer walls and allow better insulating out over the walls. I am not sure I would do that any differently other than up it to R-75. I used 6 mil plastic as a vapor barrier through the whole house, and if I did it again I would take better care with it.

My house was the first one to use Tyvek in my area, and I would probably not change that. Non expanding foam was not around in 1980, so I stuffed fiberglass around the windows and doors for windproofing, certainly better ways of doing that now. My windows are triple pane on the north and double on the south and east. My crawl space was insulated on the outside of the foundation walls, but a few years back I had the inside walls and header of the crawlspace sprayed with 4 inchs of foam. My crawl space now stays 59 degrees all winter. It used to get down to 38. I also blew the vents shut, and then need to put a dehumidifier in. My humidity now stays at 35%. The end result of the crawlspace work was I now have higher radon than I would like and will do a radon mitigation in the crawlspace this spring.

I wish windows were better. Even the best are like big holes in the wall. Some of the european windows look good but they are hugely expensive. My non carpetted floors are still colder than I would like. I have thought about spraying foam on the under side of the floor, but would do it in sections to make sure I still keep the crawlspace warm with waste heat from the floor.

I used wood and electrical baseboard heat until this year when I switched to a gas heating stove. Still don't have the first gas bill, but the electric bill was 462 KwH worth it for the month of December.


I don't know were the point of diminishing returns is with insulation, but 30 years later I think I am under that point, and would build the next one with MORE insulation.

It also is very quiet.

I live in Wyoming so it is very cold in the winter and hot in the summer. Right now it is -7 degrees, last summer we had days upon days of the high 90s. The whole hose until last summer was cooled with a 16000 BTU window unit.

 

[pybyr]

One technique that I've seen (and used in rennovating my kitchen) is to run 1x3 strapping horizontally, nailed to 6" vertical studs on the inside of the wall structure, on 18 inch centers.

You reduce "thermal bridging" immensely, but with far less material and labor than the double stud wall- and it is simple to weave into rennovations of an existing structure if you are opening up the walls on the inside.

 

[GaryGary]

One technique that I've seen (and used in rennovating my kitchen) is to run 1x3 strapping horizontally, nailed to 6" vertical studs on the inside of the wall structure, on 18 inch centers.

You reduce "thermal bridging" immensely, but with far less material and labor than the double stud wall- and it is simple to weave into rennovations of an existing structure if you are opening up the walls on the inside.

Some detailed info on these horizontally strapped walls:
http://www.builditsolar.com/Projects/Conservation/MooneyWall/MooneyWall.htm


And, a couple more detailed descriptions of strapped walls in new construction here:
http://www.builditsolar.com/Projects/SolarHomes/constructionps.htm#Stick
The "Gimmie Shelter" links.

This does seem like a good way to go, and it can be used on retrofits and new construction.

Gary