Terra-Dome Earth Shelter Build

[sajurcaju]

Hi Steve,

Sounds like progress is being made. Were you thinking of using solar hot water for the hydronic heat? I have thought about that for our house. My problem, and you may be different, is if the sun is shining, I don't need it. If we have long cloudy stretch, it would be nice by about the third day to take some heat in, but the sun isn't bright enough. I would need to heat the water in a very large super insulated tank in sunny weather and draw from it in cloudy weather.

Some solar sites like ..::REvision Asset Management Systems::.. I have visited say this isn't a good matchup due to the btu's the solar would need to provide. Plus, when I would need it the most, mid-dec thru mid feb, there is the least sun to begin with. I notice evacuated tube type collectors are getting pricey. The link is to revisionenergy.com. It works but won't give up on the wrong name.

Good luck in your research.
Dave.

I'd like to use solar for both the hot water and the hydronic heat. As I learn more about it, I'm starting to think they might be two different setups. A large hot water heat storage tank makes sense for the hot water, but I have a hard time thinking that you could possibly store enough heat to matter on the hydronic side, compared to all the heat stored in the concrete already. I'm still in early stages on this, haven't actually done any calculations comparing the heat storage.

I am planning on making my own panels. Commercial panels are pretty pricey. There is a *lot* of apparently excellent information at this site:
BuildItSolar: Solar energy projects for Do It Yourselfers to save money and reduce pollution
This is the collector that looks good right now:
Experimental Solar Collector Using Hybrid Copper/Aluminum Construction

Steve

 

[dave1949]

I'd like to use solar for both the hot water and the hydronic heat. As I learn more about it, I'm starting to think they might be two different setups. A large hot water heat storage tank makes sense for the hot water, but I have a hard time thinking that you could possibly store enough heat to matter on the hydronic side, compared to all the heat stored in the concrete already. I'm still in early stages on this, haven't actually done any calculations comparing the heat storage.

I am planning on making my own panels. Commercial panels are pretty pricey. There is a *lot* of apparently excellent information at this site:
BuildItSolar: Solar energy projects for Do It Yourselfers to save money and reduce pollution
This is the collector that looks good right now:
Experimental Solar Collector Using Hybrid Copper/Aluminum Construction

Steve

Well, without a lot of direct solar gain, you may be able to just let the hydronic run in the slab whenever the collector temp exceeds the floor temp, for example. You would be storing heat that way in the slab itself. I think that is a normal approach.

I am afraid if I did that, I would have too much heat. I would be combining direct-gain passive and active methods. As it is, I open a couple windows for about 3-4 hours in the afternoon on sunny days like we have had this week.

One of my wife's co-workers put in a 30 tube evacuated-tube system last summer. He says they are getting nearly all of their domestic hot water from it. He has two kids and wife. I don't have any other tech details on his system.

I don't know what's up with the price of the commercial panels, maybe too much easy tax credit money floating around. I thought they used to be more reasonable. A ten year guarantee on the tubes is rather short too.
Dave.

 

[sajurcaju]

Well, without a lot of direct solar gain, you may be able to just let the hydronic run in the slab whenever the collector temp exceeds the floor temp, for example. You would be storing heat that way in the slab itself. I think that is a normal approach.

I am afraid if I did that, I would have too much heat. I would be combining direct-gain passive and active methods. As it is, I open a couple windows for about 3-4 hours in the afternoon on sunny days like we have had this week.

One of my wife's co-workers put in a 30 tube evacuated-tube system last summer. He says they are getting nearly all of their domestic hot water from it. He has two kids and wife. I don't have any other tech details on his system.

I don't know what's up with the price of the commercial panels, maybe too much easy tax credit money floating around. I thought they used to be more reasonable. A ten year guarantee on the tubes is rather short too.
Dave.

I also suspect that the result of tax credits is an increase in prices. Besides, I like doing this sort of stuff myself. Unfortunately, making panels yourself means no tax credits

As I said earlier, I'm just starting to think about solar and how it applies to an earth sheltered house. Higher temp heat storage (other than the slab) allows coasting through days with poor sunshine and no reduction of slab temp, but it seems like it would take a *lot* of heat storage. The other approach as you say would be to just put heat into the slab until satisfied and then dump the excess (more likely, dump it into the DHW solar side). This means you coast through low sun days, with slab temperatures gradually dropping. Maybe workable, I don't know (yet).

Steve

 

[dave1949]

I also suspect that the result of tax credits is an increase in prices. Besides, I like doing this sort of stuff myself. Unfortunately, making panels yourself means no tax credits

As I said earlier, I'm just starting to think about solar and how it applies to an earth sheltered house. Higher temp heat storage (other than the slab) allows coasting through days with poor sunshine and no reduction of slab temp, but it seems like it would take a *lot* of heat storage. The other approach as you say would be to just put heat into the slab until satisfied and then dump the excess (more likely, dump it into the DHW solar side). This means you coast through low sun days, with slab temperatures gradually dropping. Maybe workable, I don't know (yet).

Steve

I think the net cost of DHW is about the same if you buy factory components and assemble/install yourself, or pay for a complete installed system and get the credits. Funny coincidence

The only way to get a lower cost is to build the collector panels yourself, and buy the pump, controls, etc. - so I think you are on the right track. You could buy or build the storage tank.

Looking at Apricus evacuated tube specs just for fun, their site calculator says you would need 82 evacuated tubes in Portland, Maine in the month of January to raise the temp of a 500 gal. tank 60*F (80*F -> 140*F) in one (average January) day. Ka-Ching! I am assuming once the tank temp. was down to 80*, you would stop circulating in the hydronic.

A 500 gal. tank would be storing 375,300 usable btu's at 140*F.

That's about 4.5 hours of boiler run time for 90Kbtu unit running at 92% efficiency.

(Heating 1gal. of water by 1 degree F. requires 8.34 btu's)
Whatever you do, have fun and keep us posted
Dave.

 

[sajurcaju]

Looking at Apricus evacuated tube specs just for fun, their site calculator says you would need 82 evacuated tubes in Portland, Maine in the month of January to raise the temp of a 500 gal. tank 60*F (80*F -> 140*F) in one (average January) day. Ka-Ching! I am assuming once the tank temp. was down to 80*, you would stop circulating in the hydronic.

A 500 gal. tank would be storing 375,300 usable btu's at 140*F.

That's about 4.5 hours of boiler run time for 90Kbtu unit running at 92% efficiency.

(Heating 1gal. of water by 1 degree F. requires 8.34 btu's)
Whatever you do, have fun and keep us posted
Dave.

OK, I got inspired to actually look up heat storage in concrete compared to water. I've got 3x24'x24'x4" of heated concrete. It turns out that concrete only has about 1/4 the heat capacity of water, so this much concrete compares (thermal capacity wise) to about 1000 gallons of water. Since the storage water can be a lot hotter than the concrete, it looks like enough heat could be stored to be useful over a few days of clouds. A 500 gallon tank would probably help a lot. Now all I have to do is find time this summer to do some of this stuff.

Steve

 

[dave1949]

OK, I got inspired to actually look up heat storage in concrete compared to water. I've got 3x24'x24'x4" of heated concrete. It turns out that concrete only has about 1/4 the heat capacity of water, so this much concrete compares (thermal capacity wise) to about 1000 gallons of water. Since the storage water can be a lot hotter than the concrete, it looks like enough heat could be stored to be useful over a few days of clouds. A 500 gallon tank would probably help a lot. Now all I have to do is find time this summer to do some of this stuff.

Steve

I think you could have a good sized tank if you can insulate it well. For example, my 60 gal. SuperStore DHW tank claims a <0.5*F loss per hour. If you can get the loss down low, stored heat will stick around a long while. I suppose there is too big also where the collectors just can't produce enough btu's to handle the volume. I don't know how to calc that if you build your own collectors.

You could start with a smaller tank and see how that goes. You could tell after a while if you have more heat capacity than storage. Or, if you were building an open vent tank where the tank water is just a transfer medium between heat exchange coils, you could adjust the water level/volume to match the available btu's. You would have to keep the exchange coils immersed at least.

I'm sorry to have to tell you this, but the way you get time for outdoor summer projects is by not doing your unfinished indoor projects
Dave.

 

[RichNJKubota]

Steve,

I added a evacuated glass tube solar hot water system a few years ago. It works well. Not many details but you could take a look at our simple website:
Rich & Margies Web Pages

We use thermal heat storage too. On a sunny day like we had today the concrete mass and house goes from 70F in the morning to 73.5 by evening. This will get us thru one cold night.
There is a guy down the road from me that has 17 arrays of evacuated glass tubes to heat his conventional cape style house. Each array has 20 tubes. He says it works well.

 

[SamWalton]

We are getting ready for the plumber to install the black and gray water drain and vent systems. We marked the centers of walls where he will be locating pipe that must be contained inside these walls. The Dewalt auto leveling laser system makes it so simple even on these odd angles of the dome.

 

[dave1949]

Steve,

I added a evacuated glass tube solar hot water system a few years ago. It works well. Not many details but you could take a look at our simple website:
Rich & Margies Web Pages

We use thermal heat storage too. On a sunny day like we had today the concrete mass and house goes from 70F in the morning to 73.5 by evening. This will get us thru one cold night.
There is a guy down the road from me that has 17 arrays of evacuated glass tubes to heat his conventional cape style house. Each array has 20 tubes. He says it works well.

That's a nice home and energy set up, thanks for sharing.
Dave.

 

[SamWalton]

We are getting ready for the plumber by getting our rigid conduits in place and removing the stone base where they will be digging. Our pipes are for the heat pump, future well water, hydronic solar panels. All these pipes go through the footings.