solar-thermal panels

[Raspy]

GT2,

From your brief description I can't say too much.

Using gypcrete instead of the tube fin systems is a very good idea. I avoid fins at all cost and have found them to be completely unnecessary. Even if you have no mortar of any kind, avoid the fins.

A very large built in storage tank like the one shown is OK. It's a lot of work! Use a lot of storage and not so many panels to avoid overheating in the warm season. I have ben associated with a couple of systems like that that had up to 1200 gallons of storage. One had only, I think, 6 collectors. It as on the coast and worked quite well with little or no backup. One that I built had an above ground storage of 1000 gallons with 6 collectors and a small propane tankless water heater for backup. This one has gypcrete and the first one had concrete floors.

Often these type systems must have relatively large pumps and corrosion can be a problem or the fiberglass tanks can be a problem. I have an exceptional corrosion inhibitor that I use that is non toxic and lasts the life of the system. I also have a love/hate relationship with Grundfos pumps.

We can get into much more details if you'd like because I love talking about this stuff.

I don't know what you mean by a solar loop running through a propane fired water tank. Do you mean just plumbing a water heater in series as backup?

Some info on delivery temps and strategy in an in-slab radiant system might help. 90 degrees is just about break even. It will hold the house and raise it some, but very slowly. 120 degrees is all you'll ever need and should be about the limit you ever send to the floor. Maybe a bit more under special circumstances. There are three phases of floor temperatures. The first is cold. Meaning you notice it right away and don't want to be bearfooted, the house feels cold. Next is invisible. This means you just don't notice the floor when walking on it. The house is generally pleasant. The floor is probably around 70-75 degrees. The third is where the floor greets you when you walk into the kitchen or bathroom. It's very nice and gets your attention. This is good for entries and bathrooms and it is probably about 80 to 90 degrees. Any floor warmer than about 87 degrees for an extended amount of time will heat the house to where you are too hot unless there is very poor insulation.

Using the floor for storage can be helpful, but it is likely to be more of a problem. A minimum threshold temp is fine, but above that we become uncomfortable and a slave to the system. Radiant floors are most comfortable when we can vary their temps. Some examples of this are: Sleep in a cool room and arrive in a warm bathroom in the morning. Let the bath cool during the day. A warm kitchen floor in the morning but cooler during the afternoon. Guest bedrooms cold until needed. One kid likes his room warm and the other likes it cool. An office might get morning sun and have a lot of computer heat loss. But is used at 3:00 in the morning and needs heat then. The entry floor might be warm in the evening and settle down during the night to save energy. Etc. Programmable thermostats are definitely your friend. Outside sensors are a waste of time. Generally speaking, setting and leaving the thermostat at one setting means a variable inside temp because of all the other influences such as the sun, cooking, lighting, activity, etc. A varying thermostat setting matches the house to the users and saves anergy. Measuring the outside temp in order to decide the delivery temp does not take into account that we want to change the floor temp and do it relatively rapidly in order to accommodate our lifestyles.

Feeding the floor with 90 degree water will not drive the floor to 90 degrees because of the heating load. But 90 degrees at the solar panels is very efficient.

Try not to ever send any heat from your backup system into your storage system. This is very important and means you will have to find a way to switch to backup and direct that energy to the floor only. This can be done with a heat exchanger that heats a closed loop floor system from the open loop tank. The closed loop circuit can also be diverted through a backup heater that is also part of that loop. Switching is done with differential solar controllers and circulators. You can choose solar only, automatic, or backup only.

Thanks for putting up with my ramblings.


John

 

[Redneck in training]

I like the boiler part but will defer to Wetspirit as this is more of his expertise.

Google Image Result for http://www.evergreenenergy.ie/img23.gif

http://www.google.co.th/imgres?imgu...mage_result&resnum=4&ct=image&ved=0CBwQ9QEwAw

Here is a automatic wood burning boiler. Works like gas or oil. Google biomass or wood chip boiler.
I know a guy who made a fully automatic horse manure boiler for his horse stables. He would just put few front loaders of manure in the hopper every few days. He couldn't find a manufacturer so unfortunatelly there is only one prototype.

 

[GT2]

GT2,



I don't know what you mean by a solar loop running through a propane fired water tank. Do you mean just plumbing a water heater in series as backup?


Using the floor for storage can be helpful, but it is likely to be more of a problem. A minimum threshold temp is fine, but above that we become uncomfortable and a slave to the system. Radiant floors are most comfortable when we can vary their temps. Some examples of this are: Sleep in a cool room and arrive in a warm bathroom in the morning. Let the bath cool during the day. A warm kitchen floor in the morning but cooler during the afternoon. Guest bedrooms cold until needed. One kid likes his room warm and the other likes it cool. An office might get morning sun and have a lot of computer heat loss. But is used at 3:00 in the morning and needs heat then. The entry floor might be warm in the evening and settle down during the night to save energy. Etc. Programmable thermostats are definitely your friend. Outside sensors are a waste of time. Generally speaking, setting and leaving the thermostat at one setting means a variable inside temp because of all the other influences such as the sun, cooking, lighting, activity, etc. A varying thermostat setting matches the house to the users and saves anergy. Measuring the outside temp in order to decide the delivery temp does not take into account that we want to change the floor temp and do it relatively rapidly in order to accommodate our lifestyles.



Try not to ever send any heat from your backup system into your storage system. This is very important and means you will have to find a way to switch to backup and direct that energy to the floor only. This can be done with a heat exchanger that heats a closed loop floor system from the open loop tank. The closed loop circuit can also be diverted through a backup heater that is also part of that loop. Switching is done with differential solar controllers and circulators. You can choose solar only, automatic, or backup only.

Thanks for putting up with my ramblings.


John

John, thanks for the " ramblings", very helpful.

I saw a standard looking tank propane water heater that had a copper coil in the bottom for running external solar water thru. To pre- heat the tank.
I thought I could run the solar water thru it first then on to the floors, or would there be too much temp drop?

I plan to use different loops in different areas like you describe. I will use thermostatic controllers on the manifolds also.

So your saying do not use back up heat to heat the storage tank? If possible, elaborate?
Your saying use a heat exchanger on the incoming line to the heating system itself instead of the storage, and / or by-pass the storage tank itself?
Thanks, Tim

 

[crazyal]

I sure would be looking into a wood fired boiler of some sort with storage with all that available firewood. Although sometimes it is easier to buy your energy than exert energy to get it. $450 a year is not bad though for all your hot water AND back up heat! Do you have enough floor area to carry the house heating needs?

The house is a post and beam with foam panels so it requires very little to heat even on the coldest nights. I have a small to mid size soapstone stove that I can run all night, usually the biggest problem is I over heat the house and wake up to mid 80's in the living room.

The house is 1900sqf, not too large but the living room walls are 12' with a 12:12 pitch roof so it's about 22' high. All the rooms on both floors connect to it so spreading the heat from the stove isn't hard. If I went with solar panels it would be mainly for DW heating only and most likely from April to October. Those are the months the furnace would never run.

 

[jdmar]

I've been toying with the idea of adding some myself. I've been looking at the evacuated tube style. They may cost more but from what I've been told the style with the copper tubes that run back and forth tend to expand and contract and leak. Here's a link:

http://www.rstreps.com/pdf/install-vacuum-tube.pdf

The water only goes across the header and if a tube breaks the system still works. Plus they are suppose to work better in shade.

Be careful. I love the technology of the evac tubes...in some areas. In Vermont you get a lot of snow. The evac tubes do NOT get warm on the outside so snow does not melt off them as well as other collectors. What makes them efficient at absorbing heat also keeps the outside too cool to effectively melt snow.
Peter

 

[magicheater]

The house is a post and beam with foam panels so it requires very little to heat even on the coldest nights. I have a small to mid size soapstone stove that I can run all night, usually the biggest problem is I over heat the house and wake up to mid 80's in the living room.

The house is 1900sqf, not too large but the living room walls are 12' with a 12:12 pitch roof so it's about 22' high. All the rooms on both floors connect to it so spreading the heat from the stove isn't hard. If I went with solar panels it would be mainly for DW heating only and most likely from April to October. Those are the months the furnace would never run.

I was under the impression you had storage tanks already. How much storage would you be considering for the DHW? How much of your house has radiant floors? The way I understand how you heat is that you use a wood stove and use the radiant floors for back-up, when you are gone lets say? Is this correct?

 

[crazyal]

Be careful. I love the technology of the evac tubes...in some areas. In Vermont you get a lot of snow. The evac tubes do NOT get warm on the outside so snow does not melt off them as well as other collectors. What makes them efficient at absorbing heat also keeps the outside too cool to effectively melt snow.
Peter

I'm not too worried about snow since I really don't care about using them in the dead of winter (I'd be happy with April to October) and with a 12:12 pitch roof snow doesn't stay up there. However there was a link to a website at the beginning of this thread that had a link to a couple of side by sides of the two. What one of them found is that the evac tubes frost over and don't thaw very quickly. That could mean the loss of a month or two so I doubt I'll go that route.

 

[crazyal]

I was under the impression you had storage tanks already. How much storage would you be considering for the DHW? How much of your house has radiant floors? The way I understand how you heat is that you use a wood stove and use the radiant floors for back-up, when you are gone lets say? Is this correct?

The whole house has radiant floor heat. I love walking barefoot in the middle of winter on the tiles. I have a 57 tank right now but have the plumbing in place to add something like a Rheem 80 or 120 gallon tank.

Because my furnace isn't the type that just stays hot I was thinking on having a circ pump that would turn on once the storage tank reached a temp higher than the primary tank. That way the solar panels would also heat up the primary tank. If the temp of the solar tank drops below the set point the boiler would keep the primary tank at temp and just be fed warm water from the solar tank. That way the furnace should never come on unless we (my GF and I) used up both tanks.

 

[magicheater]

The whole house has radiant floor heat. I love walking barefoot in the middle of winter on the tiles. I have a 57 tank right now but have the plumbing in place to add something like a Rheem 80 or 120 gallon tank.

Because my furnace isn't the type that just stays hot I was thinking on having a circ pump that would turn on once the storage tank reached a temp higher than the primary tank. That way the solar panels would also heat up the primary tank. If the temp of the solar tank drops below the set point the boiler would keep the primary tank at temp and just be fed warm water from the solar tank. That way the furnace should never come on unless we (my GF and I) used up both tanks.

When do you use the floors for heat You burn 2-3 cords of wood to heat the house but have radiant floors Do you run the floors off the water heater or have the boiler and the wood stove going at the same time? Please clarify for me how you use what you have in place at the moment.

 

[Raspy]

Tim,

I'm not sure you'll want to run the radiant water through the water heater on the way to the radiant system. On the way to the radiant storage tank, yes, but not on the way to the radiant floors. If you have a separate water heater with a loop, as you describe, you might just run the solar panel return line through the water heater heat exchanger on it's way to the main storage tank that will then heat the radiant later. The radiant schedule is not the same as the hot water schedule. And the radiant system can operate at a lower temp than the DHW. Plus, hopefully, you won't need to store energy in the radiant floor. At least no more than to bring it up to a threshold temp.

On the radiant manifold loops. Yes, be sure to run different loops for different rooms. 1/2 inch barrier PEX is the most practical tubing and the loops should be set up to be relatively close in length. Arrange them at 9" or 12" on center with a 6" OC first pass near entry doors and in the bathrooms. Bathroom loops can be considerably shorter than bedroom loops because we want higher flow rates in the bath. Try not to exceed 300 linear feet per loop. Three 200' loops would be better than two 300' lengths. Loops can run through hallways to get to bedrooms and kitchens, etc. This heats the hall without a thermostat in that area and provides a convenient run of tube. I run all tubes above the floor, meaning don't go to the trouble to route tubes in joist bay spaces. Sometimes this means very close tube spacing in a hall, for instance, and that's fine.

You mentioned thermostatic controllers on the manifold loops. I want to be very specific here, so bear with me. I only use telestats, or motorized valves. No thermostatic valves that attempt to regulate the temperature going through them or of the temperature of the floor. This leads to a bigger conversation, but the theory is to move a lot of water at an adequate temp, as opposed to a regulated flow at a certain temp designed to hold the floor at a certain temp. Thermostatic controls fall into the category of "maintaining" a certain temp all the time. Telestats fall into the category of delivering heat rapidly, and actually do it more evenly and effectively. The proper control strategy is to use a wall thermostat that is programmable, or in some cases, a floor sensing thermostat. Rapid flow at an adequate temp is the idea here. To understand the thinking here imagine a room with serpentine radiant piping. Maybe it has 15 runs across the room at 9"OC. The hot water comes in and moves back and forth across the room, giving up energy and cooling as it goes. A very slow flow will mean a large differential between the supply hot and the return cool. This means that the room got progressively cooler and cooler supply water in different areas and therefore will be cooler, and heat slower, in different areas. It also means we deliver less energy to that room, in total, than if the water was flowing faster. Faster means more even heat and more energy delivery. A floor gives up it's heat to the environment based on the temperature differential between it an the room. A warmer floor equals more delivery to the surroundings. A small differential in the radiant supply and return temps means more energy delivery than a large differential because all of the floor experienced the warmest water. So, a warm relatively high flow makes the room heat the best and delivers the max energy.