jwalden
Registered Users
New Member
Posts:3
 |
| 07/17/2009 12:44 PM |
|
| I'm in the process of designing a new home which should be tight and well-insulated, with 3200 sq ft, 6" frame construction over a basement, and will have closed-cell spray foam insulation in the walls and roof, and 2" polyiso insulation board under and around the basement. I want to use a radiant floor heating system. Originally I wanted to build a system that could use solar hot water with a boiler for back-up, to heat the house in the heating season and the swimming pool in the summer- but I'm having some difficulty locating any engineers in my area who have experience with such a project. Does anyone know if such a project is even feasible? Any suggestions regarding proper engineering or design of such a project? |
|
|
|
|
|
|
NRT.Rob
Registered Users
Advanced Member
Posts:733
|
| 07/17/2009 1:06 PM |
|
| where are you located? solar feasibility for heating depends on your location and your heat load, among other things. more northerly areas with typical loads generally do not find it cost effective, if that is a deciding factor. |
|
-=Northeast Radiant Technology=-
NRTradiant.com |
|
|
BadgerBoilerMN
Registered Users
Basic Member
Posts:311
|
| 07/17/2009 7:04 PM |
|
| I design radiant floor, pool heating and domestic hot water systems using ModCon high efficiency condensing boilers (95 AFUE) for most of the northern tear states and provinces. Solar assist is possible but requires "whole house" collector arrays to satisfy heating loads. If you spend more to heat your house than to cool it, you may be in a solar friendly climate, but even in these milder climates fossil fuels will be needed for backup when making domestic hot water. |
|
MA
www.badgerboilerservice.com |
|
|
dmaceld
Registered Users
Advanced Member
Posts:805
|
| 07/19/2009 7:57 PM |
|
Posted By jwalden on 07/17/2009 12:44 PM
Originally I wanted to build a system that could use solar hot water with a boiler for back-up, to heat the house in the heating season and the swimming pool in the summer- but I'm having some difficulty locating any engineers in my area who have experience with such a project. Does anyone know if such a project is even feasible? Any suggestions regarding proper engineering or design of such a project?
The single greatest obstacle to using solar for space heating is the heating load is greatest when the energy production is lowest. Solar supply and space heating demand are 180° out of phase with each other. Most heat is needed during the night, when of course the sun isn't overhead, and in the winter when the sun, and solar energy, is the lowest. That's why you're having problems finding someone to design the system. Probably for most folks, even many rich ones, it's not physically nor financially viable.
That being said, capturing solar energy during the day and storing it for the night is doable, primarily with water storage, but at what cost? Capturing summer solar energy and storing it for winter use is a nut that hasn't really been cracked yet. I tried to figure it out and gave up rather quickly, and I'm a stubborn, reasonably resourceful, engineer.
For domestic hot water and swimming pool heating the case is altogether different, and much more practical.
Another practical issue you're dealing with. As you reduce the energy consumption of your house it becomes more and more difficult to get a reasonable pay back on a capital intensive energy production system. Think of it in these terms. If you're building the Aswan dam then you want to use huge Caterpillar dump trucks with 50 cubic yard dump beds. If you're filling up the kid's sandbox you don't even want to use a city street department dump truck!
|
|
Building house - what a way to spend retirement! It's done! We're living in it! |
|
|
baron
Registered Users
New Member
Posts:19
|
| 07/19/2009 10:21 PM |
|
All that makes sense.... However I am presently installing a radiant system and want to use solar to PRE heat the water. Main water supply goes first to the solar tank ( 115 gallon) that has a loop heat transfer from the panel (s). Then the preheated water goes to a Buderus? wall hung boiler that I am told is 98% efficient? I am not sure whether to use a propane fired or oil fired unit for overall cost benefit to me. I am hoping on most days to heat the water from a cold 45 degrees up to at least 75 degrees. Then the boiler won't work as hard. Part of this reasoning is that I have a panel and a tank already! Otherwise the extra expense MAY not pencil out as cost effective.
Any feedback on this system is appreciated!
Regards Jeff
|
|
|
|
|
dmaceld
Registered Users
Advanced Member
Posts:805
|
| 07/20/2009 1:02 AM |
|
Posted By baron on 07/19/2009 10:21 PM
All that makes sense.... However I am presently installing a radiant system and want to use solar to PRE heat the water. Main water supply goes first to the solar tank ( 115 gallon) that has a loop heat transfer from the panel (s). Then the preheated water goes to a Buderus? wall hung boiler that I am told is 98% efficient? I am not sure whether to use a propane fired or oil fired unit for overall cost benefit to me. I am hoping on most days to heat the water from a cold 45 degrees up to at least 75 degrees. Then the boiler won't work as hard. Part of this reasoning is that I have a panel and a tank already! Otherwise the extra expense MAY not pencil out as cost effective.
Any feedback on this system is appreciated!
Regards Jeff
I don't remember the URL now, but one of the Universities in Oregon has info on solar energy intensities around the country. A search on solar, Oregon, university, will probably find it. From their charts you can probably get some idea about how many Btus of energy you are likely to capture for various panel designs, areas, and orientations during various times of the year. You will also have to decide what orientation you will want for the panels. More vertical will capture more winter sun, for heating, and more toward horizontal will capture more summer sun, for pool heating. Or maybe you'll want to come up with a scheme to change the panel orientation throughout the year.
How much panel do you have? From what little I pursued the subject for myself, and looking at photos of space heating setups, you'll need to cover almost an entire south facing roof to capture enough energy during the winter.
What's the 45 to 75 temp rise? That must be for DHW only, right? The temp of the return water in your radiant system is probably going to be over 75. You quite possibly are looking at radiant loop temps with the cold side running at temps close to or greater than your solar loop. That in itself works against using solar tied in directly for space heating. Surely you're not planning on an open loop radiant system, are you?
More info about your planned design would be helpful. Do you have heat load calcs on a room by room basis, and the corresponding loop temperatures, spacings, and lengths? Before you can really make a determination about the feasiblility of augmenting the boiler with solar you need to have the entire heat load requirement nailed down pretty firmly.
|
|
Building house - what a way to spend retirement! It's done! We're living in it! |
|
|
NRT.Rob
Registered Users
Advanced Member
Posts:733
|
| 07/20/2009 7:48 AM |
|
you can preheat for domestic, but you can't really "preheat" for heating in most cases. You can in some windows of opportunity, but in general if the boiler is running you don't want the water running back to the solar tank, or you can raise your solar tank temp with boiler energy which reduces your solar collection and storage ability.
If you're talking about 45 degree water though you are talking about solar domestic hot water, not heating. that's easy. pipe the solar tank into an electric on demand to "boost it", or use an on demand warranteed for solar applications, and if the solar isn't working, the tank isn't hot. If it is, it is.
You can instead do this with a boiler and indirect in a separate tank, but I personally think that's kind of silly in most cases. Then you can have a 130 degree solar tank and still "kick on" the boiler to heat the second tank for maintenance demands. and you need a recirc system if you want the solar to ever heat both tanks.
Or if you tank has two sets of coils you can heat the top half of the tank with the boiler to do domestic. but I don't like that either because it kills half of your solar storage capability.
Or, you misunderstand how heating works and you think you use stone cold water to heat your house ;) In reality, the water circulating around your system will never be below room temperature and will often be 10 or 20 degrees cooler than the supply temp going out to the system. |
|
-=Northeast Radiant Technology=-
NRTradiant.com |
|
|
baron
Registered Users
New Member
Posts:19
|
| 07/20/2009 1:37 PM |
|
Hmmm I have run into a couple of guys that know what they talk of. I don't particularly as you may have guessed. I am flying by the seat of my pants here. I want to make some incoming cold water hotter. I will use the Solar stream 115 gal tied into a panel to preheat this water. Then this water would go to a boiler which would heat up and circulate hot water thru the loops in my floor from a separate small (60 gal) heat transfer tank for domestic hot water as well. So the solar system stands apart and used only as a pre heater.
What am I missing here?
I am using 4 Rehau pro balance manifolds. One has 5 loops , 4 loops, 2 loops and 2 loops. All runs are 170 feet more or less using 1/2" pex on 8" spacing. I am getting ready to call the gypcrete guy to pour the floor.
REgards Jeff
|
|
|
|
|
NRT.Rob
Registered Users
Advanced Member
Posts:733
|
| 07/20/2009 2:10 PM |
|
you do not take incoming cold water to heat your heating system. Your heating system recirculates the same water over and over.
incoming cold water should only move on to your faucets. That can easily be preheated. solar tank to indirect and on to the faucets, great. but you don't draw your heating system water out of your indirect tank, so unless you have another set of coils in your 115 gallon tank, you aren't doing heating system stuff here, just domestic. |
|
-=Northeast Radiant Technology=-
NRTradiant.com |
|
|
baron
Registered Users
New Member
Posts:19
|
| 07/20/2009 7:31 PM |
|
Now there's a revelation! thanks for that. What about open loop system? I had inquired to Rinnai water heater corp about using one of their top of the line flash heaters and got this reply:
"Rinnai water heaters can only be used for heating in open loop systems. This means you must also provide domestic hot water. I have attached two diagrams of how you can go about setting up combination systems."
If you would like I could post the diagrams and get some feedback. I hear in Europe they use this method alot for domestic hot water and also radiant floor heat.
Regards Jeff
|
|
|
|
|
dmaceld
Registered Users
Advanced Member
Posts:805
|
| 07/20/2009 9:28 PM |
|
Posted By baron on 07/20/2009 7:31 PM
What about open loop system?
Do a search in this forum for open loop and Legionnaires' disease. It'll give you something to chew on!
|
|
Building house - what a way to spend retirement! It's done! We're living in it! |
|
|
NRT.Rob
Registered Users
Advanced Member
Posts:733
|
| 07/21/2009 6:40 AM |
|
| open loop systems are very poor ideas, as is using an on demand hot water heater for a heat source in most cases. and even in that case, you are recirculating water, not drawing new water from the ground for heating. Only during domestic demands are you bringing in new water. |
|
-=Northeast Radiant Technology=-
NRTradiant.com |
|
|
Blueridge company
Registered Users
Basic Member
Posts:211
|
| 07/21/2009 9:46 AM |
|
We sell Rinnai tankless units, and on occasion get people that want to use them for a heat plant. This or any tankless unit is not our preferred system. We would much prefer to direct you to a modulating boiler. That said it can be done, However the pump has to be sized properly, there is a large amount of head created by the unit.
Legionnaires is a huge concern when making a open loop system, Personally I would never have one in my home. Water needs to be circulated daily. This can be done properly with a TACO SR504-EXP-1 with a PC600-2 post purge card (runs the pumps daily). To hold the Rinnai warranty in place you need to have an access or hose bib to the domestic water, water in water out. However if you never use the water from the appliance it will be pretty nasty after a short time frame.
Dan
|
|
Dan
BlueRidgeCompany.com |
|
|
jebatty
Registered Users
New Member
Posts:5
|
| 07/22/2009 6:33 AM |
|
| 115 gal storage with a 20F delta-T only is about 20,000 btu's, which doesn't provide much heat for very long. With about 10,000 btu per 10F delta-T, the higher you can load the tank and the lower you can use the water for radiant, the better you will do. I use a wood gasification boiler with 1000 gal pressurized storage - plenty of heat for a long time on a single burn. |
|
|
|
|
Dana1
Registered Users
Advanced Member
Posts:702
|
| 07/22/2009 10:22 AM |
|
Pool heating is a much lower-temp proposition than domestic hot water heating. You might consider using EPS insulation under the paved area surrounding the pool, and using the pavement as the pool heating solar collector using embedded PEX. (This has the dual-advantage of cooling the paved area surrounding the pool as well.) The glazing required for DHW collectors cuts the collection efficiency for lower-temp apps like pool heating (which is why all commercial pool-heating collectors are unglazed. If it's in a freeze prone climate, setting it up as a drain-back is recommended. The pumping power required for such a system can be lower than roof-mounted collectors too since there's very little gravitational head to overcome.
Then set up any DHW or space-heating collectors with something more-appropriate to the higher-temp application, not some super-combined solar thermal Rube-Goldberg contraption (much as I love clever hacks...) |
|
|
|
|
Blueridge company
Registered Users
Basic Member
Posts:211
|
| 07/23/2009 12:41 AM |
|
so, Dana,
could we stain the concrete around the pool charcoal, load it with 3/4 pex on a 12 inc pattern and temp sensed motor zone valve to the pool, natural drain down in the winter by running thru the pool filter?
I like it, how could one measure BTU per 100 square feet of concrete collector?
Dan |
|
Dan
BlueRidgeCompany.com |
|
|
baron
Registered Users
New Member
Posts:19
|
| 07/23/2009 10:27 AM |
|
Wood gasification boiler? What's that? We have alot of firewood up here in the N Sierra Mtns. I am really scared of doing this radiant project and getting hooked in to fossil fuel! But I do want warm floors.
|
|
|
|
|
Dana1
Registered Users
Advanced Member
Posts:702
|
| 07/23/2009 12:42 PM |
|
Posted By Blueridge company on 07/23/2009 12:41 AM
so, Dana,
could we stain the concrete around the pool charcoal, load it with 3/4 pex on a 12 inc pattern and temp sensed motor zone valve to the pool, natural drain down in the winter by running thru the pool filter?
I like it, how could one measure BTU per 100 square feet of concrete collector?
Dan
You probably don't need to make it charcoal or asphalt (as been done in the Netherlands and elsewhere to retrieve parking-lot or driveway heat), but surely you won't want titanium-white. I'm thinkin' reds & browns or dark-stone exposed-aggregate would be fine.
From a design point of view this may be a bit difficult, since while there have been many successful experimental and DIY systems set up, I doubt there is a huge database out there for characterizing it. The solar basics like shading-factors, insolation at horizontal placement, etc need to be considered as well.
My best guess would be that even with more aesthetic poolside pavement it wouldn't take more than 2-3x the area to get the equivalent output of optimally-angled unglazed commercial pool solar collectors. You probably don't need more than R4-R6 under it to work well- the slab<-->soil delta-T is going to be pretty small most of the time, a few 10s of degrees F or so.
Any backup heat would be plumbed as a separate system (or as a separate loop controlled by zone valves, etc.) If you have the solar exposure and a reasonable amount of paved area to deal with, the cost of the experiment is low, and the potential return quite high. If in mid-summer you need to cool the pool (as is often the case in the SW), using the slab as a night-sky radiator should be pretty effective too.
Some ideas & design details might be gleaned here:
http://www.pacificgunite.com/solar%20pool%20heating.htm
or here:
http://web.univ-pau.fr/~scholle/ecosystemes/6-ref/60-5-en.htm
or here:
http://www.invisibleheating.co.uk/UserFiles/File/IHS%20brochures/Road%20Energy%20System%20Brochure.pdf
It just seems like a better-integrated higher-aesthetic and very reasonable approach to low-temp solar than an oversized collection of higher-temp panelized solar thermal that would cost easily 5x as much (and have to run in heat-dump mode half the time.)
|
|
|
|
|
Dana1
Registered Users
Advanced Member
Posts:702
|
| 07/23/2009 12:43 PM |
|
| (I'm not sure why the formatting didn't work on that post?? I know there were some carriage returns in there!) |
|
|
|
|
Jesse Thompson
Registered Users
New Member
Posts:60
|
|