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May 14, 2008
Solar hot water and radiant floor heating
Following a recent post on solar water and electric, it seems a lot of people are interested in pursuing solar energy options and are having a hard time finding reliable information and real-life experience. Anyway, that's been my impression as I've been doing research on installing a solar hot water system coupled with radiant floor heating throughout a 3 story brownstone.
Here's what I found: even though solar hot water would SEEM to be the ideal match for a radiant floor heating system, the engineers my architects have retained are adamantly opposed to pursuing this. The rationale is that, ironically, in summer you end up producing way too much hot water, and if you don't have a way of dumping it into a pool or hot tub, for instance, you just have to dump thousands of gallons of hot water down the drain. Instead, we have scaled back the hot water system to produce enough water for domestic use only, and will install a high efficiency condensing boiler (whatever the hell that is) to heat water for the radiant floor system.
As for a PV installation, I have been advised on many fronts that now is not the time for that (despite the on-again off-again federal and state incentives). In the near future, rapid technical progress on PV panels may alter that calculation. So we are preparing for an eventual PV installation by reinforcing the roof and putting in an electrical junction box (or something like that).
Anyway, that has been my experience to date in the world of solar solutions. I am curious if anyone else has attempted or actually installed a solar hot water and radiant floor system.
Comments
Have you been advised that reinforcing the roof for solar panels is necessary? Are you putting in posts or the like for future panel mounts and, if so, can you share information on their spacing, flashing details etc.?
Thanks
Posted by: johnife at May 14, 2008 2:49 PM
Its true its hard to get a straight answer on this stuff. I'm deciding on solar hot water this week and this is what I gather, currently: I'm not using radiant floor heating, but I can tie the solar hot water into my boiler/hot water heat system, with an indirect heat exchange. It seems fairly straightforward. I've been told that the excess heat in the summer will not be a problem, but if it was, I could just cover some or all of the panels. On a flat roof in Brooklyn, this really isn't a problem, so I'm not sure why people talk about flushing excess hot water down a drain. There is also a solution for airconditioning with the hot water (not sure how it works, but somehow the heat drives the pumps of the hvac) I'm not clear yet on how much 3 panels will help with heating in the winter, but since the efficiency is much great with solar hot water, it seems its better to use the roof space for that than PV which I'm also planning on installing. I will definitely post on my decisions and the progress with installing in the future.
Posted by: hegelian at May 14, 2008 4:26 PM
Let me also add in direct response to some of the issues Beatlife raised: on the issue of impending technology it seems like its been around the corner for 15 years. The newer cheaper PV panels are not for the consumer market yet and it seems that they're so much less efficient that they won't work on a typical brownstone roof which has quite limited space. Also, if the prices did come down to $1 a watt or so presumably the tax credits would cease. It seems to me major changes in the financing of a PV system are far enough away as to make it smart to do now. Also, the system should pay for itself in 10-15 years and the life is much longer than that, so it seems like it would be a good return on investment regardless.
On the other point, have you asked your engineers why you can't just integrate the solar water into your existing hot water heating system?
Posted by: hegelian at May 14, 2008 4:31 PM
Afaik, there should not be any problem "producing too much hot water"...using my simplistic engineering know-how, if you shut off the circulation you will get no more heat. Is this not true? The solar water panels cannot "overheat" can they?
Dumping thousands of gallons of water sounds simply ridiculous; it that were true, no solar system could ever be considered "green."
Also, as 4:31 says, making it produce hot water will increase its utility and push off the point you have to shut it off.
Are you sure these engineers know anything about solar?
Posted by: cmu at May 14, 2008 5:02 PM
About as green as that hybrid car paul macartney just had flown from japan to england in a private cargo plane.
Posted by: guest at May 14, 2008 7:51 PM
My name is chester birchwood,and i represent Innovative Cooling Solutions.My specialty is on hvac and solar innovation for buildings.
On this blogging event,a comment was made about the solar use is considered wasteful due to excessive dumping of hot water in the summer.NO SUCH THING HAPPENS!The excess heat from the panels is re-directed towards a heat dissipator on the roof(which looks like a convector radiator)which is removed by wind currents.A likely use of the excess heat is for heating pools/spas or even create a drying room in the basement for laundry.Currently the existing panels are more efficient than solar power(pv),which is only 16% efficiency,while solar thermal is about 70% efficient.Solar air-conditioning can be done but currently it is too costly(about $50000 for a whole brownstone).Any questions can be directed to me at birchwood chester @yahoo.com or look at solarpanelsplus.com.
Posted by: guest at May 14, 2008 9:44 PM
What is the ball park cost of installing a solar system on a brownstone roof to supply hot water only to a two family? We currently use a 50 gallon gas hot water heater. I am asking about water only (showers, sink, washing machine, etc.) not radiant heat for floors.
Posted by: guest at May 14, 2008 11:07 PM
Johnife, I think these things have to mounted on steel beams attached to the raised brick sides of your roof. This is an expensive proposition, but it seems like solar hot water is worth the expense.
I met Chester who chimed in today and am looking into a solar thermal system with him that will interface with my boiler and domestic hot water use. He claims this can but gas bills in half.
Posted by: hegelian at May 14, 2008 11:31 PM
A 1 panel 80 Gallon system would cost about 5-8K depending on what type of panel and how its installed
Posted by: hegelian at May 14, 2008 11:46 PM
OP here. I need to make some clarifications to my original post. But first, to those of you who asked: uh yes, I did vet the engineering group. They are LEED certified and have done many solar installations, both thermal and PV, around the world. Although, most if not all of their projects are large-scale museum type deals, not single-family brownstones - so maybe that is an issue.
Anyway, here's the deal: if I install sufficient panels to provide my domestic hot water needs - which are fairly constant through summer and winter, then any additional panels that I install in order to produce hot water for the radiant floor system will be superfluous for roughly 7 months of the year. Originally, I said that this would produce large amounts of excess heat - oh, and by the way, the system is vulnerable to overheating and can be damaged if excess heat is not flushed. This statement seemed to cause a lot of disbelief in follow-up posts. However, even Chester, who also protested my point, then went on to say that the hot water could be used in a pool or spa, or somehow dissipated by the wind or redirected to a "drying room." So I guess there is excess heat after all.... I think the problem was that I said that hot water would need to be flushed - this is of course a worse case scenario. Apparently, my engineering group has been involved in projects where they store the excess heat in summer in huge concrete fields.
Then there is the option of taking the additional solar panels off-line in summer, or covering them, etc. I guess this is possible, but I was advised against this whole scenario because it would not make sense financially. Basically, I would have to install a very expensive system, around 50K worth, in order to provide enough hot water for my whole house heating requirements. This system would then be totally under-used for roughly half the year.
So I apologize for getting everybody riled up about the "flushing the water" comment. My main point, and I think it still stands, is that using solar thermal for radiant floor systems has serious issues - unless the installation can take advantage of large amounts of hot water production in summer - so I guess the answer is I need pool in my backyard. Anyone want to help me shovel?
Posted by: beatlife at May 15, 2008 10:23 PM
Not certain why either removing some of the tubes (if you use a solar tube system) or covering some is such a bad idea - or why that makes the system less viable financially. Seems to me, if the system is financially viable because of the winter heating, then who cares if some of it goes offline in the summer?
Also I'm curious about the $50K price tag. Does that include the radiant flooring? The system I'm looking at is closer to $12K and will store enough BTU's per day to offset more than 50% of water heating, or at least that is the claim. I'm not doing any radiant heating, just preheating the water to the boiler that will supply cast iron radiators...
Posted by: hegelian at May 15, 2008 10:50 PM
The comment about having excess hot water and dumping it does not make any sense to me. Solar hot water systems used in this climate typically have a heat transfer fluid that transfers heat to water via a heat exchanger, so if water is not run through the exchanger b/c a need for hot water has not been triggerd then you are not producing excess hot water.
Have you ruled out using a solar system for its current typical use of supplying your house with domestic hot water? Keeping the technologies separate for your domestic hot water and your home heating, at this stage of technology, may be the best bet. The DOE estimates that you can reduce your hot water energy bills by up to 80% using solar hot water. In our climate you won't produce 100% of your hot water needs, but in the summer my research has shown that you can meet up to 90% of your needs, 60% in the winter, so there is never a waste issue. See my website www.ecobrownstone.com for an article about water heating which has a section on solar thermal systems.
A condensation boiler, by the way, is a very efficient technology (runs 96% to 97% efficient, as opposed to standard boilers that can go up to 86% efficient). They are more efficient because they have individualized compartments that "fire" separately for a given zone, so the entire boiler does not fire up if the thermostat only triggers on the parlor floor, for example. What's more, one of the "zones" can be a hot water heater so it's like having an on-demand hot water heater running on gas, and solar thermal can be tied into the hot water storage tank used from the condensation boiler to further reduce boiler burns. Condensation boilers also burn more cleanly with far less particulate matter than conventional boilers, and they are "direct venting" which means they can vent out of a side wall so you do NOT need to run a vent stack all the way up from the basement to the roof. We are in the process of writing a detailed article about heating and cooling, including condensation boilers, to be published in the next couple of weeks so check the website (www.ecobrownstone.com) if you'd like more information.
Also, the site will be chronicling in great detail the entire renovation of a 5-story brownstone at 168 Clinton St. in Brooklyn Heights which is just commencing, so you might find other useful information on the site as well (the site has gone live just recently, in connection with this project).
--Noreen
Posted by: Ecobrownstone at May 15, 2008 11:55 PM
oops, I see you posted a clarification while I was drafting my comment, so some of my comments are moot.
Posted by: Ecobrownstone at May 16, 2008 12:01 AM
this comment was made earlier but people make systems with a "radiator" in the loop on the roof that dissipates excess heat (steam). there are systems designed this way. also, you don't have to size some kind of massive system to get *some* radiant floor heat gain, you can size it down to a reasonable amount and get some heating gain but likely not 100% or even 80% of your heat from the sun. think of it as something like a pre-heat for winter instead of covering all of the heating, this would still cut down on heating bills. also, if you're already installing a HW system on yr roof, then i don't understand why costs are going to be so much crazier by adding another collector for your heating.
and for the person who said "About as green as that hybrid car paul macartney just had flown from japan to england in a private cargo plane", you are completely wrong dude. go learn some stuff and come back to the discussion if you want to contribute.
Posted by: guest at May 16, 2008 10:03 PM
I do hope people don't go ahead and install this system without first figuring out how to avoid having the excess hot water in Summer. Dumping excess water cold or hot down the sewers is BAD.
Water is the new oil. We can't waste it and on top of it we can't overtax the sewers with excess water dumping.
Posted by: guest at May 17, 2008 12:18 PM
you could size the system to pre-heat your boiler water for the winter (not for domestic hot water, or only for some) and then in the fall and spring it could provide both domestic and heat, then in the summer it could provide just domestic.
----
Excerpt from the Civil War News... "As he prepared for his Shenandoah Valley Campaign, Sheridan assembled the makings of what would be the largest field hospital of the Civil War. Immediately following the … Battle at Winchester, a 500-tent hospital was constructed (and in) …operation for three months as what is now referred to as an evacuation hospital. The tents featured a unique radiant floor heating system, which proved invaluable in the cold fall and early winter months of 1864."
_____________________________________________
the heating system was adopted from the frontiers during the gold rush in the 1840/50’s. The hospital site is being restored and there is a reenactment each year of the hospital in action including a demonstration of the heating system...it was the Civil Wars version of a MASH unit.
Tent Hospitals
The common pre-war United States Army practice was to requisition buildings to serve as hospitals. However, early in the war the isolation of some battle sites and unprecedented patient volume compelled the increasing use of tents. Surgeon Bernard J. D. Irwin established the first regular tent hospital after the Battle of Shiloh in April, 1862. The practice soon spread to the Army of the Potomac medical system under Surgeon Jonathan Letterman. Union commander in the Shenandoah Valley, Major General Philip Sheridan, insisted that every aspect of the developing medical system be made available to his Middle Military Division when he took command.
The standard hospital tent in use was 14 feet long and wide and 4½ feet high with flaps that allowed it to be buttoned to others to make a larger ward. Each tent could hold eight patients and normally was pitched two paces apart from others in rows called "streets." Every effort was made to make the tents as comfortable as possible. Boards were laid over sleepers for flooring and each tent was surrounded by a drainage ditch to keep the interior dry. Tents were heated with the so-called "California Plan." A pit was dug about 2½ feet deep in front of the tent from which a trench the same depth extended the length of the tent to its outside rear. There a chimney of some sort was built. The trench was covered with stones or sheet iron. The resulting system provided a crude, but comfortable form of radiant heat. Storehouses, kitchens and officers were placed in spare tents or temporary structures and shelters convenient to the hospital streets.
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A Rose by any other name
The Chinese called it a "Kang", for the Manchuria, it was known as ''Nahan", the Koreans an "Ondol", the Romans a "Hypocaust"...they were all forms of radiant heating and still used to this day.
The heating system used at the Civil war hospital was a form of ancient heat...it was referred to as the "Californian System" which may be a result of the Asian cultural and architectural influence in California during the era of building the railroads and the Gold Rush.
Sleeping like a Stone
The other night Dong Kwang was talking about the difference between sleeping areas here and in Korea. Traditionally, people sleep on the floor in Korea, he told us. And the floor is made of stone, or concrete.
But isn’t it very hard - and very cold, we enquired? No, he explained. There is a hole under the floor, with a fire in it, and hot air passes underneath the entire stone floor so that it’s very comfortable to sleep on it.
Posted by: guest at May 19, 2008 6:23 AM
The following is from: "The Medical and Surgical History of the War of the Rebellion. (1861-65.) Part III, Volume II, Chapter XIV.--The Medical Staff and Materia Chirugica"
"The bedsteads used in the hospital tents were cots of a light frame-work of stout wood, provided with four folding legs and furnished with a jointed support near the head. The whole frame-work was covered with sacking, and throughout the war proved a most useful and satisfactory hospital cot. It was light, strong, easily transported, and was comfortable to the patient.
Various modes were employed for heating hospital tents in the field. Wood-burning stoves were largely used, their chief objection being the difficulty of transportation. The plan which was most generally in vogue, particularly in the Army of the Potomac, and which gave the utmost satisfaction, was that known as the California plan. A pit was dug about two-and-a-half feet deep outside the door of the hospital tent; from this a trench passed longitudinally through the tent, terminating outside its farther or closed extremity. At this point, a chimney was formed by barrels placed one upon the other, or by some other simple plan. The joints and crevices of this chimney were cemented with clay. The trench in the interior of the tent was roofed over with plates of sheet-iron issued for that purpose by the Quartermaster's Department. A fire was built in the pit, and the resulting heat, radiating from the sheet-iron plates, kept the interior of the tent warm and comfortable even in the coldest weather. In the western armies, in the trench in the interior of the tent, railroad iron was placed in regular layers and covered with iron plates when possible to procure them, or with stone slabs. Occasionally funnel-shaped stoves, open at the bottom, resting upon the ground, and provided with a short pipe, were used."
'HEADQUARTERS FOURTH DIVISION, ARMY OF THE OHIO,
FIELD OF SHILOH, April 12, 1862.
Medical Volume of the Medical and Surgical History of the War.
Posted by: guest at May 19, 2008 6:31 AM
thankyou. this post has been the most useful i've found so far regarding excess heat in the summer. but, to clarify a misconception: you can't simply stop circulating the fluid and ignore the sun, just as you cannot leave your boiler burning continously and only draw off hot water when you need it. the sun is pouring energy into the system, and you are drawing it off by heating your domestic hopt water, and also heating your house. in the summer, you are not drawing off the energy to heat your house, so something must be done. one option: plant a tree! small deciduous trees on your roof would shade some of your collectors in the summer, but not as much in the winter. they would also improve air quality as a whole...
as for me, i'm still trying to figure out what to do with the excess, as i have a sloped roof.
Posted by: guest at July 9, 2008 12:01 AM
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