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…
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.
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 http://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
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…
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?
A 1 panel 80 Gallon system would cost about 5-8K depending on what type of panel and how its installed
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.
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.
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.
About as green as that hybrid car paul macartney just had flown from japan to england in a private cargo plane.
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?