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Retrofit radiant floor heating
We are having a LOT of snow for this area, and we've had a half dozen power outages of 6-8 hours so far this year. It gets mighty cold sometimes and the two fireplaces aren't cutting it. Our 13kw genset will run everything we need except the heatpump, and it would cost maybe $8-10k to install one large enough to power that.
I was thinking of retrofitting a radiant floor system on the main floor of our house, heated by the propane hot water heater. A number of companies advertise these (radiantec comes to mind). Most of our main floor is wood so we don't have to deal with the insulating characteristics of carpet, and the basement ceiling is fully accessible. They claim you don't need a heat exchanger but I'd install one anyway to insure the safety of our potable water.
I'm interested in knowing if anyone has used one of these sytems and, if so, what your experiences were.
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Retrofit radiant floor heating
I have designed a few radiant flooring systems, mainly in new constuction. These have always been fed from the boiler system, not the domestic hot water system; however, the water temperatures would be fairly close to optimum for a radiant floor system so it might work .
I agree with your concern about circulating the domestic water directly through the floor piping, mainly because of stagnant water sitting there and then being re-circulated to your domestic hot water tank. A potable water heat exchanger would help with that by reducing the volume of stagnant potable water. The system could incorporate a timer to circulate the domestic side occasionally and minimize this problem in the off season. Stagnant water can be a breeding ground for bad things including Legionella.
Be sure to use a piping material designed for this type of service such as PEX (cross-linked polyethylene). We usually specify the piping to also include an oxygen barrier to prevent entry of oxygen through the piping. This is important if there are any ferrous metal components in the system; however, may not be needed in your application.
One of the major equipment and material manufacturers for this type of system is Wirsbo.
Most of our experience has been with piping embedded in a gypcrete or lightweight concrete slab. I have seen but not used systems that snap the tubing into a sheet metal plate installed under wood floors. That type system may be adaptable to a retrofit installation.
Does your water heater have the required heating capacity? It probably is, but just something to check.
You said the generator couldn’t run your heatpump. Is it a split system? Could the generator run the fan portion of the indoor unit? If so, you could install a hot water coil in the ductwork, and run the fan and a small pump on generator power. This is sometimes done around here as the normal source of heat where natural gas is available. See http://www.apollohydroheat.com This could become your normal aux heating system depending on electrical vs. propane cost in your area. When on generator power, since there is no power to the outdoor unit, the space temperature would continue to fall (usually only one or two degrees) until there is a call for aux heat, then the pump would start and you have heat.
If you are wired with a generator panel, put the indoor unit and pump on the generator panel, and the outdoor unit on the normal power panel. If you keep the existing strip heaters, put them on the normal power panel, and add a toggle switch somewhere to determine which aux heating system to use electric strip or hot water.
One last thought, check the size of your existing strip heater. It may be small enough to run from the generator since there is no compressor starting in rush current to deal with. 13 kw is a pretty good sized generator around here for a house. In emergency mode, many get along with 5kw units.
Hope this wasn’t an over kill answer.
- JParker
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Retrofit radiant floor heating
Thanks, JParker, not an overkill answer at all. The heatpump is a 6 ton three zone geothermal unit with a 14.4/19.2 KW strip heater as aux third stage heat. There are three separate disconnects on the unit and one of them serves the fan only (I think).
I hadn't thought about a hot water coil - that's an idea. The difficulty as I see it is that the entire heatpump is in the basement wedged between the basement floor and ceiling. The supply duct goes through a chase to the attic and branches off, and it's all framed in so it would be hard to get to. The return air comes out the basement ceiling and passes through three filters (EAC, media, and UV) so there isn't much room for a coil there either. Still, it's an intriguing idea. I'm having a guy out to purge our geothermal loop and I'll ask him what he thinks.
Companies like Radiantec push using the hot water heater as the hot water source. Our hot water heater is a HUGE 90-100 gallon Bradford-white unit that has a very fast recovery rate so it might work. If not we could always plumb in a small boiler (which would double the expense of the system). They sell these systems as retrofit using the sheet metal reflectors under the subfloor. I'm not sure how well these work though. I suspect I could do this for a couple of thousand bucks, which would be quite economical compared to a new genset.
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So much for the little strip heater concept.
No problem, as much as I have learned from the people on this board, its the least I could do.
Geothermal HP, great to hear. I really like those, very efficient when done right.
Horizontal or Vertical?
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It's a vertical WaterFurnace unit.
Actually, I hate it. Not only has it been unreliable, but it uses double the KW power than WaterFurnaces projections said it would. I log the consumption of each circuit feeding the unit and I know exactly what it uses, and WaterFurnace was way, way off.
Yes, we are using less than others in the area with similar sized homes but due to their erroneous projections the payback will never be realized. And the system is installed correctly - we've had three other contractors out looking at it and they have found no problems. Plus, we've had blower door tests (the house is tight with a 0.28 ACH) and duct pressurization and sealing tests.
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Sorry, I meant the ground exchanger. Is it vertical wells or horizontal trenches.
Based on the problems you mentioned, and the fact that this is very unusual from our experience with geothermal, I would like to get more details if you are interested in an opinion from an informed 3rd party.
If so, please drop me an e-mail.
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We have a horizontal loop.
It's very generous of you to offer advice. I'm sort of at my wits end on this, so I could use an informed third party opinion. I'll put together some information and send it to you. Your profile doesn't list your email address but if you send a blank email to me (ken at qsolv dot com) I'll have it. I really, really appreciate it.
I sent a letter to the president of WaterFurnace, explained our situation, sent them copies of their energy consumption estimate vs. measured consumption numbers, and offered to pay half the expenses if they'd send a tech out to evaluate the system and they refused. Our dealer dropped them due to excessive warranty claims and insufficient warranty reimbursement. I think they're a crappy company.
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Sorry, I though it was in my profile.
I sent you one just after my book was posted, and am working on a second with a few questions you may need to look up.
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Thanks, John, your email was trapped by my spam filter but I got it and whitelisted your name. If you get a bounce notice just ignore it.
Thanks,
Ken
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Ken, It might be easier and more comfortable to install 1 or 2 direct-vent propane heaters with millivolt (self-powered) thermostats. You have the propane, your outages seem to be relatively short, and an electric-free backup would allow worry-free winter vacations. During the 1998 ice storm I put a 35,000 BTU Empire unit in my garage to prevent freeze-up. Was so happy with it I added another smaller unit upstairs last year.
These are not high-tech heaters, but they are inexpensive, reliable, easy to install, and do keep you warm with absolutely no electricity!
Just my 2cents, but a radiant project is.... a PROJECT.
Fireplaces become less efficient as the temperature plunges, though they make the room cheery....
bliz
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