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Solar Powered / Assisted Hot Water Radiators?

Tremolux Member Posts: 28
Our 1930 brick rehab is progressing, but "renewable" HVAC remains elusive.

In the middle of the country, it gets very cold in Winter with hot & humid Summers.

Most of the existing radiators were long, low, thin, and broken wide open.

The pipes, on the other hand, passed a pressures test and are ready to go.

New radiators are available, flat panel solar hot water collectors are available, high efficiency gas boilers are available, and well insulated holding tanks are available.

Can they be made to work together to produce enough hot water to justify the cost?

Maybe even do radiant floor tubing under tile in a few rooms?

We know that lower temperatures than originally designed might work, but only if the size of the radiators is increased. ( Since the originals were low and thin, low and thick might be the only available fix short of moving pipes around. )

The relatives of the previous owner installed a new 40 gallon commercial quality water heater before they decided to sell the house. Once a proper flue liner is installed, it will be very hard to justify the coast of a solar potable hot water array.

We'll be getting a new reading on our solar exposure soon ... a neighbor has indicated a willingness to part with a few Oak branches, and we'd happily lose another Elm.

The very last thing we want is to run ducts for everything, and that's what the heat-pump contractors want to use with their geothermal loops. ( 8 - 10 tons from 10 holes )

Window A/C is acceptable .. we can live with it, especially since we're insulating and sealing air leaks. Mini-splits could be added later, we suspect, but they evidently aren't very compatible with geothermal systems.

Right now the simplest, least hassle renewable we've found is a PV array on the roof hooked to the electric utility. Every other retrofitted "solution" we've seen either has very long payback, or absurd upfront costs plus a requirement for poking numerous holes in solid, historic, structures.

Thanks for your time and attention.


  • hot_rod
    hot_rod Member Posts: 22,479
    run some different calcs

    You can download the RET screen software for free. Then you can run solar thermal with or without heat, PV, ground source, etc. Enter your current fuel costs to look at ROI and the economics.

    Repair and up-keep cost can be factored in, even recycle cost at the end of expected lifecycle. Software is the best way to answer these questions, anything else is a guess.

    For SDHW it depends on how much hot water you use, how much you are paying per therm, expected increase in energy cost, Federal, state and local incentives, installation costs, etc.

    It really varies from location to location and job to job. In many cases a solar thermal DHW pre-heat can show a return in under 10 years, some in under 5 years.

    ROI is the number to look at, remember a quality SDHW system has a life expectancy of 20- 25 years, maybe more.

    If you read Tom Lanes "Lessons Learned" take, SDHW is a 14- 33% return on your money, puts money in your pocket after payoff, and every dollar saved is equal to $1.38- 1.78 in taxable income. Better than many safe investments, currently.

    Others look at it as their way of buying some energy independence. Some customers invest in solar just to make a "green" statement.

    Yes ST can be used to supplement some space heating, the systems can be expanded by adding collectors. There are some very low temperature heat emitters hitting the market. panel rads that can work down to 90F supply temperatures, great match for solar.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • zacmobile
    zacmobile Member Posts: 211
    edited July 2010

    it sort of depends on your personal factors whether or not the cost is justified but it can all be certainly done. A note on the geo option, you don't have to install a full-on ducted forced air system, you could use a water to water unit (s) to supply warm water to low temperature radiators designed for 120-130°F and mini-split style chilled water units for cooling select hot spots say on the upper floor. http://www.multiaqua.com/
  • Royboy
    Royboy Member Posts: 223
    low temp radiators

    hr - can you give us any more details on the low-temp radiators that you mention. low-temp delivery is good for solar, good for condensing boilers.

    I'm intrigued to find out what the strategy is on these to be more effective at low-temp than "regular" panel radiators.

    myson gives these correction factors for figuring output from their panels for different air-water temp differentials:

    output correction factor / delivery water temp less air temp

    0.605 / 72˚F

    0.700 / 81˚F

    0.798 / 90˚F

    0.898 / 99˚F

    1.000 / 108˚F

    1.104 / 117˚F

    1.211 / 126˚F
  • hot_rod
    hot_rod Member Posts: 22,479
    high output radiators

    Roy, here are some links that explains the Jaga DBE system. Basically a small group of fans that fit inside the radiators. It is run by a small micro processor and modulates the fans based on fluid temperature.

    They had a seminar at the RPA Reno event and they showed some outputs with supply temperature as low as 90F for an extreme.

    Basically turning a radiator convector into a forced convection emitter

    Yeah, Myson had the Solar-Vectors years ago, same concept. This approach takes advantage of ECM motor technology, reset technology and microprocessor controls.

    You need either 12V or 120V at the radiators to run the system.



    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
This discussion has been closed.