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Is there an electric system that can heat water for radiant floor heat, domestic hot water and air conditioning?

kinney89396 | Posted in Green Products and Materials on

I am constructing a new 1000 sq.ft single story with 6′ crawl space. Two bedroom, 1 1/2 bath cottage. I would like to have electric solar panels on the roof to offset 90 – 95% of the load. Does this sound doable? I have unobstructed S SE exposure and can fit approx. 20 panels on the roof. This is on Long Island New York

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  1. GBA Editor
    Martin Holladay | | #1

    To answer the question in the title of your post: yes, there is such a system. It is an air-to-water heat pump called the Daikin Altherma. An HVAC system using the Daikin Altherma is cripplingly expensive -- you'll pay a huge upcharge for having bragging rights that allow you to say that one heat pump does everything.

    Two GBA readers have shared information on the cost of an Altherma system. Mike O'Brien was quoted $22,000 to install an Altherma in his house, while Nick Lehto was quoted $36,000 to install an Altherma system in his 1,800-square-foot house.

    There are cheaper ways to do it. Probably the easiest way to go is to install one or two ductless minisplit units to provide space heat and cooling, and to install a heat-pump water heater or electric-resistance water heater to provide DHW.

    By the way, a PV (solar electric system) uses PV modules (panels) that aren't standardized in output. A PV module might be rated at 50 watts, or it might be rated at 500 watts. So it's hard to know what you mean by "20 panels." If you are aiming for a net-zero-energy house, you will probably need a PV system sized between 4 kW and 12 kW, depending on the efficiency of your home's envelope and how many gadgets you use.

  2. jj1 | | #2

    Hi Mike: as a fellow Long Island Power Authority rate payer, you are undoubtedly familiar with LIPA's 20/21/22 cents per KWHr all-in rate structure. No rate relief appears realistic anytime soon in view of the Hurricane Sandy repair costs and the Shoreham debacle. Your goal should be achievable if your design heating and cooling loads are sufficiently low. Some ideas how to get there:
    --model the pre-construction house with a good energy modeling package such as PHPP. There is a good cadre of knowledgeable energy modeler/consultants in the NYC/Brooklyn/Long Island area.
    --if your design loads are low enough, your plan (and net zero) should be workable in LI's climate without running out of roof space for PV panels. Martin's suggestion of 1 or 2 ductless mini splits (the Fujitsu and Mitsubishi Hyper Heat single head systems COP/ambient temp curves work well in the Long Island climate) is very cogent. Otherwise, if your site has acccess to natural gas, a small 93%+ AFUE condensing 2 stage (or variable speed) ECM blower furnace can be quite cost effective.
    --LIPA provides a significant PV rebate, NY State provides a 25% tax credit, and the feds provide a 30% tax credit for qualified residential PV installations of 10 KW or smaller, which should fit your application (as modeled) and roof space. Be aware that LIPA is in the process of lowering the current $1.60 per watt PV rebate, so submit your application ASAP before February 28 if possible. LIPA's website has details, an application form, and links to the list of PV installers qualified under LIPA's program. You should be able to find a PV installer priced near the $4 per watt range currently on Long Island for this size range. After rebate/credit, your cost per KWHr should be significantly below LIPA's 20+ cents/KWHr rates. More importantly, the KWHr cost should remain essentially constant going forward except for a possible inverter replacement. Try and install a roof with a 40-50+ year design life to avoid removing the PV system to re-roof prematurely.

  3. heinblod | | #3

    " Does this sound doable? "


    As Jan Juran says: get professional planners and builders in, make written contracts (including fines) checked by a lawyer.


    About Thermia heatpumps:

    Check the search engine for "energy plus houses", "solar houses" etc..

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