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Heating water....

Post in 'The Green Room' started by James02, Jan 31, 2013.

  1. woodgeek

    woodgeek Minister of Fire

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    If you have a space for a HeatPumpWaterHeater? It will use fewer kWh than many if not most commercially installed solar DHW systems.

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  2. Seasoned Oak

    Seasoned Oak Minister of Fire

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    How does a simple water pump use more KW than a compressor?
  3. GaryGary

    GaryGary Feeling the Heat

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    Hi Wood,
    Where does that number come from -- does not seem right to me?

    My solar water heater with a Grundfos pump uses 55 watts for pumping for maybe 4 hours a day for 0.2 KWH a day.

    Gary
  4. johnny1720

    johnny1720 Member

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    My house has an electric when I moved in 6 years ago. It blew apart one day, I made the jump to a propane on demand it costs me $35.00 per month (or less). We take 2 showers, and 2 baths. We run the dishwasher every day along with the washing machine. When I installed the propane on demand my bill went down almost $70 per month. For me it was a no brainer and it has served me will for the last 5 years with out issue.
  5. nate379

    nate379 Guest

    You were spending over $100 a month in electric JUST to heat hot water?! :eek:


  6. johnny1720

    johnny1720 Member

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    No,

    My electric bill went down $70.00 each month, then I got a propane bill which was $35 per month. I think my old electric tank was really sucking the juice must have been going to ground or something
  7. woodgeek

    woodgeek Minister of Fire

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    Most commercially installed residential solar DHW systems have a 'solar fraction' around 50-60%, the rest comes from a backup heater, usually a coil. A HPWH with a EF = 2.2, versus EF = 1 for a resistive backup (assume parasitic losses are supplied by the solar for 'free'), uses only 1/2.2 or 45% as much as a normal electric tank. IOW, it uses about the same amount of electricity as a typical commercial solar DHW system using coil backup with a 55% solar fraction, (and not costing the elec used by the pump). Oh yeah, and commercial solar costs 3x more than HPWH.

    For some fraction numbers, look at: http://www.greenbuildingadvisor.com/blogs/dept/musings/solar-thermal-dead
  8. Seasoned Oak

    Seasoned Oak Minister of Fire

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    THe space i have the water heater in is heated finished basement area. A HP water heater would decrease the air temp only to have the main heating unit re heat it up again. Not efficient in my case.
  9. woodgeek

    woodgeek Minister of Fire

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    Got it. My old heater was in a (conditioned) laundry room, but it had a wall adjoining a (semi-conditioned) garage. I put the new heater in the garage, and plumbed it in through the wall, with no increase in run length. Of course, every situation is different.
  10. GaryGary

    GaryGary Feeling the Heat

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    Hi,
    That solar fraction seems low to me.
    Even my old system did better than 90%
    http://www.builditsolar.com/Experimental/PEXColDHW/Performance.htm

    I agree that commercially installed solar hot water is a lot more expensive than it should be, but prices vary a lot depending on where you are and who does the installing. We have a really good outfit in Bozeman that does commercial installs for $5000, which less the 30% federal and $1000 MT rebates is $2500.

    Gary
  11. Seasoned Oak

    Seasoned Oak Minister of Fire

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    Any install would be done by me,heck id probably build the collectors as well. I built passive solar sun room that slashed my heating bill by 20-25% 10 years ago.
  12. Huskyforlife

    Huskyforlife Member

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    Using an oil boiler to heat water is not cost effective any way you look at it, when you add the high cost of oil up, the poor efficiency, and the excessive maintenance. It's just terrible. If you have an unfinished basement then I'd recommend to anyone to get a Heat Pump WH like the GE Geospring. The heat it will taking from your conditioned space will be negligible during the winter and it will dehumidify your basement. At my previous residence I switched from an Oil Boiler with a storage tank $1200/yr to a HPWH $200/yr so the payback way about a year. Of course now out here in midwest we have natural gas which is dirt cheap (during the summer the majority of the bill is the fixed connection fee).
    woodgeek likes this.
  13. Bret Chase

    Bret Chase Minister of Fire

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    I have an oil HWH.... I will replace it with something else when it dies.... not sure what though...
  14. woodgeek

    woodgeek Minister of Fire

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    It seems too low to me too....but that's what studies find in the field. I am sure that your solar fraction is 90%, b/c you monitor it closely. Also, one can get a higher fraction by over-building capacity (which usually requires some summer heat shedding). But solar fraction is not tracked/checked in many pro instals, which are often undersized for clueless homeowners (for higher profit?), and it is often pitifully (as in bordering in scam) low. Also, how many homeowners, when a pump or part fails, just run on the backup for a long time before they get around to getting it fixed?
  15. peakbagger

    peakbagger Minister of Fire

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    Solar hot water driven by DC pump and 50 watt solar panel. That covers me from about Mid april to mid October with enough water that I dint need naything else. After that I have a hot water maker on a separate zone that can either be on oil or wood. I usually just heat up the tank every few days from my wood wood boiler. I keep it at about 170 deg F and have a honeywell tempering valve with some sort of sceondary protection to keep it from sending out over 140deg F. The solar system turns into a preheater in winter so I dont need much from the hot water tank to get 140 deg F. The SHW tank has an electric backup element but I have never hooked it up.
  16. woodgeek

    woodgeek Minister of Fire

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    So, 6 mos of 100% solar fraction, and 6 mos of what % you think?
  17. jebatty

    jebatty Minister of Fire

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    Off-peak electric, two staged water heaters, 100 gal of storage, separate meter. Added 6+" fiberglass insulation to tanks, install U-shaped heat traps, and insulated all hot water piping. Cost for wife and me was $4-5.00 per month; estimate doubling of that now that daughter and 4-year old have joined the household as of the end of December.
  18. Seasoned Oak

    Seasoned Oak Minister of Fire

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    Problem with a separate meter is its $15 a month JUST for the meter. Plus hot water for 2 people showers,washing dishes ect $5.00?
    HOw does that happen? For sure it dont include the meter charge.
  19. peakbagger

    peakbagger Minister of Fire

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    My winter time SHW temp is usually 90 degrees. Using the 80 degree max temp rise off of flat plates guideline that gets me down to about 10 degrees outdoor temp. Much lower than that and the pump doesnt put out enough head to pump the glycol around. On some cold sunny days, I hear the pump running but all its doing is deadheading. Considering my water sources is a deep well, lets assume 45 degrees F into the tank so a 45 degree rise from SHW and another 50 degree rise to get to 140 deg F. Of course I probably only run the shower at 110 deg F so my tempering valve is actually impacting the SHW fraction. MY SHW went in before the wood boiler, if i did it again I wouldnt have bought the extra panel cutting down on my capital costs.
  20. jebatty

    jebatty Minister of Fire

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    This isn't quite true with out co-op electric company. We have 3 meters, one for general service, one for electric heat which can be interrupted, and one for off-peak dhw. My statement of $4-5/mo included charge for power, power cost adjustment, and distribution. I did not include one flat charge of $12.00, which is the same whether one meter or 3 meters, and it's called basic charge. There is no separate or additional charge for additional meters.
  21. Seasoned Oak

    Seasoned Oak Minister of Fire

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    That must be a sub-meter with one main meter on a single line. Here in PA PP&L power was just granted a rate increase that included a jump in the Meter charge From $8 to $15 Almost double. If you have a seperate line for your garage thats another charge as well.

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