Electric Hot Water Tank

RRRAAAYYY2RRRAAAYYY2 Registered Users Posts: 11 ✭✭
I replaced my 220volt electric hot water heater this weekend with a power vent natural gas unit. It was under a government rebate and cost me $340 all together. This has left me with a perfectly functional 220volt hot water heater.

My initial plan is add this back in line before my new hot water heater. I want to remove the skin, and then the insulation. I then want to reattach the skin with a vent hooked up to it. So that I can connect my dryer vent tube to the vent. Then when I use my dryer the hot air will wrap inside the skin and hopefully add some heat to the water sitting in the tank.

My house was built in 1911 and has an old basement and crawl spaces, etc. The dryer currently vents back in it. So this will help cool the dryer's output in the summer a little bit. And might take the chill off the cold water before entering the new hot water heater.

Some questions I have about this project:

1.) Can I wrap the 636 white exhust pipe with copper heat recover pipe. I have seen it advertised for waste water recovery, but not sure about the exhaust pipe. Also I have no source for the pipe, doesnt seem like anyone in Canada sells it, options for vendors?

2.) Also wondering if I bought a 50-100 watt solar panel and direct wired it to the element in the electric water tank, if it would work. I am a professional when it comes to DC voltage, not overly familar with AC. But assume that the element would work with positive on one side and negative on the other.

Not as well as if it was AC. Maybe not at all? I dont know, so I am asking for advice. How would it effect the solar panel if it was basically using 100% of its output, plus some?

Thoughts, suggestions? I want to do this project fairly soon as the tank still has water in it. (Removed on Saturday)

Comments

  • BB.BB. Super Moderators, Administrators Posts: 31,061 admin
    Re: Electric Hot Water Tank
    RRRAAAYYY2 wrote: »
    My initial plan is add this back in line before my new hot water heater. I want to remove the skin, and then the insulation. I then want to reattach the skin with a vent hooked up to it. So that I can connect my dryer vent tube to the vent. Then when I use my dryer the hot air will wrap inside the skin and hopefully add some heat to the water sitting in the tank.
    I would expect this to not work very well... One of the big problems with dryer venting is long runs where the exhaust air cools and condenses the water out of the air to the walls, which also attracts the lint--eventually causing the ducting to plug up (decreasing dryer efficiency as there is less air moving through the clothes).

    Over time, the water+lint may also corrode the tank too. If this is a gas dryer, there are also acids which may speed the process too.
    My house was built in 1911 and has an old basement and crawl spaces, etc. The dryer currently vents back in it. So this will help cool the dryer's output in the summer a little bit. And might take the chill off the cold water before entering the new hot water heater.

    You are direct venting the dryer into the basment/crawl spaces? Or are you venting through the basement/crawl space outside?

    Assuming your are up north (Ontario)--Venting the moist air into the home is going to create humidity problems too (I assume electric dryer?).

    Some questions I have about this project:
    1.) Can I wrap the 636 white exhaust pipe with copper heat recover pipe. I have seen it advertised for waste water recovery, but not sure about the exhaust pipe. Also I have no source for the pipe, doesn't seem like anyone in Canada sells it, options for vendors?

    You can just use copper line--But the schedule PVC vent pipe (I assume that is what 636 pipe is) will not conduct heat very well at all--You might as well just purchase extra pipe and run it back and forth to put the waste heat into your home directly.

    However, several issues--One, you will need to run it 1/4" per foot and put a condensate drain at the low point in the system. Second, dryers usually only support a limited run of pipe with a couple of 90 degree fittings before the air flow restrictions cause problems moving enough air to dry the clothes (with out adding an extraction fan inline somewhere--they do sell these fans). And lastly, you probably need someway to get brush into the ducting to clean the lint out once every year or so...
    2.) Also wondering if I bought a 50-100 watt solar panel and direct wired it to the element in the electric water tank, if it would work. I am a professional when it comes to DC voltage, not overly familiar with AC. But assume that the element would work with positive on one side and negative on the other.
    Yes, it will work... No, it is probably not very practical. Photovoltaic panels are very expensive and operate in current mode--between the panel efficiency and and the non-P=Vmp*Imp IV curve match--you probably will only be gathering a few percent of the energy from the sun on the panel into the cold water.

    Pretty much any solar thermal collector will collect 10's of times as much heat (sun to water heat transfer) as the panels can be >50% efficient.
    Not as well as if it was AC. Maybe not at all? I dont know, so I am asking for advice. How would it effect the solar panel if it was basically using 100% of its output, plus some?
    For this setup--There is no difference between AC and DC through the water heater element...

    For example, say you get a 2,400 watt 240 VAC water heater element:
    • Power=V^2/R; R = V^2/P = 240 VAC^2/2,400 watts = 24 Ohms
    Assume you are looking at 17.5 volt Vmp solar panels (common voltage for 12 volt battery charging):
    • Power = V^2 / R = 17.5^2 / 24 Ohms = 12 watts
    Say you put 8 panels in series (higher voltage/more power):
    • (8*17.5 volts)^2 / 24 ohms = 816 watts
    • 816 watts / 8 panels = 104 watts per panel
    That would be with optimum sun on the panels--Solar panels are current mode sources (output current is pretty much proportional amount of sunlight hitting panel). So, as the sun falls, the output current drops, and the voltage will fall (V=I*R). And since heat output changes with the square of the voltage into a resistive heater--1/2 voltage will be 1/4 the heat output. Dropping your system efficiency as soon as the system operates at less than Full/Designed voltage/current.

    How much water will a few hours of 800 watts of heat raise the temperature:
    • 1 watt = 3.413 BTU per hour
    • 800 watts * 3.413 Btu * 2 hours = 5,461 BTU
    • BTU = 1 degree F rise per lbs of water
    • 7.481 lbs per gallon of water
    • 80 gallon electric water heater
    • 5,461 BTU / (8lbs per gallon * 80 gallons) = 9.1 degrees F per day
    Assuming I got the numbers/formula/power estimates close enough for a back of the envelope calculation... And say you can get solar panels at $3.00 per watt--Those 800 watts of panels will cost you around $2,400 to rise your water tank by less than 10 degrees per day...

    Probably not worth it...
    Thoughts, suggestions? I want to do this project fairly soon as the tank still has water in it. (Removed on Saturday)

    You could buy/build a solar thermal collector and mount that on your roof... Solar Thermal collectors do lend themselves to Do-It-Yourself projects (copper line, metal plate, box with insulation/glass top). Circulate water/human safe antifreeze from panel to water heater with solar powered water pump, and away you go... (it is a plumbing job--with the long term issues of any plumbing system--Leaking pipes, tanks, bad water pumps, air locks, freezes, etc.).

    I have a thread with lots of random information on designing your Solar PV system and links to various DIY type projects:

    Working Thread for Solar Beginner Post/FAQ
    Solar Shed and other Solar Thermal Links (some solar thermal links)

    I see from another thread you have already built a nice solar thermal wall for your home--So, solar hot water is the way I would suggest you go with the the old water heater.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Electric Hot Water Tank

    Ever seen the inside of a hot water tank? They're lined with glass. Although they radiate heat all too well from the inside out, trying it the other way 'round probably won't be very effective. The surface-area-to-volume ratio is pretty horrible on a cylinder, for one thing.
    Dryer outlet heat isn't as hot as you might think either. And you don't want a lot of bends in the air duct, as the dryer won't exhaust properly. This leads to lint build-up - and fires. Dryer fires from lint in the air duct are the #2 cause of home fires, right behind over-loaded electrical cords.

    On the other hand, using the elements as a dump for excess solar power is quite common. Batteries full, solar diverts to elements, uses power that otherwise would go 'unharvested'. Also a good diversion load for wind power.
    But a standard element is 3500 Watts. You can get lower Wattage ones and even 120 VAC versions for some. Still, it's a big difference between a 100 Watt solar panel and a 1500 Watt heating element. Don't expect much.

    I think you'd enjoy looking at some of the projects at BuildItSolar: http://www.builditsolar.com/
  • azrcazrc Solar Expert Posts: 43
    Re: Electric Hot Water Tank
    RRRAAAYYY2 wrote: »
    Then when I use my dryer the hot air will wrap inside the skin and hopefully add some heat to the water sitting in the tank.

    In thermodynamics, there is a concept known as availabilility that deals with how much and at what efficiencies you can extract (transfer) energy from one system to another. If you look at the available amount of energy contained in dryer exhaust, it is very low for a number of reasons, the biggest being the low relative temperature. If it was coming out at 2000F you might get something, but it is coming out at less than 200F.

    Assuming that you could extract the energy from the warm air, there is just not that much thermal momentum in warm humid air compared with a tank of water. It would be like trying to cool down a room with a bag of ice and a fan. Yes the room will cool down, but not appreciably.
  • RRRAAAYYY2RRRAAAYYY2 Registered Users Posts: 11 ✭✭
    Re: Electric Hot Water Tank

    Thank you for the replies. The main reason I was going to do this was the dryer is sitting there already, and so is the tank. Never expected much from it, thought it might be a bit better than just having the tank sit there. I have heard of several people just using a tank to hold water at room temperature or there abouts before going in the hot water heater.

    The 636 pipe is the ehaust pipe on my new NG power vent heater. Probably reaches around 120-130f on the outside of the pipe.

    The dryer vent currently, and has always, just vented into the basement. It does alter the humdity, but also about 60% of the floor is dirt anyway.

    I had wanted to do the solar collector type water heater. But the antifreeze and how to get it in and out of the tank had me stumped. I have lots of 3/4" copper tube, and several patio doors left over to make boxes out of.
  • solar_davesolar_dave Solar Expert Posts: 2,367 ✭✭✭✭
    Re: Electric Hot Water Tank
    RRRAAAYYY2 wrote: »
    Thank you for the replies. The main reason I was going to do this was the dryer is sitting there already, and so is the tank. Never expected much from it, thought it might be a bit better than just having the tank sit there. I have heard of several people just using a tank to hold water at room temperature or there abouts before going in the hot water heater.

    The 636 pipe is the ehaust pipe on my new NG power vent heater. Probably reaches around 120-130f on the outside of the pipe.

    The dryer vent currently, and has always, just vented into the basement. It does alter the humdity, but also about 60% of the floor is dirt anyway.

    I had wanted to do the solar collector type water heater. But the antifreeze and how to get it in and out of the tank had me stumped. I have lots of 3/4" copper tube, and several patio doors left over to make boxes out of.


    One way to prevent freezing is to have a drain down system and only pump to it when the temps are correct to do so.
  • icarusicarus Solar Expert Posts: 5,400 ✭✭✭✭
    Re: Electric Hot Water Tank

    First, an auto drain back preheat tank system is very easy to make, now that you have the tank and the glass. (Also many solar water heater controllers have an anti-freeze cycle that will circulate some water though the collector if it isn't too cold, other wise do the drain back.

    Secondly, while I applaud the idea of using the captive heat from the dryer I think you are buying more trouble than it is worth. The potential to make the dryer less efficient as well as having lint build up issues is a problem IMHO.

    Dryers work best with the shortest possible vents and the fewest fittings.

    I would do a DIY solar water heat long before I would try to recapture the dryer heat.

    Tony
  • solar_davesolar_dave Solar Expert Posts: 2,367 ✭✭✭✭
    Re: Electric Hot Water Tank

    I have to agree with Tony, there is a huge amount of info about DYI solar hot water collectors.
    http://www.builditsolar.com/Projects/WaterHeating/water_heating.htm

    My commercial system is basically a drain back with an electric HW heater not wired as the 80 gallon pre storage tank, with a high efficiency Energy Star 50 gallon gas unit as the backup. We used 3 therms ($20 with $17 of that for the right to be connected) of gas last month (mostly cause I found the pilot on in the gas fireplace, Duh!) It should be less next month. Before the Solar the bill in summer was typically $40.

    The Goldline controller fires the pump motor only when the panel temp is 13 deg F above the tank temps and pumps until the tank temp hits the preset of 140 deg F.
  • jcgee88jcgee88 Solar Expert Posts: 154 ✭✭
    Re: Electric Hot Water Tank
    RRRAAAYYY2 wrote: »
    I replaced my 220volt electric hot water heater this weekend with a power vent natural gas unit. It was under a government rebate and cost me $340 all together.

    What model and manufacturer for the new water heater did you buy?

    I ask because from what I have seen, power vented gas water
    heaters which have the requisite Energy Factor to be eligible for
    the Federal Tax credit seem to cost quite a bit more than what
    you paid. Your $340 after Fed tax credit puts you in the $500
    ballpark, most of the high EF, natural gas water heaters I've
    looked with power venting are in the $1200+ range.

    John
  • Dave AngeliniDave Angelini Solar Expert Posts: 5,501 ✭✭✭✭✭
    Re: Electric Hot Water Tank

    Not sure about the specific rebates but in my opinion, any balance of system components used to make a solar hot water system with collectors that meet the intent are good. Add it all up and claim the 30%.
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • solar_davesolar_dave Solar Expert Posts: 2,367 ✭✭✭✭
    Re: Electric Hot Water Tank
    Not sure about the specific rebates but in my opinion, any balance of system components used to make a solar hot water system with collectors that meet the intent are good. Add it all up and claim the 30%.

    Got the same thing from my solar thermal installer, a new water heater is part of a total solar thermal add, so can be applied to the 30% solar tax credit and in my case the utility rebate.
  • RRRAAAYYY2RRRAAAYYY2 Registered Users Posts: 11 ✭✭
    Re: Electric Hot Water Tank
    jcgee88 wrote: »
    What model and manufacturer for the new water heater did you buy?

    I ask because from what I have seen, power vented gas water
    heaters which have the requisite Energy Factor to be eligible for
    the Federal Tax credit seem to cost quite a bit more than what
    you paid. Your $340 after Fed tax credit puts you in the $500
    ballpark, most of the high EF, natural gas water heaters I've
    looked with power venting are in the $1200+ range.

    John

    I bought a GE 50 gallon from Home Depot. They gave me 10% off so my intial cost was $740 plus tax (forgot the tax in the first comment, which is $96.20) It cost me $300 for the install. I am getting a $700 rebate from my Provincial and Federal Government.
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