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Old 10-15-2008, 04:46 PM   #31
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Tankless or tank, but not both


18 KW for tankless
5.5 KW for tanks element
9KW for aux heat
3KW for heat pump
3KW for house hold lighting, fridge
Equals 35.5 KW
At 240 volts, equals 148 amps.
On a balanced panel box/electrical system, you are safe by 12 amps.

But, thats with the heat pump compressor already running, so no starting current figured into it.

Didn't include clothes dryer, range, hair dryers, or any electrical use in a shop/garage.
Also, no resi system is balanced.
You should consider upgrading your electrical service.

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Old 10-15-2008, 04:52 PM   #32
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Tankless or tank, but not both


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18 KW for tankless
5.5 KW for tanks element
The premise of this thread was one or the other, no?

If you added the aux heat into that mix (dunno how feasible it is for you), you'd be in even better shape.

Then again, I was wrong about the photovoltaics, so maybe I should just shut up..
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Old 10-15-2008, 05:10 PM   #33
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Tankless or tank, but not both


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Originally Posted by beenthere View Post
18 KW for tankless
5.5 KW for tanks element
9KW for aux heat
3KW for heat pump
3KW for house hold lighting, fridge
Equals 35.5 KW
At 240 volts, equals 148 amps.
On a balanced panel box/electrical system, you are safe by 12 amps.
I want to run either tankless, or tank, not both, remember?

Heat pump is 2KW (2 ton).
There's no way I'd ever see 3KW for lighting. Every single light in the house combined is about 2700, including the garage and outside lights.

Hot water: 75 amps
Backup heat: < 40 amps (including fan)
Heat pump: 9 amps (measured with amp clamp)
Every single light on: 22.5 amps (more than I would have imagined)

= 146.5

Compressor: 15 amps
Computers (2) w/monitors: 2.6 amps
TV's (2) with sound system: maybe 3 amps
Microwave: 7.5 amps
Dryer: 20 amps?
Range: 20 amps?

= 214.6

So, *possible* to exceed 200... In reality, it'll never happen. Evar.
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Old 10-15-2008, 05:24 PM   #34
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Tankless or tank, but not both


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I think we're missing each other here...

As long as the solar collector is able to keep the tank temp above ITS set point, the element will never come on. The only reason to have an element in the tank at all, is to guarantee enough heat to make a < 100 amp tankless sufficient, even in the dead of winter, when the solar isn't saving me anything anyhow.

I'm planning to use my existing 50 gal tank with an external heat exchanger and see how that does. If it's not enough, I can always upgrade later.
Yes were are missing each other.

The point is, why have solar hot water if the tanked water heater is already heating the water? The pump on the solar hot water system will never come on if there is already hot water in the tank.

Setting this up like you intend is a waste of time and resources.

It would be as efficient as sending it to me.

Want my address?
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Old 10-15-2008, 05:30 PM   #35
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Tankless or tank, but not both


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The point is, why have solar hot water if the tanked water heater is already heating the water? The pump on the solar hot water system will never come on if there is already hot water in the tank.
Of course it will. The solar system is perfectly capable of heating the tank to 180* on sunny days.

Element maxes at 90*.
Solar maxes at 180*.
Tankless heats UP to 140* when required.
Mixing valve tempers DOWN to 140* when required.

Tank less than 90* = cost of normal electric hot water.
Tank less than 140* = cheap hot water.
Tank more than 140* = free hot water.

Make sense?
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Old 10-15-2008, 06:00 PM   #36
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Tankless or tank, but not both


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Of course it will. The solar system is perfectly capable of heating the tank to 180* on sunny days.

Element maxes at 90*.
Solar maxes at 180*.
Tankless heats UP to 140* when required.
Mixing valve tempers DOWN to 140* when required.

Tank less than 90* = cost of normal electric hot water.
Tank less than 140* = cheap hot water.
Tank more than 140* = free hot water.

Make sense?
Are you going to install a 200 degree pressure/relief valve and get a tank that is rated for that kind of pressure? Here is what happens when tanks like that fail. http://www.youtube.com/watch?v=JmJoy...ture=rec-fresh

You would have to get a 200 degree pressure/relief valve on the tankless also and I don't know if they are rated to handle those kinds of temperatures.

Plus with 180 degree water it can scald you in less than a second with severe burns.

Playing with temperatures like that is risky. If you have kids you might rethink having those water temperatures in your house.

I am a retired Paramedic and have seen what very hot water can to to people.
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Old 10-15-2008, 06:02 PM   #37
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People run solar tanks upwards of 180* all the time. That's what tempering valves are for.

I suspect you could be getting a lot more out of your solar setup than you are...
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Old 10-15-2008, 06:57 PM   #38
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Tankless or tank, but not both


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People run solar tanks upwards of 180* all the time. That's what tempering valves are for.

I suspect you could be getting a lot more out of your solar setup than you are...
My solar hot water system runs at 180. But I also have a much more robust system than you will. My heat exchanger is open and not pressurized and has over 500 gallons of water in one tank and 275 in another. I just got a 1000 gallon tank for $100 and intend to put that in service.

I can heat my water and my home with what I have right now unless the sun doesn't shine for a few days.

Once the hot water in my hot water tank (120 gallons) reaches 140 degrees the valve closes and the water is returned to the solar panel unless I need heat in the house, then it is routed through the heat pipes and my modified A coil till the house is warm enough.

When there is no sun I can heat my home and hot water for over 3 days.

If the delta T between the solar panels and the storage tank drops below 15 degrees the pump shuts off.

With 110 sg ft of solar panels I have more hot water than I know what to do with.

I think I get a lot more out of my system that just about any one else's system in the world. Most solar hot water systems don't have enough storage and they lose a lot of potential heat. Mine runs so well I don't have an electric water heater that is hooked up. I suppose that if the weather gets so bad that the sun doesn't shine for a week or so I might have to hook up the hot water tank but so far I haven't had a need for it in 5 years.

Once I get my 1000 gallon tank in the system I should be good to go for 2 weeks without sun.

Wanna hear the good part. I don't have more than $1500 into my system.
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Old 10-15-2008, 07:32 PM   #39
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My solar hot water system runs at 180. But I also have a much more robust system than you will.
How do you know how robust my system will or will not be? As far as I know there's no problem putting 180* water in a plane old water heater, as long as you install a proper expansion tank.

Quote:
Originally Posted by Marvin Gardens View Post
Once the hot water in my hot water tank (120 gallons) reaches 140 degrees the valve closes and the water is returned to the solar panel unless I need heat in the house, then it is routed through the heat pipes and my modified A coil till the house is warm enough.
So I'm confused. You say your system runs at 180*, but then you say your tank doesn't get above 140*. Huh?

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Originally Posted by Marvin Gardens View Post
With 110 sg ft of solar panels I have more hot water than I know what to do with.
Yeah, I bet. That is A LOT of collector area.

Quote:
Originally Posted by Marvin Gardens View Post
I think I get a lot more out of my system that just about any one else's system in the world.
But it takes 110 Ft^2 and a lot of water storage to do it. Geez.

Quote:
Originally Posted by Marvin Gardens View Post
Wanna hear the good part. I don't have more than $1500 into my system.
Are you using home made flat plates? I'm planning to spend the extra cash on evacuated tubes because they work better in cold weather and indirect sun light. If I was in a dryer/hotter climate, I'd use flat plates as well.

What happens when your tanks get below 140? Does your water just get cooler and cooler until the sun comes out? I don't mind paying a few bucks a month during the winter to ensure that I always get 140* at the tap. I can always upgrade the tank (or add one) if I feel it doesn't store enough heat. And, if I heat the tank to 180*, that's a lot of reserve I can burn through before the tankless ever has to kick on.
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Old 10-15-2008, 08:00 PM   #40
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Tankless or tank, but not both


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How do you know how robust my system will or will not be? As far as I know there's no problem putting 180* water in a plane old water heater, as long as you install a proper expansion tank.
I know because I have seen a lot of systems and none of them have even come close to my heat production.

Plus it is all controlled by a computer and radio controlled temperature sensors that control all the solenoid valves.

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So I'm confused. You say your system runs at 180*, but then you say your tank doesn't get above 140*. Huh?
My storage tanks get to 180. My water tank for bathing and showers are set for 140.

Quote:
Originally Posted by gp_wa View Post
Yeah, I bet. That is A LOT of collector area.

But it takes 110 Ft^2 and a lot of water storage to do it. Geez.
This is why my system will probably be more robust that yours. Most people don't a have 7 panels because of the lack of room.

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Are you using home made flat plates? I'm planning to spend the extra cash on evacuated tubes because they work better in cold weather and indirect sun light. If I was in a dryer/hotter climate, I'd use flat plates as well.
I got them all on craigslist for free or next to free. I had to rebuild several of them since the insulation was toast.

Evacuated tubes are nice. They work on ultraviolet which is around even on cloudy days.

But too expensive for me. I am cheap and prefer to heat my water as cheap as I can.

Quote:
Originally Posted by gp_wa View Post
What happens when your tanks get below 140? Does your water just get cooler and cooler until the sun comes out? I don't mind paying a few bucks a month during the winter to ensure that I always get 140* at the tap. I can always upgrade the tank (or add one) if I feel it doesn't store enough heat. And, if I heat the tank to 180*, that's a lot of reserve I can burn through before the tankless ever has to kick on.
It does get cold. I have never had that happen in 5 years but there is no contingency plan. I guess I could hook up the hot water tank if needed.
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Old 10-15-2008, 08:06 PM   #41
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My storage tanks get to 180. My water tank for bathing and showers are set for 140.
A simple tempering valve would allow you to run the domestic hot water tank to 180 as well.
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Old 10-15-2008, 08:30 PM   #42
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A simple tempering valve would allow you to run the domestic hot water tank to 180 as well.
Not really necessary.

I have over 700 gallons of 180 degree water now and when I put in the 1000 gallon tank I will have 1700 gallons of 180 degree water which is equal to roughly 500 KW of power in heated water and another 120 gallons of water that is 40 degrees warmer is not going to make much difference.

That's only 10 KW more energy which is only a 2% increase.

If I needed more heat I would just get another big tank.
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Old 10-15-2008, 09:54 PM   #43
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If I needed more heat I would just get another big tank.
Ya know... I believe you
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Old 10-15-2008, 10:08 PM   #44
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Tankless or tank, but not both


Your range is more then 20 amps.

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