Designing Complete System

System · December 2008

I need help with a very specific-use-system....all power generated will be used to heat water & glycol in two seperate water heaters.

Power Producing Components:
a) Using a micro-hydro generator I can generate approx. 120W - 24/7/365.
b) Install two 120W solar panels (already have)
c) Install a wind turbine (have not determined exact model at this point)

Power To Be Used To:
a) heat glycol in a water heater (A) to supply a radiant floor heating system
b) heat water in a water heater (B) for household use

How I would like to have the system flow:
micro-hydro & solar panels & wind turbine charges goes directly to a charge controller.....charge controller sends 12V current directly to a DC water heater element in water heater A with the glycol.....when glycol reached 120 degrees a high/low temp relay switch disconnects current from A and sends it to a DC element in water heater B. When the temp in A falls below 110 degrees.....current is disconnected from B and reconnected to A.

This is all that I want to use the energy for and I do NOT want to use batteries.

My questions are:
- If the power goes through a regulator, why can't it go directly to dc water heater elements?
- Does anyone have suggestions that can make this work?

Thanks
Roger

mike95490 · December 2008

Re: Designing Complete System

Use a black pipe in a greenhouse box to heat your water/mix

Use solar PV to run the electric pump directly.

Solar thermal collection is way more efficient than electric production.

See an example here:
Solar Shed
500 gal storage @ 180F
http://www.builditsolar.com/Projects/SpaceHeating/SolarShed/solarshed.htm

System2 · December 2008

Re: Designing Complete System

Mike

You have a great system!! Unfortunately, solar will not work for me. We are in a valley and no spot on our property receives more than 3 hours direct sunlight per day in the winter.

Fortunately, we do live on a large stream, so we are going with hydro = free power 24/7/365. The system is quite simple, I'm just looking for a way to get away from batteries since I don't need electricity stored for any purpose.

Thanks

BB. · December 2008

Re: Designing Complete System

Many solar charge controller can also be programmed to operate in "Shunt" mode...

For example, you would connect your water turbine directly to a battery and let it run... The shunt mode controller would monitor the battery voltage and, when the battery is charged, it would turn on and supply electricity to your heating element.

Problem is, of course--every solar charge controller I am aware of requires the use of a battery for it to first turn on and, probably for proper shunt operation.

But, I am missing something here--because, I don't believe, you need a charge controller at all...

You can go down to your electrical supply house (or a Graingers or McMasters, or something like that) and get a mechanical thermostat with a double throw switch... Contact A is closed and Contact B is open below xxx degrees. Above xxx degrees, contact A is opened and contact B is closed... And you could add more thermostats down the road (to prevent source B from overheating, etc.).

For example, go to grainger.com and search for Granger part number 4XB82 and you will find a 120 VAC 10 amp SPDT thermostat, adjustable with 10F differential...

My only other suggestion is you put a properly rated diode (backwards) across each switch contact set to prevent arcing ("snubbing diode"--assuming you are running/switching DC current).

There are a lot of other thermostats in the catalog if you don't like this particular one.

-Bill

mike95490 · December 2008

Re: Designing Complete System

1) not my system, just a link to "a" system.

> a) Using a micro-hydro generator I can generate approx. 120W - 24/7/365.

Pfffftttt. 120W is an aquarium heater. Useless for heating a house. Could heat water to brush your teeth with. Sorry. You will heat your slab floor faster by just scuffing your shoes along it.

Wind - if you are in a valley - forget it, unless there is so much wind, the treetops "grow" sideways.

Hydro requires a LARGE head and flow, to get much power out of it. What is the "Fall" of the stream on your property?

Say you need 1000W for the floor heater loop, and 500W for the DHW (domestic hot water). That's 1500W. at 120VAC, that's 12.5 amps

At 48V, about 31 amps. That's some pretty serious wire you need, from the generator, to your heater. At least 10 ga, if they are next to each other, and likely 6ga for any appreciable length run. What heating elements have you found , other than 120V/240V ? That should be what drives your system voltage, the elements.

If you can find a hydro turbine that can put out 1500w (or even 800W) 24/7, you will be in fat city, but I think that will take a substantial stream to do that. But you will have enough fish parts to have a good chowder.

System2 · December 2008

Re: Designing Complete System

But, I am missing something here--because, I don't believe, you need a charge controller at all...

This is exactly the info that I'm looking for...thanks!!!! The more research that I do also leads me to believe that a charge controller is not needed. A heating elements can take the direct charge from the hydro generator

You can go down to your electrical supply house (or a Graingers or McMasters, or something like that) and get a mechanical thermostat with a double throw switch... Contact A is closed and Contact B is open below xxx degrees. Above xxx degrees, contact A is opened and contact B is closed... And you could add more thermostats down the road (to prevent source B from overheating, etc.).

For example, go to grainger.com and search for Granger part number 4XB82 and you will find a 120 VAC 10 amp SPDT thermostat, adjustable with 10F differential...

Again, exactly what I'm looking for!!

My only other suggestion is you put a properly rated diode (backwards) across each switch contact set to prevent arcing ("snubbing diode"--assuming you are running/switching DC current).

Can you explain this in more detail? I'm familiar with using blocking diodes with solar panels, but you lost me on this application. Yes, I am running DC current

Roger

System2 · January 2009

Re: Designing Complete System

> a) Using a micro-hydro generator I can generate approx. 120W - 24/7/365.
Correction, that should read 180W

Pfffftttt. 120W is an aquarium heater. Useless for heating a house. Could heat water to brush your teeth with. Sorry. You will heat your slab floor faster by just scuffing your shoes along it.?????....dc heating elements are used as dump loads. DC elements are available is many different sizes. We used to live on a sailboat with a wind turbine. The excess power went to a dc element that kept our water very hot (when the wind blew) That is the nice thing about hydro...it always runs

Hydro requires a LARGE head and flow, to get much power out of it. What is the "Fall" of the stream on your property? Depends on the generator. There are low head - high flow and there are high head - low flow generators. We have 75 gpm with a 30' head. Per the manufacturer this will produce over 200W, but I'm calculating everything on 180W at the element. The water heater has two elements...one DC and one AC. The AC will kick in when the glycol falls below 100 degrees

Thanks

BB. · January 2009

Re: Designing Complete System

Ok, you are running DC...

Most switches are rated for pretty high currents at 120/240 VAC because the AC arc that forms when the switch opens will self extinguish by itself pretty quickly because with AC current, the current flow stops and reverses direction some 120 per second (or maybe higher--depending on the rpm of the alternator and the number of poles).

DC current, on the other hand, even at low voltages, will sustain an arc very nicely (the "better" arc welders typically will have a DC setting--high frequency arc welders are a different animal--but not to worry here).

Here is a link that describes a couple of way to install a diode to help protect your switch contacts. Another link here...

Even so, the thermostat contacts may not be heavy enough for your loads--and you will have to use the thermostat to controller a larger relay to turn on and off your loads (probably just use the voltage from your alternator to power the relay).

-Bill

PS: I should have made is clearer and said put the diode across each load path...

icarus · January 2009

Re: Designing Complete System

Just as an exercise,,,

1kwh~3400 BTU
180x24=4.32kwh=14,688 BTU/day

1 gallon of water~8.34lbs
1 degree F temp rise = 8.34 BTUs

30 gallons of water~250#
14,688 BTUs into 250#(30 gallons) of water ~59f temp rise.

The average well temperature is ~50f. Add in the 59f rise leaves you 109f water,,, just about hot enough for a good shower. Just enough volume for two good showers. Not an insignificant amount.

BTUs are BTUs, it doesn't matter if you need 100,000 BTU/day to heat your house, if you get ~14.6k "free" it reduces your load that much.

Now if you want to put a $$ value, the 4.3 kwh might run $.10-.15 per kwh or $.43-.64. So at say $.50/day and the hardware costs $500 the payoff would be about 2.7 years.

Happy new year!

Tony

PS I must have too much time on my hands,,,My wife is away and I don't really want to start a new project!

System2 · January 2009

Re: Designing Complete System

icarus wrote: »

Just as an exercise,,,

1kwh~3400 BTU
180x24=4.32kwh=14,688 BTU/day

1 gallon of water~8.34lbs
1 degree F temp rise = 8.34 BTUs

30 gallons of water~250#
14,688 BTUs into 250#(30 gallons) of water ~59f temp rise.

The average well temperature is ~50f. Add in the 59f rise leaves you 109f water,,, just about hot enough for a good shower. Just enough volume for two good showers. Not an insignificant amount.

BTUs are BTUs, it doesn't matter if you need 100,000 BTU/day to heat your house, if you get ~14.6k "free" it reduces your load that much.

Now if you want to put a $$ value, the 4.3 kwh might run $.10-.15 per kwh or $.43-.64. So at say $.50/day and the hardware costs $500 the payoff would be about 2.7 years.

Happy new year!

Tony

PS I must have too much time on my hands,,,My wife is away and I don't really want to start a new project!

Excellent info!! BUT, there are a few things that I need to clarify.

I'm heating glycol in a 30 gal water heater to feed the radiant floor system. The dc element will be used to maintain the temperature in a closed loop system. The temp of the glycol will need to be raised to 120f.

During the summer, the system's charge will be redirected to a water heater that is the first in a series of two water heaters. It's function will be to warm the water that is then fed to the primary water heater, so the primary will be heating warm water rather than 50f water.

Roger

icarus · January 2009

Re: Designing Complete System

Roger,

If I am reading you correctly, you are going to add heat to both the radiant loop and the domestic hot water heater. Is that correct?

If you are using this as a dump load because you don't have another use for it?
As Mike suggests, there are probably more efficient ways to heat your glycol loop and your DHW rather than with electricity, especially PV generated.

If you are heating you water solely with grid electricity now, then indeed you will gain from your system, but IMHO there may be some better way to use your electricity.

Tony

BB. · January 2009

Re: Designing Complete System

You will still have a temperature rise/drop from the heater--it is the way the physics works...

For example, say 180 watts=615 BTU's per hour (1 WH=3.414 BTU)... Say your radiant floor heater 120F inlet, 80F outlet... 1BTU = raising 1lb of water 1 degree F, 8.34lbs per gallon of water...

Then the circulation pump capacity supported by 180 watts of electric heat (steady state water tank temperature) would be:

180 WH * 3.414 BTU / [(120F-80F)*(8.34lbspergallon)] = 1.84 gallons per hour

Or, if you assume 120F in and 110F out:

180 WH * 3.414 BTU / [(120F-80F)*(8.34lbspergallon)] = 7.4 gallons per hour

In any event--if the amount of heat equivalent to ~2x 90 watt light bulbs in your room helps your radiant heating and you have enough electricity for your needs--go for it. But don't spend too much money on your implementation... The amount of power is not that great--and the "sustaining" heater does not really do much in the way of overall heating or efficiency.

-Bill

System2 · January 2009

Re: Designing Complete System

BB. wrote: »

The amount of power is not that great--and the "sustaining" heater does not really do much in the way of overall heating or efficiency.
-Bill

Well, this is why I came here and asked the question!! All of your comments have been very helpful!!

The new home that we are building is very well insulated....we are using structural insulated panels that envelope the structure. People that I have talk with that have used these panels say they save >30% in heating cost.

Perhaps the most effecient use will be to use a battery based system so a larger wattage elements can be used. I will need to do some more research and run the numbers on cycle times vs element sizes.

Thanks Again!!
Roger

Designing Complete System

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