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oil pan 4 04-25-16 03:59 PM


Originally Posted by Kramer (Post 49881)
I live in the South as well, and AC accounts for about a third of my usage. I want to build an ice storage system that i think will be much cheaper more robust then any battery bank. My idea is to put a few hundred partially water filled soda bottles in a tank and then fill in the voids with a glycol mix. My thought is that this way the expanding ice will not damage the tank or any piping since the bottles will be able to move freely as they freeze. Then, I just pump the glycol from the tank, and then through indoor evap coils (now converted to glyco/air heat exchangers) as needed throughout the day or night. The only need for batteries would be to power the coolant recirc pump. The AC compressor and condenser fan can run only when the sun shines.

I don't think that will work very well.
I use glycol coolers and splits at work.
For example a 5 ton split condenser has 1/4 line feeding liquid refrigerant going to it.
The 5 ton glycol cooler needs 36gpm and has 1 inch lines going to it.

MEMPHIS91 04-25-16 04:53 PM

Yep I could not agree more with everything ya'll have said. I'm not trying to disagree, just trying to really answer Randens question by saying YES I am thinking of going off grid, even though it means BIG changes. And large expense. And large head ache. And probably a mental breakdown every time someone turns on a light, or watch a dvd for longer than 10 minutes at a time.
My question still remains, what would be the best (not perfect) but best with todays market, battery system to achieve that goal. Assume I was handed a $100,000 check (me installing myself of course) and could ONLY spend it on solar.

oil pan 4 04-25-16 05:29 PM

Well you are going to need a backup generator.
The best batteries are true deep cycle lead acid wired for 24 or 48v.
Use MPPT charge controller.
Don't put in one large too big to fail charge controller or inverter, because it will quit some day. Use smaller charge controllers and more than one inverter. Large inverters tend to be very inefficient on very low loads and gobble up far more power in stand by mode. Smaller modular inverters and charge controllers will make upgrades easier so you aren't ripping out everything and replacing it all during an upgrade.
Go one size up from what is recommended for DC wiring.
Switch over all heating loads to direct combustion.

Kramer 04-25-16 07:53 PM


Originally Posted by oil pan 4 (Post 49887)
I don't think that will work very well.
I use glycol coolers and splits at work.
For example a 5 ton split condenser has 1/4 line feeding liquid refrigerant going to it.
The 5 ton glycol cooler needs 36gpm and has 1 inch lines going to it.

Is the glycol used to cool the ambient air or to cool the condenser? We have AC systems at the power plant where I work which use glycol to cool the condenser, however since the glycol is cooled by a cooling tower it is close to the outdoor temp. Since it is warm to start with, it takes a lot flow to remove much heat from the condenser. Not much delta T. For my idea to work, the water flowing through the evap would be near 0C. This is not as cold as the refrigerant for which the unit is designed, however, the entire evap will be liquid filled unlike with refrigerant which is undergoing a phase change in the evap. Sorry Memphis91, I'm getting off topic.
The Fe-Ni seems interesting, I think it would be cheaper if produced in volume.

oil pan 4 04-25-16 09:55 PM

That was 2 different units.
I was trying to say is there is no way enough glycol can be pumped through the tiny evaporator inlet lines.
The glycol where I work is cooled down to near freezing with ammonia refrigeration.
The glycol to air heat exchanger is huge compared to phase changing refrigerant.

oil pan 4 04-25-16 11:58 PM

For going off grid try to eliminate heating that uses forced air ductwork.
In Japan they like those little kerosene space heaters.

Kramer 04-26-16 12:01 AM

I have a few larger heat exchangers, sounds like they might be a better choice since I won't get the benefit of the phrase change. Thanks for the advice. I used to spend some time in the Taos-Red river area. Is that close to you?

oil pan 4 04-26-16 12:42 AM

The red river area is about a 4 hour drive north from where I live.
Its actually kind of nice up that way.

jeff5may 04-26-16 07:00 AM

OK, so I'm going to try to address the issue of space heating/cooling, combining the off-grid requirement of Jake (Memphis), the phase change storage of Kramer, and the advice of Oil Pan.

It should be possible to install enough solar panels and a small and efficient enough heat pump to satisfy cooling demand with the solar power gathered during the day. The most effective way to do this would be to install two heat exchangers indoors: one that feeds directly off the refrigerant loop, and one that feeds off the cold store. Another intermediate brazed-plate exchanger could be installed that fed off refrigerant and exchanged heat with the cold store. Both the refrigerant-to-air (DX) and the refrigerant-to-glycol (BP) should be TXV metered. When the house calls for cooling demand, the air handler would cool the house air quickly and efficiently. When no cooling was being called for, the BPHX would extract heat from the cold store. The outdoor unit would run constantly as long as the cold store was above a certain destination temperature, let's say -5 degC. Once the cold store froze solid, the outdoor unit would not run unless there was cooling demand called for indoors.

At night, the outdoor unit would not run. When cooling was called for, glycol would flow through the second indoor HX then through the cold store. A large enough cold store would stay at or very near 0 degC all night. Due to the reduced heat load, the cold store would only need to be massive (not supermassive). When the sun came up in the morning, the outdoor unit would start charging the cold store for the next night.

In heating mode, the same strategy could be used. When the sun was shining, the outdoor unit could charge heat into the store while no heat was being called for by the house. There are two factors that make this setup less effective for heating, though. For one, the store would not change phase, so the amount of heat it could sequester would be much less. For two, a balance point exists where an alternate heat source would be more economical to run. At the high end, it becomes inefficient to charge the heat store above a certain temperature. At the low end, the outdoor heat exchanger becomes ineffective at gathering heat from chilly outdoor air. Outside of this range, it is wiser to burn wood or natural gas to meet heating demand. During a cloudy cold spell, it might make sense to level the load out by burning backup fuel, diverting the reduced solar power to the battery bank.

Another need that could be satisfied with this type of system that was not mentioned is domestic hot water (DHW). Jake has built a heat pump water heater, and has proven that a small (dehumidifier or refrigerator) amount of capacity can serve his family and a house full of guests without running out of hot water. A small heat exchanger (desuperheater) could be rigged at the compressor outlet that served only the DHW tank. This HX would not rob an excessive amount of heat from the rest of the system, and would self-regulate at a temperature that would not yield scalding hot water.

A major goal of this type of rig would be to not run off of battery power at all. Space heating and cooling is a huge load, and would lay waste to precious battery power that would better be saved for lighting, ventilation, and electrical infrastructure.

randen 04-26-16 08:18 AM

The solar panels 10 kw's worth should be showing up this week. 4 kw's will be covering the pergola the rest 6 kw's will rest on the flat roof. The first order of business will to have the 4 kw pergola interrupt the grid supply and power the home while the sun is available.

My summer usage is about 20 kwh per day. As we head into the winter the geo-thermal units (3) starts to really flex their muscles and 100 kwh per day. Now I must qualify this as I'm also factoring in my business usage running a machine shop and running a geo-thermal (DIY) there as well.

I have a spread sheet on my usage in 2009 the price was $0.13 /kwh and we had been notified April 1st the price is now $0.26/ kwh Doubling in seven yrs. Without going to deeply into the math and ROI its going to workout nicely by installing the solar.

Now batteries I see some anecdotal information. I'm currently working with large format Nimh that were manufactured in 1999. Under load testing they are shown the have still a 80 to 90 % of their capacity remaining. Now yes they do have some internal losses during storage. How ever Lithium batteries have not demonstrated this loss during extended storage. These chemistries are completely different and light yrs better than Lead-acid.
Better yet you can actually buy them now and they are not pie in the sky just around the corner technologies. I can go down the scrap yard and buy 20 kw's of battery out of a volt or leaf and put them to work. If I treat them properly in a residential type charge discharge they will last for decades.


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