90% of the electric bill in the desert at this time of the year is HVAC. The rest of the house doesn't need so much power and only requires a small low cost battery for night time.
Freeze about 2 tons of water during the day and then sink heat into the ice at night. Maybe 2/3rds of the solar power goes to running the conventional AC or heat pump during the day and 1/4 goes to freezing water for evening and night time cooling.
Load level with the freezer unit and the much smaller battery. When the power from the PV is temporarily reduced by clouds the freezer unit would cut off while the heat pump would remain running. The clouds should cool things off anyway.
In winter the heat pump would melt a tank of paraffin for night time heating.
Sounds good. You got room for that much water? IIRC, there's energy losses involved in pushing a given amount of heat farther than it 'needs' to be -- so it may be more efficient to find a substance that freezes at
60 degrees F or so, is cheap, easy to handle, has a significant heat of fusion, and isn't something that would turn the entire neighborhood into a superfund site if the tank leaks. Maybe some other wax, from the same place you're getting your 80-degree (or 100 degree, or whatever) paraffin.
Note that I managed to dodge taking thermodynamics in school -- so go do your own math on this.
If it was a good idea someone would be already doing it. Daytime power is at ON-Peak rates. You'd be better off to use night-time OFF-peak rates to freeze some ice for you to sit on during the daytime ;-)
Since I'm now chief cook and bottle-washer while my wife recuperates from 5 hours of back surgery, I do all clothes and dish-washing in the early morning... (summer) ON-Peak here is 1PM to 9PM. ...Jim Thompson
| James E.Thompson | mens |
| Analog Innovations | et |
I worked on several projects during the late 70's and early 80's that were making and storing cold water at night and then using it to cool buildings during the day. The largest was an IBM facility near Tucson that was 14 buildings and around 1.5 million sq ft. If my memory is correct, it had 13 large storage tanks. I forget how many millions of gallons of water.
Evaporative cooling is popular in AZ. Even though it wastes precious water a binary system can cut energy costs by 80% except in August. MasterKool swamp cools air before it enters the condenser. Hard & salty Colorado Rive r water eats through Al and fouls everything up so unless they were on a we ll with a water softener most residential customers went back to high delta T high energy consumption AC.
Probably a cooling tower + storage tanks. They ran the cooling tower at ni ght with off peak power from the coal powered plant
That's one reason to go with a higher delta T [lower COP] and freeze water: It reduces the size of the heat storage by an order of magnitude.
Another reason is ice making equipment is off the shelf, cheaper than batte ry storage by an order of magnitude on a / joule basis.
A 3rd reason is the blower at night doesn't need to draw as much power.
There are more issues here than pure thermo and heat exchange.
A lot of swimming pools in SoCal are empty because of lack of water so the question isn't "got room" but "got water?"
Just stick the ice maker in the empty pool, the PV on the roof and call it a day.
If an idea requires tweaking from the git go, get another idea.
There's way too much low hanging fruit on the ground to tweak.
I'm real big on back of envelope calculations when I wake up at 2 am.
I woke up at 1 am a couple of weeks ago wondering, "hey, I just happened to coincidentally wake up in the middle of an earth quake! What are the odds of that?" I looked up at the massive ceiling fan and tried to detect any wobble, to calculate the stresses that any change in angular momentum would put on whatever was keeping it from falling on my left foot.
Finally I got up, turned off the fan and went back to sleep.
Actually the cooling was done via 'chillers' which are industrial size heat pumps.
However the higher the delta T that you are trying to create the less efficient the system will be. Like any system there are trade offs. A smaller temperature difference requires more storage but it takes less total energy. Like many cases, you are trading off the initial cost of the storage system versus operating costs.
The major reason for running the chillers at night is that it is much easier to make cold water when it is cooler outside. In Tucson, there can be major differences between day and night time temperatures. That was the main reason that the cold water storage system was able to save on energy costs. Now there is probably a different price for night time versus day time energy use. However I do not know if that was true in
ater a binary system can cut energy costs by 80% except in August. MasterK ool swamp cools air before it enters the condenser. Hard & salty Colorado River water eats through Al and fouls everything up so unless they were on a well with a water softener most residential customers went back to high d elta T high energy consumption AC.
t night with off peak power from the coal powered plant
Evaporative cooling will only get you down so far. Then you need ac or hea t pump.
ter: It reduces the size of the heat storage by an order of magnitude.
The delta T is 60 degrees C in the summer afternoon desert sun so maybe a 1
00,000 BTU/hr refrigeration unit freezing a high latent heat phase change m aterial at 50 degrees might be better than a icemaker freezing 2 tons water /day.
But what is that material?
If you have an empty swimming pool you might try using sensible heat like I BM.
Storage goes up mostly because any material with the right freezing point, say, 50 C, will probably have a much lower latent heat of fusion than H2O.
attery storage by an order of magnitude on a / joule basis.
As opposed to Phoenix which is still over 40 C when they close the bars.
Back then it was definitely cheaper at night so IBM found a nice dove tail, lower rates & lower temperatures.
Soon power will be cheaper during the day because solar is so cheap.
Most off-grid homes have a smaller % of roof area paneled than the SDG&E or SoCal Edison deals which are supplying energy to the rest of the neighborh ood during peak usage.
So there is plenty of room to add more panels to power the ice maker as wel l as the AC.
This would save some money even if you stayed on the grid because you would n't draw much energy from the grid at night.
With off grid solar it would really save a lot of money. Off grid homes ty pically have a shed full of batteries + a propane engine for back up power.
If you wanted to go off grid in hot areas it would be much cheaper to trade most of the batteries and/or the engine for an ice maker and more solar pa nels.
Several patents cover PV on motor vehicles powering a small freezer for instant cold ac. Shorter trips are very common so it would save a considerable amount of fuel. The regular ac would only draw power from the engine on longer trips.
There should always be a cold non alcoholic drink at the ready near the front seat.
Phoenix is always over 40C in August when high humidity traps heat. Stucco and the rest of the building heat up so much it takes all night for the in terior to cool off the rest of the summer. If you try to hose down a wall or sidewalk in California they'll geotag you with the water stazi app.
Last year I took out a bad attic fan. The high temp. limit, 70C, was marke d on the motor. The new motor will be dead in another year or so.
Wood shake is a popular roof cover here because it doesn't evaporate like a sphalt composition w/ a dead attic fan.
It might be years before you know you have a leak.
You can freeze during the day - there is a less popular heat pump refrigeration type that uses ammonia and no moving parts - it simply has a thermostatically controlled heating element at a specific point in the plumbing.
A small array of curved reflectors/collectors would suffice to focus a beam of sunlight on the bit that needs to get hot.