Chill Out with the Batteries

[AzRoute66]

An Elitech RC-4 I found on Amazon. I think it is RC-4, $20, the one without humidity and with the probe. Some things about the one button user interface and the software will look quirky at first glance, but most of it makes sense when you realize that these were designed to monitor cargo as their first job. The software will give you a nice graph and one click export to Excel, text, and PDF. I haven't tried the alarm functions but I have had it in the freezer and the attic, and it was on the roof for a month. Good agreement with the thermometers I trust.

[sensij]

I love this little temp logger, I wish I had one as cheap/good/easy for DCV.

If you don't mind sharing, which temp logger are you using?

[J.P.M.]

Yeah, I plotted dew point and relative humidity as well as air and water temps. Thanks again to sensij for the MesoWest weather data reminder. I would say my provided air is much closer to the water temp than 20 degrees. If I re-run this in the spring or summer (and I probably will if I have no other task for the logger), I'll spot check it with the infrared on the vent registers. I love this little temp logger, I wish I had one as cheap/good/easy for DCV.

Some swamp coolers are better than others. 20 F. (Air outlet - dew point) of temp. diff. is s rough estimate. Reasonably well designed commercial and industrial cooling towers will do about 10 F., maybe a bit less, depending on particulars. Much lower than that 10 F. delta T starts to get expensive. Long, boring story for most. Most residential swamp coolers "working" operating efficiency will often run in the neighborhood of ~~ 50 % or so, ballpark, depending on media pad material, design, how often they are cleaned and the big factors of air cleanliness and water hardness.

Very loosely translating that efficiency into numbers, that means if the outside dry bulb temp. temp. is, say 90 F., and the outside dew point temp. is, say 50 F., a delta T of 90 - 50 = 40 F., at 50% eff., the cooler will reduce the air temp. by 40 F.*.5 = 20 F., giving an air temp. at the cooler outlet of 90 - 20 = 70 F. or so.

As a practical matter, mostly because it's moving relatively fast, the air coming out of the cooler directly at the cooler outlet may give the psychometric perception of being cooler than that 70 F., for much the same psychometric reasons that standing in front of a fan seems a cooler (or warmer if the moving air is warmer) place to be.

For the same dew point and dry bulb temps., cleaner and thus more efficient media pads will tend to increase the inlet to outlet temp. differences, increasing the system efficiency.

[AzRoute66]

Yeah, I plotted dew point and relative humidity as well as air and water temps. Thanks again to sensij for the MesoWest weather data reminder. I would say my provided air is much closer to the water temp than 20 degrees. If I re-run this in the spring or summer (and I probably will if I have no other task for the logger), I'll spot check it with the infrared on the vent registers. I love this little temp logger, I wish I had one as cheap/good/easy for DCV.

[J.P.M.]

Just to put a bow on a part of this, I measured the past four weeks and the swamp cooler reservoir water averaged 60 degrees when most daytime temperatures ran into the 90s and relative humidity was all over the place. The swing on the water temp was + or - 10 degrees, so recirculation at night to replace chilled water in a insulated battery enclosure should ensure it starts the day from 55 to 60 degrees. But even 70 degrees would be helpful in a garage that is going to get to 100 degrees on most summertime days.

FWIW, and probably of no particular significance or importance to you, but the water temp. in a swamp cooler is a pretty decent indicator of the average dew point temp. A swamp cooler works the same way a cooling tower works, but not as efficiently, with swamp coolers usually getting the moistened air to within about 20 deg. F. or so of the water temp.

[AzRoute66]

Just to put a bow on a part of this, I measured the past four weeks and the swamp cooler reservoir water averaged 60 degrees when most daytime temperatures ran into the 90s and relative humidity was all over the place. The swing on the water temp was + or - 10 degrees, so recirculation at night to replace chilled water in a insulated battery enclosure should ensure it starts the day from 55 to 60 degrees. But even 70 degrees would be helpful in a garage that is going to get to 100 degrees on most summertime days.

[J.P.M.]

Actually they are talking about thermal (IR) radiation from the panels as the source of cooling. The night sky is a thermodynamic black body of very low temperature. Much much lower than the air temperature.
This is why an array of panels may show a temperature less than the ambient air temperature in the early morning after losing heat to the sky all night.
Note that to take full advantage of the low radiation temperature you need to insulate the panels to prevent them from being warmed by the ambient air.

As I wrote, the Zomeworks application is for outside, although it will probably work inside with the nocturnal cooling feature not employed. I'm not sure if the underside of the covers on the Zomeworks device is insulated but it looks as though it is..

A clear night sky is close to being a blackbody, but as a practical matter, it's less than a true blackbody for reasons having to do with the sky temperature not being uniform over the sky dome and the atmosphere radiating within only certain wavelengths. Clouds will also have an effect. Empirical correlations using the surface dew point and hour from midnite often show an effective nite sky temp. of something like 5 to 15 deg. C below ground ambient temp. for a good portion of the U.S., with the greater temp. differences being under clear skys and dry air at higher elevations above sea level. Such temp. depressions seem to correlate reasonably well with measurements of radiative cooling effects.

[littleharbor]

OK , not real good with terminology and I don't know anything about Geothermal cooling but while talking with a neighbor in Baja he was contemplating building an underground battery bunker which isn't too revolutionary but he mentioned he wanted to dig a underground cooling loop where air could be slowly circulated and the ground would regulate the air temperature. I just thought about this conversation after you mentioned your talent with a back hoe. Is this is out of the box enough or just out there? I'm sure there are plenty of issues to deal with if this idea would be attempted but it gets so damn hot down there some folks are willing to try anything to help their batteries.

[Mike90250]

Thats how they made ice in the desert 500 years ago, insulated shallow pans under the night sky

http://www.fieldstudyoftheworld.com/persian-ice-house-how-make-ice-desert/

[AzRoute66]

Thanks to all for all of the input. As suggested, this has never been thought of as other than a diversion or opportunity load.

I do like the freezer idea, but not crazy about the access to the batteries, Well insulated and I'm pretty sure most have a built in drain in the bottom which would be a plus. Would be easy to vent one too. I think I might want to remove the 'guts' and reposition them level so I could 'mount' a chest or upright freezer with the door hinge on top and door swinging out/up to facilitate access. Not out of the question.

I had already decided that any homemade box/small room would have elevated battery rack(s) and a tilted plastic/fiberglass pan/bottom to a drain for any excess fluids from cleaning, rinsing, etc.

As I mentioned up front, a swamp cooler was my first instinct and thanks to Sunking for validating that, as well as his rules of thumb for heat impacts to battery lifetime - but, his idea of a pit was both inspired and outside the box. My prowess with a backhoe has been well documented in my circle of friends and is frequently mentioned when no other means of disparaging me seems appropriate.

I actually exchanged a couple of emails with Zomeworks this morning about using my existing (and constantly running in the summer) evaporative cooling reservoir as an alternative heat sink for a Cool Box using a couple of lines and a small pump, They not only had some nice recommendations on bladder capacity and flows (vice pure convection which they do with large hose diameters), but THEY were the ones that noted that if I was not able to fully utilize the heat radiant capabilities of their product (due to it being in a closed garage), that I build a homemade cool box of my own. Very nice of them. To this end I put a temperature logger in the reservoir pan of my swamp cooler and will go fetch it in a couple of weeks.

Somehow, using the cold water from my existing cooler sounds better to me than just using the air output of a separate cooler. I'm sure I'll think of all of the reasons why over time.

At any rate, still mostly thinking out loud and open to all alternatives and observations.

[inetdog]

sensij, - At their website, the photos are all disclaimered with "Cool Cells must have full view of the night sky to function properly." This clearly has more to do with airflow over the lid/radiators than star gazing.

Actually they are talking about thermal (IR) radiation from the panels as the source of cooling. The night sky is a thermodynamic black body of very low temperature. Much much lower than the air temperature.
This is why an array of panels may show a temperature less than the ambient air temperature in the early morning after losing heat to the sky all night.
Note that to take full advantage of the low radiation temperature you need to insulate the panels to prevent them from being warmed by the ambient air.

[Wy_White_Wolf]

I made a beer fridge once w/ a couple of room mates. It had two holes drilled in it, one for the CO2 line and one for the tap in the door. No reason why they couldn't have been a vent/drain.

I'm a homebrewer so I have one that holds 4 corny kegs and 1 that's a temp controlled ferment chamber.

[J.P.M.]

Yes, thanks for that idea that the battery mass will assist in retaining any injected cooling. That is the trick, right? The same insulation that keeps outside generated heat out keeps inside generated heat in.

You're welcome. Depending on the volume and weight of the batteries, WWW's idea may well accomplish much the same purpose as constructing a box with less construction and less hassle. I'd just be conservative in the vent/drain sizing however, and see if local codes or common sense issues I'm most likely ignorant about come into play.

BTW, and not to sound condescending, but every good vent needs a good drain. One hole in the top will only let stuff out if an equal amount of stuff can get in to replace it, probably at or close to the bottom. That also brings up the idea of reverse thermosiphoning, or bad stuff going in the wrong direction. Not being well versed in battery containment venting, I'd put holes top & bottom, run them outside, put bug screens on them and dampers as required/allowed by code and common sense, directioned depending on the density of the off gasses relative to air.

On the thermal issues: Insulation works because it slows down heat transfer from where it is warmer to where it is colder.

The better the insulation, and/or the smaller the heat transfer surface is (the container outside surface area, top, bottom and sides), the slower the batteries will change temperature, either warmer or colder.

The more massive the batteries, the slower the temp. change of the batteries.

The least amount of temperature change (note, temperature change, not necessarily heat transfer, although that will be less heat transfer if a lot of insulation is used) will occur when a large thermal mass is heavily insulated. That ratio of thermal mass/overall heat loss is what something called the thermal time constant is all about. Long story. This is the Reader's Digest version.

To a first approximation, and as an example, for the same insulated box, if the contents of the box have a heat capacity of, say 1,000 units of thermal energy per deg. of temperature, the temperature of the contents will change only 1/10th as much over any similar time period as the same insulated box that contains material with only 100 units of thermal energy per deg. of temperature.

Thermally massive stuff loses temperature (but not necessarily thermal energy) a lot slower than non thermally massive stuff. That's one reason people make the mistake of thinking that stone houses are well insulated. Truth is, stone is a crappy insulator, even if it's 2 ft. thick, but because it has such a large thermal mass, it stays warmer/colder longer in response to environmental changes. That's a result of a long thermal time constant (a large numerator in the thermal mass/heat loss quotient) at work.

If you have lead acid batteries, they're heavy, and depending on how much of the volume the acid takes up, and because lead is about as heavy as its specific heat is low, treating the thermal mass of a battery as about the same as an equal volume of water may be a decent 1st approximation. If so, the batteries have a lot of thermal mass and that mass is pretty compact. So, putting the batteries in a well insulated box and circulating cooler air through the box at night may be a possible solution, depending on how much waste heat is generated during charge/discharge cycles.

You were/are on the right track for one possible solution. Just remember safety.

[J.P.M.]

So what's stopping a person from putting a vent in the freezer? It don't take much to vent the H2 and since you also want it from the highest point that works out with cold air wanting to stay in the freezer.

WWW

I made a beer fridge once w/ a couple of room mates. It had two holes drilled in it, one for the CO2 line and one for the tap in the door. No reason why they couldn't have been a vent/drain.

[Sunking]

Sunking, - From you, I was hoping to evoke some kind of anecdotal point concerning battery lifetime vs temperature, or a mathematical treatise on weeks/degree C. The easy bait was the duty cycle that a 450W unit would require to cool 25 - 50 sq ft 'room' with a battery mass of ____. A rant of why a 64 degree thermostat setting was just plain stupid would have been appreciated. But all I get from you is --- you can't generate enough power to run your part time 450W load from a 4,000W array during a six sun-hour day. Really? Just for you, I am going to treat it as a diversion load for the duration.

How big of a battery RU? How many volts? Did not take note you are running 4000 watt panels.

OK for each 15 degrees F you go above 75 cuts battery life in half. For each 10 degrees F you go above 75 adds roughly 5% capacity, and vice versa for every 10 degrees below 75 you loose 5% capacity.

Use a Swamp Cooler rather than a Window Shaker. Not only will it keep things cool, but add a fair amount of humidity which will do the batteries good because that will slow down evaporation of battery fluid. A Window Shaker will remove what little humidity you have making it even dryer. A Swamp cooler should use 200 watts or less last time I looked. Whatever it is will be less than 450 watts.

Ever think of a pit? Or inside your cool home?