jmcroy
New Member
- Joined
- Jan 20, 2020
- Messages
- 6
Necessary / helpful to keep battery compartment cool if ambient is 100 F but low C-rates on charge/discharge on the LiFePO4 batteries? This would be for an off-grid solar install in South Georgia, USA, where it is hot and humid. It seems I could double or triple the life by not letting the battery compartment get so hot. Has anyone experience with this? I don't think much self-heating will occur, as I should be pushing low C-rates. But I'm worried about the ambient temperature's effect on battery longevity. ..I've also wondered if I could boost the life of the inverter and other electronics by not exposing them to 100F+ south Georgia heat.
Also, in trying to answer my question as to whether it was even possible, I did some tests on my own using a 12V peltier mini-fridge to cool 1 cubic foot of volume and a (I think it's 4.7 cu ft.) mini-fridge that uses a compressor. My conclusion was that the (compressor) refrigerator was superior for cooling in-terms of energy efficiency, which is a big motivation of mine in this small system. Consumed 15W to keep compressor fridge 49 F at 70 F ambient. Consumed 35W to keep (my much smaller volume) other compartment 80-81 F at 110 F ambient temps. The data I collected, along with some explanation (copied/pasted from another post) is below, if you have a use for it.
Let me know if I made a mistake. I am learning.
Info on test:
I took a cheap 12V peltier fridge and rigged up a compartment out of an old styrofoam cooler. 12V fridge was affixed to the top of the cooler and sealed-up such that the 12V peltier could cool the approximately 1 cubic foot volume that was the styrofoam cooler. styrofoam cooler then placed inside of an insulated dog house where I used hair driver to keep ambient temp (in the dog house) 110 F+. I gave power to the peltier with temp control loop to try to get to 25 C / 77 F and watched the temps as hairdrier was applied. An hour after starting to heat-up the doghouse, the temp increased inside of the 1 cubic foot volume to 27 C, after which the temp controller kicked-on and stayed on, trying to cool the volume with peltier back to 25 C / 77 F. For the next 6 hours, dog house temp I kept at 110 F+, and the 1 ft cubed volume stayed at 80 - 81 F for the duration. I think the system was at steady state, so I concluded that it was possible to cool such a volume to ~ 81 F when it's 110 F outside. Peltier power consumption I measured to be 35W. This was 1 peltier with heat sink and fan - 35W to run it all.
So I concluded 35W of peltier could likely adequately cool such a 1 cubic foot volume to 25 C / 77 F, if it was 100F - 105F outside.
I did something similar with a mini-fridge (but ambient temps were ~70 F instead of 110 F. I think fridge is about 4 cubic feet in volume. Inside and outside of fridge started at 70 F. After starting the fridge, the compressor ran for 27 min to get the temp in the fridge down to 49 F. While compressor on, fridge consumed ~ 115W. After the initial cool-down to get the fridge to setpoint, I just let it cycle on and off as-needed to maintain the temperature inside of the fridge. The next few hours it cycled a handful of times, and I concluded I could maintain about a 20 F dT (fridge 49 F ambient 69-70 F) with 15 W on-average of power. So the fridge would actually only run for like 5 minutes, then it would hit setpoint and turn off for like 30 minutes plus. 1 complete cycle I said was about 37 min. 5 min/37 min = 0.13 and some change. So that's 13% or whatever it was that the fridge was actually on and consuming power. 115W * 0.13 and some change gave me 15W.
Insulation I'm sure was better in the fridge than my cheap styrofoam cooler. And ambient temperatures were different between the 2 trials. But the test confirms what I've been reading - and that's that vap-compression is more energy efficient than peltier. Surge loads are of course to be considered - no surge loads for peltier, which is a plus if system size constraints.
so in summary, this is what I concluded / learned:
peltier consuming 35W continuous can maintain 1 cubic foot of volume to 80-81 F with 110F ambient temps. peltier had heat sink and fan too. 35W accounts for all of it.
compressor/mini-fridge can maintain 49 F with 69-70 F ambient temps of a 4 - 5 cubic foot volume with 15W on-average power. Fridge only needed to run a few minutes per hour (5 minutes out of every 37 minutes) to maintain temps.
THEREFORE - fridge is probably better in-terms of energy efficiency.
more pics:
Also, in trying to answer my question as to whether it was even possible, I did some tests on my own using a 12V peltier mini-fridge to cool 1 cubic foot of volume and a (I think it's 4.7 cu ft.) mini-fridge that uses a compressor. My conclusion was that the (compressor) refrigerator was superior for cooling in-terms of energy efficiency, which is a big motivation of mine in this small system. Consumed 15W to keep compressor fridge 49 F at 70 F ambient. Consumed 35W to keep (my much smaller volume) other compartment 80-81 F at 110 F ambient temps. The data I collected, along with some explanation (copied/pasted from another post) is below, if you have a use for it.
Let me know if I made a mistake. I am learning.
Info on test:
I took a cheap 12V peltier fridge and rigged up a compartment out of an old styrofoam cooler. 12V fridge was affixed to the top of the cooler and sealed-up such that the 12V peltier could cool the approximately 1 cubic foot volume that was the styrofoam cooler. styrofoam cooler then placed inside of an insulated dog house where I used hair driver to keep ambient temp (in the dog house) 110 F+. I gave power to the peltier with temp control loop to try to get to 25 C / 77 F and watched the temps as hairdrier was applied. An hour after starting to heat-up the doghouse, the temp increased inside of the 1 cubic foot volume to 27 C, after which the temp controller kicked-on and stayed on, trying to cool the volume with peltier back to 25 C / 77 F. For the next 6 hours, dog house temp I kept at 110 F+, and the 1 ft cubed volume stayed at 80 - 81 F for the duration. I think the system was at steady state, so I concluded that it was possible to cool such a volume to ~ 81 F when it's 110 F outside. Peltier power consumption I measured to be 35W. This was 1 peltier with heat sink and fan - 35W to run it all.
So I concluded 35W of peltier could likely adequately cool such a 1 cubic foot volume to 25 C / 77 F, if it was 100F - 105F outside.
I did something similar with a mini-fridge (but ambient temps were ~70 F instead of 110 F. I think fridge is about 4 cubic feet in volume. Inside and outside of fridge started at 70 F. After starting the fridge, the compressor ran for 27 min to get the temp in the fridge down to 49 F. While compressor on, fridge consumed ~ 115W. After the initial cool-down to get the fridge to setpoint, I just let it cycle on and off as-needed to maintain the temperature inside of the fridge. The next few hours it cycled a handful of times, and I concluded I could maintain about a 20 F dT (fridge 49 F ambient 69-70 F) with 15 W on-average of power. So the fridge would actually only run for like 5 minutes, then it would hit setpoint and turn off for like 30 minutes plus. 1 complete cycle I said was about 37 min. 5 min/37 min = 0.13 and some change. So that's 13% or whatever it was that the fridge was actually on and consuming power. 115W * 0.13 and some change gave me 15W.
Insulation I'm sure was better in the fridge than my cheap styrofoam cooler. And ambient temperatures were different between the 2 trials. But the test confirms what I've been reading - and that's that vap-compression is more energy efficient than peltier. Surge loads are of course to be considered - no surge loads for peltier, which is a plus if system size constraints.
so in summary, this is what I concluded / learned:
peltier consuming 35W continuous can maintain 1 cubic foot of volume to 80-81 F with 110F ambient temps. peltier had heat sink and fan too. 35W accounts for all of it.
compressor/mini-fridge can maintain 49 F with 69-70 F ambient temps of a 4 - 5 cubic foot volume with 15W on-average power. Fridge only needed to run a few minutes per hour (5 minutes out of every 37 minutes) to maintain temps.
THEREFORE - fridge is probably better in-terms of energy efficiency.
more pics: