Off grid heating/ac minisplit efficiency
i am building a 2000 sq ft cabin off grid, relying on solar (with batteries), lp generator, and heated floor by on demand boiler. What is the most efficient way to cool the cabin in the summer? Minisplit?
Comments
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Where is this cabin located? What's the typical humidity there?
Single pipe 392sqft system with an EG-40 rated for 325sqft and it's silent and balanced at all times.
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Open windows?
Depending on the heat load 1 to 3_Tons of cooling will be needed. can the solar handle that kind of start-up load?
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Hi, Have you looked at the passive stuff, like white or reflective roofing, low E glass, and good shading to keep summer sun out?
Yours, Larry
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window up high that open
Same low.
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Mini splits don't have the inrush of typical AC unit as all the bits are inverter controlled. They do ramp up to near full power when doing periodic oil recovery but as long as you size for max power, you should be fine.
One thing to watch in off grid is power quality especially in remote areas with lighting. Make sure you have surge protection on your main panel and the AC itself.
For off grid, you want heat that is guaranteed to work 100%. Generators have a nasty habit of not starting when you are not there, so can't be relied on for power for heat (your boiler and pumps need surprising amounts of power once you calculate it). Best to install a pilot operated heat source such as a through the wall vented heater that can keep your place from freezing even with power out.
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Minisplits want clean AC power with good Hertz control.
As do modern boilers that have a fair amount of electronics inside.
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Anything with electronics inside is going to run on DC, why would it care about frequency or anything else?
That said I'm still waiting to hear where they are, maybe a swamp cooler will work.
Single pipe 392sqft system with an EG-40 rated for 325sqft and it's silent and balanced at all times.
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the computers that control everything require a clean sign wave.
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The PCs I build certainly don't seem to.
Why would something that's runs 100% on DC need anything special as far as the AC side?
Single pipe 392sqft system with an EG-40 rated for 325sqft and it's silent and balanced at all times.
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Hi, My experience with off grid stuff has been clear that pure sine wave power is needed for electronics. Even modified sine wave is considered to be "dirty power" and makes electronics get all glitchy. Even LEDs have problems with anything but clean power.
Yours, Larry1 -
LEDs I could see because I do not believe they have actual power supplies in them like anything computerized would.
I don't know .
@mattmia2 have you seen SMPS have issues with AC power quality? If so, why?
Single pipe 392sqft system with an EG-40 rated for 325sqft and it's silent and balanced at all times.
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AI Overview
+4
Clean sine wave power, often referred to as "pure sine wave," is a smooth, continuous waveform that closely resembles the power supplied by utility companies. It's produced bypure sine wave invertersand is ideal for powering sensitive electronic devices because it minimizes interference and damage.0 -
The power requirement has to do with the power supply in the widget, whatever that is. If that power supply can cope with off-frequency components — spikes or harmonics — then no problem, and some types of power supplies can. Oddly enough what little observation I've done suggests that either the power supply is actually charging a battery which in turn runs the item — such as a laptop computer or (shudder) a Nest, for example — or inherently doesn't care, such as LED lights, or is in high end enough equipment to afford very high frequency switching power supplies (a lot of current high end high fidelity things) or supplies with hefty capacitors and chokes. Otherwise the high frequency grundge on the input power gets through to the computer and confuses it…
Once in a while really grundgy power can have enough high frequency harmonics to overheat a transformer — but that seems to be rare.
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England0 -
Hmm, "Grundge Power"… @Jamie Hall , you might have come up with the inspired name for a band! 🙀🎶
Yours, Larry
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No SMPS runs it's transformer at 60hz. It rectifies it and runs it through a high frequency oscillator. That's kinda my point.
And any modern computer or even cell phone charger is usually a SMPS not a linear supply.
But maybe there's something I'm missing. It's quite possible, that's why I'm asking. So far personally I've never experienced this with any of my equipment.
Single pipe 392sqft system with an EG-40 rated for 325sqft and it's silent and balanced at all times.
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li have Walk In freezers that work fine on a generator. Use an intelatraul controller and it won’t work.
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I believe you.
My question is why.
Single pipe 392sqft system with an EG-40 rated for 325sqft and it's silent and balanced at all times.
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sine Wave!
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Sigh.
Single pipe 392sqft system with an EG-40 rated for 325sqft and it's silent and balanced at all times.
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Minisplits all have power factor correction on the input, not just a simple rectifier. The power factor correction ic needs to sync up to the grid and expects a reasonable sine wave to run properly. Some have better control and will run with noisy power, not all.
Most modern PV inverters are sine wave. The ones I've put a scope on (Outback and Schneider SW) had very clean output. Can't say the same thing about generators though.
Since AC runs mostly during the day in the summer and usually when there is a lot of sun, the minsplit will be running of the PV inverter. I don't see power quality being an issue as long as the inverter has sufficient output.
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Computers have switching power supplies. The first thing they do with input power is switch it on and off 100,000 times per second (roughly) because inductive and capacitive reactance increase with frequency - thus one can make them 1,666 times smaller than they need to be for 60 Hz. Then they rectify that (turn it into DC.) The input power could be DC - the wave form doesn't matter.
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When I lived off-grid I had no AC but I did have a propane refrigerator. Propane AC exists. Unless you're living in the desert I hope you can figure out how to keep cool passively - don't forget awnings. Even in town I have 2 layers of thermal curtains to pull across the windows to minimize cooling costs - though that means I need light during the day.
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My offgrid cabin is in the southern Black Hills of South Dakota at 5500 ft. above sea level. Super low humidity. I hesitate doing a light colored roof because I appreciate the solar heat to melt snow in the winter. I am hoping to rent the cabin to tourists in the summer so it needs some form of AC (I personally just open windows).
Thank you for all your great insights. I appreciate it.0 -
Thermal chimney. Check out the visitor center at zion NP. A tall, dark colored chimney/roof stack heats the air in the chimney, which rises, pulling air in behind it. The building itself is relatively open, and surrounded by well shaded foyer and gathering space. The heated chimney air rises and pulls in cooled shaded air from around the building. Even when it's 100F out, the inside of the building stays <80F without any active cooling. Check it out. Very cool.
But it requires very specific and thoughtful architecture design and foresight, and I doubt you want to redesign at this point. Given low humidity, and the limited nature of necessary cooling (assuming it doesn't really get >100F?) a swamp cooler is likely your most efficient option, but tourists won't be thrilled with it. A minisplit will be your most efficient (and easiest) option for active cooling. Be prepared for tourists to try to use it for heat as well, which might be ok and really efficient in the shoulder seasons.
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I have minimal experience with non-sinusoidal power sources impacting downstream loads; I can only personally report on 1 situation:
A desktop computer supplied by an UPS followed by a surge suppressor followed by the computer itself. Everything was just fine until we lost mains power at which point the UPS started turning the computer on and off rapidly.
The output of the UPS was sufficiently ugly to interact poorly with the filtering in the surge suppressor. This tripped the UPS protection circuitry and the unit shut down and then tried to restart. Rinse and repeat.
My understanding is that many power supplies are designed with the expectation of single frequency sinusoidal power. The response to 'dirty' power will be unknown because no attempt was made to design for the out of bounds supply conditions. Some systems will rectify the dirty input just fine, create good enough intermediate DC to feed the switching circuitry, and produce clean regulated output.
My hunch is that if there is a problem with 'dirty power' supplying an inverter based minisplit, it will be caused by noise filtering or power factor correction circuitry on the power input rectifier of the minisplit. The noise filtering is almost certainly there to reduce switching noise coming from the minisplit.
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