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Off grid system advice

RyanG222

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Oct 12, 2021
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We are in the process of building a 4300 square foot fishing/hunting lodge on an island off Mississippi coast. I have researched, called salesman, solar companies, and still left very confused with designing a system to run a few things while off generator power.

When we are not occupying the lodge I would like to run the following:

-a whole house dehumidifier system (specs attached below).
- a refrigerator/freezer
- 5-10 led lights on a dusk/dawn sensor
- possibly a small window AC and a fan for when only one or two of us would be there.

The window AC and fan are not 100% necessary but if it wouldn’t increase the system size/cost drastically I would like the capability to run them.

The whole dehumidifier would be on a thermostat so would not run full time. Basically works as needed base on set humidity level parameters.

I like the idea of the hybrid solar kits from shopsolarkits.com like pictures below due to the 10 year warranty on batteries. I’m not opposed to building my own though.

Any advice will be appreciated.


Thanks in advance!

Ryan
 

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Really need to get it into a watt hour requirement.

The dehumidifier runs on 1500 watts, so that is quite power hungry.

Without the watt hour requirement, my guess is 10 kw of panels and 30 kwh of batteries. The 6 kwh kit you pictured may work for my RV and Air Conditioning, but I highly doubt a lodge your size.

Getting a generator is fairly easy and most have a lot of play for what they would run, but with solar, its 10X the price of a generator, at least, so a realistic kwh requirement is pretty important.
 
Agree. That's a 10 to 20kw of solar at least. The AC and dehumidifier use a bunch of power and how much they run greatly affects how much power they will use.
 
As it appears there is a generator available, my suggestion would be to measure the kWh requirements with a recording device to establish a baseline of the energy required for the intended usage. Attempting to guesstimate using specifications is difficult due to unknown duty cycles of the appliances, additionally do a worst case scenario to allow for some margin of safety.

Think about using mini split A/C units, they can be used to compartmentalize a home for time of use, they also work as dehumidifiers, which is what I use in the tropics, the high efficiency Diakin 28 SEER 9k BTU I have uses 152W intermittently in ECO silent mode to keep my bedroom at a reasonable temperature, but taking the moisture out of the air is more important.

Seems odd to use solar as backup to a generator, usually the generator is the backup being that it more expensive to use over time.
 
I would consider a couple of 1 ton mini splits. They do a great job of dehumidifying and will cool too. To be unattended would be hard to size with out going too big. Then the human factor. I know a guy with a deer camp for family he returned to camp around 11 am to find the front door wide open, no one around and 25 degrees outside. The lp heating running and cold inside.
 
I appreciate the responses, let me clarify a few things.

The solar will only be used while away from our lodge. It’s main use will be to keep the humidity down while the lodge is locked up and no one there. The refrigerator would be a nice bonus to be able to keep items in vs cleaning it out everytime we shut down. The lodge will only go a few days and at most a few weeks at time of being shut down. We have a 40kw generator we use for main power only while the lodge is occupied.

The AC I was referring to would be a small window unit for a 12x12 room to run while sleeping only. This would only be used if one or two of us go out and stay a night or two. We could save diesel by not running the generator. (This is not a huge concern but if I could have enough battery power to run we would utilize it). Main concern is dehumidifier.

The dehumidifier system would only run 6-8 hrs a day at most. It’s a stand alone system as shown in photos above.

We are in Mississippi and on an island so humidity is an issue. When we close up camp for a few days/weeks the inside humidity level will rise and cause mold to grow on ceilings.

Thanks for the responses!
 
This issue with "small window AC" is the power requirements very widely, in addition to insulation factor of the room, temp differences, etc. My SEER 33 split unit AC in my bedroom draws 800 watts for the first hour, then drops down to maintaining the temp and drawing 60 watts all night. This is in a highly insulated house with the outside temp at night being 85F. My solar system can handle the load without issue.

The AC unit in my camper, not know for efficiency, poor insulation walls, draws 1,500 watts, all night under the same conditions. My solar system could not handle the load all night.

Your best bet is to get a killawatt meter, plug it into the AC and dehumidifier, let them run over 24 hours under expected conditions, and get some real world numbers.
 
Makes sense. We are in the process of roughing in and insulating the house right now. It will be several months before I would be able to run a true test.

Forget the idea of the window unit for now. If anyone could help with the requirements base on the dehumidifier on the spec sheet of OP that would help for now. I have several decisions to make based on materials to use going forward. If I can get an reasonably priced solar set up for running dehumidifier I would use standard drywall for interior. Without the dehumidifier the cost is greatly increased for using a paperless drywall. So basically if the cost difference will in the two types of drywall will offset the cost of solar and dehumidifier system it would be beneficial to do. Cost in drywall difference is over 10k.
 
So if you are in that stage of construction, I highly suggest looking into split unit ACs. The good ones have a "Dry" mode that work as a dehumidifier. They tend to be far more efficient then stand alone units. It's far cheaper to save power, then to generate it.

I have this model in my bedroom.
 
That standalone dehumidifier, running 8 hours a day, will use 13kwh of power. (13.5 amps x 120v x 8 hours = 12,960wh a day) You can use a calculator here.

So, back of the napkin math,
5kw of solar panels + mounting = $2,500
32890 watt hours of battery = $25,000
5kw Inverter combo = $5,000

So $32,500 should be about right. This is very rough guess and if you DIY and shop around, you can go cheaper.
 
Would love to do Splits but they are not feasible for our lay out. We have 14 different rooms so our guest and members have their own rooms. We would have to have a split in every room. I could possibly add a spilt to both main rooms on 1st/second floor and leave all doors open when we are not there. That would be reasonable cost wise and from what your saying would likely keep the humidity down.
 
Another option may be to just run small stand alone dehumidifier on each floor. They would likely have to be replaced often and life expectancy isn’t as long. If I’m calculating correct they would require much less power than the whole home system.
 

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Here are specs if a stand alone dehumidifier with a timer so we could cut down on run time as needed.
 

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Here are specs if a stand alone dehumidifier with a timer so we could cut down on run time as needed.

If you look at the efficiency ratings of the two units, the first one does 5.7 liters per kwh and the smaller portable one does 1.3 liters per kwh. So the hole house one is far more efficient in removing water for the power is consumes. It's just uses a lot of power. It's basically a AC unit in itself as that is how they work.

What are your current plans for AC in the building? Could you do a per room split unit and not do other AC/Heating?
 
Right now we are roughed in for a 4 ton unit upstairs and a 5 ton downstairs. The cost of both units installed is much less than doing splits in each room.
 
You sure on that? They make up to 8 zone mini splits. Regardless, I am a hobbyist AC guy at best, so I am going to make the assumption that your AC guys knows best. That is a big building.

But the original guesstimate of $32k for a system that can power the hole house unit off solar is the best number I can come up with given your building. I am unsure if the small portable units will remove the liters you need for that size of space.
 
Just for kicks, I would contact a number of commercial hvac firms with engineers on staff. Maybe your AC contractor can do this. Before you close stuff in, have them explore a ducted whole-house air exchanger with dehumidification as part of the AC system as that may “cost” a whole lot less to run than AC or an effective but not integrated dehumidifier. Sortofa low volume air conditioner that’s mostly ineffective for cooling but dries the air.
I’ve heard of such things but here in New England never had a call to acquire that for any projects.
 
RyanG222:

You seem to be dead set on dehumidifiers, and are discounting some good advice as to other options. Let me phrase this a different way: it would be a good idea to have a load calculation done for your method of construction, and then pick your system accordingly. There will be a cost, of course, but you might be surprised at the results.

I've done a lot of HVAC work, boilers, mini-splits, etc. In most cases, A/C will outperform dehumidifiers, and it has the added benefit of actually cooling specific areas. My experience is that once you have worked with a properly executed mini split system, you won't go back to conventional ducting. In your case, you could put a couple of mini splits in some strategic locations to dehumidify the bulk of the space, and then have a different solution for particular rooms. And, like the other poster mentioned, there are many units out there that can handle multiple heads.

There are many, many options for how you actually set them up. Fan coils, ceiling cassettes, direct 1 to1 units, consoles, etc. And they are inverter driven with soft starts. Very efficient, quiet, and much easier to run off a PV system.

I've owned commercial buildings that had mixed use, with businesses and apartments, and put in a lot of 3-7.5 ton units. Never again. They waste enormous amounts of energy, and are hard to control in a manner that suits a variety of inhabitants. We now do hydronic and mini splits. Some VRF. Google that if you want to know more.

Good luck with your project!
 
Running Dehumidifiers in the summer when you have AC is just silly. A dehumidifier is just an air conditioner that doesn't dump the heat produced out side. So they cool the air down to get the moisture out and then heat is back up. AC cools the air down and gets the moisture out but dumps the heat created outside.

If you need dehumidification in the winter and your outside temps get cold then they are ok to run.

One minisplit or window unit can do the dehumidification you need and provide overall comfort at the same time.
 
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