Advice Requested on Cooling EG4 System

[wpns]

A mini spit can throttle all the way down to 200 to 400 watts and still maintain the set point once it's got there.

While it _can_, in reality there's a lower limit, below which it starts cycling on and off:

And either way, the number that it idles down to will depend on how much heat energy it has to remove, which is somewhat independent of the size of the unit.

 

[Quattrohead]

Inverter based AC's never turn off the compressors.
They get down to the Target Temp and then use the lowest compressor speed "Idle" to maintain the Temperature.

Both of mine absolutely do turn the compressor and fan off but keep the inside fan running dead slow.

 

[rogerheflin]

Inverter based AC's never turn off the compressors.
They get down to the Target Temp and then use the lowest compressor speed "Idle" to maintain the Temperature.

I have a 5-ton 20 seer central air inverter unit(variable compressor, variable fan, and variable gas valve) and it definitely turns off everything but the control board when it does not need to cool or heat, unless I override and have told it to run the fan all of the time. Any other way would FAIL energy star (and whatever is similar in other countries) if it only dropped to a 200-400w idle at all times. Turning off drops the power consumption so much that cycle off/on as needed is needed to pass any efficiency requirement.

 

[robby]

Both of mine absolutely do turn the compressor and fan off but keep the inside fan running dead slow.

My Panasonic Mini splits are always running the compressors.
That is what an Inverter AC is all about, it matches the heat being added to the room and keeps the temperature constant. There is always heat being added to a room in the summer! What Brand/ Model AC is this?

 

[wpns]

My Panasonic Mini splits are always running the compressors.
That is what an Inverter AC is all about, it matches the heat being added to the room and keeps the temperature constant. There is always heat being added to a room in the summer! What Brand/ Model AC is this?

My old Lennox and my new Mitsubishi both goto zero (or just fans/remote control receivers) when they get low enough. While we'd like to think of them as having an infinitely adjustable range, I'd bet it's an easy power of two(*), and as @rogerheflin said, this allows them to go to essentially zero power which makes their Energy Star numbers look good.

I'm hoping more than 16, though you never know, there are 3 motors, so they'd claim 12 bits or 4096 discrete control points. While they could do 256 steps, I bet someone saved a penny...

 

[rogerheflin]

My old Lennox and my new Mitsubishi both goto zero (or just fans/remote control receivers) when they get low enough. While we'd like to think of them as having an infinitely adjustable range, I'd bet it's an easy power of two(*), and as @rogerheflin said, this allows them to go to essentially zero power which makes their Energy Star numbers look good.

I'm hoping more than 16, though you never know, there are 3 motors, so they'd claim 12 bits or 4096 discrete control points. While they could do 256 steps, I bet someone saved a penny...

Really slow motor speeds don't work well (for compressors--the fluid being compressed leaks out of the seals faster than the motor compresses it) so technically they aren't infinitely adjustable there is a min speed below which compressor won't work.

 

[robby]

While it _can_, in reality there's a lower limit, below which it starts cycling on and off:
View attachment 253577
And either way, the number that it idles down to will depend on how much heat energy it has to remove, which is somewhat independent of the size of the unit.

I don't have dedicated CT's on My AC units but that graph is saying to me that it only cycles off for 3-4 minutes! every hour and ranges from 580W to 350W about 99% of the time. I am assuming that at 13:30pm you shut it off for about 80 minutes?
Mine goes from about 1200W on high speed down to about 350W on low speed.
Its seem to have about 3 power levels, but the high speed is only on until the room cools down, maybe for 45 minutes when I first turn it on.
Then like yours I am pulling 350W on low speed, but on mine it is pulling 350W of power both day and night which was a significant savings over my old compressors that would kick on at 1000W then run for an hour and then stop for 10 minutes and the kick on again for 30 minutes rinse and repeat all day.

 

[Quattrohead]

I think all of the cheap Amazon Chinese type mini's will completely shut down the compressor and fan on the outside unit.
But they do keep the indoor fan running to monitor the temp and keep the room air moving.

 

[robby]

I think all of the cheap Amazon Chinese type mini's will completely shut down the compressor and fan on the outside unit.
But they do keep the indoor fan running to monitor the temp and keep the room air moving.

You are probably right.
I have only ever bought one no name Chinese Inverter AC in desperation and I was really annoyed that after just one cleaning I could not get the front panel to latch down properly, it vibrated when the AC was running so I had to tape it down.

 

[akitawpo]

I live in Puerto Rico (very hot / humid also) and have two 6000 Xps. Started with some fans on the shed they were installed. Even with the fans on the shed where the XPs were installed, once solar started the temps I saw reported by Solar Assistant (no clue where the reference inside the inverter was) were creeping to 120 degrees. And this was not at full sun / production. So I decided on getting 12k Mini split set to 72 degrees. On 8500 watts solar production and 1000 watts inverting covering house loads and the ac temps reported on SA sat at 82 degrees.

 

[rogerheflin]

I live in Puerto Rico (very hot / humid also) and have two 6000 Xps. Started with some fans on the shed they were installed. Even with the fans on the shed where the XPs were installed, once solar started the temps I saw reported by Solar Assistant (no clue where the reference inside the inverter was) were creeping to 120 degrees. And this was not at full sun / production. So I decided on getting 12k Mini split set to 72 degrees. On 8500 watts solar production and 1000 watts inverting covering house loads and the ac temps reported on SA sat at 82 degrees.

82 in the inverter with the room temp 72? Any idea how much power the mini-split was consuming? I would suspect that you could turn the temp up a bit higher as the internal inverter temps will be expected to go 10-20 above ambient and the inverter is rated to run in fairly hot outside temps, meaning that 120 internally is likely nothing to worry about (much like a computer cpu). They rate the inverter to run 113F ambient(they do not say what the internal temp will be for 113F cooling air) and if that is correct the internal fans would be sized and spin up so that it cools enough with a high ambient temp.

 

[Quattrohead]

Both of my 18kpv sit around 104 to 109F internally until they are working the MPPT's hard, then they peak up to 115F. At this point though, over 6kw of PV has kicked the fans on and it actually cools down to around 91F.
All these are with the garage AC set to 78F.

At the previous house, they were in an unconditioned garage that regularly hit 100F and the 18kpv would hit 140F before spinning up the fans.

 

[akitawpo]

82 in the inverter with the room temp 72? Any idea how much power the mini-split was consuming? I would suspect that you could turn the temp up a bit higher as the internal inverter temps will be expected to go 10-20 above ambient and the inverter is rated to run in fairly hot outside temps, meaning that 120 internally is likely nothing to worry about (much like a computer cpu). They rate the inverter to run 113F ambient(they do not say what the internal temp will be for 113F cooling air) and if that is correct the internal fans would be sized and spin

I guess from an electronics perspective I like the idea of having it working a little "colder". Efficiency should be better and longetivity too. AC consumption is around 600 watts when sun its on full blast and prooducing 8500 watts of PV.
I do agree that having it at 78 deg should work too.

 

[jolondon]

There is definitely a trade-off between trying to cool a system using a mini split and using a significant amount of your stored solar power just to keep your solar power system cool.

Note that if you are near the ocean, those rackmount batteries will not last long, as the salt in the air (and the dust) will deposit a conductive/corrosive material, which cooling fans will only make worse. In that case, you either need to use the all weather wallmount batteries, or provide an air-conditioned space for the batteries to live in.

I am very kilometeres away from the ocean so no salt in the. Just hot humid area although the shed holding the batteries/inverter is entirely in teh shade. I wonder if I should try and use the fan first. Is there any data on how 85 degrees/85% humidity will impact lithium batteries and an inverter? The draw of these 12000 btu ac's is listed as around 1.2 kw but I suppose if it is running slowly..and i am looking at a SEER 21 high efficienty unit..the power consumption could be much less.

 

[jolondon]

While it _can_, in reality there's a lower limit, below which it starts cycling on and off:
View attachment 253577
And either way, the number that it idles down to will depend on how much heat energy it has to remove, which is somewhat independent of the size of the unit.

thanks..what is the number of btu and seer rating on your AC?

 

[jolondon]

I live in Puerto Rico (very hot / humid also) and have two 6000 Xps. Started with some fans on the shed they were installed. Even with the fans on the shed where the XPs were installed, once solar started the temps I saw reported by Solar Assistant (no clue where the reference inside the inverter was) were creeping to 120 degrees. And this was not at full sun / production. So I decided on getting 12k Mini split set to 72 degrees. On 8500 watts solar production and 1000 watts inverting covering house loads and the ac temps reported on SA sat at 82 degrees.

So the AC is using 1000 watts to cool from 82 to 72 degrees?

 

[akitawpo]

So the AC is using 1000 watts to cool from 82 to 72 degrees?

No, at that time I had my whole house running of the imverter. My usual house consumption is 500/600watts with the things I had on at the time. So I would guess 400watts trying to cool the shed at 100 deg ouside temp and with the full solar production charging batteries too.

 

[wpns]

thanks..what is the number of btu and seer rating on your AC?

Mitsubishi 18KBTU is 18 SEER

https://www.mitsubishitechinfo.ca/sites/default/files/SB_MSZ-HM18NA-U1_MUZ-HM18NAH-U1_202210.pdf

 

[jolondon]

No, at that time I had my whole house running of the imverter. My usual house consumption is 500/600watts with the things I had on at the time. So I would guess 400watts trying to cool the shed at 100 deg ouside temp and with the full solar production charging batteries too.

okay..do yoiu know the seer rating on the AC? Also what is the official consumption level of the AC....it should say so in the specificatoins. If it is similar to mine I can guess that I can run at 400 watts too.

 

[jolondon]

No, at that time I had my whole house running of the imverter. My usual house consumption is 500/600watts with the things I had on at the time. So I would guess 400watts trying to cool the shed at 100 deg ouside temp and with the full solar production charging batteries too.

so are you are expending 400 watts to cool 500 watts of consumption?

 

[jolondon]

The 10" one I linked will move 630 CFM of air.
The 6" Inline duct one will move 400 CFM of Air.
I have purchased and used the 4" , 6" and 10" AC Infinity fans. For what you are doing get the 10"

BTW a typical Inverter Fan moves about 100 CFM on the highest speed and there may be two on the Inverter.
That difference is why a 10" high speed fan can compensate for hotter and more humid weather.

BTW make sure the cabinet is big enough to work with and has space for expansion should more batteries need to be added.

okay two more questions. I understand the average recommended cfm is 1 cfm per square foot using lxw calculation. If I just cover the four batteries and the inverter as you suggest that would be 43 square feet or 107 square feet including height (2m x 2m x 2.5). At the most that is 107 CFM. Isn't the fan you recommend at 631 CFM ridiculous overkill? The entire bodega is about 322 square feet. The walls are prefab concrete and I will someone seal the .5 meter ventilatnoi space toward the roof. Couldn't I just ventilate the entire spaceusing that fan? Also, I noticed that this fan is 830 CFM, more than the one you recommend. I would also be able to point it righer at the inverter fans. Thoughts?

 

[rogerheflin]

okay two more questions. I understand the average recommended cfm is 1 cfm per square foot using lxw calculation. If I just cover the four batteries and the inverter as you suggest that would be 43 square feet or 107 square feet including height (2m x 2m x 2.5). At the most that is 107 CFM. Isn't the fan you recommend at 631 CFM ridiculous overkill? The entire bodega is about 322 square feet. The walls are prefab concrete and I will someone seal the .5 meter ventilatnoi space toward the roof. Couldn't I just ventilate the entire spaceusing that fan? Also, I noticed that this fan is 830 CFM, more than the one you recommend. I would also be able to point it righer at the inverter fans. Thoughts?

Most of the fans from that company (he mentioned) come with speed controllers that allow you to change the speed.

The ones I have (6") have 6 to 8 speeds (various models) and go from quiet to quite loud. So long as you have a variable speed you will be able to try different speeds.

 

[robby]

Don't blow the fan air directly onto the equipment. So long as the room is sealed properly a forced air system works better if you are pulling out hot air near the Top of the room with the Fan and sucking in cooler air from the bottom through a vent.
The $80 dollar Infinity controllers have a mode that allows you to set a temp scale so that the Fan throttles up or down according to the inside target temperature.

 

[jolondon]

Don't blow the fan air directly onto the equipment. So long as the room is sealed properly a forced air system works better if you are pulling out hot air near the Top of the room with the Fan and sucking in cooler air from the bottom through a vent.
The $80 dollar Infinity controllers have a mode that allows you to set a temp scale so that the Fan throttles up or down according to the inside target temperature.

thanks.

 

[k490]

Thanks..what is the temperature now of the room or near the inverter?

I set mine to 82-83 near the inverter. When I want to work in the garage ill set it to 79F it felt nice to me which oddly in my house using a 4 ton old roof top single compressor AC unit to feel comfortable it had to be set to 75F. I suspect the difference is the fact that the mini-split evaporator is in the room not losing so much in the duct work. I never had a mini-split was really impressed the other thing is the mini-split draws hot air in from the top which is more efficient where a ducted system hot air can get trapped in rooms. If I hadn't just bought my goodman ducted rooftop unit 2 years ago I would have converted the house to ductless.