Running 5000 BTU air conditioner solar

[J.P.M.]

Use the formula switching out EER and SEER to find watts. That is where you get doctored numbers to lead one way or the other.

SEER was developed as a single value for a "typical" U.S. climate with significant cooling loads. As such, it has shortcomings that can lead to bad decisions.

There are approximate formulas to compare EER to SEER. For a particular application, the one line formulas are mostly useless. I understand the differences of how COP (EER) and SEER are calculated. My point is that using SEER, partly because of the bin method it uses (which is no more than the frequency distribution of cooling hours throughout the U.S.), but other factors as well besides regional weather/climate variation. An SEER's relevance to reality in Minneapolis will be quite different than its relevance to reality with respect to weather/climate in Tucson. Mfgs. currently make furnaces with regional differences noted. It can be done. The regional inaccuracy is a key and crucial, but not the only weakness of the SEER logic

Another shortcoming of SEER is that it takes no account of any latent cooling load with no specific reference to humidity control, either in what, or how, such latent loads may affect performance or comfort. As building envelopes become tighter, that humidity control becomes more important for comfort and health reasons.

Another consideration, although I can't rag on the SEER method for this one too much, is that it doesn't consider duct heat gain (think of ductwork in an uninsulated attic/crawlspace) or how duct pressure drop losses will affect flow rates and thus thermal performance. For the most part those types of losses only occur in distributed systems and don't occur in minisplits. Just muddies the water more.

I'd also note that SEER applies ONLY to devices used for cooling, and not to heat pumps. For that application, Heating Seasonal Performance Factor is used (HSPF). The methodology is somewhat similar, but the numbers are numerically a whole lot smaller, reflecting the reality that getting heat out of things that are already relatively cold ("pumping " heat "up") is relatively harder to do. Typically, and while not endorsing that method for rating heat pump systems any more than the SEER method for rating cooling systems, a typical air source heat pump HSPF might be of the order of 8 - 10 or so translating to a COP of ~ 2.3 - 2.9 or so, depending on climate. And that's before considering parasitic but necessary losses for such things as coil defrost in high(er) dewpoint applications/climates.

Thus, using SEER and applying it to heat pump systems in heating mode can give an already murky situation confusing twist. If that ACDC12C unit with a somewhat incredulous SEER of 22 or so, and BTW up from a more quantifiable and reality based EER of 12.5 is somehow thought to have that type of performance in heat pump mode, doing so may lead potential users astray as to what's the best method to supply heat to a dwelling.

[littleharbor]

Down in Baja, some nights we prefer a pedestal fan aimed right at us to the AC with windows closed up. The fans evaporative cooling on otherwise sweating, hot skin works pretty well. I'm laughing, thinking of the mental picture this explanation may cause, but from experience I can say, the fan really works. Ceiling fans look nice but are just about useless in this scenario.

[Bala]

So you have cold air down low and hot air higher up. I've wondered about doing something with some big ducting up to the house from the creek area then a very tall heat absorbing chimney. The heat rises up the chimney. During the day the effect can be amplified by the sun heating up the chimney also. As long as you keep the house closed up except those ducts maybe you could pull in passive cool air. If it wasnt quite enough maybe a small battery and solar panel system could run a fan to help at night. That or just go sleep by the creek

The worst time here when you would really need cooling is night time, very high humidity. So if I were to put in a pipe I would need a decent fan, so it would be a drain on my existing system. A lot of continuous watts of a long time. There is no way I could close up the house, it would be to stuffy.

I could sleep by the creek but the mozzies would be horrendous.

This house was built for no A/C, if it gets to a point where we cant stand it any longer I will sell up and move to a house with mains power and then have all the A/C I want.

[Sunking]

???

Use the formula switching out EER and SEER to find watts. That is where you get doctored numbers to lead one way or the other.

[bcroe]

The difference in the COP for refrigeration (3.66) vs. the COP when the unit is in
heat pump mode (3.42) is inherent in the thermodynamics

My view is simpler. When heating, the energy running the compressor contributes to the output.
When cooling, that energy must first be removed, the remainder goes to cooling. Bruce Roe

[bcroe]

Lacking complete figures, I note a few other things. The inverter driven compressors seem to provide
advantages, and the latest units seem to use 410A refrigerant. I expect a small window shaker will
be completely out of the running.

But given reasonable performance, the determining factor might here that direct PV panel operation is
possible. In my case effective heat pump operation down to -13F is the most important. Bruce Roe

[nomadh]

I live in the tropics so the ground is not cold but there is a deep creek behind the house and the air is cooler down the bottom of the creek, I did think about putting in a pipe and fan to draw the cool air up.

But being off grid generally means you are a power saver/miser or very rich, so the gain from what little cool air I would get was not worth the sacrifice of power.

I have seen and read about quite a few off grid homes, they are portrayed as being the best thing since sliced bread, but you dont very often see follow ups in 5 years to see if their batteries are still ok, or how much generator run time they need to live the life they want to.

My house is just as unbearable during the night when it is monsoon season so having an A/C unit that only runs during the day is not worth my while.

I suppose what Im trying to say is do a lot of research and consider all factors, not just sales hype and what you want to hear.

So you have cold air down low and hot air higher up. I've wondered about doing something with some big ducting up to the house from the creek area then a very tall heat absorbing chimney. The heat rises up the chimney. During the day the effect can be amplified by the sun heating up the chimney also. As long as you keep the house closed up except those ducts maybe you could pull in passive cool air. If it wasnt quite enough maybe a small battery and solar panel system could run a fan to help at night. That or just go sleep by the creek

[J.P.M.]

Yep like SEER.

???

[Sunking]

At the end of the day, the COP (and EER - and note, not SEER) is a much more reliable number to hang a hat on. It'll be subject to much less B.S. manipulation.

Yep like SEER.

[J.P.M.]

Yes it is, as listed on my ENERGY UNITS sheet awhile back. For the record the heat pump
I mentioned is EER/COP of 12.5/3.66 for cooling and a 3.42 COP for heating. If you can find
those specs on any lower tech unit, I would bet this one is much superior, before we even
start considering losses in things like charge controllers, batteries, and inverters. Bruce Roe

Those and other things like fans or pumps, coil heaters for frost prevention, etc. etc. are what I learned to call parasitic losses. They will always be part of any operating system. The difference in the COP for refrigeration (3.66) vs. the COP when the unit is in heat pump mode (3.42) is inherent in the thermodynamics and is, at least as far as that science is concerned, separate from losses from supporting/ancillary equipment. The 3.66 COP for cooling may be a bit higher than some other units on the market, but not remarkably so. I've got a 13 yr. old 5 ton A/C unit that has a measured COP of ~ 3.2. Usually, but not always and not inherently guaranteed, the larger the unit, the higher the COP. A lot of it has to do with the working fluid and vapor pressure-temp. relations. See P-V and T-S diagrams from thermodynamic or HVAC texts. There's a lot more to consider with respect to safe, serviceable, reliable and economical refrigeration/heat pump systems design than COP alone. Most operate a long way from Carnot efficiency for a lot of practical reasons.

At the end of the day, the COP (and EER - and note, not SEER) is a much more reliable number to hang a hat on. It'll be subject to much less B.S. manipulation.

[Sunking]

Real simple: divide the EER of a unit (not the SEER) by 3.412 and Voila' COP.

The magic of 3.412 and another real useful formula from 3.412 is: How many watts will that Window Shaker use?

Watts = BTU / EER

[bcroe]

Real simple: divide the EER of a unit (not the SEER) by 3.412 and Voila' COP.

Yes it is, as listed on my ENERGY UNITS sheet awhile back. For the record the heat pump
I mentioned is EER/COP of 12.5/3.66 for cooling and a 3.42 COP for heating. If you can find
those specs on any lower tech unit, I would bet this one is much superior, before we even
start considering losses in things like charge controllers, batteries, and inverters. Bruce Roe

[J.P.M.]

I am in agreement, the problem is getting every units COP to use in comparisons. Bruce Roe

Real simple: divide the EER of a unit (not the SEER) by 3.412 and Voila' COP.

[bcroe]

To my opinion only, that SEER crap was conjured up by marketers as little more than
yet another way to muddy the waters and separate folks from their money.

Better yet is to go by the COP of a device which is the ratio of the energy sought in either cooling (refrigeration),
or heating (a heat pump) to the energy that's input to achieve the desired result.

I am in agreement, the problem is getting every units COP to use in comparisons. Bruce Roe

[jflorey2]

I just saw the show on Discovery Channel building Off the Grid. This guy dug big Trench around his place set up ducting in the trench and had air being sucked out through the floor pumped through the tubing in the cold ground back into his place for AC. I wonder how cold it actually is.? Would this work in Florida?

It would work. It's expensive and you need a lot of land to do it well. A geothermal heat pump is a lot cheaper/easier to install.

I'm going to be on a tight budget .

Then off grid probably isn't for you.