Can an 800 sq. ft. Cabin be Cooled with One Window AC Unit?

[NEpowerandlight]

That's what I'm afraid of. The ceiling is beautiful from the inside, with whitewashed pine boards and natural-color exposed rafters, but I don't think it is insulated hardly at all. As far as I can tell, it's a layer of boards covered with tar paper and then a metal roof. It's possible that the layer of black material between the boards and the metal is not just tar paper, but it's not very thick in any case. I may have to forego the beauty and add insulation to the visible underside of the ceiling.

I've read a lot about the benefits of a mini-split, most notably better efficiency. However, every time I compare them to window A/C units of similar capacity (24,000 BTU) it seems like the wattage consumption is about the same, and the window units are about a fifth of the price. :-/

If you want the warranty that comes with most mini splits you need a licensed HVAC contractor to make the line set connections. Even my utility company wanted the contractors number before I would be eligible for a rebate. That's gonna cost you an extra $500 - $1500 or higher if if you have multiple indoor units.

I just moved from a 1400 sq ft. home that I could cool with 2 10k btu window units with no problem. The house was small cape cod built in the 50's and not well insulated. I could run one unit at a time on 95% of the days. Downstairs during the day and upstairs at night.

The 2nd floor was converted in to living space without insulating. It would be 20 degrees hotter up there i the summer and 10 - 15 degrees cooler than the rest of the house. They did run one duct to the second floor to heat 450 sq ft of poorly insulted space.

The "new" house has a 20 year old propane forced heater and a central air unit. The propane bill was crazy high last year so I bought 2 mini split system to replace them. The innovair 30.5 SEER 12k unit and a 18K Daikin 2 zone system. Total cost $5k for both and $1700 for the line set connections by a licensed HVAC contractor. I installed the indoor units minus the line sets and the outdoor units including the electrical connections.

Looking at my electric bill I can see that on a cool night (40's) between midnight and 6 am they are using a couple hundred watts at most. On a cold night ( teens) they pull 300 - 500 watts max over that 6 hr. period. From what I understand they burn more electric producing heat that they do cooling, but I could be wrong.

Sorry for the wordy response but I saw similarities since we used window units for 30 years and they were fairly cheap to run during summers in NJ.

 

[Vigo]

From what I understand they burn more electric producing heat that they do cooling, but I could be wrong.

I think that's usually true, but just has to be kept in context that a mini split running at its absolute worst efficiency is still making heat more efficiently than a space heater or other electric heating element, and usually it's massively better.

 

[SparkyGage]

I know this is an old thread, but I thought I would share my experience (draw your own conclusions and adjust for your climate/conditions):

Building: 20x40 Red Metal roof and Tan Metal Walls on 2x4 wood stud frame
Foundation: concrete slab
Insulation: Roof and eves are spray foam, walls are fiberglass batons
Doors and windows: Insulated vinyl
Ceilings: 8' residents area, 10' shop area.
Summer Shading: West (40') wall shaded constantly, East (40') gets full sun, South (20') wall and doorway gets full sun until noon.
Location: Arkansas. Summer highs 100-110, humidity can be above 60% at almost any temperature.
Heat sources: Refrigerator, Freezer, various electronics.
One full time occupant.

This building is cooled with a 9k 110v window AC unit that is located on the east wall window and mainly works to cool the back (residents) half. A curtain separates the doorway from the back half to the front. In the front I have a de-humidifier set to 55%.

July-August results: the residents side stays in the mid 70's and the shop side stays in the low 80's. Ceiling fans help circulate the air. We've had a few high humidity nights my daughter has come in and spent the night in the main house, but for the most part is comfortable in the apartment. My shop side is fine for me most of the time I need it. For us, humidity is the big factor in whether it is "cool" enough to occupy: the lower we can get the humidity, the higher the temp we can regularly handle.

Future plans: I am intending to put in a pair of 9k mini-split heat pumps, more for heating efficiency and free up the window.

 

[Doggydogworld]

This building is cooled with a 9k 110v window AC unit that is located on the east wall window and mainly works to cool the back (residents) half. A curtain separates the doorway from the back half to the front. In the front I have a de-humidifier set to 55%.

Interesting info. That's good performance from a window unit. What type of dehumidifier? Most heat up the air.

Also, I guarantee your relative humidity is not >60% when the temperature is >100F.

 

[SparkyGage]

Interesting info. That's good performance from a window unit. What type of dehumidifier? Most heat up the air.

Also, I guarantee your relative humidity is not >60% when the temperature is >100F.

A Frigidair 50pint in the shop. In july and august I empty it daily. About $350 at Home Depot. I have one in my master bath as well. Yes, it does have a slight heating affect when it first kicks on, but somewhere along a "run" it cools for a few minutes. Don't fully understand the process it uses, just know it lowers the humidity enough to keep the house comfortable on a higher thermostat setting.

Arkansas humidity, particularly in the Ouachita and Southern Ozark Mountains, is jungle like. South West/Central Arkansas along the Louisiana boarder is river bottom and swamp. So while 60%+ at a 100 degrees is not a norm, we will get summer pop up showers that will pour for 5-15 minutes, then steam off, so yes we can get these crazy high humidity for a few hours after. Right now where I am we have "nice" weather meaning it's 87 and 59% as I'm typing this.

 

[glandpuck]

It seems to me you are asking the wrong question. Say you asked the following: I have an 800 sq. foot cabin that I want to cool and I have this much power in wattage available. What would be the best way to do it?

Now, I know that I purchased a 5,000 BTU cheap portable window AC unit from Lowes in California. Running on max it consumes about 500-600 watts top at 120 volts AC. Ambient air can be 105 and unit blows about 50 degrees F. So if your bed were near the window and the AC was blowing across you, you would sleep just fine.

 

[Doggydogworld]

A Frigidair 50pint in the shop. In july and august I empty it daily. About $350 at Home Depot.

They're basically small air conditioners. If you buy a tiny window A/C but instead set it over a bucket in the middle of the room you have yourself a dehumidifier. Water will condense out of the humid indoor air onto the cold evaporator coil then drip into the bucket.

Of course if you put that A/C in a window, as intended, it'll reduce indoor humidity while also pumping heat from indoors to outdoors. So your indoor air gets both drier and cooler.

Dehumidifiers don't have an "outdoor side". So they first blow indoor air over a cold evaporator coil, just like an A/C. But then they blow that same air over the hot condenser coil, which heats it right back up. So that air goes from warm and humid, to cool and dry, to warm and dry. Plus the pumping process itself creates extra heat and, unlike a window A/C, a dehumidifier has no way to exhaust it to the outside air. So the air ends up warmer than it originally was.

Right now where I am we have "nice" weather meaning it's 87 and 59% as I'm typing this.

That's a dew point of 71F, common in humid areas. Corpus Christi, TX dew point is 74F as I type this. 110 and 60% would be a 93F dew point. That's never been recorded in the US. Freak weather events have produced a couple of 90s and an unverified 91.

Record Dew Point Temperatures | Weather Extremes

Just recently the Minnesota State Climate Office issued a statement declaring the 88° dew point temperature measured at Moorhead (on the Red River across from Fargo, North Dakota) between 7pm and 9pm on July 19, 2011 as a new all-time state record for the highest such reading ever observed. This...

www.wunderground.com

 

[SparkyGage]

They're basically small air conditioners. If you buy a tiny window A/C but instead set it over a bucket in the middle of the room you have yourself a dehumidifier. Water will condense out of the humid indoor air onto the cold evaporator coil then drip into the bucket.

Of course if you put that A/C in a window, as intended, it'll reduce indoor humidity while also pumping heat from indoors to outdoors. So your indoor air gets both drier and cooler.

Dehumidifiers don't have an "outdoor side". So they first blow indoor air over a cold evaporator coil, just like an A/C. But then they blow that same air over the hot condenser coil, which heats it right back up. So that air goes from warm and humid, to cool and dry, to warm and dry. Plus the pumping process itself creates extra heat and, unlike a window A/C, a dehumidifier has no way to exhaust it to the outside air. So the air ends up warmer than it originally was.


That's a dew point of 71F, common in humid areas. Corpus Christi, TX dew point is 74F as I type this. 110 and 60% would be a 93F dew point. That's never been recorded in the US. Freak weather events have produced a couple of 90s and an unverified 91.

Record Dew Point Temperatures | Weather Extremes

Just recently the Minnesota State Climate Office issued a statement declaring the 88° dew point temperature measured at Moorhead (on the Red River across from Fargo, North Dakota) between 7pm and 9pm on July 19, 2011 as a new all-time state record for the highest such reading ever observed. This...

www.wunderground.com

Ok, but you didn't misunderstand me to say that I was using the AC in the middle of a room and not in a window, correct?
I assumed the dehumidifier had generated some heat (anything that uses electricity does), but it doesn't seem to be an issue. This one is rated for about 500wt. Before my daughter moved into the apartment side, I wasn't running an AC in the shop at all and it still stayed in the 80s during the summers of '20 and '21 despite 100F outside temps (set for 50%). So the dehumidifiers net heat output is not significantly more that that of the refrigerator and freezer (the other two items that ran all the time in that building). Airflow through the two entrances are the main sources of moisture in as it's fairly well sealed, and also low traffic.

As to the dew-point and humidity, I see what you are saying but 100F at 60% humidity is a dew-point of 83.6F and I found two entries for official NWS readings of 84 in Arkansas and 4 more for 83 ( I could only find records for the four main Arkansas NWS stations https://www.weather.gov/lzk/wxcntl3.htm ). I completely agree that it's probably not state wide, but I still believe after one of these pop up showers, a hygrometer would register 60% for 30minutes to an hour while it steams off. (I'm sure the NWS must factor out spikes from their readings).

Regardless, like the Texas coast, summer in Arkansas is a sticky sauna.

 

[Whats-n-Watts]

I know this is a stupid question, and there are many factors that go into a cooling design, way more than we could dig into here, so this is a Hail Mary play. Please be kind even if you think I'm an idiot. The downstairs is 800 ft^2, of which 180 ft^2 is the bedroom. The living room and kitchen are part of one big open area. There is also a 200 ft^2 open loft area. The cabin has an 9/12 pitch metal roof and insulated pine walls. The ceiling is around 20 ft. up, I guess. The question is, hypothetically, is it possible to cool a whole cabin with one downstairs window A/C unit in the 24000 BTU range?

I'm cooling a 24x24 house single story with an open floor plan with ease using a 14,000 btu 115v window unit. That's in South East Ga. The house is properly insulated and all cracks were caulked during construction. Point being how efficient the home is determines how easy or difficult it is to cool or heat a house. Location plays a huge factor as well. We have 115 degree heat index days here. A cooler climate of course requires smaller cooling capacity.
Many variables to your question.

 

[Solarcabin Channel]

Looks like this is an old post but I will chime in anyway.

Depends on how insulated and sealed the house is and how many BTU the AC unit puts out and average ambient temperature.

I would say yes because a 5000BTU window unit will cool down my 400 sqft cabin on low and was too cold for me so I switched to a 45 watt evap cooler.

 

[hvacsolarcanada]

I personally installed a kanartic heatpump with only 4x 400 Panels with enough batteries for extended solutions... but now it only run the heatpump for the winter (testing)
I have the DIY 12k BTU model which I installed myself. Installation was very easy and when I had a question regarding wiring I got a response to my late evening email almost immediately at 10pm which really impressed me. The wireless control of the unit is very convenient. I use the app to control my unit and can turn it on and off using voice commands via my Google Home. The cooling and heating is fantastic but I was skeptical the unit would produce heat when outdoor temps were -30c or cooler. My friends that have other mini-split brands told me their units stopped producing heat when outdoor temps were at about -15c. This morning it was -32c outside here in Manitoba when I turned my mini-split on and the air coming out of the unit which I measured with a laser temperature gun was 37c!!! Wow am I impressed!


I plan to install a 24kBTU later on other part of the cottage :

DIY Mini split ZERO Heat pump 24000 BTU 22.3 SEER High Efficiency 5M-1

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