Split AC Condensors in the sun vs shade and its efficiency? - Page 1
Forum section: electronics / general

author: Fried Chicken
author_rank: Regular Contributor
timestamp: April 13, 2025, 01:44:16 am
content: This genuinely could be a mythbusters question. I'm seeing not-that-much information about this online, and where it's discussed, there doesn't seem to be a consensus.With the apocalyptic summer around the corner, I noticed one of the Split AC condensers gets sunlight during the hot afternoon, the other is shaded by a tree. In my mind: of course solar heating is an issue. That condenser should be as cool as possible. The faster and harder that refrigerant gets cooled, the less the pump has to work, and the more efficiently the unit can remove heat from the house.That said, I see plenty of hvac condensers exposed bare on roofs without any shading or otherwise.Here's a reddit thread I found on the matter:https://old.reddit.com/r/explainlikeimfive/comments/vjyyrz/eli5_would_air_conditioners_be_more_efficient_in/The top comment claims it makes no difference.Other comments suggest it makes a difference, and AC condensers are thus intentionally placed on the shady side of the house.This commentreferences three peer reviewed articles on their placement (haven't looked at these yet).Finally I likeThis guy'sanswer:Quote from: that guyI like his answer, but I think he's missing a variable here:The efficiency of air conditioning units is not linear. As temperatures get higher the efficiency goes down, as the delta the compressor has to achieve rises. Say it's 95°F outside and you want to air condition to 75°F. That's 20°F of cooling. The sun heating the condenser unit could push that effective outside air temperature up to say 97°F, meaning a 22°F delta, an additional 10% difference. And then you factor in the compressors non-linearity, and that number becomes even worse.Anyway, I base this off of something I read during last summer's heat death, where the high electricity bills were explained by the decreasing efficiency of the AC units under those higher temperatures.I'd really like a clear answer on this... this genuinely feels like a mythbusters question to me.

author: John B
author_rank: Frequent Contributor
timestamp: April 13, 2025, 02:12:08 am
content: Even if the external sheet metal is heated, the real difference would be if the coils and fins themselves are being heated by the sun. If you can heat or cool the coils (depending on whether you're heating or cooling inside the house) then that of course would make a difference to efficiency.

author: bdunham7
author_rank: Super Contributor
timestamp: April 13, 2025, 02:30:23 am
content: Quote from: Fried Chicken on April 13, 2025, 01:44:16 amThe effect on the AC system is overwhelmingly based on the air temperature that it sees. I think the temperature of the case will have minimal effect on the air temperature when it is operating because a fan is moving large volumes of air through the system. So if the unit is in a spot where the air temp is high, then that makes a difference. Otherwise probably not.

author: Fried Chicken
author_rank: Regular Contributor
timestamp: April 13, 2025, 03:43:54 am
content: Quote from: John B on April 13, 2025, 02:12:08 amI would think it's a pretty safe assumption that the external sheet metal is getting heated, that will transfer into the incoming air... as well as the coils themselves being directly heated. That energy is definitely going into the unit.Quote from: bdunham7 on April 13, 2025, 02:30:23 amI like mr. reddit guy's BTU equation, but I can't help but think something is being overlooked in the equation.Anecdotal evidence suggests a "definite" difference, but the industry also isn't stupid. Were it so important, likely you'd see more condenser units with some sort of shading... but variables abound.

author: bdunham7
author_rank: Super Contributor
timestamp: April 13, 2025, 05:03:39 am
content: Quote from: Fried Chicken on April 13, 2025, 03:43:54 amThe issue wouldn't be the BTU/h capability of the system, it would be more about the heat capacity of the volume of air that is moving through the condensor unit and how much of the heat is transferred to the air before it goes through the compressor coils. I think that will be a very small percentage of the total energy incident on the system due to solar radiation.

author: Siwastaja
author_rank: Super Contributor
timestamp: April 13, 2025, 05:50:02 am
content: The fan pushes a lot of air through the coil, so actual air temperature dominates. That being said, sunshine also warms up air by warming surfaces like streets / walls, creating a hotter microclimate. A single tree would not do much to reduce that however, since air also moves. But maybe there can be several degrees C of difference between, say, Northern vs. Southern side of a building in a sunny day. So the answer is, you can see a difference but it's small. If you can freely choice the install location, you would be wise to choose a shaded location, but if that costs you any extra e.g. in refrigerant line length, that would probably eat any benefits both in efficiency and money.

author: ejeffrey
author_rank: Super Contributor
timestamp: April 13, 2025, 06:07:52 pm
content: Yeah my guess is that sunny vs shady side of the house would make a difference. Out directly in the sun vs shaded by a small tree but still surrounded by hot pavement would probably not make a big difference.Overall replacing stone and concrete with vegetation reduces the heat island effect and probably helps.

author: edpalmer42
author_rank: Super Contributor
timestamp: April 13, 2025, 06:45:04 pm
content: I've had personal experience with an air conditioner and sunshine.- 12000 BTU/hr- 10.7A rated power drain @ 120V- mounted in full sun, all day long- not a split unit - just a through-wall installation in an existing sleeveThe sleeve caused restricted airflow over the condensor coil that resulted in blowing the 15A circuit breaker. Improving the airflow reduced the current drain to ~13A. If the wind happened to blow the hot exaust air back towards the air intake, the breaker would still blow.Cooling the condensor with a water system dropped the current to normal, and even below normal, but because it was just tap water there was corrosion and build-up on the condensor. I live in a rather dry climate so there isn't much condensation on the evaporator coil. I believe that large commercial air conditioners sometimes use a distilled or filtered water spray to cool the condensor.Current drain on a cloudy day is always less than on a sunny day. Even on a 30C cloudy day, current drain is normal.My interpretation of all this is that anything that increases the temperature of the condensor coil is bad because the compressor works harder and draws more power and likely causes the temperature of the cold air to increase. This isn't a particularly high-tech unit so I don't know what would happen with an inverter unit, for example.

author: nctnico
author_rank: Super Contributor
timestamp: April 13, 2025, 07:02:29 pm
content: Quote from: ejeffrey on April 13, 2025, 06:07:52 pmIndeed. I have a large enough tree (Platanus) in front of my house to shade the entire front (including our bedroom). Once the tree gets leaves, the cooling effect is significant. I planted the tree there on purpose to keep the house cool.

author: Bill158
author_rank: Regular Contributor
timestamp: April 13, 2025, 08:34:32 pm
content: My compressor/condenser unit is on the ground of the South West side of the house. So I get the Sun shining on it in the afternoons on the two sides of the unit that have the most coil area and on one side with 1/2 of the full coil area. However there is storage shed directly across (3') from the unit that will put part of the unit (the 1/2 area and one full area) in shade when the Sun is past overhead and moving into the West (2pm). Then a carport awning that will shield the whole unit after about 4pm. So between the shed and the awning, the unit gets increasing shade (2pm to 4pm) most of the afternoon. Now I know this isn't exactly a "scientific" measurement, but monitoring the temperature of the air coming out of one ceiling vent I can observe the air becoming a few degrees F cooler when the unit is completely shaded after 4PM. I am "assuming" that the temp of the outside air across the coils is at least constant or maybe getting a little hotter between 2 pm and 4 pm. Therefore I "feel" that shading the coils from the Sun does make a difference in the cooling capacity. Of course there is always the humidity that is a factor. The higher the humidity then the warmer the air is coming from the ceiling vent. I can measure that. I have measured the condenser/evaporator coil's water output by collecting it and I can get up to 2 to 3 gallons of water per day in my area. I am sure that there are a lot of other factors that enter into this whole issue.I have always wondered why the evaporator's water wasn't directed back to the condenser coils and allow to flow over the coils, just like what happens in window units? This condensed water is "pure" and has no dissolved minerals in it, as best as I can measure with a soft water "hardness" measuring strip. It is pretty much "distilled" water. Then there are AC coil cleaners (Simple Green makes one) that will removed corrosion from the fins without harming them (according to the label). I applied a "treatment" a few weeks ago and will do this again in a few weeks.Just one man's opinion.Bill

author: UnijunctionTransistor
author_rank: Frequent Contributor
timestamp: April 17, 2025, 03:49:20 pm
content: As Bill158 mentioned, the window a/c units always (or almost always) have a ring around the condenser’s fan blades, to kick up the water condensation into the coils.It may not be much, but if manufacturers almost universally include it, it must increase the unit’s efficiency.By the same token, any additional external heating on the condenser’s coils may have a detrimental effect on the efficiency.It is true that many installations have the condenser/compressor unit exposed to the full sun, but I believe that the house design dictates this.Myself I have always placed the unit on a location where it is shaded starting from the afternoon into the evening, when the south Texas sun heats surfaces very significantly. I also surround the unit’s slab with grass, to minimize radiant heating into the unit.I know this is anecdotal, but from my discussions with acquaintances, I am always the one with the lowest summertime electric bill. I also use a programmable thermostat, which properly set up, it helps significantly.

author: Siwastaja
author_rank: Super Contributor
timestamp: April 17, 2025, 04:02:20 pm
content: Quote from: UnijunctionTransistor on April 17, 2025, 03:49:20 pmWindow units have more compact design leading to smaller coil and fan size and less airflow, therefore evaporating water helps more. This is even more important in those single-hose units that cause unwanted ventilation; these benefit greatly from limiting airflow to minimum and therefore spraying water to the condenser to maximize cooling with that limited air flow, to the point of some having a water reservoir where water can be added!Split units have large coil and large fan, so more airflow, so gains from spraying water to the coil would be smaller. And it would be more complicated to arrange, as the distance between the water-generating indoor evaporator and the outdoor condenser can be pretty long. Plus, the outdoor unit can be higher up, so a pump which can generate some pressure would be needed, and a pipeline which never leaks even with pressure in it. Not worth the small gain.