[westes]

We have an outside Lennox residential HVAC unit. Are there any advantages to putting the unit into the shade? Currently the unit is south facing and directly into the sun. Obviously that has to increase the temperature of the unit, but I'm not sure how that will affect its performance or efficiency.

 

[beenthere]

Little to no effect.

 

[gwoner]

Doesn't matter in the least.

 

[Shophound]

A shaded condenser might run a tad cooler, but the main problem occurs when certain people get it in their head to shade it, come up with some crazy shading contraption, and end up blocking air circulation around the unit. That will undo any small benefit the shading might bring.

The best thing that a condenser can see to enjoy a long and useful life is to experience a life of a consistently cleaned coil. Dirty coils kill efficiency, performance, and ultimately it can take out a compressor. A clean condenser that sits in the sun all day and runs year after year...I've seen that plenty.

 

[mark beiser]

I wish I had a link to it, but some organization did a pretty good study on it and found that it is possible to gain up to 3% efficiency by shading the whole area the outdoor unit is in, if you can do so without causing any restriction to airflow through the area.

They also found that most attempts at shading the unit, or the area the unit is in, actually negatively effect the efficiency of the system.

The sun shining on the unit has very little to do with it, it is all about the temperature of the air entering the condenser coil. If you can shade the whole area, without restricting airflow through the area at all, the air will pick up less heat from surrounding objects before being pulled across the condenser coil.


Your best bet is to make sure the area around the unit is free of obstructions, even landscaping, for at least a few feet, and that there is good ground cover around the unit, no loose dirt or mulch that can get sucked up into the coil.
If it is an area where good turf grass won't grow, some landscaping cloth and smooth gravel is good. Not lava rocks though, since they are not very friendly on your service technicians knees.

 

[westes]

A shaded condenser might run a tad cooler, but the main problem occurs when certain people get it in their head to shade it, come up with some crazy shading contraption, and end up blocking air circulation around the unit. That will undo any small benefit the shading might bring.

The best thing that a condenser can see to enjoy a long and useful life is to experience a life of a consistently cleaned coil. Dirty coils kill efficiency, performance, and ultimately it can take out a compressor. A clean condenser that sits in the sun all day and runs year after year...I've seen that plenty.

Is there anything a home owner can do to clean the coils without opening the unit up, or does it really require a professional to take it apart? How often should it get cleaned?

 

[Norml]

Good question!

I too want to take care of my investment. They are in the shade of deciduous trees.

I have a air compressor and a leaf blower .... How about a good blow-down? Garden hose?

I remember years ago hosing down was told me to be the way to clean, but I am thinking rust is more likely. Nowadays, we all own leaf blowers.

 

[motoguy128]

I thought there was an advantage to placing the unit on the north or east wide of a home. The ambient air temp in the sunny side of the house would be a few degrees cooler.

Also, most winds from storms come from the West or South, I find, so the unit is protected soemwhat form storm debris.

With a heat pump however, the sunny side of the home offers some sun in the afternoon which may reduce the number of defrost cycles. Direct sun exposure on cold days can melt some ice on the coils between cycles.


I wouldn't spend money to move a unit however. The best placement would be where it's furthest from bedrooms, windows or occupied spaces. Where it's not under trees, and where it's not likely to get pee'd on by pets.

 

[quickcat46]

I must disagree with the opinion that exposing your equipment to the full sun does not affect the equipment efficiency or life expectancy.
The air being pulled across the condensing coil must be at least 120 degrees of any unit sitting in the direct sun. This has no effect whatsoever on the efficency?
The entire unit, all electrical components and housing the fan motor and assorted components are basically working in a oven at 140 degrees having no effect?
How many techs have ever touched a condenser in July and moved that hand off quick.
A stable more consistent day in day out environment is much better for the life of any equipment.
Again I would say that this is my personal experience from seeing many units that needed to be replaced at a 12-15 yrs old that are in the direct sun. Compared to the number of 20-25 yr old systems sitting in a shaded area, not saying it doesn't happen both ways.
Nothing will take the place off regularly scheduled maintenance, but a ideal location sure doen't hurt and very well will extend the life of your equipment

 

[trane]

I must disagree with the opinion that exposing your equipment to the full sun does not affect the equipment efficiency or life expectancy.
The air being pulled across the condensing coil must be at least 120 degrees of any unit sitting in the direct sun. This has no effect whatsoever on the efficency?
The entire unit, all electrical components and housing the fan motor and assorted components are basically working in a oven at 140 degrees having no effect?
How many techs have ever touched a condenser in July and moved that hand off quick.
A stable more consistent day in day out environment is much better for the life of any equipment.
Again I would say that this is my personal experience from seeing many units that needed to be replaced at a 12-15 yrs old that are in the direct sun. Compared to the number of 20-25 yr old systems sitting in a shaded area, not saying it doesn't happen both ways.
Nothing will take the place off regularly scheduled maintenance, but a ideal location sure doen't hurt and very well will extend the life of your equipment

I think you are confusing what a thermometer reads in the sun and why. The air temperature is the same in the shade or sun but radiant heat from the sun will make a thermometer read higher. For it to make any difference you would have to shade an area large enough to supply all the air thats required for the A/C.

 

[Shophound]

Is there anything a home owner can do to clean the coils without opening the unit up, or does it really require a professional to take it apart? How often should it get cleaned?

Cleaning the coils correctly is best left to a pro. They should be backflushed, and on some condensers there is more than one row of coils. A good pro will have the right knowledge, skill, and depending on how dirty the coils are, cleaning solutions to do the job well.

 

[ACFIXR]

shade?

this does not work!

 

[motoguy128]

I think you are confusing what a thermometer reads in the sun and why. The air temperature is the same in the shade or sun but radiant heat from the sun will make a thermometer read higher. For it to make any difference you would have to shade an area large enough to supply all the air thats required for the A/C.

That same radiant heat also warms the unit's casing and the surronding ground around the unit. The ambient air temp will be warmer in the sun vs. in the shade.

I also argee with Quckcat that havign the electrical components sitting in a 100F box rather than a 120F box is advantagous. We put A/C in our MCC at my work for a reason. The rating on a VFD is about 20% lower in higher tempratures vs. normal room temperature.

 

[DeAngel]

The debate continues with opposing points of view.

According to the Department of Energy, "Plant trees or shrubs to shade air conditioning units but not to block the airflow. Place your room air conditioner on the north side of the house. A unit operating in the shade uses as much as 10% less electricity than the same one operating in the sun."

http://www.energy.gov/summer.htm

However, I believe the study Mark Beiser referred to is "Measured Impacts of Air Conditioner Condenser Shading by D.S. Parker, S.F. Barkaszi, Jr., and J.K. Sonne of the Florida Solar Energy Center (FSEC). They conclude that any savings produced by localized AC condenser shading are quite modest (<3%) and that the risk of interrupting air flow to the condenser may outweigh shading considerations. The preferred strategy may be a long-term one: locating AC condensers in an unobstructed location on the shaded north side of buildings and depending on extensive site and neighborhood-level landscaping to lower localized air temperatures.

http://www.fsec.ucf.edu/en/publications/html/FSEC-PF-302-96/

So the best solution comes from shophound. An annual tune-up of your air conditioner by a service expert can improve your unit’s efficiency by as much as 20 percent as well as lengthen its performance life.

http://energyefficiencyarkansas.org/media/1166/cooling.pdf

 

[motoguy128]

According to the Department of Energy, "Plant trees or shrubs to shade air conditioning units but not to block the airflow. Place your room air conditioner on the north side of the house. A unit operating in the shade uses as much as 10% less electricity than the same one operating in the sun."

http://www.energy.gov/summer.htm

While I agree with that... and it passes the "logic test"....

...Just because the feFeds ds say it's true, doesn't mean much to me. They also believe in global warming and as a result solutions have ben suggested such as placing limits on livestock and taxing coal fired boilers into obsolescenece.... which make up about 2/3 of the electricity supplied in the US.

 

[trane]

That same radiant heat also warms the unit's casing and the surronding ground around the unit. The ambient air temp will be warmer in the sun vs. in the shade.

I also argee with Quckcat that havign the electrical components sitting in a 100F box rather than a 120F box is advantagous. We put A/C in our MCC at my work for a reason. The rating on a VFD is about 20% lower in higher tempratures vs. normal room temperature.

A thermometer placed in the sun will read the same temperature as one in the shade if its protected from radiant heat. For this to have any effect on the temperature of air that an A/C needs you would have to shade enough air that the A/C won't pull any from area's that have radiant heat.

 

[motoguy128]

A thermometer placed in the sun will read the same temperature as one in the shade if its protected from radiant heat. For this to have any effect on the temperature of air that an A/C needs you would have to shade enough air that the A/C won't pull any from area's that have radiant heat.

I would agree with that, and there is fair amount of shaded surfaces to keep the ambient temp a few degrees cooler even as hte A/C draws in air from non-shaded areas.

But what about the heating of the metal case and coils themselves? Doesn't that affectively make the coil surface warmer, creating the same effect as having a high ambient air temp???

I think it would reduce heat transfer sgnificantly for 1-2 minutes as it cools off towards ambient temp at start-up, but the constant sun heating the unit would then continue durign the entire run time.

 

[Shophound]

I would agree with that, and there is fair amount of shaded surfaces to keep the ambient temp a few degrees cooler even as hte A/C draws in air from non-shaded areas.

But what about the heating of the metal case and coils themselves? Doesn't that affectively make the coil surface warmer, creating the same effect as having a high ambient air temp???

I think it would reduce heat transfer sgnificantly for 1-2 minutes as it cools off towards ambient temp at start-up, but the constant sun heating the unit would then continue durign the entire run time.

I look at this matter from the perspective of knowing the three forms of heat transfer: convection, conduction, radiation.

Air flowing over the condenser coils and out of the unit via the condenser fan = convection (forced)

Heat rejection from condenser coil into air flowing over coil = conduction (the coil conducts heat from the condensing liquid into the air stream over the coil - the air is the heat sink)

Surfaces of condensing unit and nearby surfaces, such as the ground, siding of the house, nearby paving, etc. = radiation

Regarding radation, bear in mind that radiant heat does not transfer heat until it strikes a solid object. Therefore if a brick wall behind the condensing unit, for example, is 120 degrees and the condenser coil is cooler, radiant heat will have an effect on the coil surface. To what extent would require measurement/data logging, but the thermodynamics are present regardless.

Take an infrared thermometer with you sometime and visit a condensing unit sitting out in the sun running on a hot day. Measure the coil surface temperature in several spots, and measure nearby surfaces in several spots. How hot bare soil can get on a sunny day is an eye opener. Brick walls, paving, etc. also similar. Next compare these sunny areas to sunny areas of ground cover/lawn/shrubbery. A bit cooler, yes? Plants also add the component of evaporative cooling to the mix, since plants are undergoing transpiration/photosynthesis while in the light.

 

[motoguy128]

Thanks Shophound, for better explaining what I knew was occuring.

Now, how much more energy depends on the unit. A high SEER unit with a fair or poor EER, may suffer. A unit with a high EER, may not see much change.

 

[beenthere]

The air being pulled across the condensing coil must be at least 120 degrees of any unit sitting in the direct sun. This has no effect whatsoever on the efficency?

The air temp is not 120°.
Although it feels like it when your standing there.

But if you check the actual air temp the unit is pulling in. Its the same temp as the ambient air.