I know AC's have some temperature differential limitation between outside and inside ambient - something along the lines of 30 degrees or so.

It's particular hot (but dry) these days. Part of the AC system (condenser?) is outside, part (evaporator?) is 'inside' in the attic. Both areas get pretty hot.

Can I improve the AC temp differential and thereby cool the house lower by spraying cold water onto the refrigerant coils outside? Or would that not make a difference / be in fact bad (but how different than just natural rain)?

quote:

spraying cold water onto the refrigerant coils outside

Where I live the water has so much lime, soon the coils would be covered.

It depends on the outside humidity but in general, yes.

I think they make drizzlers to do specifically what you’re describing.

quote:

Originally posted by konata88:
Can I improve the AC temp differential and thereby cool the house lower by spraying cold water onto the refrigerant coils outside? Or would that not make a difference / be in fact bad (but how different than just natural rain)?

That was an option when I replaces the AC at the house a few years ago. It has built-in misters that continuously spray the coils when the unit is running. I think the number they quoted me was a cup of water per hour.

I passed on the option. I found that the biggest improvement to maintaining the desired temperature in the house was to not let the interior ever heat up

Yes you can. When it's super hot outside you can end up with high head pressure. Spraying a mist on the condenser coils can help with that by one cooling the condenser coils with water and two the evaporative effects of the water. The best thing you can do as a homeowner to squeeze efficiently out of a system is to make sure your coils inside and out are clean so that you can reject the most heat possible outside and absorb the most heat possible inside.

On a crazy hot day you can set a mister pointed at condenser coils to help. We do it with our chillers on the hottest days of the year.

Temperature differential is dependant on the sizing of the equipment, during a load calculation.

Misters will help to a small degree, but the minerals left behind from the water ends up doing more damage then good.

Highly recommend against any watering set-ups.

Thanks guys.

I think our water is naturally pretty soft. Never have any issues in the toilet, shower, sinks, water heater, hot pot / coffee makers. Have never had to descale anything in this house (unlike prior houses). That being said, I won't make a habit of misting the condenser (yet). And coils (at least outside ones) seem very clean, even after 20 years.

I did a quick test since it sounded okay to do so: seems like I had an immediate drop of about 2-3 degrees! From 71 to about 68 (outside temp is about 105). So, not causal but seems like there is a benefit; but even if so, not sure how long it will last.

I'll look into mister systems and pros/cons - at least for occasional use. But will definitely consider larger size when replacing.

Coils have aluminum fins and most water when evaporated is alkaline
Not a good mix
Just make sure outdoor coil is clean and air filter is too at air handler
If it's 105 OSA temp, even 75 inside is mighty damn nice and comfortable

Its 105 here also and my stat is set at 77, real nice!

Don't know of any areas that have summer design temp over 105

Thx. Yea, the temp is nice but the house isn’t getting below 80; it hovers around 81-82 and runs a long time.

I’d like to get it down to about 76-78. But output at 70 isn’t doing it.

When was the last time your system was gone over by a competent tech?

quote:

Originally posted by konata88:
Thx. Yea, the temp is nice but the house isn’t getting below 80; it hovers around 81-82 and runs a long time.

I’d like to get it down to about 76-78. But output at 70 isn’t doing it.

If the supply air is only 70 with a return temp of 82 you might have a bigger problem at hand. You should be getting a 16-22 drop from return to supply, so your vents should be putting out between 60 and 66 degree air. Even then with temps over 100 and depending on your home design, insulation value, etc you might never get down to the mid 70s inside. But I would definitely get a professional checkup if it's been awhile or never.

Definitely have a reputable AC company look over your system, windows & insulation. Here in the Valley of the Sun, summertime temperatures routinely get over 100 degrees. We keep our inside temperature at 78-80, and most of the people we know keep it lower than that.

Instead of a mister system, you could use a swamp cooler AKA evaporative cooler to cool the air going into the AC condenser, increasing the effectiveness of the AC system.

I had service a couple of years ago. Checked pressure and replaced the caps. System seemed to look fine.

The house temp per various thermometers and the thermostat is about 80. The air coming out of the vents is about 70. This even if the ac is running for long periods. Outside air is over 100. Even near midnight the temp is above 90.

80 is not bad but a little warm when sleeping still. Would like to get to mid 70s; don’t mind being a little warm during the day. But don’t like to sweat when sleeping.

ETA: with outside temp about 90, air coming out the vent is about 65. Outside air temp does seem to influence the temp of the air coming out of the vent. 10 degree delta outside about a 5 degree delta coming out the vent?

Serviced two yrs ago, was it working fine at the time?

Yes. It had a nice differential but we didn’t have the heat then that we do now. I think the ac works well if outside is 90 or less. 115, not so much.

I feel your pain, Konata.

It was 105 yesterday here and mid to late afternoon our AC went out. Our system was working great until it wasn’t, able to get downstairs down to 70 earlier in the afternoon.

Our system is only 3 years old. A tech from the installing company will be here in a few hours. I have a suspicion the compressor isn’t kicking as everything else seems ok. Airflow is normal, but there is NO temp differential between supply and return.

We've been getting temps up to around 112~114 degrees and my system keeps the house at 77 very easily.

Gotta be something wrong with the OPs AC.

I'm certainly no HVAC expert, but ISTM your A/C is undersized, is old and tired, or is in need of attention; or your home is exceptionally energy inefficient, or all or some combination of those.

Our A/C, even before we replaced it last year, would easily cool our home to 76°F, regardless of outdoor temperature/humidity and sun load, with outdoor temps into the mid-to-high 90's F. The new unit does so even more efficiently. Our A/C is slightly over-sized for our house. Going the next size down would have made it slightly under-sized.

Mind you: We don't hit 100°F plus temperatures, often, but we do get into the upper-90's with truly oppressive humidity.

Compare to our next-door-neighbor to one side. Identical floor plan, except for a different addition than ours, whose A/C is undersized. When it's hot and sunny out his A/C runs continuously.

Come to think of it: We have about two to three times the glass exposure on the southern exposure as does he, as well.

quote:

Originally posted by konata88:
Yes. It had a nice differential but we didn’t have the heat then that we do now. I think the ac works well if outside is 90 or less. 115, not so much.

The outside air temperature shouldn't have an effect on the inside differential. Obviously houses aren't hermetically sealed, but essentially it's a closed system where you're cooling the inside air only. If the system had the correct differential last time it was checked but doesn't now obviously something has changed. They always say start with the filter(s); make sure it's clean of course, but also check that it's the correct filtration rating for your system. If you use a filter that's too high of a MERV rating it can reduce airflow which basically chokes your system to inefficiency. A lot of people recommend using minimum rated filters and changing them more often vs expensive high MERV. After that it could be lots of things like refrigerant, dirty coils, or other mechanical stuff that you need a pro to diagnose.