Besides insulation and air conditioning unit, what else is there to check if my A/C isn't keeping me cool?

Question

I live in an apartment home where the indoor temperature has risen to above 80 degrees Fahrenheit daily for the past two months. The outdoor temperature regularly reaches 100 degrees and the weather has been very dry.

I am sweating as I type this post.

I have been bugging my apartment manager for months now to fix the situation.

A while back, a technician came to my unit and pointed an infrared temperature sensor at my vents and it read out 60 degrees. However, the air coming out doesn't feel that cool to me. Two weeks ago, they installed a new A/C unit outside my unit. This morning, a crew came to install new insulation.

I would think that it would cover everything, but the temperature is still 82 degrees at 21:50h. I arrived home at about 18:00h and the temperature was 84 degrees.

I paid an almost $200 electric bill for my one bedroom apartment last month and I still sweat at home every day. This is crazy!

Since the A/C unit and the insulation have been replaced, what is the next thing to be looking at to get the situation fixed?

Answer 1

First, I feel your pain. I'm in Houston at my girlfriend's place; we live in a single family house, and the A/C is running all day even with the thermostat at 84 degrees. I work from home, so I can't let it go up higher than that. Our outside thermometer recorded 106 degrees today.

The things that we've added to the house to help keep cool, besides new insulation and having the A/C unit checked, include a bunch of things. First, a little theory. Your apartment heats up because of the sun heating the building primarily, and secondarily because of infiltration from the outside of warm air.

I'm going to just assume that your landlord isn't willing to replace your windows and doors with low-E dual-paned units. I've done this to my house in Bryan, TX and it literally cut my utility bill in half.

The first thing we did with her place, where the landlord is also not willing to rip out a ton of windows and replace them, was to get blinds with reflective shades in all of the windows, and external solar shades or screens where possible. Remember: Black stuff is OK on the outside of the structure, because black absorbs heat (and you don't care about the heat if it's on the outside) -- and white things on the inside of the structure, because you want the heat to not be absorbed and to just be reflected back out.

The second thing we did was to get a better thermostat for the house. The old one was a manual one with mercury in it; the new one has a digital timer and a bunch of other features that include breaks for things like the compressor coils to defrost.

The third thing we did was start replacing the A/C filter frequently... at least once a month.

It might help to suggest more if we knew what kind of A/C unit you have (is it one of those high-rise below-window units, or a 'real' one with a compressor and air exchanger in a closet or attic?), and what kind of structure (concrete or wood frame) you're in.

Answer 2

Karl's answer is spot on, I just had one thing to add. All things considered, the best you will be likely to accomplish with your average residential A/C is about a 30-degree F drop from the outside temperature.

The reason why is very simple; the compressor unit on the outside of your house has to use the outside air as a radiator (much like your car) to cool the liquid Freon after the compressor has liquefied it. The hotter the outside air, the less energy can be taken out of the coolant, meaning it still has that energy back at the evaporator when it's allowed to boil back into a gas. The more energy the liquid has, the warmer the gas will be. With Freon, the temperature delta you get from the boiling liquid is about 40°F, and then considering the inherent inefficiencies of blowing air across a cooled evaporator coil, plus a whole lot of heat sources you simply will not be able to eliminate (especially in an apartment where you can't do major structural renovations), the best you'll get is about a 30° cooler temperature inside vs outside.

That means that with the scorchers Texas has had over the past month (approaching and even exceeding 110°F; some days it's been hotter in Dallas than the high desert of Phoenix), you could end up struggling to get to 80°F inside. In these situations, you might consider adding a window or other self-contained A/C unit. These units will use the inside air (which your central HVAC has cooled by 30°F) to cool its compressor coil, meaning its evaporator coil (and the air passing through it) can be another 30-40 degrees F cooler. However, you're going to pay a higher cost in terms of dollars-per-degree to add this secondary cooling system. Also, the air from the inside used by the second A/C will be exhausted outside, which will cause outside air to be drawn in anywhere it can be, warming up the outlying rooms. So, you'll trade a comfortable temperature in one room for warmer temperatures in the rest of the house.