Category Archives: space conditioning

Minisplit cooling pause

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A typical summer in Chicago comes with heat and humidity that is every now and then interrupted by cooler spells with lower dew points. Those spells can be pleasant enough for us to stop running the minisplit in cooling mode and instead open the windows.

Once the heat and humidity roars back into town, we shut the windows in a hurry and power up the minisplit for that pleasant cool breeze. Except, there isn’t much pleasantness in that breeze, unless you enjoy a musty and mildew-drenched flavor.

If you abruptly stop the minisplit in cooling mode, the fins on the evaporator/condenser will still be drenched in condensate droplets. It is not easy to see in the above pictures, but believe me, the droplets are hiding in there.

And they will be sitting there for several days like a bunched up, wet towel in the corner of someone’s bathroom. If, after a few days, you dare to pick up that towel and give a sniff, you experience a similar flavor to that of the minisplit after it had been paused for a few hours or days. It is a death knell to indoor air quality (IAQ).

The good news is that this is an easy to solve problem. Rather than abruptly stopping the minisplit in cooling mode, switch it to low speed fan mode, and let it run for half a day or overnight. The fan keeps drawing air across the fins and will slowly dry them out.

It’s like taking your wet towel and hanging it up to dry. That towel definitely will smell a lot better – and so will your minisplit once you start it up again in cooling mode.

If you would also like to dry out the condensation collection pan at the bottom of the indoor unit, keep the minisplit in fan mode for a good day. This is definitely recommended at the end of the cooling season (end of summer).

And if you turn off cooling mode for a week or longer before starting it up again, you may want to consider cleaning the condensate drain line, as described in the previous post, just to be on the safe side.

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Minisplit cooling startup

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Cooling season has started. Our living space has been comfortable in terms of temperature and humidity since we turned off the heating mode on our minisplit back in March. Now it is time to bring the temperature and humidity down a notch so that we can sleep comfortably at night.

The last time the minisplit ran in cooling mode was about eight or nine months ago. Since that time, dust may have accumulated in the condensate collection pan. Once that dust mixes with the first condensate from the heat exchanger coils, it may cake up and block the drain line that is supposed to safely evacuate the water to the outside.

If that is the case, you will notice water droplets on the luvers and a water puddle on the floor under the minisplit.

It’s time to turn the minisplit off and clean that condensate drain line. Or, even better, as a routine maintenance item, preemptively clean the condensate drain line at the beginning of each cooling season.

To do so, find the discharge point of your drain line, which typically would be outside the building. Take a wet/dry shop vacuum with a narrow nozzle. Fit the nozzle over the drain line and proceed to evacuate any water, dust and crud that may have accumulated in the drain line since it last ran in cooling mode. Once the vacuum doesn’t pull any more water or crud out of the drain, start up the minisplit in cooling mode and monitor whether you get any more spillover from the condensate collection plan on the indoor unit. If you do, repeat the cleaning process. If you don’t, great job, and enjoy your cool building interior!

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Minisplit winter operation

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Our minisplit kept us cool during the dogs days of summer this year, and without having our electrical bill going through the roof.

But the minisplit can do more! Because it’s an air-source heat pump, it also can heat the building during the cold season. And that was something I wanted to put to the test when it recently was really cold outside.

Like I mentioned in the video, I simplified my explanation about how the system works. If you would like to read a more comprehensive and accurate description, you can find it in a previous blog post with the title “Mini what?”

The morning after I took the video, our outdoor temperature had dropped to -5F, the specified minimum operating temperature. I turned the minisplit on and indeed, it still was putting out heat.

While the outdoor unit was almost inaudible during the summer when we ran the minisplit in cooling mode, it was humming away pretty good in the heating mode, as you can hear in the video. I assume that the compressor has to work harder at these cold temperatures, thus the increased noise. Not that it matters. All windows are firmly shut anyway, keeping the noise out.

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Minisplit start up

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The most exciting moment is when you get to start up a new gadget – like our minisplit.

The vacuum pump had been pulling air and moisture out of the cooling lines. Once we had an acceptable vacuum pressure, James Pruyn, our installer, disconnected the pump and opened the refrigerant valve on the outdoor unit. That allowed the lines and indoor unit to be charged with the R410A refrigerant.

We were able to power up the system, and after tinkering a minute with the remote control, we got the indoor unit to spit out cool air. I had to go back and fix the leak on the condensation line, but other then that, everything ran smoothly.

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I like the summer sounds of cicadas and crickets chirping, but I dislike the ever annoying humming of air conditioners. I had been very concerned about the noise levels of our minisplit–not only of the indoor unit, but also the outdoor unit.

The indoor unit runs very quietly, even at full fan speed in cooling mode. When on low speed or “dry” mode, it makes no audible noise. I literally have to put my hand up to the unit to check that there is airflow because I can’t hear it.

The next check was the noise level on the outdoor unit. I saw the cooling fan running but could not hear anything. I had to climb up next to the unit to confirm that the compressor was cranking. I could hear my neighbor’s small window AC unit, but not our minisplit.

That was welcome news. It meant that even if we have a bedroom window open, we would not have to deal with the annoying humming that you typically would expect from an AC compressor.

A couple of weeks after the installation, James Pruyn called to asked how the system was running.

During the dog days of summer, I had the minisplit sometimes running during the day, but mostly at night, and mostly in “dry” mode. It turns the fan speed to low and slowly moves the indoor air over the cold heat exchanger coil of the indoor unit. This maximizes the moisture removal and at the same time keeps the indoor air temperature steady. On the few occasions when I had to lower the indoor air temperature, I switched to minisplit to “cool” mode at high fan speed for an hour or two. After that, the “dry” mode was able to maintain the desired temperature. To help with the distribution of the conditioned air, we used a small energy efficient pedestal fan to blow the air into the north or south part of the building.

In short, the minisplit was able to maintain a comfortable temperature and comfortable humidity levels (below 60% relative humidity) on the “low” setting at most times. James called it a perfectly sized system. He was right. And I should give credit to Lindsey Elton at the Eco Achievers, because she ran the energy model to determine what our cooling load would be and what size minisplit we should install. Thank you Lindsey!

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Minisplit installation – indoor unit

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While the vacuum pump is cranking away, let’s take a look at the indoor unit installation.

The indoor unit is also referred to as the evaporator, because of the phase change that takes place in the refrigerant when in cooling mode. It is a box (compact wall unit) measuring roughly 36 by 12 by 12 inches.

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The location of the compact wall unit had been determined during the rough-in. We placed it centrally located on the south wall in the dining room.

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The central location is key as there is no duct system that distributes the cool air (thus the term ductless minisplit). But with the cool air discharged from the compact wall unit in the dining room, it also reaches the living room, bedrooms and kitchen. That said, we may need to use a fan to facilitate the distribution of the cool air across the rooms.

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Our installer, James Pruyn, started by mounting the wall hook bracket onto which the compact wall unit will hang.

The recommended clearance for the compact wall unit is two and a half inches or greater from the ceiling and six feet or greater from the floor. We executed the rough-in of the cooling lines and condensate drain accordingly and have a ten inch clearance from the ceiling and eight foot two inch clearance from the floor.

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During the installation, we ran into a couple of flaws in the compact wall unit that are worthwhile mentioning.

The screws on the electrical terminals for the wire connections stripped. Thanks to James’ improv skills, we managed to get the wires safely connected after all.

At the end of the installation, James advised me to keep a very close eye on the condensation line once I turned the minisplit on. He connected the line from the wall unit to the line I had roughed in. But he pointed out that the provided barbed connection was very flimsy and suspected that it may leak.

And he was spot on. The connection was not watertight. Our solution was to fit a barbed coupling into the flimsy barbed connection that came with the unit. We got it watertight with a little bit of teflon tape and a screw clamp.

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