Tag Archives: heating and cooling

Minisplit winter operation

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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2016 heating savings

It is friggin cold outside, and I can’t shake the urge to keep talking about heating related matters, so here we go again:

One goal of our deep energy retrofit was to save energy, and along with it, some Benjamin Franklins. The money we invested in tightening and insulating the building was meant to save us dollars on our heating bill, for instance.

But how would we measure how much we save? Our problem was that we had no starting point. We bought our building as a foreclosure in 2009 and thus had no data – no access to utility bills – that would tell us what it took to keep the building heated and comfortable.

That said, there are plenty of buildings in our neighborhood that could serve as a comparable (comp). Not only are they the same construction type, but also in the same energy deficient shape as our building was before we started with our deep energy retrofit.

I found a building that was a good match, and the owner that was happy to share their utility data with us.

To compare apples to apples – or in this case, therms to therms – I calculated the amount of therms used per square foot per month for both buildings. Our building’s natural gas consumption is reflected in the blue bars, while the comp, or pre-retrofit state, is reflected in the red bars.

Data reflections

Why is there natural gas used during the summer months (off heating season)? Because in both cases natural gas is used to produce domestic hot water, i.e. washing the dishes, running the washing machine on warm or hot cycle, taking a shower, etc.

You may have seen me bragging about turning our heat on as late as mid November. If you look at the consumption for November 2016, you see that we mostly used domestic hot water while our neighbor in the comp building had the boiler already buzzing away.

Looking at the big picture, our building consumed 0.200 therms/square foot over the course of one year, while the comp usage was at 1.464. Our deep energy retrofit improvements appear to have reduced our natural gas consumption by 1.264 therms/square foot/year. That equals a reduction in our heating needs from November 2015 through December 2016 by a whopping 86%!

For our metric friends (i.e. the world with the exception of the U.S.): Our natural gas consumption equated 63.04 kWh (or 226.95 MJ) per square meter, while the comp came in at 461.83 kWh (or 1662.59 MJ) per square meter.

I typically don’t like to measure the improvements in cost savings, as supply cost and taxes may vary between jurisdictions or energy companies. In addition, the fixed costs on the gas bill, although often small, prevent accurate scaling to a square foot basis.

Yet getting an approximation of the monetary savings would give us a sense of the potential return on investment. We paid $0.27 for natural gas per square foot over the course of a year. The cost of the comp were $1.47. The estimated total cost savings for the 2,900 square foot of conditioned space in our building from November 2015 through December 2016 would be in the range of $3,400.

Yes – I am beaming right now! Yet, this somehow seems too good to be true. I think the flaw with my analysis is that I have based it on one comp only. I plan to find another couple of buildings that I could include in the analysis. That should give me a number that would be easier to defend.

Stay tuned, because I will keep you posted!

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Buying a foreclosure – Part 8

Welcome waste (energy)

Start of the 2016 heating season


Minisplit start up

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.



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

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.


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.


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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Minisplit installation – outdoor unit

How do I prevent the minisplit outdoor unit from multiplying overnight?

Usually the outdoor unit is mounted on the building near ground level, but above the snow line, where it is easy to access and service. While visiting Sweden this summer, I saw a number of cottages with minisplits installed just that way.

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I am inspired by this but won’t attempt to duplicate it, because I am in Chicago. Some people may label a minisplit “green” because of its efficiency, and others may just see green when looking at it – green like Benjamin Franklins. I may be left with just the minisplit shell in the best case scenario, or with an outdoor unit that grew legs overnight and walked away.

This baby has to be mounted higher on the building, off the ground where it is difficult to reach…and fairly difficult to install, unless you have a small scaffold.

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Fortunately, there are convenient wall mounting brackets for the minisplit, which we anchored into the exterior brick wall. Our installer, James Pruyn, fixed the outdoor unit on the bracket arms and connected the supply and return cooling lines we had roughed-in a couple of years back.

And then there was the electrical connection. Our 12,000 Btu minisplit runs on 220 volt, not the typical 110 volt. When I roughed-in the cooling lines, I also made sure to run an electrical conduit from the circuit breaker panel to the building exterior. I also had set aside two slots in the circuit breaker that would give us the needed 220 volts. All that was left to do was to install an emergency disconnect on the outside, pull the electrical cables through the empty conduit, and connect the cables to the minisplit.

The outdoor unit comes pre-charged with R410A refrigerant. But before we could charge the whole system (cooling return and supply lines and indoor unit), we needed to remove any remaining air and moisture. James connected a vacuum pump to the minisplit, and from then on it was a waiting game, as we waited until there was sufficient vacuum pressure.

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Well then – lets wait…

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