Climate Change Energy Users

Multi-stage heat pumps are the cat’s jammies

My friend Simon St. Laurent posted a video on Facebook that goes into the mechanics—and efficiencies—of a heat pump.

Homes in Savannah are primarily cooled and heated by heat pumps. The house we bought had a 2.5 ton unit, with the interior portion in the attic. Being new to HVAC systems installed in the attics, we weren’t familiar with the important rule to these units:

You have to treat your condensate pipes at least 4 times a year for them to remain unclogged at all times.

It wasn’t until we saw water dripping down the wall from the air intake vent that we realized we had a problem. Water had been collecting in the plenum (that’s the piece that holds the HVAC in a vertical system and provides duct attachment) and badly rusted it. The cost to replace the plenum was enough, and the system only a few years shy of replacement, so we decided to replace the system with a new one.

For the size of the unit, I performed my own analysis using the extremely difficult to use Manual J calculations and determined we really needed a 2.7 ton heat pump. Because of the smaller size, our unit was running for longer periods of time, but it also wasn’t short cycling—the unit wasn’t turning on and off too frequently. Short cycling is the death of an HVAC unit, which is why HVAC companies typically recommend a smaller unit if your home needs fall between unit sizes. Still, constant running isn’t highly efficient, either.

When we bought our new unit, we went with a 3-ton unit, which normally would be a little too large for our smallish house. However, we also bought a multi-stage rather than a single-stage heat pump. Specifically, we bought a 5-stage heat pump from Carrier.

A multi-stage heat pump doesn’t just run on and off, it also runs at lower capacities, with matching lower speed fan. The unit runs longer, but uses less energy because it’s running at a lower speed compression. You also don’t get sudden blasts of high heat or freezing cold that you would with a single stage heat pump. And you rarely hear our unit because, for the most part, it runs at stage 1 or stage 2.

We could have gone with a full ‘infinity’ stage unit, with an infinite number of stages, but our small home and smaller unit size doesn’t justify the additional expense. We could have also gone with a two stage unit—a very popular option—but I liked the idea of the unit being able to run at even lower speeds than what you normally get with a two-stage. Our system can run as low as 25% capacity versus the typical 70% capacity you get with a two-stage.

Unlike single-stage heat pumps, you don’t set cooling temps uncomfortably high and heating temps uncomfortably low in order to save on energy use. The real key is find your comfortable temperatures, but when you vary them throughout the day, do so gradually. When you change the temperature by one degree, the unit is able to power down but still meet the new temperature demand. With the smart thermostat we bought, the unit actually anticipates the temperature change and begins to gradually cool or heat to meet it.

We’ve had the unit for one year and I did an analysis of *energy use for the year. I found we used 17% less energy than the previous year. This doesn’t seem like much until you consider that we’ve set the house for more comfortable temperatures, especially in the hotter summer. In addition, we had a hotter summer in 2022 over 2021, as well as a freakish period of below 20 degree weather this winter. (We used a base heater in the garage during the subzero weather to keep garage pipes unfrozen. Without this demand, our energy use would have been 19% less for the year.)

I estimate the new unit will pay for itself in energy savings within 5 to 7 years. The savings will pay for the higher cost of a multi-stage system within two years.

Heat pumps aren’t for everyone. But unless you live in the frigid north, keep them in mind the next time you replace your HVAC. And if you get a heat pump, get a multi-stage unit.

*Only compare energy use, because electrical companies tend to screw with costs throughout the year.

Climate Change Weather

Floods. Again.

Recovered from the Wayback Machine.

Ike continues to rain destruction down in its path. It’s good to hear the storm surges weren’t as bad along the Gulf, but they were bad enough. Hopefully, though, loss of life will be minimal.

Ike just passed through the St. Louis area with both wind and rain. A lot of rain that combined with the remnants of Lowell from the Pacific. Sad as it is to say, we’re again looking at major flooding along the Meramec, Missouri, and Mississippi rivers.

This will be our third major flooding event in six months.

Climate Change Places

Katrina comparisons

Recovered from the Wayback Machine.

It is difficult to be sympathetic to people in Iowa and Missouri when you read some webloggers who gloat about how “well” their state did compared to how well the people did in New Orleans after Katrina. I think it’s time to take a closer look at events; to get some perspective on both events.

Early estimates put the number of damaged or lost homes in Iowa at about 8,000 to 10,000 homes, based on the number of displaced people. I estimate from the numbers I’ve heard in the last few weeks that Missouri will end up with about 500 to 1000 damaged or destroyed homes.

The number of homes destroyed by Katrina varies widely, but I’ve seen estimates from 275,000 to over 850,000 homes, many of them in New Orleans. In fact, 80% of the city was impacted, and only 45% of the New Orleans population has been able to return to New Orleans, years after the storm.

I couldn’t find numbers of people killed in the recent floods here in the midwest, but from an old estimate, we lost about 30 people. Over 1836 people died from Katrina, and the long term impact of the flood could result in thousands more dying.

Though we like to think floods along the Mississippi are sudden, this one was not. We had all the indications of a bad flood building up along the Mississippi beginning in April. The people impacted by New Orleans had three days, four tops, to prepare.

The people in Missouri and Iowa were not cut off and isolated. Most had neighbors and friends who helped. The people in New Orleans were shoved into a coliseum or left marooned on damaged bridges, as the surrounding communities would not let them leave the city. Why? Because rumors talked about roving bands of thugs shooting everything in sight; rumors proven to be untrue, but still persisting in places like Wikipedia—an article I nominate for being the worst edited, most inaccurate, and outdated article in Wikipedia. These people were left without water and food, in intense heat for days. No comfortable Red Cross shelters for them.

River floods like the recent flooding in the Midwest impact across class lines, especially after the federal buy outs resulting from the the 1993 flood. The flood in New Orleans impacted on some of the poorest people in this country. People who were then bused as far away as Salt Lake City, and cut adrift.

This recent flooding is terrible, and I don’t want to downplay the awfulness of the event, or the extent of the damage and the help that will be needed to rebuild in Iowa and Missouri. At the same time, it angers me to see those pontificating in how “better” we handled the flood than the folks handled Katrina in New Orleans and the rest of the south. Especially when the purpose for such comparisons is politically, and even racially, motivated.